P selectin (SELP) is a 140kDa protein that is stored in the alpha-granules of platelets and Weibel-Palade bodies of endothelial cells. SELP mediates rapid rolling of leukocyte rolling over vascular surfaces during the initial steps in inflammation through interaction with PSGL1. P selectin is a cell adhesion molecule on the surface of activated endothelial cells. Cellular adhesion molecules are a large family of proteins that attach the cytoskeleton and intracellular signaling cascades with the extracellular environment. SELP is a calcium-dependent receptor for myeloid cells that binds to sialylated forms of Lewis blood group carbohydrate antigens on neutrophils and monocytes. This protein redistributes to the plasma membrane during platelet activation and degranulation and mediates the interacton of activated endothelial cells or platelets with leukocytes.
Semaphorins are a family of secreted and cell-bound signaling molecules defined by the presence of a common 500 aa Sema domain. They are best characterized in relation to axon guidance during development of the nervous system. The functions of Semaphorins 3A (SEMA3A) are mediated primarily through binding to the Neuropilin-1 (Npn-1) and Plexin-A1 coreceptor complex. Neuropilins lack a signaling-competent cytoplasetmic domain and ensure semaphorin binding, whereas the transmembrane receptor plexin mediates the intracellular response. As the first identified vertebrate semaphorin, SEMA3A functions either as a chemorepulsive agent inhibiting axonal outgrowth, or as a chemoattractive agent stimulating the growth of apical dendrites. In both cases, the protein is vital for normal neuronal pattern development. Its overexpression is associated with schizophrenia which is seen in various human tumor cell lines, and aberrant release is associated with the progression of Alzheimer's disease
Semaphorin-4A (SEMA4A) belongs to the semaphorin family which contains a Ig-like C2-type domain, a PSI domain and a Sema domain. SEMA4A is expressed from day 10 in the embryo, and low levels are found between days 10-12. SEMA4A is a cell surface receptor for PLXNB1, PLXNB2, PLXNB3 and PLXND1 that plays an important role in cell-cell signaling. It plays a role in priming antigen-specific T-cells, promotes differentiation of Th1 T-helper cells, and thereby contributes to adaptive immunity. SEMA4A promotes phosphorylation of TIMD2, inhibits angiogenesis, and promotes axon growth cone collapse, Inhibits axonal extension by providing local signals to specify territories inaccessible for growing axons.
Semaphorin-4C is a protein which belongs to the semaphorin family, contains 1 Ig-like C2-type domain, 1 PSI domain, 1 Sema domain. As cell surface receptor for PLXNB2, it plays an important role in cell-cell signaling. PLXNB2 binding promotes downstream activation of RHOA and phosphorylation of ERBB2 at 'Tyr-1248'. It required for normal brain development, axon guidance and cell migration, Probable signaling receptor which may play a role in myogenic differentiation through activation of the stress-activated MAPK cascade.
SEMA4D is a member of the semaphorin family,contains one Ig-like C2-type domain, one PSI domain and one Sema domain. SEMA4D is strongly expressed in lymphoid tissues, especially in the thymus, as well as in the nervous tissues. However, SEMA4D is expressed at lower levels in testes, brain, kidney, small intestine, prostate, heart, placenta, lung and pancreas, but not in colon and liver. SEMA4D is a cell surface receptor for PLXN1B and PLXNB2 that plays an important role in cell-cell signaling. SEMA4D is involved in a number of fundamental biological processes such as promoting reorganization of the actin cytoskeleton, the migration of cerebellar granule cells and of endothelial cells and signaling via SRC and PTK2B/PYK2, which then mediates activation of phosphatidylinositol 3-kinase and of the AKT1 signaling cascade. Not only these, it plays a role in axonal growth cone guidance in the developing central nervous system. Semaphorin-4D / SEMA4D may play a functional role in the immune system, as well as in the nervous system. It could induce B-cells to aggregate and improves their viability (in vitro). SEMA4D is involved in regulating dendrite and axon branching and morphogenesis and promoting interaction with PLXNB1 mediates activation of RHOA.
Semaphorin 4D (SEMA4D or CD1) is a member of the semaphorin family of proteins and an important mediator of the movement and differentiation of multiple cell types, including those of the immune, vascular, and nervous systems. VEGF and SEMA4D had a positive correlation with the malignant degree of ovarian cancer, and SEMA4D can serve as an independent prognostic factor. SEMA4D was the first semaphorin described to have immune functions and serves important roles in T cell priming, antibody production, and cell-to-cell adhesion. Proteolytic cleavage of SEMA4D from the cell surface gives rise to a soluble fragment of SEMA4D (sSEMA4D). Similar to the transmembranal form, sSEMA4D is thought to have immunoregulatory properties.
Semaphorins are secreted, transmembrane, and GPI-linked proteins, defined by cysteine-rich semaphorin protein domains, that have important roles in a variety of tissues. Humans have 20 semaphorins, Drosophila has five, and two are known from DNA viruses. Semaphorins are found in nematodes and crustaceans but not in non-animals. They are grouped into eight classes on the basis of phylogenetic tree analyses and the presence of additional protein motifs. Semaphorins have been implicated in diverse developmental processes such as axon guidance during nervous system development and regulation of cell migration. Semaphorin-5A, also known as Semaphorin-F, Sema F, SEMA5A and SEMAF, is a single-pass type I membrane protein which belongs to thesemaphorin family. Semaphorin5A / SEMA5A contains onePSI domain, oneSema domain and sevenTSP type-1 domains. It may act as positive axonal guidance cues. Semaphorin5A / SEMA5A is an axon regulator molecule and plays major roles during neuronal and vascular development. It plays an essential role in embryonic development. Semaphorin5A / SEMA5A induces endothelial cell migration from pre-existing vessels. It also plays a role in autism, reducing the ability of neurons to form connections with other neurons in certain brain regions.
Protein Z-dependent protease inhibitor, also known as PZ-dependent protease inhibitor, SERPINA10 and ZPI, is a secreted protein which belongs to theserpin family. It is expressed by the liver and secreted in plasma. SERPINA10 / Serpin-A10 inhibits factor Xa activity in the presence of protein Z, calcium and phospholipid. Serpins are a group of proteins with similar structures that were first identified as a set of proteins able to inhibit proteases. The acronym serpin was originally coined because many serpins inhibit chymotrypsin-like serine proteases (serine protease inhibitors).Over 1000 serpins have now been identified, these include 36 human proteins, as well as molecules in plants, fungi, bacteria, archaea and certain viruses. Serpins are the largest and most diverse family of protease inhibitors. Most serpins control proteolytic cascades, certain serpins do not inhibit enzymes, but instead perform diverse functions such as storage (ovalbumin, in egg white), hormone carriage proteins (thyroxine-binding globulin, cortisol-binding globulin) and tumor suppressor genes (maspin). Most inhibitory serpins target chymotrypsin-like serine proteases. These enzymes are defined by the presence of a nucleophilic serine residue in their catalytic site. Some serpins inhibit other classes of protease. A number of such serpins have been shown to target cysteine proteases. These enzymes differ from serine proteases in that they are defined by the presence of a nucleophilic cysteine residue, rather than a serine residue, in their catalytic site.
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