The essential role of histone H3 Lys9 di-methylation and MeCP2 binding in MGMT silencing with poor DNA methylation of the promoter CpG island.
Silencing of the O (6)-methylguanine-DNA methyltransferase (MGMT) gene, a key to DNA repair, is involved in carcinogenesis. Recent studies have focused on DNA hypermethylation of the promoter CpG island. However, cases showing silencing with DNA hypomethylation certainly exist, and the mechanism involved is not elucidated. To clarify this mechanism, we examined the dynamics of DNA methylation, histone acetylation, histone methylation, and binding of methyl-CpG binding proteins at the MGMT promoter region using four MGMT negative cell lines with various extents of DNA methylation. Histone H3K9 di-methylation (H3me2K9), not tri-methylation, and MeCP2 binding were commonly seen in all MGMT negative cell lines regardless of DNA methylation status. 5Aza-dC, but not TSA, restored gene expression, accompanied by a decrease in H3me2K9 and MeCP2 binding. In SaOS2 cells with the most hypomethylated CpG island, 5Aza-dC decreased H3me2K9 and MeCP2 binding with no effect on DNA methylation or histone acetylation. H3me2K9 and DNA methylation were restricted to in and around the island, indicating that epigenetic modification at the promoter CpG island is critical. We conclude that H3me2K9 and MeCP2 binding are common and more essential for MGMT silencing than DNA hypermethylation or histone deacetylation. The epigenetic mechanism leading to silent heterochromatin at the promoter CpG island may be the same in different types of cancer irrespective of the extent of DNA methylation.
Zhao
Wei
W
Division of Molecular Biology and Genetics, Department of Biomolecular Sciences, Faculty of Medicine, Saga University, Saga 849-8501.
Soejima
Hidenobu
H
Higashimoto
Ken
K
Nakagawachi
Tetsuji
T
Urano
Takeshi
T
Kudo
Shinichi
S
Matsukura
Shiroh
S
Matsuo
Shuzo
S
Joh
Keiichiro
K
Mukai
Tsunehiro
T
D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D045744:Cell Line, Tumor; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D000077209:Decitabine; D015870:Gene Expression / Q000187:drug effects; D020868:Gene Silencing; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D008239:Lysine / Q000378:metabolism*; D051783:Methyl-CpG-Binding Protein 2; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000187:drug effects; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D006657:Histones; D006877:Hydroxamic Acids; C066141:MBD1 protein, human; C489325:MBD2 protein, human; C115369:MBD3 protein, human; C497392:MECP2 protein, human; D051783:Methyl-CpG-Binding Protein 2; D012097:Repressor Proteins; D014157:Transcription Factors; C012589:trichostatin A; D000077209:Decitabine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D008239:Lysine; D001374:Azacitidine