VRK1 is a member of the vaccinia-related kinase (VRK) family of serine/threonine protein kinases. Serine/threonine protein kinases are tumor suppressor that controls the activity of AMP-activated protein kinase family members; thereby playing a role in various processes such as cell metabolism; cell polarity; apoptosis and DNA damage response. VRK1 contains 1 protein kinase domain and localizes to the nucleus. VRK1 gene is widely expressed in human tissues and has increased expression in actively dividing cells; such as those in testis; thymus; fetal liver; and carcinomas. As a serine/threonine kinase; VRK1 phosphorylates 'Thr-18' of p53/TP53 and may thereby prevent the interaction between p53/TP53 and MDM2. Defects in VRK1 are the cause of pontocerebellar hypoplasia type 1 (PCH1); also called pontocerebellar hypoplasia with infantile spinal muscular atrophy or pontocerebellar hypoplasia with anterior horn cell disease. PCH1 is characterized by an abnormally small cerebellum and brainstem; central and peripheral motor dysfunction from birth; gliosis and anterior horn cell degeneration resembling infantile spinal muscular atrophy.
V-Set and Immunoglobulin Domain-Containing Protein 2 (VSIG2) is presumably a 50-60 kDa single-pass type I transmembrane (glyco)protein which contains one Ig-like C2-type (immunoglobulin-like) domain and one Ig-like V-type (immunoglobulin-like) domain. VSIG2 is highly expressed in the stomach; colon; prostate; trachea and thyroid glands and weakly in bladder and lung. V-set domains are Ig-like domains resembling the antibody variable domain. V-set domains are found in diverse protein families; including immunoglobulin light and heavy chains; in several T-cell receptors such as CD2 (Cluster of Differentiation 2); CD4; CD80; and CD86; in myelin membrane adhesion molecules; in junction adhesion molecules (JAM); in tyrosine-protein kinase receptors; and in the programmed cell death protein 1 (PD1). It shows expression in stomach and prostate by Northern blot; and likely participates in cell adhesion. Human VSIG2 precursor is 327 amino acids in length.
V-set and immunoglobulin domain-containing protein 4(VSIG4) is a transmembrane protein contains a signal peptide, a V-type Ig-like domain, a C2-type Ig-like domain, several potential O-glycosylation sites, and an intracellular domain with 2 potential phosphorylation sites and is structurally related to the B7 family of immune regulatory proteins. This protein is also a receptor for the complement component 3 fragments C3b and iC3b.The main function is strong negative regulator of T-cell proliferation and IL2 production and it is also potent inhibitor of the alternative complement pathway convertases. It abundantly expressed in several fetal tissues such as adult tissues, highest expression in lung and placenta and it also expressed in resting macrophages.
VSIG4 (V-set and immunoglobulin domain containing 4); also known as complement receptor of the immunoglobulin superfamily (CRIg) and Z39Ig; is a type I transmembrane glycoprotein. It is a B7 family-related protein and an Ig superfamily member. In contrast to the B7 family members which contain two IgG domains; VSIG4 contains one complete V-type Ig domain and a truncated C-type Ig domain. VSIG4 is exclusively expressed on tissue resident macrophages and binds to multimers of C3b and iC3b that are covalently attached to particle surfaces. No VSIG4 expression appears to be present in T and B cells. VSIG4 functions as a negative regulator of T cell activation; and may be involved in the maintenance of peripheral T cell tolerance; and is also identified as a potent suppressor of established inflammation. Mouse VSIG4 is synthesized as a 280 amino acid precursor that contains a signal sequence; an V-type Ig domain (aa 36-115); one potential N-linked glycosylation site; and a single transmembrane domain. The V-type Ig domain of mouse VSIG4 shares 86% and 80% aa sequence identity with the V-type Ig domains of rat and human VSIG4; respectively.
V-Set and Immunoglobulin Domain-Containing Protein 4 (VSIG4) is a 45-50 kDa macrophage-specific transmembrane glycoprotein that belongs to the B7 family-related protein and an Ig superfamily member. In contrast to the B7 family members which contain two IgG domains; VSIG4 contains one complete V-type Ig domain and a truncated C-type I g domain. VSIG4 is abundantly expressed in several fetal tissues. In adult tissues; the highest expression of VSIG4 is in lung and placenta. It is also expressed in resting macrophages. No VSIG4 expression appears to be present in T and B cells. The specific expression of VSIG4 on resting macrophages in tissue suggests that this inhibitory ligand may be important for the maintenance of T cell unresponsiveness in healthy tissues. VSIG4 functions as a negative regulator of T cell activation; and may be involved in the maintenance of peripheral T cell tolerance; and is also identified as a potent suppressor of established inflammation. VSIG4 is a phagocytic receptor; strong negative regulator of T-cell proliferation and IL2 production. It is a potent inhibitor of the alternative complement pathway convertases. Human VSIG4 is 399 amino acids (aa) in length. It is a type I transmembrane (TM) glycoprotein that contains a 264 aa extracellular domain (ECD) (aa 20 - 283) and a 95 aa cytoplasmic region.
V-set and immunoglobulin domain-containing protein 8(VSIG8) is a single-pass type I membrane protein.The human VSIG8 cDNA encodes 414 amino acids (aa) including a 21 aa signal sequence; a 242 aa extracellular domain (ECD) containing 2 Ig-like V-type (immunoglobulin-like) domains; a 21 aa transmembrane domain and a 130 aa cytoplasmic domain.The funtion of VSIG8 is not clear.
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