SARS-Coronavirus Open Reading Frame-8b triggers intracellular stress pathways and activates NLRP3 inflammasomes

Shi, Chong-Shan; Nabar, Neel R.; Huang, Ning-Na; Kehrl, John H.

Intracellular protein aggregation contributes to the pathogenesis of a variety of diseases and is both propagated by and contributes to inflammation 37, 38 . Protein aggregates have long been observed after viral infection; viruses are known to use aggregates as scaffolds for replication and/or for shielding from host degradation 39 . In our study, ORF8b appears to be degraded by the autophagy-lysosome system, as treatment with bafilomycin A1 increases ORF8b levels. The aggregation ability of ORF8b may be protective against degradation, as we consistently observed that the anti-aggregation V77K mutant is expressed at lower levels than ORF8b. It has previously been reported that ORF8ab and ORF8b induce ER stress 40 , which is consistent with our findings showing accumulation of CHOP by ORF8b expression dependent on V77. We also find induction of lysosomal stress and activation of TFEB by ORF8b. Both ER stress and TFEB have been shown to propagate the inflammatory response, with TFEB directly promoting the transcription of inflammatory cytokines 26, 41, 42 . This may be a cellular mechanism by which ORF8b activates the innate immune response in macrophages and contributes to SARS-CoV pathogenesis.