ACTIVATION OF CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE (CAM-KINASE)-IV BY CAM-KINASE KINASE IN JURKAT T-LYMPHOCYTES/

Ca2+/calmodulin-dependent protein kinase IV (CaM-kinase IV), a member of the CaM-kinase family involved in transcriptional regulation, is st imulated by Ca2+/CaM but also requires phosphorylation by a CaM-kinase kinase for full activation. In this study we investigated the physiol oscal role of a CaM-kinase cascade in Jurkat T human lymphocytes throu gh antigen receptor (CD3) signaling. Total and Ca2+-independent CaM-ki nase IV activities were increased 8-14-fold by anti-CD3 antibody. This CD3-mediated activation involved phosphorylation since the immunoprec ipitated CaM-kinase IV from stimulated Jurkat cells could be subsequen tly inactivated in vitro by protein phosphatase 2A. CaM-kinase IV immu noprecipitated from unstimulated Jurkat cells or CD3-negative mutant J urkat cells could be activated in vitro 10-40-fold by CaM-kinase kinas e purified from rat brain or thymus, whereas CaM-kinase IV from CD3 st imulated wild-type Jurkat cells was only activated to 2-3-fold by exog enous CaM-kinase kinase. CaM-kinase IV activation was triggered by Ca2 + acting through calmodulin since activation could also be elicited by ionomycin treatment, and CD3-mediated activation was blocked by the c almodulin antagonist calmidazolium. These data are consistent with a C aM-kinase cascade in which CaM-kinase TV is activated by a CaM-kinase kinase cascade triggered by elevated intracellular calcium in Jurkat c ells.