Regulation of the rat glutathione S-transferase A2 gene by glucocorticoids: involvement of both the glucocorticoid and pregnane X receptors.
Regulation of the rat glutathione S-transferase A2 gene by glucocorticoids: involvement of both the glucocorticoid and pregnane X receptors.
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发表时间：
2001-09
影响因子：
3.6
通讯作者：
K. Falkner;J. Pinaire;G. Xiao;T. Geoghegan;R. Prough
中科院分区：
文献类型：
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作者：
K. Falkner;J. Pinaire;G. Xiao;T. Geoghegan;R. Prough
糖皮质激素在培养的肝细胞中以双相方式调节大鼠谷胱甘肽s -转移酶A2 （GSTA2）基因，在低浓度（10—100 nM）下抑制基因表达，而在高浓度（>.1 μ m）下诱导基因表达。高浓度的糖皮质激素受体（GR）拮抗剂RU38486（5—10微米）也能诱导GSTA2的表达。这些效应在转染含有1.6千碱基对GSTA2 5'侧序列的荧光素酶报告基因和GR、妊娠X受体（PXR）或两者组合的表达质粒的HepG2细胞中重现。当仅表达GR时，地塞米松t-丁乙酸酯（1 μ m t- budex）对基因表达的抑制作用为60% ~ 75%。当PXR表达时，基础基因和t- bu - dex依赖基因的表达量分别增加了2倍以上。当共转染两种受体的表达质粒时，在很宽的t-Bu-DEX浓度范围内观察到基因表达的双相调节。其他孕激素类类固醇诱导GSTA2表达，如预期的pxr依赖过程。由于在PXR-RXR α异源二聚体的5'侧区没有发现典型的应答元件，因此使用缺失分析在-700和-683碱基对之间确定了妊娠应答区；这个20bp的区域包含抗氧化响应元件（ARE）。当ARE序列突变时，基础、t-丁基对苯二酚和17 α -羟基孕烯醇酮诱导的表达全部丢失。这些结果表明PXR与ARE结合因子相互作用，引发GSTA2的妊娠诱导反应。
Glucocorticoids regulate the rat glutathione S-transferase A2 (GSTA2) gene in a biphasic manner in cultured hepatocytes that repress gene expression at low concentration (10--100 nM) but induce gene expression at high concentration (>1 microM). High concentrations of the glucocorticoid receptor (GR) antagonist RU38486 (5--10 microM) also induced the expression of GSTA2. These effects were reproduced in HepG2 cells transfected with a luciferase reporter containing 1.6 kilobase pairs of 5'-flanking sequence of GSTA2 and expression plasmids for either GR, pregnane X receptor (PXR) or a combination of both. Dexamethasone t-butylacetate (1 microM t-Bu-DEX) repressed gene expression between 60 to 75% when only GR was expressed. When PXR was expressed, both basal and t-Bu-DEX-dependent gene expression was increased over 2-fold, respectively. Biphasic regulation of gene expression was observed over a broad range of t-Bu-DEX concentrations when expression plasmids for both receptors were cotransfected. Other steroids of the pregnane class induced GSTA2 expression as expected for a PXR-dependent process. Because no canonical responsive element for the PXR-RXR alpha heterodimer was observed in the 5'-flanking region of the construct, deletion analysis was used to identify a pregnane responsive region between base pairs -700 and -683; this 20-bp region contains the antioxidant response element (ARE). When the ARE sequence was mutated, basal, t-butylhydroquinone- and 17 alpha-hydroxypregnenolone-inducible expression were all lost. These results suggest that PXR interacts with factors binding to the ARE to elicit the pregnane inductive response for GSTA2.