ABSTRACT
We have synthesized a tris-sulfotyrosyl dodecapeptide (3S-peptide-I) that corresponds to the major autophosphorylation domain within the insulin receptor beta-subunit and showed that it potently inhibited insulin receptor dephosphorylation by protein tyrosine phosphatases (PTPases) in vitro. 3S-peptide-I also inhibited tyrosine dephosphorylation of a synthetic peptide by the recombinant PTPase PTP-1B, indicating that 3S-peptide-I interacts directly with PTPase, causing its inactivation. The peptide had no effect on the activity of serine/threonine phosphatases, PP-1 and PP-2A, or alkaline phosphatase. Furthermore, we found that the introduction of a N-stearyl derivative of 3S-peptide-I in CHO/HIRc cells caused a significant increase in insulin-stimulated phosphorylation of the insulin receptor. In contrast, ligand-stimulated phosphorylation of epidermal growth factor (EGF) receptor in CHO cells overexpressing EGF receptors was not affected by the presence of N-stearyl-3S-peptide-I. These data suggest that by inhibiting dephosphorylation of the insulin receptor in intact cells, 3S-peptide-I may specifically enhance insulin signalling.