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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.

Lee JH, Jung NH, Lee BH, Kim SH, Jun JH - Allergy Asthma Immunol Res (2013)

Bottom Line: 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.This induction was suppressed by exogenous PGE2 and enhanced by blockage of the endogenous PGE2 effect by the PKA inhibitor or AKAP disruptors.The induction of HO-1 inhibited LPS-induced NF-κB p-65 nuclear expression and translocation.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Eulji Hospital, Eulji University School of Medicine, Seoul, Korea.

ABSTRACT

Purpose: 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.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of the proposed mechanism by which PGE2 signaling amplifies COX-2 expression through an autocrine manner in LPS-stimulated macrophages. Upon LPS binding to the toll-like receptor 4 (TLR4), the NF-κB signaling pathway becomes activated, leading to an increase in COX-2 expression, which in turn activates cAMP/PKA/AKAP through the production of PGE2. The PKA-AKAP complex blocks HO-1 activity, which results in enhanced translocation of NF-κB p65 to the nucleus.
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Figure 7: Schematic representation of the proposed mechanism by which PGE2 signaling amplifies COX-2 expression through an autocrine manner in LPS-stimulated macrophages. Upon LPS binding to the toll-like receptor 4 (TLR4), the NF-κB signaling pathway becomes activated, leading to an increase in COX-2 expression, which in turn activates cAMP/PKA/AKAP through the production of PGE2. The PKA-AKAP complex blocks HO-1 activity, which results in enhanced translocation of NF-κB p65 to the nucleus.

Mentions: This study elucidates the role of HO-1 in the positive feedback regulation of COX-2 expression by TLR4 stimulation and characterizes some of the molecular mechanisms involved in this phenomenon. Our results show that (1) endogenous and exogenous PGE2 enhance COX-2 expression in macrophages stimulated with the TLR4 ligand LPS; (2) PKA-AKAP signaling has an important role in PGE2 potentiation of LPS-induced COX-2 expression; (3) suppression of HO-1 expression by LPS-induced endogenous PKA-AKAP signaling is essential to augment COX-2 expression; (4) induction of HO-1 attenuates LPS-induced COX-2 expression through the inhibition of LPS-induced NF-κB p65 activation and translocation. Suppression of HO-1 by endogenous PKA signaling is involved in amplifying the expression of COX-2 induced by LPS. The proposed mechanism by which PGE2, cAMP, PKA, AKAP, and HO-1 interrelate in potentiating LPS-induced COX-2 expression is depicted in the model illustrated in Fig. 7.


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.

Lee JH, Jung NH, Lee BH, Kim SH, Jun JH - Allergy Asthma Immunol Res (2013)

Schematic representation of the proposed mechanism by which PGE2 signaling amplifies COX-2 expression through an autocrine manner in LPS-stimulated macrophages. Upon LPS binding to the toll-like receptor 4 (TLR4), the NF-κB signaling pathway becomes activated, leading to an increase in COX-2 expression, which in turn activates cAMP/PKA/AKAP through the production of PGE2. The PKA-AKAP complex blocks HO-1 activity, which results in enhanced translocation of NF-κB p65 to the nucleus.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3756181&req=5

Figure 7: Schematic representation of the proposed mechanism by which PGE2 signaling amplifies COX-2 expression through an autocrine manner in LPS-stimulated macrophages. Upon LPS binding to the toll-like receptor 4 (TLR4), the NF-κB signaling pathway becomes activated, leading to an increase in COX-2 expression, which in turn activates cAMP/PKA/AKAP through the production of PGE2. The PKA-AKAP complex blocks HO-1 activity, which results in enhanced translocation of NF-κB p65 to the nucleus.
Mentions: This study elucidates the role of HO-1 in the positive feedback regulation of COX-2 expression by TLR4 stimulation and characterizes some of the molecular mechanisms involved in this phenomenon. Our results show that (1) endogenous and exogenous PGE2 enhance COX-2 expression in macrophages stimulated with the TLR4 ligand LPS; (2) PKA-AKAP signaling has an important role in PGE2 potentiation of LPS-induced COX-2 expression; (3) suppression of HO-1 expression by LPS-induced endogenous PKA-AKAP signaling is essential to augment COX-2 expression; (4) induction of HO-1 attenuates LPS-induced COX-2 expression through the inhibition of LPS-induced NF-κB p65 activation and translocation. Suppression of HO-1 by endogenous PKA signaling is involved in amplifying the expression of COX-2 induced by LPS. The proposed mechanism by which PGE2, cAMP, PKA, AKAP, and HO-1 interrelate in potentiating LPS-induced COX-2 expression is depicted in the model illustrated in Fig. 7.

Bottom Line: 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.This induction was suppressed by exogenous PGE2 and enhanced by blockage of the endogenous PGE2 effect by the PKA inhibitor or AKAP disruptors.The induction of HO-1 inhibited LPS-induced NF-κB p-65 nuclear expression and translocation.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Eulji Hospital, Eulji University School of Medicine, Seoul, Korea.

ABSTRACT

Purpose: 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.

No MeSH data available.


Related in: MedlinePlus