Abstract 5355: Intragenic ATM hypermethylation as a mediator of increased breast cancer risk associated with high serum folate.
Authors: Brennan Kevin P. , Ricceri Fulvio , Vineis Paolo , Brown Robert , Flanagan James M. 
Published: August 2014

Background: Cancer cells display epigenetic as well as genetic abnormalities, however, little is known about the possible contribution of epigenetic variability to cancer risk prior to disease. We have previously reported a breast cancer risk marker at the ATM gene, ATMmvp2a, at which hypermethylation, detectable in blood prior to disease onset, is associated with increased breast cancer risk (OR=1.89). However, we do not yet understand the mechanism of increased risk, nor potential causes of increased hypermethylation at this locus. In the current study, we investigated environmental effects on ATM methylation as a mechanism of increased breast cancer risk. We hypothesised that methylation at this ATM locus may be dependent on the one-carbon metabolism pathway, which provides methyl groups from dietary micronutrients including folate, and on interaction with the MTHFR gene T677C polymorphism previously implicated in this pathway.

Methods: ATM methylation was measured by bisulphite pyrosequencing of blood DNA samples (n=71) from the EPIC study, for which 28 serum metabolite levels and environmental factors were known. We also measured ATM methylation in a second set of control individuals (n=288) for which dietary measures were available from questionnaire data. The MTHFR T677C polymorphism was genotyped in all individuals by Pyrosequencing.

Results: Linear regression revealed that ATM hypermethylation was associated with serum folate levels (p=0.006, n=71), but not with dietary folate levels inferred from questionnaire data (p=0.626, n=288). ATM methylation was on average 7% higher in the highest serum folate quintile compared with quintiles 1-4, and was within the range associated with breast cancer risk. While MTHFR genotype was associated with serum folate levels, hypermethylation of ATM was independent of MTHFR status. We found an intriguing association between folate and ATM methylation with fasting status, where dietary folate was associated with fasting (3.98e-07, n=288), and ATM methylation appeared lower in individuals who had fasted (p= 1.852e-06, n=288).

Conclusions: We conclude that the previously reported increased risk of breast cancer with over-supplementation of folate may be partially mediated via hypermethylation of ATM and other loci. Validation of these finding in larger studies is required, adjusting for MTHFR SNP status, fasting, and other potential modifiers, including age and alcohol consumption. Functional analysis is warranted to determine the biological significance of ATM hypermethylation, and to explain the apparent paradox of association of DNA methylation with both transient environmental factors and long-term cancer risk.

Citation Format: Kevin P. Brennan, Fulvio Ricceri, Paolo Vineis, Robert Brown, James M. Flanagan. Intragenic ATM hypermethylation as a mediator of increased breast cancer risk associated with high serum folate. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5355. doi:10.1158/1538-7445.AM2013-5355