A Rice Transmembrane bZIP Transcription Factor, OsbZIP39, Regulates the Endoplasmic Reticulum Stress Response
A Rice Transmembrane bZIP Transcription Factor, OsbZIP39, Regulates the Endoplasmic Reticulum Stress Response
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DOI：
10.1093/pcp/pcr157
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发表时间：
2012-01-01
影响因子：
4.9
通讯作者：
Takaiwa, Fumio
中科院分区：
文献类型：
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作者：
Takahashi, Hideyuki;Kawakatsu, Taiji;Takaiwa, Fumio
内质网（ER）通过激活细胞内信号转导途径对未折叠蛋白在其内腔中的积累（ER应激）作出反应。这些途径被称为ER应激反应或未折叠蛋白反应。在这项研究中，三个水稻碱性亮氨酸拉链（bZIP）转录因子（OsbZIP 39，OsbZIP 50和OsbZIP 60）含有推定的跨膜结构域（TMDs）在其C-末端区域被确定为ER压力传感器换能器的候选人。其中一种蛋白OsbZIP 39在本研究中进行了表征。OsbZIP 39被证明与微粒体作为一个膜整合的蛋白质，使用亚细胞分级分离方法。当OsbZIP 39的全长和不含TMD的截短形式（OsbZIP 39 delta C）与绿色荧光蛋白（GFP）融合并转染到水稻原生质体中时，分别在细胞质和细胞核中鉴定出蛋白质。这表明OsbZIP 39可以通过蛋白水解切割转化为可溶性截短形式，随后易位至细胞核。OsbZIP 39 delta C的表达在水稻原生质体瞬时测定中明显激活了结合蛋白1（BiP 1）启动子。OsbZIP 39 delta C在稳定转基因水稻中的过表达也导致了在缺乏ER胁迫的情况下包括BiP 1和OsbZIP 50在内的几个ER胁迫响应基因的上调。然而，在OsbZIP 39 delta C过表达系中，OsbZIP 50 mRNA不经历IRE 1（肌醇需要蛋白1）介导的胞质剪接，这是其激活所必需的。这些数据表明，OsbZIP 39可能直接参与了几个ER应激反应基因的调控。
The endoplasmic reticulum (ER) responds to the accumulation of unfolded proteins in its lumen (ER stress) by activating intracellular signal transduction pathways. These pathways are known as the ER stress response or the unfolded protein response. In this study, three rice basic leucine zipper (bZIP) transcription factors (OsbZIP39, OsbZIP50 and OsbZIP60) containing putative transmembrane domains (TMDs) in their C-terminal regions were identified as candidates of the ER stress sensor transducer. One of these proteins, OsbZIP39, was characterized in this study. OsbZIP39 was shown to associate with microsomes as a membrane-integrated protein using the subcellular fractionation method. When the full length and a truncated form of OsbZIP39 without the TMD (OsbZIP39 delta C) was fused to green fluorescent protein (GFP) and transfected into rice protoplasts, the proteins were identified in the cytoplasm and nucleus, respectively. This suggests that OsbZIP39 may be converted into a soluble truncated form by proteolytic cleavage and subsequently translocated to the nucleus. Expression of OsbZIP39 delta C clearly activated the binding protein 1 (BiP1) promoter in a rice protoplast transient assay. Overexpression of OsbZIP39 delta C in stable transgenic rice also led to the up-regulation of several ER stress response genes including BiP1 and OsbZIP50 in the absence of ER stress. However, in the OsbZIP39 delta C-overexpressing line, OsbZIP50 mRNA did not undergo IRE1 (inositol-requiring protein 1)-mediated cytoplasmic splicing that is required for its activation. These data indicate that OsbZIP39 may be directly involved in the regulation of several ER stress response genes.