PNNL

Abstract

While dispensable for viral replication, coronavirus (CoV) accessory open reading frame proteins (ORFs) often play critical roles during infection and pathogenesis. Utilizing a previously generated mutant, we demonstrate that the absence of all four MERS-CoV accessory ORFs (deletion of ORF3, 4a, 4b, and 5) has major implications on viral replication and pathogenesis. Importantly, attenuation of the dORF3-5 mutant is primarily driven by dysregulated host responses including disrupted cell processes, augmented IFN pathway activation, and robust inflammation. In vitro replication attenuation also extends to in vivo models allowing use of dORF3-5 as a live-attenuated vaccine platform. Finally, examination of ORF5 implicates a partial role in modulation of NFkB mediated inflammation. Together, the results demonstrate the importance of MERS-CoV accessory ORFs for pathogenesis and highlight them as potential targets for surveillance and therapeutic treatments moving forward. Importance The initial emergence and periodic outbreaks of MERS-CoV highlight a continuing threat posed by zoonotic pathogens to global public health. In these studies, mutant virus generation demonstrates the necessity of accessory ORFs in regards to MERS-CoV infection and pathogenesis. With this in mind, accessory ORF functions can be targeted for both therapeutic and vaccine treatments in response to MERS-CoV and related group 2C viruses. In addition, disrupting accessory ORFs in parallel may offer a rapid response platform to attenuation of future emergent strains based on both SARS and MERS-CoV accessory ORF mutants.