Peptide rescues GLUT4 recruitment, but not GLUT4 activation, in insulin resistance.

Insulin-stimulated GLUT4 recruitment to the plasma membrane is impaired in insulin resistance. We recently reported that a cell permeable phosphoinositide-binding peptide induces GLUT4 recruitment as potently as insulin, but does not activate GLUT4 to initiate glucose uptake. Here we investigated whether the peptide-induced GLUT4 recruitment is intact in insulin resistance. The expression levels of GLUT1 and GLUT4 were unaffected by chronically treating 3T3-L1 adipocytes with insulin. GLUT4 recruitment by acute insulin stimulation after chronic insulin treatment was significantly reduced, but was fully restored by the peptide treatment. However, subsequent acute insulin stimulation to activate GLUT4 failed to increase glucose uptake in peptide-pretreated cells. Insulin-stimulated GLUT1 recruitment was unaffected by the peptide pretreatment. These results suggest that the GLUT4 recruitment signal caused by the peptide is intact in insulin resistance, but GLUT4 activation that occurs subsequent to recruitment is not rescued by the peptide treatment.