Ubiquitination is involved in glucose-mediated downregulation of GIP receptors in islets

作者：Zhou Jie; Livak Mauren F A; Bernier Michel; Muller Denis C; Carlson Olga D; Elahi Dariush; Maudsley Stuart; Egan Josephine M^*

来源：American Journal of Physiology - Endocrinology And Metabolism, 2007, 293(2): E538-E547.

DOI：10.1152/ajpendo.00070.2007

• pancreatic islet
• cyclic adenosine monophosphate
• insulin
• multivesicular body
• glucose-dependent insulinotropic polypeptide

Glucose-dependent insulinotropic polypeptide (GIP) is a gastrointestinal hormone that has a potent stimulatory effect on insulin release under conditions of normal glucose tolerance. However, its insulinotropic effect is reduced or even absent entirely in type 2 diabetic patients. In this study, we addressed the role of glucose concentration in the diabetic range of >= 11 mM, i.e., hyperglycemia per se, as a cause of the lack of response to GIP. Culturing rat and human pancreatic islets in >= 11 mM glucose for up to 24 h resulted in prevention of GIP-mediated intracellular cAMP increase compared with culturing in 5 mM glucose. Western blot analysis revealed a selective 67 +/- 2% (rat) and 60 +/- 8% ( =human) decrease of GIP-R expression in islets exposed to >= 11 mM glucose compared with 5 mM glucose (P < 0.001). We further immunoprecipitated GIP-R from islets and found that GIP-R was targeted for ubiquitination in a glucose- and time-dependent manner. Downregulation of GIP-R was rescued by treating isolated islets with proteasomal inhibitors lactacystin and MG-132, and the islets were once again capable of increasing intracellular cAMP levels in response to GIP. These results suggest that the GIP-R is ubiquitated, resulting in downregulation of the actions of GIP.

• 出版日期2007-8