Arsenic Carcinogenesis and Interference With Histone mRNA

 描述（由申请人提供）：对外周血单核细胞（PMBC）中砷诱导的基因表达的分析表明组蛋白簇基因表达显著增加：在50个上调最多的砷诱导基因中，22个是复制依赖性典型组蛋白基因。经典组蛋白基因是多细胞生物中信使RNA（mRNA）在3'端不以poly（A）尾终止的唯一基因。有趣的是，砷暴露诱导典型组蛋白mRNA的多聚腺苷酸化。这伴随着组蛋白表达的增加和茎环结合蛋白（SLBP）的耗竭。SLBP是加工复制依赖的典型组蛋白前体mRNA的关键因子。已经显示，SLBP的缺失导致组蛋白mRNA错误加工，产生具有聚（A）尾的典型组蛋白mRNA。在砷暴露后的各种细胞类型中，SLBP的mRNA编码也下降，而没有其他因素需要处理典型组蛋白mRNA的改变，这表明SLBP表达的减少是砷诱导的典型组蛋白mRNA的多聚腺苷酸化和组蛋白表达增加的主要原因。将poly（A）尾添加到典型组蛋白mRNA将增加mRNA的稳定性，允许聚腺苷酸化的组蛋白不仅存在于S期，而且也存在于细胞周期的其他阶段。事实上，在砷处理后，具有poly（A）尾的典型组蛋白H3在有丝分裂期间比未处理的细胞高3- fod。砷的这些作用可能是非常破坏核小体的组装和转录，并可能参与介导砷致癌作用。我们的研究主要集中在金属，表观遗传学和癌症，重点是金属诱导的组蛋白修饰变化以及它们如何影响转录。然而，我们从未观察到任何金属在如此低的浓度（0.1-0.5 µM）下对组蛋白基因的诱导产生如此深远的影响。在这个项目中，我们将研究砷暴露如何导致SLBP的丢失，重点是磷酸化依赖的降解过程的激活，以及SLBP启动子的表观遗传变化。我们还将确定砷诱导收购的聚（A）含有典型的组蛋白H3的核小体组装，转录，细胞周期和基因组稳定性方面的后果。此外，我们将研究在砷暴露的存在和不存在下SLBP的耗竭和重新表达对细胞转化的影响。最后，我们将研究砷暴露在小鼠体内是否会诱导SLBP的丢失，增加含有典型组蛋白mRNA和组蛋白蛋白的poly（A）。

 DESCRIPTION (provided by applicant): Analysis of arsenic-induced gene expression in peripheral blood mononuclear cells (PMBCs) demonstrated a profound increase in the histone cluster gene expression: of the 50 most upregulated arsenic induced genes, 22 were replication-dependent canonical histone genes. The canonical histone genes are the only genes in multicellular organisms whose messenger RNA (mRNA) does not terminate at the 3' end with a poly (A) tail. Intriguingly, arsenic exposure induced polyadenylation of the canonical histone mRNA. This was accompanied by an increase in histone protein expression and a depletion of stem loop binding protein (SLBP). SLBP is a key factor in processing replication-dependent canonical histones pre-mRNA. It has been shown that depletion of SLBP results in histone mRNA misprocessing, generating canonical histone mRNAs with poly (A) tails. The mRNA coding for SLBP was also decreased in various cell types following arsenic exposure, whereas none of the other factors needed to process canonical histone mRNA were altered, suggesting that the reduction of SLBP expression is the major cause of arsenic-induced polyadenylation of canonical histone mRNA and the increase in histone protein expression. The addition of the poly (A) tail to the canonical histone mRNA will increase the mRNA stability, allowing for the polyadenylated histones to be present not only in the S phase, but in other phases of the cell cycle as well. In fact, after arsenic treatment canonical histone H3 with a poly (A) tail was 3- fod higher during mitosis compared to untreated cells. These effects of arsenic could be very disruptive to nucleosome assembly and transcription and may be involved in mediating arsenic carcinogenesis. Our research has focused on metals, epigenetics and cancer, with an emphasis on metal induced changes in histone modifications and how they impact transcription. However, we have never observed any metal that causes such a profound effect on the induction of histone genes and at such low concentrations (0.1-0.5 µM). In this project, we will investigate how arsenic exposure results in the loss of SLBP, focusing on the activation of a phosphorylation dependent degradation process, and epigenetic changes in the SLBP promoter. We will also determine the consequences of arsenic-induced acquisition of poly (A) containing canonical histone H3 in terms of nucleosome assembly, transcription, cell cycle, and genomic stability. In addition, we will examine the impact of depletion and re-expression of SLBP in the absence and presence of arsenic exposure on cell transformation. Finally, we will study whether arsenic exposure in mice induces a loss of SLBP, increases poly (A) containing canonical histone mRNA and histone protein in vivo.