(Scanned from the applicant's description) Resistance to insulin is a feature of patients with Type I and Type II diabetes mellitus. Our prior studies have shown that correlations exist between insulin resistance, decreased insulin receptor (IR) tyrosine kinase activity, and an increased content of membrane glycoprotein PC-1. PC-1 is a class H exoprotein with phosphodiesterase activity whose physiological function is not well understood, and is under the control of growth factors, cytokines, and glucocorticoids. PC-1interacts with the alpha subunit of the JR in a region between residues 485-599. This region serves as a connecting domain between the alpha subunit ligand binding domain and the beta subunit tyrosine kinase domain. We have found that transfection and overexpression of PC-1 into cultured cells se1ectively reduces both IR tyrosine kinase activity and JR signaling. We hypothesize, therefore, that PC-1 plays a role in insulin resistance. We now plan to document further that PC-1 is an important regulator of insulin action and 2 to further understand how PC-1 influences IR signaling. We propose the following: First, we will overexpress PC-1 in transgenic mice to determine whether in this species PC-1 causes insulin resistance. Second, We will study the effect of PC-1 on insulin sensitive cells: mouse 3T3 L1 adipocytes and rat L6 muscle cells. Third, we will investigate the mechanisms that cause PC-1 overexpression. Employing fibroblasts and muscle cells from insulin resistant patients, we will determine whether overexpression is caused by transcriptional or post-transcriptional mechanisms. Fourth, we have data. both in vitro and in vivo, indicating that PC-1 directly interacts with the IR alpha subunit. We will investigate the interactions of PC-1 with the IR by elucidating how and where PC-1 binds to the JR. For this purpose, we will employ direct binding studies. In addition, mutants of both the IR and PC-1 will be produced to locate discrete sites of protein-protein interaction. These series of studies should provide important new information, therefore, as to role of PC-1 in insulin resistance and the molecular mechanisms whereby PC-1 inhibits IR function.
