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穿过质膜的受调节运动。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，许多其他必需的基因产物仍有待鉴定和表征。使用比较的方法，我们最近克隆和功能特点的一种新型的有机溶质和类固醇转运蛋白（OST）从滑冰，小鼠和人类基因组。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（OST α，OST β）的共表达产生的。与基因家族成员的大多数其他转运蛋白相比，OST α和OST β在小鼠或人类基因组中没有同源物。此外，这些基因在进化上是保守的，并且能够在不同物种之间进行功能互补。蛋白质的转运功能和细胞定位的初步表征表明，OST α-OST β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剂。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起作用。这些初步研究与以下假设一致，即OST α-OST β a是一种异聚体转运蛋白，定位于关键上皮组织的基底外侧膜，并用于调节类固醇衍生分子的分布。为了验证这一假设，拟议的研究旨在：（1）确定OST α和OST β的组织表达以及细胞和亚细胞分布，（2）产生并功能性表征Osta敲除小鼠，（3）检查OST α和OST β是否形成异源二聚体或异源多聚体，和（4）鉴定对于质膜递送和/或转运活性的功能性表达至关重要的OST α和OST β蛋白的区域。总的来说，这些研究应该提供基本的信息，这种新的转运蛋白调节哺乳动物的胆汁酸和类固醇体内平衡的机制。

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.