Testing Candidate Insulin-Action Genes by siRNA Inhibition

Grant Winner

  • Grady Campbell – College of Medical Sciences

Dean

  • Harold Laubach – College of Medical Sciences

Abstract

Award Winners

Type 2 diabetes ranks among the top ten causes of death in most developed nations, and its worldwide incidence is rapidly increasing. Central to type 2 diabetes is loss of sensitivity of cells to insulin. A major consequence is failure of skeletal muscle cells to move insulin-sensitive glucose transporters (GLUT4) to surface membranes where they lower blood glucose by transporting glucose from the bloodstream into the muscle cells. With insufficient GLUT4 translocation to muscle cell surfaces hyperglycemia and its harmful effects ensue. The normal process of GLUT4 translocation is poorly understood, so gene expression profiling using insulin-treated rat L6 muscle cells was used to identify mRNAs regulated by insulin. Because biology is efficient, when insulin increases an mRNA it is likely that the mRNA gives rise to a protein that is important to the cellular actions of insulin. Translocation of GLUT4 from inside the cell to the cell surface is carried out by normal intracellular trafficking mechanisms, so mRNAs increased by insulin and normally involved in trafficking may be hypothesized to be involved in GLUT4 translocation. Four insulin-regulated mRNAs were found in the gene expression profiling that encode proteins having roles in intracellular trafficking: ArgBP2, BIN1, caveolin 3 all increased and kinesin-related protein 1 (KRP1) decreased. Real-time RT-PCR showed a statistically significant difference in mRNA level change due to insulin between the decreased KRP1 and the three increased mRNAs. This application is to fund studies to test the hypothesis that proteins corresponding to these mRNAs carry out activities important to insulin action. Small interfering RNAs (siRNA) will be utilized to inhibit expression of each of these four proteins in insulin-induced cells, and cells will be assayed to determine if GLUT4 translocation is thereby inhibited. This knowledge would enhance our understanding at the molecular level of how cells respond to insulin.