FUNCTION Catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides (PubMed:2001362, PubMed:20676357, PubMed:21245143, PubMed:25678563, PubMed:21593166). Exerts a strong chemotactic effect on leukocytes partly through activation of one of its membrane receptors BSG/CD147, initiating a signaling cascade that culminates in MAPK/ERK activation (PubMed:11943775, PubMed:21245143). Activates endothelial cells (ECs) in a pro-inflammatory manner by stimulating activation of NF-kappa-B and ERK, JNK and p38 MAP-kinases and by inducing expression of adhesion molecules including SELE and VCAM1 (PubMed:15130913). Induces apoptosis in ECs by promoting the FOXO1-dependent expression of CCL2 and BCL2L11 which are involved in EC chemotaxis and apoptosis (PubMed:31063815). In response to oxidative stress, initiates proapoptotic and antiapoptotic signaling in ECs via activation of NF-kappa-B and AKT1 and up-regulation of antiapoptotic protein BCL2 (PubMed:23180369). Negatively regulates MAP3K5/ASK1 kinase activity, autophosphorylation and oxidative stress-induced apoptosis mediated by MAP3K5/ASK1 (PubMed:26095851). Necessary for the assembly of TARDBP in heterogeneous nuclear ribonucleoprotein (hnRNP) complexes and regulates TARDBP binding to RNA UG repeats and TARDBP-dependent expression of HDAC6, ATG7 and VCP which are involved in clearance of protein aggregates (PubMed:25678563). Plays an important role in platelet activation and aggregation (By similarity). Regulates calcium mobilization and integrin ITGA2B:ITGB3 bidirectional signaling via increased ROS production as well as by facilitating the interaction between integrin and the cell cytoskeleton (By similarity). Binds heparan sulfate glycosaminoglycans (PubMed:11943775). Inhibits replication of influenza A virus (IAV) (PubMed:19207730). Inhibits ITCH/AIP4-mediated ubiquitination of matrix protein 1 (M1) of IAV by impairing the interaction of ITCH/AIP4 with M1, followed by the suppression of the nuclear export of M1, and finally reduction of the replication of IAV (PubMed:30328013, PubMed:22347431).FUNCTION (Microbial infection) May act as a mediator between human SARS coronavirus nucleoprotein and BSG/CD147 in the process of invasion of host cells by the virus (PubMed:15688292).FUNCTION (Microbial infection) Stimulates RNA-binding ability of HCV NS5A in a peptidyl-prolyl cis-trans isomerase activity-dependent manner.CATALYTIC ACTIVITY [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0)ACTIVITY REGULATION Binds cyclosporin A (CsA). CsA mediates some of its effects via an inhibitory action on PPIase.SUBUNIT Interacts with protein phosphatase PPP3CA/calcineurin A (PubMed:12218175, PubMed:12357034). Interacts with PRPF19 isoform 2 (via N-terminus) (By similarity). Interacts with isoform 2 of BSG/CD147 (PubMed:15688292, PubMed:11353871, PubMed:11943775, PubMed:21245143). Interacts with FOXO1; the interaction promotes FOXO1 dephosphorylation, nuclear accumulation and transcriptional activity (PubMed:31063815). Interacts with integrin ITGA2B:ITGB3; the interaction is ROS and peptidyl-prolyl cis-trans isomerase (PPIase) activity-dependent and is increased in the presence of thrombin (By similarity). Interacts with MAP3K5 (PubMed:26095851). Interacts with TARDBP; the interaction is dependent on the RNA-binding activity of TARDBP and the PPIase activity of PPIA/CYPA and the acetylation of PPIA/CYPA at Lys-125 favors the interaction (PubMed:25678563). Interacts with HNRNPA1, HNRNPA2B1, HNRNPC, RBMX, HNRNPK and HNRNPM (PubMed:25678563).SUBUNIT (Microbial infection) Interacts with HIV-1 capsid protein (PubMed:20364129, PubMed:8513493).SUBUNIT (Microbial infection) Interacts with human SARS coronavirus nucleoprotein.SUBUNIT (Microbial infection) Interacts with measles virus nucleoprotein.SUBUNIT (Microbial infection) Interacts with influenza A virus matrix protein 1.SUBUNIT (Microbial infection) Interacts with HCV NS5A; the interaction stimulates RNA-binding ability of NS5A and is dependent on the peptidyl-prolyl cis-trans isomerase activity of PPIA/CYPA.INTERACTION Secretion occurs in response to oxidative stress in vascular smooth muscle through a vesicular secretory pathway that includes Rho GTPase signaling, actin remodeling, and myosin II activation.ALTERNATIVE PRODUCTS Acetylation at Lys-125 markedly inhibits catalysis of cis to trans isomerization and stabilizes cis rather than trans forms of the HIV-1 capsid. PPIA acetylation also antagonizes the immunosuppressive effects of cyclosporine by inhibiting the sequential steps of cyclosporine binding and calcineurin inhibition (PubMed:20364129, Ref.12). Acetylation at Lys-125 favors its interaction with TARDBP (PubMed:25678563).SIMILARITY Belongs to the cyclophilin-type PPIase family. PPIase A subfamily.ONLINE INFORMATION Cyclophilin entry
