Hirsch-Ernst K I, Ziemann C, Foth H, Kozian D, Schmitz-Salue C, Kahl G F
Department of Toxicology, Institute of Pharmacology and Toxicology, University of Göttingen, Germany.
J Cell Physiol. 1998 Sep;176(3):506-15. doi: 10.1002/(SICI)1097-4652(199809)176:3<506::AID-JCP7>3.0.CO;2-S.
Mammalian liver exhibits expression of members of the family of multidrug resistance (mdr) transporters (P-glycoproteins). P-glycoprotein isoforms encoded by mdr1 genes participate in extrusion of an array of xenobiotics into the bile. Induction of mdr1b mRNA expression has been shown to occur in rat hepatocytes in response to hepatotrophic growth factors. As the cytokine tumor necrosis factor alpha (TNF-alpha) is known to exert a direct mitogenic effect on hepatocytes, its influence on mdr1b expression was investigated. In primary rat hepatocytes cultured in the absence of TNF-alpha, a time-dependent increase in basal expression of mdr1b mRNA and in immunodetectable P-glycoprotein was observed. In cells treated with TNF-alpha (4,000 U/ml) for 3 days, expression of mdr1b mRNA and of immunodetectable P-glycoprotein was induced approximately twofold. Moreover, intracellular steady-state levels of the mdr1 substrate rhodamine 123 were decreased in cells pretreated with TNF-alpha in comparison to controls, indicating an increase in functional transporter(s) mediating dye extrusion. Treatment of hepatocytes with antioxidants (1 mM ascorbic acid and 2% dimethyl sulfoxide) for 3 days markedly suppressed mdr1b mRNA and P-glycoprotein expression both in cells cultured in the presence of TNF-alpha and in the absence of the cytokine, but did not fully abolish mdr1b mRNA induction by TNF-alpha, supporting the notion that reactive oxygen species participate in regulation of basal mdr1b gene expression during hepatocyte culture. In conclusion, the present data indicate that by inducing mdr1b expression in hepatocytes, TNF-alpha may affect the capacity of the liver for extrusion or detoxification of endogenous or xenobiotic mdr1 substrates.
哺乳动物肝脏中存在多药耐药（mdr）转运蛋白家族（P-糖蛋白）成员的表达。由mdr1基因编码的P-糖蛋白异构体参与将一系列外源性物质排入胆汁。研究表明，在大鼠肝细胞中，肝营养生长因子可诱导mdr1b mRNA表达。由于已知细胞因子肿瘤坏死因子α（TNF-α）对肝细胞具有直接的促有丝分裂作用，因此研究了其对mdr1b表达的影响。在无TNF-α培养的原代大鼠肝细胞中，观察到mdr1b mRNA的基础表达以及免疫可检测的P-糖蛋白呈时间依赖性增加。在用TNF-α（4000 U/ml）处理3天的细胞中，mdr1b mRNA和免疫可检测的P-糖蛋白的表达被诱导增加了约两倍。此外，与对照组相比，用TNF-α预处理的细胞中mdr1底物罗丹明123的细胞内稳态水平降低，表明介导染料外排的功能性转运蛋白增加。用抗氧化剂（1 mM抗坏血酸和2%二甲基亚砜）处理肝细胞3天，可显著抑制在有TNF-α存在和无细胞因子培养的细胞中mdr1b mRNA和P-糖蛋白的表达，但并未完全消除TNF-α对mdr1b mRNA的诱导作用，这支持了活性氧参与肝细胞培养过程中基础mdr1b基因表达调控的观点。总之，目前的数据表明，TNF-α通过诱导肝细胞中mdr1b的表达，可能会影响肝脏对内源性或外源性mdr1底物的外排或解毒能力。
