Arachidonic acid induces mobilization 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 genes. We previously demonstrated that AA induces c-jun gene expression in the stromal cell line +/+.1 LDA 11 by a signaling pathway involving activation of the c-jun amino-terminal kinase (JNK). This study investigated the role of calcium in AA signaling of c-jun activation in +/+.1 LDA 11 cells. AA (10-50 microM) caused a rapid dose-dependent rise in cytosolic calcium. AA-induced calcium mobilization involved both influx of extracellular calcium and the release of intracellular calcium. The importance of calcium was investigated by variation of the extracellular calcium concentration, chelation of intracellular calcium and by calcium ionophore-induced influx of extracellular calcium. AA-induced c-jun gene expression and increased luciferase activity of a construct containing the high affinity AP-1 binding site was decreased 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 microM) prior to stimulation with AA. Similarly, chelation of intracellular calcium decreased AA-induced JNK activation. On the contrary, changes in the extracellular calcium concentration had no effect. Also, ionophore A23187 failed to induce c-jun and JNK activation either alone than in combination with AA. These results suggested that calcium was required for AA-dependent activation of c-jun, but that calcium alone was insufficient to induce activation of c-jun. Thus, release of calcium from intracellular stores is implicated in the signaling pathway of AA-induced c-jun activation in stromal cells.