Insulin-degrading enzyme is capable of degrading receptor-bound insulin |
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Authors: | K Yonezawa K Yokono K Shii J Hari S Yaso K Amano T Sakamoto Y Kawase H Akiyama M Nagata |
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Institution: | Second Department of Internal Medicine, Kobe University School of Medicine, Japan. |
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Abstract: | In the investigation of the intracellular sites of insulin degradation, it might be important whether receptor-bound insulin could be a substrate for insulin-degrading enzyme (IDE). Insulin receptor and IDE were purified from rat liver using a wheat germ agglutinin column and monoclonal anti-IDE antibody affinity column, respectively. 125I]insulin-receptor complex was incubated with various amounts of IDE at 0 degree C in the presence of disuccinimidyl suberate and analyzed by reduced 7.5% SDS-PAGE and autoradiography. With increasing amounts of IDE, the radioactivity of 135 kd band (insulin receptor alpha-subunit) decreased, whereas that of 110 kd band (IDE) appeared then gradually increased, suggesting that IDE could bind to receptor-bound insulin. During incubation of insulin-receptor complex with IDE at 37 degrees C, about half of the 125I]insulin was dissociated from the complex. However, the time course of 125I]insulin degradation in this incubation was essentially identical to that of free 125I]insulin degradation. Cross-linked, non-dissociable receptor-bound 125I]insulin was also degraded by IDE. Rebinding studies to IM-9 cells showed that the receptor binding activity of dissociated 125I]insulin from insulin-receptor complex incubated with IDE was significantly (p less than 0.001) decreased as compared with that without the enzyme. These results, therefore, show that IDE could recognize and degrade receptor-bound insulin, and suggest that IDE may be involved in insulin metabolism during receptor-mediated endocytosis through the degradation of receptor-bound insulin in early neutral vesicles before their internal pH is acidified. |
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