Structural gene products of the Ah locus. Transcriptional regulation of cytochrome P1-450 and P3-450 mRNA levels by 3-methylcholanthrene.
Structural gene products of the Ah locus. Transcriptional regulation of cytochrome P1-450 and P3-450 mRNA levels by 3-methylcholanthrene.
复制标题
Ah 基因座的结构基因产物。
作者：
F. Gonzalez;R. Tukey;D. Nebert
小鼠肝细胞色素P1-450和P3-450分别代表与诱导的芳烃（苯并[a]芘）羟化酶和乙酰苯胺4-羟化酶活性最密切相关的多环烃诱导的P-450的那些形式。这两种蛋白由Ah受体控制：C57 BL/6 N小鼠具有高亲和力受体; DBA/2N小鼠具有低亲和力受体。3-甲基胆蒽在技术上可能的最高剂量诱导C57 BL/6 N，但DBA/2N小鼠的蛋白质，而足够高剂量的2，3，7，8-四氯二苯并-p-二恶英（TCDD）诱导两种蛋白质在两个近交系小鼠品系。在体外核转录试验中分别使用含有与P1-450和P3-450 mRNA互补的DNA的质粒，以确定诱导反应的机制。在C57 BL/6 N小鼠中，P1-450和P3-450基因的转录率在3-甲基胆蒽处理后早在3小时就急剧增加，并在12小时达到最高水平，分别为对照值的20倍和15倍。相比之下，在3-甲基胆蒽处理的DBA/2N小鼠中没有发现任何基因的增加。TCDD给药后，DBA/2N小鼠中P1-450和P3-450基因转录率均升高。有一个3至6小时的滞后期之间的早期发病的增强转录速率和P1-450和P3-450 mRNA的后期上升。P3-450 mRNA的基础和诱导水平比P1-450 mRNA的基础和诱导水平高约5倍。这些数据证实，3-甲基胆蒽和TCDD诱导反应，由Ah受体，介导的主要是通过增加特定的基因转录。
Mouse liver cytochromes P1-450 and P3-450 represent those forms of polycylic hydrocarbon-induced P-450 most closely associated with induced aryl hydrocarbon (benzo[a] pyrene) hydroxylase and acetanilide 4-hydroxylase activity, respectively. These two proteins are controlled by the Ah receptor: C57BL/6N mice possess the high-affinity receptor; DBA/2N mice, the poor-affinity receptor. 3-Methylcholanthrene at the highest dose technically possible induces both proteins in C57BL/6N but not DBA/2N mice, whereas sufficiently high doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induce both proteins in both inbred mouse strains. Plasmids containing DNA complementary to P1-450 and P3-450 mRNA, respectively, were used in an in vitro nuclear transcription assay to determine the mechanism of the induction response. In C57BL/6N mice, transcriptional rates of the P1-450 and P3-450 genes increase dramatically as early as 3 hr after 3-methylcholanthrene treatment and at 12 hr reach maximal levels of 20- and 15-fold, respectively, above control values. In contrast, no increase in either gene is found in 3-methylcholanthrene-treated DBA/2N mice. Following TCDD administration, both P1-450 and P3-450 gene transcription rates are elevated in DBA/2N mice. There is a 3- to 6-hr lag period between the early onset of enhanced transcription rates and the later rise in P1-450 and P3-450 mRNA. Basal and induced levels of P3-450 mRNA are about 5-fold greater than those of P1-450 mRNA. These data confirm that the 3-methylcholanthrene and TCDD induction responses, governed by the Ah receptor, are mediated principally through an increase in specific gene transcription.