Centrosomal Kinase PLK4 Regulates NLRP3 Inflammasome Activation By Phosphorylating NEK7

The NLRP3 inflammasome is a multi-protein complex that governs the activation of Caspase-1 and the production and release of pro-inflammatory cytokines IL-1β and IL-18 in macrophages.Dysregulation of NLRP3 inflammasome has been associated with various autoimmune and inflammatory diseases.Recent studies have demonstrated that NLRP3 inflammasome activation requires the association of NLRP3 with NEK7,a serine/threonine kinase that regulates cell cycle.Despite the importance of NEK7 in NLRP3 inflammasome activation,how NLRP3-NEK7 interaction is regulated remains unclear.Here,we find that PLK4,a polo-like kinase with the best known function in regulating centriole duplication during the cell cycle,down-regulates the activation of NLRP3 inflammasome by modulating the association of NEK7 with NLRP3.Pharmacological inhibition or sh RNA-mediated silencing of PLK4 enhanced Caspase-1 activation,mature IL-1β secretion,and ASC speck formation.In vitro phosphorylation and mass spectrometrical analyses demonstrated that among the components of NLRP3 inflammasome PLK4 selectively phosphorylated NEK7 at Ser204.Further study with a site-specific phospho-antibody revealed that NEK7 Ser204 was phosphorylated during LPS priming and that inhibition of PLK4 reduced this phosphorylation and the NEK7-NLRP3 interaction.In line with this,mutation of NEK7Ser204 to non-phosphorylatible Ala augmented the NEK7-NLRP3 interaction and NLRP3 inflammasome activation.These data suggest that PLK4 suppress the activation of NLRP3 inflammasome by phosphorylating NEK7 at Ser204 and thus inhibiting the association of NEK7 with NLRP3.These findings identify the key cell cycle regulator PLK4 as a novel negative regulator of NLRP3 inflammasome activation which acts via controlling the phosphorylation of another cell cycle regulator NEK7,establish a link between centrosomes and inflammasomes,and provide new therapeutic targets for the treatment of inflammatory diseases.