Mechanism of phospholipase D activation induced by prostaglandin D 2 in osteoblast-like cells: Function of Ca 2+/calmodulin

Abstract

Prostaglandin D 2 (PGD 2) stimulated the formation of choline in a dose-dependent manner in the range between 10 nM and 10 μM. 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 μM). The formation of choline stimulated by a combination of PGD 2 and 12- O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, was additive. Staurosporine, an inhibitor for protein kinases, enhanced the PGD 2-induced formation of choline, but H-7, another inhibitor for protein kinases, had little effect. PGD 2 stimulated Ca 2+ influx from extracellular space dose-dependently. The depletion of extracellular Ca 2+ by EGTA reduced the PGD 2-induced formation of choline. W-7 and trifluoperazine dihydrochloride, antagonists of calmodulin, dose-dependently inhibited the PGD 2-induced choline formation. These results strongly suggest that PGD 2 activates phospholipase D in a Ca 2+/calmodulin dependent manner in osteoblast-like cells, and that protein kinase C is not essential for the PGD 2-induced activation of phospholipase D.