Rethinking residual p53 function in HPV-positive cervical cancer cells

Human papillomavirus (HPV)-driven cancers remain some of the most prevalent cancers globally. HPV E7 induces unscheduled cellular DNA replication in the infected cell; the resulting apoptotic signaling is counteracted by high-risk HPV E6 oncoprotein, which promotes cell proliferation by targeting many cellular proteins for ubiquitin-mediated proteasomal degradation, including the p53 apoptotic tumor suppressor. E6 oncoprotein forms a heterodimeric complex with the ubiquitin ligase E6AP to recruit and degrade p53, inhibiting pro-apoptotic cellular signaling and disrupting cell cycle progression, leading to increased tumor cell growth. In addition, E6 oncoproteins bind p53, inhibiting its transcriptional transactivation function and disrupting the activation of the p21-Waf1-Cip1 pathway. However, residual p53 activity has been reported in HPV-positive cell lines, indicating a potential gain-of-function role for p53 in HPV-positive cervical cancer cells. To examine this, we used CRISPR-Cas9 ribonucleic protein complex to generate an HPV-positive p53 knockout (KO) HeLa cell line. We observed that the growth and metabolic activity of p53 KO cells are severely reduced. Transcriptomic analysis of these cells revealed gain-of-function (GOF) p53 activities and enrichment of wild-type p53 pathways. Immunoprecipitation analysis confirmed a pool of GOF p53 in these transformed cells. This study thus re-emphasizes the question of the role of residual p53 and provides a model system to investigate its functional mechanism in HPV-positive cervical cancer cells. IMPORTANCE: Cervical cancer is the fourth most common cause of cancer in women globally, with an estimated 660,000 new cases yearly, and is one of the leading causes of cancer death, with around 350,000 deaths worldwide in 2022. One of the key degradation targets of human papillomavirus (HPV) is the p53 tumor suppressor; however, residual amounts of the protein are still detected in HPV-positive cells. In this study, we created a p53-knockout cell line to determine if residual p53 has any gain-of-function growth-promoting activities. Our results demonstrate that cells without p53 grow slower, indicating that residual p53 has tumor-promoting functions and a conformation like that of mutant p53 when in complex with E6, indicating alternative mechanisms by which HPV can subvert the function of p53.