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

描述(由申请人提供)：所有细胞功能最终依赖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参与这些运输过程的一些基因，但很明显，还有许多其他重要的基因产物仍有待鉴定和表征。采用比较的方法，我们最近从溜冰鞋、小鼠和人类基因组中克隆并鉴定了一种新型的有机溶质和类固醇转运蛋白(OST)。这种转运蛋白是由两种独特的基因产物-有机溶质转运蛋白-α和-β(OSTpha，OSTbeta)共同表达而产生的。与大多数其他属于基因家族成员的转运蛋白不同，OSTpha和OSTbeta在小鼠或人类基因组中没有同源基因。此外，这些基因在进化上是保守的，能够在不同物种之间在功能上相互补充。对这些蛋白的转运功能和细胞定位的初步表征表明，OSTpha-OSTbeta是肠、肾和其他上皮组织中胆汁酸和其他类固醇重吸收的关键调节因子。转运的底物包括雌酮3-硫酸酯、脱氢表雄酮3-硫酸酯、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发挥作用。这些初步研究与OSTpha-OSTbetaa是一种异构体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膜，并用于调节类固醇衍生分子的处置。为了验证这一假说，建议的研究旨在：(1)确定OSTpha和OSTbeta的组织表达、细胞和亚细胞分布，(2)建立OstA基因敲除小鼠并对其进行功能鉴定，(3)检查OSTpha和OSTbeta是否形成异二聚体或异多聚体，以及(4)确定OSTpha和OSTbeta蛋白中对质膜递送和/或转运活性的功能表达至关重要的区域。总体而言，这些研究应该提供关于这种新型转运蛋白调节哺乳动物胆汁酸和类固醇稳态的机制的基本信息。

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.