Induction of genomic instability by HPV E6 and E7

描述（由申请人提供）：人乳头瘤病毒（HPV）感染是必要的，但不是发展为宫颈癌的充分条件。由HPV引起的基因组不稳定可能使细胞积累致癌所必需的额外遗传异常，并与致癌的因果作用有关。人乳头状瘤病毒E6和E7癌基因在原代人角质形成细胞（phk）中的表达可导致多倍体，多倍体通过纺锤体断裂和DNA损伤而增强。以前，人们假设E6和E7通过废除有丝分裂纺锤体检查点诱导多倍体，E6降解肿瘤抑制因子p53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。相反，它们在微管断裂后取消有丝分裂后检查点诱导多倍体。有趣的是，p53降解缺陷的E6突变体也会诱导多倍体。此外，我们的研究表明Cdk4和Cdk1在e6诱导的多倍体中起重要作用。此外，E7通过再复制诱导多倍体，以应对DNA损伤，这是一个连续的DNA复制过程，没有中间的有丝分裂。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不依赖p53诱导多倍体的过程中起着重要作用，E7诱导再复制需要修饰Cdt1， E6/E7诱导的多倍体将加速向非整倍体和癌症的发展。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，并为确定药物开发的靶点提供希望。

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.