Function of the MRP Family

描述(申请人提供)：MRP1和MRP2是MRP家族的创始成员，参与细胞对抗癌药物的耐药性和体内的药物处置。我们实验室和其他实验室的研究表明，MRP家族现在扩展到9个成员。在之前的资助期间，我们重点分析了MRP3和MRP4在体内的功能，并阐明了MRP6、MRP7和MRP8的功能特性。为此，我们建立并分析了MRP6、MRP7和MRP8异位表达的mrp3和mrp4基因敲除小鼠和细胞系。利用我们的mrp3基因敲除小鼠，我们证明了mrp3在肝脏中作为外源物质硫酸盐代谢物的基侧外排泵发挥作用，并类似地保护胆汁淤积症肝脏免受胆汁酸等内源性化合物的影响。我们对mrp4基因敲除小鼠的研究表明，mrp4是抗病毒核苷酸类似物PMEA的体内耐药因子，限制了该药物对大脑的渗透，并与mrp3一样，在肝细胞硫酸盐的基侧排出中发挥作用。MRP6、MRP7和MRP8被确定为亲脂性阴离子转运体，能够赋予细胞对抗癌天然产物(MRP6、MRP7)和核苷类药物(MRP8)的耐药性。在本申请中，我们建议将MRP4的药理功能定义为抗癌药物的体内耐药因子，以及抗癌药物的血-脑和血-脑脊液屏障的组成部分。此外，我们将通过测定MRP9的耐药能力和底物选择性来完成对新发现的MRP家族成员的研究-MRP9是唯一功能特性尚未确定的MRP。这些研究将提供对降低化疗药物有效性的因素的洞察，以及这些不寻常的泵参与的与医学相关的生理过程。

DESCRIPTION (provided by applicant): MRP1 and MRP2, founding members of the MRP family, are involved in cellular resistance to anticancer agents and drug disposition in the body. Studies in our laboratory and others now indicate that the MRP family extends to 9 members. In the previous funding period we focused on the analysis of the in vivo functions of MRP3 and MRP4, and on the elucidation of the functional properties of MRP6, MRP7 and MRP8. To accomplish this we developed and analyzed mrp3 and mrp4 knock-out mice and cell lines in which MRP6, MRP7 and MRP8 were ectopically expressed. Using our mrp3 knock-out mice, we showed that the Mrp3 functions in liver as a basolateral efflux pump for sulfate metabolites of xenobiotics, and that it similarly protects cholestatic liver from endogenous compounds such as bile acids. Our studies on Mrp4 knockout mice showed that Mrp4 is an in vivo resistance factor for the antiviral nucleotide analog PMEA, restricts penetration of this agent into brain, and like Mrp3, functions in the basolateral extrusion of sulfates from hepatocytes. MRP6, MRP7 and MRP8 were determined to be lipophilic anion transporters that are able to confer cellular resistance to anticancer natural product (MRP6, MRP7) and nucleoside-based agents (MRP8). In this application we propose to define the pharmacological functions of MRP4 as an in vivo resistance factor for anticancer agents, and as a component of the blood-brain and blood-cerebrospinal fluid barriers for anticancer agents. In addition, we will complete our investigation of the newly discovered MRP family members by determining the drug resistance abilities and substrate selectivity of MRP9 - the only MRP whose functional properties have not been determined to any extent. These studies will provide insights into factors that reduce the effectiveness of chemotherapeutic agents, as well as into medically relevant physiological processes in which these unusual pumps are involved.