Gregory Philip A, Lewinsky Rikke H, Gardner-Stephen Dione A, Mackenzie Peter I
Department of Clinical Pharmacology, Flinders Medical Centre, Bedford Park, South Australia 5042, Australia.
Mol Pharmacol. 2004 Apr;65(4):953-63. doi: 10.1124/mol.65.4.953.
The human UDP-glucuronosyltransferases (UGT) -1A8 and -1A10 are exclusively expressed in extrahepatic tissues and primarily in the gastrointestinal tract, whereas UGT1A9 is expressed mainly in the liver and kidneys. We have demonstrated previously that the UGT1A8 and UGT1A10 genes, in contrast to the UGT1A9 gene, are regulated via an initiator-like element in their proximal promoters. To determine the elements that contribute to the gastrointestinal expression of UGT1A8 and -1A10, we conducted deletion analysis of the UGT1A8, -1A9, and -1A10 promoters in the colon-derived cell line Caco2. DNA elements contributing significantly to UGT1A8, -1A9, and -1A10 promoter activity were found to reside primarily within 140 base pairs of the transcription start site. Within this region, putative binding sites for the intestine-specific transcription factor, caudal-related homeodomain protein 2 (Cdx2), and hepatocyte nuclear factor 1 (HNF1) were identified. Using gel shift and functional assays, HNF1alpha was demonstrated to bind to and activate the UGT1A8, -1A9, and -1A10 promoters. In contrast, Cdx2 bound to and activated the UGT1A8 and -1A10 promoters but could not activate the UGT1A9 promoter. A single base pair difference between the UGT1A8 and -1A10 promoters, three base pairs downstream of the consensus Cdx2 site, contributed to the observed difference in Cdx2 binding and Cdx2-mediated promoter activation of these two promoters. In addition, Cdx2 was shown to cooperate with HNF1alpha to synergistically activate the UGT1A8, -1A9, and -1A10 promoters. These studies provide insight into the mechanisms controlling the extrahepatic expression of the UGT1A8, -1A9, and -1A10 genes.
人类尿苷二磷酸葡萄糖醛酸基转移酶（UGT）-1A8和-1A10仅在肝外组织中表达，主要在胃肠道中表达，而UGT1A9主要在肝脏和肾脏中表达。我们之前已经证明，与UGT1A9基因不同，UGT1A8和UGT1A10基因是通过其近端启动子中的类起始子元件进行调控的。为了确定促成UGT1A8和-1A10在胃肠道表达的元件，我们在结肠来源的细胞系Caco2中对UGT1A8、-1A9和-1A10启动子进行了缺失分析。发现对UGT1A8、-1A9和-1A10启动子活性有显著贡献的DNA元件主要位于转录起始位点的140个碱基对内。在该区域内，鉴定出了肠道特异性转录因子尾相关同源结构域蛋白2（Cdx2）和肝细胞核因子1（HNF1）的假定结合位点。使用凝胶迁移和功能测定法，证明HNF1α能结合并激活UGT1A8、-1A9和-UT1A10启动子。相比之下，Cdx2能结合并激活UGT1A8和-1A10启动子，但不能激活UGT1A9启动子。UGT1A8和-1A10启动子之间的一个单碱基对差异，位于共有Cdx2位点下游三个碱基对处，导致了这两个启动子在Cdx2结合和Cdx2介导的启动子激活方面观察到的差异。此外，Cdx2被证明能与HNF1α协同激活UGT1A8、-1A9和-1A10启动子。这些研究为控制UGT1A8、-1A9和-1A10基因肝外表达的机制提供了见解。
