Interleukin-6 Synthesis Induced by Prostaglandin E 2: Cross-Talk Regulation by Protein Kinase C

Abstract

We previously showed that prostaglandin E 2 (PGE 2) stimulates multiple intracellular signaling pathways as follows: by activation of adenylate cyclase; phosphoinositide (PI)-hydrolyzing phospholipase C and phosphatidylcholine (PC)-hydrolyzing phospholipase D; and by induction of Ca 2+ influx in osteoblast-like MC3T3-E1 cells. In this study, we investigated the effect of PGE 2 on the synthesis of interleukin-6 (IL-6) and its regulatory mechanism in MC3T3-E1 cells. PGE 2 significantly stimulated IL-6 secretion in a dose-dependent manner in the range between 1 nmol/L and 10 μmol/L. A23187, a calcium ionophore, or dibutyryl-cAMP significantly induced IL-6 secretion. The effect of a combination of A23187 and dibutyryl-cAMP on IL-6 secretion was additive. The depletion of extracellular Ca 2+ by EGTA reduced the PGE 2-induced IL-6 secretion. EP 1 receptor antagonist inhibited the PGE 2-induced IL-6 secretion. H-89, an inhibitor of cAMP-dependent protein kinase, decreased the PGE 2-induced IL-6 secretion. EP 2 receptor agonist alone stimulated IL-6 secretion. However, EP 4 receptor antagonist had little effect on IL-6 secretion. Calphostin C, a specific inhibitor of protein kinase C (PKC), enhanced the secretion of IL-6 induced by PGE 2. The stimulative effect of PGE 2 on IL-6 secretion was significantly enhanced in PKC downregulated MC3T3-E1 cells. Pertussis toxin enhanced PGE 2-induced IL-6 secretion. These results strongly suggest that PGE 2 stimulates IL-6 synthesis through both Ca 2+ mobilization from extracellular space via EP 1 receptor and cAMP production via EP 2 receptor in osteoblast-like cells, and that the PKC activation by PGE 2 itself regulates oversynthesis of IL-6.