Abstract 1896: Selenium and isothiocyanates increases TrxR1 and GI-GPx expression but DNA methylation of LINE-1 remains unchanged in Caco-2 cells
Authors: Lawrence Barrera N. , Belshaw Nigel J. , Johnson Ian T. , Cassidy Aedin , Bao Yongping 
Published: February 2011

Abstract
Currently, there is significant interest in the field of diet-gene interactions and the mechanisms by which food compounds regulate gene expression through epigenetic events to modify cancer susceptibility. Evidence from epidemiological, in vivo and in vitro studies have suggested that the chemopreventive effect of cruciferous vegetables is attributed to the glucosinolate break-down products, isothiocyanates (ITCs). Similarly, selenium (Se) is an integral part of many cellular antioxidant enzymes and like isothiocyanates has been inversely associated with the incidence of cancer as a result of influencing multiple pathways in the development of cancer. However, their efficacy might depend on the chemical form in which they are administered. We therefore examined the synergistic effect of two forms of selenium, selenium-methylselenocysteine (Se-MSC) and selenite (200nM) with ITCs (6µM) such as iberin and sulforaphane on the expression of antioxidant selenoenzymes such as thioredoxin-reductase (TrxR1) and gastrointestinal glutathione peroxidise (GI-GPx) in an in vitro model using Caco-2 cells. Our preliminary results suggest that the simultaneous addition of Se-MSC and iberin significantly induced TrxR1 and GI-GPx mRNA and protein expression more than either compound alone by ∼6 fold (p&lt;0.001).
In addition to the antioxidant protection provided by these selenoproteins, DNA methylation is essential for normal development, but aberrant DNA methylation patterns are a hallmark of most cancers and include global DNA hypomethylation, region-specific hypermethylation and increased DNA methyltransferases (DNMTs) activity. We therefore also examined the impact of Se and ITCs on DNA methylation, specifically examining factors modulating DNMT1, 3A, 3B expression and methylation of the LINE-1 retrotransposon, a surrogate marker of global DNA methylation. Caco-2 cells were treated with Se-MSC and selenite using 0.2, 0.5, 1, 2 and 5µM, in addition to the ITCs (6µM) after 5 and 10 days of treatment. Our initial data suggests that methylation of LINE-1 in the control group was indeed low (55%) and treatment of cells with DNMT inhibitor 5-aza-2 deoxycytidine resulted in a 45% reduction in LINE-1 methylation as expected. Unexpectedly, none of the food compounds or dose used in this study modified significantly the methylation status of LINE-1. Interestingly, although the methylation levels of this marker remain unchanged, the mRNA expression of the DNMTs showed the tendency to decrease, following the same pattern in the different treatments and time courses albeit with small differences, which suggests that both de novo and maintenance DNMTs work in concert to create and propagate methylation patterns. However, only DNMT3B showed a significant reduction of 35 and 38% after 10 days of treatment with Se-MSC (500nM) (p=0.04) and selenite (1µM) (p=0.035) respectively.
Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1896.