Post-translational control of IL-1β via the human papillomavirus type 16 E6 oncoprotein: a novel mechanism of innate immune escape mediated by the E3-ubiquitin ligase E6-AP and p53

PLoS Pathog. 2013;9(8):e1003536. doi: 10.1371/journal.ppat.1003536. Epub 2013 Aug 1.

Abstract

Infections with high-risk human papillomaviruses (HPVs) are causally involved in the development of anogenital cancer. HPVs apparently evade the innate immune response of their host cells by dysregulating immunomodulatory factors such as cytokines and chemokines, thereby creating a microenvironment that favors malignancy. One central key player in the immune surveillance interactome is interleukin-1 beta (IL-1β) which not only mediates inflammation, but also links innate and adaptive immunity. Because of its pleiotropic physiological effects, IL-1β production is tightly controlled on transcriptional, post-translational and secretory levels. Here, we describe a novel mechanism how the high-risk HPV16 E6 oncoprotein abrogates IL-1β processing and secretion in a NALP3 inflammasome-independent manner. We analyzed IL-1β regulation in immortalized keratinocytes that harbor the HPV16 E6 and/or E7 oncogenes as well as HPV-positive cervical tumor cells. While in primary and in E7-immortalized human keratinocytes the secretion of IL-1β was highly inducible upon inflammasome activation, E6-positive cells did not respond. Western blot analyses revealed a strong reduction of basal intracellular levels of pro-IL-1β that was independent of dysregulation of the NALP3 inflammasome, autophagy or lysosomal activity. Instead, we demonstrate that pro-IL-1β is degraded in a proteasome-dependent manner in E6-positive cells which is mediated via the ubiquitin ligase E6-AP and p53. Conversely, in E6- and E6/E7-immortalized cells pro-IL-1β levels were restored by siRNA knock-down of E6-AP and simultaneous recovery of functional p53. In the context of HPV-induced carcinogenesis, these data suggest a novel post-translational mechanism of pro-IL-1β regulation which ultimately inhibits the secretion of IL-1β in virus-infected keratinocytes. The clinical relevance of our results was further confirmed in HPV-positive tissue samples, where a gradual decrease of IL-1β towards cervical cancer could be discerned. Hence, attenuation of IL-1β by the HPV16 E6 oncoprotein in immortalized cells is apparently a crucial step in viral immune evasion and initiation of malignancy.

Publication types

  • Clinical Trial

MeSH terms

  • Cell Line, Transformed
  • Cell Transformation, Viral / genetics
  • Cell Transformation, Viral / immunology*
  • Female
  • Human papillomavirus 16 / genetics
  • Human papillomavirus 16 / immunology*
  • Human papillomavirus 16 / metabolism
  • Humans
  • Immunity, Innate*
  • Interleukin-1beta / genetics
  • Interleukin-1beta / immunology*
  • Interleukin-1beta / metabolism
  • Male
  • Oncogene Proteins, Viral / genetics
  • Oncogene Proteins, Viral / immunology*
  • Oncogene Proteins, Viral / metabolism
  • Protein Processing, Post-Translational / genetics
  • Protein Processing, Post-Translational / immunology*
  • Proteolysis*
  • Repressor Proteins / genetics
  • Repressor Proteins / immunology*
  • Repressor Proteins / metabolism
  • Tumor Escape / genetics
  • Tumor Escape / immunology*
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / immunology*
  • Tumor Suppressor Protein p53 / metabolism
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / immunology*
  • Ubiquitin-Protein Ligases / metabolism

Substances

  • E6 protein, Human papillomavirus type 16
  • IL1B protein, human
  • Interleukin-1beta
  • Oncogene Proteins, Viral
  • Repressor Proteins
  • TP53 protein, human
  • Tumor Suppressor Protein p53
  • UBE3A protein, human
  • Ubiquitin-Protein Ligases

Grant support

This work was supported by the German Cancer Research Center (DKFZ). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.