EGF (Epidermal Growth Factor) is a small 53 amino acid residue protein that is involved in normal cell growth, oncogenesis, and wound healing. This protein shows both strong sequential and functional homology with hTGF-Alpha (human type-Alpha Transforming Growth Factor), which is a competitor for EGF receptor sites. EGF binds to a specific high-affinity, low-capacity receptor on the surface of responsive cells known as EGFR (Epidermal growth factor receptor). EGFR is a member of the ErbB (Erythroblastic Leukemia Viral Oncogene Homolog) family receptors, a subfamily of four closely related receptor tyrosine kinases: EGFR (ErbB1), Her2/c-neu (ErbB2), Her3 (ErbB3) and Her4 (ErbB4). In response to toxic environmental stimuli, such as ultraviolet irradiation, or to receptor occupation by EGF, the EGFR forms Homo- or Heterodimers with other family members. Binding of EGF to the extracellular domain of EGFR leads to receptor dimerization, activation of the intrinsic PTK (Protein Tyrosine Kinase) activity, tyrosine autophosphorylation, and recruitment of various signaling proteins to these autophosphorylation sites located primarily in the C-terminal tail of the receptor. Tyrosine phosphorylation of the EGFR leads to the recruitment of diverse signaling proteins, including the Adaptor proteins GRB2 (Growth Factor Receptor-Bound Protein-2) and Nck (Nck Adaptor Protein), PLC-Gamma (Phospholipase-C-Gamma), SHC (Src Homology-2 Domain Containing Transforming Protein), STATs (Signal Transducer and Activator of Transcription), and several other proteins and molecules. The evolutionary conservation of all the components of the EGFR signaling pathway in Nematode, Fruit fly, Mouse, and Man underscores the biological significance of this signaling pathway. Furthermore, aberrant regulation of the activity or action of EGFR and other members of the RTK family have been implicated in multiple cancers, including those of brain, lung, mammary gland, and ovary (Ref.1 & 2).
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