In Kuwait, human coronavirus OC43 (HCoV-OC43) causes 25-30% of common cold, and 8.8% of respiratory infections in hospitalised patients. It is also associated with severe respiratory symptoms in infants, elderly, and immunocompromised patients. Our previous results showed that the expression of antiviral genes in human embryonic kidney (HEK) 293 cells is downregulated in the presence of HCoV-OC43 proteins. To understand the role of HCoV-OC43 proteins in antagonizing antiviral responses of the host, we investigated the effect of HCoV-OC43 structural and accessory proteins on the transcriptional activation of interferon-stimulated response element (ISRE), interferon-beta (IFN-beta) promoter, and nuclear factor kappa B response element (NF-kappaB-RE).
HCoV-OC43 ns2a, ns5a, membrane (M), and nucleocapsid (N) mRNA were amplified and cloned into the pAcGFP1-N expression vector, followed by transfection in HEK-293 cells. Two days post-transfection, the cells were co-transfected with a reporter vector containing firefly luciferase under the control of ISRE, IFN-beta promoter, or NF-kappaB-RE. Renilla luciferase vector was used as an internal control for transfection efficiency. Following 24 hours of incubation, the cells were treated with either IFN or tumour necrosis factor (TNF) for 6 hours. Thereafter, promoter activity was assayed using the dual-luciferase reporter assay system. Influenza NS1 protein was used as positive control for antagonism.
The transcriptional activity of ISRE, IFN-beta promoter, and NF-kappaB-RE was downregulated in the presence of ns2a, ns5a, M, or N protein as there was a sharp fall in firefly luciferase levels. Overall, HCoV-OC43 proteins reduced firefly luciferase levels for ISRE and IFN-beta promoter by at least ten fold, whereas for NF-kappaB-RE the firefly luciferase levels were reduced by at least five fold.
HCoV-OC43 has the ability to block the activation of different antiviral signaling pathways.
W. Widad Al-Nakib,
W. Chehadeh, None