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Abstract
The NLRP3 inflammasome has an important function in inflammation by promoting the processing of pro-IL-1β and pro-IL-18 to their mature bioactive forms, and by inducing cell death via pyroptosis. Here we show a critical function of the E3 ubiquitin ligase Pellino2 in facilitating activation of the NLRP3 inflammasome. Pellino2-deficient mice and myeloid cells have impaired activation of NLRP3 in response to toll-like receptor priming, NLRP3 stimuli and bacterial challenge. These functions of Pellino2 in the NLRP3 pathway are dependent on Pellino2 FHA and RING-like domains, with Pellino2 promoting the ubiquitination of NLRP3 during the priming phase of activation. We also identify a negative function of IRAK1 in the NLRP3 inflammasome, and describe a counter-regulatory relationship between IRAK1 and Pellino2. Our findings reveal a Pellino2-mediated regulatory signaling system that controls activation of the NLRP3 inflammasome.
Highlights
The NLRP3 inflammasome has an important function in inflammation by promoting the processing of pro-IL-1β and pro-IL-18 to their mature bioactive forms, and by inducing cell death via pyroptosis
Given the previously described roles for Pellino[1] and Pellino[3] in Toll-like receptors (TLR) signaling pathways, we initially compared the responsiveness of bone marrow-derived macrophages (BMDMs) from wild type (WT) and Pellino2deficient mice to 24 h challenge with a wide array of TLR ligands, as measured by induction of the TLR-responsive proteins IL-6
We extended our studies on the physiological relevance of the role of Pellino[2] in responding to LPS and in promoting inflammasome activation by comparing the responsiveness of BMDMs from WT and Peli2−/− mice to the Gram negative bacteria Citrobacter rodentium (C. rodentium) and Escherichia coli (E. coli)
Summary
The NLRP3 inflammasome has an important function in inflammation by promoting the processing of pro-IL-1β and pro-IL-18 to their mature bioactive forms, and by inducing cell death via pyroptosis. IRAK1 subsequently interacts with the E3 ubiquitin ligase TNF receptor-associated factor 6 (TRAF6) and TAK1 kinase that activates the IkappaB (IκB) kinase (IKK) complex to phosphorylate and promote proteasomal degradation of IκB proteins, key inhibitors of the NFκB transcription factor[6]. This allows for nuclear translocation of NFκB. The secretion of mature IL-1β requires two signals Innate receptors, such as TLR4, is engaged by its ligand lipopolysaccharide (LPS) in Gram negative bacteria, to activate NFκB and induce transcription of the gene encoding the inactive proIL-1β precursor[11] with a second signal triggering inflammasome activation. In addition to revealing the first physiological role for Pellino[2], this study maps an entirely new regulatory pathway that controls NLRP3 activation
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