title: Distinct roles for insulin and insulin-like growth factor-1 receptors in pancreatic beta-cell glucose sensing revealed by RNA silencing.
abstract: The importance of the insulin receptor (IR) and the insulin-like growth factor-1 receptor (IGF-1R) for glucose-regulated insulin secretion and gene expression in pancreatic islet beta-cells is at present unresolved. Here, we have used small interfering RNAs (siRNAs) to silence the expression of each receptor selectively in clonal MIN6 beta-cells. Reduction of IR levels by >90% completely inhibited glucose (30 mM compared with 3 mM)-induced insulin secretion, but had no effect on depolarization-stimulated secretion. IR depletion also blocked the accumulation of preproinsulin (PPI), pancreatic duodenum homoeobox-1 (PDX-1) and glucokinase (GK) mRNAs at elevated glucose concentrations, as assessed by quantitative real-time PCR analysis (TaqMan). Similarly, depletion of IGF-1R inhibited glucose-induced insulin secretion but, in contrast with the effects of IR silencing, had little impact on the regulation of gene expression by glucose. Moreover, loss of IGF-1R, but not IR, markedly inhibited glucose-stimulated increases in cytosolic and mitochondrial ATP, suggesting a role for IGF-1R in the maintenance of oxidative metabolism and in the generation of mitochondrial coupling factors. RNA silencing thus represents a useful tool for the efficient and selective inactivation of receptor tyrosine kinases in isolated beta-cells. By inhibiting glucose-stimulated insulin secretion through the inactivation of IGF-1R, this approach also demonstrates the existence of insulin-independent mechanisms whereby elevated glucose concentrations regulate PPI, PDX-1 and GK gene expression in beta-cells.
authors.affiliation: Henry Wellcome Laboratories for Integrated Cell Signalling and Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Da Silva Xavier
authors.forename: Qingwen
authors.initials: Q
authors.lastname: Qian
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Cullen
authors.forename: Guy A
authors.initials: GA
authors.lastname: Rutter
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003981:Diazoxide / Q000494:pharmacology; D005786:Gene Expression Regulation; D005941:Glucokinase / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D018398:Homeodomain Proteins; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology; D000078790:Insulin Secretion; D051379:Mice; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism*; D011384:Proinsulin / Q000235:genetics / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000502:physiology*; D011972:Receptor, Insulin / Q000235:genetics / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D018398:Homeodomain Proteins; D007328:Insulin; D011498:Protein Precursors; D012333:RNA, Messenger; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; C013737:preproinsulin; D000255:Adenosine Triphosphate; D011384:Proinsulin; D005941:Glucokinase; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; D005947:Glucose; D003981:Diazoxide