G-CSF Upregulates the Expression of Aquaporin-9 through C/EBP-Beta to Enhance the Cytotoxic Activity of Arsenic Trioxide to Acute Myeloid Leukemia Cells

Arsenic trioxide (ATO) is the first-line drug for the treatment of acute promyelocytic leukemia (APL). Aquaporin-9 (AQP9), a transmembrane transporter, is required for leukemia cells to uptake ATO. APL cells express high levels of AQP9, while other types of acute myeloid leukemia (AML) cells express much lower levels of AQP9, which limits the transportation and the cytotoxic activity of ATO in those types of leukemia. Recently, we found that granulocyte colony stimulating factor (G-CSF) can significantly upregulate the expression of AQP9 in AML cell lines (THP-1 and HL-60), and can significantly enhance the intracellular concentrations of ATO, when compared with the treatment with ATO alone. We also found that the combination of ATO and G-CSF inhibited the cell proliferation and induced cell apoptosis more significantly than the treatment with ATO or G-CSF alone. The overexpression of AQP9 with lentivirus in HL-60 or THP-1 cells significantly enhanced the cytotoxic activity of ATO, while the knock-down of AQP9 gene with small interfering RNA (siRNA) significantly attenuated the combination effect of G-CSF and ATO. Moreover, we found that the upregulation of AQP9 by G-CSF depends on the upregulation of C/EBP-beta, the transcription factor downstream of G-CSF. In conclusion, our study suggests that the pretreatment of G-CSF could significantly enhance the cytotoxic activity of ATO in AML cells through the upregulation of AQP9, and that the combination of G-CSF and ATO would be a potential therapeutic strategy for AML patients.