The Aryl Hydrocarbon Receptor Attenuates Tobacco Smoke-induced Cyclooxygenase-2 and Prostaglandin Production in Lung Fibroblasts through Regulation of the NF- B Family Member RelB

Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2008; 283(43):28944-57. DOI: 10.1074/jbc.M800685200
Source: PubMed


Diseases such as chronic obstructive pulmonary disease and lung cancer caused by cigarette smoke affect millions of people
worldwide. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that influences responses to certain
environmental pollutants such as tobacco smoke. However, the physiological function(s) of the AhR is unknown. Herein we propose
that the physiologic role of the AhR is to limit inflammation. We show that lung fibroblasts from AhR–/– mice produce a heightened inflammatory response to cigarette smoke, typified by increased levels of cyclooxygenase-2 (COX-2)
and prostaglandins (PGs), when compared with wild type (AhR+/+) fibroblasts. This response was dependent on AhR expression as transient transfection of an AhR expression plasmid into AhR–/– fibroblasts significantly attenuated the smoke-induced COX-2 and PG production, confirming the anti-inflammatory role of
the AhR. The AhR can interact with NF-κB. However, the heightened inflammatory response observed in AhR–/– fibroblasts was not the result of NF-κB (p50/p65) activation. Instead it was coupled with a loss of the NF-κB family member
RelB in AhR–/– fibroblasts. Taken together, these studies provide compelling evidence that AhR expression limits proinflammatory COX-2 and
PG production by maintaining RelB expression. The association between RelB and AhR may represent a new therapeutic and more
selective target with which to combat inflammation-associated diseases.

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    • "In addition to Cox-2, HuR has thousands of target genes [77] and stabilizes mRNAs that encode proteins associated with a variety of cellular functions including cell cycle (cyclin D1), proliferation (c-Fos), apoptosis (Bcl-2, cytochrome C) and inflammation (TLR4, IL-6, IL-8) [78]. The AhR regulation of these functions is established [4], [5], [24], [79], [80] opening the possibility that AhR retention of nuclear HuR may have important implications for the regulation of genes beyond the control of Cox-2. "
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    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.
    Full-text · Article · Sep 2013 · PLoS ONE
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    • "Cell culture. Primary mouse lung fibroblasts from C57BL/6 mice were obtained and cultured as described previously (Baglole et al., 2005, 2008). Cells were grown in six-well plates in Modified Eagle's Medium (MEM) þ 10% fetal bovine serum (FBS) and supplemented with pyruvate, glutamine, sodium bicarbonate, and gentamicin. "
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    ABSTRACT: The aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, mediates toxicity of several classes of xenobiotics and also has important physiological roles in differentiation, reproduction, and immunity, although the endogenous ligand(s) mediating these functions is/are as yet unidentified. One candidate endogenous ligand, 2-(1′H-indolo-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE), is a potent AhR agonist in vitro, activates the murine AhR in vivo, but does not induce toxicity. We hypothesized that ITE and the toxic ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), may modify transcription of different sets of genes to account for their different toxicity. To test this hypothesis, primary mouse lung fibroblasts were exposed to 0.5μM ITE, 0.2nM TCDD, or vehicle for 4 h, and total gene expression was evaluated using microarrays. After this short-term and low-dose treatment, several hundred genes were changed significantly, and the response to ITE and TCDD was remarkably similar, both qualitatively and quantitatively. Induced gene sets included the expected battery of AhR-dependent xenobiotic-metabolizing enzymes, as well as several sets that reflect the inflammatory role of lung fibroblasts. Real time quantitative RT-qPCR assay of several selected genes confirmed these microarray data and further suggested that there may be kinetic differences in expression between ligands. These data suggest that ITE and TCDD elicit an analogous change in AhR conformation such that the initial transcription response is the same. Furthermore, if the difference in toxicity between TCDD and ITE is mediated by differences in gene expression, then it is likely that secondary changes enabled by the persistent TCDD, but not by the shorter lived ITE, are responsible. © The Author 2009. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For permissions, please email: [email protected] /* */
    Full-text · Article · Nov 2009 · Toxicological Sciences
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    • "Furthermore, thrombin induced increases in IKKα/β and IκBα phosphorylation , IκBα degradation, and κB-luciferase activity. Consistent with our study, NF-κB plays a critical role in regulating tobacco smokeinduced COX-2 expression in lung fibroblasts to mediate lung inflammation and cancer (Baglole et al., 2008; Martey et al., 2004). Therefore, these results suggest that NF-κB activation is required for COX-2 expression by thrombin stimulation of human lung fibroblasts. "
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    ABSTRACT: There is growing evidence that increased expression of cyclooxygenase-2 (COX-2) in the lungs of patients is a key event in the pathogenesis of lung diseases. In this study, we investigated the involvement of the extracellular signal-regulated kinase (ERK), IkappaB kinase alpha/beta (IKKalpha/beta), and nuclear factor-kappaB (NF-kappaB) signaling pathways in thrombin-induced COX-2 expression in human lung fibroblasts (WI-38). Treatment of WI-38 cells with thrombin caused increased COX-2 expression in a concentration- and time-dependent manner. Treatment of WI-38 cells with PD 98059 (2-[2-amino-3-methoxyphenyl]-4H-1-benzopyran-4-one, a MEK inhibitor) inhibited thrombin-induced COX-2 expression and COX-2-luciferase activity. Stimulation of cells with thrombin caused an increase in ERK phosphorylation in a time-dependent manner. In addition, treatment of WI-38 cells with Bay 117082, an IkappaB phosphorylation inhibitor, and pyrrolidine dithiocarbamate (PDTC), an NF-kappaB inhibitor, inhibited thrombin-induced COX-2 expression. The thrombin-induced increase in COX-2-luciferase activity was also blocked by the dominant negative IkappaBalpha mutant (IkappaBalphaM). Treatment of WI-38 cells with thrombin induced IKKalpha/beta and IkappaBalpha phosphorylation, IkappaBalpha degradation, and kappaB-luciferase activity. The thrombin-mediated increases in IKKalpha/beta phosphorylation and kappaB-luciferase activity were inhibited by PD 98059. Taken together, these results suggest that the ERK-dependent IKKalpha/beta/NF-kappaB signaling pathway plays an important role in thrombin-induced COX-2 expression in human lung fibroblasts.
    Preview · Article · Aug 2009 · European journal of pharmacology
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