Dalton T P, Dieter M Z, Matlib R S, Childs N L, Shertzer H G, Genter M B, Nebert D W
Department of Environmental Health, University of Cincinnati Medical Center, Cincinnati, Ohio, 45267-0056, USA.
Biochem Biophys Res Commun. 2000 Jan 7;267(1):184-9. doi: 10.1006/bbrc.1999.1913.
Using the Cre-lox system, we have generated a cytochrome P450 1A1 Cyp1a1(-/-) knockout mouse by deletion of the translated portions of the Cyp1a1 gene. These mice are viable and demonstrate no obvious phenotype, compared with wild-type littermates. As a first step toward characterizing genes that might be expected to compensate for loss of CYP1A1, constitutive expression of [Ah] gene battery members was examined. In a cultured hepatoma CYP1A1 metabolism-deficient mutant line that does not express Cyp1a2, we have previously shown that constitutive transcriptional up-regulation of other [Ah] gene battery members occurs; these results are consistent with the elevation of a putative endogenous ligand (EL) for the Ah receptor that is a substrate for CYP1A1. The [Ah] battery includes Cyp1a2, NAD(P)H:quinone oxidoreductase (Nqo1), and three other Phase II genes. Examining mRNA, protein, and enzyme activity, we demonstrate that the absence of CYP1A1 has no effect on the hepatic constitutive expression of Cyp1a2 or Nqo1. We postulate that CYP1A1 and CYP1A2 might have overlapping substrate specificity for metabolism of the EL, such that basal CYP1A2 in the liver can compensate for the loss of CYP1A1.
利用Cre-lox系统，我们通过缺失Cyp1a1基因的翻译部分，培育出了细胞色素P450 1A1（Cyp1a1(-/-)）基因敲除小鼠。与野生型同窝小鼠相比，这些小鼠能够存活且未表现出明显的表型。作为表征可能补偿CYP1A1缺失的基因的第一步，我们检测了[Ah]基因簇成员的组成型表达。在一个不表达Cyp1a2的培养肝癌CYP1A1代谢缺陷突变株中，我们先前已表明其他[Ah]基因簇成员会发生组成型转录上调；这些结果与作为CYP1A1底物的Ah受体假定内源性配体（EL）水平升高一致。[Ah]基因簇包括Cyp1a2、NAD(P)H：醌氧化还原酶（Nqo1）以及其他三个II相基因。通过检测mRNA、蛋白质和酶活性，我们证明CYP1A1的缺失对Cyp1a2或Nqo1的肝脏组成型表达没有影响。我们推测CYP1A1和CYP1A2在EL代谢方面可能具有重叠的底物特异性，因此肝脏中的基础CYP1A2能够补偿CYP1A1的缺失。
