Evidence for role of phospholipase A₂ in phosphatidic acid-induced signaling to c-fos serum response element activation

The activity of exogenous phosphatidic acid (PA) to transactivate c-fos serum response element (SRE) was investigated by transient transfection analysis. Incubation of Rat-2 fibroblast cells with exogenous PA caused a stimulation of c-fos SRE-linked luciferase activity in a dose- and time-dependent manner. The SRE stimulation by PA was dramatically reduced by either pre-treatment with mepacrine, an inhibitor of phospholipase A₂ (PLA₂), or co-transfection with antisense cytosolic phospholipase A₂ (cPLA₂) oligonucleotide, whereas lysophosphatidic acid (LPA)-induced SRE activation was not affected. Consistent with this specific requirement for PLA₂ by PA, the translocation of cPLA₂ protein was rapidly induced followed by PA treatment. Together, these results suggest that PLA₂, especially cPLA₂, plays a critical role in the nuclear signaling cascade of PA in Rat-2 fibroblast cells.