Fardel O, Lecureur V, Corlu A, Guillouzo A
INSERM U 49, Unité de Recherches Hépatologiques, Hôpital de Pontchaillou, Rennes, France.
Biochem Pharmacol. 1996 Jun 14;51(11):1427-36. doi: 10.1016/0006-2952(96)00081-0.
Expression of P-glycoprotein (P-gp), a plasma membrane glycoprotein involved in multidrug resistance and encoded by mdr genes, was investigated in nonparenchymal rat liver epithelial (RLE) cells in response to acute exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs). High levels of mdr mRNAs were evidenced by Northern blotting in two independent RLE cell lines after treatment by either 3-methylcholanthrene (MC) or benzo-(a)pyrene. MC-mediated mdr mRNA induction was demonstrated to be dose-dependent; it occurred through enhanced expression of the mdr 1 gene, as indicated by reverse transcriptase-polymerase chain reaction analysis using rat mdr gene-specific primers and paralleled an induction of a 140 kDa P-gp as demonstrated by Western blotting. In addition, MC-induced P-gp appeared to be fully functional because RLE cells exposed to MC displayed enhanced cellular efflux of rhodamine 123, a known P-gp substrate, compared to their untreated counterparts. Analysis of time-course induction revealed that mdr mRNA levels were maximally increased when RLE cells were treated for 48 to 96 hr and returned to low levels after the PAH was removed. In contrast to P-gp, both cytochrome P-450 1A1 and cytochrome P-450 1A2 were not detected after exposure to MC, thus indicating that these liver detoxification pathways are not coordinately regulated with P-gp in RLE cells. In addition, MC-mediated P-gp regulation was not associated with major cellular disturbances such as alteration of protein synthesis and, thereby, differed from the known mdr mRNA induction occurring in response to cycloheximide. Moreover, cotreatment with MC and cycloheximide led to a superinduction of mdr mRNAs, thus suggesting that the effects of the two xenobiotics were, at least partly, additive. In contrast to MC and benzo(a)pyrene, 2,3,7,8-tetrachlorodibenzo-p-dioxin and benzo(e)pyrene were unable to increase P-gp expression. These results indicate that some PAHs can act as potent inducers of P-gp in RLE cells and may be interpreted as an adaptive reaction of these cells in lowering cellular accumulation of toxic drugs, including carcinogens transported by P-gp and, therefore, conferring protection on these compounds.
多药耐药相关蛋白（P-糖蛋白，P-gp）是一种参与多药耐药的质膜糖蛋白，由mdr基因编码。本研究调查了非实质大鼠肝上皮（RLE）细胞在急性暴露于致癌性多环芳烃（PAHs）后P-糖蛋白的表达情况。用3-甲基胆蒽（MC）或苯并(a)芘处理后，通过Northern印迹法在两个独立的RLE细胞系中证实了高水平的mdr mRNA。MC介导的mdr mRNA诱导呈剂量依赖性；通过使用大鼠mdr基因特异性引物的逆转录-聚合酶链反应分析表明，它是通过mdr 1基因表达增强而发生的，并且与Western印迹法显示的140 kDa P-糖蛋白的诱导平行。此外，MC诱导的P-糖蛋白似乎具有完全功能，因为与未处理的细胞相比，暴露于MC的RLE细胞对罗丹明123（一种已知的P-糖蛋白底物）的细胞外排增强。时间进程诱导分析表明，当RLE细胞处理48至96小时时，mdr mRNA水平最大程度增加，在去除PAH后恢复到低水平。与P-糖蛋白相反，暴露于MC后未检测到细胞色素P-450 1A1和细胞色素P-450 1A2，因此表明这些肝脏解毒途径在RLE细胞中与P-糖蛋白的调节不相关。此外，MC介导的P-糖蛋白调节与主要的细胞紊乱无关，如蛋白质合成的改变，因此不同于已知的因环己酰亚胺而发生的mdr mRNA诱导。此外，MC与环己酰亚胺共同处理导致mdr mRNA的超诱导，因此表明这两种外源性物质的作用至少部分是相加的。与MC和苯并(a)芘相反，2,3,7,8-四氯二苯并-p-二恶英和苯并(e)芘不能增加P-糖蛋白的表达。这些结果表明，一些PAHs可以作为RLE细胞中P-糖蛋白的有效诱导剂，并且可以解释为这些细胞在降低包括由P-糖蛋白转运的致癌物在内的有毒药物的细胞内积累方面的一种适应性反应，从而对这些化合物起到保护作用。
