Analysis of unfolded protein response in hematological malignancy

未折叠蛋白反应(UPR)在多种肿瘤中被激活，并可能在肿瘤生长中发挥关键作用。然而，UPR在白血病中的作用仍不清楚。因此，为了明确UPR在白血病发生中的作用，我们研究了表达有代表性的癌基因BCR-Abl(B-A)的细胞系中UPR的激活。B-A组UPR相关蛋白X盒结合蛋白(XBP1)、葡萄糖调节蛋白78(GRP78)和磷酸化真核细胞翻译起始因子2α(eIF2α)表达增加。利用荧光素酶分析，我们观察到bcr-Abl诱导了顺式作用的UPR元件的高水平转录活性。此外，与UPR相关的基因，即剪接形式的XBPI、GRP78和RNA依赖的蛋白激酶的细胞抑制物p58IPK，在B-A中的mRNA水平增加。用肌醇需要酶Lα(IRE1α)或激活转录因子6(ATF6)显性-阴性突变体抑制UPR，可减弱bcr-Abl对依托泊苷和伊马替尼诱导的细胞凋亡的保护作用，但对bcr-abl转化细胞的增殖无影响。定量逆转录聚合酶链式反应检测发现，Ph阳性原代白血病细胞中UPR相关基因的表达明显高于对照组。因此，我们的结果提示，UPR是bcr-Abl的下游靶点，并且在Ph阳性白血病细胞中发挥bcr-Abl的抗凋亡作用。

The unfolded protein response (UPR) is activated in various tumors and may play a crucial role in tumor growth. However, the role of the UPR in leukemia remains unclear. Therefore, to define the role of the UPR in leukemogenesis, we investigated UPR activation in a cell line expressing the representative oncogene Bcr-Abl (B-A). The expression of UPR-related proteins, namely, X-box-binding protein (XBP1) and glucose-regulated protein 78 (GRP78), and of phosphorylated eukaryotic translation initiation factor 2α (eIF2α) was increased in B-A. Using a luciferase assay, we observed that Bcr-Abl induced high levels of the transcriptional activity of the cis-acting UPR element. Moreover, the mRNA levels of the UPR-related genes, namely, spliced form of XBPI; GRP78; and p58IPK, a cellular inhibitor of the RNA-dependent protein kinase, increased in B-A. UPR inhibition using inositol-requiring enzyme lα (IRE1α) or activating transcription factor 6 (ATF6) dominant-negative mutants diminished the ability of Bcr-Abl to protect the cells from etoposide- and imatinib-induced apoptosis; however, it had no effect on the proliferation of Bcr-Abl-transformed cells. We also noted that the expression of UPR-related genes in primary leukemia cells from Philadelphia chromosome (Ph) -positive cells was higher than that in the control by quantitative reverse transcription-polymerase chain reaction assay. Thus, our results suggested that UPR is a downstream target of Bcr-Abl and plays an anti-apoptotic role of Bcr-Abl in Ph-positive leukemia cells.