MicroRNA-29b induces global DNA hypomethylation and tumor suppressor gene reexpression in acute myeloid leukemia by targeting directly DNMT3A and 3B and indirectly DNMT1

Abstract

Aberrant DNA hypermethylation contributes to myeloid leukemogenesis by silencing structurally normal genes involved in hematopoiesis. MicroRNAs (miRNAs) are noncoding RNAs that regulate gene expression by targeting protein-coding mRNAs. Recently, miRNAs have been shown to play a role as both targets and effectors in gene hypermethylation and silencing in malignant cells. In the current study, we showed that enforced expression of miR-29b in acute myeloid leukemia cells resulted in marked reduction of the expression of DNA methyltransferases DNMT1, DNMT3A, and DNMT3B at both RNA and protein levels. This in turn led to decrease in global DNA methylation and reexpression of p15 INK4b and ESR1 via promoter DNA hypomethylation. Although down-regulation of DNMT3A and DNMT3B was the result of a direct interaction of miR-29b with the 3 untranslated regions of these genes, no predicted miR-29b interaction sites were found in the DNMT1 IntroductionDNA methylation consists of an enzymatic addition of a methyl group at the carbon 5 position of cytosine in the context of the sequence 5Ј-cytosine-guanosine (CpG) and is mediated by DNA methyltransferases (DNMTs). 1 The promoter regions of approximately 50% of human genes contain regions of DNA with a cytosine and guanine content greater than expected (so-called CpG islands) that, once hypermethylated, mediate gene transcriptional silencing. 2 Distinct roles in genomic methylation have been reported for DNMT isoforms. Whereas DNMT1 preferentially replicates already existing methylation patterns, DNMT3A and 3B are responsible for establishing de novo methylation. 2 Silencing of structurally normal tumor suppressor genes by aberrant DNA hypermethylation has been reported in hematologic malignancies, including subsets of acute myeloid leukemia (AML). 3,4 Although the mechanisms leading to aberrant DNA hypermethylation remain to be fully elucidated, increased levels of DNMT1 and DNMT3A and 3B have been observed in malignant myeloid blasts compared with normal bone marrow (BM) mononuclear cells (MNCs), suggesting that DNMT overexpression contributes to gene promoter hypermethylation and in turn to leukemogenesis. 4 Growing evidence supports a role for microRNAs (miRNAs) as both targets and effectors in aberrant mechanisms of DNA hypermethylation. 5,6 miRNAs are noncoding RNAs of 19 to 25 nucleotides in length that regulate gene expression by inducing translational inhibition or cleavage of their target mRNAs through base pairing at partially or fully complementary sites. 7 Several groups have shown that miRNAs are altered in human malignancies and can function as tumor suppressor genes or oncogenes through expression regulation of their target genes. 7 Similar to tumor suppressor genes, miRNAs with tumor suppressor activity are often located in deleted genomic areas or are silenced by mutations or promoter hypermethylation in malignant cells. 5,[8][9][10] Saito et al recently demonstrated that miR-127 is silenced by promoter DNA hypermethylation and down-regulated in human bladder ...

MicroRNA-148a Can Regulate Runt-Related Transcription Factor 3 Gene Expression via Modulation of DNA Methyltransferase 1 in Gastric Cancer

“…Thus miR148a could downregulate DNMT expression, which decreased the methylation of RUNX3, and RUNX3 protein levels increased. Our findings are consistent with several studies that provide evidence for miRNA-induced regulation of promoter methylation through DNMTs (Braconi et al, 2010;Garzon et al, 2009;Li et al, 2012;Pan et al, 2010;Wang et al, 2012;Zhao et al, 2011).…”

“…We believe that in gastric cancer this miRNA-epigenetic feedback may further lead to the downregulation of methylation-sensitive genes, such as P16, RUNX3, and E-cadherin, through the hypermethylation of promoters. We must note that miR-152 , miR-126 (Zhao et al, 2011), and miR-29 (Garzon et al, 2009;Li et al, 2012) have also been observed to target DNMT1. Consequently, our further studies will focus on these miRNAs, which may cooperatively target DNMT1 and further regulate the expression of methylation-sensitive genes.…”

HOTAIR Epigenetically Modulates PTEN Expression via MicroRNA-29b: A Novel Mechanism in Regulation of Liver Fibrosis

“…24,25 Recent studies showed that DNMTs may be a target of miR-29 family. 26,27 Based on these, the effects of loss of HOTAIR on the miR-29 family were examined. In vivo and in vitro, HOTAIR knockdown increased miR-29b level with no effect on miR-29a and miR-29c levels ( Figures 6A and 6B).…”

NRF2-driven miR-125B1 and miR-29B1 transcriptional regulation controls a novel anti-apoptotic miRNA regulatory network for AML survival

“…18,[20][21][22][23][24][25][26][27][28] Here we examine the expression of genes listed in Supplementary Table 3 for their response to transfection of control miRNA, miR-125B antagomiR, miR-29B mimic and miR-125B antagomiR in combination with miR-29B mimic. Figure 6a shows that MYBL2, AKT2, CDK4 and SP1 are inhibited by miR-29B mimic in THP-1 cells; we also observe that AKT2 and CDK4 are further inhibited by the addition of miR-125B antagomiR.…”