EFFECT OF PROSTAGLANDIN-F(2-ALPHA) ON CA2+ INFLUX IN OSTEOBLAST-LIKE CELLS - FUNCTION OF TYROSINE KINASE

We previously reported that pertussis toxin-sensitive GTP-binding protein is involved in prostaglandin F2alpha (PGF2alpha)-induced phosphoinositide (PI) hydrolysis in osteoblast-like MC3T3-E1 cells [Miwa et al. (1990): Biochem Biophys Res Commun 1 71:1229-1235]. In the present study, we investigated the mechanism of PGF2alpha-induced Ca2+ influx in MC3T3-E1 cells. PGF2alpha-induced formation of total inositol phosphates (IPs) was markedly reduced by the depletion of extracellular Ca2+ with EGTA. On the other hand, the depletion of extracellular Ca2+ had little effect on PGF2alpha-induced inositol 1,4,5-trisphosphate formation. PGF2alpha stimulated Ca-45(2+) influx dose dependently, attaining a maximum effect at 10 nM. Dose of PGF2alpha above 10 nM caused less than maximal stimulation. Genistein, an inhibitor of protein tyrosine kinase, which by itself had little effect on Ca-45(2+) influx, significantly suppressed the PGF2alpha-induced Ca-45(Ca2+) influx in a dose-dependent manner in the range between 1 mug/ml and 0.1 mg/ml. Sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, enhanced the PGF2alpha-induced Ca-45(2+) influx. Genistein also suppressed the PGF2alpha-induced total IPs formation dose dependently in the range between 1 mug/ml and 0.1 mg/ml. However, it had little effect on the PGF2alpha-induced inositol 1,4,5-trisphosphate formation. The pretreatment with pertussis toxin had little effect on the PGF2alpha-induced Ca-45(2+) influx. These results strongly suggest that PGF2alpha stimulates Ca2+ mobilization from extracellular space and PI hydrolysis via independent pathways in osteoblast-like cells, and the PGF2alpha-induced Ca2+ influx is regulated by protein tyrosine kinase, resulting in the promotion of PI hydrolysis. (C) 1994 Wiley-Liss, Inc.