Nuclear factor erythroid 2-related factor 2 (NRF2) plays important roles in antiviral host cell defenses. We assessed the potential of the NRF2 activators 4-octyl itaconate (4OI), bardoxolone (BARD), and sulforaphane (SFN), and the exportin-1 (XPO1) blocker selinexor (SEL) to inhibit highly pathogenic (SARS-CoV-2) and seasonal (hCoV-229E) coronaviruses in cellular models. We find that NRF2 knock-out enhances infection by both viruses, but that the compounds restrict these viruses in a largely NRF2-independent manner. 4OI and SEL are most effective against SARS-CoV-2 when added to media before infection, and they reduce cell entry of SARS-CoV-1 and -2 spike protein VSV pseudotypes >10-fold. Strikingly, the compounds downregulate ACE2, TMPRSS2, and XPO1 mRNA and protein, whereby 4OI diminishes STAT3 phosphorylation and represses the XPO1 gene promoter. 4OI dramatically reduces ACE2 half-life, which requires ubiquitin E3 ligases NEDD4L and MDM2, but is mediated by the lysosomal pathway. XPO1 knock-down reduces CoV-229E replication and reveals that efficacy of the compounds against CoV-229E depends on XPO1 expression in the order SEL > 4OI > SFN > BARD, suggesting that especially BARD restricts hCoV-229E via another, unknown, target. Taken together, these results suggest that "NRF2 activators" can restrict human coronaviruses by targeting an NRF2-independent network involving ACE2, TMPRSS2, and XPO1.
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