Activation of Ca²⁺/calmodulin-dependent protein kinase II by stimulation with bradykinin in neuroblastoma x glioma hybrid NG108-15 cells

To elucidate the mechanisms of the initracellular signal transduction elicited with bradykinin in NG108-15 neuroblastoma x glioma hybrid cells, we examined the activation of Ca²⁺/calmodulin-dependent protein kinase II (CaM kinase II) by bradykinin stimulation. When the extract of NG108-15 cells was immunoprecipitated with the affinity-purified antibody to brain CaM kinase II, a 50-kDa protein in the immunoprecipitate mainly became autophosphorylated in a Ca²⁺/calmodulin-dependent manner. The result suggest that the 50-kDa protein is the subunit of CaM kinasee II in NG108-15 cells.The Ca²⁺/calmodulin-independent activity (autonomous activity) of the enzyme increased twice within 10 s by stimulation with 1 μM bradykinin in the cells. The increase in the autonomous activity of the enzyme had two phases: the transient early-peak phase and the long late-plateau phase. The former was abolished by the pretreatment of the cells with 10 mM caffeine or 20 μM BAPTA-AM, and the latter was abolished by the removal of the extracellular Ca²⁺ with 1 mM EGTA or by the pretreatment with 1 μM nifedipine. Stimulation of ³²P-labeled NG108-15 cells with 1 μM bradykinin increased the autophosphorylation of CaM kinase II and this increase was abolished by pretreatment with caffeine or BAPTA-AM. Theseesults suggest that CaM kinase II is activated via the inositol phospholipid signaling pathway induced with bradykinin in NG108-15 cells.