PHOSPHOTYROSINE SPECIFIES THE PHOSPHORYLATION BY PROTEIN-KINASE CK2 OF A PEPTIDE REPRODUCING THE ACTIVATION LOOP OF THE INSULIN-RECEPTOR PROTEIN-TYROSINE KINASE

Protein kinase CK2 is a ubiquitous Ser/Thr-specific protein kinase res ponsible for the phosphorylation of many proteins implicated in signal transduction. It phosphorylates both threonyl and seryl residue(s) of the insulin receptor beta-subunit. In this study, a series of peptide s, reproducing all the threonyl sites of the intracellular domain of t he insulin receptor that display the consensus sequence for CK2, has b een synthesized and used as substrate for purified rat liver CK2. The only peptide readily phosphorylated is the one reproducing the activat ion loop of the insulin receptor (EIYET(1160)DYYA), including three ty rosines (Y1158, Y1162 and Y1163) whose phosphorylation through an inte rmolecular autocatalytic process promotes the activation of the recept or kinase. The phosphorylation efficiency of T1160 is increased almost 20-fold if these three tyrosines are previously phosphorylated. By us ing variably phosphorylated peptides, the tyrosine mainly responsible for such a hierarchical phosphorylation process has been identified as Y1163. It can be concluded, from these data, that T1160 situated in t he activation loop of the insulin receptor, represents an excellent ta rget for CK2, its phosphorylation being triggered by the previous auto phosphorylation of the three tyrosyl residues surrounding it, with spe cial reference to Y1163. These data are consistent with the implicatio n of CK2 in the regulation of the activation process of the insulin re ceptor protein tyrosine kinase. Copyright (C) 1996 Elsevier Science Lt d