Okumura Fumika, Li Yong, Itoh Norio, Nakanishi Tsuyoshi, Isobe Masakazu, Andrews Glen K, Kimura Tomoki
Department of Toxicology, Faculty of Pharmaceutical Sciences, Setsunan University, Osaka 573-0101, Japan.
Biochim Biophys Acta. 2011 Jan;1809(1):56-62. doi: 10.1016/j.bbagrm.2010.10.004. Epub 2010 Oct 28.
Metallothionein (MT) is a small, cysteine-rich protein active in zinc homeostasis, cadmium detoxification, and protection against reactive oxygen species. Mouse MT-I gene transcription is regulated by metal response element-binding transcription factor-1 (MTF-1), which is recruited to the promoter by zinc. We examined alterations in the chromatin structure of the MT-I promoter associated with enhanced transcriptional activation. MTF-1 proved essential for zinc-induced epigenetic changes in the MT-I promoter. Chromatin immunoprecipitation assays demonstrated that zinc treatment rapidly decreased Lys⁴-trimethylated and Lys⁹-acetylated histone H3 in the promoter and decreased total histone H3 but not histone H3.3. Micrococcal nuclease sensitivity of the MT-I promoter was increased by zinc. Thus, the chromatin structure in the promoter may be locally disrupted by zinc-induced nucleosome removal. Without MTF-1 these changes were not observed, and an MTF-1 deletion mutant recruited to the MT-I promoter by zinc that did not recruit the coactivator p300 or activate MT-I transcription did not affect histone H3 in the MT-I promoter in response to zinc. Interleukin-6, which induces MT-I transcription independently of MTF-1, did not reduce histone H3 levels in the promoter. Rapid disruption of nucleosome structure at the MT-I promoter is mediated by zinc-responsive recruitment of an active MTF-1-coactivator complex.
金属硫蛋白（MT）是一种富含半胱氨酸的小蛋白，在锌稳态、镉解毒以及抵御活性氧方面发挥作用。小鼠MT-I基因转录受金属反应元件结合转录因子-1（MTF-1）调控，锌可将MTF-1招募至启动子区域。我们研究了与转录激活增强相关的MT-I启动子染色质结构变化。结果表明，MTF-1对于锌诱导的MT-I启动子表观遗传变化至关重要。染色质免疫沉淀分析显示，锌处理可迅速降低启动子中赖氨酸⁴-三甲基化和赖氨酸⁹-乙酰化组蛋白H3水平，并降低总组蛋白H3水平，但不影响组蛋白H3.3。锌可增加MT-I启动子对微球菌核酸酶的敏感性。因此，启动子中的染色质结构可能因锌诱导的核小体去除而局部破坏。若没有MTF-1，则不会观察到这些变化，并且通过锌招募至MT-I启动子但不招募共激活因子p300或不激活MT-I转录的MTF-1缺失突变体，对锌刺激下的MT-I启动子中的组蛋白H3无影响。白细胞介素-6可独立于MTF-1诱导MT-I转录，但不会降低启动子中的组蛋白H3水平。MT-I启动子处核小体结构的快速破坏是由活性MTF-1-共激活因子复合物的锌响应招募介导的。
