Is believed to be a multifunctional and multicompartmentalprotein involved in inflammation and infection processes, ribosomebiogenesis, protein synthesis in mitochondria, regulation of apoptosis, transcriptional regulation and pre-mRNA splicing. At the cell surfaceis thought to act as an endothelial receptor for plasma proteins of thecomplement and kallikrein-kinin cascades. Putative receptor for C1q;specifically binds to the globular 'heads' of C1q thus inhibiting C1;may perform the receptor function through a complex with C1qR/CD93. Incomplex with cytokeratin-1/KRT1 is a high affinity receptor forkininogen-1/HMWK. Can also bind other plasma proteins, such ascoagulation factor XII leading to its autoactivation. May function tobind initially fluid kininogen-1 to the cell membrane. The secretedform may enhance both extrinsic and intrinsic coagulation pathways. Itis postulated that the cell surface form requires docking withtransmembrane proteins for downstream signaling which might be specificfor a cell-type or response. By acting as C1q receptor is involved inchemotaxis of immature dendritic cells and neutrophils and is proposedto signal through CD209/DC-SIGN on immature dendritic cells, throughintegrin alpha-4/beta-1 during trophoblast invasion of the decidua, andthrough integrin beta-1 during endothelial cell adhesion and spreading. Signaling involved in inhibition of innate immune response isimplicating the PI3K-AKT/PKB pathway. Required for protein synthesis inmitochondria. In mitochondrial translation may beinvolved in formation of functional 55S mitoribosomes; the functionseems to involve its RNA-binding activity. May be involved in thenucleolar ribosome maturation process; the function may involve theexchange of FBL for RRP1 in the association with pre-ribosomeparticles. Involved in regulation of RNA splicing by inhibiting theRNA-binding capacity of SRSF1 and its phosphorylation. Is required forthe nuclear translocation of splicing factor U2AF1L4. Involved inregulation of CDKN2A- and HRK-mediated apoptosis. Stabilizesmitochondrial CDKN2A isoform smARF. May be involved in regulation ofFOXC1 transcriptional activity and NFY/CCAAT-binding factor complex-mediated transcription. May play a role in antibacterial defense as itcan bind to cell surface hyaluronan and inhibit Streptococcuspneumoniae hyaluronate lyase. May be involved in modulation of theimmune response; ligation by HCV core protein is resulting insuppression of interleukin-12 production in monocyte-derived dendriticcells. Involved in regulation of antiviral response by inhibitingDDX58- and IFIH1-mediated signaling pathways probably involving itsassociation with MAVS after viral infection. [1-20]

MLPLLRCVPRVLGSSVAGLRAAAPASPFRQLLQPAPRLCTRPFGLLSVRAGSERRPGLLRPRGPCACGCGCGSLHTDGDKAFVDFLSDEIKEERKIQKHKTLPKMSGGWELELNGTEAKLVRKVAGEKITVTFNINNSIPPTFDGEEEPSQGQKVEEQEPELTSTPNFVVEVIKNDDGKKALVLDCHYPEDEVGQEDEAESDIFSIREVSFQSTGESEWKDTNYTLNTDSLDWALYDHLMDFLADRGVDNTFADELVELSTALEHQEYITFLEDLKSFVKSQ