Abstract
BackgroundSTAT5 plays an important role in the transformation of hematopoietic cells by BCR-ABL. However, the downstream target genes activated by STAT5 in chronic myeloid leukemia (CML) cells remain largely unclear. Here, we investigated the mechanistic functional relationship between STAT5A-regulated microRNA and CML cell apoptosis.MethodsThe expression of USP15, Caspase-6, STAT5A-regulated miR-202-5p and STAT5A was detected by qRT-PCR and Western blotting in CML cell lines and PBMCs of CML patients. Cell apoptosis was evaluated by flow cytometry. Both gain- and loss-of-function experiments were used to investigate the roles of USP15, miR-202-5p and STAT5A in CML. Luciferase reporter assay detected the effect of miR-202-5p on USP15 expression. Xenograft animal model was used to test the effect of anti-miR-202-5p and pimozide on K562 cell xenograft growth.ResultsUSP15 expression was significantly downregulated in CML cell lines and PBMCs of CML patients. Depletion of USP15 increased, whereas overexpression of USP15 reduced the resistance of CML cells to Imatinib. Further, decreased deubiquitinating activity of USP15 by USP15 downregulation led to reduced caspase-6 level, thus attenuating CML cell apoptosis. Mechanistically, miR-202-5p was upregulated in K562G cells and negatively regulated USP15 expression by directly targeting USP15 3′-UTR. Correspondingly, upregulation of miR-202-5p enhanced the resistance of CML cells to Imatinib by inhibiting cell apoptosis. Importantly, STAT5A was upregulated in CML cells and directly activated miR-202-5p transcription by binding to the pre-miR-202 promoter. Pimozide induced CML cell apoptosis and significantly reduced K562 cell xenograft growth in vivo by blocking STAT5A/miR-202-5p/USP15/Caspase-6 regulatory axis.Conclusionswe provide the first evidence that de-regulated STAT5A/miR-202-5p/USP15/Caspase-6 regulatory axis suppresses the apoptosis of CML cells, targeting this pathway might be a promising therapeutic approach for the treatment of CML.
Highlights
STAT5 plays an important role in the transformation of hematopoietic cells by BCR-ABL
The results showed that the expression of ubiquitin-specific peptidase 15 (USP15) was dramatically downregulated in acute leukemia including Acute Myeloid Leukemia (AML) and Acute Lymphoblastic Leukemia (ALL)comparing to the matched normal cells
A decreased USP15 expression was found in chronic myeloid leukemia (CML) but there was no significant difference between healthy donors and CML patients (Additional file 1: Fig. S1)
Summary
STAT5 plays an important role in the transformation of hematopoietic cells by BCR-ABL. The downstream target genes activated by STAT5 in chronic myeloid leukemia (CML) cells remain largely unclear. We investigated the mechanistic functional relationship between STAT5A-regulated microRNA and CML cell apoptosis. Chronic myeloid leukemia (CML) is a clonal disease of pluripotent hematopoietic cells characterized by the expression of the BCR/ABL1 fusion gene, which encodes a constitutively active tyrosine kinase BCR-ABL [1, 2]. The elevated activity of BCR-ABL tyrosine kinase initiates CML and approximately 30% of acute lymphoblastic leukemia (ALL) by stimulating proliferation signals, such as Ras, phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) and signal transducer and activator of transcriptions (STATs) as well as by inhibiting apoptosis signals, such as Ras-dependent signaling pathway [3, 4]. The mechanistic and functional links among STAT5-regulated microRNA, USP15 and target protein of USP15 in CML cells remain poorly understood
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