TRANSCRIPTIONAL REGULATION OF CYTOCHROME P450 GENES

细胞色素P450通过诱导物依赖性和组织- 具体路径。 大多数P450参与外源性 包括化学致癌物在内的化学物质在肝脏中表达， 一些P450存在于肝外组织如肺、肾和肝内， 胃肠道 组织特异性基因表达受 通过组织富集的转录因子。 老鼠被用作 研究P450基因肝脏特异性表达的模型系统。 共转染反式激活试验用于确定 肝脏富集的转录因子参与控制 CYP 2D 5 P450基因启动子。 这些研究表明，肝脏- 富集因子C/EBP-β和通用转录因子Sp1 协同控制CYP 2D 5的表达。 DNA结合研究表明 Sp1与C/EBP-β相互作用，以增加其结合C/EBP-β的能力。 CYP 2D 5基因上游的DNA片段。 在没有Sp1的情况下， C/EBP-β不能直接与该DNA元件结合。 缺失和 突变分析被用来确定C/EBP- β和Sp1是它们协同作用所必需的。 进一步 了解肝脏富集转录因子在P450基因中的作用 表达，条件性敲除小鼠正在产生。 基因组 几个肝脏富集的转录因子的克隆分离自 129/SV基因文库，并用于制备条件敲除 含有Lox重组信号的构建体， 基因的区域。 重组酶基因Cre被融合到 CYP 2C 6启动子，以产生将在细胞中表达该蛋白质的小鼠。 青春期的肝脏 因此，在培育敲除和CYP 2C 6-Cre小鼠时， 转录因子基因在成年人中特异性地被消除 并分析P450基因的表达。

Cytochrome P450s are regulated through inducer-dependent and tissue- specific pathways. Most P450s involved in metabolism of foreign chemicals including chemical carcinogens are expressed in liver, although some P450s are found in extrahepatic tissues such as lung, kidney and the gastrointestinal tract. Tissue-specific gene expression is governed through tissue-enriched transcription factors. The rat is being used as a model system to study liver-specific expression of P450 genes. Cotransfection trans-activation assays are being used to determine which liver-enriched transcription factors are involved in control of the CYP2D5 P450 gene promoter. These studies revealed that the liver- enriched factor C/EBP-beta and the general transcription factor Sp1 cooperate to control expression of CYP2D5. DNA binding studies suggest that Sp1 interacts with C/EBP-beta to increase its ability to bind to a segment of DNA upstream of the CYP2D5 gene. In the absence of Sp1, C/EBP-beta can not directly bind to this DNA element. Deletion and mutagenesis analysis are being used to determine which regions of C/EBP- beta and Sp1 are required for their cooperative interactions. To further understand the role of liver-enriched transcription factors in P450 gene expression, conditional knockout mice are being generated. Genomic clones to several liver-enriched transcription factors were isolated from an 129/SV gene library and used to prepare conditional knockout constructs that contain the Lox recombination signals flanking exonic regions of the genes. The recombinase gene Cre is being fused to the CYP2C6 promoter to generate a mouse that will express this protein in the liver at puberty. Thus, upon breeding the knockout and CYP2C6-Cre mice, the transcription factor genes will be abolished specifically in adult mice and the expression of P450 genes will be analyzed.