Candidate Insulin Action mRNAs in Skeletal Muscle

Grant Winner

Dean

Abstract

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 permit uptake of glucose from the bloodstream into the muscle cells and thus lower blood glucose. 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 has been completed 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 in the cell, so an mRNA normally involved in trafficking and increased by insulin may be hypothesized to be involved in GLUT4 translocation. Three insulin-regulated mRNAs were found in the gene expression profiling that encode proteins having roles in intracellular trafficking: ArgBP2, BIN1 (amphiphysin 2), and caveolin 3. This application is to fund studies to test the hypothesis that protein levels corresponding to these mRNAs increase during insulin stimulation, and that expression of the proteins is required for GLUT4 translocation. Western blot analysis will be utilized to determine if protein levels increase with insulin. RNA interference to silence expression of each of these proteins in insulin-induced cells will show if there is a critical role for that protein in GLUT4 trafficking activity. This knowledge would enhance our understanding at the molecular level of how cells respond to insulin.