Kawashima Sachiyo, Kobayashi Kaoru, Takama Kaori, Higuchi Tomoaki, Furihata Tomomi, Hosokawa Masakiyo, Chiba Kan
Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University, Inohana 1-8-1, Chiba 260-8675, Japan.
Drug Metab Dispos. 2006 Jun;34(6):1012-8. doi: 10.1124/dmd.106.009365. Epub 2006 Mar 15.
CYP2C9 and CYP2C19 are clinically important drug-metabolizing enzymes. The expression level of CYP2C9 is much higher than that of CYP2C19, although the factor(s) responsible for the difference between the expression levels of these genes is still unclear. It has been reported that hepatocyte nuclear factor 4alpha (HNF4alpha) plays an important role in regulation of the expression of liver-enriched genes, including P450 genes. Thus, we hypothesized that HNF4alpha contributes to the difference between the expression levels of these genes. Two direct repeat 1 (DR1) elements were located in both the CYP2C9 and CYP2C19 promoters. The upstream and downstream elements in these promoters had the same sequences, and HNF4alpha could bind to both elements in vitro. The transactivation levels of constructs containing two DR1 elements of the CYP2C9 promoter were increased by HNF4alpha, whereas those of the CYP2C19 promoter were not increased. The introduction of mutations into either the upstream or downstream element in the CYP2C9 gene abolished the responsiveness to HNF4alpha. We also examined whether HNF4alpha could bind to the promoter regions of the CYP2C9 and the CYP2C19 genes in vivo. The results of chromatin immunoprecipitation assays showed that HNF4alpha could bind to the promoter region of the CYP2C9 gene but not to that of the CYP2C19 promoter in the human liver. Taken together, our results suggest that HNF4alpha is a factor responsible for the difference between the expression levels of CYP2C9 and CYP2C19 in the human liver.
CYP2C9和CYP2C19是临床上重要的药物代谢酶。CYP2C9的表达水平远高于CYP2C19，尽管导致这两个基因表达水平差异的因素仍不清楚。据报道，肝细胞核因子4α（HNF4α）在包括P450基因在内的肝脏富集基因的表达调控中起重要作用。因此，我们推测HNF4α导致了这些基因表达水平的差异。在CYP2C9和CYP2C19启动子中均发现了两个直接重复序列1（DR1）元件。这些启动子中的上游和下游元件具有相同的序列，并且HNF4α在体外可与这两个元件结合。含有CYP2C9启动子两个DR1元件的构建体的反式激活水平因HNF4α而增加，而CYP2C19启动子的反式激活水平未增加。在CYP2C9基因的上游或下游元件中引入突变消除了对HNF4α的反应性。我们还检测了HNF4α在体内是否能与CYP2C9和CYP2C19基因的启动子区域结合。染色质免疫沉淀试验结果表明，在人肝脏中，HNF4α可与CYP2C9基因的启动子区域结合，但不能与CYP2C19启动子区域结合。综上所述，我们的结果表明HNF4α是导致人肝脏中CYP2C9和CYP2C19表达水平差异的一个因素。
