Chen Danqi, Fang Lei, Mei Shenglin, Li Hongjie, Xu Xia, Des Marais Thomas L, Lu Kun, Liu X Shirley, Jin Chunyuan
Department of Environmental Medicine and Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York, USA.
Department of Bioinformatics, School of Life Sciences, Tongji University, Shanghai, China.
Environ Health Perspect. 2017 Sep 21;125(9):097019. doi: 10.1289/EHP1275.
Formaldehyde (FA) is an environmental and occupational chemical carcinogen. Recent studies have shown that exogenous FA causes only a modest increase in DNA adduct formation compared with the amount of adducts formed by endogenous FA, raising the possibility that epigenetic mechanisms may contribute to FA-mediated carcinogenicity.
We investigated the effects of FA exposure on histone modifications and chromatin assembly. We also examined the role of defective chromatin assembly in FA-mediated transcription and cell transformation.
Cellular fractionation and Western blot analysis were used to measure the levels of histone modifications in human bronchial epithelial BEAS-2B cells and human nasal RPMI2650 cells in the presence of FA. Chromatin immunoprecipitation (ChIP) and micrococcal nuclease (MNase) digest assays were performed to examine the changes in chromatin assembly and accessibility after FA exposure. RNA sequencing (RNA-seq) and real-time polymerase chain reaction (PCR) were used to examine transcriptional dysregulation. Finally, anchorage-independent cell growth ability was tested by soft agar assay following FA exposure.
Exposure to FA dramatically decreased the acetylation of the N-terminal tails of cytosolic histones. These modifications are important for histone nuclear import and subsequent chromatin assembly. Histone proteins were depleted in both the chromatin fraction and at most of the genomic loci tested following FA exposure, suggesting that FA compromises chromatin assembly. Moreover, FA increased chromatin accessibility and altered the expression of hundreds of cancer-related genes. Knockdown of the histone H3.3 gene (an H3 variant), which mimics inhibition of chromatin assembly, facilitated FA-mediated anchorage-independent cell growth.
We propose that the inhibition of chromatin assembly represents a novel mechanism of cell transformation induced by the environmental and occupational chemical carcinogen FA. https://doi.org/10.1289/EHP1275.
甲醛（FA）是一种环境和职业化学致癌物。最近的研究表明，与内源性FA形成的加合物量相比，外源性FA仅导致DNA加合物形成适度增加，这增加了表观遗传机制可能促成FA介导的致癌作用的可能性。
我们研究了FA暴露对组蛋白修饰和染色质组装的影响。我们还研究了有缺陷的染色质组装在FA介导的转录和细胞转化中的作用。
使用细胞分级分离和蛋白质免疫印迹分析来测量在存在FA的情况下人支气管上皮BEAS-2B细胞和人鼻RPMI2650细胞中组蛋白修饰的水平。进行染色质免疫沉淀（ChIP）和微球菌核酸酶（MNase）消化试验，以检查FA暴露后染色质组装和可及性的变化。使用RNA测序（RNA-seq）和实时聚合酶链反应（PCR）来检查转录失调。最后，在FA暴露后通过软琼脂试验测试非锚定依赖性细胞生长能力。
暴露于FA显著降低了胞质组蛋白N末端尾巴的乙酰化。这些修饰对于组蛋白核输入和随后的染色质组装很重要。FA暴露后，染色质部分和大多数测试的基因组位点中的组蛋白均减少，这表明FA损害了染色质组装。此外，FA增加了染色质可及性并改变了数百个癌症相关基因的表达。敲低组蛋白H3.3基因（一种H3变体），模拟对染色质组装的抑制，促进了FA介导的非锚定依赖性细胞生长。
我们提出，染色质组装的抑制代表了环境和职业化学致癌物FA诱导细胞转化的新机制。https://doi.org/10.1289/EHP1275
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