DIRECT EVIDENCE FOR TYROSINE AND THREONINE PHOSPHORYLATION AND ACTIVATION OF MITOGEN-ACTIVATED PROTEIN-KINASE BY VASOPRESSIN IN CULTURED RAT VASCULAR SMOOTH-MUSCLE CELLS

Mitogen-activated protein (MAP) kinases are members of a 40-45-kDa fam ily of serine/threonine protein kinases that phosphorylate several sub strates including microtubule-associated protein-2, S6 kinase, and mye lin basic protein. Activity of MAP kinases is regulated by growth fact ors that stimulate the phosphorylation of threonine 188 and tyrosine 1 90 in the kinase. In this paper direct evidence is presented for tyros ine and threonine phosphorylation of MAP kinase in concert with elevat ed activity in response to vasopressin in primary cultures of vascular smooth muscle cells. Activation of MAP kinase is correlated with acti vation of S6 kinase activity related to S6 kinase II. Data support the concept that the activation of MAP kinase by vasopressin is mediated by pertussis toxin-independent biochemical pathways.