Cayla Cécile, Schaak Stéphane, Crassous Pierre-Antoine, Buffin-Meyer Bénédicte, Delage Christine, Paris Hervé, Senard Jean-Michel, Denis Colette
INSERM, U858/I2MR, Department of Renal and Cardiac Remodelling, team #8, 1 avenue Jean Poulhès, BP 84225, 31432 Toulouse Cedex 4, France.
Eur J Pharmacol. 2008 Jun 24;588(1):33-40. doi: 10.1016/j.ejphar.2008.04.006. Epub 2008 Apr 8.
alpha(2A)-adrenoceptors are expressed on intestinal cells and they participate in the control of epithelial functions such as solute and water transport or cell proliferation. In pathological conditions, pro-inflammatory cytokines secreted by lymphocytes are responsible for modification of intestinal cell characteristics including phenotype switch and changes in the expression of pumps and ion channels. Using the HT29 cell line as a model, the present work examined the effect of two inflammatory cytokines, interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha), on the expression of the human alpha(2A)-adrenoceptor. Exposure of cells to either IFNgamma or TNFalpha resulted in a concentration- and time-dependent diminution of [(3)H]RX821002 binding sites, which is preceded by a large decrease in the amount of alpha(2A)-adrenoceptor mRNA. The cytokines did not affect the receptor mRNA half-life, but inhibited the activity of a luciferase construct containing the promoter region of alpha(2A)-adrenoceptor gene, indicating that a decrease in the transcription rate is primarily responsible for the diminution of receptor expression. Exposure of cells to either IFNgamma or TNFalpha caused increased production of reactive oxygen species and transient phosphorylation of extracellular signal-regulated kinase (Erk1/2). The effect of cytokines was mimicked by H(2)O(2) but was unaffected by the addition of anti-oxidants. The blockade of Erk1/2 activation by PD98059 blunted the effect of TNFalpha but not of IFNgamma. In conclusion, the present findings demonstrate that IFNgamma and TNFalpha diminish the alpha(2A)-adrenoceptor expression in HT29 cells by decreasing the transcription rate without modifying the stability of mRNA. The transcription inhibition is however triggered via different signalling pathways. The results suggest that cytokine-mediated down-regulation of alpha(2A)-adrenoceptor could contribute to the pathogenesis of inflammatory bowel disease.
α(2A)-肾上腺素能受体在肠道细胞中表达，它们参与上皮功能的调控，如溶质和水的转运或细胞增殖。在病理状态下，淋巴细胞分泌的促炎细胞因子会导致肠道细胞特性的改变，包括表型转换以及泵和离子通道表达的变化。本研究以HT29细胞系为模型，检测了两种炎性细胞因子——干扰素-γ（IFNγ）和肿瘤坏死因子-α（TNFα）对人α(2A)-肾上腺素能受体表达的影响。将细胞暴露于IFNγ或TNFα中，均导致[(3)H]RX821002结合位点呈浓度和时间依赖性减少，在此之前α(2A)-肾上腺素能受体mRNA的量大幅下降。细胞因子不影响受体mRNA的半衰期，但抑制了含有α(2A)-肾上腺素能受体基因启动子区域的荧光素酶构建体活性，表明转录速率降低是受体表达减少的主要原因。将细胞暴露于IFNγ或TNFα中会导致活性氧的产生增加以及细胞外信号调节激酶（Erk1/2）的瞬时磷酸化。细胞因子的作用可被H(2)O(2)模拟，但不受抗氧化剂添加影响。PD98059对Erk1/2激活的阻断减弱了TNFα的作用，但不影响IFNγ的作用。总之，本研究结果表明，IFNγ和TNFα通过降低转录速率而不改变mRNA稳定性，减少了HT29细胞中α(2A)-肾上腺素能受体的表达。然而，转录抑制是通过不同的信号通路触发的。结果提示，细胞因子介导的α(2A)-肾上腺素能受体下调可能参与炎症性肠病的发病机制。
