Date of Award

1989

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular and Cellular Biology and Pathobiology

College

College of Graduate Studies

First Advisor

Maria G. Buse

Second Advisor

Rosalie K. Crouch

Third Advisor

Gary Landreth

Fourth Advisor

George E. Lindenmayer

Fifth Advisor

Barry Ledford

Abstract

Activation of the insulin receptor tyrosine kinase in vitro and in vivo was studied in two rat models of insulin resistance: hypercortisolemia and streptozotocin-induced diabetes. In control rats, intravenous insulin administration resulted in dose-dependent in vivo activation of the skeletal muscle insulin receptor kinase. Chronic cortisone treatment did not affect the kinase activity of receptors solubilized from muscle after activation with insulin in vivo or in vitro. In contrast, diabetes depressed skeletal muscle insulin receptor kinase activation in vivo by ~50%. Diabetes impaired the in vitro insulin stimulation of receptor kinase activity from skeletal muscle and liver towards the substrate histone H2b, but not towards the synthetic substrate poly glu-tyr (4:1). To understand the mechanisms underlying the substrate selective effects of diabetes, kinetics of insulin receptor tyrosine kinase activity solubilized from control and diabetic liver were examined. Both substrates, histone H2b and poly glu-tyr (4:1), inhibited insulin-stimulated autophosphorylation and exogenous kinase activity when substrates were added prior to activation of receptors with ATP. Inhibition of insulin-stimulated exogenous kinase activity by H2b was more marked with diabetic-derived insulin receptors, resulting in a ~70% lower maximal kinase activity towards this substrate compared to receptors isolated from control rats. When receptors were allowed to autophosphorylate prior to addition of H2b, substrate inhibition of kinase activity was minimal or absent and the difference in maximal kinase activity between control- and diabetic- derived receptors was reduced to ~25%. Kinetics of insulin receptor kinase activity towards poly glu-tyr (4:1) were unaltered by diabetes. Effects of substrate-inhibition and diabetes on insulin receptor kinase activity showed tissue-specific differences. Liver-derived H2b kinase activity was inhibited to a greater extent by H2b than that from muscle, and the effects of diabetes were greater in liver than muscle. The intrinsic (uninhibited) muscle insulin receptor tyrosine kinase was unimpaired by diabetes. Conclusions: The insulin resistance associated with hypercortisolemia occurs distal to the receptor kinase. In vivo activation of the skeletal muscle insulin receptor tyrosine kinase is impaired by diabetes. Diabetes associated impairment of the insulin receptor kinase activated in vitro reflects mainly enhanced susceptibility of the receptor to inhibition by some substrates, e.g., H2b. This defect, which may result in impaired signalling appears selective for substrates.

Rights

All rights reserved. Copyright is held by the author.

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