Nuclear corepressor for KRAB domain-containing zinc finger proteins (KRAB-ZFPs). Mediates gene silencing by recruiting CHD3, a subunit of the nucleosome remodeling and deacetylation (NuRD) complex, and SETDB1 (which specifically methylates histone H3 at 'Lys-9' (H3K9me)) to the promoter regions of KRAB target genes. Enhances transcriptional repression by coordinating the increase in H3K9me, the decrease in histone H3 'Lys-9 and 'Lys-14' acetylation (H3K9ac and H3K14ac, respectively) and the disposition of HP1 proteins to silence gene expression. Recruitment of SETDB1 induces heterochromatinization. May play a role as a coactivator for CEBPB and NR3C1 in the transcriptional activation of ORM1. Also a corepressor for ERBB4. Inhibits E2F1 activity by stimulating E2F1-HDAC1 complex formation and inhibiting E2F1 acetylation. May serve as a partial backup to prevent E2F1-mediated apoptosis in the absence of RB1. Important regulator of CDKN1A/p21(CIP1). Has E3 SUMO-protein ligase activity toward itself via its PHD-type zinc finger. Also specifically sumoylates IRF7, thereby inhibiting its transactivation activity. Ubiquitinates p53/TP53 leading to its proteosomal degradation; the function is enhanced by MAGEC2 and MAGEA2, and possibly MAGEA3 and MAGEA6. Mediates the nuclear localization of KOX1, ZNF268 and ZNF300 transcription factors. In association with isoform 2 of ZFP90, is required for the transcriptional repressor activity of FOXP3 and the suppressive function of regulatory T-cells (Treg) (PubMed:23543754). Probably forms a corepressor complex required for activated KRAS-mediated promoter hypermethylation and transcriptional silencing of tumor suppressor genes (TSGs) or other tumor-related genes in colorectal cancer (CRC) cells (PubMed:24623306). Required to maintain a transcriptionally repressive state of genes in undifferentiated embryonic stem cells (ESCs) (PubMed:24623306). In ESCs, in collaboration with SETDB1, is also required for H3K9me3 and silencing of endogenous and introduced retroviruses in a DNA-methylation independent-pathway (By similarity). Associates at promoter regions of tumor suppressor genes (TSGs) leading to their gene silencing (PubMed:24623306). The SETDB1-TRIM28-ZNF274 complex may play a role in recruiting ATRX to the 3'-exons of zinc-finger coding genes with atypical chromatin signatures to establish or maintain/protect H3K9me3 at these transcriptionally active regions (PubMed:27029610). (Microbial infection) Plays a critical role in the shutdown of lytic gene expression during the early stage of herpes virus 8 primary infection. This inhibition is mediated through interaction with herpes virus 8 protein LANA1. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein sumoylation. Interacts with SETX (PubMed:23149945). Oligomer; the RBCC domain homotrimerizes and interacts with one molecule of KRAB to form the KRAB-KAP1 corepressor complex. Binding to a KRAB domain is an absolute requirement for silencing gene expression. Interacts with CEBPB and NR3C1. Interacts with a number of KRAB-ZFP proteins including ZNF10, ZFP53, ZFP68, ZNF382 and ZNF256. Interacts with NCOR1, NR3C1 and CHD3. Interacts with CEBPB (via the RING-type and PHD-type zinc fingers). Component of a ternary complex that includes TRIM28, a HP1 protein (CBX1, CBX3 OR CBX5), a KRAB domain-containing protein, and DNA. Interacts with CBX5 (via the PxVxL motif); the interaction occurs in interphase nuclei and competes for binding POGZ. Interacts with POGZ; the interaction competes for interaction with CBX5. Interacts with SETDB1; the interaction is enhanced by KAP1 sumoylation, stimulates SETDB1 histone methyltransferase activity and gene silencing. Interacts (via the PHD-type zinc finger) with UBE2I; the interaction is required for sumoylation and repressor activity. Component of the TRIM28/KAP1-ERBB4-MDM2 complex involved in connecting growth factor and DNA damage responses. Interacts directly with ERBB4; the interaction represses ERBB4-mediated transcription activity. Interacts with MDM2; the interaction contributes to p53/TP53 inactivation. Component of the TRIM28/KAP1-MDM2-p53/TP53; involved in regulating p53/TP53 stabilization and activity. Interacts (via the leucine zipper alpha helical coiled-coil) with E2F1 (central region); the interaction inhibits E2F1 acetylation and transcriptional activity. Interacts with PPP1CA; the interaction dephosphorylates TRIM28 at Ser-824 and forms a complex at the p21 promoter site. Interacts with PPP1CB; the interaction is weak but is increased on dephosphorylation at Ser-824. Interacts with FES/FPS. Interacts with SMARCAD1. Interacts with, and sumoylates IRF7. Interacts with MAGEC2. Part of a complex composed of TRIM28, HDAC1, HDAC2 and EHMT2 (PubMed:21549307). Interacts with AICDA (By similarity). Interacts (via the RBCC domain) with KOX1 (via the KRAB domain), ZNF268 (via the KRAB domain) and ZNF300 (via the KRAB domain); the interactions increase KOX1, ZNF268 and ZNF300 nuclear localization activities. The large PER complex involved in the histone methylation is composed of at least PER2, CBX3, TRIM28, SUV39H1 and/or SUV39H2; CBX3 mediates the formation of the complex. Interacts with isoform 2 of ZFP90. Forms a complex with FOXP3 in the presence of isoform 2 of ZFP90. Interacts with NR4A3; the interactions potentiates NR4A3 activity on NurRE promoter (By similarity). Interacts (unphosphorylated or phosphorylated form) with ZBTB1 (via BTB domain) (PubMed:24657165). Probably part of a corepressor complex containing ZNF304, TRIM28, SETDB1 and DNMT1 (PubMed:24623306). Interacts with ATRX. Forms a complex with ATRX, SETDB1 and ZNF274 (PubMed:27029610). Interacts with ZFP568; the interaction mediates ZFP568 transcriptional repression activity (By similarity). Interacts with RRP1B (PubMed:19710015). Interacts with CRY1 (By similarity). Interacts with ZNF263; recruited to the SIX3 promoter along with other proteins involved in chromatin modification and transcriptional corepression where it contributes to transcriptional repression (PubMed:32051553). Interacts with CYREN (via XLF motif) (By similarity). Interacts with TRIM17; this interaction prevents TRIM28 activity (PubMed:30042493). Interacts with ZNF746 (PubMed:31856708). (Microbial infection) Interacts with herpes virus 8 protein LANA1; this interaction facilitates establishment of viral latency. Associated with centromeric heterochromatin during cell differentiation through CBX1. Expressed in all tissues tested including spleen, thymus, prostate, testis, ovary, small intestine, colon and peripheral blood leukocytes. The HP1 box is both necessary and sufficient for HP1 binding. The PHD-type zinc finger enhances CEBPB transcriptional activity. The PHD-type zinc finger, the HP1 box and the bromo domain, function together to assemble the machinery required for repression of KRAB domain-containing proteins. Acts as an intramolecular SUMO E3 ligase for autosumoylation of bromodomain. The RING-finger-B Box-coiled-coil/tripartite motif (RBCC/TRIM motif) is required for interaction with the KRAB domain of KRAB-zinc finger proteins. Binds four zinc ions per molecule. The RING finger and the N-terminal of the leucine zipper alpha helical coiled-coil region of RBCC are required for oligomerization. Contains one Pro-Xaa-Val-Xaa-Leu (PxVxL) motif, which is required for interaction with chromoshadow domains. This motif requires additional residues -7, -6, +4 and +5 of the central Val which contact the chromoshadow domain. ATM-induced phosphorylation on Ser-824 represses sumoylation leading to the de-repression of expression of a subset of genes involved in cell cycle control and apoptosis in response to genotoxic stress. Dephosphorylation by the phosphatases, PPP1CA and PP1CB forms, allows sumoylation and expression of TRIM28 target genes. Sumoylation/desumoylation events regulate TRIM28-mediated transcriptional repression. Sumoylation is required for interaction with CHD3 and SETDB1 and the corepressor activity. Represses and is repressed by Ser-824 phosphorylation. Enhances the TRIM28 corepressor activity, inhibiting transcriptional activity of a number of genes including GADD45A and CDKN1A/p21. Lys-554, Lys-779 and Lys-804 are the major sites of sumoylation. In response to Dox-induced DNA damage, enhanced phosphorylation on Ser-824 prevents sumoylation and allows de-repression of CDKN1A/p21. Auto-ubiquitinated; enhanced by MAGEA2 and MAGEC2. Citrullinated by PADI4. ADP-ribosylated by SIRT6, promoting TRIM28/KAP1 interaction with CBX5, thereby contributing to the packaging of LINE-1 retrotransposon elements into transcriptionally repressive heterochromatin. Belongs to the TRIM/RBCC family.