The N-end rule ubiquitin ligase UBR2 mediates NLRP1B inflammasome activation by anthrax lethal toxin

• Published in: The EMBO journal 2019-07, Vol.38 (13), p.e101996
• Main Authors: Xu, Hao, Shi, Jianjin, Gao, Hang, Liu, Ying, Yang, Zhenxiao, Shao, Feng, Dong, Na
• Format: Article
• Language: English
• Subjects: Animals; Antigens, Bacterial - adverse effects; Apoptosis Regulatory Proteins - chemistry; Apoptosis Regulatory Proteins - metabolism; Bacterial Toxins - adverse effects; Caspase 1 - metabolism; CRISPR-Cas Systems; Gene Knockout Techniques; HEK293 Cells; Humans; Inflammasomes - drug effects; Macrophages - drug effects; Macrophages - metabolism; Mice; Protein Domains; Proteolysis - drug effects; RAW 264.7 Cells; RNA, Small Interfering - pharmacology; Ubiquitin-Conjugating Enzymes - metabolism; Ubiquitin-Protein Ligases - chemistry; Ubiquitin-Protein Ligases - metabolism; Ubiquitination - drug effects
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.2019101996

Anthrax lethal toxin (LT) is known to induce NLRP1B inflammasome activation and pyroptotic cell death in macrophages from certain mouse strains in its metalloprotease activity-dependent manner, but the underlying mechanism is unknown. Here, we establish a simple but robust cell system bearing dual-fluorescence reporters for LT-induced ASC specks formation and pyroptotic lysis. A genome-wide siRNA screen and a CRISPR-Cas9 knockout screen were applied to this system for identifying genes involved in LT-induced inflammasome activation. UBR2, an E3 ubiquitin ligase of the N-end rule degradation pathway, was found to be required for LT-induced NLRP1B inflammasome activation. LT is known to cleave NLRP1B after Lys44. The cleaved NLRP1B, bearing an N-terminal leucine, was targeted by UBR2-mediated ubiquitination and degradation. UBR2 partnered with an E2 ubiquitin-conjugating enzyme UBE2O in this process. NLRP1B underwent constitutive autocleavage before the C-terminal CARD domain. UBR2-mediated degradation of LT-cleaved NLRP1B thus triggered release of the noncovalent-bound CARD domain for subsequent caspase-1 activation. Our study illustrates a unique mode of inflammasome activation in cytosolic defense against bacterial insults.