title: Critical role of histone methylation in tumor suppressor gene silencing in colorectal cancer.
abstract: The mechanism of DNA hypermethylation-associated tumor suppressor gene silencing in cancer remains incompletely understood. Here, we show by chromatin immunoprecipitation that for three genes (P16, MLH1, and the O(6)-methylguanine-DNA methyltransferase gene, MGMT), histone H3 Lys-9 methylation directly correlates and histone H3 Lys-9 acetylation inversely correlates with DNA methylation in three neoplastic cell lines. Treatment with the histone deacetylase inhibitor trichostatin A (TSA) resulted in moderately increased Lys-9 acetylation at silenced loci with no effect on Lys-9 methylation and minimal effects on gene expression. By contrast, treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5Aza-dC) rapidly reduced Lys-9 methylation at silenced loci and resulted in reactivation for all three genes. Combined treatment with 5Aza-dC and TSA was synergistic in reactivating gene expression through simultaneous effects on Lys-9 methylation and acetylation, which resulted in a robust increase in the ratio of Lys-9 acetylated and methylated histones at loci showing dense DNA methylation. By contrast to Lys-9, histone H3 Lys-4 methylation inversely correlated with promoter DNA methylation, was not affected by TSA, and was increased moderately at silenced loci by 5Aza-dC. Our results suggest that reduced H3 Lys-4 methylation and increased H3 Lys-9 methylation play a critical role in the maintenance of promoter DNA methylation-associated gene silencing in colorectal cancer.
authors.affiliation: Department of Leukemia, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kondo
authors.forename: LanLan
authors.initials: L
authors.lastname: Shen
authors.forename: Jean-Pierre J
authors.initials: JP
authors.lastname: Issa
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002352:Carrier Proteins; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation / Q000187:drug effects; D000077209:Decitabine; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D008239:Lysine / Q000378:metabolism; D008745:Methylation; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011233:Precipitin Tests / Q000379:methods; D011401:Promoter Regions, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C012589:trichostatin A; D000077209:Decitabine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000070957:MutL Protein Homolog 1; D008239:Lysine; D001374:Azacitidine