Phosphatidic acid (PA) stimulates phospholipase C-β1 (PLC-β1) activity and promotes G protein stimulation of PLC-β1 activity. The isoform dependence for PA regulation of PLC-β activity as well as the role of PA in modulating regulation of PLC-β activity by protein kinase C (PKC) and G protein subunits was determined. As compared to PLC-β1, the phospholipase C-β3 (PLC-β3) isoform was less sensitive to PA, requiring greater than 15 mol % PA for stimulation. PLC-β3 bound weakly to PA. PKC had little effect on PA stimulation of PLC-β3 activity. PKC, however, inhibited PA stimulation of PLC-β1 activity through a mechanism dependent on the mol % PA. Stimulation by 7.5 mol % PA was completely inhibited by PKC. Increasing the PA and Ca2+ concentration attenuated PKC inhibition. The binding of PLC-β1 to PA containing phospholipid vesicles was also reduced by PKC, in a manner dependent on the mol % PA. PA increased the stimulation of PLC-β1 activity by Gαq but had little effect on the stimulation by βy subunits. These results demonstrate that PA stimulation of PLC-β activity is tightly regulated, suggesting the existence of a distinct PA binding region in PLC-β1. PA may be an important component of a receptor mediated signaling mechanism that determines PLC-β1 activation.
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