FUNCTION OF CA2-D ACTIVATION-INDUCED BY PROSTAGLANDIN-F2-ALPHA IN OSTEOBLAST-LIKE CELLS - INVOLVEMENT OF TYROSINE KINASE( INFLUX IN PHOSPHOLIPASE)

We previously reported that prostaglandin F-2 alpha (PGF(2 alpha)) ind uces Ca2+ influx from the extracellular space via protein tyrosine kin ase in osteoblast-like MC3T3-E1 cells and that PGF(2 alpha) stimulates phosphatidylcholine-hydrolyzing phospholipase D in these cells (6, 12 ), In this study, we examined the relationship between the tyrosine ki nase-regulated Ca2+ influx by PGF(2 alpha) and the activation of phosp holipase D in MC3T3-E1 cells, The depletion of extracellular Ca2+ by [ ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) markedly reduc ed the PGF(2 alpha)-induced formation of choline, Genistein, an inhibi tor of protein tyrosine kinases, which by itself had little effect on choline formation, significantly suppressed the formation of choline i nduced by PGF(2 alpha)in a dose-dependent manner. Tyrphostin, an inhib itor of protein tyrosine kinases chemically distinct from genistein, a lso suppressed the PGF(2 alpha)-induced formation of choline, Sodium o rthovanadate, an inhibitor of protein tyrosine phosphatases, significa ntly enhanced the PGF(2 alpha)-induced formation of choline, These res ults strongly suggest that the phospholipase D activation by PGF(2 alp ha) is dependent on extracellular Ca2+ in osteoblast-like cells and th at protein tyrosine kinase is involved in the activation of phospholip ase D.