Overexpression of MBD2 in Glioblastoma Maintains Epigenetic Silencing and Inhibits the Antiangiogenic Function of the Tumor Suppressor Gene BAI1

Abstract

Brain Angiogenesis Inhibitor 1 (BAI1) is a putative G protein-coupled receptor with potent anti-angiogenic and anti-tumorigenic properties that is mutated in certain cancers. BAI1 is expressed in normal human brain, but it is frequently silenced in glioblastoma multiforme (GBM). In this study we show this silencing event is regulated by overexpression of methyl-CpG-binding domain protein 2 (MBD2), a key mediator of epigenetic gene regulation, which binds to the hypermethylated BAI1 gene promoter. In glioma cells, treatment with the DNA demethylating agent 5-aza-2′-deoxycytidine (5-Aza-dC) was sufficient to reactivate BAI1 expression. Chromatin immunoprecipitation (ChIP) showed that MBD2 was enriched at the promoter of silenced BAI1 in glioma cells and that MBD2 binding was released by 5-Aza-dC treatment. RNAi-mediated knockdown of MBD2 expression led to reactivation of BAI1 gene expression and restoration of BAI1 functional activity, as indicated by increased anti-angiogenic activity in vitro and in vivo. Taken together, our results suggest that MBD2 overexpression during gliomagenesis may drive tumor growth by suppressing the anti-angiogenic activity of a key tumor suppressor. These findings have therapeutic implications since inhibiting MBD2 could offer a strategy to reactivate BAI1 and suppress glioma pathobiology.

Expression of DNMTs and MBD2 in GIST

“…DNMT3L lacks the methyltransferase catalytic domain but is involved in the establishment of DNA methylation by recruiting or activating other de novo DNMTs (16)(17)(18). MBD2 is capable of binding specifically to methylated DNA and can repress transcription from methylated gene promoters (19). Notably, MBD2 has also been reported to function as a demethylase to activate transcription (20), as DNA methylation causes gene silencing.…”

“…A common assumption is that the abnormal expression of DNMTs and MBD2 may contribute to tumor progression through hypermethylation-mediated TSG inactivation in CpG islands. A number of studies have proven that tumors exhibit a high expression of DNMT and MBD2 (19,22). However, their involvement in GIST has yet to be elucidated.…”

Relationships among MTHFR a1298c Gene Polymorphisms and Methylation Status of Dact1 Gene in Transitional Cell Carcinomas

“…The processs is promoted by DNA methyltransferases, which use S-adenosyl-methionine as the methyl donor (Batra and Mishra , 2007). 5-methyl-cytosine is formed through the addition of a methyl group to the fifth carbon position of the cytosinepyrimidine ring by DNA methyltransferases (Zhu et al, 2011). DNA methylation is an epigenetic mechanism which plays an important part in regulating gene expression at the transcription level (Huang and Vieira , 2006).…”

Epigenetics and ncRNAs in Brain Function and Disease: Mechanisms and Prospects for Therapy

“…DNA methylation also plays an important role in glioblastoma [104] and these compounds are now also under investigation as possible therapies for these cancers. Thus, treatment of glioma cells with 5-aza-dC was able to reactivate the expression of the brain angiogenesis inhibitor (BAI1), which is normally silenced in gliomas, by recruitment of the methyl-CpG-binding domain protein 2 (MBD2) to the hypermethylated BAI1 promoter [105]. The major limitation of small molecule-mediated epigenetic therapies is that they are non-specific in nature and therefore have the potential for multiple off-target gene expression effects.…”