Possible involvement of p38 MAP kinase in prostaglandin E1-induced ALP activity in osteoblast-like cells

Abstract

Prostaglandins are now recognized to be important regulators for both bone formation and resorption. Among them, prostaglandin E 1 (PGE 1) has been reported to stimulate cAMP accumulation and to induce alkaline phosphatase (ALP) activity, a marker of differentiation, in osteoblast-like cells. Recently, we have shown that p38 mitogen-activated protein (MAP) kinase pathway regulates ALP activity in response to activation of Gi protein-coupled receptors in mouse osteoblast-like MC3T3-E1 cells (Suzuki et al., Endocrinology 140 (1999) 3177). In the present study, we investigated whether p38 MAP kinase is involved in ALP activation by PGE 1 in MC3T3-E1 osteoblast-like cells. PGE 1 dose-dependently enhanced ALP activities in the concentration range between 1 nM and 1 μM in MC3T3-E1 cells. SB203580, a specific inhibitor of p38 MAP kinase, blocked the increase in ALP activity induced by PGE 1. Further analysis with western blotting suggested that PGE 1 induced an increase in tyrosine (Tyr) phosphorylation of p38 MAP kinase. Both Bt 2cAMP, a permeable analogue of cAMP, and forskolin, which directly activates adenylate cyclase, also induced an increase in Tyr phosphorylation of p38 MAP kinase. H-89, a potent inhibitor of protein kinase A (PKA), significantly suppressed PGE 1-induced Tyr phosphorylation of p38 MAP kinase. The results of this study suggest that PGE 1 stimulates p38 MAP kinase through the activation of PKA, resulting in the enhancement of ALP activity.