CYP7A1基因-204位点A/C变异对启动子活性的影响

CYP7A1（cholesterol 7α-hydroxylase ）在胆固醇向胆汁酸代谢途径中起着至关重要的作用.为研究该基因启动子区-204位点A/C多态性是否影响基因表达, 利用荧光素酶作为报告基因，将含有A或C等位基因的启动子区片段分别正向和反向插入不含启动子的pGL3 basic质粒载体中，再以重组体转染4种细胞株,采用双荧光素酶报告基因检测系统测定酶活性并进行比较.实验结果表明，2种基因型的正向序列启动子活性均高于相应的反向序列，含有A等位基因的启动子片段活性比含有C等位基因的片段低约1/3.TRANSFAC数据库分析显示，当-204位点等位基因为C时,可能存在1个Zic3结合位点.研究结果提示，CYP7A1基因启动子区-204位点A/C变异可减少启动子活性从而影响基因表达，其原因可能为1个潜在的Zic3结合位点的丧失.

The A-204C Polymorphism in CYP7A1 Gene Affects Its Promoter Activity

cholesterol 7α-hydroxylase gene ( CYP7A 1 ) plays a key role in the catabolism of cholesterol into bile acids. To investigate whether the A-204C polymorphism in CYP7A1 gene affects the gene expression,using luciferase as the reporter gene, four recombinants were constructed by inserting forward or reverse sequence with A or C allele at the polymorphism site into the promoter-less vector pGL3-basic. The constructs were then transfected into four cell lines and the luciferase activity of each expression vector was examined by dual luciferase reporter gene assay system. The results showed that activities of the forward sequence of both genotypes were higher than that of reverse sequence. Promoter activity of the recombinants with A allele was about one third lower than that with C allele. According to the analysis with TRANSFAC database, there may exist a Zic3 binding site when there is the C allele at -204. Our study indicates that the A-204 C polymorphism in CYP7A1 promoter region decreases its promoter activity and thus represses the gene expression, possibly due to the lack of a potential Zic3 binding site.