Infection with human papillomavirus (HPV) 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. Genomic instability in the form of polyploidy has been implicated in a causal role in carcinogenesis. Expression of the HPV E6 and E7 oncogenes alone in human keratinocytes also leads to polyploidy, which is enhanced by spindle disruption and DNA damage. Previously, it was thought but not directly shown that E6 and E7 induce polyploidy by abrogating the spindle checkpoint and that degradation of the tumor suppressor p53 by E6 is important for its ability to induce polyploidy. However, our recent studies demonstrate that E6 and E7 do not have a significant effect on the spindle checkpoint in primary human keratinocytes (PHKs). Instead, our results suggest that E6 and E7 abrogate the postmitotic checkpoint to induce polyploidy after microtubule disruption. In addition, E7, and to a lesser extent E6, induce polyploidy in response to DNA damage through re-replication, a process of successive rounds of DNA replication without an intervening mitosis. Interestingly, E6 mutants defective in p53 degradation also induced polyploidy. To further explore the mechanisms by which E6 and E7 induce polyploidy, we propose the following specific aims: 1). To explore the p53-independent functions of E6 in abrogating the postmitotic checkpoint. 2). To elucidate the molecular basis underlying E7-induced re-replication. This application investigates under-studied cell cycle processes and challenges existing dogmas. These studies will shed light on mechanisms by which HPV induces genomic instability and hold promise for the development of drugs that target this process in pre- cancer lesions. 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 development of drugs that target this process. ? ? ?
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| Heilman, Susan A; Nordberg, Joshua J; Liu, Yingwang et al. (2009) Abrogation of the postmitotic checkpoint contributes to polyploidization in human papillomavirus E7-expressing cells. J Virol 83:2756-64 |
