Yoshida H, Haze K, Yanagi H, Yura T, Mori K
HSP Research Institute, Kyoto Research Park, Kyoto 600-8813, Japan.
J Biol Chem. 1998 Dec 11;273(50):33741-9. doi: 10.1074/jbc.273.50.33741.
When unfolded proteins accumulate in the endoplasmic reticulum (ER), transcription of glucose-regulated proteins (GRPs) representing ER-resident molecular chaperones is markedly induced via the unfolded protein response (UPR) pathway. In contrast to recent progress in the analysis of yeast UPR, both cis-acting elements and transactivators responsible for mammalian UPR have remained obscure. Here, we analyzed the promoter regions of human GRP78, GRP94, and calreticulin genes and identified a novel element designated the ER stress response element (ERSE). ERSE, with a consensus of CCAATN9CCACG, was shown to be necessary and sufficient for induction of these GRPs. Using yeast one-hybrid screening, we isolated a human cDNA encoding a basic leucine zipper (bZIP) protein, ATF6, as a putative ERSE-binding protein. When overexpressed in HeLa cells, ATF6 enhanced transcription of GRP genes in an ERSE-dependent manner, whereas CREB-RP, another bZIP protein closely related to ATF6, specifically inhibited GRP induction. Endogenous ATF6 constitutively expressed as a 90-kDa protein was converted to a 50-kDa protein in ER-stressed cells, which appeared to be important for the cellular response to ER stress. These results suggest that, as in yeast, bZIP proteins are involved in mammalian UPR, acting through newly defined ERSE.
当未折叠蛋白在内质网（ER）中积累时，代表内质网驻留分子伴侣的葡萄糖调节蛋白（GRP）的转录通过未折叠蛋白反应（UPR）途径被显著诱导。与酵母UPR分析的最新进展相反，负责哺乳动物UPR的顺式作用元件和反式激活因子仍然不清楚。在这里，我们分析了人类GRP78、GRP94和钙网蛋白基因的启动子区域，并鉴定出一个新的元件，称为内质网应激反应元件（ERSE）。ERSE的共有序列为CCAATN9CCACG，已证明它对于诱导这些GRP是必要且充分的。通过酵母单杂交筛选，我们分离出一个编码碱性亮氨酸拉链（bZIP）蛋白ATF6的人类cDNA，作为一种假定的ERSE结合蛋白。当在HeLa细胞中过表达时，ATF6以ERSE依赖的方式增强GRP基因的转录，而与ATF6密切相关的另一种bZIP蛋白CREB-RP则特异性抑制GRP的诱导。在内质网应激细胞中，内源性ATF6以90 kDa蛋白的形式组成性表达，转化为50 kDa蛋白，这似乎对细胞对内质网应激的反应很重要。这些结果表明，与酵母一样，bZIP蛋白通过新定义的ERSE参与哺乳动物的UPR。
