EGFR

The EGFR family of receptor tyrosine kinases (RTK) comprises four distinct receptors: the EGFR (also known as ErbB-1/HER1), ErbB-2 (neu, HER2), ErbB-3 (HER3) and ErbB-4 (HER4). All EGFR family members are characterized by a modular structure consisting of an extracellular ligand-binding domain, a single hydrophobic transmembrane region, and the intracellular part harbouring the highly conserved tyrosine kinase domain. The ErbB family of receptor tyrosine kinases (RTKs) couples binding of extracellular growth factor ligands to intracellular signaling pathways regulating diverse biologic responses, including proliferation, differentiation, cell motility, and survival. Ten growth factors and their ErbB specificities are: EGF, amphiregulin (AR), and TGF bind ErbB-1; betacellulin, heparin binding EGF-like growth factor, and epiregulin bind both ErbB-1 and ErbB-4; the neuregulins (also called heregulins and Neu differentiation factors) NRG-1 and NRG-2 bind ErbB-3 and ErbB-4; and NRG-3 and NRG-4 bind ErbB-4. No known ligand binds ErbB-2. The three best characterized signaling pathways induced through ErbBs are Ras–mitogen-activated protein kinase (Ras-MAPK), phosphatidylinositol 3_ kinase-protein kinase B (PI3K-PKB/Akt), and phospholipase C–protein kinase C (PLC-PKC) pathways.