Epigenetic silencing of interferon-kappa in human papillomavirus type 16-positive cells

Cancer Res. 2009 Nov 15;69(22):8718-25. doi: 10.1158/0008-5472.CAN-09-0550. Epub 2009 Nov 3.

Abstract

We have investigated interferon-kappa (IFN-kappa) regulation in the context of human papillomavirus (HPV)-induced carcinogenesis using primary human foreskin keratinocytes (HFK), immortalized HFKs encoding individual oncoproteins of HPV16 (E6, E7, and E6/E7), and cervical carcinoma cells. Here, IFN-kappa was suppressed in the presence of E6, whereas its expression was not affected in HFKs or E7-immortalized HFKs. Transcription could be reactivated after DNA demethylation but was decreased again upon drug removal. Partial reactivation could also be accomplished when E6 was knocked down, suggesting a contribution of E6 in IFN-kappa de novo methylation. We identified a single CpG island near the transcriptional start site as being involved in selective IFN-kappa expression. To prove the functional relevance of IFN-kappa in building up an antiviral response, IFN-kappa was ectopically expressed in cervical carcinoma cells where protection against vesicular stomatitis virus-mediated cytolysis could be achieved. Reconstitution of IFN-kappa was accompanied by an increase of p53, MxA, and IFN-regulatory factors, which was reversed by knocking down either IFN-kappa or p53 by small interfering RNA. This suggests the existence of a positive feedback loop between IFN-kappa, p53, and components of IFN signaling pathway to maintain an antiviral state. Our in vitro findings were further corroborated in biopsy samples of cervical cancer patients, in which IFN-kappa was also downregulated when compared with normal donor tissue. This is the first report showing an epigenetic silencing of type I IFN after HPV16 oncogene expression and revealing a novel strategy on how high-risk HPVs can abolish the innate immune response in their genuine host cells.

MeSH terms

  • Blotting, Western
  • Cell Line, Tumor
  • CpG Islands
  • DNA Methylation
  • Down-Regulation
  • Female
  • Gene Expression
  • Gene Expression Regulation*
  • Gene Silencing / physiology*
  • Human papillomavirus 16 / immunology
  • Humans
  • Interferon Type I / biosynthesis
  • Interferon Type I / genetics*
  • Keratinocytes / virology
  • Oncogene Proteins, Viral / biosynthesis
  • Oncogene Proteins, Viral / genetics
  • Papillomavirus Infections / complications
  • Papillomavirus Infections / genetics*
  • RNA, Small Interfering
  • Repressor Proteins / biosynthesis
  • Repressor Proteins / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / physiology*
  • Transcription, Genetic
  • Tumor Suppressor Protein p53 / metabolism
  • Uterine Cervical Neoplasms / genetics
  • Uterine Cervical Neoplasms / virology

Substances

  • E6 protein, Human papillomavirus type 16
  • Interferon Type I
  • Oncogene Proteins, Viral
  • RNA, Small Interfering
  • Repressor Proteins
  • Tumor Suppressor Protein p53
  • interferon kappa