Abstract 4445: The estrogen related receptor alpha regulates one carbon metabolism and DNA methylation
Authors: Vernier Mathieu , Audet-Walsh Etienne , Tam Ingrid , Deblois Geneviève , Giguère Vincent 
Published: July 2016

Besides genetic alterations, epigenetic mechanisms such as DNA methylation are implicated in the acquisition of malignant phenotype, and thus, the use of epigenetic drugs is a promising strategy for anti-cancer therapy. DNA methylation is the process by which DNA methyltransferase enzymes (DNMT) add methyl groups to cytosines, using S-adenosine methionine (SAM) as a methyl donor.Therefore, this process relies both on the expression of the DNMTs and on the availability of SAM, which is a component of the one carbon metabolism pathway. In the context of breast cancer, cell metabolism is tightly regulated by the orphan nuclear receptor estrogen-related receptor alpha (ERRa) and thus, we wondered whether ERRa could regulate SAM levels and, by extension, DNA methylation.

By analyzing chromatin immunoprecipitation experiments followed by DNA sequencing (ChIP-seq) of ERRa conducted in different breast cancer cell lines, we discovered that ERRa is located on the promoter of many genes implicated in one carbon metabolism. Inhibition of ERRa by RNA interference or with the chemical inhibitor C29 modified the mRNA levels of these genes and induced changes in SAM levels. Interestingly, we also observed ERRa binding on the promoter of DNMT1 and genetic and pharmacological inhibition of ERRa reduced DNMT1 expression at the mRNA and protein levels. Altogether, these changes ultimately decreased global DNA methylation in breast cancer cell lines, suggesting that ERRa is a major driver of this epigenetic mechanism. Surprisingly, genetic inhibition of DNMT1 or treatment with the DNMT inhibitor (DNMTi) SGI-1027 reduced the protein levels of ERRa in these cells, unraveling the existence of a feedback loop between these two pathways. Therefore, we explored whether treating breast cancer cells with a combination of C29 and SGI-1027 would represent a good therapeutic approach. We treated breast cancer cells with a given concentration of C29 and increased concentrations of SGI-1027 for 24h and observed that C29 highly sensitized these cells to the DNMTi. Further investigations on xenograft models will be conducted to validate these results in vivo and next-generation sequencing will be performed in the context of ERRa inhibition to study the global DNA methylation alterations and the consequences on gene expression.

In conclusion, we have uncovered a novel crosstalk between cell metabolism and epigenetics that lead to a better understanding of the regulation of these events and their influence on cancer cell biology and drug sensitivity. We propose that targeting these two pathways with a combination therapy possesses great therapeutic potential for breast cancer and may be efficacious in other cancers as well.

Citation Format: Mathieu Vernier, Etienne Audet-Walsh, Ingrid Tam, Geneviève Deblois, Vincent Giguère. The estrogen related receptor alpha regulates one carbon metabolism and DNA methylation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4445.