MAPK pathways control the cellular processes such as proliferation, differentiation and apoptosis. Abnormal MAPK signaling plays a key role in the development and progression of cancers. The dual-specificity MAPK phosphatases (DUSPs) act as negative regulators of MAPK activity in normal tissues. DUSP1 (dual-specificity MAPK phosphatase-1) is able to inactivate the ERK, p38, and JNK in resulting the cell cycle and apoptosis, and it has been reported to be lost in a variety advanced cancers. However, its function is little known in CML cells. In this study, we have investigated the function of DUSP1 in CML cell proliferation.
The cells used in this study were human CML cell lines, K562, Meg01 and SHG3 cells. Primary CML cells (ALDHhi cells) were obtained from the bone marrow of CML (CP) patients (n=12). Human normal ALDHhi cells were isolated from bone marrow of healthy volunteers after obtaining informed consents. For analysis of DUSP1 mRNA expression, quantitative RT-PCR was performed in all cell lines treated with Abl kinase inhibitors (STI571, AMN107, and BMS354825). For cell survival analysis and the levels of p-ERK1/2, p-p38, and p-ATF2 in CML cells, MTT assays, western blot and cell cycle analysis were performed in all cell lines transfected with DUSP1 shRNA or cDNA. For colony analysis, the colonies of CFU-GEMM, CFU-GM, and BFU-E were counted in CML stem/progenitor cells transfected with DUSP1 cDNA or shiRNA, or treated with Abl kinase inhibitors.
In CML cell lines, the expressions of DUSP1 mRNA and protein were significantly increased by treatment with Abl kinase inhibitors or transfection with Bcr-Abl shRNA. In CML cells treated with Abl kinase inhibitors or transfection with Bcr-Abl shRNA, CML cell proliferation was inhibited, and the phosphorylation levels of p-ERK1/2, p-p38, and p-ATF2 were markedly decreased compared to the untreated cells.
In addition, the overexpression of DUSP1 induced G1 cell cycle arrest indicating down regulation of cyclin D1 expression in CML cells. Moreover, in CML cells transfected with DUSP1 shRNA, the inhibition of CML cell proliferation by the Abl kinase inhibitors were weakened. In CML stem/progenitor cells (ALDHhi cells) obtained from patients with CML, the expression of DUSP1 mRNA was suppressed, and the transfection with Bcr-Abl shRNA or treatment with Abl kinase inhibitors increased the expression of DUSP1 mRNA and protein, and decreased the counts of CFU-GEMM, CFU-GM and BFU-E.
Our results demonstrated that the expression of DUSP1 was suppressed by Bcr-Abl in CML cells, and the depletion of DUSP1 promotes cell cycle progression through the induction of cyclin D1 expression, and stimulates CML cell proliferation through the continuous phosphorylation of ERK1/2, p38, and ATF2. Moreover, the induction of DUSP1 expression inhibited the proliferation of CML stem/progenitor cells.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.