Involvement of phosphatidylcholine hydrolysis by phospholipase C in prostaglandin F2?-induced 1,2-diacylglycerol formation in osteoblast-like MC3T3-E1 cells

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Abstract
We previously demonstrated that a prostaglandin F2Α (PGF2Α)-induced, sustained increase in 1,2-diacylglycerol (DAG) production was important for proliferation in osteoblast-like MC3T3-E1 cells. The 1,2-DAG formation is mediated by various enzymes, such as phos-phoinositide (PI)-specific phospholipase C (PLC), phospholipase D (PLD), and phosphatidylcholine (PC)-specific phospholipase C (PC-PLC). In the present study, to elucidate the mechanism of the 1,2-DAG formation, we have examined the PGF2Α-induced production of [3H]phosphorylcholine, a product of PC-PLC activity, in [3H]choline-labeled MC3T3-E1 cells. The PGF2Α-induced [3H]phosphorylcholine production was inhibited by genistein, a potent protein tyrosine kinase inhibitor, and increased by vanadate, a potent protein tyrosine phosphatase inhibitor. However, there were no effects after treatment with protein kinase C (PKC) inhibitors, the guanosine triphosphate (GTP) binding protein activator, NaF/AlCl3, a Ca2+-ionophore, or the potent activator of PKC, phorbol 12-myristate 13-acetate (PMA), suggesting that a tyrosine kinase(s) was involved in the PGF2Α-induced [3H]phosphorylcholine formation. Furthermore, a PGF2Α analogue, 16-(3-trifluoromethylphenoxy)-Ω-tetranor-trans-Δ2 PGF2Α methyl ester (ONO-995), stimulated the proliferation of MC3T3-E1 cells to a level similar to that seen with PGF2Α, and also caused phosphorylcholine and 1,2-DAG generation. However, neither an increase in intracellular free calcium ion ([Ca2+]i) levels by PI-PLC, nor phosphatidylethanol formation (and choline production) by PC-PLD were observed. From these results, we conclude that PGF2Α-induced 1,2-DAG accumulation was mediated mainly via tyrosine kinase(s)-dependent PC hydrolysis by PLC activity in osteoblast-like MC3T3-E1 cells.

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