Species-specific IL-1β is an inflammatory sensor of Seneca Valley Virus 3C Protease

by Xiangyu Huang, Zhenchao Zhao, Cheng Zhu, Lvye Chai, Ya Yan, Ye Yuan, Lei Wu, Minjie Li, Xiaohan Jiang, Haiwei Wang, Zheng Liu, Pingwei Li, Xin Li

Inflammasomes play pivotal roles in inflammation by processing and promoting the secretion of IL-1β. Caspase-1 is involved in the maturation of IL-1β and IL-18, while human caspase-4 specifically processes IL-18. Recent structural studies of caspase-4 bound to Pro-IL-18 reveal the molecular basis of Pro-IL-18 activation by caspase-4. However, the mechanism of caspase-1 processing of pro-IL-1β and other IL-1β-converting enzymes remains elusive. Here, we observed that swine Pro-IL-1β (sPro-IL-1β) exists as an oligomeric precursor unlike monomeric human Pro-IL-1β (hPro-IL-1β). Interestingly, Seneca Valley Virus (SVV) 3C protease cleaves sPro-IL-1β to produce mature IL-1β, while it cleaves hPro-IL-1β but does not produce mature IL-1β in a specific manner. When the inflammasome is blocked, SVV 3C continues to activate IL-1β through direct cleavage in porcine alveolar macrophages (PAMs). Through molecular modeling and mutagenesis studies, we discovered that the pro-domain of sPro-IL-1β serves as an ’exosite’ with its hydrophobic residues docking into a positively charged 3C protease pocket, thereby directing the substrate to the active site. The cleavage of swine IL-1β (sIL-1β) generates a monomeric and active form of sIL-1β, initiating the downstream signaling. Thus, these studies provide IL-1β is an inflammatory sensor that directly detects viral protease through an independent pathway operating in parallel with host inflammasomes.