MERS coronaviruses from camels in Africa exhibit region-dependent genetic diversity

Chu, Daniel K. W.; Hui, Kenrie P. Y.; Perera, Ranawaka A. P. M.; Miguel, Eve; Niemeyer, Daniela; Zhao, Jincun; Channappanavar, Rudragouda; Dudas, Gytis; Oladipo, Jamiu O.; Traoré, Amadou; Fassi-Fihri, Ouafaa; Ali, Abraham; Demissié, Getnet F.; Muth, Doreen; Chan, Michael C. W.; Nicholls, John M.; Meyerholz, David K.; Kuranga, Sulyman A.; Mamo, Gezahegne; Zhou, Ziqi; So, Ray T. Y.; Hemida, Maged G.; Webby, Richard J.; Roger, Francois; Rambaut, Andrew; Poon, Leo L. M.; Perlman, Stanley; Drosten, Christian; Chevalier, Veronique; Peiris, Malik

To specifically investigate whether the ORF4b deletion contributed to reduced replication competence, we compared recombinant EMC (rgEMC-WT) with an isogenic virus that was deleted in ORF4b (rgEMCΔ4b). We found rgEMCΔ4b viral titers did not significantly differ from rgEMC-WT at 24 h replication, in contrast with BF785 and Nig1657 viruses where replication was significantly reduced at this time. Thus, the ORF4b deletions in BF785 and Nig1657 were likely not major contributors to the reduced virus replication observed in clade C1 virus-infected cells. At 48 h post infection rgEMC-WT replicated to modestly lower titers compared with rgEMCΔ4b. The rgEMCΔ4b virus elicited significantly higher mRNA expression of IFN-β, IFN-λ1, CXCL10 (IP-10), ISG15, and MX1 in rgEMCΔ4b-infected cells. Previous evidence for an IFN antagonist role for ORF4b protein (10, 11) was based solely on the overexpression of ORF4b, while our data were generated from an isogenic deletion mutant virus. Increased mRNA of type I IFN and type III IFN as well as TNF-α suggests that ORF4b has effects on IRF-3 as well as NFκB pathways.