Li H C, Kupfer D
Worcester Foundation for Biomedical Research Shrewsbury, MA 01545, USA.
J Biochem Mol Toxicol. 1998;12(6):315-23. doi: 10.1002/(sici)1099-0461(1998)12:6<315::aid-jbt1>3.0.co;2-6.
Our earlier investigation demonstrated that methoxychlor treatment induced hepatic cytochrome P450 2B1/2B2 and 3A proteins in rats and enhanced their respective enzymatic activities. To determine the mechanism of the methoxychlor-mediated induction and whether methoxychlor acts as a frank inducer and not merely by causing stabilization of the cytochrome P450 proteins or of their mRNAs, we assessed the effect of methoxychlor treatment on the transcriptional rate and mRNA levels of these hemeproteins by nuclear run-on and northern blot analyses. Methoxychlor treatment markedly elevated the transcriptional rates of cytochrome P4502B1/2B2 and 3A. Also, higher levels of mRNA of these CYPs were observed. By contrast, mRNA levels of CYP1A1/1A2 were not affected. Using a nuclear run-on method that apparently measures specifically the transcription initiation rate of CYP2B1 and 2B2, we observed that the transcriptional rate of 2B2 was increased substantially more than that of CYP2B1. This differential induction of CYP2B2 versus 2B1 may account for the discrepancy between the levels of induced CYP2B protein and the much lower-than-expected CYP2B-mediated enzymatic activity observed in our earlier study.
我们早期的研究表明，甲氧滴滴涕处理可诱导大鼠肝脏中的细胞色素P450 2B1/2B2和3A蛋白，并增强它们各自的酶活性。为了确定甲氧滴滴涕介导的诱导机制，以及甲氧滴滴涕是否作为一种真正的诱导剂，而不仅仅是通过使细胞色素P450蛋白或其mRNA稳定，我们通过核转录分析和Northern印迹分析评估了甲氧滴滴涕处理对这些血红素蛋白转录速率和mRNA水平的影响。甲氧滴滴涕处理显著提高了细胞色素P4502B1/2B2和3A的转录速率。此外，还观察到这些细胞色素P450的mRNA水平更高。相比之下，CYP1A1/1A2的mRNA水平未受影响。使用一种明显专门测量CYP2B1和2B2转录起始速率的核转录方法，我们观察到2B2的转录速率比CYP2B1的转录速率增加得更多。CYP2B2与2B1的这种差异诱导可能解释了我们早期研究中观察到的诱导型CYP2B蛋白水平与远低于预期的CYP2B介导的酶活性之间的差异。
