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SIRT1 affects DNA methylation of polycomb group protein target genes, a hotspot of the epigenetic shift observed in ageing.

ABSTRACT: SIRT1 is likely to play a role in the extension in healthspan induced by dietary restriction. Actions of SIRT1 are pleiotropic, and effects on healthspan may include effects on DNA methylation. Polycomb group protein target genes (PCGTs) are suppressed by epigenetic mechanisms in stem cells, partly through the actions of the polycomb repressive complexes (PRCs), and have been shown previously to correspond with loci particularly susceptible to age-related changes in DNA methylation. We hypothesised that SIRT1 would affect DNA methylation particularly at PCGTs. To map the sites in the genome where SIRT1 affects DNA methylation, we altered SIRT1 expression in human intestinal (Caco-2) and vascular endothelial (HuVEC) cells by transient transfection with an expression construct or with siRNA. DNA was enriched for the methylated fraction then sequenced (HuVEC) or hybridised to a human promoter microarray (Caco-2).The profile of genes where SIRT1 manipulation affected DNA methylation was enriched for PCGTs in both cell lines, thus supporting our hypothesis. SIRT1 knockdown affected the mRNA for none of seven PRC components nor for DNMT1 or DNMT3b. We thus find no evidence that SIRT1 affects DNA methylation at PCGTs by affecting the expression of these gene transcripts. EZH2, a component of PRC2 that can affect DNA methylation through association with DNA methyltransferases (DNMTs), did not co-immunoprecipitate with SIRT1, and SIRT1 knockdown did not affect the expression of EZH2 protein. Thus, it is unlikely that the effects of SIRT1 on DNA methylation at PCGTs are mediated through direct intermolecular association with EZH2 or through effects in its expression.SIRT1 affects DNA methylation across the genome, but particularly at PCGTs. Although the mechanism through which SIRT1 has these effects is yet to be uncovered, this action is likely to contribute to extended healthspan, for example under conditions of dietary restriction.

SUBMITTER: Wakeling LA

PROVIDER: S-EPMC4480908 | biostudies-literature | 2015 Jun

REPOSITORIES: biostudies-literature

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SIRT1 affects DNA methylation of polycomb group protein target genes, a hotspot of the epigenetic shift observed in ageing.

Wakeling Luisa A LA Ions Laura J LJ Escolme Suzanne M SM Cockell Simon J SJ Su Tianhong T Dey Madhurima M Hampton Emily V EV Jenkins Gail G Wainwright Linda J LJ McKay Jill A JA Ford Dianne D

Human genomics 20150624

<h4>Background</h4>SIRT1 is likely to play a role in the extension in healthspan induced by dietary restriction. Actions of SIRT1 are pleiotropic, and effects on healthspan may include effects on DNA methylation. Polycomb group protein target genes (PCGTs) are suppressed by epigenetic mechanisms in stem cells, partly through the actions of the polycomb repressive complexes (PRCs), and have been shown previously to correspond with loci particularly susceptible to age-related changes in DNA methyl ...[more]

PMID: 26104761

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Project description:Beneficial effects of SIRT1 on healthspan are likely to be pleiotropic and may include effects on DNA methylation. We demonstrated recently that manipulating SIRT1 in human cells affected DNA methylation of a panel of test genes, and that genes with expression modified by dietary restriction corresponded with genes that underwent changes in DNA methylation during ageing. Here we tested the hypothesis that genes particularly susceptible to SIRT1-induced effects on DNA methylation across the genome map to genes for which DNA methylation changes during ageing. We increased or reduced SIRT1 expression in human intestinal (Caco-2) and vascular endothelial (HuVEC) cells by transient transfection with an expression construct or with siRNA, respectively. Effects on DNA methylation were measured by enriching for the methylated fraction then either sequencing (HuVEC) or hybridising to a human promoter microarray (Caco-2). Effects using these two different cell lines and techniques for analysis were remarkably consistent. Genes with a DNA methylation status affected by SIRT1 manipulation were enriched for those that undergo age-dependent changes in DNA methylation, thus supporting our hypothesis. Polycomb group protein target genes (PCGTs), which are suppressed by epigenetic mechanisms in stem cells and have been shown previously to correspond with loci particularly susceptible to age-related changes in DNA methylation, were over-represented within the set of genes showing altered DNA methylation in response to SIRT1 manipulation in both cell lines. We thus propose that effects of SIRT1 to extend healthspan include influences on the DNA methylation status of genes affected during ageing, in particular PCGTs. Analysis of methylation profiles of Caco-2 cells meeting the following conditions: SIRT1 overexpressed by transfection with pCMV6-ENTRY-SIRT1 (2 replicates), corresponding vector control (2 replicates), each of the siRNAs that target SIRT1 (1 & 2 replicates, respectively) and control siRNA (2 replicates).

Project description:BACKGROUND: The human EED protein, a member of the superfamily of Polycomb group (PcG) proteins with WD-40 repeats, has been found to interact with three HIV-1 components, namely the structural Gag matrix protein (MA), the integrase enzyme (IN) and the Nef protein. The aim of the present study was to analyze the possible biological role of EED in HIV-1 replication, using the HIV-1-based vector HIV-Luc and EED protein expressed by DNA transfection of 293T cells. RESULTS: During the early phase of HIV-1 infection, a slight negative effect on virus infectivity occurred in EED-expressing cells, which appeared to be dependent on EED-MA interaction. At late times post infection, EED caused an important reduction of virus production, from 20- to 25-fold as determined by CAp24 immunoassay, to 10- to 80-fold based on genomic RNA levels, and this decrease was not due to a reduction of Gag protein synthesis. Coexpression of WTNef, or the non-N-myristoylated mutant NefG2A, restored virus yields to levels obtained in the absence of exogenous EED protein. This effect was not observed with mutant NefDelta57 mimicking the Nef core, or with the lipid raft-retargeted fusion protein LAT-Nef. LATAA-Nef, a mutant defective in the lipid raft addressing function, had the same anti-EED effect as WTNef. Cell fractionation and confocal imaging showed that, in the absence of Nef, EED mainly localized in membrane domains different from the lipid rafts. Upon co-expression with WTNef, NefG2A or LATAA-Nef, but not with NefDelta57 or LAT-Nef, EED was found to relocate into an insoluble fraction along with Nef protein. Electron microscopy of HIV-Luc producer cells overexpressing EED showed significant less virus budding at the cell surface compared to control cells, and ectopic assembly and clustering of nuclear pore complexes within the cytoplasm. CONCLUSION: Our data suggested that EED exerted an antiviral activity at the late stage of HIV-1 replication, which included genomic RNA packaging and virus assembly, resulting possibly from a mistrafficking of viral genomic RNA (gRNA) or gRNA/Gag complex. Nef reversed the EED negative effect on virus production, a function which required the integrity of the Nef N-terminal domain, but not its N-myristoyl group. The antagonistic effect of Nef correlated with a cellular redistribution of both EED and Nef.

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SIRT1 affects DNA methylation of polycomb group protein target genes, a hotspot of the epigenetic shift observed in ageing.

Publications

SIRT1 affects DNA methylation of polycomb group protein target genes, a hotspot of the epigenetic shift observed in ageing.

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