Trauner M, Arrese M, Soroka C J, Ananthanarayanan M, Koeppel T A, Schlosser S F, Suchy F J, Keppler D, Boyer J L
Liver Center and Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8019, USA.
Gastroenterology. 1997 Jul;113(1):255-64. doi: 10.1016/s0016-5085(97)70103-3.
BACKGROUND & AIMS: The excretion of various organic anions into bile is mediated by an adenosine triphosphate-dependent conjugate export pump, which has been identified as the canalicular isoform of the multidrug resistance protein (Mrp2). Mrp2 function is impaired in various experimental models of intrahepatic and obstructive cholestasis, but the underlying molecular mechanisms are unclear. The aim of this study was to investigate these molecular mechanisms.
The effects of endotoxin, ethinylestradiol, and common bile duct ligation (CBDL) on Mrp2 protein, messenger RNA (mRNA) expression, and Mrp2 tissue localization were determined in rat livers by Northern blotting, Western analysis, and tissue immunofluorescence. To assess whether changes were specific for Mrp2, we also examined the expression of canalicular ecto-adenosine triphosphatase (ecto-ATPase) and mdr P-glycoproteins (P-gp).
All three cholestatic models resulted in a marked decrease in Mrp2 protein (P < 0.01) and its tissue localization at the canalicular membrane. Mrp2 mRNA levels diminished profoundly after endotoxin (P < 0.0005) and CBDL (P < 0.05), but did not change after ethinylestradiol. In contrast to Mrp2, protein expression of ecto-ATPase and P-gp remained unchanged in endotoxin- and ethinylestradiol-treated animals, whereas P-gp levels increased after CBDL (P < 0.05).
Down-regulation of Mrp2 expression may explain impaired biliary excretion of amphiphilic anionic conjugates in these models of cholestasis.
多种有机阴离子向胆汁中的排泄由一种三磷酸腺苷依赖性共轭物输出泵介导，该泵已被鉴定为多药耐药蛋白（Mrp2）的胆小管异构体。在各种肝内和梗阻性胆汁淤积的实验模型中，Mrp2功能受损，但其潜在的分子机制尚不清楚。本研究旨在探讨这些分子机制。
通过Northern印迹法、Western分析和组织免疫荧光法，测定内毒素、乙炔雌二醇和胆总管结扎（CBDL）对大鼠肝脏中Mrp2蛋白、信使核糖核酸（mRNA）表达及Mrp2组织定位的影响。为评估这些变化是否对Mrp2具有特异性，我们还检测了胆小管外核苷三磷酸酶（ecto-ATPase）和多药耐药P-糖蛋白（P-gp）的表达。
所有三种胆汁淤积模型均导致Mrp2蛋白显著减少（P < 0.01）及其在胆小管膜的组织定位减少。内毒素（P < 0.0005）和CBDL（P < 0.05）处理后，Mrp2 mRNA水平显著降低，但乙炔雌二醇处理后未发生变化。与Mrp2不同，内毒素和乙炔雌二醇处理的动物中，ecto-ATPase和P-gp的蛋白表达保持不变，而CBDL处理后P-gp水平升高（P < 0.05）。
Mrp2表达下调可能解释了这些胆汁淤积模型中两亲性阴离子共轭物胆汁排泄受损的原因。
