Mechanisms of arsenic-induced chromosomal instability and carcinogenesis

描述（由申请人提供）：长期暴露于砷与几种恶性肿瘤的发生高度相关，包括皮肤癌、肺癌和膀胱癌。尽管过去进行了大量的研究，但砷化合物促进致癌的机制在很大程度上仍不清楚。流行病学研究表明，砷暴露诱导微核、染色体畸变和非整倍体的形成，这可能是癌症发生的罪魁祸首，因为大多数实体肿瘤是非整倍体。在细胞分裂过程中，高保真DNA复制和染色体补体对子细胞的忠实分布对维持染色体的稳定性至关重要。我们之前已经证明，三氧化二砷[As(III)]会损害紫杉醇诱导的p53缺陷细胞和p53精通细胞的有丝分裂停滞。我们最近的研究表明，As（III）通过抑制BubR1（一种细胞周期检查点蛋白）的激活诱导染色体不稳定性，导致黑色素瘤和HeLa细胞中后期促进复合物/环体（APC/C）的非预定激活。激活的APC/C明显导致野生型p53细胞中姐妹染色单体过早分离、姐妹染色单体异常交换和双染色体形成。此外，BubR1单倍体不足的小鼠暴露于紫外线照射后容易发生皮肤病变（增生）。鉴于已有文献记载的As（III）对诱导核异常的作用，我们假设As（III）破坏bubr1依赖性纺锤体检查点，导致APC/C的非预定激活，染色体不稳定，以及由于DNA复制和染色体分离过程失调而导致的肿瘤转化。为了验证这一假设，我们将(1)阐明As（III）诱导染色体不稳定性的分子基础，重点研究Emi1->APC/C->geminin->Cdt1调控轴；(2)确定As（III）是否与纺锤体检查点缺陷协同促进染色体不稳定性和体外致癌转化。(3)确定As（III）是否促进BubR1单倍体不足小鼠的自发肿瘤发展，并研究As（III）是否作为一种共同致癌物促进紫外线照射诱导的小鼠皮肤肿瘤发生。该项目的长期目标是了解与As（III）相关的生物学特性是否至少部分归因于其对APC/C活性的扰动，从而导致对细胞分裂过程中DNA复制和染色体分离控制至关重要的蛋白质的失调。我们预计，这条研究路线将导致确定癌症干预的关键分子靶点，以及改善砷化合物的有害影响。

DESCRIPTION (provided by applicant): Chronic exposure to arsenic is highly associated with the occurrence of several types of malignancies, including skin, lung and bladder cancer. Despite extensive studies in the past, the mechanism by which arsenic compounds promote carcinogenesis remains largely unclear. Epidemiological studies reveal that arsenic exposure induces the formation of micronuclei, chromosomal aberrations, and aneuploidy, which may be a culprit in the genesis of cancer since most solid tumors are aneuploid. High fidelity DNA replication and faithful distribution of the chromosomal complement to daughter cells during cell division are of paramount importance to the maintenance of chromosomal stability. We previously demonstrated that arsenic trioxide [As(III)] compromises paclitaxel-induced mitotic arrest in both p53-deficient and proficient cells. We have recently shown that As(III) induces chromosomal instability by suppressing the activation of BubR1, a cell cycle checkpoint protein, leading to unscheduled activation of anaphase promoting complex/cyclosome (APC/C) in melanoma and HeLa cells. Activated APC/C apparently causes premature separation of sister chromatids, aberrant sister chromatid exchanges, and diplochromosome formation in cells with wild-type p53. Moreover, mice with haploinsufficiency of BubR1 are prone to the development of skin lesions (hyperplasia) after exposure to UV irradiation. Given the documented effect of As(III) on the induction of nuclear abnormalities, we hypothesize that As(III) compromises the BubR1-dependent spindle checkpoint, resulting in unscheduled activation of APC/C, chromosomal instability, and neoplastic transformation owing to dysregulation of DNA replication and chromosome segregation processes. To test this hypothesis, we will (1) elucidate the molecular basis by which As(III) induces chromosomal instability with an emphasis on studying the Emi1->APC/C->geminin->Cdt1 regulatory axis, (2) determine if As(III) synergizes with spindle checkpoint deficiency in promoting chromosomal instability and oncogenic transformation in vitro, (3) determine if As(III) enhances spontaneous tumor development in BubR1 haploinsufficient mice and investigate if As(III) functions as a co-carcinogen in promoting skin tumorigenesis induced by UV irradiation in these mice. The long term goal of the project is to understand whether the biological properties associated with As(III) are at least partly due to its action on the perturbation of APC/C activities, causing deregulation of proteins crucial for the control of DNA replication and chromosomal segregation during cell division. We anticipate that this line of research will lead to the identification of key molecular targets for cancer intervention, as well as for ameliorating the detrimental effects of arsenic compounds. PUBLIC HEALTH RELEVANCE: Arsenic is an environmental carcinogen. Epidemiological and laboratory studies show that arsenic exposure is closely correlated with micronuclei and aneuploidy formation. This proposal intends to elucidate the molecular basis by which As(III) affects chromosomal stability and induces aneuploidy by perturbing the function of key molecules that regulate surveillance systems of dividing cells.