HPV-inactive cell populations arise from HPV16-transformed human keratinocytes after p53 knockout

Virology. 2021 Feb;554:9-16. doi: 10.1016/j.virol.2020.12.005. Epub 2020 Dec 10.


HPV-inactive head and neck and cervical cancers contain HPV DNA but do not express HPV E6/E7. HPV-positive primary head and neck tumors usually express E6/E7, however they may produce HPV-inactive metastases. These observations led to our hypothesis that HPV-inactive cancers begin as HPV-active lesions, losing dependence on E6/E7 expression during progression. Because HPV-inactive cervical cancers often have mutated p53, we investigated whether p53 loss may play a role in the genesis of HPV-inactive cancers. p53 knockout (p53-KO) by CRISPR-Cas9 resulted in a 5-fold reduction of E7 mRNA in differentiation-resistant HPV16 immortalized human keratinocytes (HKc/DR). E7 expression was restored by 5-Aza-2 deoxycytidine in p53 KO lines, suggesting a role of DNA methylation in this process. In-situ hybridization showed that p53 KO lines consist of mixed populations of E6/E7-positive and negative cells. Hence, loss of p53 predisposes HPV16 transformed cells to losing dependence on the continuous expression of HPV oncogenes for proliferation.

Keywords: CRISPR-Cas9; Cervical cancer; HPV inactive Cancer; HPV16; Head and neck cancer; Human papillomavirus; SIX1; p53.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • CRISPR-Cas Systems
  • Cell Line, Transformed
  • Cell Proliferation
  • Cell Survival
  • Cell Transformation, Viral*
  • Gene Expression
  • Gene Knockout Techniques
  • Genes, p53
  • Human papillomavirus 16 / genetics
  • Human papillomavirus 16 / physiology*
  • Humans
  • Keratinocytes / physiology*
  • Keratinocytes / virology*
  • Loss of Function Mutation
  • Oncogene Proteins, Viral / genetics*
  • Oncogene Proteins, Viral / metabolism
  • Papillomavirus E7 Proteins / genetics*
  • Papillomavirus E7 Proteins / metabolism
  • Repressor Proteins / genetics*
  • Repressor Proteins / metabolism
  • Transfection
  • Tumor Suppressor Protein p53 / genetics*
  • Tumor Suppressor Protein p53 / physiology


  • E6 protein, Human papillomavirus type 16
  • Oncogene Proteins, Viral
  • Papillomavirus E7 Proteins
  • Repressor Proteins
  • TP53 protein, human
  • Tumor Suppressor Protein p53
  • oncogene protein E7, Human papillomavirus type 16