Modulation of histone methylation and MLH1 gene silencing by hexavalent chromium.
Hexavalent chromium [Cr(VI)] is a mutagen and carcinogen, and occupational exposure can lead to lung cancers and other adverse health effects. Genetic changes resulting from DNA damage have been proposed as an important mechanism that mediates chromate's carcinogenicity. Here we show that chromate exposure of human lung A549 cells increased global levels of di- and tri-methylated histone H3 lysine 9 (H3K9) and lysine 4 (H3K4) but decreased the levels of tri-methylated histone H3 lysine 27 (H3K27) and di-methylated histone H3 arginine 2 (H3R2). Most interestingly, H3K9 dimethylation was enriched in the human MLH1 gene promoter following chromate exposure and this was correlated with decreased MLH1 mRNA expression. Chromate exposure increased the protein as well as mRNA levels of G9a a histone methyltransferase that specifically methylates H3K9. This Cr(VI)-induced increase in G9a may account for the global elevation of H3K9 dimethylation. Furthermore, supplementation with ascorbate, the primary reductant of Cr(VI) and also an essential cofactor for the histone demethylase activity, partially reversed the H3K9 dimethylation induced by chromate. Thus our studies suggest that Cr(VI) may target histone methyltransferases and demethylases, which in turn affect both global and gene promoter specific histone methylation, leading to the silencing of specific tumor suppressor genes such as MLH1.
Sun
Hong
H
Nelson Institute of Environmental Medicine, New York University School of Medicine, 57 Old Forge Road, Tuxedo, New York 10987, USA.
Zhou
Xue
X
Chen
Haobin
H
Li
Qin
Q
Costa
Max
M
D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors* / Q000235:genetics*; D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002857:Chromium / Q000633:toxicity*; D019175:DNA Methylation / Q000187:drug effects* / Q000502:physiology; D020868:Gene Silencing / Q000187:drug effects* / Q000502:physiology; D006657:Histones / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics*; D011994:Recombinant Proteins / Q000302:isolation & purification; D018411:Spodoptera / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D006657:Histones; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D002857:Chromium; C074702:chromium hexavalent ion; D000070957:MutL Protein Homolog 1