Carboxyl-terminal fusion of E7 into Flagellin shifts TLR5 activation to NLRC4/NAIP5 activation and induces TLR5-independent anti-tumor immunity

Sci Rep. 2016 Apr 11:6:24199. doi: 10.1038/srep24199.

Abstract

Flagellin has the capacity to activate both Toll-like receptor 5 (TLR5) and Nod-like receptor C4 (NLRC4)/neuronal apoptosis inhibitory protein 5 (NAIP5) inflammasome signaling. We fused E7m (the inactivated E7 of human papillomavirus) to either end of the flagellin protein, and the resulting recombinant flagellin-E7m proteins (rFliCE7m and rE7mFliC) were used as immunogens. Both fusion proteins activated receptor signaling to different degrees. rE7mFliC-induced TLR5 activity was 10-fold higher than that of rFliCE7m, whereas rFliCE7m activated the NLRC4/NAIP5 pathway more strongly. Therefore, these recombinant proteins provided a tool to investigate which signaling pathway is critical for the induction of antigen-specific T cell responses and anti-tumor immunity. We demonstrated that rFliCE7m induced higher levels of E7-specific IFN-gamma-secreting cells and cytotoxic T lymphocytes (CTLs) than rE7mFliC, and a single injection with rFliCE7m but not rE7mFliC inhibited E7-expressing tumor growth in vivo. Furthermore, we confirmed that CD8(+) T cells played a major role in the anti-tumor immunity induced by rFliCE7m. These findings suggested that the NLRC4/NAIP5 intracellular signaling pathway was critical for the induction of anti-tumor immunity. These observations provide important information for the rational design of flagellin-based immunotherapy.

MeSH terms

  • Animals
  • Bone Marrow Cells / cytology
  • CARD Signaling Adaptor Proteins / metabolism*
  • CD8-Positive T-Lymphocytes / cytology
  • CD8-Positive T-Lymphocytes / drug effects
  • CD8-Positive T-Lymphocytes / immunology
  • Cell Line
  • Circular Dichroism
  • Enzyme-Linked Immunospot Assay
  • Female
  • Flagellin / genetics
  • Flagellin / metabolism*
  • Genes, Reporter
  • HEK293 Cells
  • Humans
  • Immunity, Innate
  • Interferon-gamma / analysis
  • Interferon-gamma / metabolism
  • Macrophages / cytology
  • Macrophages / drug effects
  • Macrophages / immunology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Neuronal Apoptosis-Inhibitory Protein / metabolism*
  • Papillomavirus E7 Proteins / genetics
  • Papillomavirus E7 Proteins / metabolism*
  • Recombinant Fusion Proteins / biosynthesis
  • Recombinant Fusion Proteins / immunology
  • Recombinant Fusion Proteins / pharmacology
  • Signal Transduction / drug effects
  • Toll-Like Receptor 5 / deficiency
  • Toll-Like Receptor 5 / genetics
  • Toll-Like Receptor 5 / metabolism*

Substances

  • CARD Signaling Adaptor Proteins
  • Neuronal Apoptosis-Inhibitory Protein
  • Papillomavirus E7 Proteins
  • Recombinant Fusion Proteins
  • Toll-Like Receptor 5
  • oncogene protein E7, Human papillomavirus type 16
  • Flagellin
  • Interferon-gamma