Toll-like receptor 4-mediated inflammation triggered by extracellular IFI16 is enhanced by lipopolysaccharide binding

• Published in: PLoS pathogens 2020-09, Vol.16 (9), p.e1008811-e1008811
• Main Authors: Iannucci, Andrea, Caneparo, Valeria, Raviola, Stefano, Debernardi, Isacco, Colangelo, Donato, Miggiano, Riccardo, Griffante, Gloria, Landolfo, Santo, Gariglio, Marisa, De Andrea, Marco
• Format: Article
• Language: English
• Subjects: Arthritis; Binding; Biology and Life Sciences; Cell cycle; Clear cell-type renal cell carcinoma; Cytokines; Damage patterns; Disease; E coli; Experiments; Extracellular matrix; Funding; Genetic aspects; Health aspects; Humans; Immune response; Immune system; Immunoprecipitation; Inflammation; Inflammation - immunology; Inflammation - metabolism; Inflammation - pathology; Inflammatory bowel disease; Interleukin 6; Interleukin 8; Kidney Neoplasms - immunology; Kidney Neoplasms - metabolism; Kidney Neoplasms - pathology; Leukemia - immunology; Leukemia - metabolism; Leukemia - pathology; Lipid A; Lipids; Lipopolysaccharides; Lipopolysaccharides - metabolism; Medicine; Medicine and Health Sciences; Monocytes; MyD88 protein; Myeloid Differentiation Factor 88 - metabolism; NF-kappa B - metabolism; Nuclear Proteins - metabolism; Pediatrics; Phosphoproteins - metabolism; Protein binding; Proteins; Public health; Research and Analysis Methods; Signal Transduction; Surface plasmon resonance; TLR4; TLR4 protein; Toll-Like Receptor 4 - metabolism; Toll-like receptors; Transcription activation; Transcription factors; Tumor Cells, Cultured; Tumor necrosis factor-α
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1008811

Damage-associated molecular patterns (DAMPs) are endogenous molecules activating the immune system upon release from injured cells. Here we show that the IFI16 protein, once freely released in the extracellular milieu of chronically inflamed tissues, can function as a DAMP either alone or upon binding to lipopolysaccharide (LPS). Specifically, using pull-down and saturation binding experiments, we show that IFI16 binds with high affinity to the lipid A moiety of LPS. Remarkably, IFI16 DAMP activity is potentiated upon binding to subtoxic concentrations of strong TLR4-activating LPS variants, as judged by TLR4-MD2/TIRAP/MyD88-dependent IL-6, IL-8 and TNF-α transcriptional activation and release in stimulated monocytes and renal cells. Consistently, using co-immunoprecipitation (co-IP) and surface plasmon resonance (SPR) approaches, we show that IFI16 is a specific TLR4-ligand and that IFI16/LPS complexes display a faster stimulation turnover on TLR4 than LPS alone. Altogether, our findings point to a novel pathomechanism of inflammation involving the formation of multiple complexes between extracellular IFI16 and subtoxic doses of LPS variants, which then signal through TLR4.