Arsenic Carcinogenesis and Interference With Histone mRNA

 描述(申请人提供)：外周血单核细胞(PMBC)中砷诱导基因表达的分析表明，组蛋白簇基因表达显著增加：在50个最上调的砷诱导基因中，22个是复制依赖的典型组蛋白基因。组蛋白基因是多细胞生物体中仅有的信使RNA(MRNAs)不在3‘端终止的基因。有趣的是，砷暴露诱导了典型的组蛋白mRNA的聚腺苷酸化。伴随而来的是组蛋白表达的增加和茎环结合蛋白(SLBP)的缺失。SLBP是处理复制依赖的典型组蛋白Pre-mRNA的关键因素。研究表明，SLBP的缺失会导致组蛋白mRNA的错误加工，产生带有Poly(A)尾巴的规范的组蛋白mRNAs。在砷暴露后，不同类型的细胞中SLBP的编码基因也减少，而处理标准组蛋白mRNA所需的其他因子都没有改变，这表明SLBP表达的减少是砷诱导组蛋白基因多聚腺苷化和组蛋白表达增加的主要原因。多聚(A)尾的加入将增加组蛋白信使核糖核酸的稳定性，使多腺化的组蛋白不仅存在于S时相，而且也存在于细胞周期的其他时相。事实上，在砷处理后，带有聚(A)尾巴的典型组蛋白H3在有丝分裂期间比未处理的细胞高3-FOD。砷的这些作用可能对核小体组装和转录产生很大的破坏作用，可能参与了砷的致癌过程。我们的研究集中在金属、表观遗传学和癌症方面，重点是金属诱导的组蛋白修饰的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微米)下对组蛋白基因的诱导产生如此深刻的影响。在这个项目中，我们将研究砷暴露如何导致SLBP的丢失，重点是激活依赖磷酸化的降解过程，以及SLBP启动子的表观遗传学变化。我们还将从核小体组装、转录、细胞周期和基因组稳定性等方面确定砷诱导的含有规范性组蛋白H3的聚(A)的后果。此外，我们还将研究在没有和存在砷暴露的情况下，SLBP的枯竭和重新表达对细胞转化的影响。最后，我们将研究小鼠暴露砷是否会导致SLBP的丢失，增加体内含有规范性组蛋白mRNA和组蛋白的聚(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.