Human AQP5 Plays a Role in the Progression of Chronic Myelogenous Leukemia (CML)

Aquaporins (AQPs) have previously been associated with increased expression in solid tumors. However, its expression in hematologic malignancies including CML has not been described yet. Here, we report the expression of AQP5 in CML cells by RT-PCR and immunohistochemistry. While normal bone marrow biopsy samples (n = 5) showed no expression of AQP5, 32% of CML patient samples (n = 41) demonstrated AQP5 expression. In addition, AQP5 expression level increased with the emergence of imatinib mesylate resistance in paired samples (p = 0.047). We have found that the overexpression of AQP5 in K562 cells resulted in increased cell proliferation. In addition, small interfering RNA (siRNA) targeting AQP5 reduced the cell proliferation rate in both K562 and LAMA84 CML cells. Moreover, by immunoblotting and flow cytometry, we show that phosphorylation of BCR-ABL1 is increased in AQP5-overexpressing CML cells and decreased in AQP5 siRNA-treated CML cells. Interestingly, caspase9 activity increased in AQP5 siRNA-treated cells. Finally, FISH showed no evidence of AQP5 gene amplification in CML from bone marrow. In summary, we report for the first time that AQP5 is overexpressed in CML cells and plays a role in promoting cell proliferation and inhibiting apoptosis. Furthermore, our findings may provide the basis for a novel CML therapy targeting AQP5.

水通道蛋白（Aquaporins, AQPs）此前被证实可在实体瘤中呈现表达上调的特征。然而，其在包括慢性髓性白血病（Chronic Myeloid Leukemia, CML）在内的血液系统恶性肿瘤中的表达情况至今尚未见报道。本研究通过逆转录聚合酶链反应（Reverse Transcription-Polymerase Chain Reaction, RT-PCR）与免疫组织化学技术，检测了CML细胞中水通道蛋白5（AQP5）的表达水平。正常骨髓活检样本（n=5）未检测到AQP5表达，而32%的CML患者样本（n=41）呈现AQP5阳性表达。此外，在配对临床样本中，随着甲磺酸伊马替尼耐药的出现，AQP5的表达水平显著升高（p=0.047）。我们进一步发现，在K562细胞中过表达AQP5可显著促进细胞增殖；同时，靶向AQP5的小干扰RNA（small interfering RNA, siRNA）可降低K562与LAMA84两种CML细胞的增殖速率。此外，通过免疫印迹（immunoblotting）与流式细胞术（flow cytometry）实验，我们证实：在AQP5过表达的CML细胞中，BCR-ABL1的磷酸化水平升高；而经AQP5 siRNA处理的CML细胞中，其磷酸化水平则显著降低。值得注意的是，经AQP5 siRNA处理的细胞中，半胱天冬酶9（caspase9）的活性显著升高。最后，荧光原位杂交（Fluorescence In Situ Hybridization, FISH）结果显示，骨髓来源的CML样本中未检测到AQP5基因扩增现象。综上，本研究首次报道了AQP5在CML细胞中过表达，且其可促进细胞增殖、抑制细胞凋亡。此外，本研究结果可为以AQP5为靶点的新型CML治疗策略提供理论基础。