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Ma, Yuexi

University of British Columbia

Dietary factors, like polyphenols naturally occurring in plants, exert influences on human health via epigenetic mechanisms that alter gene expression without changing DNA sequence. We have previously performed genome-wide DNA methylation and expression analyses in human mammary epithelial cells and healthy rats’ livers, respectively, which were exposed to berry polyphenols with estrogenic activity (i.e., phytoestrogens). Using these datasets, we identified hypermethylated and/or downregulated genes enriched with functional categories that disrupt homeostasis and health maintenance, and promote aging, e.g., by limiting DNA break repair (RNF169) or promoting ribosomal biogenesis (rDNA). Existing evidence suggests that DNA methylation may be governed by chromatin regulatory proteins such as SIRT1 deacetylase. SIRT1 may interact with DNA methylating enzymes (e.g., DNMT3B) to repress transcription. Interestingly, SIRT1 was reported as a possible target of phytoestrogens. However, it remains unknown whether SIRT1 and its interaction with DNMT3B play a mechanistic role in phytoestrogen-mediated epigenetic effects in normal mammary epithelial cells. Thus, we test a hypothesis that phytoestrogens suppress genes related to homeostatic imbalance and aging, via SIRT1-mediated effects on DNA methylation. Human MCF10A mammary epithelial cells were treated with phytoestrogens, pterostilbene (PTS) and genistein (GEN). PTS and GEN decreased MCF10A cell growth with 50% inhibition and less than 10% dead cells at 11µM and 22µM concentrations respectively, as compared with vehicle-treated cells (control). SIRT1 occupancy at the selected hypermethylated phytoestrogen-target genes, RNF169 and rDNA, was accompanied by consistent promoter hypermethylation and gene downregulation in response to GEN, but not PTS. GEN-mediated DNA hypermethylation and SIRT1 occupancy were linked to a robust DNMT3B binding at both RNF169 and rDNA promoters. This was not observed in cells exposed to PTS, suggesting a distinct mechanism of action. Although both SIRT1 and DNMT3B bind to RNF169 and rDNA promoters upon GEN, the two proteins do not co-occupy the regions, as confirmed by double-ChIP. Through siRNA SIRT1 depletion, GEN does not decrease expression of rDNA anymore, suggesting that SIRT1 is required for epigenetic suppression of rDNA upon GEN. In conclusion, these findings further our understanding of SIRT1 role in epigenetic mechanisms mediating the impact of the environment-diet on cell biology.

Text

2025-04-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87884

Human Nutrition

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/