Silenced tumor suppressor genes reactivated by DNA demethylation do not return to a fully euchromatic chromatin state.
Histone H3 lysine 9 (H3K9) and lysine 27 (H3K27) trimethylation are properties of stably silenced heterochromatin whereas H3K9 dimethylation (H3K9me2) is important for euchromatic gene repression. In colorectal cancer cells, all of these marks, as well as the key enzymes which establish them, surround the hMLH1 promoter when it is DNA hypermethylated and aberrantly silenced, but are absent when the gene is unmethylated and fully expressed in a euchromatic state. When the aberrantly silenced gene is DNA demethylated and reexpressed following 5-aza-2'-deoxycytidine treatment, H3K9me1 and H3K9me2 are the only silencing marks that are lost. A series of other silenced and DNA hypermethylated gene promoters behave identically even when the genes are chronically DNA demethylated and reexpressed after genetic knockout of DNA methyltransferases. Our data indicate that when transcription of DNA hypermethylated genes is activated in cancer cells, their promoters remain in an environment with certain heterochromatic characteristics. This finding has important implications for the translational goal of reactivating aberrantly silenced cancer genes as a therapeutic maneuver.
McGarvey
Kelly M
KM
Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins University, 1650 Orleans Street, Baltimore, MD 21231, USA.
Fahrner
Jill A
JA
Greene
Eriko
E
Martens
Joost
J
Jenuwein
Thomas
T
Baylin
Stephen B
SB
D048868:Adaptor Proteins, Signal Transducing; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics; D045744:Cell Line, Tumor; D002843:Chromatin / Q000235:genetics* / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D000077209:Decitabine; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D045325:HCT116 Cells; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics; D011401:Promoter Regions, Genetic; D000094742:Secreted Frizzled-Related Proteins
D048868:Adaptor Proteins, Signal Transducing; D001374:Azacitidine; D002352:Carrier Proteins; D002843:Chromatin; D000077209:Decitabine; D006657:Histones; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins; C501486:MLH1 protein, human; C117636:SFRP1 protein, human; D000094742:Secreted Frizzled-Related Proteins