Glucocorticoid receptor, C/EBP, HNF3, and protein kinase A coordinately activate the glucocorticoid response unit of the carbamoylphosphate synthetase I gene
Glucocorticoid receptor, C/EBP, HNF3, and protein kinase A coordinately activate the glucocorticoid response unit of the carbamoylphosphate synthetase I gene
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DOI：
10.1128/mcb.18.11.6305
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发表时间：
1998-11-01
影响因子：
5.3
通讯作者：
Lamers, WH
中科院分区：
文献类型：
--
作者：
Christoffels, VM;Grange, T;Lamers, WH
一个单一的远上游增强子足以赋予肝细胞特异性，糖皮质激素和环腺苷酸诱导门静脉周围表达的氨甲酰磷酸合成酶I（CPS）基因。为了确定增强子依赖性激活的机制，已经分析了增强子的组成和功能。DNA酶I保护和凝胶迁移率变动分析显示存在环AMP反应元件、糖皮质激素反应元件（GRE）和肝脏富集的转录因子家族HNF 3和C/EBP的几个位点。通过对基因敲除小鼠的分析来评估与增强子相互作用的转录因子在肝脏中CPS表达调节中的体内相关性。在糖皮质激素受体和C/EBP α缺陷小鼠中观察到CPS mRNA水平的强烈降低，而CPS mRNA在C/EBP β敲除小鼠和HNF 3 α和-γ双敲除小鼠中正常表达。(The不能评估HNF β的作用，因为相应的敲除小鼠在胚胎第10天死亡。在肝癌细胞中，增强子的大部分活性包含在103-bp片段内，其活性取决于GRE、HNF 3、酸性C/EBP位点的同时占据，因此满足糖皮质激素应答单位的要求。另一方面，在成纤维细胞样CHO细胞中，CPS增强子中的GRE在CPS启动子的反式激活中不与C/EBP和HNF 3元件合作。在肝细胞瘤和CHO细胞中，环AMP的表达刺激主要取决于糖皮质激素途径的完整性，这表明该途径与环AMP（蛋白激酶A）途径之间存在串扰。
A single far-upstream enhancer is sufficient to confer hepatocyte-specific, glucocorticoid- and cyclic AMP-inducible periportal expression to the carbamoylphosphate synthetase I (CPS) gene. To identify the mechanism of hormone-dependent activation, the composition and function of the enhancer have been analyzed. DNase I protection and gel mobility shift assays revealed the presence of a cyclic AMP response element, a glucocorticoid response element (GRE), and several sites for the liver-enriched transcription factor families HNF3 and C/EBP. The in vivo relevance of the transcription factors interacting,vith the enhancer in the regulation of CPS expression in the liver was assessed by the analysis of knockout mice. A strong reduction of CPS mRNA levels was observed in glucocorticoid receptor- and C/EBP alpha-deficient mice, whereas the CPS mRNA was normally expressed in C/EBP beta knockout mice and in HNF3 alpha and -gamma double-knockout mice. (The role of HNF beta could not be assessed, because the corresponding knockout mice die at embryonic day 10), In hepatoma cells, most of the activity of the enhancer is contained within a 103-bp fragment, which depends for its activity on the simultaneous occupation of the GRE, HNF3, acid C/EBP sites, thus meeting the requirement of a glucocorticoid response unit. In fibroblast-like CHO cells, on the other hand, the GRE in the CPS enhancer does not cooperate with the C/EBP and HNF3 elements in transactivation of the CPS promoter. In both hepatoma and CHO cells, stimulation of expression by cyclic AMP depends mainly on the integrity of the glucocorticoid pathway, demonstrating cross talk between this pathway and the cyclic AMP (protein kinase A) pathway.