Human X-box binding protein 1 （XBP1）, an important transcription factor, participates in many signal transduction processes. To further investigate the biological function of XBP1, sequences of XBP1 promoter and its two deletion mutants were first determined using bioinformatic analysis. The report vectors containing XBP1 promoter and its deletion mutants were then constructed, namely, p1-XBPlp, p2-XBPlp, and p3-XBPlp. Each reporter vector was separately transfected into HepG2, L02, K562, SMMC-7721, HSF, and Lipocyte lto Cell line using FuGENE 6 transfection reagents. The activity of chloramphenicol acetyltransferase （CAT） in each group of transfected cells was detected by ELISA assay, which in turn reflects the transcription activity of the XBP1 gene promoter. The activity involving p3-XBPlp was the highest in HepG2, which was 12.4-fold of that of pCAT3-Basic. The activities of p3-XBPlp in K562 and SMMC-7721 were the second and the third highest, which were 10.9-fold and 10.0-fold of that of the pCAT3-Basic, respectively. The CAT activity in L02 was lower than that in the above-mentioned abnormal cell, and no reporter activity was detected in HSF and Ito Cell. The XBP1 transcription and expression in K562, HepG2 and SMMC-7721 were found to be higher than that in L02, HSF and Ito cells, based on the results of real-time RT-PCR and Western blot. The XBP1 transcription and expression in L02, HSF was lower, whereas that in Ito cells was totally lacking. The result was similar to that of CAT-ELISA. Therefore, the XBP1 gene promoter can drive its downstream gene expression and its activity is cell line-dependent. The core sequence of XBP1 promoter was found between -227bp and 66bp sequence. This sequence was closely associated with the transcriptional activity of XBP1 promoter.
在哺乳动物细胞,X盒结合蛋白1(X-box binding protein 1,XBP1)是一种具有重要作用的蛋白质。哺乳动物细胞中,当未折叠蛋白质在内质网蓄积时会激活一种细胞内信号转导系统,即未折叠蛋白质反应(UPR)。哺乳动物细胞定位于内质网膜的IRE1α,可通过二聚化而激活其自身的蛋白激酶及核糖核酸酶活性,从而部分地转导UPR信号。活化的IRE1α在XBP1 mRNA的两个位点对其进行切割反应,诱导一种非传统剪接反应。这种剪接反应会产生一种功能性XBP1转录因子,可作为内质网应激反应时的传感器。同时,在内质网应激反应时还有另一种转录激活因子6(ATF6)蛋白酶解系统发挥作用。
