Arachidonic acid induces mobilisation of calcium stores and c-jun gene expression: evidence that intracellular calcium release is associated with c-jun activation

Arachidonic acid (AA) plays a signaling role in the induction of several ge nes. We previously demonstrated that AA induces c-jun gene expression in th e stromal cell line +/+.1 LDA 11 by a signaling pathway involving activatio n of the c-jun amino-terminal kinase (JNK), This study investigated the rol e of calcium in AA signaling of c-jun activation in +/+.1 LDA 11 cells. AA (10-50 mu M) caused a rapid dose-dependent rise in cytosolic calcium. AA-in duced calcium mobilization involved both influx of extracellular calcium an d the release of intracellular calcium. The importance of calcium was inves tigated by variation of the extracellular calcium concentration, chelation of intracellular calcium and by calcium ionophore-induced influx of extrace llular calcium. AA-induced c-jun gene expression and increased luciferase a ctivity of a construct containing the high affinity AP-1 binding site was d ecreased in cells preincubated with the intracellular calcium chelator 1,2- bis(o-aminophenoxy)-eThane-N,N,N',N',-tetraacetic acid tetra(aceToxymethyl- esTer) (BAPTA-AM, 10 mu M) prior to stimulation with AA. Similarly, chelati on of intracellular calcium decreased AA-induced JNK activation. On the con trary, changes in the extracellular calcium concentration had no effect. Al so, ionophore A23187 failed to induce c-jun and JNK activation either alone than in combination with AA. These results suggested that calcium was requ ired for AA-dependent activation of c-jun, but that calcium alone was insuf ficient to induce activation of c-jun, Thus, release of calcium from intrac ellular stores is implicated in the signaling pathway of AA-induced c-jun a ctivation in stromal cells.