Okey A B, Mason M E, Gehly E B, Heidelberger C, Muncan J, Dufresne M J
Eur J Biochem. 1983 May 2;132(2):219-27. doi: 10.1111/j.1432-1033.1983.tb07351.x.
C3H/1OT1/2 clone 8 mouse fibroblasts (C3H/1OT1/2 cells) exhibit induction of aryl hydrocarbon hydroxylase (cytochrome P1-450) when exposed in culture to benzo(a)pyrene, benz(a)anthracene or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but do not display the induction response when treated with 3-methylcholanthrene (MCA), the classical inducer of cytochrome P1-450. Induction of cytochrome P1-450 is regulated by the Ah receptor which initially binds inducing chemicals in the cytoplasm, after which the inducer x receptor complex translocates into the nucleus. Cytosolic and nuclear forms of the Ah receptor can be detected in C3H/1OT1/2 cells using [3H]TCDD as the radioligand in culture, but specific Ah receptor binding is not detectable within C3H/1OT1/2 cells incubated with [3H]MCA. In contrast, in Hepa-1c1 cells, which exhibit cytochrome P1-450 induction when treated with MCA, cytosolic and nuclear Ah receptor can be detected by incubation of the cells either with [3H]MCA or with [3H]TCDD. Nonradioactive MCA is able to compete with [3H]TCDD for Ah receptor sites in C3H/1OT1/2 cells, but the relative potency of MCA as a competitor is lower within C3H/1OT1/2 cells than in C3H/1OT1/2 cytosol during extracellular incubation. Specific binding of [3H]MCA to Ah receptor can be detected by incubation of [3H]MCA with C3H/1OT1/2 cytosol outside the cell. The selective loss of response to MCA as a cytochrome P1-450 inducer (while retaining response to other inducers) appears to be due to defective interaction of MCA with the Ah receptor within the intracellular environment. The specific molecular alteration which makes the MCA x receptor complex ineffective within C3H/1OT1/2 cells is unknown. Some fibroblast lines other than C3H/1OT1/2 also selectively fail to respond to MCA; thus, this variation in Ah receptor function may not be due to a mutational change in the Ah regulatory gene which codes for the Ah receptor.
C3H/1OT1/2克隆8小鼠成纤维细胞（C3H/1OT1/2细胞）在培养过程中暴露于苯并(a)芘、苯并(a)蒽或2,3,7,8-四氯二苯并对二恶英（TCDD）时，会表现出芳烃羟化酶（细胞色素P1 - 450）的诱导，但用细胞色素P1 - 450的经典诱导剂3-甲基胆蒽（MCA）处理时则不显示诱导反应。细胞色素P1 - 450的诱导由Ah受体调节，Ah受体最初在细胞质中结合诱导化学物质，之后诱导剂 - 受体复合物转移到细胞核中。在培养过程中，使用[3H]TCDD作为放射性配体，可以在C3H/1OT1/2细胞中检测到Ah受体的胞质和核形式，但在用[3H]MCA孵育的C3H/1OT1/2细胞中无法检测到特异性Ah受体结合。相反，在Hepa - 1c1细胞中，用MCA处理时会表现出细胞色素P1 - 450的诱导，通过用[3H]MCA或[3H]TCDD孵育细胞可以检测到胞质和核Ah受体。非放射性MCA能够在C3H/1OT1/2细胞中与[3H]TCDD竞争Ah受体位点，但在细胞外孵育期间，MCA作为竞争者在C3H/1OT1/2细胞中的相对效力低于在C3H/1OT1/2胞质溶胶中的相对效力。通过在细胞外将[3H]MCA与C3H/1OT1/2胞质溶胶孵育，可以检测到[3H]MCA与Ah受体的特异性结合。作为细胞色素P1 - 450诱导剂对MCA反应的选择性丧失（同时保留对其他诱导剂的反应）似乎是由于MCA在细胞内环境中与Ah受体的相互作用缺陷所致。使MCA - 受体复合物在C3H/1OT1/2细胞中无效的具体分子改变尚不清楚。除C3H/1OT1/2外的一些成纤维细胞系也选择性地对MCA无反应；因此，Ah受体功能的这种变化可能不是由于编码Ah受体的Ah调节基因突变引起的。
