Receptor-coupled G proteins mediate contraction and Ca++ mobilization in isolated intestinal muscle cells.

Guanosine 5'-O-(gamma-thio)triphosphate (GTP[S]), NaF and cholecystokinin-octapeptide (CCK-8) were used to examine the participation of G proteins in agonist-induced contraction of smooth muscle cells isolated separately from circular and longitudinal muscle layer of guinea pig intestine. All three agents stimulated inositol 1,4,5-triphosphate (InsP3) production and protein kinase C activity to the same extent in permeabilized (GTP[S] and CCK-8) and nonpermeabilized (NaF and CCK-8) muscle cells. InsP3 production was 9 to 13 times higher in circular muscle cells consistent with preferential hydrolysis of phosphatidylinositol 4,5-biphosphate in this cell type. InsP3 production and protein kinase C activation in permeabilized muscle cells were abolished by guanosine 5'-O-(beta-thio)diphosphate (10 microM). Maximal concentrations of GTP[S] (100 microM), CCK-8 (1 nM) and InsP3 (1 microM) elicited similar increases in [Ca++]i, net 45Ca++ efflux and contraction in permeabilized circular, but not longitudinal, muscle cells [( Ca++]i: 224 +/- 35 nM, 279 +/- 29 nM and 288 +/- 45 nM increase above basal level; 45Ca++ efflux: 35 +/- 2%, 34 +/- 3% and 37 +/- 3% decrease in cell Ca++ content; contraction: 26 +/- 2%, 24 +/- 2% and 25 +/- 2% decrease in cell length). The responses to GTP[S] and CCK-8 were abolished by guanosine 5'-O-(beta-thio)diphosphate (10 microM) and heparin (10 micrograms/ml), whereas the response to InsP3 was abolished by heparin only. Maximal concentrations of NaF and CCK-8 elicited similar increases in [Ca++]i and contraction in nonpermeabilized circular and longitudinal muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)


Omega-conotoxin-sensitive calcium channels modulate autonomic neurotransmission in guinea pig airways.

omega-Conotoxin GVIA, a peptide derived from the marine snail Conus geographus, is an antagonist of the neuronal N type voltage-sensitive calcium channels associated with neurotransmitter release. The present study investigated effects of this peptide on neurally mediated responses in airways isolated from the guinea pig to determine whether airway nerves are modulated by omega-conotoxin-sensitive calcium channels. Electrical field stimulation was used to induce neurally mediated tachykininergic excitatory responses in guinea pig bronchus and cholinergic excitatory and nonadrenergic noncholinergic inhibitory responses in guinea pig trachea. Exogenous agonists were administered to induce contractile (acetylcholine, substance P) or relaxation (sodium nitroprusside) responses. Tissues were incubated with omega-conotoxin (1 microM) or its vehicle (10 mM acetic acid) for 30 min before establishing frequency- or concentration-response relationships to the various stimuli. Frequency-response curves for neurally mediated cholinergic, nonadrenergic nocholinergic inhibitory and tachykininergic responses were shifted to the right by omega-conotoxin to a similar extent (4- to 5-fold). omega-Conotoxin had no effect on contractile responses elicited by exogenous acetylcholine or substance P or on relaxations induced by sodium nitroprusside. These findings indicate that neurotransmission in afferent tachykininergic kininergic nerves and in efferent cholinergic excitatory and nonadrenergic noncholinergic inhibitory nerves in the airways is modulated by a prejunctional omega-conotoxin-sensitive mechanism.


Immunochemical characterisation of a 29-Kda surface-associated molecule of Entamoeba histolytica and its recognition by serum from patients with amoebiasis.

A 29-Kda cytotoxic molecule of axenically-grown pathogenic Entamoeba histolytica (strain HM1) was purified from an amoebic extract by immuno-affinity chromatography with monoclonal antibodies. Immunoreactivity of the purified 29-Kda molecule altered significantly (p less than 0.01) after exposure to heat or trypsin, but remained unaltered after treatment with sodium metaperiodate. The 29-Kda molecule was recognised by serum from each of 13 patients with amoebic liver abscess. In an ELISA system, the molecule produced significantly higher (p less than 0.01) OD readings with these serum samples than with samples from asymptomatic cyst passers. No serum from healthy subjects or from patients with idiopathic ulcerative colitis or giardiasis had antibodies that reacted with the 29-Kda molecule. The immune response to the 29-Kda amoebic protein in man may indicate a specific role for this molecule in invasive amoebiasis.


Model for the differential stabilities of rhinovirus and poliovirus to mild acidic pH, based on electrostatics calculations.

Previous calculations of electrostatic interactions in the rhinovirus capsid have identified a subset of histidine residues, paired with lysine or arginine, that may be involved in pH-induced conformational changes related to viral uncoating. Further calculations with the finite difference method, accounting for the dielectric environment of the ionizable groups, suggest that charge burial in the crystal conformation will prevent protonation of these histidine residues in the pentamer-pentamer interface. Calculations with a modelled pentamer-pentamer interface in which three beta-strands are removed recover mildly acidic pKa values for the histidines. These results are discussed in the context of the structural interactions of these three beta-strands, which form a beta-sheet extension from the rest of the capsid, and with regard to the conformation of the homologous beta-sheet extension in poliovirus, which also possesses homologous histidine-lysine/arginine pairs. A model is developed in which the structural stability of the beta-sheet extension is related to the difference in acid stability of rhinovirus and poliovirus. It is suggested that, for poliovirus prior to cell receptor binding, the beta-sheet extension is stable at pH 3, the pentamer-pentamer interface histidines remain buried, and the virus is acid-stable. Cell receptor binding of poliovirus destabilizes the beta-sheet extension and the acid lability that is proposed to result could be involved in viral uncoating. For rhinovirus it is suggested that the observed conformational change in the absence of cell receptor binding involves a further acidic pH-activated process or conformational fluctuations that rearrange the beta-sheet extension and expose the pentamer-pentamer interface histidine residues to the acidic medium. Sequence analysis and electrostatics calculations reveal an aspartic acid in the beta-sheet extension that may have different pKa values in rhinovirus and poliovirus.


Interdomain salt bridges modulate ligand-induced domain motion of the sulfate receptor protein for active transport.

The refined crystal structure of the liganded form of the Salmonella typhimurium sulfate-binding protein, a periplasmic receptor of active transport, is made up of two globular domains bisected by a deep cleft wherein the dehydrated sulfate is completely engulfed and bound by hydrogen bonds and van der Waals' forces. Two salt bridges (between Glu15 and Arg174 and between Asp68 and Arg134) span the cleft opening. To elucidate the role of the inter-domain salt bridges in the ligand-induced domain motion, the acidic residues were changed (singly and together) to their corresponding amide side-chains by site-directed mutagenesis of the recombinant Escherichia coli sulfate-binding protein. Rapid kinetics and equilibrium measurements of sulfate binding to the purified mutant proteins demonstrate that these salt bridges stabilize the closed liganded form of the receptor and modulate the rate of cleft opening. Our results have new implications in understanding the dynamics of many other multidomain proteins that undergo similar large-scale domain motions.


NF-IL6, a member of the C/EBP family, regulates E1A-responsive promoters in the absence of E1A.

A cDNA encoding NF-IL6, an interleukin-6 (IL-6)-regulated human nuclear factor of the C/EBP family, is demonstrated to complement the transactivation function of E1A. The endogenous NF-IL6 level varies according to cell type and correlates positively with an IL-6-regulated cellular E1A-substituting activity that was described recently (J.M. Spergel and S. Chen-Kiang, Proc. Natl. Acad. Sci. USA 88:6472-6476, 1991). When expressed by transfection in cells which contain low levels of NF-IL6 and are incapable of complementing the function of E1A proteins, NF-IL6 also transactivates the E1A-responsive E2ae and E1B promoters, to the same magnitude as E1A. Activation by NF-IL6 is concentration dependent and sequence specific: mutational studies of the E2ae promoter suggest that the promoter-proximal NF-IL6 recognition site functions as a dominant negative regulatory site whereas the promoter-distal NF-IL6 recognition site is positively regulated at low NF-IL6 concentrations and negatively regulated when the NF-IL6 level is high. Consistent with these functions, NF-IL6 alone is sufficient to complement an E1A deletion mutant dl312 in viral infection, when expressed at appropriate concentrations. These results identify NF-IL6 as a sequence-specific cellular nuclear factor which regulates E1A-responsive genes in the absence of E1A.


Simian virus 40 large T-antigen expression decreases the G1 and increases the G2 + M cell cycle phase durations in exponentially growing cells.

The effect of simian virus 40 large T-antigen (Tag) expression on the cell cycle of exponentially growing, established, mouse NIH 3T3 fibroblasts was examined by using a sensitive flow cytometric assay to analyze nonselected cells immediately after infection with a Tag-encoding recombinant retrovirus. Tag expression resulted in reduced percentages of G1-phase cells and increased percentages of S- and G2 + M-phase cells compared with cell populations infected with a control virus not encoding the Tag gene. Cell cycle-blocking drugs were used to examine the exit rate for each of the cell cycle phases, G1, S, and G2 + M, for Tag-expressing and Tag-nonexpressing cells growing in the same cell culture dish. As a result of Tag expression, the duration of the G1 phase was decreased (average G1-phase exit duration decreased by 18%) and the duration of the G2 + M phase was increased (average G2 + M exit duration increased by 29%). The duration of S phase was unaffected by Tag expression.


Characterization of early pathogenic effects after experimental infection of calves with bovine immunodeficiency-like virus.

The early pathogenic effects of bovine immunodeficiency-like virus (BIV) were studied in calves experimentally inoculated with BIV. All animals inoculated with BIV R29-infected cells seroconverted by 6 weeks postinoculation, and BIV was recoverable from each animal at 2 weeks postinoculation. However, levels of BIV replication in vivo appeared to be low. In situ hybridization studies indicated that during peak periods of viral replication in vivo, less than 0.03% of peripheral blood mononuclear cells were expressing detectable levels of viral RNA. Moreover, the levels of viral RNA in these cells in vivo were less than 1/10 the levels observed in persistently infected cells in vitro. BIV-inoculated calves had significantly higher numbers of circulating lymphocytes, and follicular hyperplasia was observed in lymph nodes, hemal nodes, and spleen. The histopathological changes observed in BIV-infected calves were similar to changes found early after infection with the immunosuppressive lentiviruses, including human immunodeficiency virus type 1.


Divergent envelope E2 alphavirus sequences spanning amino acids 297 to 352 induce in mice virus-specific protective immunity and antibodies with complement-mediated cytolytic activity.

We have proposed a general algorithm for identification of potential immunoprotective domains (cassettes) on the envelope E2 polypeptide of alphaviruses (H. Grosfeld, B. Velan, M. Leitner, S. Cohen, S. Lustig, B.E. Lachmi, and A. Shafferman, J. Virol. 63:3416-3422, 1989). To assess the generality of our approach, we compared analogous E2 cassettes from Sindbis virus (SIN) and Semliki Forest virus (SFV), two alphaviruses which are philogenetically very remote. The antigenically distinct SFV E2 and SIN E2 cassettes exhibit comparable immunological characteristics. Most significantly, the SIN E2 LMN cassette cluster (E2 amino acids 297 to 352 fused to beta-galactosidase), like the analogous SFV E2 LMN cassettes, elicited high titers of antivirus antibodies in mice and proved to be highly effective in protection against lethal challenge. Mice immunized with SIN E2 LMN were completely protected against intracerebral challenge of 10 to 100 50% lethal doses of different neurovirulent SIN strains. Anti-SIN LMN antibodies, like anti-SFV LMN antibodies, lacked in vitro neutralizing activity, yet both exerted protection against homologous challenge upon transfer to mice. The two antibody preparations exhibited virus-specific complement-mediated cytolysis of cells infected with the homologous but not heterologous virus. These results suggest a possible mechanism for virus-specific E2 LMN-induced protection and demonstrate the generality of our methodology for deciphering immunogenic and protective domains in alphavirus systems. Results suggest also that the E2 LMN sequence of any given alphavirus should be considered as a component of a synthetic vaccine against that specific virus.


Isolation and partial characterization of infectious molecular clones of feline immunodeficiency virus obtained directly from bone marrow DNA of a naturally infected cat.

Replication-competent molecular clones of feline immunodeficiency virus (FIV) were isolated directly from the DNA of bone marrow cells of a naturally FIV-infected cat. After transfection in a feline kidney cell line (CrFK) and subsequent cocultivation with peripheral blood mononuclear cells (PBMC), the viral progeny of the clones was infectious for PBMC but not for CrFK cells. PBMC infected with these clones showed syncytium formation, a decrease in cell viability, and gradual loss of CD4+ cells. The restriction maps of these clones differed from those obtained for previously described molecular clones of FIV derived from cats in the United States. The predicted amino acid sequence similarity of the envelope genes of the two clones was 99.3%, whereas the similarities of the sequences of the clones to those of two molecular clones from the United States, Petaluma and PPR, were 86 and 88%, respectively. Most of the differences between the amino acid sequences of the two clones and those of the clones from the United States were found in five different hypervariable (HV) regions, HV-1 through HV-5. The viral progeny of one of these clones was inoculated into two specific-pathogen-free cats. The animals seroconverted, and the virus could be reisolated from their PBMC.


Characterization of human cytomegalovirus UL84 early gene and identification of its putative protein product.

The DNA sequence and transcription pattern of human cytomegalovirus early gene UL84 were analyzed. This gene was mapped within a 2.6-kb PstI fragment located between 0.534 and 0.545 map unit of the large unique segment of the human cytomegalovirus genome, which is adjacent to the pp65 and pp71 genes. A 2.0-kb mRNA was transcribed from this region in the same leftward direction as the mRNAs of the pp65 and pp71 genes. The message was first detected at 2.5 h postinfection and reached a maximal level between 72 and 96 h postinfection. The nucleotide sequences of the 2.6-kb PstI genomic DNA fragment and the cDNA derived from this region were determined. The resulting data revealed a polyadenylation signal (AATAAA) located 14 nucleotides upstream from the poly(A) tail of the cDNA and a 1,761-bp open reading frame capable of encoding a 65-kDa polypeptide. A potential leucine zipper was found in the N-terminal half of the peptide molecule between amino acids 114 and 135. In addition, a different periodic leucine repeat with leucine at every eighth position was found between amino acids 325 and 373. The transcriptional initiation site of this early gene was determined by primer extension analysis. A putative TATA box (TATTTAA) located 24 bp upstream of the cap site and several inverted repeats were found in the region further upstream of the TATA box. To test whether the open reading frame of this cDNA encodes a virus-specific protein, the cDNA was overexpressed in Escherichia coli as a fusion protein used to generate antibodies in rabbits. A protein with a molecular size of 65 kDa was detected in the infected-cell extracts harvested at 6 to 72 h postinfection, but not in purified virions, using immunoblot analysis. Both nuclear and cytoplasmic fluorescences were found at late stages of virus infection. From the results obtained, we postulate that UL84 may be a stable, virus-specific, nonstructural protein capable of forming a homo- or heterodimeric molecule.


Sequential phosphorylation of the phosphoprotein of vesicular stomatitis virus by cellular and viral protein kinases is essential for transcription activation.

The phosphoprotein (P) and the large protein (L) constitute the RNA-dependent RNA polymerase of vesicular stomatitis virus (VSV). We show that phosphate-free P protein expressed in bacteria is transcriptionally inactive when reconstituted with L protein and viral N-RNA template free of cellular protein kinase. Phosphorylation of P protein by a cellular kinase(s) was essential for transcription as well as for further phosphorylation by an L-associated kinase, the two kinases acting in a sequential (cascade) manner. Phosphate groups introduced by cell kinase were stable, whereas those due to L kinase underwent a turnover which was coupled to ongoing transcription. We present a model for the phosphorylation pathway of P protein and propose that continued phosphorylation and dephosphorylation of P protein may represent a transcriptional regulatory (on-off) switch of nonsegmented negative-strand RNA viruses.


Partial purification of adeno-associated virus Rep78, Rep52, and Rep40 and their biochemical characterization.

We have used differential cell extraction and conventional chromatography to separate and partially purify the four adeno-associated virus (AAV) nonstructural proteins Rep78, Rep68, Rep52, and Rep40. In the cytoplasmic extracts Rep52 and Rep40 were present in greater abundance than Rep68 and Rep78, with Rep78 being the least abundant. In nuclear extracts the four Rep proteins were approximately equal in abundance. Regardless of the subcellular fraction examined, three of the Rep proteins (Rep78, Rep68, and Rep40) consisted of two protein species with slightly different mobilities during polyacrylamide gel electrophoresis. In contrast, Rep52 consisted of only one protein species. Both Rep78 and Rep68 were capable of binding efficiently to AAV terminal hairpin DNA substrates, but we could not detect site-specific DNA binding by Rep52 and Rep40. Like Rep68, Rep78 had both an ATP-dependent trs endonuclease and a DNA helicase activity. Both Rep78 and Rep68 cut the terminal AAV sequence at the same site (nucleotide 124). The binding, trs endonuclease, and DNA helicase activities comigrated during sucrose density gradient centrifugation with a mobility expected for a monomer of the protein, suggesting that the three biochemical activities were intrinsic properties of the larger Rep proteins. The chromatographic behavior and the DNA-binding properties of the four Rep proteins identified at least two domains within the rep coding region, an exposed hydrophobic domain within the C-terminal end (amino acids 578 to 621) and a region within the N terminus (amino acids 1 to 214) which was necessary for binding to the terminal repeat sequence. No site-specific nuclease activity was seen in the presence of nucleotide analogs ATP-gamma-S or AMP-PNP, suggesting that ATP hydrolysis was required for the endonuclease reaction. Furthermore, although ATP was the only cofactor which would support the trs endonuclease activity of Rep78, Rep68 nuclease activity was seen in the presence of several other nucleotide cofactors, including CTP, GTP, and UTP.


Association between the herpes simplex virus major DNA-binding protein and alkaline nuclease.

Herpes simplex virus encodes seven proteins which have been shown to be both necessary and sufficient for in vitro replication of origin-containing plasmids. We have shown previously that one of these proteins, the major DNA-binding protein mDBP, forms a complex with alkaline nuclease, which is not one of the seven essential proteins. In this study, we have employed immunological reagents and a series of deletion mutants to investigate this complex further. We have determined the regions of mDBP which are important in the formation of this complex, and we have shown that the intranuclear locations of alkaline nuclease and major DNA-binding protein overlap.


JC virus and simian virus 40 enhancers and transforming proteins: role in determining tissue specificity and pathogenicity in transgenic mice.

When introduced into the germ line of mice, the simian virus 40 (SV40) T antigen under the control of its own transcriptional enhancer and promoter selectively induced tumors in the choroid plexus as well as thymic hyperplasia and kidney pathology. In contrast, the JC virus (JCV) T antigen under the control of its own regulatory sequences induced hypomyelination of the central nervous system and tumors of neural origin. Since SV40 and JCV have extensive sequence homology, except for their transcriptional control regions, these observations suggest but do not prove that, although the diseases induced by the two viruses, are consequences of the transforming gene, they are determined predominantly by the respective viral enhancers and promoters. To test this hypothesis, the regulatory regions of the two viruses were exchanged, and transgenic mice were derived with either chimeric construct. Like wild-type JCV, the construct containing the SV40 T antigen under the control of the JCV regulatory region induced hypomyelination of the central nervous system and neural tumors. Surprisingly, mice with this construct also developed choroid plexus carcinomas. Like the wild-type SV40 transgenic mice, mice with the JCV T antigen under the control of the SV40 enhancer and promoter developed choroid plexus tumors and renal pathology. Unexpectedly, they also had hyperplasia of the thyroid follicular cells. These findings not only provide direct evidence for the specificity of the respective viral regulatory region but also, more importantly, show that the transforming genes play a critical role in determining viral pathogenesis.


Finite life span of hybrids formed by fusion of different simian virus 40-immortalized human cell lines.

Simian virus 40 (SV40) genes are able to induce immortalization of normal human cells after a culture crisis during which unknown cellular genetic changes presumably occur. To determine whether these genetic changes are always identical, we performed somatic cell hybridization analysis of an SV40-immortalized human bronchial epithelial cell line, BET-1A. Fusion of BET-1A with an SV40-immortalized fibroblast cell line resulted in hybrids that senesced, indicating that these cell lines are in different complementation groups for immortalization.


Feline leukemia virus subgroup B uses the same cell surface receptor as gibbon ape leukemia virus.

Pseudotypes of gibbon ape leukemia virus/simian sarcoma-associated virus (GALV/SSAV) and feline leukemia virus subgroup B (FeLV-B) have been constructed by rescuing a Moloney murine leukemia virus vector genome with wild-type GALV/SSAV or FeLV-B. The resulting recombinant viruses utilized core and envelope proteins from the wild-type virus and conferred resistance to growth in L-histidinol upon infected cells by virtue of the HisD gene encoded by the vector genome. They displayed the host range specificity of the rescuing viruses and could be neutralized by virus-specific antisera. Receptor cross-interference was observed when the GALV/SSAV or FeLV-B pseudotypes were used to superinfect cells productively infected with either GALV/SSAV or FeLV-B. Although murine cells are resistant to FeLV-B infection, murine cells expressing the human gene for the GALV/SSAV receptor became susceptible to FeLV-B infection. Therefore GALV/SSAV and FeLV-B utilize the same cell surface receptor.


Identification of cognate genes among heterologous strains of group B rotavirus.

The genetic relatedness of group B rotavirus (GBR) strains has previously been documented by hybridization with probes derived from whole genomic sequences, but the relationship of individual genes of heterologous GBR strains has not been evaluated. Definition of cognate GBR genes would facilitate investigation of the determinants of group specificity, serotype identity, and neutralization epitopes. Therefore, we investigated the genetic relatedness of three GBR strains by means of Northern (RNA) blot hybridization with isotopically labeled probes prepared from each of the 11 genes of the IDIR strain of GBR. Under low-stringency conditions, hybridization between each of the IDIR gene probes and genomic RNA from the ADRV strain of GBR was observed. Genomic RNA obtained from a bovine strain of GBR hybridized with 9 of the 11 IDIR gene probes. In most cases, cognate genes of each of the GBR strains appeared to migrate to similar positions following polyacrylamide gel electrophoresis. However, the electropherotype positions of GBR genes 5, 6, and 7 were different for each of the three GBR strains. Identification of these genomic segments among GBR strains should prove helpful in future evaluations of GBR structure and function.


In vitro resolution of adeno-associated virus DNA hairpin termini by wild-type Rep protein is inhibited by a dominant-negative mutant of rep.

An adeno-associated virus (AAV) genome with a Lys-to-His (K340H) mutation in the consensus nucleotide triphosphate binding site of the rep gene has a dominant-negative DNA replication phenotype in vivo. We expressed both wild-type (Rep78) and mutant (Rep78NTP) proteins in two helper-free expression systems consisting of either recombinant baculoviruses in insect cells or the human immunodeficiency virus type 1 long terminal repeat promoter in human 293 cell transient transfections. We analyzed nuclear extracts from both expression systems for the ability to complement uninfected HeLa cell cytoplasmic extracts in an in vitro terminal resolution assay in which a covalently closed AAV terminal hairpin structure is converted to an extended linear duplex. Although both Rep78 and Rep78NTP bound to AAV terminal hairpin DNA in vitro, Rep78 but not Rep78NTP complemented the terminal resolution assay. Furthermore, Rep78NTP was trans dominant for AAV terminal resolution in vitro. We propose that the dominant-negative replication phenotype of AAV genomes carrying the K340H mutation is mediated by mutant Rep proteins binding to the terminal repeat hairpin.


Production of infectious hepatitis delta virus in vitro and neutralization with antibodies directed against hepatitis B virus pre-S antigens.

Hepatitis delta virus (HDV) particles were produced in Huh7 human hepatoma cells by transfection with cloned hepatitis B virus (HBV) DNA and HDV cDNA. The particles were characterized by their buoyant density, the presence of encapsidated viral RNA, and their ability to infect primary cultures of chimpanzee hepatocytes. Successful infection was evidenced by the appearance of increasing amounts of intracellular HDV RNA after exposure to particles. Infection was prevented when particles were incubated with antibodies directed against synthetic peptides specific for epitopes of the pre-S1 or pre-S2 domains of the HBV envelope proteins before exposure to hepatocytes. These data demonstrate that HDV particles produced in vitro are infectious and indicate (i) that infectious particles are coated with HBV envelope proteins that contain the pre-S1 and pre-S2 regions, (ii) that epitopes of the pre-S1 and pre-S2 domains of HBV envelope proteins are exposed at the surface of HDV particles, and (iii) that antibodies directed against those epitopes have neutralizing activity against HDV.


Induction of polyomavirus DNA replication by carcinogens in polyomavirus-transformed rat cells: evidence that the viral enhancer is not the primary target in the induction pathway.

In the polyomavirus (Py)-transformed rat cell line designated LPT, replication of the integrated Py DNA can be induced by exposure of the cells to carcinogens. In view of the observation that enhancer elements are essential components of the Py origin of replication, it appeared plausible that the induction is triggered by synthesis or modification of an enhancer-binding protein which is required for activation of the viral origin. To test this hypothesis, we have used a plasmid containing a modified Py origin (test plasmid), in which the Py enhancer has been replaced with five repeats of the yeast GAL4 upstream activating sequence, and a plasmid encoding the GAL4 transcriptional activator protein. Previous studies in which these two plasmids were cotransfected into mouse cells that are permissive for Py showed that the GAL4 protein can transactivate the modified Py origin and cause replication of the test plasmid. When similar cotransfection assays were performed in LPT cells, no replication of the test plasmid was observed unless the cells were exposed to the carcinogen mitomycin C subsequent to the transfection, in which case replication of the test plasmid was induced. Control experiments showed that even though the GAL4 protein was required for the induction, its concentration was not affected by the exposure to mitomycin C. These results indicate that the primary target in the induction pathway is not an enhancer-binding protein; instead, the induction appears to be triggered by changes in other components of the replication initiation complex which may be associated with the origin core.


v-mos proteins encoded by myeloproliferative sarcoma virus and its ts159 mutant.

The myeloproliferative sarcoma virus (MPSV) v-mos protein was predicted to be identical in size to p39c-mos because of an observed one-base deletion in the seventh codon of the env-mos open reading frame, which would allow translation to initiate at the methionine equivalent to codon 32 of the env-mos gene. On the basis of published results, p39c-mos is known to have greatly reduced in vitro protein kinase activity compared with p37env-mos encoded by Moloney murine sarcoma virus. Unexpectedly, the relative activity of the MPSV v-mos protein kinase was comparable to that of p37env-mos. Consistent with this finding, the size of MPSV v-mos protein was found to be similar to the size of p37env-mos. Moreover, the pattern and sizes of phosphorylated bands produced by autophosphorylation of the MPSV v-mos protein were similar to those of p37env-mos. These results were confirmed by in vitro transcription-translation of the MPSV v-mos gene. Resequencing portions of the MPSV mos gene failed to show the deletion within codon 7. Except for the codon 262 deletion, other mutations characteristic of MPSV and temperature-sensitive MPSV v-mos genes were confirmed. A glycine-to-arginine mutation at residue 338 of the MPSV env-mos sequence, previously shown to cause thermosensitivity of the mutant virus (termed ts159) transforming function, yielded a v-mos protein that had significantly reduced protein kinase activity in vitro. These findings indicate that MPSV, like other Moloney murine sarcoma virus strains, also encodes a functional env-mos protein.


Naturally occurring point mutation in the C terminus of the polymerase gene prevents duck hepatitis B virus RNA packaging.

A duck hepatitis B virus (DHBV) genome cloned from a domestic duck from the People's Republic of China has been sequenced and exhibits no variation in sequences known to be important in viral replication or generation of gene products. Intrahepatic transfection of a dimer of this viral genome into ducklings did not result in viremia or any sign of virus infection, indicating that the genome was defective. Functional analysis of this mutant genome, performed by transfecting the DNA into a chicken hepatoma cell line capable of replicating wild-type virus, indicated that viral RNA is not encapsidated. However, virus core protein is made and can assemble into particles in the absence of encapsidation of viral nucleic acid. Using genetic approaches, it was determined that a change of cysteine to tyrosine in position 711 in the polymerase (P) gene C terminus led to this RNA-packaging defect. By site-directed mutagenesis, it was found that while substitution of Cys-711 with tryptophan also abolished packaging, substitution with methionine did not affect packaging or viral replication. Therefore, Cys-711, which is conserved in all published sequences of DHBV, may not be involved in a disulfide bridge structure essential to viral RNA packaging or replication. Our results, showing that a missense mutation in the region of the DHBV polymerase protein thought to be primarily the RNase H domain results in packaging deficiency, support the previous findings that multiple regions of the complex hepadnaviral polymerase protein may be required for viral RNA packaging.


The ICP4 binding sites in the herpes simplex virus type 1 glycoprotein D (gD) promoter are not essential for efficient gD transcription during virus infection.

Activation of the early and late genes of herpes simplex virus type 1 during infection in tissue culture requires functional immediate-early regulatory protein ICP4. ICP4 is a specific DNA-binding protein which recognizes a variety of DNA sequences, many of which contain the consensus ATCGTC. In general, mutations which impair the ability of ICP4 to bind to DNA also eliminate its ability to activate viral early and late promoters both in transfection assays and in the infected cell. However, the role of ICP4 binding sites in the viral genome is unclear; many early and late promoters do not contain consensus binding sites in their vicinity. The glycoprotein D (gD) gene contains two well-characterized ICP4 binding sites upstream of its promoter and a third downstream of the transcription start site. Multimerization of one of these sites has been shown to increase the response of the gD promoter to ICP4 in transfection assays, while their removal reduces stimulation of the gD promoter by ICP4 in vitro. To assess the role of these binding sites during virus infection, we have constructed a recombinant viral genome which has mutations affecting all three. Comparison of the amounts of gD RNA synthesized by the recombinant and wild-type viruses indicated that the mutations had little or no effect on the activity of the gD promoter. Therefore, either the sites have no essential role in gD promoter regulation in the presence of all of the herpes simplex virus type 1 IE polypeptides during a normal infection or they can be functionally substituted by other ICP4 binding sites elsewhere in the genome.


Novel GACG-hairpin pair motif in the 5' untranslated region of type C retroviruses related to murine leukemia virus.

We searched for the presence of common RNA structural motifs in mammalian type C retroviruses related to murine leukemia viruses and the closely related avian spleen necrosis virus. A novel motif consisting of a pair of hairpins, called hairpin pair motif, was detected in the 5' untranslated regions of the genomes of these retroviruses. A combination of computational analyses that included the assessment of phylogenetic sequence conservation by multiple alignment, the search for regions with unusual RNA folding properties, and the analysis of RNA secondary structure by suboptimal free-energy calculations highlighted the significance of this hairpin pair motif. The hairpin pair motif encompasses 70 to 80 nucleotides between the splice donor site and the gag translational initiation codon of these viruses. The motif is composed of two adjacent hairpins both with a perfectly conserved GACG tetraloop. We propose that the novel GACG-hairpin pair motif described here constitutes an essential component of the regulatory machinery in these type C retroviruses.


Mutations in both the 2B and 2C genes of hepatitis A virus are involved in adaptation to growth in cell culture.

Oligonucleotide-directed mutagenesis of an infectious cDNA clone of wild-type hepatitis A virus was performed to determine which mutations acquired in the nonstructural 2B and 2C genes during adaptation to growth in cell culture were effective in enhancing virus growth in vitro. Results of transfection assays demonstrated that one mutation in the 2B gene and two mutations in the 2C gene were responsible for an increased efficiency in growth, but growth enhancement required the participation of at least two of the three mutations.


Interaction of Epstein-Barr virus nuclear antigen 1 with the viral latent origin of replication.

The Epstein-Barr virus latent origin of replication (oriP) requires only one viral protein, the Epstein-Barr virus nuclear antigen 1 (EBNA-1), for activity. oriP consists of two spatially separated, essential sequence elements, regions I and II, both of which contain multiple EBNA-1-binding sites. Region II contains, or is close to, the site at which DNA synthesis initiates. The role of region I, a transcriptional enhancer in cells that express EBNA-1, in replication is not understood. To determine how the binding of EBNA-1 to sites in region II leads to the initiation of DNA synthesis and to investigate the role of region I, EBNA-1 has been overproduced in insect cells by using a baculovirus vector and purified to homogeneity, and the interaction of EBNA-1 with oriP has been examined. Footprinting experiments demonstrated that EBNA-1 binds to oriP in a sequence-specific manner and bends or untwists the DNA at two symmetry-related sites in region II. Distortion of region I by EBNA-1 was not detected, suggesting that differences in the spacing of binding sites in regions I and II and resulting protein-protein interactions underlie differences in their biological properties. KMnO4 footprinting experiments did not reveal significant single-stranded structures in region II, suggesting that cellular proteins may recognize the EBNA--region II complex and unwind the DNA duplex. Region I did not quantitatively or qualitatively alter the interaction of EBNA-1 with region II. The contribution of an A + T-rich sequence in region II to replication was investigated by a mutational analysis. The results indicated that the overall A + T-rich nature of this sequence is not essential for replication of oriP-bearing plasmids. Nuclease protection experiments performed with these mutagenized plasmids provided additional evidence for protein-protein interactions in region II.


Single amino acid changes in the viral glycoprotein M affect induction of alpha interferon by the coronavirus transmissible gastroenteritis virus.

Transmissible gastroenteritis virus, an enteropathogenic coronavirus of swine, is a potent inducer of alpha interferon (IFN-alpha) both in vitro and in vivo. Previous studies have shown that virus-infected fixed cells or viral suspensions were able to induce an early and strong IFN-alpha synthesis by naive lymphocytes. Two monoclonal antibodies directed against the viral membrane glycoprotein M (29,000; formerly E1) were found to markedly inhibit virus-induced IFN production, thus assigning to M protein a potential effector role in this phenomenon (B. Charley and H. Laude, J. Virol. 62:8-11, 1988). The present report describes the selection and characterization of a collection of 125 mutant viruses which escaped complement-mediated neutralization by two IFN induction-blocking anti-M protein monoclonal antibodies. Two of these mutants, designated H92 and dm49-4, were found to exhibit a markedly reduced interferogenic activity. IFN synthesis by lymphocytes incubated with purified suspensions of these mutants was 30- to 300-fold lower than that of the parental virus. The transcription of IFN-alpha genes following induction by each mutant was decreased proportionally, as evidenced by Northern (RNA) blot analysis. The sequence of the M gene of 20 complement-mediated neutralization-resistant mutants, including the 2 defective mutants, was determined by direct sequencing of genome RNA. Thirteen distinct amino acid changes were predicted, all located at positions 6 to 22 from the N terminus of the mature M protein and within the putative ectodomain of the molecule. Two substitutions, Thr-17 to Ile and Ser-19 to Pro, were assumed to generate the defective phenotypes of mutants dm49-4 and H92, respectively. The alteration of an Asn-Ser-Thr sequence in dm49-4 virus led to the synthesis of an M protein devoid of a glycan side chain, which suggests a possible involvement of this structure in IFN induction. Overall, these data supported the view that an interferogenic determinant resides in the N-terminal, exposed part of the molecule and provided further evidence for the direct role of M protein in the induction of IFN-alpha by transmissible gastroenteritis virus. The acronym VIP (viral interferogenic protein) is proposed as a designation for this particular class of proteins.


A cyclic AMP-responsive DNA-binding protein (CREB2) is a cellular transactivator of the bovine leukemia virus long terminal repeat.

To gain insight into the cellular regulation of bovine leukemia virus (BLV) trans activation, a lambda-gt11 cDNA library was constructed with mRNA isolated from a BLV-induced tumor and the recombinant proteins were screened with an oligonucleotide corresponding to the tax activation-responsive element (TAR). Two clones (called TAR-binding protein) were isolated from 750,000 lambda-gt11 plaques. The binding specificity was confirmed by Southwestern (DNA-protein) and gel retardation assays. Nucleotide sequence analysis revealed that TAR-binding protein is very similar to the CREB2 protein. It contains a leucine zipper structure required for dimerization, a basic amino acid domain, and multiple potential phosphorylation sites. A vector expressing CREB2 was transfected into D17 osteosarcoma cells. In the absence of the tax transactivator, the CREB2 protein and the cyclic AMP-dependent protein kinase A activate the BLV long terminal repeat at a basal expression level: trans activation reached 10% of the values obtained in the presence of tax alone. These data demonstrate that CREB2 is a cellular factor able to induce BLV long terminal repeat expression in the absence of tax protein and could thus be involved in the early stages of viral infection. In addition, we observed that in vitro tax-induced trans activation can be activated or inhibited by CREB2 depending on the presence or absence of protein kinase A. These data suggest that the cyclic AMP pathway plays a role in the regulation of viral expression in BLV-infected animals.


Influence of adeno-associated virus on adherence and growth properties of normal cells.

It has been shown previously that infection of newly established cell cultures from malignant human tumors with adeno-associated parvovirus type 2 or type 5 results in growth arrest and cell death. Here we report that the additionally observed antiproliferative effect on diploid human fibroblasts is transient and is connected to a reduced number of cells in S phase. Progression through the cell cycle is disturbed either in G0/G1 or at the G1/S boundary, but an additional arrest in G2 cannot be excluded. DNA synthesis and cell proliferation are resumed when cells are recultured after loosening of cell-matrix adhesions by trypsin treatment. In contrast, they are not resumed by solely providing growth factors via higher amounts of fetal calf serum. The results suggest that cell adherence is altered in adeno-associated parvovirus-infected human embryo fibroblasts.


Second-site homologous recombination in Epstein-Barr virus: insertion of type 1 EBNA 3 genes in place of type 2 has no effect on in vitro infection.

This study was undertaken to develop a general strategy for the introduction of mutations into specific sites in the Epstein-Barr virus (EBV) genome. Previous approaches were limited by the need for physical linkage of the transfected EBV DNA fragment to a positive selection marker. In our experiments, a positive selection marker was introduced into one site in the EBV genome and a distant, nonlinked, marker was introduced into another site. Each marker was on a large EBV DNA fragment and was inserted into the genome by transfection into cells carrying a resident EBV genome. The resident EBV genome was simultaneously induced to replicate by using a cotransfected expression plasmid for the EBV immediate-early transactivator, Z (J. Countryman, H. Jenson, R. Seibl, H. Wolf, and G. Miller, J. Virol. 61:3672-3679, 1987; G. Miller, M. Rabson, and L. Heston, J. Virol. 50:174-182, 1984). Eleven percent of the resultant EBV genomes which incorporated the positive selection marker also incorporated the nonlinked marker. Both markers uniformly targeted the homologous EBV genome site. In this way novel EBV recombinants were constructed in which the EBV type 1 EBNA 3A, EBV type 1 EBNA 3A and 3B, or EBV type 1 EBNA 3A, 3B, and 3C genes were introduced into a largely type 2 EBV genome, replacing the corresponding type 2 gene(s). No difference was observed in primary B-lymphocyte growth transformation, in latent EBV gene expression, or in spontaneous lytic EBV gene expression. These new recombinants should be useful for ongoing analyses of the type specificity of the immune response.


Alterations to influenza virus hemagglutinin cytoplasmic tail modulate virus infectivity.

The influenza virus hemagglutinin (HA) contains a cytoplasmic domain that consists of 10 to 11 amino acids, of which five residues have sequence identity for 10 of 13 HA subtypes. To investigate properties of these conserved residues, oligonucleotide-directed mutagenesis was performed, using an HA cDNA of influenza virus A/Udorn/72 (H3N2) to substitute the conserved cysteine residues with other residues, to delete the three C-terminal conserved residues, or to remove the entire cytoplasmic domain. The altered HAs were expressed in eukaryotic cells, and the rates of intracellular transport were examined. It was found that substitution of either conserved cysteine residue within the cytoplasmic domain did not affect the rate of intracellular transport, whereas deletion of residues within the C-terminal domain resulted in delayed cell surface expression. All the altered HAs were biologically active in hemadsorption and fusion assays. To investigate whether the wild-type HA and HAs with altered cytoplasmic tails could complement the influenza virus temperature-sensitive transport-defective HA mutant A/WSN/33 ts61S, the HA cDNAs were expressed by using a transient expression system and released virus was assayed by plaque analysis. The wild-type HA expression resulted in a release of approximately 10(3) PFU of virus per ml. Antibody neutralization of complemented virus indicated that the infectivity was due to incorporation of wild-type H3 HA into ts61S virions. Sucrose density gradient analysis of released virions showed that each of the HA cytoplasmic domain mutants was incorporated into virus particles. Virions containing HAs with substitution of the cysteine residues in the cytoplasmic domain were found to be infectious. However, no infectivity could be detected from virions containing HAs that had deletions in their cytoplasmic domains. Possible roles of the HA cytoplasmic domain in forming protein-protein interactions in virions and their involvement in the initiation of the infection process in cells are discussed.


Simian virus 40 T-antigen DNA helicase is a hexamer which forms a binary complex during bidirectional unwinding from the viral origin of DNA replication.

The role of simian virus 40 (SV40) large tumor antigen (T antigen) as a DNA helicase at the replication fork was studied. We found that a T-antigen hexamer complex acts during the unidirectional unwinding of appropriate DNA substrates and is localized directly in the center of the fork, contacting the adjacent double strand as well as the emerging single strands. When bidirectional DNA unwinding, initiated at the viral origin of DNA replication, was analyzed, a larger T-antigen complex that is simultaneously active at both branch points of an unwinding bubble was observed. The size and shape of this helicase complex imply that the T-antigen dodecamer complex, assembled at the origin and active in the localized melting of duplex DNA, is subsequently also used to continue DNA unwinding bidirectionally. Then, however, the dodecamer complex does not split into two hexamer subunits that track along the DNA; rather, the DNA is threaded through the intact complex, with the concomitant extrusion of single-stranded loops.


Human papillomavirus type 1 E4 proteins differing by their N-terminal ends have distinct cellular localizations when transiently expressed in vitro.

Two major human papillomavirus type 1 (HPV-1) E4 proteins are found in large amounts in productively infected differentiating wart cells, a 17-kDa protein translated from an E1-E4 transcript and a processed 16-kDa protein lacking the E1 amino acids at least. The functions of the E4 proteins are still unknown. We have designed an in vitro system allowing the transient expression of three forms of HPV-1 E4 proteins: the 17-kDa E1-E4 protein, an E4 protein without the five E1 amino acids (E4-3200), and E4 protein initiated at the E4 ATG located upstream of the splice acceptor site (E4-3181). The E4-3181 protein has five additional N-terminal amino acids compared with E4-3200. The E4-3181 protein has not yet been detected in vivo but could, in principle, be translated from any transcript encoding the E2 protein. The constructs were transfected in two keratinocyte lines, one derived from a rabbit transplantable carcinoma (VX2R) and the other from a human penile carcinoma (SK-p). E4 transcripts with the expected size were detected in both cell lines by Northern (RNA) blot analysis. Surprisingly, the E4 proteins were found only in the VX2R cells by radioimmunoprecipitation and immunofluorescence experiments. The E1-E4 and the E4-3200 proteins were both cytoplasmic and were associated with granules reminiscent of the cytoplasmic inclusions pathognomonic of the HPV-1 infection. Moreover, each protein showed a specific staining pattern of the inclusions. In contrast, the E4-3181 protein was essentially intranuclear and perinuclear. Thus, HPV-1 E4 proteins differing in their N-terminal ends have distinct cellular localizations and arrangements. It is tempting to assume that this may relate to different roles.


Herpes simplex virus infection can occur without involvement of the fibroblast growth factor receptor.

Basic fibroblast growth factor (bFGF) has been reported to block uptake of herpes simplex virus type 1 (HSV-1) and plaque formation on arterial smooth muscle cells, suggesting a role for the bFGF receptor in HSV entry (R. J. Kaner, A. Baird, A. Mansukhani, C. Basilico, B. D. Summers, R. Z. Florkiewicz, and D. P. Hajjar, Science 248:1410-1413, 1990). We confirmed the effect of bFGF on infection of this cell type with HSV-1 and HSV-2 and found the same result with umbilical vein endothelial cells. However, bFGF does not inhibit plaque formation on any other cell type we tested. Furthermore, there is no correlation between the level of expression of the bFGF receptor and the effect of bFGF. HEp-2 and A431 cells express barely detectable levels of receptor, and yet they are fully permissive for HSV infection in a bFGF-insensitive manner. Thus, interaction of virus with the bFGF receptor is not required for infection of many cell types. In addition, infection of smooth muscle cells is not prevented by incubation of virus with an anti-bFGF antibody, arguing against the hypothesis that virion-associated bFGF acts as a bridge between virus and receptor (A. Baird, R. Z. Florkiewicz, P. A. Maher, R. J. Kaner, and D. P. Hajjar, Nature [London] 348:344-346, 1990).


Glycoprotein IV of bovine herpesvirus 1-expressing cell line complements and rescues a conditionally lethal viral mutant.

Glycoprotein IV (gIV) of bovine herpesvirus 1 (BHV-1), a homolog of herpes simplex virus glycoprotein D, represents a major component of the viral envelope and a dominant immunogen. To analyze the functional role of gIV during BHV-1 replication, cell line BUIV3-7, which constitutively expresses gIV, was constructed and used for the isolation of gIV- BHV-1 mutant 80-221, in which the gIV gene was replaced by a lacZ expression cassette. On complementing gIV-expressing cells, the gIV- BHV-1 replicated normally but was unable to form plaques and infectious progeny on noncomplementing cells. Further analysis showed that gIV is essential for BHV-1 entry into target cells, whereas viral gene expression, DNA replication, and envelopment appear unchanged in both noncomplementing and complementing cells infected with phenotypically complemented gIV- BHV-1. The block in entry could be overcome by polyethylene glycol-induced membrane fusion. After passaging of gIV- BHV-1 on complementing cells, a rescued variant, BHV-1res, was isolated and shown to underexpress gIV in comparison with its wild-type parent. Comparison of the penetration kinetics of BHV-1 wild type, phenotypically complemented gIV- BHV-1, and BHV-1res indicated that penetration efficiency correlated with the amount of gIV present in virus particles. In conclusion, we show that gIV of BHV-1 is an essential component of the virion involved in virus entry and that the amount of gIV in the viral envelope modulates the penetration efficiency of the virus.


Utilization of heterologous alphavirus junction sequences as promoters by Sindbis virus.

We used Sindbis virus, an alphavirus, as a model to study the evolution of the recognition of viral cis-acting sequences. During the life cycle of alphaviruses, a full-length minus-strand RNA is made and serves as a template for both genomic RNA replication and subgenomic mRNA transcription. Transcription initiates at an internal promoter site, the junction sequence, to produce a subgenomic mRNA. The junction sequences of alphaviruses are highly conserved, but they do contain a number of base differences. These could have been essentially neutral mutations during evolution, such that any of the contemporary sequences can be recognized efficiently by any of the alphaviruses. Alternately, the changes could have resulted in significant functional divergence, such that the contemporary viruses can no longer recognize heterologous junction sequences as promoters. To distinguish between these possibilities, we constructed Sindbis virus derivatives with two subgenomic mRNA promoters. One is the wild-type Sindbis virus promoter used for expression of the structural proteins. The other is either the minimal Sindbis virus promoter or the corresponding junction sequences from other alphaviruses, which are placed upstream of the bacterial chloramphenicol acetyltransferase (CAT) gene. RNA analyses were used to determine the relative promoter strengths of the various junction sequences. The results showed that all but two were recognized as promoters by Sindbis virus. CAT enzyme assays were used to measure the accumulation of CAT protein made from mRNAs transcribed by using the heterologous junction sequences as promoters. Most of the viruses expressed amounts of CAT enzyme within 10-fold of each other. The two viruses with junction sequences that were not recognized as promoters did not give significant CAT expression. We conclude that, with respect to Sindbis virus, the junction sequences are functionally conserved; i.e., most of the contemporary nucleotide differences in the junction sequences are neutral or near-neutral mutations. The functional conservation suggests that neither the cis-acting sequence nor the cognate binding site of the transcription factor can change independently. This type of coupled evolution between cis-acting sequences and their cognate viral protein binding sites may be a general phenomenon. For example, it explains the ubiquitous presence of conserved cis-acting sequences in each of the families of RNA viruses. There are implications of this hypothesis for the design of antiviral drugs.


Pseudorabies virus envelope glycoproteins gp50 and gII are essential for virus penetration, but only gII is involved in membrane fusion.

To investigate the function of the envelope glycoproteins gp50 and gII of pseudorabies virus in the entry of the virus into cells, we used linker insertion mutagenesis to construct mutant viruses that are unable to express these proteins. In contrast to gD mutants of herpes simplex virus, gp50 mutants, isolated from complementing cells, were able to form plaques on noncomplementing cells. However, progeny virus released from these cells was noninfectious, although the virus was able to adsorb to cells. Thus, the virus requires gp50 to penetrate cells but does not require it in order to spread by cell fusion. This finding indicates that fusion of the virus envelope with the cell membrane is not identical to fusion of the cell membranes of infected and uninfected cells. In contrast to the gp50 mutants, the gII mutant was unable to produce plaques on noncomplementing cells. Examination by electron microscopy of cells infected by the gII mutant revealed that enveloped virus particles accumulated between the inner and outer nuclear membranes. Few noninfectious virus particles were released from the cell, and infected cells did not fuse with uninfected cells. These observations indicate that gII is involved in several membrane fusion events, such as (i) fusion of the viral envelope with the cell membrane during penetration, (ii) fusion of enveloped virus particles with the outer nuclear membrane during the release of nucleocapsids into the cytoplasm, and (iii) fusion of the cell membranes of infected and uninfected cells.


Characterization of the Epstein-Barr virus BZLF1 protein transactivation domain.

Initiation of the Epstein-Barr virus (EBV) lytic cycle is dependent on expression of the viral transactivator Zta, which is encoded by the BZLF1 gene. Described here is an initial mapping of the regions of Zta involved in activating transcription. The data indicate that the amino-terminal 153 amino acids of Zta are important for activity, and in particular the region from residues 28 to 78 appears to be critical for Zta function. However, other features of Zta may be important for activity since a Gal4-Zta chimeric protein, generated by fusing the amino-terminal 167 residues of Zta to the DNA binding domain of the yeast transactivator Gal4, transactivated a minimal promoter containing one upstream Gal4 binding site but was unable to exhibit synergistic transactivation when assayed with a reporter containing five upstream Gal4 binding sites.


Characterization of the regulatory functions of the equine herpesvirus 1 immediate-early gene product.

Use of the translation-inhibiting drug cycloheximide has indicated that the equine herpesvirus 1 (EHV-1) immediate-early (IE) gene, the sole EHV-1 IE gene, encodes a major viral regulatory protein since IE mRNA translation is a prerequisite for all further viral gene expression (W.L. Gray, R. P. Baumann, A. T. Robertson, G. B. Caughman, D. J. O'Callaghan, and J. Staczek, Virology 158:79-87, 1987). An EHV-1 IE gene expression vector (pSVIE) in combination with chimeric EHV-1 promoter-chloramphenicol acetyltransferase (CAT) reporter constructs was used in transient transfection assays to characterize the regulatory functions of the IE gene product. These experiments demonstrated that (i) the EHV-1 IE gene product is a bifunctional protein capable of both positive and negative modulation of gene expression; (ii) the IE gene product possesses an autoregulatory function which represses the IE promoter; (iii) IE autoregulation is dependent on IE promoter sequences mapping within positions -288 to +73 relative to the transcription initiation site (+1) of the IE gene; (iv) the IE gene product can independently activate the EHV-1 tk promoter (an early promoter) by as much as 60-fold; (v) two EHV-1 beta-gamma (leaky late) promoters, those of IR5 (gene 5 in the inverted repeat) and the glycoprotein D gene, demonstrate a requirement for both the IE gene product as well as a gene product encoded within the EHV-1 XbaI G fragment for significant activation; and (vi) the IE gene product is capable of activating heterologous viral promoters.


Monoclonal antibodies to the spike protein of feline infectious peritonitis virus mediate antibody-dependent enhancement of infection of feline macrophages.

Antibody-dependent enhancement of virus infection is a process whereby virus-antibody complexes initiate infection of cells via Fc receptor-mediated endocytosis. We sought to investigate antibody-dependent enhancement of feline infectious peritonitis virus infection of primary feline peritoneal macrophages in vitro. Enhancement of infection was assessed, after indirect immunofluorescent-antibody labelling of infected cells, by determining the ratio between the number of cells infected in the presence and absence of virus-specific antibody. Infection enhancement was initially demonstrated by using heat-inactivated, virus-specific feline antiserum. Functional compatibility between murine immunoglobulin molecules and feline Fc receptors was demonstrated by using murine anti-sheep erythrocyte serum and an antibody-coated sheep erythrocyte phagocytosis assay. Thirty-seven murine monoclonal antibodies specific for the nucleocapsid, membrane, or spike proteins of feline infectious peritonitis virus or transmissible gastroenteritis virus were assayed for their ability to enhance the infectivity of feline infectious peritonitis virus. Infection enhancement was mediated by a subset of spike protein-specific monoclonal antibodies. A distinct correlation was seen between the ability of a monoclonal antibody to cause virus neutralization in a routine cell culture neutralization assay and its ability to mediate infection enhancement of macrophages. Infection enhancement was shown to be Fc receptor mediated by blockade of antibody-Fc receptor interaction using staphylococcal protein A. Our results are consistent with the hypothesis that antibody-dependent enhancement of feline infectious peritonitis virus infectivity is mediated by antibody directed against specific sites on the spike protein.


RNA sequence variants in live poliovirus vaccine and their relation to neurovirulence.

Mutant analysis by polymerase chain reaction and restriction enzyme cleavage (MAPREC) was used to study sequence heterogeneity and stability in attenuated poliovirus type 3 at positions in which the vaccine virus differs from its wild-type progenitor. Of seven genomic positions tested, only two (positions 472 and 2493) show nucleotide heterogeneity. Propagation of the vaccine virus in cell cultures leads to rapid selection of virus with reversions at these two positions of the genome. The relative abundance of reversions at position 472 correlates with the results of monkey neurovirulence tests, while the mutation at position 2493 is not directly associated with neurovirulence of the virus in monkeys. Instead, the abundance of mutations at the latter position correlates with the source of the seed virus and its passage level. These results further indicate that MAPREC at position 472 can be used to assess the quality of poliovirus type 3 vaccine.


Hepatitis B virus X protein activates transcription factor NF-kappa B without a requirement for protein kinase C.

The hepatitis B virus X protein stimulates transcription from a variety of promoter elements, including those activated by transcription factor NF-kappa B. A diverse group of extra- and intracellular agents, including growth factors and the human immunodeficiency virus tat protein, have been shown to require a functional protein kinase C (PKC) system to achieve activation of NF-kappa B. In this study we have investigated the molecular mechanism by which X protein activates NF-kappa B. We demonstrate that in hepatocytes, X protein induces a maximal activation of NF-kappa B corresponding to the sequestered pool of factor, which is also activated by phorbol esters. To determine whether X protein requires activation of PKC to stimulate transcription by NF-kappa B, we attempted to prevent transactivation by X protein in the presence of the PKC inhibitors calphostin C and H7. We show that PKC inhibitors do not block X protein activation of NF-kappa B, whereas they largely impair activation by phorbol esters. In addition, activation of PKC is correlated with its translocation from the cytoplasm to the plasma membrane. The subcellular distribution of PKC was investigated by introducing X protein from a replication-defective adenovirus vector, followed by immunochemical detection of PKC in cell fractions. These data also indicate that X protein stimulates transcription by NF-kappa B without the activation and translocation of PKC.


Platelet-derived growth factor receptor (beta-subunit) immunoreactivity in soft tissue tumors.

Using a well characterized monoclonal antibody (PR7212) to the beta-subunit of the platelet-derived growth factor receptor (PDGF-R(beta) and the avidin-biotin peroxidase method on frozen sections, we analyzed PDGF-R(beta) expression in 71 nonepithelial lesions as well as normal mesenchymal tissues. PDGF-R(beta) reactivity was observed in normal salivary gland, normal cutaneous and visceral fibroblasts, muscularis mucosa of bowel, and endothelial cells; squamous carcinoma was negative. Interestingly, hepatocytes and lymph node histiocytes were also positive. Positive tumors included malignant fibrous histiocytoma (6/6), benign and malignant smooth muscle tumors (5/6 leiomyoma, 8/9 leiomyosarcoma), liposarcoma (4/4), synovial sarcoma (6/7), angiosarcoma (2/2), and sarcoma NOS (2/2). Fibromatosis cases were also positive (2/2). In many tumors, the reactive fibroblasts and vascular components were also reactive. The characteristic pattern of reactivity in fibroblastic lesions highlighted thin cytoplasmic extensions or strands not visible in normal hematoxylin and eosin-stained sections. Expression of PDGF-R(beta) was not necessarily correlated with the presence of PDGF. We conclude that PDGF-R(beta) expression can be identified in a wide variety of mesenchymal lesions and postulate that its presence may be important in the mechanism of growth of these tumors.


Enteroviral infection of mice with severe combined immunodeficiency. Evidence for direct viral pathogenesis of myocardial injury.

Inbred mice with genetically determined severe combined immunodeficiency (SCID) lack mature T and B lymphocyte functions. To distinguish direct viral effects in the pathogenesis of myocarditis from those mediated by antigen-specific and histocompatibility-complex-restricted host immunity, we inoculated coxsackievirus B3 into homozygous young adult SCID mice. We found that infected SCID mice invariably developed extensive myocarditis between 7 and 14 days postinoculation with high subsequent mortality. Histopathologic examination of the infected SCID myocardium indicated multiple foci of cardiomyocyte necrosis and a delayed pleomorphic inflammatory infiltrate. Immunohistochemically, the coxsackievirus B3-infected SCID heart contained frequent clusters of macrophages (Mac-1+) as well as other cells that may represent nonspecific phagocytic or cytolytic effectors. In situ hybridization with radiolabeled cDNA probes for enteroviral genome indicated a significant excess of positive-strand genome in the SCID myocardium compared with that in similarly infected non-SCID controls, with hybridization signals localized primarily to cardiomyocytes. In vitro culture confirmed persistent viremia and a vast excess of infective virus in the SCID myocardium relative to infected non-SCID controls. Thus, direct viral mechanisms in the production of cardiomyocyte injury in coxsackievirus B3-infected mice appear to be more important than previously recognized, particularly in the setting of unrestricted viral proliferation.


Herpes simplex virus type 1 replicates in the lens and induces cataracts in mice.

In a mouse model, cataracts were produced after corneal inoculation with herpes simplex virus type 1 (HSV-1) strain F. Viral antigen was detected in vivo by the immunoperoxidase technique in lens fibers and occasionally in lens epithelial cell nuclei at 4 and 5 days postinoculation. HSV-1 replication within the lens was further demonstrated by virus isolation from lenses that had been inoculated in vitro. Lens lesions in mice were present as early as 4 days postinoculation and by later times (23 to 60 days postinoculation), severe degenerative changes typical of cataracts were present in many of the lenses examined histologically. Viral DNA was detected in extracts of lenses from infected animals at 5 and 11 days postinoculation. In contrast to HSV-1 F, the KOS strain of HSV-1 produced intraocular infection and cataracts at a much lower frequency in mice. Lens lesions appear to be induced directly by viral replication within the lens; however, other mechanisms involving inflammation in adjacent eye structures may also be involved in the pathogenesis of these lesions. Based upon these data, it is reasonable to consider the possibility that HSV-1 may be involved in the production of cataracts in humans in some cases.


Transgenic mice expressing polyoma virus large T antigen in astrocytes develop severe dysmyelination of the central nervous system.

Transgenic mice were generated using a construct that encodes mouse polyoma virus large T antigen, one of three oncogenic products of the "early region" of the polyoma viral genome. Of 16 transgenic families developed, 1 was characterized by a neurologic disorder consisting of constant tremor and recurrent seizures. Morphologic analysis of the central nervous system (CNS) of affected transgenic mice included: classical light and electron microscopic examination; immunohistochemical assessment of the presence and localization of myelin-specific proteins, of the astrocyte marker glial fibrillary acidic protein, of the oligodendrocyte marker galactosyl cerebroside, and of large T; double immunolabeling of glial fibrillary acidic protein or galactosyl cerebroside and large T to identify the CNS cell type in which large T is expressed; and in situ hybridization to study myelin basic protein gene expression. Our results suggest that polyoma large T is expressed in astrocytes, possibly resulting in altered glial-glial interactions causing impaired oligodendroglial development and secondary dysmyelination. Transgenic oligodendrocytes exhibit features of immaturity, failing to myelinate axons properly and producing morphologic phenotypes of early stages of myelination, such as numerous mesaxonal profiles. Myelin proteins are markedly reduced in transgenic CNS, and myelin basic protein transcripts, while present, are generally decreased. We believe that expression of large T in astrocytes could influence the complex and dynamic interactions between astrocytes and oligodendrocytes, perhaps with regard to the molecular (trophic) signals in the local CNS environment, bringing about arrested oligodendroglial maturation and hypomyelination. This raises intriguing questions concerning the importance of glial-glial interactions in the CNS and the complex levels of control involved in biological expression of genetic information in glial cells.


Peripheral neuropathy induced by 2',3'-dideoxycytidine. A rabbit model of 2',3'-dideoxycytidine neurotoxicity.

The nucleoside analog 2',3'-dideoxycytidine (ddC) is a potent inhibitor of the reverse transcriptase of human immunodeficiency virus and a DNA chain terminator. In clinical trials in patients with acquired immunodeficiency syndrome, ddC treatment has been associated with a dose-limiting and dose-dependent, painful, sensorimotor peripheral neuropathy. In search of an animal model for ddC-induced neurotoxicity we studied 36 New Zealand White rabbits (3 males/3 females/group) given 0, 10, 50, 100, 150, or 250 mg/kg/day of ddC, by oral intubation, for 13 or 18 weeks. Rabbits in the 150 and 250 mg/kg/day groups were sacrificed at 13 weeks because of hematopoietic toxicity. After 16 weeks, rabbits in the 50 and 100 mg/kg/day groups showed hindlimb paresis and/or gait abnormalities. Nerve conduction velocities and amplitudes in the 100 mg/kg/day rabbits were reduced by 30 to 50%. The most prominent pathologic changes in peripheral nerve and ventral roots of ddC-treated rabbits were (a) myelin splitting and intramyelinic edema, (b) demyelination and remyelination of axons, and (c) axonal loss. Treatment-related histologic lesions were not observed in spinal cord, brain, or retina. The pathology in these ddC-treated rabbits is consistent with a peripheral myelinopathy and axonopathy. This represents the first clinical, electrophysiologic, and pathologic description of an animal model of a peripheral neuropathy induced by a nucleoside analog.


Ultrastructure of peripheral neuropathy induced in rabbits by 2',3'-dideoxycytidine.

The nucleoside analogue, 2',3'-dideoxycytidine (ddC), an inhibitor of human immunodeficiency virus reverse transcriptase, mediates virologic and immunologic improvements in acquired immunodeficiency syndrome patients. However, in clinical studies ddC treatment is associated with a dose-limiting peripheral neuropathy. The purpose of this study was to characterize the ultrastructural features of the peripheral neuropathy induced in rabbits. Rabbits received 0, 10, 50, or 100 mg/kg/day of ddC for 18 weeks. A prominent ultrastructural change induced by ddC in sciatic nerve and ventral root was separation of myelin lamellae at the intraperiod line and vacuolation and fragmentation of myelin sheaths. Many demyelinated and remyelinated axons were observed. Although pathologic alterations in Schwann cells were evident by the presence of lipid droplets and myelin figures, their formation was not considered a primary event. Axons containing abnormal cytoplasmic components were occasionally observed. Other changes included redundance of Schwann cell basal lamina and the presence of lipid droplets and/or myelin figures within endoneurial fibroblasts and macrophages. The results of this study indicate that ddC induces a myelinopathy in rabbits characterized by myelin splitting and intramyelinic edema and an axonopathy that may be secondary to the myelin changes.


A comparison of risk factors in juvenile-onset and adult-onset recurrent respiratory papillomatosis.

The clinical triad of a firstborn delivered vaginally to a young (teenage) mother has been previously noted among juvenile onset recurrent respiratory papillomatosis (JO-RRP) patients. This study was based on a questionnaire survey of JO-RRP patients, adult onset recurrent respiratory papillomatosis (AO-RRP) patients, and juvenile and adult controls. The survey results revealed that the complete or partial triad was observed in 72% of JO-RRP patients, 36% of AO-RRP patients, 29% of juvenile controls, and 38% of adult controls. As compared with juvenile controls, JO-RRP patients were more often firstborn (P less than .05), delivered vaginally (P less than .05), and born to a teenage mother (P less than .01). Among adult participants, AO-RRP patients reported more lifetime sex partners (P less than .01) and a higher frequency of oral sex (P less than .05) than reported by adult controls. AO-RRP and JO-RRP appear to have distinguishable epidemiologic features indicating that the mode of human papillomavirus (HPV) transmission is different in these two disorders.


Evidence for antagonistic activity of endothelin for clonidine induced hypotension and bradycardia.

Effect of endothelin (ET) on clonidine induced cardiovascular effects was studied in male Sprague-Dawley rats. Clonidine (75 micrograms/kg, iv) produced significant decrease in blood pressure and heart rate. ET-1 (50 ng/kg, iv) pretreatment completely antagonized the hypotension and bradycardia induced by clonidine. ET-2 (50 ng/kg, iv) and ET-3 (50 ng/kg, iv) had similar antagonistic effect on clonidine induced hypotension and bradycardia. The antagonistic effect of ET lasted for several hours, however, 4 hours after ET pretreatment only partial blockade of clonidine induced hypotension and bradycardia was observed. This indicated that the antagonistic effect of ET was reversible. Initial hypertensive response induced by high dose of clonidine (750 micrograms/kg, iv) could not be antagonized by ET-1, ET-2 or ET-3, while phenoxybenzamine, an alpha adrenoceptor antagonist, blocked the hypertensive response of clonidine. Thus, ET has no antagonistic effect on the initial hypertensive response but antagonizes the hypotensive and bradycardic effect induced by clonidine. Clonidine induced hypotension and bradycardia are mediated through central alpha 2 adrenoceptors while hypertension is mediated through peripheral alpha 2 adrenoceptors. It is concluded that central alpha 2 adrenoceptors are different from peripheral alpha 2 adrenoceptors and ET antagonizes the effect of clonidine only on central alpha 2 adrenoceptors but has no antagonistic activity on peripheral alpha 2 adrenoceptors.


Properties and functions of human placental opioid system.

Human placental villus tissue contains opioid receptors and peptides. Kappa opioid receptors (the only type present in this tissue) were purified with retention of their binding properties. The purified kappa receptor is a glycoprotein with an apparent molecular weight of 63,000. Two opioid receptor mediated functions were identified in trophoblast tissue, namely regulation of acetylcholine and hormonal (human chorionic gonadotrophin and human placental lactogen) release. Placental content of kappa receptors increases with gestational age. Term placental content of kappa receptors correlates with route of delivery (higher in those abdominally obtained). Opioid use and/or abuse during pregnancy affects placental receptor content at delivery, as well as its mediated functions. Opioid peptides identified in placental extracts were beta-endorphin, methionine enkephalin, leucine enkephalin and dynorphins 1-8 and 1-13. Dynorphin 1-8 seem to be the predominant opioid peptide present in placental villus tissue.


Simultaneous effects of the platelet 5-HT2 and alpha 2-adrenergic receptor populations on phosphoinositide hydrolysis.

The interaction of multiple receptor populations on a common second messenger system is a critical aspect of cell function and may be involved in pathology. We studied the interactions of the 5-HT2, alpha 2-adrenergic and prostaglandin (PGI2) receptors on phosphoinositide (PI) turnover in human platelets. Serotonin and epinephrine (EPI) stimulated PI hydrolysis in a dose-dependent manner. The PI turnover response to serotonin was mediated by the 5-HT2 receptor. The PI response to EPI was mediated by alpha 2-adrenergic receptors. An additive PI turnover response was generated by the combination of 5-HT and EPI. The sum of the maximal responses to 5-HT (72.5 +/- 4.9%) and EPI (56.0 +/- 4.2%) approximated the maximal response (129.3 +/- 9.5) to the combination. Prostacyclin (PGI2) at 1 microgram/mL reduced PI turnover by 21.8 +/- 1.1%. The PI response to 5-HT and EPI was not significantly altered once the reduction in the baseline PI turnover by PGI2 is taken into account. Similarly, PGI2 did not reduce PI hydrolysis stimulated by a combination of 5-HT (0.2 mM) and EPI (0.1 mM) once the decrease in baseline was taken into account (p greater than 0.20). The summation of serotonin stimulation of PI turnover by a combination of both epinephrine and serotonin was blocked by either yohimbine or ketanserin. These studies indicate: (1) the pool of phospholipases appears to exceed the maximal capacity of the individual alpha 2-adrenergic and 5-HT2 receptor populations to activate this second messenger system. (2) inhibition of serotonin or epinephrine-stimulated PI turnover by prostacyclin is due to a lowering of basal PI turnover. Future studies should examine other cell systems to assess the generalizability of these findings regarding the differences in effects on a second messenger system when activated by one receptor population as opposed to two different receptor types.


Non-isopeptide-selective endothelin receptors in human Girardi heart cells.

We characterized the endothelin (ET) receptor in Girardi heart (GH) cells derived from human atrium. The ET isopeptides ET-1, ET-2 and ET-3 induced the monotonous and long-lasting rise in cytosolic free Ca2+ concentration [( Ca2+]i) with almost the same potency in GH cells. Scatchard analysis of [125I]ET-1 and [125I]ET-3 binding revealed that GH cells have almost the same number of binding sites for either labeled ligand. All ET isopeptides displaced either [125I]ET-1 or [125I]ET-3 binding in GH cells almost equipotently. These results reveal that the functional ET receptors in GH cells are of the ETB-type. GH cells are the first cell line to be found to express the functional ETB-receptor.


Mapping T-cell receptor-peptide contacts by variant peptide immunization of single-chain transgenics.

To test models of T-cell recognition, mice transgenic for T-cell receptor alpha or beta chain have been immunized with variant peptides that force changes in the resulting T-cell response. In particular, charge substitutions on the peptide often elicit reciprocal charges in the junctional (CDR3) sequences of T-cell receptor V alpha or V beta chains, indicating direct T-cell receptor-peptide contact, and allowing derivation of a topology for the T-cell receptor-MHC interaction. At one position on the peptide, variants transformed a homogeneous V beta response into a very heterogeneous one.


MutT protein specifically hydrolyses a potent mutagenic substrate for DNA synthesis.

Errors in the replication of DNA are a major source of spontaneous mutations, and a number of cellular functions are involved in correction of these errors to keep the frequency of spontaneous mutations very low. We report here a novel mechanism which prevents replicational errors by degrading a potent mutagenic substrate for DNA synthesis. This error-avoiding process is catalysed by a protein encoded by the mutT gene of Escherichia coli, mutations of which increase the occurrence of A.T----C.G transversions 100 to 10,000 times the level of the wild type. Spontaneous oxidation of dGTP forms 8-oxo-7,8-dihydro-2'-dGTP (8-oxodGTP), which is inserted opposite dA and dC residues of template DNA with almost equal efficiency, and the MutT protein specifically degrades 8-oxodGTP to the monophosphate. This indicates that elimination from the nucleotide pool of the oxidized form of guanine nucleotide is important for the high fidelity of DNA synthesis.


Depletion of intracellular calcium stores activates a calcium current in mast cells.

In many cell types, receptor-mediated Ca2+ release from internal stores is followed by Ca2+ influx across the plasma membrane. The sustained entry of Ca2+ is thought to result partly from the depletion of intracellular Ca2+ pools. Most investigations have characterized Ca2+ influx indirectly by measuring Ca(2+)-activated currents or using Fura-2 quenching by Mn2+, which in some cells enters the cells by the same influx pathway. But only a few studies have investigated this Ca2+ entry pathway more directly. We have combined patch-clamp and Fura-2 measurements to monitor membrane currents in mast cells under conditions where intracellular Ca2+ stores were emptied by either inositol 1,4,5-trisphosphate, ionomycin, or excess of the Ca2+ chelator EGTA. The depletion of Ca2+ pools by these independent mechanisms commonly induced activation of a sustained calcium inward current that was highly selective for Ca2+ ions over Ba2+, Sr2+ and Mn2+. This Ca2+ current, which we term ICRAC (calcium release-activated calcium), is not voltage-activated and shows a characteristic inward rectification. It may be the mechanism by which electrically nonexcitable cells maintain raised intracellular Ca2+ concentrations and replenish their empty Ca2+ stores after receptor stimulation.


Inositol 1,3,4,5-tetrakisphosphate activates an endothelial Ca(2+)-permeable channel.

Receptor-mediated increases in the cytosolic free calcium ion concentration in most mammalian cells result from mobilization of Ca2+ from intracellular stores as well as transmembrane Ca2+ influx. Inositol 1,4,5-trisphosphate (InsP3) releases calcium from intracellular stores by opening a Ca(2+)-permeable channel in the endoplasmic reticulum. But the mechanism and regulation of Ca2+ entry into nonexcitable cells has remained elusive because the entry pathway has not been defined. Here we characterize a novel inositol 1,3,4,5-tetrakisphosphate (InsP4) and Ca(2+)-sensitive Ca(2+)-permeable channel in endothelial cells. We find that InsP4, which induces Ca2+ influx into acinar cells, enhances the activity of the Ca(2+)-permeable channel when exposed to the intracellular surface of endothelial cell inside-out patches. Our results suggest a molecular mechanism which is likely to be important for receptor-mediated Ca2+ entry.


9-cis retinoic acid stereoisomer binds and activates the nuclear receptor RXR alpha.

Vitamin A (retinol) and its natural derivatives are required for many physiological processes. The activity of retinoids is thought to be mediated by interactions with two subfamilies of nuclear retinoic acid receptors, RAR and RXR. The RARs bind all-trans retinoic acid (t-RA) with high affinity and alter gene expression as a consequence of this direct ligand interaction. RXR alpha is activated by t-RA, yet has little binding affinity for this ligand. t-RA may be converted to a more proximate ligand that directly binds and activates RXR alpha, and we have developed a method of nuclear receptor-dependent ligand trapping to test this hypothesis. Here we report the identification of a stereoisomer of retinoic acid, 9-cis retinoic acid, which directly binds and activates RXR alpha. These results suggest a new role for isomerization in the physiology of natural retinoids.


Herpesvirus saimiri encodes homologues of G protein-coupled receptors and cyclins.

Herpesvirus saimiri (HVS) is a T-lymphotropic gammaherpesvirus which establishes asymptomatic infections in its natural host the squirrel monkey (Saimiri sciureus), but which causes fatal lymphoproliferative diseases in other New World primates. Sequencing studies show HVS is closely related to the human B-lymphotropic gammaherpesvirus Epstein-Barr virus (EBV). However, despite the general colinearity between the genomes of HVS and EBV, HVS contains genes not found in EBV or in the genomes of any of the other sequenced herpesviruses. We have identified two genes, occurring in a region of divergence between HVS and EBV, that have cellular homologues. One of these, ECRF3, is homologous to the genes encoding the human cytomegalovirus (HCMV) and cellular G protein-coupled receptor family of proteins. The other HVS gene, ECLF2, is homologous to the genes encoding cellular cyclins and to our knowledge is the first reported example of a viral cyclin. The presence of G protein-coupled receptor and cyclin homologues in HVS suggests that these genes may be important in the regulation of viral and cellular processes during productive and/or latent infection of host cells, and in particular may be of relevance in the transformation and rapid proliferation of T cells during HVS infections of hosts susceptible to HVS-induced lymphoproliferative diseases.


Two new combinations of estrogen and progestogen for prevention of postmenopausal bone loss: long-term effects on bone, calcium and lipid metabolism, climacteric symptoms, and bleeding.

Bone mass, calcium and lipid metabolism, climacteric symptoms, bleeding, blood pressure, and weight changes were studied in 62 healthy postmenopausal women at 3-month intervals throughout 2 years of treatment with continuous estradiol valerate (2 mg) plus cyproterone acetate (1 mg), sequential estradiol valerate (2 mg) plus levonorgestrel (75 micrograms), or placebo. During the 2 years of the study, bone mineral content of the distal and ultradistal regions of the forearm (measured by single-photon absorptiometry) remained unchanged in the hormone groups, whereas bone mineral content at these sites decreased by 5 and 6%, respectively, in the placebo group. Bone mineral density in the spine (measured by dual-photon absorptiometry and dual-energy x-ray absorptiometry) increased by 3-4% in the hormone groups and decreased by 2% in the placebo group. Biochemical estimates of bone turnover (serum alkaline phosphatase and fasting urinary calcium/creatinine) decreased significantly to premenopausal levels in the hormone groups, but remained unchanged in the placebo group. Serum concentrations of total and low-density lipoprotein cholesterol were significantly reduced by 5-10% (P less than .05-.01) in the estradiol + cyproterone acetate group and by 10-15% (P less than .001) in the estradiol valerate + levonorgestrel group. There were no significant changes in high-density lipoprotein cholesterol in the hormone groups. Virtually no changes were observed in the placebo group. Climacteric symptoms and hot flushes were significantly reduced in both hormone groups compared with the placebo group.(ABSTRACT TRUNCATED AT 250 WORDS)


Molecular cloning of a calmodulin-dependent phosphatase from murine testis: identification of a developmentally expressed nonneural isoenzyme.

A unique isoform of the catalytic subunit of calmodulin-dependent protein phosphatase (CaM-PrP) was cloned from a murine testis library. The cDNA sequence of 1964 base pairs contained an open reading frame encoding a protein of 513 amino acids (Mr approximately 58,706), the predicted isoelectric point of which (pI 7.1) was much more basic than those of brain isoforms (pI 5.6-5.8). The deduced amino acid sequence was 77-81% identical to two other murine CaM-PrP genes and displayed a distinct Southern blot hybridization pattern, indicating that it was derived from a separate gene (type 3). High amounts of a 2800-nucleotide mRNA transcript were observed in testis, whereas mRNA species were not detectable in brain; thus, it seems likely that this CaM-PrP represents a nonneural isoenzyme. Measurements of CaM-PrP mRNA during testicular development showed a dramatic increase in expression during weeks 4-6, correlating with the later stages of spermatogenesis. These data suggest that this phosphatase isoform may be involved in germ-cell function and are consistent with the report of a flagellum-associated form of CaM-PrP that may regulate sperm motility [Tash, J. S., Krinks, M., Patel, J., Means, R. L., Klee, C. B. & Means, A. R. (1988) J. Cell Biol. 106, 1625-1633].


Primary structure and functional expression of the human cardiac tetrodotoxin-insensitive voltage-dependent sodium channel.

The principal voltage-sensitive sodium channel from human heart has been cloned, sequenced, and functionally expressed. The cDNA, designated hH1, encodes a 2016-amino acid protein that is homologous to other members of the sodium channel multigene family and bears greater than 90% identity to the tetrodotoxin-insensitive sodium channel characteristic of rat heart and of immature and denervated rat skeletal muscle. Northern blot analysis demonstrates an approximately 9.0-kilobase transcript expressed in human atrial and ventricular cardiac muscle but not in adult skeletal muscle, brain, myometrium, liver, or spleen. When expressed in Xenopus oocytes, hH1 exhibits rapid activation and inactivation kinetics similar to native cardiac sodium channels. The single channel conductance of hH1 to sodium ions is about twice that of the homologous rat channel and hH1 is more resistant to block by tetrodotoxin (IC50 = 5.7 microM). hH1 is also resistant to mu-conotoxin but sensitive to block by therapeutic concentrations of lidocaine in a use-dependent manner.


Cortical neurons express nerve growth factor receptors in advanced age and Alzheimer disease.

Using a monoclonal antibody directed against the primate nerve growth factor (NGF) receptor, we examined the expression of NGF receptors within neuronal perikarya of normal adult human cerebral cortex (27-98 years old) and individuals with Alzheimer disease (AD). This expression of cortical NGF receptors was compared with that seen in other neurological diseases and normal human development as well as in young and aged nonhuman primates. NGF receptor-containing cortical neurons were not observed in young adults (less than 50 years old) and were observed only infrequently in non-demented elderly individuals (50-80 years old). In contrast, numerous NGF receptor-containing cortical neurons were seen in AD patients of all ages and in one 98-year-old nondemented patient. In advanced age and AD, numerous NGF receptor-positive neurons were located within laminae II-VI of temporal association cortices whereas only a few were seen in the subicular complex, entorhinal cortex, parahippocampal gyrus, and amygdaloid complex. These perikarya appeared healthy, with bipolar, fusiform, or multipolar morphologies and extended varicose dendritic arbors. These neurons failed to express neurofibrillary tangle-bearing material. In contrast to AD, NGF receptor-containing cortical neurons were not observed in Parkinson disease, Pick disease, or Shy-Drager syndrome. The NGF receptor-containing cortical neurons seen in advanced age and AD were similar in morphology to those observed in human fetal cortex. No NGF receptor-containing cortical neurons were observed in young or aged nonhuman primates. These findings suggest that neurons within the human cerebral cortex exhibit plasticity in their expression of NGF receptors in AD and extreme advanced aging.


Cloning of the alpha 1 subunit of a voltage-dependent calcium channel expressed in pancreatic beta cells.

The isoforms of the alpha 1 subunits of voltage-dependent Ca2+ channels expressed in human pancreatic islets were identified by using a pair of degenerate oligonucleotide primers and the polymerase chain reaction (PCR) to amplify mRNAs encoding alpha 1 subunit-like sequences. The sequences of the PCR products indicate that islets express the heart-type alpha 1 subunit as well as a second isoform whose complete sequence has not been previously reported. The sequences of cloned cDNAs encoding the human beta-cell, or neuroendocrine-type, alpha 1 subunit indicate that it is composed of 2181 amino acids. It shares 68%, 64%, and 41% identity with the sequences of the alpha 1 subunits of rabbit heart, skeletal muscle, and brain, respectively, and is predicted to have a similar structure including four homologous domains composed of six membrane-spanning segments each. RNA blotting studies indicate that the beta-cell-type alpha 1 subunit is also expressed in brain as well as in the insulin-producing cell lines RINm5F and beta TC-3; however, it could not be detected by RNA blotting in a third cell line, HIT-T15. In situ hybridization studies revealed expression of beta-cell-type alpha 1 subunit mRNA in beta cells of rat pancreatic islets, implying that this protein may play a role in the regulation of insulin secretion.


Regulation of DNA replication in vitro by the transcriptional activation domain of GAL4-VP16.

Studies of DNA viruses have provided evidence that eukaryotic transcriptional activator proteins can enhance the efficiency of DNA replication as well as transcription. The mechanism of this effect was studied in vitro using the chimeric transcription factor GAL4-VP16 and a DNA template containing GAL4 binding sites adjacent to the simian virus 40 origin of DNA replication. The binding of GAL4-VP16 prevented the repression of DNA replication which otherwise occurred when the template was assembled into chromatin. Relief of repression by GAL4-VP16 required both its DNA-binding and transcriptional activation domains but did not require RNA synthesis. The results are consistent with a general model in which transcriptional activators stimulate eukaryotic DNA replication by modifying the outcome of the competition between initiation factors and histones for occupancy of the origin.


Identification of a 1,25-dihydroxyvitamin D3-response element in the 5'-flanking region of the rat calbindin D-9k gene.

The rat calbindin D-9k gene is transcriptionally regulated by 1,25-dihydroxyvitamin D3 in the intestine. We have examined the 5'-flanking region of this gene and identified a 1,25-dihydroxyvitamin D3-responsive element (DRE) between nucleotides -489 and -445. This element confers 1,25-dihydroxyvitamin D3 responsiveness through its native promoter and the heterologous thymidine kinase promoter, and it contains the sequence GGGTGTCGGAAGCCC, which is homologous to the other previously identified DREs. Incubation of this element with the 1,25-dihydroxyvitamin D3 receptor produced a specific protein-DNA complex, which shifted to a higher molecular weight form upon the addition of a monoclonal antibody specific to the 1,25-dihydroxyvitamin D3 receptor. Therefore, the 5'-flanking region of the rat calbindin D-9k gene contains a DRE that mediates the enhanced expression of this gene by 1,25-dihydroxyvitamin D3 in the intestine.