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ABSTRACT: While DNA methyltransferase1 (DNMT1) is classically known for its functions as a maintenance methyltransferase enzyme, additional roles for DNMT1 in gene expression are not as clearly understood. Several groups have shown that deletion of the catalytic domain from DNMT1 does not abolish repressive activity of the protein against a reporter gene. In our studies, we examine the repressor function of catalytically inactive DNMT1 at endogenous genes. First, potential DNMT1 target genes were identified by searching for genes up-regulated in HCT116 colon cancer cells genetically disrupted for DNMT1 (DNMT1(-/-) hypomorph cells). Next, the requirement for DNMT1 activity for repression of these genes was assessed by stably restoring expression of wild-type or catalytically inactive DNMT1. Both wild-type and mutant proteins are able to occupy the promoters and repress the expression of a set of target genes, and induce, at these promoters, both the depletion of active histone marks and the recruitment of a H3K4 demethylase, KDM1A/LSD1. Together, our findings show that there are genes for which DNMT1 acts as a transcriptional repressor independent from its methyltransferase function and that this repressive function may invoke a role for a scaffolding function of the protein at target genes.
Nucleic Acids Research 01/2012; 40(10):4334-46. · 8.03 Impact Factor
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Heather M O'Hagan,
Wei Wang,
Subhojit Sen,
Christina Destefano Shields,
Stella S Lee,
Yang W Zhang,
Eriko G Clements, Yi Cai,
Leander Van Neste,
Hariharan Easwaran,
Robert A Casero,
Cynthia L Sears,
Stephen B Baylin
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ABSTRACT: Cancer cells simultaneously harbor global losses and gains in DNA methylation. We demonstrate that inducing cellular oxidative stress by hydrogen peroxide treatment recruits DNA methyltransferase 1 (DNMT1) to damaged chromatin. DNMT1 becomes part of a complex(es) containing DNMT3B and members of the polycomb repressive complex 4. Hydrogen peroxide treatment causes relocalization of these proteins from non-GC-rich to GC-rich areas. Key components are similarly enriched at gene promoters in an in vivo colitis model. Although high-expression genes enriched for members of the complex have histone mark and nascent transcription changes, CpG island-containing low-expression genes gain promoter DNA methylation. Thus, oxidative damage induces formation and relocalization of a silencing complex that may explain cancer-specific aberrant DNA methylation and transcriptional silencing.
Cancer cell 11/2011; 20(5):606-19. · 25.29 Impact Factor
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ABSTRACT: Epigenetic silencing of genes in association with aberrant promoter DNA hypermethylation has emerged as a significant mechanism in the development of human cancers. Such genes are also often targets of the polycomb group repressive complexes in embryonic cells. The polycomb repressive complex 2 (PRC2) has been best studied in this regard. We now examine a link between PRC1 and cancer-specific gene silencing. Here, we show a novel and direct association between a constituent of the PRC1 complex, CBX7, with gene repression and promoter DNA hypermethylation of genes frequently silenced in cancer. CBX7 is able to complex with DNA methyltransferase (DNMT) enzymes, leading us to explore a role for CBX7 in maintenance and initiation of gene silencing. Knockdown of CBX7 was unable to relieve suppression of deeply silenced genes in cancer cells; however, in embryonal carcinoma (EC) cells, CBX7 can initiate stable repression of genes that are frequently silenced in adult cancers. Furthermore, we are able to observe assembly of DNMTs at CBX7 target gene promoters. Sustained expression of CBX7 in EC cells confers a growth advantage and resistance to retinoic acid-induced differentiation. In this setting, especially, there is increased promoter DNA hypermethylation for many genes by analysis of specific genes, as well as through epigenomic studies. Our results allow us to propose a potential mechanism through assembly of novel repressive complexes, by which the polycomb component of PRC1 can promote the initiation of epigenetic changes involving abnormal DNA hypermethylation of genes frequently silenced in adult cancers.
Cancer Research 09/2009; 69(15):6322-30. · 7.86 Impact Factor
