Epidermal growth factor (EGF) is the founding member of the EGF family that also includes TGF-alpha, amphiregulin (AR), betacellulin (BTC), epiregulin (EPR), heparin-binding EGF-like growth factor (HB-EGF), epigen, and the neuregulins (NRG)-1 through-6. Members of the EGF family share a structural motif, the EGF-like domain, which is characterized by three intramolecular disulfide bonds that are formed by six similarly spaced conserved cysteine residues. All EGF family members are synthesized as type I transmembrane precursor proteins that may contain several EGF domains in the extracellular region. The mature proteins are released from the cell surface by regulated proteolysis. The 1207 amino acid (aa) human EGF precursor contains nine EGF domains and nine LDLR class B repeats. The mature protein consists of 53 aa and is generated by proteolytic excision of the EGF domain proximal to the transmembrane region. Mature human EGF shares 70% aa sequence identity with an mature mouse and rat EGF. EGF is present in various body fluids, including blood, milk, urine, saliva, seminal fluid, pancreatic juice, cerebrospinal fluid, and amniotic fluid. Four ErbB (HER) family receptor tyrosine kinases including EGFR/ErbB1, ErbB2, ErbB3 and ErbB4, mediate responses to EGF family members. These receptors undergo a complex pattern of ligand induced homo-or hetero-dimerization to transduce EGF family signals . EGF binds ErbB1 and depending on the context, induces the formation of homodimers or heterodimers containing ErbB2. Dimerization results in autophosphorylation of the receptor at specific tyrosine residues to create docking sites for a variety of signaling molecules. Biological activities ascribed to EGF include epithelial development, angiogenesis, inhibition of gastric acid secretion, fibroblast proliferation, and colony formation of epidermal cells in culture.
As a member of the epidermal growth factor receptor (EGFR) family, EGFR protein is type I transmembrane glycoprotein that binds a subset of EGF family ligands including EGF, amphiregulin, TGF-α, betacellulin, etc. EGFR protein plays a crucial role in signaling pathway in the regulation of cell proliferation, survival and differentiation. Binding of a ligand induces EGFR protein homo- or heterodimerization, the subsequent tyrosine autophosphorylation and initiates various down stream pathways (MAPK, PI3K/PKB and STAT). In addition, EGFR signaling also has been shown to exert action on carcinogenesis and disease progression, and thus EGFR protein is proposed as a target for cancer therapy currently.
Neutrophil elastase, also known as Elastase-2, Bone marrow serine protease, Medullasin, ELANE, and ELA2, is a serine proteinase in the same family as chymotrypsin and has broad substrate specificity. Secreted by neutrophils during inflammation, it destroys bacteria and host tissue. As with an other serine proteinases, ELANE / ELA2 contains a charge relay system composed of the catalytic triad of histidine, aspartate, and serine residues that are dispersed throughout the primary sequence of the polypeptide but that are brought together in the three dimension conformation of the folded protein.ELANE / ELA2 is an important protease enzyme that when expressed aberrantly can causeemphysemaor emphysematous changes. This involves breakdown of the lung structure and increased airspaces. Elastases form a subfamily of serine proteases that hydrolyze many proteins in addition to elastin. ELANE / ELA2 hydrolyzes proteins with anin specialized neutrophil lysosomes, called azurophil granules, as well as proteins of the extracellular matrix following the protein's release from activated neutrophils. ELANE / ELA2 may play a role in degenerative and inflammatory diseases by its proteolysis of collagen-IV and elastin of the extracellular matrix. ELANE / ELA2 degrades the outer membrane protein A (OmpA) of E. coli as well as the virulence factors of such bacteria as Shigella, Salmonella and Yersinia. Defects in ELANE are a cause of cyclic haematopoiesis (CH), also known as cyclic neutropenia. CH is an autosomal dominant disease in which blood-cell production from the bone marrow oscillates with an 21-day periodicity. Defects in ELANE are also the cause of autosomal dominant severe congenital neutropenia type 1 (SCN1) which is a heterogeneous disorder of hematopoiesis.
ENPEP, also known as aminopeptidase A, is a member of the peptidase M1 family. Members of this family are involved in response to cadmium ion and proteolysis. They located in 6 components and are expressed in 26 plant structures. ENPEP is expressed by epithelial cells of the proximal tubule cells and the glomerulus of the nephron. It also can be detected in a variety of other tissues. ENPEP probably plays a role in regulating growth and differentiation of early B-lineage cells. It also may play a role in the catabolic pathway of the renin-angiotensin system. ENPEP is a zinc-dependent membrane-bound aminopeptidase that catalyzes the cleavage of glutamatic and aspartatic amino acid residues from the N-terminus of polypeptides. It degrades vasoconstricting angiotensin II into angiotensin III and therefore helps to regulate blood pressure.
Epithelial Cell Adhesion Molecule (EpCAM), also known as GA733-2 antigen, is a type â…transmembrane glycoprotein composed of an extracellular domain with two EGF-Like repeats and a cystenin-rich region, a transmembrane domain and a cytoplasmic domain. It modulates cell adhesion and proliferation. Its overexpression has been detected in many epithelial tumours and has been associated with high stage, high grade and a worse survival in some tumour types. EpCAM has been shown to function as a calcium-independent homophilic cell adhesion molecule that does not exhibit any obvious relationship to the four known cell adhesion molecule superfamilies. However, recent insights have revealed that EpCAM participates in not only cell adhesion, but also in proliferation, migration and differentiation of cells. In addition, recent study revealed that EpCAM is the Wnt-beta-catenin signaling target gene and may be used to facilitate prognosis. It has oncogenic potential and is activated by release of its intracellular domain, which can signal into the cell nucleus by engagement of elements of the wnt pathway.
Endothelial protein C receptor (EPCR), also known as activated protein C receptor (APC receptor) or PROCR, is a receptor for Protein C. Protein C plays an important role in many metabolism processes in humans and other animals after activated by binding to Endothelial protein C receptor (EPCR). Because of the EPCR is found primarily on endothelial cells (cells on the inside of blood vessels), activated protein C is found maily near endothelial cells. Protein C is pleiotropic, with two main functions: anticoagulation and cytoprotection. Which function will be performed depend on whether or not protein C remains bind to EPCR after activated. The anticoagulation occurs when it does not. In this case, protein C functions as an anticoagulant by irreversibly proteolytically inactivating Factor Va and Factor VIIIa, turning them into Factor Vi and Factor VIIIi respectively. When still bound to EPCR, activated protein C performs its cytoprotective effects, acting on the effector substrate PAR-1, protease-activated receptor-1. To a degree, APC's anticoagulant properties are independent of its cytoprotective ones, in that expression of one pathway is not affected by the existence of the other.
EPHA3 gene belongs to the ephrin receptor subfamily of the protein-tyrosine kinase family. EPH and EPH-related receptors have been implicated in mediating developmental events, particularly in the nervous system. The ephrin receptors are divided into 2 groups based on the similarity of their extracellular domain sequences and their affinities for binding ephrin-A and ephrin-B ligands. EPHA3 gene encodes a protein that binds ephrin-A ligands. EPHA3 is involved in the retinotectal mapping of neurons. It may also control the segregation but not the guidance of motor and sensory axons during neuromuscular circuit development.
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