title: Suppression of Heme Oxygenase-1 by Prostaglandin E2-Protein Kinase A-A-Kinase Anchoring Protein Signaling Is Central for Augmented Cyclooxygenase-2 Expression in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages.
abstract: OBJECTIVE
  Prostaglandin (PG) E2 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 PGE2 on COX-2 expression is critical for homeostasis during toll-like receptor (TLR)-mediated inflammatory processes. The mechanism of PGE2-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 PGE2 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 PGE2 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 PGE2 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 PGE2 and enhanced by blockage of the endogenous PGE2 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 PGE2. The induction of HO-1 inhibited LPS-induced NF-κB p-65 nuclear expression and translocation.
  
  
  CONCLUSIONS
  AKAP plays an important role in PGE2 regulation of COX-2 expression, and the suppression of HO-1 by PGE2-cAMP-PKA-AKAP signaling helps potentiate the LPS-induced COX-2 expression through a positive feedback loop in RAW 264.7 macrophages.
authors.affiliation: Department of Internal Medicine, Eulji Hospital, Eulji University School of Medicine, Seoul, Korea.
authors.forename: Jae-Hyoung
authors.initials: JH
authors.lastname: Lee
authors.forename: Nam-Hee
authors.initials: NH
authors.lastname: Jung
authors.forename: Byoung-Hoon
authors.initials: BH
authors.lastname: Lee
authors.forename: Sang-Hoon
authors.initials: SH
authors.lastname: Kim
authors.forename: Jin Hyun
authors.initials: JH
authors.lastname: Jun
keywords: Cyclooxygenase-2; heme oxygenase-1; lipopolysaccharide; macrophages; prostaglandin E2