Dexamethasone disrupts intracellular pH homeostasis to delay coronavirus infectious bronchitis virus cell entry via sodium hydrogen exchanger 3 activation

ABSTRACT Coronavirus entry into host cells enables the virus to initiate its replication cycle efficiently while evading host immune response. Cell entry is intricately associated with pH levels in the cytoplasm or endosomes. In this study, we observed that the sodium hydrogen exchanger 3 (Na + /H + exchanger 3 or NHE3), which is strongly activated by dexamethasone (Dex) to promote cell membrane Na + /H + exchange, was critical for cytoplasmic and endosomal acidification. Dex activates NHE3, which increases intracellular pH and blocks the initiation of coronavirus infectious bronchitis virus (IBV) negative-stranded genomic RNA synthesis. Also, Dex antiviral effects are relieved by the glucocorticoid receptor (GR) antagonist RU486 and the NHE3 selective inhibitor tenapanor. These results show that Dex antiviral effects depend on GR and NHE3 activities. Furthermore, Dex exhibits remarkable dose-dependent inhibition of IBV replication, although its antiviral effects are constrained by specific virus and cell types. To our knowledge, this is the first report to show that Dex helps suppress the entry of coronavirus IBV into cells by promoting proton leak pathways, as well as by precisely tuning luminal pH levels mediated by NHE3. Disrupted cytoplasmic pH homeostasis, triggered by Dex and NHE3, plays a crucial role in impeding coronavirus IBV replication. Therefore, cytoplasmic pH plays an essential role during IBV cell entry, probably assisting viruses at the fusion and/or uncoating stages. The strategic modulation of NHE3 activity to regulate intracellular pH could provide a compelling mechanism when developing potent anti-coronavirus drugs. IMPORTANCE Since the outbreak of coronavirus disease 2019, dexamethasone (Dex) has been proven to be the first drug that can reduce the mortality rate of coronavirus patients to a certain extent, but its antiviral effect is limited and its underlying mechanism has not been fully clarified. Here, we comprehensively evaluated the effect of Dex on coronavirus infectious bronchitis virus (IBV) replication and found that the antiviral effect of Dex is achieved by regulating sodium hydrogen exchanger 3 (NHE3) activity through the influence of glucocorticoid receptor on cytoplasmic pH or endosome pH. Dex activates NHE3, leading to an increase in intracellular pH and blocking the initiation of negative-stranded genomic RNA synthesis of coronavirus IBV. In this study, we identified the mechanism by which glucocorticoids counteract coronaviruses in cell models, laying the foundation for the development of novel antiviral drugs.