Ca(2+)-dependent activation of c-jun NH(2)-terminal kinase in primary rabbit proximal tubule epithelial cells

Previous work from this laboratory demonstrated that arachidonic acid activates c-jun NH(2)-terminal kinase (JNK) through oxidative intermediates in a Ca(2+)-independent manner (Cui X and Douglas JG. Arachidonic acid activates c-jun N-terminal kinase through NADPH oxidase in rabbit proximal tubular epithelial cells. Proc Natl Acad Sci USA 94: 3771-3776, 1997.). We now report that JNK can also be activated via a Ca(2+)-dependent mechanism by agents that increase the cytosolic Ca(2+) concentration (Ca(2+) ionophore A(23187), Ca(2+)-ATPase inhibitor thapsigargin) or deplete intracellular Ca(2+) stores [intracellular Ca(2+) chelator 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM]. The activation of JNK by BAPTA-AM occurs despite a decrease in cytosolic Ca(2+) concentration as detected by the indicator dye fura 2, but appears to be related to Ca(2+) metabolism, because modification of BAPTA with two methyl groups increases not only the chelation affinity for Ca(2+), but also the potency for JNK activation. BAPTA-AM stimulates Ca(2+) influx across the plasma membrane, and the resulting local Ca(2+) increases are probably involved in activation of JNK because Ca(2+) influx inhibitors (SKF-96365, nifedipine) and lowering of the free extracellular Ca(2+) concentration with EGTA reduce the BAPTA-induced JNK activation.