Abstract
The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor that responds to man-made environmental toxicants, has emerged as an endogenous regulator of cyclooxygenase-2 (Cox-2) by a mechanism that is poorly understood. In this study, we first used AhR-deficient (AhR(-/-) ) primary pulmonary cells, together with pharmacological tools to inhibit new RNA synthesis, to show that the AhR is a prominent factor in the destabilization of Cox-2 mRNA. The destabilization of Cox-2 mRNA and subsequent suppression of cigarette smoke-induced COX-2 protein expression by the AhR was independent of its ability to bind the dioxin response element (DRE), thereby differentiating the DRE-driven toxicological AhR pathway from its anti-inflammatory abilities. We further describe that the AhR destabilizes Cox-2 mRNA by sequestering HuR within the nucleus. The role of HuR in AhR stabilization of Cox-2 mRNA was confirmed by knockdown of HuR, which resulted in rapid Cox-2 mRNA degradation. Finally, in the lungs of AhR(-/-) mice exposed to cigarette smoke, there was little Cox-2 mRNA despite robust COX-2 protein expression, a finding that correlates with almost exclusive cytoplasmic HuR within the lungs of AhR(-/-) mice. Therefore, we propose that the AhR plays an important role in suppressing the expression of inflammatory proteins, a function that extends beyond the ability of the AhR to respond to man-made toxicants. These findings open the possibility that a DRE-independent AhR pathway may be exploited therapeutically as an anti-inflammatory target.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Azo Compounds / pharmacology
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Cell Nucleus / drug effects
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Cell Nucleus / metabolism*
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Cells, Cultured
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Cyclooxygenase 2 / genetics
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Cyclooxygenase 2 / metabolism*
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DNA / metabolism*
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ELAV Proteins / metabolism*
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Fibroblasts / drug effects
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Fibroblasts / enzymology
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Fibroblasts / pathology
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Humans
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Lung / pathology
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Mice
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Models, Biological
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Prostaglandins / biosynthesis
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Protein Binding / drug effects
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Protein Structure, Tertiary
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Protein Transport / drug effects
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Pyrazoles / pharmacology
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RNA Stability / drug effects
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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RNA, Small Interfering / metabolism
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Receptors, Aryl Hydrocarbon / antagonists & inhibitors
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Receptors, Aryl Hydrocarbon / chemistry
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Receptors, Aryl Hydrocarbon / deficiency
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Receptors, Aryl Hydrocarbon / metabolism*
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Smoking / adverse effects*
Substances
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2-methyl-2H-pyrazole-3-carboxylic acid (2-methyl-4-o-tolylazophenyl)amide
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Azo Compounds
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ELAV Proteins
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Prostaglandins
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Pyrazoles
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RNA, Messenger
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RNA, Small Interfering
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Receptors, Aryl Hydrocarbon
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DNA
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Ptgs2 protein, mouse
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Cyclooxygenase 2
Grants and funding
This work was supported by the American Thoracic Society Research Grant; the Department of Medicine of McGill University; the Research Institute of the McGill University Health Centre; the Canada Foundation for Innovation-Leaders Opportunities Fund and the Natural Sciences and Engineering Research Council of Canada. CJB was supported by a salary award from the Fonds de recherche du Quebec-Sante (FRQ-S). MZ is the recipient of a Meakins-Christie Post-Doctoral Fellowship Award. Dr Nair is supported by a Canada Research Chair in Airway Inflammometry. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.