Functions as a key regulator of cell membrane composition by regulating protein surface expression. Also, plays a role in regulation of processes including cell migration, cell proliferation, cell contraction and cell adhesion. Regulates transepithelial migration of neutrophils into the alveolar lumen, potentially via mediation of cell surface expression of adhesion markers and lipid raft formation (PubMed:31550239). Negatively regulates caveolae formation by reducing CAV1 expression and CAV1 amount by increasing lysosomal degradation (PubMed:17609206, PubMed:14978215). Facilitates surface trafficking and the formation of lipid rafts bearing GPI-anchor proteins (PubMed:14978215). Regulates surface expression of MHC1 and ICAM1 proteins increasing susceptibility to T-cell mediated cytotoxicity (PubMed:12763482). Regulates the plasma membrane expression of the integrin heterodimers ITGA6-ITGB1, ITGA5-ITGB3 and ITGA5-ITGB1 resulting in modulation of cell-matrix adhesion (PubMed:12189152). Also regulates many processes through PTK2. Regulates blood vessel endothelial cell migration and angiogenesis by regulating VEGF protein expression through PTK2 activation (By similarity). Regulates cell migration and cell contraction through PTK2 and SRC activation (By similarity). Regulates focal adhesion density, F-actin conformation and cell adhesion capacity through interaction with PTK2 (By similarity). Positively regulates cell proliferation (By similarity). Plays a role during cell death and cell blebbing (By similarity). Promotes angiogenesis and vasculogenesis through induction of VEGFA via a HIF1A-dependent pathway (By similarity). Also plays a role in embryo implantation by regulating surface trafficking of integrin heterodimer ITGA5-ITGB3 (PubMed:16487956, PubMed:16216233). Plays a role in placental angiogenesis and uterine natural killer cell regulation at the maternal-fetal placental interface, however not required in the maternal tissues for a viable pregnancy (PubMed:28295343). Involved in the early stages of embryogenic development and cardiogenesis, potentially via regulation of epithelial-mesenchymal transition timing (PubMed:30773261). May play a role in glomerular filtration (By similarity). Interacts with PTK2; regulates PTK2 activation and localization (By similarity). Interacts with ITGB3; regulates the levels of the heterodimer ITGA5-ITGB3 integrin surface expression (By similarity). Interacts with P2RX7 (via C-terminus) (By similarity). Interacts with ITGB1; the interaction may be direct or indirect and ITGB1 has a heterodimer form (PubMed:12189152). Localizes in cytoplasm, foot processes and cell bodies of podocytes and nucleus of endothelial cells of kidney (By similarity). Localizes to the apical cell surface in the luminal epithelium and glandular epithelium (PubMed:16487956). Colocalized with ITGB1 and GPI-anchor proteins on plasma membrane (PubMed:12189152) (PubMed:14978215). Expressed in alveolar epithelial type 1, alveolar epithelial type 2 and airway epithelial cells (at protein level) (PubMed:31550239). Expressed in both the endometrial epithelial and stromal cells during the embryo implantation period (PubMed:16487956). Expressed in the corneal epithelium, the sclera, the nerve fiber layer of the inner retina and retinal ganglion cell layer, the nonpigmented epithelium of the ciliary body and the optic nerve (PubMed:12710941). Expressed from day 3 of gastrulation, expression peaks on day 6 before decreasing on days 8 and 10 (PubMed:30773261). Expressed throughout gestation in the embryo proper, trophoblastic stems cells in the ectoplacental cone and decidual cells (PubMed:28295343). Expressed in trophoblast giant cells and maternal decidua in the placenta and in the endometrium at 9.5 dpc (PubMed:28295343). Expressed in the developing heart, head and otic vesicle at 9.5 dpc (PubMed:30773261). Abundantly expressed in giant cells and weakly expressed in labyrinthine trophoblasts and spongiotrophoblasts in the junctional zone, also expressed within the cytoplasm and perinuclear region of pre-glycogen cells at 12 dpc (PubMed:28295343). Expression in all trophoblast populations reduces as placentas near term (PubMed:28295343). Induced by progesterone; initially expressed in the uterus luminal epithelium spreading to the glandular epithelium 48 hours after treatment, increases expression at the plasma membrane (PubMed:18400107). Induced by estradiol in the cytoplasm of endometrial tissue; expression is induced 48 hours after initiation of estradiol treatment (PubMed:18400107). Knockout mice show a longer time to achieve pregnancy and a reduced litter size as a result of viable knockout embryos (PubMed:28295343). Increase in fibrin deposition throughout the decidua basalis and junctional zones in placentas (PubMed:28295343). Reduced placental vasculogenesis at 9.5dpc and altered vascular organization is evident at 12.5 dpc (PubMed:28295343). Increased collagen deposition in placentas including around the placental labyrinth at 16.5 dpc (PubMed:28295343). Increase in Hif1a expression in placental decidual leukocytes at 9.5 and 12.5 dpc, expression returns to normal by 16.5 dpc (PubMed:28295343). Increase in uterine natural killer cells in the placental decidua basalis throughout gestation (PubMed:28295343). Reduced influx of neutrophils to the airspace after intrapulmonary inoculation with the chemokine Cxcl1 and an increase in interstitial neutrophils in lipopolysaccharide challenged lungs (PubMed:31550239). Increased survival during K.pneumoniae lung infection, as a result of attenuated injury to the alveolocapillary barrier and decreased systemic inflammation (PubMed:31550239). Significant decrease in bacterial burden in the lungs, bloodstream, and spleen 48 hours following K.pneumoniae suggesting enhanced pathogen clearance in the lungs and reduced extrapulmonary dissemination (PubMed:31550239). Increase in surface Cd47 and decrease in surface Icam1 and Itgb3 on alveolar epithelial type 1 cells accompanied by a reduction in the number of lipid rafts (PubMed:31550239). Increase in Cav1 and Cav2 expression in lung tissues (PubMed:31550239). Belongs to the PMP-22/EMP/MP20 family.