Function of Ca 2+ influx in phospholipase D activation induced by prostaglandin F 2α in osteoblast-like cells: Involvement of tyrosine kinase

Abstract

We previously reported that prostaglandin F 2α (PGF 2α) induces Ca 2+ influx from the extracellular space via protein tyrosine kinase in osteoblast-like MC3T3-E1 cells and that PGF 2α stimulates phosphatidylcholine-hydrolyzing phospholipase D in these cells (6, 12). In this study, we examined the relationship between the tyrosine kinase-regulated Ca 2+ influx by PGF 2α and the activation of phospholipase D in MC3T3-E1 cells. The depletion of extracellular Ca 2+ by [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) markedly reduced the PGF 2α-induced formation of choline. Genistein, an inhibitor of protein tyrosine kinases, which by itself had little effect on choline formation, significantly suppressed the formation of choline induced by PGF 2α in a dose-dependent manner. Tyrphostin, an inhibitor of protein tyrosine kinases chemically distinct from genistein, also suppressed the PGF 2α-induced formation of choline. Sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, significantly enhanced the PGF 2α-induced formation of choline. These results strongly suggest that the phospholipase D activation by PGF 2α is dependent on extracellular Ca 2+ in osteoblast-like cells and that protein tyrosine kinase is involved in the activation of phospholipase D.