Zhang J, Watson A J, Probst M R, Minehart E, Hankinson O
UCLA Jonsson Comprehensive Cancer Center, University of California, Los Angeles 90095-1732, USA.
Mol Pharmacol. 1996 Dec;50(6):1454-62.
Rare benzo[a]pyrene-resistant clones were previously isolated from the mouse hepatoma cell line, Hepa-1 (Hepa1c1c7), and shown to be deficient in induction of CYP1A1 mRNA by ligands for the aryl hydrocarbon receptor (AHR). Clones belonging to complementation group B were shown to have reduced levels of ligand binding to AHR. It is shown here that all 15 independently derived B clones analyzed had much reduced levels of AHR mRNA, but in each case, the mRNA was normal in size. Infection of B clones with a retroviral expression vector for AHR restores CYP1A1 inducibility (although viral AHR expression is progressively silenced and CYP1A1 expression progressively diminishes as the cells are maintained in culture). Treatment of the B clones with the histone deacetylase inhibitors sodium butyrate or trichostatin A restores AHR expression and also restores CYP1A1 inducibility to nearly 100% of the cells in the treated cultures. Fusion of a representative B clone with a rat hepatoma cell line restores expression to the mouse AHR gene encoded by the B clone's genome. These results demonstrate that the loss of CYP1A1 inducibility in B clones is probably totally ascribable to their reduced levels of AHR and that the clones are most probably not mutated in the AHR gene but are deficient in its expression. The evidence suggests that the reduction in expression of mRNA encoded by the endogenous AHR gene in the B clones is not due to an epigenetic alteration in chromatin structure but that the clones are probably defective either in a transcription factor for the AHR gene or in a protein required for generating an open chromatin configuration over the gene.
先前从小鼠肝癌细胞系Hepa-1（Hepa1c1c7）中分离出了罕见的抗苯并[a]芘克隆，结果表明这些克隆在芳烃受体（AHR）配体诱导CYP1A1 mRNA方面存在缺陷。属于互补组B的克隆显示出与AHR的配体结合水平降低。本文研究表明，所分析的所有15个独立衍生的B克隆的AHR mRNA水平均大幅降低，但在每种情况下，mRNA大小正常。用AHR的逆转录病毒表达载体感染B克隆可恢复CYP1A1的诱导性（尽管随着细胞在培养中维持，病毒AHR表达会逐渐沉默，CYP1A1表达也会逐渐减少）。用组蛋白脱乙酰酶抑制剂丁酸钠或曲古抑菌素A处理B克隆可恢复AHR表达，并且还可将CYP1A1诱导性恢复到处理培养物中近100%的细胞。将一个代表性的B克隆与大鼠肝癌细胞系融合可恢复由B克隆基因组编码的小鼠AHR基因的表达。这些结果表明，B克隆中CYP1A1诱导性的丧失可能完全归因于其AHR水平降低，并且这些克隆很可能在AHR基因中未发生突变，而是在其表达方面存在缺陷。证据表明，B克隆中内源性AHR基因编码的mRNA表达降低并非由于染色质结构的表观遗传改变，而是这些克隆可能在AHR基因的转录因子或在基因上产生开放染色质构型所需的蛋白质方面存在缺陷。
