Prostaglandin Endoperoxide Synthase-2 Contributes to the Endothelin/Sarafotoxin-Induced Prostaglandin E2 Synthesis in Mouse Osteoblastic Cells (MC3T3-E1): Evidence for a Protein Tyrosine Kinase-Signaling Pathway and Involvement of Protein Kinase C*

Abstract

Endothelin (ET) peptides are potent growth factors binding to G protein-coupled receptors. Sarafotoxins (S6) isolated from Atractaspis engaddensis are highly homologous to endothelins. In this study, we have investigated the effects of endothelin/sarafotoxin peptides on the prostaglandin synthesizing system in an osteoblast-like cell line, MC3T3-E1. ET-1, ET-2, beta-ET, and S6b rapidly stimulated prostaglandin E2 production within 5 min, whereas ET-3, S6a, and S6c did not. ET-1, ET-2, beta-ET, S6b, and S6a induced prostaglandin synthesis after 3 h of incubation. Antagonizing these effects with BQ-123, PD 142893, BQ-788, and S6c suggests signaling through an ET(A) receptor subtype in osteoblasts. Long-term prostaglandin synthesis was blocked by NS-398, and reduced to short-term levels by cycloheximide and actinomycin D, indicating induction of PGHS-2. There was only minor enhancement of cAMP accumulation by the agonists, which had no effect on prostaglandin synthesis. Induction of PGHS-2 was furthermore demonstrated by Northern blot analysis of PGHS-2 messenger RNA. Depletion of protein kinase C with TPA largely blunted the response. Genistein, an inhibitor of protein tyrosine kinases, also blocked long-term prostaglandin E2 formation. We conclude that in osteoblast-like MC3T3-E1 cells, ET-1, ET-2, beta-ET, S6b, and S6a peptides induce PGHS-2 through a protein tyrosine kinase-dependent and protein kinase C-dependent pathway, signaling through ET(A) receptor occupancy.