Gonzalez F J, Crespi C L, Czerwinski M, Gelboin H V
Laboratory of Molecular Carcinogenesis, National Institutes of Health, Bethesda, Maryland 20892.
Tohoku J Exp Med. 1992 Oct;168(2):67-72. doi: 10.1620/tjem.168.67.
Cytochromes P450 are a large group of membrane-associated heme protein monooxygenases, most of which are responsible for metabolizing foreign compounds. Chemical carcinogens, which are ingested or absorbed into the body as inert forms, are metabolically activated by P450s to electrophilic metabolites capable of binding to and mutating DNA. Different P450 forms are responsible for activation of the various classes of chemical carcinogens including the arylamines, polycyclic aromatic hydrocarbons, nitrosamines and aflatoxins. Thus, the cellular constituency and levels of P450s could determine the fate of a particular carcinogen and the risk of humans to exposure. To study the catalytic activities of human P450s, human P450 cDNAs were cloned and expressed into active enzymes using cultured cells. By both transient and stable cDNA expression systems, several human P450s were found to be capable of metabolically-activating the human hepatocarcinogen aflatoxin B1. These cDNA expression systems can also be used to determine whether an unknown chemical will be activated by a human P450 and thus be toxic or mutagenic in humans. To assess the extent of interindividual variation in P450 expression, probes developed from P450 cDNAs are being used to quantify levels of P450 mRNAs in various human tissues. Studies using RNase protection revealed that the closely related CYP2B6 and CYP2B7 mRNAs could be independently quantified in liver and lung, respectively. This procedure can be used to examine expression of different P450 genes in banks of human tissue specimens.
细胞色素P450是一大类与膜相关的血红素蛋白单加氧酶，其中大多数负责代谢外来化合物。化学致癌物以惰性形式摄入或吸收进入体内后，会被细胞色素P450代谢活化为能够与DNA结合并使其突变的亲电代谢产物。不同的细胞色素P450形式负责激活各类化学致癌物，包括芳基胺、多环芳烃、亚硝胺和黄曲霉毒素。因此，细胞色素P450的细胞组成和水平可以决定特定致癌物的命运以及人类接触致癌物的风险。为了研究人类细胞色素P450的催化活性，人类细胞色素P450的互补DNA（cDNA）被克隆，并利用培养细胞表达为活性酶。通过瞬时和稳定的cDNA表达系统，发现几种人类细胞色素P450能够代谢激活人类肝癌致癌物黄曲霉毒素B1。这些cDNA表达系统还可用于确定一种未知化学物质是否会被人类细胞色素P450激活，从而判断其在人类体内是否具有毒性或致突变性。为了评估细胞色素P450表达的个体间差异程度，从细胞色素P450的cDNA开发的探针正被用于定量各种人类组织中细胞色素P450信使核糖核酸（mRNA）的水平。使用核糖核酸酶保护法的研究表明，密切相关的CYP2B6和CYP2B7 mRNA可以分别在肝脏和肺中独立定量。该方法可用于检测人类组织标本库中不同细胞色素P450基因的表达情况。
