MECHANISM OF PROSTAGLANDIN-E2-INDUCED ARACHIDONIC-ACID RELEASE IN OSTEOBLAST-LIKE CELLS - INDEPENDENCE FROM PHOSPHOINOSITIDE HYDROLYSIS

We previously reported that pertussis toxin (PTX)-sensitive (GTP-binding protein is involved in the coupling of prostaglandin E2(PGE2) receptor to phospholipase C in osteoblast-like MC3T3-E1 cells (1). In the present study, we analyzed the mechanism of PGE2-induced arachidonic acid (AA) release in MC3T3-E1 cells. PGE, stimulated the release of AA and the formation of inositol trisphosphate (IP3) dose dependently in the range between 1 nM and 10-mu-M. The effect of PGE2 on AA release (ED50 was 80 nM) was more potent than that on IP3 formation (ED50 was 0.8-mu-M). Quinacrine, a phospholipase A2 inhibitor, suppressed the PGE2-induced AA release but had little effect on the IP3 formation. NaF, a GTP-binding protein activator, mimicked PGE2 by stimulating the AA release. The AA release stimulated by a combination of PGE2 and NaF was not additive. PTX had little effect on the PGE2-induced AA release. These results strongly suggest that the AA release and the phosphoinositide hydrolysis are separately stimulated by PGE2 in osteoblast-like cells, and the PGE2-induced AA release is mediated by PTX-insensitive GTP-binding protein.