Pancreatic-type phospholipase A2 stimulates prostaglandin synthesis in mouse osteoblastic cells (MC3T3-E1) via a specific binding site.

Previously, we have reported a novel proliferative action of pancreatic group I phospholipase A2 (PLA2-I) via a specific binding site in Swiss 3T3 fibroblasts, vascular smooth muscle cells, and chondrocytes. In this study, we characterized the PLA2-I specific binding site in osteoblastic cell line (MC3T3-E1 cells) with an equilibrium binding constant (Kd) value of 1.13 nM and maximum binding capacity of 40.1 fmol/10(6) cells. PLA2-I stimulated prostaglandin E2 (PGE2) production in a concentration-dependent manner in MC3T3-E1 cells, and its EC50 value was similar to the Kd value for PLA2-I binding. This effect of PLA2-I was type-specific and did not depend on its hydrolytic activity. PLA2-I increased the activity of prostaglandin endoperoxide synthase (PES), and PLA2-I-stimulated PGE2 synthesis was inhibited by cycloheximide. Northern blot analysis showed the increase in both type-1 and type-2 PES mRNAs. These findings indicated that PLA2-I stimulated PGE2 synthesis by induction of PES via a specific binding site in osteoblastic cells.