Chromatin assembly and formaldehyde toxicity

项目总结 甲醛是一种已知的环境和职业化学致癌物。其分子机制的研究进展 甲醛诱导的致癌作用在很大程度上是未知的。DNA损伤和相关的 DNA加合物和DNA-蛋白质交联物的致突变作用一直是甲醛研究的重点 致癌性研究。然而，最近的研究表明，外源甲醛只会导致 内源性甲醛引起的DNA加合物水平以上的小幅增加。这表明 表观遗传机制可能有助于甲醛的致癌作用。我们和 其他人已经证明，甲醛与组蛋白上的赖氨酸残基反应，形成不稳定的 Schiff碱或更稳定的N6-甲酰赖氨酸，并且Schiff碱和N6-甲酰赖氨酸残基都是 对乙酰化反应难。这些发现表明，甲醛-组蛋白赖氨酸加合物可能会干扰 组蛋白赖氨酸乙酰化调控的重要细胞过程。然而，目前还不清楚是哪一种过程 受这一机制的影响。我们的细胞分馏分析的初步数据表明 甲醛暴露极大地减少了胞浆组蛋白H3和H4的赖氨酸乙酰化。这 这一发现非常有趣，因为这些修饰对组蛋白核输入和染色质至关重要 集合。我们的初步结果进一步表明，甲醛减少了组织中组蛋白的总量 染色质部分和基因组位置的组蛋白水平，表明染色质组装受到抑制。 染色质组装缺陷会导致基因表达失调和基因组不稳定，并 与不同类型的癌症直接相关。基于这些观察结果，我们假设 甲醛-组蛋白加合物影响组蛋白核输入和/或染色质组装，从而 有助于甲醛诱导的致癌作用。为了验证这一假设，在目标1中，我们将检验 新合成的组蛋白及其组装成染色质的核输入是否受到损害 在甲醛暴露之后，并确定潜在的机制。在目标2中，我们将确定 染色质组装异常对甲醛诱导的基因表达、形成的影响 DNA加合物和DNA-蛋白质交联物，以及染色体不稳定性。在目标3中，我们将调查 甲醛暴露会影响体内染色质的组装。提出的概念是一种化学物质 致癌物与新合成的组蛋白反应来调节染色质组装是一种新的方法。这项研究具有 有可能揭示化学致癌的新机制。

PROJECT SUMMARY Formaldehyde is a known environmental and occupational chemical carcinogen. The molecular mechanisms of formaldehyde-induced carcinogenesis are largely undetermined. The DNA damage and associated mutagenesis induced by DNA adducts and DNA-protein crosslinks have been the focus of formaldehyde carcinogenicity research. However, recent studies showed that exogenous formaldehyde caused only a modest increase in DNA adducts above levels caused by endogenous formaldehyde. This suggested the possibility that epigenetic mechanisms might contribute to formaldehyde-induced carcinogenicity. We and others have demonstrated that formaldehyde reacts with lysine residues on histone proteins to form a labile Schiff base or the more stable N6-formyllysine, and that both Schiff bases and N6-formyllysine residues are refractory to acetylation. These findings indicated that formaldehyde-histone lysine adducts might interfere with important cellular process regulated by histone lysine acetylation. However, it remains unknown which process is affected by this mechanism. Our preliminary data from cellular fractionation analyses demonstrate that formaldehyde exposure dramatically decreases lysine acetylations of the cytosolic histones H3 and H4. This finding is very intriguing, given that these modifications are critical for histone nuclear import and chromatin assembly. Our preliminary results further show that formaldehyde reduces the total amount of histone in the chromatin fraction and the levels of histones at genomic loci, suggesting inhibition of chromatin assembly. Defective chromatin assembly causes dysregulation of gene expression and genomic instability and was directly linked to different types of cancers. Based on these observations, we hypothesize that the formation of formaldehyde-histone adducts compromises histone nuclear import and/or chromatin assembly, thereby contributing to formaldehyde-induced carcinogenesis. To test this hypothesis, in Aim 1, we will examine whether the nuclear import of newly synthesized histones and their assembly into chromatin are compromised following formaldehyde exposure and determine the underlying mechanisms. In Aim 2, we will determine the impact of aberrant chromatin assembly on formaldehyde-induced changes in gene expression, formation of DNA adducts and DNA-protein crosslinks, and chromosome instability. In Aim 3, we will investigate whether formaldehyde exposure compromises chromatin assembly in vivo. The proposed concept that a chemical carcinogen reacts with newly synthesized histones to regulate chromatin assembly is novel. This study has the potential to reveal a new mechanism for chemical carcinogenesis.