INSULIN-RECEPTOR SUBSTRATE-1 MEDIATES THE STIMULATORY EFFECT OF INSULIN ON GLUT4 TRANSLOCATION IN TRANSFECTED RAT ADIPOSE-CELLS

Insulin signaling is initiated at least in part by activation of the insulin receptor tyrosine kinase and subsequent phosphorylation of cellular substrates such as insulin receptor substrate 1 (IRS-l). Previous studies have focused on the role of IRS-1 in the mitogenic actions of insulin. We have now investigated the possible role of IRS 1 in mediating the effect of insulin to stimulate glucose transport in a physiologically relevant insulin target tissue. In this study, we transfected rat adipose cells in primary culture with an antisense ribozyme directed against rat IRS-l. Expression of the ribozyme in these cells caused a 4.4-fold increase in the concentration of insulin required to achieve half-maximal stimulation of the translocation of cotransfected epitope-tagged GLUT4 without changing the maximal insulin response. Overexpression of human IRS-1 increased the basal cell surface GLUT4 to nearly the maximal level in the absence of insulin. When the ribozyme (specific to rat IRS-1) was cotransfected along with human IRS-1, the insulin dose-response curve was shifted to the left when compared with cells transfected with the ribozyme alone. These data provide strong support for the hypothesis that IRS-1 plays a role in insulin-stimulated glucose transport in insulin-responsive cells.