Mechanisms of arsenic-induced chromosomal instability and carcinogenesis

描述(申请人提供)：长期接触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。尽管过去进行了广泛的研究，但砷化合物促进癌症发生的机制在很大程度上仍然不清楚。流行病学研究表明，砷暴露可诱发微核、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都是非整倍体。在细胞分裂过程中，高保真的DNA复制和染色体补体在子代细胞中的忠实分布对维持染色体的稳定性至关重要。我们先前证明，三氧化二砷[As(III)]可抑制紫杉醇诱导的p53缺失和成熟细胞的有丝分裂停滞。我们最近发现，As(III)通过抑制细胞周期检查点蛋白BubR1的激活而诱导染色体不稳定，导致黑色素瘤和HeLa细胞中后期促进复合体/环体(APC/C)的非程序性激活。在野生型p53的细胞中，激活的APC/C明显导致姐妹染色单体过早分离，姐妹染色单体交换异常，并形成双倍染色体。此外，BubR1单倍体不足的小鼠在紫外线照射后容易发生皮肤损伤(增生)。鉴于已有文献证明As(III)在诱导核异常方面的作用，我们假设As(III)损害了依赖BubR1的纺锤体检查点，导致APC/C的非计划激活，染色体不稳定，以及由于DNA复制和染色体分离过程的失调而导致的肿瘤转化。为了验证这一假说，我们将(1)阐明As(Iii)诱导染色体不稳定的分子基础，重点研究Emi1-&Gt；APC/C-&gt；Gminin-&Gt；CDT1调节轴；(2)确定As(Iii)是否与纺锤体检查点缺陷在促进染色体不稳定性和体外致癌方面具有协同作用；(3)确定As(Iii)是否促进BubR1单倍体缺陷小鼠的自发肿瘤发展，并研究As(Iii)在促进紫外线照射诱导的小鼠皮肤肿瘤发生方面是否具有协同致癌作用。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是由于其对APC/C活性的扰动，导致对控制DNA复制和细胞分裂期间染色体分离至关重要的蛋白质的放松调控。我们预计，这一系列研究将有助于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.