Function of the MRP Family

描述（由申请人提供）：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药物处置。我们实验室和其他实验室的研究表明，MRP家族扩展到9个成员。在之前的资助期内，我们重点分析了MRP3和MRP4的体内功能，并阐明了MRP6、MRP7和MRP8的功能特性。为了实现这一目标，我们开发并分析了mrp3和mrp4敲除小鼠和MRP6、MRP7和MRP8异位表达的细胞系。通过mrp3敲除小鼠，我们发现mrp3在肝脏中作为外源性硫酸盐代谢物的基底外侧外排泵起作用，并且它同样可以保护胆汁淤存的肝脏免受内源性化合物（如胆汁酸）的侵害。我们对Mrp4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，限制该药物进入大脑，并且与Mrp3一样，在肝细胞的基底外侧挤出硫酸盐中起作用。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。在本应用中，我们建议将MRP4的药理学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，我们将通过确定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是唯一一个功能性质尚未确定的MRP。这些研究将深入了解降低化疗药物有效性的因素，以及这些不寻常的泵所涉及的医学相关生理过程。公共卫生相关性：本提案中的实验将通过提供为什么许多类型的癌症不能成功地用抗癌药物治疗的信息来促进公共卫生。这些信息应有助于制定更成功的代理和战略。

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. PUBLIC HEALTH RELEVANCE: The experiments in this proposal will promote public health by providing information on why many types of cancers are not successfully treated with anticancer agents. This information should assist in the development of agents and strategies that are more successful.