Phosphatidic acid potentiates Gαq stimulation of phospholipase C-β1 signaling

Phosphatidic acid (PA) is interactive with Gαq-linked agonists to stimulate GPCR signaling via phospholipase C-β1 (PLC-β1). Phorbol 12-myristate 13-acetate (PMA) increases cellular levels of PA and phospholipase D activity (PLD). This study evaluated whether PMA can stimulate PLC-β1 activity via PA, independent of GPCR input in transfected COS 7 cells. PMA alone had little effect on PLC activity in cells co-transfected with PLC-β1 and Gαq. Activated Gαq, induced by co-transfecting muscarinic cholinergic receptor (m1R), was necessary for stimulation of PLC-β1 activity by PMA. Stimulation by PMA was dependent on the PA-regulatory motif of PLC-β1 implicating PA in this mechanism. PLD1 knockdown by antisense decreased responsiveness of PLC-β1 to both PMA and carbachol. PA alone thus has little effect on PLC-β1 activity, but PA and PLD1 synergize with activated Gαq to stimulate PLC-β1 signaling. Coordinate interaction with activated Gαq may serve as an important mechanism to fine tune response to ligands while preventing spurious initiation of PLC-β signaling by PA in cells.