MECHANISM OF PHOSPHOLIPASE-D ACTIVATION-INDUCED BY PROSTAGLANDIN D-2 IN OSTEOBLAST-LIKE CELLS - FUNCTION OF CA2+ CALMODULIN/

Prostaglandin D-2 (PGD(2)) stimulated the formation of choline in a do se-dependent manner in the range between 10 nM and 10 mu M. The effect of PGD(2) on the formation of inositol phosphates (EC(50) was 20 nM) was more potent than that on the formation of choline (EC(50) was 0.5 mu M). The formation of choline stimulated by a combination of PGD(2) and 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protei n kinase C, was additive. Staurosporine, an inhibitor for protein kina ses, enhanced the PGD(2)-induced formation of choline, but H-7, anothe r inhibitor for protein kinases, had little effect. PGD(2) stimulated Ca2+ influx from extracellular space dose-dependently. The depletion o f extracellular Ca2+ by EGTA reduced the PGD(2)-induced formation of c holine. W-7 and trifluoperazine dihydrochloride, antagonists of calmod ulin, dose-dependently inhibited the PGD(2)-induced choline formation. These results strongly suggest that PGD(2) activates phospholipase D in a Ca2+/calmodulin dependent manner in osteoblast-like cells, and th at protein kinase C is not essential for the PGD(2)-induced activation of phospholipase D.