Distinct roles for insulin and insulin-like growth factor-1 receptors in pancreatic beta-cell glucose sensing revealed by RNA silencing

Biochem J. 2004 Jan 1;377(Pt 1):149-58. doi: 10.1042/BJ20031260.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Animals
  • Cell Line
  • Diazoxide / pharmacology
  • Gene Expression Regulation
  • Glucokinase / genetics
  • Glucokinase / metabolism
  • Glucose / pharmacology*
  • Homeodomain Proteins*
  • Insulin / metabolism
  • Insulin / pharmacology
  • Insulin Secretion
  • Mice
  • Pancreas / drug effects
  • Pancreas / metabolism*
  • Proinsulin / genetics
  • Proinsulin / metabolism
  • Protein Precursors / genetics
  • Protein Precursors / metabolism
  • RNA Interference
  • RNA, Messenger / metabolism
  • Receptor, IGF Type 1 / genetics
  • Receptor, IGF Type 1 / physiology*
  • Receptor, Insulin / genetics
  • Receptor, Insulin / physiology*
  • Trans-Activators / genetics
  • Trans-Activators / metabolism

Substances

  • Homeodomain Proteins
  • Insulin
  • Protein Precursors
  • RNA, Messenger
  • Trans-Activators
  • pancreatic and duodenal homeobox 1 protein
  • preproinsulin
  • Adenosine Triphosphate
  • Proinsulin
  • Glucokinase
  • Receptor, IGF Type 1
  • Receptor, Insulin
  • Glucose
  • Diazoxide