Chen Haobin, Ke Qingdong, Kluz Thomas, Yan Yan, Costa Max
Nelson Institute of Environmental Medicine, New York University Medical Center, 57 Old Forge Road, Tuxedo, New York 10987, USA.
Mol Cell Biol. 2006 May;26(10):3728-37. doi: 10.1128/MCB.26.10.3728-3737.2006.
We have previously reported that carcinogenic nickel compounds decreased global histone H4 acetylation and silenced the gpt transgene in G12 Chinese hamster cells. However, the nature of this silencing is still not clear. Here, we report that nickel ion exposure increases global H3K9 mono- and dimethylation, both of which are critical marks for DNA methylation and long-term gene silencing. In contrast to the up-regulation of global H3K9 dimethylation, nickel ions decreased the expression and activity of histone H3K9 specific methyltransferase G9a. Further investigation demonstrated that nickel ions interfered with the removal of histone methylation in vivo and directly decreased the activity of a Fe(II)-2-oxoglutarate-dependent histone H3K9 demethylase in nuclear extract in vitro. These results are the first to show a histone H3K9 demethylase activity dependent on both iron and 2-oxoglutarate. Exposure to nickel ions also increased H3K9 dimethylation at the gpt locus in G12 cells and repressed the expression of the gpt transgene. An extended nickel ion exposure led to increased frequency of the gpt transgene silencing, which was readily reversed by treatment with DNA-demethylating agent 5-aza-2'-deoxycytidine. Collectively, our data strongly indicate that nickel ions induce transgene silencing by increasing histone H3K9 dimethylation, and this effect is mediated by the inhibition of H3K9 demethylation.
我们之前曾报道，致癌镍化合物会降低整体组蛋白H4乙酰化水平，并使G12中国仓鼠细胞中的gpt转基因沉默。然而，这种沉默的本质仍不清楚。在此，我们报道镍离子暴露会增加整体H3K9单甲基化和二甲基化水平，这两者都是DNA甲基化和长期基因沉默的关键标记。与整体H3K9二甲基化上调相反，镍离子降低了组蛋白H3K9特异性甲基转移酶G9a的表达和活性。进一步研究表明，镍离子在体内干扰了组蛋白甲基化的去除，并在体外直接降低了核提取物中依赖Fe(II)-2-氧代戊二酸的组蛋白H3K9去甲基化酶的活性。这些结果首次表明了一种依赖铁和2-氧代戊二酸的组蛋白H3K9去甲基化酶活性。镍离子暴露还增加了G12细胞中gpt基因座处的H3K9二甲基化水平，并抑制了gpt转基因的表达。延长镍离子暴露导致gpt转基因沉默频率增加，而用DNA去甲基化剂5-氮杂-2'-脱氧胞苷处理可轻易逆转这种情况。总体而言，我们的数据有力地表明，镍离子通过增加组蛋白H3K9二甲基化来诱导转基因沉默，且这种效应是由对H3K9去甲基化的抑制介导的。
