Downregulation of miR-217 correlates with resistance of Ph(+) leukemia cells to ABL tyrosine kinase inhibitors.
Bottom Line: This study found that long-term exposure of chronic myelogenous leukemia (CML) K562 cells to BCR/ABL thyrosine kinase inhibitors (TKI) caused drug-resistance in association with an increase in levels of DNA methyltransferases (DNMT) and a decrease in levels of microRNA miR-217.Further studies with TKI-resistant K562 cells found that forced expression of miR-217 inhibited expression of DNMT3A through a miR-217-binding site within the 3'-untranslated region of DNMT3A and sensitized these cells to growth inhibition mediated by the TKI.In addition, a decrease in levels of DNMT3A and an increase in levels of miR-217 were noted in K562 tumors growing in immune-deficient mice that were treated with the combination of 5-AzadC and dasatinib.
Affiliation: Department of Hematology and Respiratory Medicine, Kochi Medical School, Kochi University, Nankoku, Japan.Show MeSH
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Mentions: Exposure of CEL cells to low concentration of nilotinib (10 nM, 96 h) or dasatinib (1 nM, 96 h) increased the levels of DNMT proteins.6 Similarly, exposure of K562 cells to low concentration of dasatinib (1 nM, 48–96 h) or nilotinib (10 nM, 48–96 h) increased the levels of DNMT (DNMT1, DNMT3A and DNMT3B) (data not shown). This dose of dasatinib (1 nM, 96 h) or nilotinib (10 nM, 96 h) was not able to inhibit the proliferation of these cells (data not shown). However, exposure of K562 cells to 10-fold higher concentration of dasatinib (10 nM, 96 h) or nilotinib (100 nM, 96 h) inhibited the proliferation of K562 cells and decreased levels of DNMT1 and DNMT3A (Fig.1a,b), but not DNMT3B (data not shown). Intriguingly, when K562 cells were cultured in the presence of this dose of TKI (dasatinib 10 nM, nilotinib 100 nM) for a long period, up to 12 months, these cells lost sensitivity to TKI. In parallel, levels of DNMT1 and DNMT3A were elevated (Fig.1c,d). We next compared the DNA methylation status on the promoter regions of cell cycle regulator and proapoptotic genes between K562 and dasatinib-resistant K562 (K562DR) cells by using methylation-specific PCR. It was found that DNA methylaton on the promoter region of p21waf1 and BAX was increased in K562DR cells as compared with that in K562 cells (Fig. S1).
Affiliation: Department of Hematology and Respiratory Medicine, Kochi Medical School, Kochi University, Nankoku, Japan.