Upregulation of Mir-29 in Normal Karyotype Aml Showing Dnmt3a Mutation - Abstract
Background: Acute myeloid leukemia (AML) represents a heterogeneous disorder with recurrent chromosomal alterations and molecular abnormalities. A number of molecular abnormalities have been described involving several genes such as FLT3, NPM1, CEBPA, IDH1, IDH2 and DNMT3A among AML with normal kariotype (NK-AML). DNMT3A, a member of DNA methyltransferases, is mutated in approximately 22% of de novo NK-AML; the mutation at codon R882 (R882-DNMT3A mutations) confers unfavorable outcome in this setting. Our previous data demonstrated distinctive miRNA expression patterns in some genetic groups, the aim of the study is to investigate about the miRNA profile and its role in the pathogenesis of DNMT3A mutated AML.
Methods and Results: To indagate about miRNA signature in NK-AML R882-DNMT3A mutated we performed quantitative real-time PCR (TaqMan Human MicroRNA Array, A); we studied the expression of 365 known human miRNA in 9 selected de-novo AML cases showing DNMT3A mutations. We compare miRNA expression data with our previous results obtained in 31 AML DNMT3A unmutated and we focused on an up-regulation of mir-29 family: miR-29a, miR-29b and miR-29c. So we decide to investigate expression levels of these miRNAs in additional 50 new DNMT3A mutated AML patients and we confirm the up-regulation of 2 of them: miR-29a and miR-29c. The most interesting issue is that miR-29s have been demonstrated to directly target 3’-UTR of DNMT3A and DNMT3B resulting in a global hypomethylation but also miR-29s is able to directly suppress the major DNA demethylases, TET1 and TDG. In order to better understand the pathogenesis of the subgroup of AML DNMT3A mutated and the existing correlation between miR-29s and its targets, we evaluated the expression levels of miR-29s targets DNMT3A, DNMT3B, TET1, TET2 and TDG in 50 AML DNMT3A mutated patients and in 50 patients AML DNMT3A wild type (control group) using qRT-PCR with specific TaqMan assay (Applied Biosystems). Results obtained revealed a no significant differences in expression of DNMT3A, DNMT3B and TDG; however we found significant down-regulation of the demethylases TET1 and TET2.
Conclusion: These data suggest that miR-29s act as crucial regulators of DNA methylation and probably in presence of DNMT3A mutations and TET1 down-regulation may cause a perturbation of methylation pattern. This issue may have important implications for treatment and response to hypomethylating drugs in patients affected by alterations in DNMT3A.