BiP调控IRE1启动子转录活性及蛋白表达的效应

The effect on BiP regulation of IRE1 promoter transcription activity and protein expression

正常条件下,外分泌或者跨膜的蛋白需要在内质网中完成正确的折叠。在营养缺乏、分化或其他应激状态下,内质网中的蛋白质会发生错误折叠并不断积聚,形成内质网应激(Endoplasmic reticulum stress),引发未折叠蛋白反应(Unfolded protein response)。内质网应激条件下,内质网腔中的分子伴侣结合免疫球蛋白BiP(Binding immunoglobulin protein)与需肌醇酶IRE1(Inositol-requiring kinase 1)解离并与未折叠蛋白结合从而帮助蛋白形成正确结构;同时未折叠蛋白通过与跨膜蛋白IRE1直接结合活化其内切核糖核酸酶结构域,活化的IRE1能够剪切Xbp1的mRNA使其形成有活性的转录因子进而起始分子伴侣与未折叠蛋白反应相关蛋白的表达使细胞脱离内质网应激状态。文章克隆了IRE1的启动子用荧光素酶报告基因法检测到BiP能够上调IRE1的启动子活性。通过构建IRE1启动子一系列截短体的报告基因载体确定了IRE1启动子活性的核心区域进一步通过逆转录PCR和免疫印迹在mRNA水平和蛋白水平分别检测BiP对IRE1启动子的调控作用。结果发现在内质网应激条件下分子伴侣BiP通过上调IRE1启动子转录活性增加IRE1的表达进而提高细胞处理内质网应激时未折叠蛋白的能力为揭示内质网应激条件下BiP调控IRE1转录调控机制提供理论依据,同时为阐明ER stress各信号分子之间的作用机制奠定实验基础。

Usually, secreted or transmembrane proteins complete their three-dimension folding within endoplasmic re- ticulum （ER）. Under the conditions of nutrient depletion, cell differentiation, or other stress statuses, misfolded or unfolded proteins aggregate within ER, and consequently cause ER stress and Unfolded Protein Response （UPR）. In response to ER stress, BiP （Binding immunoglobulin protein） dissociates with IREα （Inositol-requiring kinase 1） and binds to unfoldedproteins as a molecular chaperone in helping maintain their correct structure. Co-related to BiP＇s dissociation, IRElct oglimerizes and activated its endoribonuclease domain by transautophosphorylation. Activated IRElc~ then, by cleaving mRNA of Xbp 1 and activating its transcription activity, triggers UPR. In this paper, in order to determine effect of BiP on transcription activity of IRElct, we cloned promoter region of IREI^t into reporter gene analysis vector and found that BiP could upregulate promoter activity of IRElct. Then, we constructed another 6 truncated promoter reporter vectors of IRElct and pinpoint the core promoter activity region. Furthermore, both our RT-PCR and Western blot results showed that BiP could upregulate mRNA transcription level and protein expression level of IRElct. Base on these findings, we can propose that, in order to alleviate ER stress caused by the misfolded or malfolded proteins, BiP could upregulate expression of IRElct by increase its promoter activity. This study may suggest a novel signal pathway on IRElct regulation in ER stress.