miR‑29 promoter and enhancer methylation identified by pyrosequencing in Burkitt lymhoma cells: Interplay between MYC and miR‑29 regulation

Abstract

Deregulation of microRNA expression plays a significant role in several cancer types including Burkitt lymphoma (BL). MicroRNA genes may be regulated through epigenetic mechanisms, such as specific histone modifications and/or DNA methylation of CpG islands in promoter regions, or by regions that are located next to microRNA genes. Given the regulatory role of MYC in miR-29 expression, methylation as an additional mechanism for miR-29 silencing was investigated. Methylation of miR-29a/b/c in BL tumour samples and BL cell lines (BL41 and Raji) was assessed by pyrosequencing assay. BL cells were treated with 5-aza-2'-deoxicitidine (decitabine) and evaluated for miR-29a/b/c expression and methylation status. MYC, DNMT1 and DNMT3B protein expression were accessed by western blotting. For Epstein-Barr virus (EBV) microRNA (miR)-BART6 inhibition, the cells were transiently transfected with anti-BART6-5p. BL tumour samples and BL cell lines presented miR-29a/b1 and miR-29b2/c genes methylated in CpG sites located in both the promoter and enhancer regions. The treatment of BL cells with decitabine reduced methylation, induced miR-29s expression and downregulated MYC protein levels in a dose-dependent manner. Notably, inhibition of EBV miR-BART6-5p combined with decitabine enhanced miR-29 expression in an EBV-BL cell line. In conclusion, the miR-29a/b1 and miR-29b2/c genes have methylated CpG sequences at promoter and enhancer regions that may contribute to the regulation of miR-29 expression in BL tumours. The present findings indicated interplay between MYC and miR-29 regulation, highlighting the potential role of EBV-miRNAs in miR-29 regulation for BL pathogenesis.

Epigenetic Regulation of miR-92a and TET2 and Their Association in Non-Hodgkin Lymphoma

“…Aberrant methylation of levels were observed in individuals diagnosed with specific subtypes of NHL when compared to controls, BL being the most prominent. An aggressive subtype of NHL, the BL cell line Raji was identified to exhibit increased methylation in these same regions in the cell line populations, and previous studies have reported a similar increase in methylation levels to those identified in this study in other miRNA promoter regions, in both BL cell lines and BL tumours (Mazzoccoli et al, 2018;Mazzoccoli et al, 2019). Increased methylation was also observed between CLL individuals and controls in region 1 of the MIR17HG, and a previous study identified that aberrant methylation of miRNA promoter regions in circulating B-cells of CLL patients was associated with abnormal miRNA expression when compared to healthy B-cells.…”

The Extensive Regulation of MicroRNA in Immune Thrombocytopenia

“… 46 , 169 EBV miR-BART6-5p combined with dexitabine can enhance the expression of miR-29 in EBV-positive Burkitt lymphoma cell lines. 48 MiR-BART6-3p avoids RIG-I recognition by targeting RIG-I (a pattern recognition receptor), evades the host's innate immune response, and promotes EBV infection. 172 …”

“…46,169 EBV miR-BART6-5p combined with dexitabine can enhance the expression of miR-29 in EBV-positive Burkitt lymphoma cell lines. 48 MiR-BART6-3p avoids RIG-I recognition by targeting RIG-I (a pattern recognition receptor), evades the host's innate immune response, and promotes EBV infection. 172 MiR-557 is highly expressed in human megakaryocytic leukemia cells and plasma of children with ITP, its inhibitors improve ITP by regulating apoptosis-related genes and cellular immunity and activating Akt/ERK pathway.…”

“…45 The unstable chain at the 5 ′ end is selected as the guide chain, while the other chain is discarded. [46][47][48] At this point, a functional RISC, which is called a mature RISC is formed. This ribo-nuclear protein complex mediates the translational repression of target mRNA followed by deadenylation and decay.…”

Germinal Centre B Cell Functions and Lymphomagenesis: Circuits Involving MYC and MicroRNAs

“…In recent years, miR-29s have been recognized as one of the miRNAs that play a role in BL pathogenesis [145,146,147]. MiR-29s, which are downregulated in BL [65,80,121,148], regulate the expression of miRNA target genes, and their dysregulation leads to an imbalance of cellular pathways [149].…”