The receptors for insulin, insulin-like growth factor one (IGF-1) and epidermal growth factor (EGF) are members of a larger receptor family that has the property of possessing intrinsic, ligand-regulated, protein- tyrosine specific kinase activity. About half the known oncogenes also express protein-tyrosine specific kinase activity. It is generally thought that the kinase activity of these oncogenes represents an unregulated state requisite for cellular transformation, whereas the ligand-dependent activity of receptor/kinases represents the normal regulation of cellular nutrition and cell division in the appropriate biological setting. The detailed biochemical mechanism(s) governing the expression of enzymatic activity often differs from one kinase to the next. Also, the biochemical pathway(s) that are activated subsequent to expression of receptor and or oncogene kinase activity remain virtually unknown. Thus, the aims of this application are to study the structural basis by which ligand binding regulates kinase function for the above name receptors. Our previous work has shown the importance of inter- subunit communication for the ligand-dependent activation of insulin and EGF receptor kinases, although the mechanistic details are slightly different between this pair. We will continue our biochemical dissection of purified insulin and EGF receptors to further determine the details of subunit interaction, the specific receptor residues involved in ligand recognition, and other structure/function relationships important in regulating kinase function. It is also widely assumed that the receptors' kinase function will be immediately expressed by phosphorylation of a substrate that will be the next step in the cascade of events leading to profound metabolic changes. In general, this assumption has not been validated, but we have data on a potential substrate in rat fat cells that may be important in mediating some of insulin's action. We will therefore identify and characterize this substrate. The insulin receptor and its putative substrate(s) are critical molecules in the regulation of cellular glucose utilization, and are therefore important to the understanding of normal glucose homeostasis and abnormalities thereof in clinical diabetes. The EGF receptor is overexpressed in certain malignancies, and the biochemical linkage(s) between receptor function and cellular transformation is of clear relevance to understanding some types of cancer.
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