Phospholipase D1 activity is crucial for cytosolic phospholipase A2 –dependent prostaglandin E2 formation in murine osteoblastic MC3T3-E1 cells

In bone, prostaglandin E₂ (PGE₂) is highly osteogenic and formed by osteoblasts, a key modulatory event in the regulation of bone cell activity. MC3T3-E1 cells are widely used as an in vitro model of osteoblast function. It is still not clear which pathways contribute to the release of AA in these cells. In this study we have focussed on the contribution of phospholipase D (PLD) enzymes to osteoblastic PGE₂ formation after stimulation with endothelin-1 (ET-1). Using specific inhibitors of PLD1 and PLD2 we could show that PGE₂ formation was strictly dependent on PLD1 but not PLD2 activity and cytosolic phospholipase A₂ (cPLA₂) was activated by triggering through PLD1. We have identified diacyl glycerol (DAG) as a possible effector molecule which may serve as a triggering signal for PKC activation and subsequent cPLA₂ phosphorylation.