Mammalian Zinc Transporters and Zinc Homeostasis

描述（由申请人提供）：随着我们对模式生物（如酵母）中锌稳态的了解越来越详细，我们对人体细胞中锌稳态的许多基本方面仍然知之甚少。为了解决这些问题，我们将研究重点放在了SLC39A13基因的产物Zip13上。Zip13是金属离子转运蛋白ZIP家族的一员。令人惊讶的是，SLC39A13的突变最近被确定为导致一种形式的ehers - danlos综合征（EDS），一种由胶原蛋白修饰和组装缺陷引起的结缔组织疾病。考虑到Zip13和EDS之间的这种有趣的联系，我们对金属离子转运体如何导致这种疾病很感兴趣。在初步实验中，我们发现Zip13是一种锌特异性转运蛋白，定位于多种人类细胞类型的囊泡细胞器。这些囊泡的身份尚不清楚。我们提出假设，这些囊泡是锌的储存地点，Zip13负责在锌缺乏的情况下将这些储存的锌从这些隔室中运输出来。我们进一步假设，在SLC39A13突变的EDS患者中发现的胶原组装缺陷是由于内质网锌缺乏造成的，这是由于锌在其储存细胞器中被捕获。为了验证这些假设，我们将a)评估Zip13对细胞锌稳态的影响，b)确定Zip13破坏对内质网功能、胶原羟基化和内质网锌状态的影响，以及c)确定Zip13是否共定位于锌酶体，锌酶体是锌储存的泡状部位。对这些目标的追求提供了一个独特的机会来评估哺乳动物锌稳态中囊泡锌储存的功能。Zip13可能为鉴定哺乳动物细胞中锌储存的细胞器位点和表征它们的功能提供了第一个分子柄。

DESCRIPTION (provided by applicant): As our understanding of zinc homeostasis in model organisms such as yeast becomes increasingly detailed, we still know very little about many basic aspects of zinc homeostasis in human cells. To address some of these questions, we have focused our studies on Zip13, the product of the SLC39A13 gene. Zip13 is a member of the ZIP family of metal ion transporters. Surprisingly, mutations in SLC39A13 were recently identified as causing a form of Ehlers-Danlos Syndrome (EDS), a connective tissue disease that results from defects in collagen modification and assembly. Given this intriguing link between Zip13 and EDS, it was of interest to us how a metal ion transporter contributes to this disease. In preliminary experiments, we have found that Zip13 is a zinc-specific transporter that localizes to a vesicular organelle in a wide variety of human cell types. The identity of these vesicles is not yet known. We propose the hypothesis that these vesicles are storage sites for zinc and that Zip13 is responsible for transporting this stored zinc out of those compartments under conditions of zinc deficiency. We further hypothesize that the defects in collagen assembly seen in EDS patients with SLC39A13 mutations result from ER zinc deficiency due to the trapping of zinc within its storage organelle. To test these hypotheses, we will a) assess the impact of Zip13 on cellular zinc homeostasis, b) determine the effect of Zip13 disruption on ER function, collagen hydroxylation, and ER zinc status, and c) determine whether Zip13 co-localizes to the zincosome, a vesicular site of zinc storage. Pursuit of these aims provides a unique opportunity to assess the function of vesicular zinc storage in mammalian zinc homeostasis. Zip13 may provide the first molecular handle with which to identify the organellar sites of zinc storage and characterize their function in mammalian cells. PUBLIC HEALTH RELEVANCE: The processes of intracellular zinc transport and homeostasis are essential for basic cellular function, physiology, and human health. Despite this importance, however, we still know little about the specific transporter proteins involved and how they function in maintaining zinc homeostasis in human cells. This proposal is focused on Zip13, a zinc transporter recently linked to some cases of Ehlers-Danlos Syndrome, and the role this protein plays in controlling the vesicular storage of zinc.