Utilization of High Throughput CRISPR Knockout Technologies to Identify Cellular Genes Involved in Human Papillomavirus Degradation of p53

Abstract

High-risk human papillomaviruses (hrHPVs) are the causative agents for most cases of cervical cancer; they have also been linked to other anogenital cancers as well as head and neck cancers. Vaccines against HPV were introduced in the mid-2000s, and while they are effective at preventing new HPV infection, they do nothing to help the tens of millions of people currently infected with hrHPV and are not readily available in certain parts of the world. High-risk HPVs encode two oncoproteins – E6 and E7 – which target the cellular tumor suppressors p53 and Rb respectively. E6 works with other cellular proteins to ubiquitylate the cellular tumor suppressor p53, effectively marking it for degradation by the proteasome. Inhibiting E6-mediated ubiquitylation of p53 in HPV-positive cervical cancer cells leads to p53 stabilization. Since HPV-positive cancers express wild-type p53, restoration of p53 triggers cells to undergo apoptosis. To address the need for novel therapeutics to treat HPV-induced cancers, we designed a functional genomics screen to identify cellular genes that are involved in hrHPV E6-mediated degradation of p53 in cervical cancer cells. Utilizing clustered regulatory interspaced short palindromic repeats (CRISPR)/ Cas9 technology, we screened over 8,000 cellular genes to identify those that, when knocked out, stabilized p53. This screen led to the identification of cellular targets, both previously identified and novel, that contribute to p53 degradation in HPV-positive cells. We are hopeful these findings will provide potential therapeutic targets for HPV-induced cancers.