AJP - Endocrinology and Metabolism, Vol 261, Issue 5 E562-E571, Copyright © 1991 by American Physiological Society
Increased hepatic insulin proreceptor-to-receptor ratio in diabetes: a possible processing defect
D. Dardevet, K. Komori, C. Grunfeld, S. A. Rosenzweig and M. G. Buse
Department of Medicine, Medical University of South Carolina, Charleston 29425.
Hepatic insulin proreceptors and receptors were studied in control and in
ketotic diabetic rats 2-4 wk after streptozotocin treatment. Solubilized
preparations were partially purified by wheat germ agglutinin-agarose (WGA)
and lentil lectin agarose (LLA) chromatography to enrich eluates in insulin
receptors and proreceptors, respectively. After phosphorylation with
[gamma-32P]ATP, an approximately 190-kDa glycoprotein was identified in LLA
eluates as the insulin proreceptor, based on insulin dose-dependent
tyrosine autophosphorylation, immunoprecipitation with insulin
receptor-specific antibodies, and high-mannose glycosylation. Mature
approximately 95 kDa phosphorylated beta-subunits were present in both LLA
and WGA eluates. LLA also showed phosphorylated partially processed
beta-subunits (approximately 85 kDa) and proreceptors (approximately 190
kDa). Proreceptors comprised less than 1% of the total yield of hepatic
insulin receptors. The incorporation of 32P into proreceptors (per gram
liver or DNA) was 4.7- or 4.5-fold greater in diabetic vs. control rats,
whereas receptor labeling increased only 1.8- or 1.5-fold in diabetic rats.
beta-Subunit autophosphorylation per receptor was identical in control and
diabetic rats. The phosphorylation data suggested a diabetes-associated
2.6-fold increase in proreceptor-to-receptor ratios. When assessed by
cross-linking with 125I-labeled insulin or by immunoblotting,
proreceptor-to-receptor ratios were increased 1.5- and 3.1-fold,
respectively, in diabetic rats. The data suggest that uncontrolled diabetes
may alter insulin receptor processing.
