MERS-CoV Accessory ORFs Play Key Role for Infection and Pathogenesis

Abstract

While dispensable for viral replication, coronavirus (CoV) accessory open reading frame (ORF) proteins often play critical roles during infection and pathogenesis. Utilizing a previously generated mutant, we demonstrate that the absence of all four Middle East respiratory syndrome CoV (MERS-CoV) accessory ORFs (deletion of ORF3, -4a, -4b, and -5 [dORF3-5]) has major implications for viral replication and pathogenesis. Importantly, attenuation of the dORF3-5 mutant is primarily driven by dysregulated host responses, including disrupted cell processes, augmented interferon (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 NF-κB-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.

MERS-CoV infection is associated with downregulation of genes encoding Th1 and Th2 cytokines/chemokines and elevated inflammatory innate immune response in the lower respiratory tract

“…Likewise, increased levels of inflammatory IL-1β and IL-1α cytokines have been associated with tissue damage and acute inflammatory responses leading to mortality and severe pathogenesis, as well as induction of the inflammatory loop [14,18,19]. MERS-CoV evades and antagonizes the antiviral immune response, as well as the nuclear factor-κB (NF-κB) signaling pathway and the IFN signaling cascade [20][21][22]. The disease pathogenesis of MERS-CoV infection is complex, with various factors involved in the onset of severe pulmonary damage and dissemination of the virus to other organs.…”

Focus on Middle East respiratory syndrome coronavirus (MERS-CoV)

“…The flanking sequences, on both ends of the genome, contain untranslated 5 and 3 regions (UTR) ( Fig. 3) [17].…”

MERS coronavirus outbreak: Implications for emerging viral infections

“…Meanwhile non-structural protein NS3, NS4a, NS4b and NS5, as well as the structural M protein, have been implicated in IFN antagonism and inhibition of the innate immune response in cell culture studies (Canton et al, 2018;Matthews et al, 2014;Menachery et al, 2017b;Rabouw et al, 2016;Siu et al, 2014;Thornbrough et al, 2016;Yang et al, 2013Yang et al, , 2015b. Lack of homology between MERS-CoV and SARS-CoV in their accessory ORF-3, 4a, 4b and 5 genes highlights the fact that immune defense mechanisms may differ between the viruses.…”

“…Lack of homology between MERS-CoV and SARS-CoV in their accessory ORF-3, 4a, 4b and 5 genes highlights the fact that immune defense mechanisms may differ between the viruses. Deletion of MERS-CoV ORF-3 to 5 has been shown both in vitro and in vivo mouse models to impact on viral replication and pathogenesis via dysregulation of host cell responses, including increased activation of the type-1 IFN pathway and induction of inflammatory responses (Menachery et al, 2017b). ORF5 has been shown to partially modulate the inflammation-associated NF-κB transcription factor (Menachery et al, 2017b).…”

“…Deletion of MERS-CoV ORF-3 to 5 has been shown both in vitro and in vivo mouse models to impact on viral replication and pathogenesis via dysregulation of host cell responses, including increased activation of the type-1 IFN pathway and induction of inflammatory responses (Menachery et al, 2017b). ORF5 has been shown to partially modulate the inflammation-associated NF-κB transcription factor (Menachery et al, 2017b). The ORF4b-encoded NS4b protein has been shown in cell culture studies to inhibit IFN-and NF-κB-mediated signaling, IFNβ production and the (OAS)/RNaseL pathway (Matthews et al, 2014;Thornbrough et al, 2016;Yang et al, 2015b).…”