C1QBP

The human complement subcomponent C1q associates with C1r and C1s in order to yield the first component of the serum complement system. The protein encoded by this gene is known to bind to the globular heads of C1q molecules and inhibit C1 activation. This protein has also been identified as the p32 subunit of pre-mRNA splicing factor SF2, as well as a hyaluronic acid-binding protein.

complement C1q binding protein

Is believed to be a multifunctional and multicompartmental protein involved in inflammation and infection processes, ribosome biogenesis, protein synthesis in mitochondria, regulation of apoptosis, transcriptional regulation and pre-mRNA splicing. At the cell surface is thought to act as an endothelial receptor for plasma proteins of the complement 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. In complex with cytokeratin-1/KRT1 is a high affinity receptor for kininogen-1/HMWK. Can also bind other plasma proteins, such as coagulation factor XII leading to its autoactivation. May function to bind initially fluid kininogen-1 to the cell membrane. The secreted form may enhance both extrinsic and intrinsic coagulation pathways. It is postulated that the cell surface form requires docking with transmembrane proteins for downstream signaling which might be specific for a cell-type or response. By acting as C1q receptor is involved in chemotaxis of immature dendritic cells and neutrophils and is proposed to signal through CD209/DC-SIGN on immature dendritic cells, through integrin alpha-4/beta-1 during trophoblast invasion of the decidua, and through integrin beta-1 during endothelial cell adhesion and spreading. Signaling involved in inhibition of innate immune response is implicating the PI3K-AKT/PKB pathway. Required for protein synthesis in mitochondria (PubMed:28942965).
In mitochondrial translation may be involved in formation of functional 55S mitoribosomes; the function seems to involve its RNA-binding activity. May be involved in the nucleolar ribosome maturation process; the function may involve the exchange of FBL for RRP1 in the association with pre-ribosome particles. Involved in regulation of RNA splicing by inhibiting the RNA-binding capacity of SRSF1 and its phosphorylation. Is required for the nuclear translocation of splicing factor U2AF1L4. Involved in regulation of CDKN2A- and HRK-mediated apoptosis. Stabilizes mitochondrial CDKN2A isoform smARF. May be involved in regulation of FOXC1 transcriptional activity and NFY/CCAAT-binding factor complex-mediated transcription. May play a role in antibacterial defense as it can bind to cell surface hyaluronan and inhibit Streptococcus pneumoniae hyaluronate lyase. May be involved in modulation of the immune response; ligation by HCV core protein is resulting in suppression of interleukin-12 production in monocyte-derived dendritic cells. Involved in regulation of antiviral response by inhibiting DDX58- and IFIH1-mediated signaling pathways probably involving its association with MAVS after viral infection.
(Microbial infection) Involved in HIV-1 replication, presumably by contributing to splicing of viral RNA. In infection processes acts as an attachment site for microbial proteins, including Listeria monocytogenes internalin B (InlB) and Staphylococcus aureus protein A. Involved in replication of Rubella virus.

Blood coagulation, intrinsic pathway Source: Reactome
Complement activation, classical pathway Source: UniProtKB-KW
Immune response Source: ProtInc
Innate immune response Source: UniProtKB-KW
Intrinsic apoptotic signaling pathway Source: Reactome
Mature ribosome assembly Source: UniProtKB
mRNA processing Source: UniProtKB-KW
Negative regulation of defense response to virus Source: UniProtKB
Negative regulation of interferon-gamma production Source: UniProtKB
Negative regulation of interleukin-12 production Source: UniProtKB
Negative regulation of MDA-5 signaling pathway Source: UniProtKB
Negative regulation of mRNA splicing, via spliceosome Source: UniProtKB
Negative regulation of RIG-I signaling pathway Source: UniProtKB
Negative regulation of transcription by RNA polymerase II Source: UniProtKB
Phosphatidylinositol 3-kinase signaling Source: UniProtKB
Positive regulation of apoptotic process Source: UniProtKB
Positive regulation of cell adhesion Source: UniProtKB
Positive regulation of dendritic cell chemotaxis Source: UniProtKB
Positive regulation of mitochondrial translation Source: UniProtKB
Positive regulation of neutrophil chemotaxis Source: UniProtKB
Positive regulation of protein kinase B signaling Source: UniProtKB
Positive regulation of substrate adhesion-dependent cell spreading Source: UniProtKB
Positive regulation of trophoblast cell migration Source: UniProtKB
Regulation of complement activation Source: UniProtKB
RNA splicing Source: UniProtKB-KW
Viral process Source: UniProtKB-KW

Cell membrane; Secreted; Nucleus; Nucleolus; Mitochondrion matrix; Cytoplasm. Seems to be predominantly localized to mitochondria. Secreted by activated lymphocytes.

Combined oxidative phosphorylation deficiency 33 (COXPD33): An autosomal recessive disorder caused by multiple mitochondrial respiratory chain defects and impaired mitochondrial energy metabolism. Clinical manifestations are highly variable. Affected infants present with cardiomyopathy accompanied by multisystemic features involving liver, kidney, and brain. Death in infancy is observed in some patients. Children and adults present with myopathy and progressive external ophthalmoplegia.