Direct cleavage of human NLRP1 by enteroviral 3C protease triggers inflammasome activation in airway epithelium

Abstract

Viruses pose a constant threat to human health. As a result our innate immune system has evolved multiple strategies to detect the presence of intracellular viral pathogen-associated molecular patterns (PAMPs). The full repertoire of human immune sensors and their PAMP ligands are not completely understood. Here we report that human NLRP1 senses and is activated by 3C proteases (3Cpros) of enteroviruses. Mechanistically, 3Cpros cleave human NLRP1 at a single site immediately after its primate-specific PYRIN domain, leading to oligomerization of its C-terminal fragment. Expression of 3Cpros in primary human cells cause NLRP1-dependent ASC oligomerization, pyroptotic cell death and IL-1 secretion. Consistent with our observation that NLRP1 is the predominant endogenous inflammasome sensor in human airway epithelium, we find that its genetic deletion, or that of ASC, abrogates IL-18 secretion from rhinovirus (HRV)-infected primary human bronchial epithelial cells. Our findings identify the first cognate PAMP ligand for human NLRP1 and assign a new function for the NLRP1 inflammasome in human antiviral immunity and airway inflammation. These results challenge the widely held notion that viral proteases largely serve to disable host immune sensing, and suggest that the human NLRP1 inflammasome may be a therapeutic target to treat inflammatory airway diseases including asthma.