The Pleckstrin Homology Domain in Insulin Receptor Substrate-1 Sensitizes Insulin Signaling

Abstract

The NH 2 terminus of insulin receptor substrate! (IRS-I) contains a pleckstrin homology (PH) domain. We deleted the PH domain in IRS-1 (IRS-l~PH) and ex pressed the mutant in Chinese hamster ovary and 32D cells. During insulin stimulation, IRSl~PH is poorly ty rosine-phosphorylated in CHO cells, but undergoes ser ine/threonine phosphorylation. Similarly, IRSl~PH fails to undergo insulin-stimulated tyrosine phosphorylation in 32D cells, which uncouples the activation of phos phatidylinositol 3' -kinase and p70 86 k from the endoge nous insulin receptors. Overexpression of the insulin receptor in 32D 1 R cells, however, restores tyrosine phosphorylation of IRS-l~PH and rescues insulin responses including mitogenesis. Thus, while the PH domain is not required for the engagement of downstream signals, it is one of the elements in the NH 2 terminus of IRS-I that is needed for a sensitive coupling to insulin receptors, especially at ordinary receptor levels found in most cells and tissues.