Functions of the Human OST-alpha and OST-beta Proteins

描述（由申请人提供）：所有细胞功能最终取决于化学物质在质膜上的调节运动。虽然最近的研究已经描述了一些参与这些运输过程的基因，但很明显，许多其他必要的基因产物仍有待鉴定和表征。利用比较方法，我们最近克隆了一种新型的有机溶质和类固醇转运体（OST），并对其进行了功能表征，该转运体来自滑冰、小鼠和人类基因组。这种转运蛋白是由两个独特的基因产物，有机溶质转运蛋白- α和- β (OSTalpha, OSTbeta)共同表达而产生的。与大多数其他转运蛋白不同的是，OSTalpha和ostβ在小鼠或人类基因组中没有同源物。此外，这些基因是进化保守的，并且能够在不同物种之间相互补充功能。对这些蛋白的转运功能和细胞定位的初步表征表明，OSTalpha-OSTbeta是胆汁酸和其他类固醇在肠道、肾脏和其他上皮组织中重吸收的关键调节剂。转运的底物包括3-硫酸雌酮、3-硫酸脱氢表雄酮、牛磺胆酸盐、地高辛和前列腺素E2，表明在关键细胞代谢物或信号分子的处置中起作用。这些初步研究与OSTalpha-OSTbetaa是一种异质转运蛋白的假设是一致的，该转运蛋白定位于关键上皮组织的基底外膜，并调节类固醇衍生分子的配置。为了验证这一假设，拟议的研究旨在：(1)确定OSTalpha和OSTbeta的组织表达、细胞和亚细胞分布；(2)生成Osta敲除小鼠并对其进行功能表征；(3)检查OSTalpha和OSTbeta是否形成异二聚体或异多聚体；(4)确定OSTalpha和OSTbeta蛋白的区域，这些区域对质膜传递和/或运输活性的功能表达至关重要。总的来说，这些研究应该为这种新型转运体调节哺乳动物胆汁酸和类固醇稳态的机制提供基础信息。

DESCRIPTION (provided by applicant): All cell functions ultimately depend on the regulated movement of chemicals across the plasma membrane. Although recent studies have described some of the genes involved in these transport processes, it is clear that many other essential gene products remain to be identified and characterized. Using a comparative approach, we recently cloned and functionally characterized a new type of organic solute and steroid transporter (OST) from skate, mouse, and human genomes. This transporter is generated by co-expression of two unique gene products, organic solute transporter-alpha and -beta (OSTalpha, OSTbeta). In contrast with most other transporters that are members of gene families, OSTalpha and OSTbeta do not have homologues in the mouse or human genomes. Moreover, these genes are evolutionary conserved and are able to functionally complement each other across species. Preliminary characterization of the transport function and cellular localization of the proteins suggests that OSTalpha-OSTbeta is a critical regulator of the reabsorption of bile acids and other steroids in the intestine, kidney, and other epithelial tissues. Transported substrates include estrone 3-sulfate, dehydroepiandrosterone 3-sulfate, taurocholate, digoxin, and prostaglandin E2, indicating a role in the disposition of key cellular metabolites or signaling molecules. These preliminary studies are consistent with the hypothesis that OSTalpha-OSTbetaa is a heteromeric transporter that is localized to the basolateral membrane of key epithelial tissues, and serves to regulate the disposition of steroid-derived molecules. To test this hypothesis the proposed studies aim to: (1) Define the tissue expression, and cellular and sub-cellular distribution of OSTalpha and OSTbeta, (2) Generate and functionally characterize Osta knockout mice, (3) Examine whether OSTalpha and OSTbeta are forming heterodimers or heteromultimers, and (4) Identify the regions of the OSTalpha and OSTbeta proteins that are critical for plasma membrane delivery and/or functional expression of transport activity. Overall, these studies should provide fundamental information on the mechanisms by which this novel transporter regulates bile acid and steroid homeostasis in mammals.