Epidermal growth factor receptor (EGFR) is a cell surface receptor family containing four structurally related members (erb1/EGFR, erb2/HER2, erb3/HER3 and erb4/HER4). There are three basic components that make up this single polypeptide chain receptor: the extracellular ligand binding domain, the transmembrane segment and an intracellular protein tyrosine kinase (PTK) domain comprising the catalytic core and the regulatory sequences.
Upon binding of an extracellular ligand the receptor transforms the inactive monomers into homodimers (exception: the tetrametric insulin receptor) that activate its intracellular tyrosine kinase domain and autophosphorylate its C-terminal tyrosine residues. This stabilizes the active receptor conformation and creates phosphotyrosine-docking sites for proteins that transduce signals within the cell.
Transduction by activated EGFR leads to downstream effect on proteins including phosphatidyl 3-kinase (PI3K), Phospholipase (PL) C-g1, Akt, Ras, Raf and mitogen-activated protein kinase (MAPK); entities that are associated with cell proliferation, motility and survival.