Receptor tyrosine kinase

Receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine kinase proteins. Receptor tyrosine kinases have been shown not only to be key regulators of normal cellular processes but also to have a critical role in the development and progression of many types of cancer. Mutations in receptor tyrosine kinases lead to activation of a series of signalling cascades which have numerous effects on protein expression. Receptor tyrosine kinases are part of the larger family of protein tyrosine kinases, encompassing the receptor tyrosine kinase proteins which contain a transmembrane domain, as well as the non-receptor tyrosine kinases which do not possess transmembrane domains. The first RTKs to be discovered were EGF and NGF in the 1960s, but the classification of receptor tyrosine kinases was not developed until the 1970s. Approximately 20 different RTK classes have been identified. RTK class I (EGF receptor family) (ErbB family) RTK class II (Insulin receptor family) RTK class III (PDGF receptor family) RTK class IV (VEGF receptors family) RTK class V (FGF receptor family) RTK class VI (CCK receptor family) RTK class VII (NGF receptor family) RTK class VIII (HGF receptor family) RTK class IX (Eph receptor family) RTK class X (AXL receptor family) RTK class XI (TIE receptor family) RTK class XII (RYK receptor family) RTK class XIII (DDR receptor family) RTK class XIV (RET receptor family) RTK class XV (ROS receptor family) RTK class XVI (LTK receptor family) RTK class XVII (ROR receptor family) RTK class XVIII (MuSK receptor family) RTK class XIX (LMR receptor) RTK class XX (Undetermined) Most RTKs are single subunit receptors but some exist as multimeric complexes, e.g., the insulin receptor that forms disulfide linked dimers in the presence of hormone (insulin); moreover, ligand binding to the extracellular domain induces formation of receptor dimers.