Arsenic carcinogenesis and disruption of histone variant H3.3 assembly

项目摘要 砷已被确定为皮肤癌、肺癌、膀胱癌和肝癌的主要致病因子。砷 污染影响到世界上数亿人。砷的致癌性加上 大量的人暴露在这种环境中，这就迫切需要研究和了解它。 致癌机制，因此可以启动有效的治疗干预。与大多数其他基因不同， 典型的组蛋白信使RNA（mRNA）如组蛋白H3.1 mRNA不以聚（A）尾结束， 相反，它们在其3'末端具有茎环结构。茎环结合蛋白（SLBP）附着在茎环上， 典型组蛋白mRNA的3 '-加工所需的环状RNA结构。此前我们发现， 砷暴露下调SLBP水平，使经典组蛋白H3.1 mRNA获得poly（A） 尾巴H3.1 mRNA的多聚腺苷酸化似乎是致癌的，因为它诱导转录失调， 细胞周期停滞和基因组不稳定，并促进锚定非依赖性细胞生长和肿瘤 在裸鼠中形成。这些效应可能是由于变异组蛋白H3.3组装的破坏， 因为全基因组蛋白作图显示H3.1 mRNA的多聚腺苷酸化损害了H3.3 在转录、细胞身份和异染色质扩散的关键位点组装。H3.3播放 在转录、有效的DNA损伤修复、染色体的正确分离中起重要作用， 发展H3.3的敲低（其模拟H3.3组装的破坏）诱导细胞转化。 此外，H3.3突变体与各种类型的癌症有关，强调了H3.3在癌症中的重要性。 致癌作用基于这些观察结果，我们假设H3.3组装的破坏导致 来自典型组蛋白H3.1 mRNA的多聚腺苷酸化是砷诱导的 致癌作用为了验证这一假设，我们将确定多聚腺苷酸化的机制， 典型组蛋白H3.1 mRNA破坏Aim 1中变体H3.3的组装，确定是否有缺陷 H3.3组装体参与砷诱导的异常转录、细胞周期阻滞以及基因组凋亡。 目的2的不稳定性，并确定砷诱导的细胞中H3.3组装的破坏作用 转化，并探讨砷暴露是否破坏H3.3组装在体内的目的3。意义 这些研究的创新之处在于有可能揭示H3.3组装的破坏作为一种新的机制 砷诱发的致癌作用

PROJECT SUMMARY Arsenic has been identified as a prominent causal agent in skin, lung, bladder, and liver cancers. Arsenic contamination impacts hundreds of millions of people in the world. The carcinogenicity of arsenic coupled with an alarmingly large number of people exposed creates an urgency for studying and understanding its carcinogenic mechanisms so effective therapeutic intervention can be initiated. Unlike most other genes, canonical histone messenger RNAs (mRNAs) such as histone H3.1 mRNA do not end with a poly(A) tail, instead they have a stem-loop structure at their 3’ end. Stem-loop binding protein (SLBP) attaches to the stem- loop RNA structure that is required for 3’-processing of the canonical histone mRNA. Previously we found that arsenic exposure downregulates SLBP levels, allowing the canonical histone H3.1 mRNA to acquire a poly(A) tail. Polyadenylation of H3.1 mRNA appeared to be carcinogenic, since it induced transcriptional deregulation, cell cycle arrest, and genomic instability, and facilitated anchorage-independent cell growth and tumor formation in nude mice. These effects were likely resulting from disruption of variant histone H3.3 assembly, because genome-wide histone mapping showed that polyadenylation of H3.1 mRNA compromised the H3.3 assembly at the sites critical for transcription, cell identity, and heterochromatin spreading. H3.3 plays important roles in transcription, efficient DNA damage repair, proper segregation of chromosomes, and development. The knockdown of H3.3, which mimics disruption of H3.3 assembly, induced cell transformation. Furthermore, H3.3 mutants have been linked to various type of cancers, underscoring importance of H3.3 in carcinogenesis. Based on these observations, we hypothesize that disruption of H3.3 assembly resulting from polyadenylation of canonical histone H3.1 mRNA is a significant contributor to arsenic-induced carcinogenesis. To test this hypothesis, we will determine the mechanisms by which polyadenylated canonical histone H3.1 mRNA disrupts assembly of the variant H3.3 in Aim 1, determine whether defective H3.3 assembly is responsible for arsenic-induced aberrant transcription, cell cycle arrest as well as genomic instability in Aim 2, and determine the role for disruption of H3.3 assembly in arsenic-induced cell transformation and explore whether arsenic exposure disrupts H3.3 assembly in vivo in Aim 3. The significance and innovation of these studies lie in the potential to reveal disruption of H3.3 assembly as a novel mechanism of arsenic-induced carcinogenesis.