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Bronchial epithelial cells are rendered insensitive to glucocorticoid transactivation by transforming growth factor-?1.

ABSTRACT: We have previously shown that transforming growth factor-beta (TGF-beta) impairs glucocorticoid (GC) function in pulmonary epithelial cell-lines. However, the signalling cascade leading to this impairment is unknown. In the present study, we provide the first evidence that TGF-beta impairs GC action in differentiated primary air-liquid interface (ALI) human bronchial epithelial cells (HBECs). Using the BEAS-2B bronchial epithelial cell line, we also present a systematic examination of the known pathways activated by TGF-beta, in order to ascertain the molecular mechanism through which TGF-beta impairs epithelial GC action.GC transactivation was measured using a Glucocorticoid Response Element (GRE)-Secreted embryonic alkaline phosphatase (SEAP) reporter and measuring GC-inducible gene expression by qRT-PCR. GC transrepression was measured by examining GC regulation of pro-inflammatory mediators. TGF-beta signalling pathways were investigated using siRNA and small molecule kinase inhibitors. GR? level, phosphorylation and sub-cellular localisation were determined by western blotting, immunocytochemistry and localisation of GR?-Yellow Fluorescent Protein (YFP). Data are presented as the mean?±?SEM for n independent experiments in cell lines, or for experiments on primary HBEC cells from n individual donors. All data were statistically analysed using GraphPad Prism 5.0 (Graphpad, San Diego, CA). In most cases, two-way analyses of variance (ANOVA) with Bonferroni post-hoc tests were used to analyse the data. In all cases, P <0.05 was considered to be statistically significant.TGF-beta impaired Glucocorticoid Response Element (GRE) activation and the GC induction of several anti-inflammatory genes, but did not broadly impair the regulation of pro-inflammatory gene expression in A549 and BEAS-2B cell lines. TGF-beta-impairment of GC transactivation was also observed in differentiated primary HBECs. The TGF-beta receptor (ALK5) inhibitor SB431541 fully prevented the GC transactivation impairment in the BEAS-2B cell line. However, neither inhibitors of the known downstream non-canonical signalling pathways, nor knocking down Smad4 by siRNA prevented the TGF-beta impairment of GC activity.Our results indicate that TGF-beta profoundly impairs GC transactivation in bronchial epithelial cells through activating ALK5, but not through known non-canonical pathways, nor through Smad4-dependent signalling, suggesting that TGF-beta may impair GC action through a novel non-canonical signalling mechanism.

SUBMITTER: Keenan CR

PROVIDER: S-EPMC4021546 | biostudies-other | 2014 May

REPOSITORIES: biostudies-other

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Bronchial epithelial cells are rendered insensitive to glucocorticoid transactivation by transforming growth factor-β1.

Keenan Christine R CR Mok Josephine Sl JS Harris Trudi T Xia Yuxiu Y Salem Saad S Stewart Alastair G AG

Respiratory research 20140501

<h4>Background</h4>We have previously shown that transforming growth factor-beta (TGF-beta) impairs glucocorticoid (GC) function in pulmonary epithelial cell-lines. However, the signalling cascade leading to this impairment is unknown. In the present study, we provide the first evidence that TGF-beta impairs GC action in differentiated primary air-liquid interface (ALI) human bronchial epithelial cells (HBECs). Using the BEAS-2B bronchial epithelial cell line, we also present a systematic examin ...[more]

PMID: 24886104

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Project description:p38 MAPK inhibition may have additive and synergistic anti-inflammatory effects when used with corticosteroids. We investigated crosstalk between p38 MAPK inhibitors and corticosteroids in bronchial epithelial cells to investigate synergistic effects on cytokine production and the molecular mechanisms involved. Effects of the p38 MAPK inhibitor BIRB-796 and dexamethasone alone and in combination on LPS, polyI:C or TNFα -induced IL-6, CXCL8 and RANTES were assessed in 16HBEs (human epithelial cell line) and on TNFα-induced IL-6 and CXCL8 in primary human epithelial cells from asthma patients and healthy controls. 16HBEs were used to assess effects of BIRB-796 alone and in combination with dexamethasone on glucocorticoid receptor (GR) activity by reporter gene assay, expression of GR target genes and nuclear localisation using Western blot. The effects of BIRB-796 on TNFα stimulated phosphorylation of p38 MAPK and GR at serine (S) 226 by Western blot. Epithelial levels of phosphorylated p38 MAPK and GR S226 were determined by immunohistochemistry in bronchial biopsies from asthma patients and healthy controls. BIRB-796 in combination with dexamethasone increased inhibition of cytokine production in a synergistic manner. Combination treatment significantly increased GR nuclear localisation compared to dexamethasone alone. BIRB-796 inhibited TNFα-induced p38 MAPK and GR S226 phosphorylation. Phosphorylated GR S226 and p38 MAPK levels were increased in bronchial epithelium of more severe asthma patients. Molecular crosstalk exists between p38 MAPK activation and GR function in human bronchial epithelial cells, which alters GR activity. Combining a p38 MAPK inhibitor and a corticosteroid may demonstrate therapeutic potential in severe asthma. KEY MESSAGES: • Combination of corticosteroid and p38 inhibitor in human bronchial epithelial cells • Combination increased cytokine inhibition synergistically and nuclear GR • p38 MAPK inhibition reduced TNFα-induced phosphorylation of GR at S226 but not S211 • Phosphorylated GRS226 and p38 is increased in bronchial epithelium in severe asthma • Combining a p38 inhibitor and a corticosteroid may be effective in asthma treatment.

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Bronchial epithelial cells are rendered insensitive to glucocorticoid transactivation by transforming growth factor-?1.

Publications

Bronchial epithelial cells are rendered insensitive to glucocorticoid transactivation by transforming growth factor-β1.

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