Formation of the NLRP3 inflammasome inhibits stress granule assembly by multiple mechanisms

Abstract

Proper regulation of cellular response to environmental stress is crucial for maintaining biological homeostasis and is achieved by the balance between cell death processes, such as the formation of the pyroptosis-inducing NLRP3 inflammasome, and pro-survival processes, such as stress granule (SG) assembly. However, the functional interplay between these two stress-responsive organelles remains elusive. Here, we identified DHX33, a viral RNA sensor for the NLRP3 inflammasome, as a SG component, and the SG-nucleating protein G3BP as an NLRP3 inflammasome component. We also found that a decrease in intracellular potassium (K+) concentration, a key common step in NLRP3 inflammasome activation, markedly inhibited SG assembly. Therefore, when macrophages are exposed to stress stimuli with the potential to induce both SGs and the NLRP3 inflammasome, such as cytoplasmic poly(I:C) stimulation, they preferentially form the NLRP3 inflammasome but avoid SG assembly by sequestering G3BP into the inflammasome and by inducing a reduction in intracellular K+ levels. Thus, under such conditions, DHX33 is primarily utilized as a viral RNA sensor for the inflammasome. Our data reveal the functional crosstalk between NLRP3 inflammasome-mediated pyroptosis and SG-mediated cell survival pathways, and delineate a molecular mechanism that regulates cell-fate decisions and anti-viral innate immunity under stress.

Live cell protein imaging of tandem complemented-GFP11-tagged Coiled-coil domain-containing protein-124 identifies this factor in G3BP1-induced stress-granules.

“…Poly-IC is a double-stranded homopolymer used as a model RNA that activate TRIF-dependent toll-like receptor-3 (TLR3) ligand, triggering intrinsic viral response pathways and the formation of SGs [20,21]. As expected, G3BP1 stained SGs were not present in untreated cells (Fig.…”

“…A recent LC-Ms/Ms based study suggested CCDC124 protein as an interaction partner of a number of SG-localized protein including the well known SG marker protein G3BP1 [17]; and the data sets presented in https://doi.org/10.7910/DVN/EFBRHN), we decided inquire a possible colocalization of CCDC124 with G3BP1 at SGs. It was previously shown that a viral stress mimicking agent, poly-IC, induced activation of G3BP1 and the formation of cytoplasmic SGs [21]. We have analyzed SG localization of CCDC124 in U2OS cells expressing GFP11-tagged versions of this protein in a stable fashion (GFP11x 4 ::CCDC124, or CCDC124::GFP11x 4 ) in response to poly-IC treatments (Fig.…”