96-01427 Najjar Insulin regulates glucose and lipids homeostasis, gene expression, and protein synthesis through concerted actions on numerous enzymatic activities. Insulin binding to its cognate receptor activates receptor-associated tyrosine kinase which in turn, phosphorylates the receptor itself and a number of intracellular protein substrates. In recent years, considerable progress has been made in elucidating the molecular mechanism of insulin action. Pp120, an integral membrane glycoprotein, is a substrate of the insulin receptor tyrosine kinase in the liver. Among the substrates of the insulin receptor kinase, pp120 is unique because it is not phosphorylated by the highly homologous insulin like growth factor-1 receptor kinase. This is a novel finding. For years, scientists have searched for differences between the insulin and IGF-1 receptors that would explain their different actions. Insulin receptor primarily regulates metabolic pathways; The IGF-1 receptor induces proliferation. This project aims to identify specific amino acid residues in the carboxyl domain of the insulin receptor that regulate pp120 phosphorylation. Single amino acid substitution will be introduced to specific residues of the carboxyl terminus of the insulin receptor and the effects of the mutant forms on pp120 phosphorylation in transfected hepatocytes will be analyzed. Mutants of the insulin receptor will be transfected into a newly developed hepatocyte cell line genetically deficient of insulin receptor. Using this assay system, the role of pp120 phosphorylation by the insulin receptor in insulin endocytosis will be determined. These studies will expand our understanding of the molecular mechanism of the complex signal transduction pathways that are mediated by the insulin receptor. %%% Insulin regulates glucose and lipids homeostasis, gene expression, and protein synthesis through concerted actions on numerous enzymatic activities. Insulin binding to its cognate receptor activates receptor-associat ed tyrosine kinase which in turn, phosphorylates the receptor itself and a number of intracellular protein substrates. In recent years, considerable progress has been made in elucidating the molecular mechanism of insulin action. Scientists have searched, however, for differences between the insulin and IGF-1 receptors that would explain their different actions. Insulin receptor primarily regulates metabolic pathways; The IGF-1 receptor induces proliferation. Pp120 is a substrate of the insulin receptor tyrosine kinase in the liver and is not phosphorylated by the IGF-1 receptor kinase. This project aims to identify specific amino acid residues in the carboxyl domain of the insulin receptor that regulate pp120 phosphorylation. These studies will expand our understanding of the molecular mechanism of the complex signal transduction pathways that are mediated by the insulin receptor. ***
