Induction of genomic instability by HPV E6 and E7

描述(申请人提供)：人类乳头瘤病毒(HPV)感染是宫颈癌发生的必要条件，但不是充分条件。HPV引起的基因组不稳定性可能使细胞积累致癌所必需的额外遗传异常，并已被认为在致癌中起因果作用。原代人角质形成细胞(PHKs)中HPVE6和E7癌基因的表达导致多倍体，这种多倍体通过纺锤体破坏和DNA损伤而增强。以前，人们假设E6和E7通过取消有丝分裂纺锤体检查点而诱导多倍体，而E6降解抑癌基因P53来诱导多倍体。我们最近的研究表明，E6和E7对纺锤体检查点没有显著影响。取而代之的是，他们取消了有丝分裂后的检查点，在微管破裂后诱导多倍体。有趣的是，P53降解缺陷的E6突变体也会导致多倍体。此外，我们的研究表明，CDK4和CDK1在E6诱导的多倍体中起着重要作用。此外，E7通过重复复制诱导多倍体以应对DNA损伤，这是一个连续几轮DNA复制的过程，没有介入的有丝分裂。此外，我们发现DNA复制起始因子CDT1在E7诱导的再复制过程中被翻译后修饰，其不受控制的表达诱导了人类癌细胞的再复制。我们推测CDK4和CDK1的激活在E6诱导P53非依赖的多倍体过程中起重要作用，CDT1的修饰是E7诱导再次复制所必需的，而E6/E7诱导的多倍体将促进向非整倍体和癌症的进展。该提案的具体目标旨在测试这些可能性。这些研究将阐明HPV诱导基因组不稳定的机制，并有望识别药物开发的靶点。 公共卫生相关性：感染人乳头瘤病毒(HPV)会导致尖锐湿疣，并与宫颈癌的发展密切相关。HPV癌基因E6和E7对细胞周期检查点的调控导致了HPV诱导的基因组不稳定。这些研究将阐明HPV致癌的机制，并有望确定药物开发的靶点。

DESCRIPTION (provided by applicant): Human papillomavirus (HPV) infection is necessary but not sufficient for the development of cervical cancer. Genomic instability caused by HPV may enable cells to accumulate additional genetic abnormalities necessary for carcinogenesis and has been implicated in a causal role in carcinogenesis. Expression of the HPV E6 and E7 oncogenes in primary human keratinocytes (PHKs) leads to polyploidy, which is enhanced by spindle disruption and DNA damage. Previously, it was hypothesized that E6 and E7 induce polyploidy by abrogating the mitotic spindle checkpoint and that E6 degrades the tumor suppressor p53 to induce polyploidy. Our recent studies demonstrate that E6 and E7 do not have a significant effect on the spindle checkpoint. Instead, they abrogate the postmitotic checkpoint to induce polyploidy after microtubule disruption. Interestingly, E6 mutants defective in p53 degradation also induce polyploidy. Moreover, our studies suggest an important role for Cdk4 and Cdk1 in E6-induced polyploidy. In addition, E7 induces polyploidy in response to DNA damage through re-replication, a process of successive rounds of DNA replication without an intervening mitosis. Furthermore, we find that the DNA replication initiation factor Cdt1, whose uncontrolled expression induces re-replication in human cancer cells, is post-translationally modified during E7-induced re-replication. We hypothesize that activation of cdk4 and cdk1 plays an important role in p53-independent induction of polyploidy by E6, modification of Cdt1 is required for E7 to induce re-replication, and E6/E7-induced polyploidy will enhance the progression into aneuploidy and cancer. The specific aims of the proposal are designed to test these possibilities. These studies will shed light on mechanisms by which HPV induces genomic instability and hold promise for the identification of targets for drug development. PUBLIC HEALTH RELEVANCE: Infection with human papillomaviruses (HPV) induces warts and is strongly associated with the development of cervical cancer. Modulation of cell cycle checkpoints by the HPV oncogenes E6 and E7 contributes to HPV- induced genomic instability. These studies will shed light on mechanisms by which HPV induces cancer and hold promise for the identification of targets for drug development.