Forkert P G, Lord J A, Parkinson A
Department of Anatomy and Cell Biology, Queen's University, Kingston, Ontario, Canada.
Carcinogenesis. 1996 Jan;17(1):127-32. doi: 10.1093/carcin/17.1.127.
We investigated the expression of the cytochrome P450 isozyme, CYP1A1, during the course of tumor development and examined the distribution of the CYP1A1 protein in hyperplastic foci, adenomas and carcinomas. The expression of NADPH-cytochrome P450 reductase, a flavoprotein that mediates the reduction of cytochrome P450, was also determined. Mice were administered urethane (1 mg/g body wt) and were killed at 10, 22 and 52 weeks to coincide with the time at which hyperplastic foci, adenomas and carcinomas were established, respectively. Protein immunoblotting revealed that the antibody for CYP1A1 detected a protein band of approximately M(r) 56,000 in microsomes from mice treated with beta-naphthoflavone. The antibody for NADPH-cytochrome P450 reductase detected a protein band of approximately M(r) 79,000 in microsomes from control mice and mice treated with beta-naphthoflavone. Immunohistochemical studies showed that CYP1A1 was not detected constitutively in the lungs of both non-tumor- and tumor-bearing mice. Treatment with beta-naphthoflavone evoked high induction of CYP1A1 in morphologically normal tissues of all mice, with localization of the protein mainly in endothelial and alveolar type II cells. In contrast, inducibility of CYP1A1 by beta-naphthoflavone was markedly reduced in early hyperplastic foci seen 10 weeks after urethane exposure. At 22 weeks, CYP1A1 was found at low levels in both solid and papillary tumors, whereas at 52 weeks, lung carcinomas were devoid of expression of this protein. However, CYP1A1 inducibility was highly expressed in late hyperplastic foci manifested at 52 weeks. NADPH-cytochrome P450 reductase was expressed in morphologically normal lung tissue of all mice under control conditions and after treatment with beta-naphthoflavone, and was localized mainly in Clara and alveolar type II cells. In contrast, reductase expression in all tumor sites was diminished and closely paralleled that of CYP1A1. These results demonstrated progressive depression of induced CYP1A1 and reductase expression in early hyperplasias, adenomas and carcinomas, suggesting that the co-ordinate regulation of both enzymes is highly conserved during tumor development. Furthermore, these findings suggested diminished capabilities for metabolic activation of potential toxicants and/or carcinogens after neoplastic transformation.
我们研究了细胞色素P450同工酶CYP1A1在肿瘤发生过程中的表达，并检测了CYP1A1蛋白在增生灶、腺瘤和癌组织中的分布。还测定了NADPH - 细胞色素P450还原酶（一种介导细胞色素P450还原的黄素蛋白）的表达。给小鼠腹腔注射乌拉坦（1 mg/g体重），并分别在10周、22周和52周处死，这三个时间点分别对应增生灶、腺瘤和癌形成的时间。蛋白质免疫印迹显示，CYP1A1抗体在经β - 萘黄酮处理的小鼠微粒体中检测到一条分子量约为56,000的蛋白条带。NADPH - 细胞色素P450还原酶抗体在对照小鼠和经β - 萘黄酮处理的小鼠微粒体中检测到一条分子量约为79,000的蛋白条带。免疫组织化学研究表明，在未患肿瘤和患肿瘤小鼠的肺组织中均未检测到组成型表达的CYP1A1。用β - 萘黄酮处理后，所有小鼠形态学正常组织中的CYP1A1均被高度诱导，该蛋白主要定位于内皮细胞和II型肺泡细胞。相反，在乌拉坦暴露10周后出现的早期增生灶中，β - 萘黄酮对CYP1A1的诱导能力明显降低。在22周时，实体瘤和乳头状瘤中CYP1A1的表达水平较低，而在52周时，肺癌组织中未检测到该蛋白的表达。然而，在52周出现的晚期增生灶中CYP1A1的诱导能力高度表达。在对照条件下以及经β - 萘黄酮处理后，所有小鼠形态学正常的肺组织中均表达NADPH - 细胞色素P450还原酶，且主要定位于克拉拉细胞和II型肺泡细胞。相反，所有肿瘤部位的还原酶表达均降低，且与CYP1A1的表达密切平行。这些结果表明，在早期增生、腺瘤和癌组织中，诱导型CYP1A1和还原酶的表达逐渐降低，提示在肿瘤发生过程中这两种酶的协同调节高度保守。此外，这些发现表明肿瘤转化后潜在毒物和/或致癌物的代谢活化能力降低。
