人类XBP1基因5′上游DNA序列的转录激活功能分析

摘要

Objective To analyze the transcription activation and possible regulation mechanism of human X-box binding protein 1 (XBP1) gene 5′upstream DNA sequence in different cell lines. Methods Six kinds of XBP1 promoter deletion mutants were cloned into pGEM-Teasy vector, which included XBP1 gene 5′ upstream -1039 to 66 bp,-859 to 66 bp,-623 to 66 bp,-351 to 66 bp,-227 to 66 bp,-227 to -45 bp respectively. Every deletion mutant sequence was cut from Teasy-XBP1p by Kpn Ⅰ and Xho Ⅰ, and subcloned into pCAT3-Basic to produce a set of constructs termed as p1-XBP1p, p2-XBP1p, p3-XBP1p, p4-XBP1p, p5-XBP1p, p6-XBP1p, respectively. The transcription activity of each construct was detected after transiently transfecting K562, HepG2,NIH-3T3 and L02 cell with FuGENE 6 transfection reagent. Cells transfected by pCAT3-Basic or pCAT3-Promoter were used as negative and positive controls. The activity of chloramphenicol acetyltransferase(CAT), which reflects the transcription activation of the XBP1 gene promoter, was detected by ELISA after 48 hours of transfection. Results The reporter vectors of six kinds ofXBP1 promoter deletion mutants were successfully constructed, as confirmed by restriction enzyme digestion and sequencing. The activities of p4-XBP1p and p5-XBP1p were higher than the other deletion mutants in K562 and HepG2. And the activity of p5-XBP1p was the highest in HepG2. There was no activity detected from any transfected NIH-3T3. Conclusion The XBP1 gene promoter can transactivate its downstream gene to transcription. The core sequence ofXBP1 promoter was implied between -227 bp and 66 bp. This sequence was connected with the transcriptional activity ofXBP1 promoter closely. Its transcription activity varies with different cell lines.XBP1 promoter might drive gene expression with cell-type specificity.%目的分析人类转录因子X-盒结合蛋白1(X-box binding protein Ⅰ,XBP1)基因启动子在不同细胞系中转录活性的差别,研究其转录调控机制. 方法在对XBP1基因进行生物信息学分析的基础上,设计6种XBP1启动子缺失突变体,分别包括XBP1基因5′上游-1039～66 bp、-859～66 bp、-623～66 bp、-351～66 bp,-227～66 bp、-227～-45 bp,针对每一种缺失突变体构建相应的氯霉素乙酰转移酶(chloramphenicol acetyltansferase, CAT)报告基因载体,再分别瞬时转染K562、HepG2、NIH-3T3和L02细胞,应用报告基因CAT瞬时表达系统,检测XBP1每一种缺失突变体在K562、HepG2、NIH-3T3和L02 4种不同细胞中的活性差异,并进一步确定XBP1基因启动子的具体调节部位. 结果成功获得XBP1基因启动子6种缺失突变体的正确克隆和6种相应的报告基因载体p1-XBP1p,p2-XBP1p, p3-XBP1p, p4-XBP1p, p5-XBP1p, p6-XBP1p,每一种报告基因转染K562、HepG2、NIH-3T3和L02 4种不同细胞系后,p4-XBP1p和p5-XBP1p在K562、HepG2细胞中的转录活性均高于其它报告载澹琾5-XBP1p在HepG2细胞中转录活性最高;而6种报告基因载体在NIH-3T3小鼠成纤维细胞中不具有转录活性. 结论 XBP1基因的转录激活能力在不同细胞中有所差异,其表达活性具有一定的细胞类型特异性,与细胞类型和细胞状态密切相关;XBP1基因启动子的-227～66 bp区域是该启动子的核心部位,而且核心启动子区包括ATG翻译起始密码子的下游部位,这一部位是转录活性的重要部位,一旦缺失,XBP1基因启动子会丧失活性.