| [ Summary ] |
Members of the epidermal growth factor(EGF) family of tyrosine kinase receptors(erbB1-4) are involved in the regulation of cell growth and differentiation, and are found to be expressed in gastrointestinal tract and cancers. The receptors are located at the cell surface, where the binding of a ligand activates a tyrosine kinase in the intracellular region of the receptor to phosphorylates on a number of intracellular substrates which activate intracellular pathways. Multiple ligands such as EGF, transforming growth factor (TGF)-a, heparin binding EGF like growth factor(HB-EGF), tomoregulin(TR), amphiregulin, and betacellulin are known to bind directly to EGFR, none(at present) to erbB-2. A family of ligands called heregulins or neuregulins bind to both erbB-3 and erbB-4. It is now apparent that the receptors are functioning in various heterodimeric pairs, which are formed depending on their concentratinos. Both tyrosine kinase regions of heterodimeric pairs can be activated by binding particular ligands in the environment to one of heterodimeric receptors. |