The phosphorylated form of rat pp63, a hepatic glycoprotein, selectively inhibits both insulin receptor tyrosine kinase activity (IR-TKA) and insulin-mediated growth promotion, but does not affect several other insulin-mediated activities. Our new data suggest that the human protein, alpha2-HS-glycoprotein (alpha2-HSG), in its phosphorylated form, functions similarly to rat pp63 in inhibiting IR autophosphorylation, IR-TKA and insulin-dependent mitogenesis in a dose-dependent fashion, non-competitive with respect to insulin. Since our long-term objective is to investigate the role of IR-TKA in both the normal and insulin-resistant states of rats and humans, this dissection of insulin-mediated cellular functions, by pp63/alpha2-HSG, provides us with a novel approach. Using this natural IR-TKA inhibitor, we can now examine the role of IR-TKA in the delivery of specific insulin-mediated signals.
Our specific aims i nclude: (1) Investigation of effects of pp63/alpha2-HSG on metabolic and mitogenic actions of insulin and on functions of the insulin receptor in a rat hepatoma cell line, Epstein-Barr Virus transformed lymphocytes and transfected rat fibroblasts expressing normal insulin receptors, (2) Examination of synthesis and secretion of pp63/alpha2-HSG and characterization of specific activity of circulating pp63/alpha2-HSG in rat and human insulin resistant states in vivo (high-fat diet and obesity, respectively), (3) Examination of mechanisms underlying these observations by utilizing human insulin receptor mutants as well as monoclonal antibodies to the insulin receptor and to pp63/alpha2-HSG for modifying pp63/alpha2-HSG - insulin receptor interaction. Our preliminary data demonstrate that pp63 gene expression directly correlates with the degree of insulin resistance, in a rat high-fat diet model. These date support our contention that studies on regulation of pp63/alpha2-HSG specific activity will yield information critical to our understanding of impairment of insulin signaling in insulin-resistant conditions (diabetes mellitus, hypertension, obesity, and dyslipidemia).

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
1R01DK044382-01A2
Application #
3245947
Study Section
Metabolism Study Section (MET)
Project Start
1992-09-30
Project End
1995-09-29
Budget Start
1992-09-30
Budget End
1993-09-29
Support Year
1
Fiscal Year
1992
Total Cost
Indirect Cost
Name
Wayne State University
Department
Type
Schools of Medicine
DUNS #
City
Detroit
State
MI
Country
United States
Zip Code
48202
Mathews, Suresh T; Singh, Gurmant P; Ranalletta, Mollie et al. (2002) Improved insulin sensitivity and resistance to weight gain in mice null for the Ahsg gene. Diabetes 51:2450-8
Cintron, V J; Ko, M S; Chi, K D et al. (2001) Genetic mapping and functional studies of a natural inhibitor of the insulin receptor tyrosine kinase: the mouse ortholog of human alpha2-HS glycoprotein. Int J Exp Diabetes Res 1:249-63
Srinivas, P R; Deutsch, D D; Mathews, S T et al. (1996) Recombinant human alpha 2-HS glycoprotein inhibits insulin-stimulated mitogenic pathway without affecting metabolic signalling in Chinese hamster ovary cells overexpressing the human insulin receptor. Cell Signal 8:567-73
Srinivas, P R; Goustin, A S; Grunberger, G (1995) Baculoviral expression of a natural inhibitor of the human insulin receptor tyrosine kinase. Biochem Biophys Res Commun 208:879-85
Srinivas, P R; Grunberger, G (1994) Inhibitors of the insulin receptor tyrosine kinase. Pharmacol Ther 64:23-35
Srinivas, P R; Wagner, A S; Reddy, L V et al. (1993) Serum alpha 2-HS-glycoprotein is an inhibitor of the human insulin receptor at the tyrosine kinase level. Mol Endocrinol 7:1445-55