Post-transcriptional elements within NLRP3 mRNA set the activation threshold of the inflammasome.

Abstract

Abstract NOD-like receptor protein 3 (NLRP3) is an intracellular sensor and a major component of the canonical inflammasome pathway, which causes inflammation and cell death when activated by two temporally discrete signals. While novel putative activators of the NLRP3 inflammasome have been identified, the mechanisms that regulate expression of NLRP3 itself are less understood. Alternative polyadenylation (AP) is a mechanism by which cells modulate expression through varying the length of the 3′ untranslated region (3′UTR). Through AP, the longer forms may provide unique regulatory elements, that allow for differential regulation of mRNA stability and translation. Here we sought to thoroughly characterize the features of the NLRP3 3′UTR and hypothesized that AP may significantly control the threshold of inflammasome activation. We examined AP in THP-1 monocytes and found that they express both long and short forms, with the long form demonstrating decreased stability relative to the short. We have attributed these differences to the presence of AU-rich elements (ARE), as ablation of AREs results in increased stability of the long NLRP3 mRNA. Additionally, we have demonstrated that a known post-transcriptional regulator of NLRP3, miR-223, preferentially regulates the long transcript as well as augments the kinetics of pyroptotic cell death. These studies demonstrate that alternative polyadenylation of the 3′UTR of NLRP3 has a marked impact on the threshold of inflammasome activation.