title: Possible role for serine/threonine phosphorylation in the regulation of the heteroprotein complex between the hsp90 stress protein and the pp60v-src tyrosine kinase.
abstract: The abundant, cytoplasmic 90-kDa heat-shock protein associates transiently with the Rous sarcoma virus oncogenic protein tyrosine kinase, pp60v-src, directs its cellular trafficking and negatively regulates its kinase activity. Here we report that the serine/threonine phosphatase inhibitor, okadaic acid, destabilized the heat-shock protein 90-pp60v-src chaperone complex in v-src-transfected cells. Concomitant with complex destabilization by okadaic acid, phosphoserine was doubled and phosphothreonine was increased 20-fold in the heat-shock protein 90. Although phosphorylation of the total pool of immunoprecipitable pp60v-src was unchanged, okadaic acid slightly increased phosphoserine and phosphothreonine levels specifically in pp60v-src bound to heat-shock protein 90. The low level of tyrosine phosphorylation in the pp60v-src complexed with heat-shock protein 90 was further decreased by okadaic acid. Interestingly, okadaic acid-stabilized hyperphosphorylation of the heat-shock protein 90-pp60v-src complex lowered the level of pp60v-src in cell membranes, the functional location for pp60v-src. We suggest that serine/threonine phosphorylation of heat-shock protein 90 and/or pp60v-src functions as a regulatory molecular trigger to release pp60v-src from the chaperone complex at the inner surface of cell membranes.
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D051379:Mice; D019319:Okadaic Acid; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D018841:HSP90 Heat-Shock Proteins; D019319:Okadaic Acid; D013912:Threonine; D012694:Serine; D011505:Protein-Tyrosine Kinases; D015688:Oncogene Protein pp60(v-src); D010749:Phosphoprotein Phosphatases