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

We previously reported that pertussis toxin-sensitive GTP-binding prot ein is involved in prostaglandin F2alpha (PGF2alpha)-induced phosphoin ositide (PI) hydrolysis in osteoblast-like MC3T3-E1 cells [Miwa et al. (1990): Biochem Biophys Res Commun 1 71:1229-1235]. In the present st udy, we investigated the mechanism of PGF2alpha-induced Ca2+ influx in MC3T3-E1 cells. PGF2alpha-induced formation of total inositol phospha tes (IPs) was markedly reduced by the depletion of extracellular Ca2with EGTA. On the other hand, the depletion of extracellular Ca2+ had little effect on PGF2alpha-induced inositol 1,4,5-trisphosphate format ion. 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, signifi cantly suppressed the PGF2alpha-induced Ca-45(Ca2+) influx in a dose-d ependent manner in the range between 1 mug/ml and 0.1 mg/ml. Sodium or thovanadate, an inhibitor of protein tyrosine phosphatases, enhanced t he PGF2alpha-induced Ca-45(2+) influx. Genistein also suppressed the P GF2alpha-induced total IPs formation dose dependently in the range bet ween 1 mug/ml and 0.1 mg/ml. However, it had little effect on the PGF2 alpha-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 indep endent pathways in osteoblast-like cells, and the PGF2alpha-induced Ca 2+ influx is regulated by protein tyrosine kinase, resulting in the pr omotion of PI hydrolysis. (C) 1994 Wiley-Liss, Inc.