P58^IPK suppresses NLRP3 inflammasome activation and IL-1β production via inhibition of PKR in macrophages

The NLRP3 inflammasome activation is a key signaling event for activation and secretion of pro-inflammatory cytokines such as IL-1β from macrophages. p58^IPK is a molecular chaperone that regulates protein homeostasis through inhibiting eIF-2α kinases including double-stranded RNA-dependent protein kinase (PKR), which has been recently implicated in inflammasome activation. Herein we investigate the role of p58^IPK in TLR4 signaling and inflammasome activation in macrophages. Primary bone marrow-derived macrophages (BMDM) was isolated from p58^IPK knockout (KO) and wildtype (WT) mice and treated with lipopolysaccharide (LPS) and ATP to activate TLR4 signaling and stimulate inflammasome activation. Compared to WT macrophages, p58^IPK deficient cells demonstrated significantly stronger activation of PKR, NF-κ B, and JNK and higher expression of pro-inflammatory genes TNF-α and IL-1β. Coincidently, p58^IPK deletion intensified NLRP3-inflammasome activation indicated by enhanced caspase 1 cleavage and increased IL-1β maturation and secretion. Pretreatment with specific PKR inhibitor or overexpression of p58^IPK largely abolished the changes in inflammasome activation and IL-1β secretion in p58^IPK null macrophages. Furthermore, immunoprecipitation assay confirmed the binding of p58^IPK with PKR, but not other TLR4 downstream signaling molecules. Collectively, these results suggest a novel and crucial role of p58^IPK in regulation of inflammasome activation and IL-1β secretion in macrophages.