Analysis of the mechanism for the development of cholestasis induced by the altered function of efflux transporters

多药耐药相关蛋白2（MRP 2/ABCC 2）表达于胆管膜上，参与胆汁酸非依赖性胆汁流的形成，其遗传缺陷导致人类Dubin-Johnson综合征的发生。胆汁淤积也由许多后天因素引起。作为获得性胆汁淤积的机制，我们可以假设MRP 2/ABCC 2被某些致病刺激内化。在本研究中，我们已经证明，MRP 2/ABCC 2是内在的病理条件下，并提出这种内化的外排转运蛋白可能与胆汁淤积的发病机制。我们还分析了MRP 2分子的SNPs形式的定位和功能，并提出了一些类型的突变，这不是直接与MRP 2/ABCC 2分子本身的功能降低，可能与细胞内定位的改变，因此，与野生型转运蛋白相比，在体内功能降低。此外，已经证明，在病理条件下，MRP 3/ABCC 3在基底外侧膜上被诱导，以补偿MRP 2/ABCC 2的功能降低。由于胆汁淤积d的阶段的程度可能受到MRP 3/ABCC 3功能的影响，因此我们检测了人MRP 3/ABCC 3的功能。已证明MRP 3/ABCC 3接受MRP 2/ABCC 2底物，沿着单价胆汁盐，单价胆汁盐是胆汁盐输出泵（BSEP/ABCB 11）的选择性底物。结合我们对灌注肝脏的研究结果，我们可以确定MRP 3/ABCC 3作为膜蛋白，可能参与病理条件下肝细胞的拯救。MRP 3/ABCC 3诱导程度可能影响胆汁淤积的严重程度。

Multidrug resistance associate protein 2 (MRP2/ABCC2), which is expressed on the bile canalicular membrane, is involved in the formation of bile acid-independent bile flow, and its hereditary defect results in the development of Dubin-Johnson syndrome in humans. Cholestasis is also induced by many acquired factors. As the mechanism for the acquired cholestasis, it is possible for us to assume that MRP2/ABCC2 is internalized by certain kinds of pathogenic stimuli. In the present study, we have demonstrated that MRP2/ABCC2 is internalized under pathological conditions, and proposed that such an internalization of efflux transporter may be related to the pathogenesis of cholestasis. We have also analyzed the localization and function of the SNPs forms of MRP2 molecules, and suggested that some kinds of mutation, which are not directly associated with the reduced function of MRP2/ABCC2 molecules per se, may be associated with the altered intracellular localization, and therefore, with the reduced in vivo function compared with the wild type transporter. In addition, it has been demonstrated that MRP3/ABCC3 is induced on the basolateral membrane under pathological conditions, in order to compensate for the reduced function of MRP2/ABCC2. Since the extent of the stage of cholestasisd may be affected by the function of MRP3/ABCC3, we have examined the function of human MRP3/ABCC3. It was demonstrated that MRP3/ABCC3 accepts MRP2/ABCC2 substrates, along with the monovalent bile salts which are the selective substrates for the bile salt export pump (BSEP/ABCB11). Together with our findings with the perfused liver, we could identify MRP3/ABCC3 as the membrane protein which may be involved in the rescue of hepatocytes under pathological conditions. It was also suggested that the extent of MRP3/ABCC3 induction may affect the severitv of the cholestasis.