ABSTRACT
The recently identified 2019 novel coronaviruses (2019-nCoV) has caused extra-human infections. 2019-nCoV identified a global threat that is causing an outbreak of unusual viral pneumonia in patients with severe acute respiratory syndrome (SARS)-coronaviruses 2 (SARS-CoV-2). Considering the relatively high identity of the receptor-binding domain (RBD) in 2019-nCoV and SARS-CoV, it is urgent to assess the cross-reactivity of anti-SARS-CoV antibodies with 2019-nCoV spike protein, which could have important implications for rapid development of vaccines and therapeutic antibodies against 2019-nCoV. The zinc metallopeptidase angiotensin-converting enzyme 2 (ACE2) is the only known human homolog of the key regulator of blood pressure ACE. ACE2 also serves as the cellular entry point for the SARS virus, therefore, a prime target for pharmacological intervention. SARS-CoV-2 uses the SARS-CoV receptor for entry and the serine protease transmembrane protease serine 2 for spike (S) protein priming. That it is still necessary to develop novel mAbs that could bind specifically to 2019-nCoV RBD. Cell entry of coronaviruses depends on the binding of the viral S proteins to cellular receptors and S protein priming by host cell proteases. A transmembrane protease serine 2 inhibitor approved for clinical use blocked entry and might constitute a treatment option. Our results reveal important commonalities between SARS-CoV-2 and SARS-CoV infection and identify a potential target for antiviral intervention. This review will help understand the biology and potential risk of CoVs that exist in richness in wildlife such as bats. We provide a brief introduction to the pathogenesis of SARS-CoV and Middle East respiratory syndrome-CoV and interaction between the RBD of coronavirus spike protein and ACE2.
ABSTRACT
The coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is bringing an unprecedented health crisis to the world. To date, our understanding of the interaction between SARS-CoV-2 and host innate immunity is still limited. Previous studies reported that SARS-CoV-2 nonstructural protein 12 (NSP12) was able to suppress interferon-ß (IFN-ß) activation in IFN-ß promoter luciferase reporter assays, which provided insights into the pathogenesis of COVID-19. In this study, we demonstrated that IFN-ß promoter-mediated luciferase activity was reduced during coexpression of NSP12. However, we could show NSP12 did not affect IRF3 or NF-κB activation. Moreover, IFN-ß production induced by Sendai virus (SeV) infection or other stimulus was not affected by NSP12 at mRNA or protein level. Additionally, the type I IFN signaling pathway was not affected by NSP12, as demonstrated by the expression of interferon-stimulated genes (ISGs). Further experiments revealed that different experiment systems, including protein tags and plasmid backbones, could affect the readouts of IFN-ß promoter luciferase assays. In conclusion, unlike as previously reported, our study showed SARS-CoV-2 NSP12 protein is not an IFN-ß antagonist. It also rings the alarm on the general usage of luciferase reporter assays in studying SARS-CoV-2. IMPORTANCE Previous studies investigated the interaction between SARS-CoV-2 viral proteins and interferon signaling and proposed that several SARS-CoV-2 viral proteins, including NSP12, could suppress IFN-ß activation. However, most of these results were generated from IFN-ß promoter luciferase reporter assay and have not been validated functionally. In our study, we found that, although NSP12 could suppress IFN-ß promoter luciferase activity, it showed no inhibitory effect on IFN-ß production or its downstream signaling. Further study revealed that contradictory results could be generated from different experiment systems. On one hand, we demonstrated that SARS-CoV-2 NSP12 could not suppress IFN-ß signaling. On the other hand, our study suggests that caution needs to be taken with the interpretation of SARS-CoV-2-related luciferase assays.