Department of Nutritional Sciences, University of Wisconsin-Madison, 1415 Linden Drive, Madison, WI 53706, USA.
Biochem J. 2011 Apr 1;435(1):259-66. doi: 10.1042/BJ20102003.
The Msc2 and Zrg17 proteins of Saccharomyces cerevisiae are members of the cation diffusion facilitator family of zinc transporters. These proteins form heteromeric complexes that transport zinc into the ER (endoplasmic reticulum). Previous studies suggested that the ZRG17 gene is regulated in response to zinc status by the Zap1 transcription factor. Zap1 activates the expression of many genes in zinc-deficient cells. In the present study, we assessed whether ZRG17 is a direct Zap1 target gene. We showed that ZRG17 mRNA levels were elevated in zinc-limited cells in a Zap1-dependent manner and were also elevated in zinc-replete cells expressing a constitutively active allele of Zap1. Furthermore, Zrg17 protein levels correlated closely with mRNA levels. A candidate Zap1-binding site [ZRE (zinc-responsive element)] in the ZRG17 promoter was required for this induction. Using electrophoretic mobility-shift assays and chromatin immunoprecipitation, we demonstrated that Zap1 binds specifically to the ZRG17 ZRE both in vitro and in vivo. By using a chromosomal ZRG17 mutant with a non-functional ZRE, we found that Zap1 induction of ZRG17 is required for ER function as indicated by elevated ER stress under zinc-limited conditions. Together, these results establish that ZRG17 is a direct Zap1 target gene and its regulation has biological importance in maintaining ER function.
酿酒酵母的 Msc2 和 Zrg17 蛋白是锌转运体阳离子扩散促进因子家族的成员。这些蛋白质形成异源二聚体复合物,将锌转运到内质网 (endoplasmic reticulum)。先前的研究表明,ZRG17 基因受 Zap1 转录因子的锌状态调节。Zap1 激活锌缺乏细胞中许多基因的表达。在本研究中,我们评估了 ZRG17 是否是 Zap1 的直接靶基因。我们表明,ZRG17 mRNA 水平在锌限制细胞中以 Zap1 依赖的方式升高,并且在表达组成性激活 Zap1 等位基因的锌充足细胞中也升高。此外,Zrg17 蛋白水平与 mRNA 水平密切相关。ZRG17 启动子中的候选 Zap1 结合位点 [ZRE(锌反应元件)] 是这种诱导所必需的。通过电泳迁移率变动分析和染色质免疫沉淀,我们证明 Zap1 特异性地结合 ZRG17 ZRE 无论是在体外还是体内。通过使用具有非功能 ZRE 的染色体 ZRG17 突变体,我们发现 Zap1 诱导 ZRG17 是维持内质网功能所必需的,如在锌限制条件下内质网应激升高所表明的。总之,这些结果确立了 ZRG17 是 Zap1 的直接靶基因,其调节对维持内质网功能具有重要的生物学意义。