Suppression of Heme Oxygenase-1 by Prostaglandin E(2)-Protein Kinase A-A-Kinase Anchoring Protein Signaling Is Central for Augmented Cyclooxygenase-2 Expression in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages

PURPOSE: Prostaglandin (PG) E(2) is an immunomodulatory lipid mediator generated mainly via the cyclooxygenase-2 (COX-2) pathway from arachidonic acid at sites of infection and inflammation. A positive feedback loop of PGE(2) on COX-2 expression is critical for homeostasis during toll-like receptor (TLR)-mediated inflammatory processes. The mechanism of PGE(2)-regulated COX-2 expression remains poorly understood. The low-molecular-weight stress protein heme oxygenase-1 (HO-1) contributes to the anti-inflammatory, anti-oxidant and anti-apoptotic response against environmental stress. METHODS: We explored the involvement of HO-1 on PGE(2) regulation of LPS-induced COX-2 expression in RAW 264.7 macrophages. RESULTS: LPS-induced COX-2 expression in RAW 264.7 macrophages was enhanced by exogenous PGE(2) or cyclic AMP (cAMP) analogue and was suppressed by a COX inhibitor (indomethacin), a protein kinase A (PKA) inhibitor (KT5720), and A kinase anchoring protein (AKAP) disruptors (Ht31 and RIAD). This result suggests that the stimulatory effects of endogenous and exogenous PGE(2) on COX-2 expression are mediated by a cAMP-PKA-AKAP-dependent pathway. The induction of HO-1 was observed in LPS-stimulated RAW 264.7 macrophages. This induction was suppressed by exogenous PGE(2) and enhanced by blockage of the endogenous PGE(2) effect by the PKA inhibitor or AKAP disruptors. In addition, HO-1 induction by the HO activator copper protoporphyrin suppressed LPS-induced COX-2 expression, which was restored by the addition of exogenous PGE(2). The induction of HO-1 inhibited LPS-induced NF-κB p-65 nuclear expression and translocation. CONCLUSIONS: AKAP plays an important role in PGE(2) regulation of COX-2 expression, and the suppression of HO-1 by PGE(2)-cAMP-PKA-AKAP signaling helps potentiate the LPS-induced COX-2 expression through a positive feedback loop in RAW 264.7 macrophages.