BCR/ABL increases EZH2 levels which regulates XIAP expression via miRNA-219 in chronic myeloid leukemia cells

In this study, we showed that the levels of EZH2 in bone marrow mononuclear cells (BMMNCs) isolated from individuals with chronic myeloid leukemia (CML) (n=12) were significantly greater than those in BMMNCs isolated from healthy volunteers (n=6) as well as individuals with Philadelphia chromosome-negative myeloproliferative neoplasms. Lentiviral transduction of the BCR/ABL gene in Ba/F3 cells increased EZH2 levels in parallel with phosphorylation of STAT5. Notably, chromatin immunoprecipitation assays showed that STAT5A bound to a promoter region of the EZH2 gene, resulting in an increase in the transcriptional activity of EZH2 in leukemia cells. Importantly, downregulation of EZH2 by short hairpin RNAs (shRNAs) inhibited the expression of XIAP and increased the miR-219 levels associated with a decrease in hypermethylation of miR-219-1 CpG islands. Moreover, overexpression of miR-219 decreased the levels of XIAP in CML cells. Since the 3'-untranslated region (3'-UTR) of XIAP contains miR219-5p-complementary binding site, miR-219 might modulate the expression of XIAP through binding of miR-219 on the 3'-UTR of XIAP. Taken together, BCR/ABL positively regulates the expression of EZH2 via STAT5 signaling. EZH2 modulates epigenetic changes at DNA methylated regions encoding miR-219 and downregulates the level of miR-219, resulting in upregulation of XIAP.