Increased hepatic insulin proreceptor-to-receptor ratio in diabetes: a possible processing defect.
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.
Dardevet
D
D
Department of Medicine, Medical University of South Carolina, Charleston 29425.
Komori
K
K
Grunfeld
C
C
Rosenzweig
S A
SA
Buse
M G
MG
D000818:Animals; D003432:Cross-Linking Reagents; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D006596:Hexosaminidases / Q000494:pharmacology; D015151:Immunoblotting; D007328:Insulin / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation; D011498:Protein Precursors / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000378:metabolism*; D012995:Solubility; D014909:Wheat Germ Agglutinins
D003432:Cross-Linking Reagents; D007328:Insulin; D011498:Protein Precursors; D014909:Wheat Germ Agglutinins; C051512:insulin proreceptor; D011972:Receptor, Insulin; D006596:Hexosaminidases