Epigenetic silencing of O6-methylguanine DNA methyltransferase gene in NiS-transformed cells.
Nickel (Ni) compounds are potent carcinogens and can induce malignant transformation of rodent and human cells. To uncover the molecular mechanisms of nickel sulfide (NiS)-induced cell transformation, we investigated epigenetic alterations in a set of DNA repair genes. The silencing of the O(6)-methylguanine DNA methyltransferase (MGMT) gene locus and upregulation of DNA methyltransferase 1 (DNMT1) expression was specifically detected in NiS-transformed human bronchial epithelial (16HBE) cells. In addition, we noted epigenetic alterations including DNA hypermethylation, reduced histone H4 acetylation and a decrease in the ratio of Lys-9 acetylated/methylated histone H3 at the MGMT CpG island in NiS-transformed 16HBE cells. Meanwhile, we identified concurrent binding of methyl-CpG-binding protein 2, methylated DNA-binding domain protein 2 and DNMT1 to the CpG island of the MGMT promoter, demonstrating that these components collaborate to maintain MGMT methylation in NiS-transformed cells. Moreover, depletion of DNMT1 by introduction of a small hairpin RNA construct into NiS-transformed cells resulted in a 30% inhibition of cell proliferation and led to increased MGMT gene expression by reversion of the epigenetic modifications at the MGMT promoter region. MGMT suppression and hypermethylation at the CpG island of the MGMT promoter occurred 6 days after NiS treatment, indicating that epigenetic modifications of MGMT might be an early event in tumorigenesis. Taken together, these observations demonstrate that epigenetic silencing of MGMT is associated with DNA hypermethylation, histone modifications and DNMT1 upregulation, which contribute to NiS-induced malignant transformation.
Ji
Weidong
W
Faculty of Preventive Medicine, School of Public Health, Sun Yat-Sen University, 74 Zhongshan Road 2, Guangzhou 510080, People's Republic of China.
Yang
Linqing
L
Yu
Lei
L
Yuan
Jianhui
J
Hu
Dalin
D
Zhang
Wenjuan
W
Yang
Jianping
J
Pang
Yaqin
Y
Li
Wenxue
W
Lu
Jiachun
J
Fu
Juan
J
Chen
Jiakun
J
Lin
Zhongning
Z
Chen
Wen
W
Zhuang
Zhixiong
Z
D015153:Blotting, Western; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D020868:Gene Silencing; D006657:Histones / Q000235:genetics; D006801:Humans; D047468:Immunoprecipitation; D009532:Nickel / Q000633:toxicity*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D025521:Tumor Suppressor Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism
D002273:Carcinogens; D006657:Histones; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; D009532:Nickel; D015254:DNA Modification Methylases; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; C017558:nickel sulfide