title: Silencing effect of CpG island hypermethylation and histone modifications on O6-methylguanine-DNA methyltransferase (MGMT) gene expression in human cancer.
abstract: O6-methylguanine-DNA methyltransferase (MGMT) repairs the cytotoxic and mutagenic O6-alkylguanine produced by alkylating agents such as chemotherapeutic agents and mutagens. Recent studies have shown that in a subset of tumors, MGMT expression is inversely linked to hypermethylation of the CpG island in the promoter region; however, how the epigenetic silencing mechanism works, as it relates to hypermethylation, was still unclear. To understand the mechanism, we examined the detailed methylation status of the whole island with bisulfite-sequencing in 19 MGMT non-expressed cancer cell lines. We found two highly methylated regions in the island. One was upstream of exon 1, including minimal promoter, and the other was downstream, including enhancer. Reporter gene assay showed that methylation of both the upstream and downstream regions suppressed luciferase activity drastically. Chromatin immunoprecipitation assay revealed that histone H3 lysine 9 was hypermethylated throughout the island in the MGMT negative line, whereas acetylation on H3 and H4 and methylation on H3 lysine 4 were at significantly high levels outside the minimal promoter in the MGMT-expressed line. Furthermore, MeCP2 preferentially bound to the CpG-methylated island in the MGMT negative line. Given these results, we propose a model for gene silencing of MGMT that is dependent on the epigenetic state in cancer.
authors.affiliation: Division of Molecular Biology and Genetics, Department of Biomolecular Sciences, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan.
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Nakagawachi
authors.forename: Hidenobu
authors.initials: H
authors.lastname: Soejima
authors.forename: Takeshi
authors.initials: T
authors.lastname: Urano
authors.forename: Wei
authors.initials: W
authors.lastname: Zhao
authors.forename: Ken
authors.initials: K
authors.lastname: Higashimoto
authors.forename: Yuji
authors.initials: Y
authors.lastname: Satoh
authors.forename: Shiroh
authors.initials: S
authors.lastname: Matsukura
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kudo
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Kitajima
authors.forename: Haruhito
authors.initials: H
authors.lastname: Harada
authors.forename: Koichi
authors.initials: K
authors.lastname: Furukawa
authors.forename: Hideki
authors.initials: H
authors.lastname: Matsuzaki
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Emi
authors.forename: Yusaku
authors.initials: Y
authors.lastname: Nakabeppu
authors.forename: Kohji
authors.initials: K
authors.lastname: Miyazaki
authors.forename: Mutsuo
authors.initials: M
authors.lastname: Sekiguchi
authors.forename: Tsunehiro
authors.initials: T
authors.lastname: Mukai
mesh_terms: D018899:CpG Islands / Q000502:physiology*; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing / Q000502:physiology; D006151:Guanosine / Q000031:analogs & derivatives* / Q000378:metabolism*; D006657:Histones / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D009369:Neoplasms / Q000378:metabolism; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics* / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D006657:Histones; D006151:Guanosine; C046175:6'-O-methylguanosine; D019853:O(6)-Methylguanine-DNA Methyltransferase