SARS-CoV-2 NSP16 promotes IL-6 production by regulating the stabilization of HIF-1α

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiologic agent of coronavirus disease 2019 (COVID-19). Severe and fatal COVID-19 cases often display cytokine storm i.e. significant elevation of pro-inflammatory cytokines and acute respiratory distress syndrome (ARDS) with systemic hypoxia. Understanding the mechanisms of these pathogenic manifestations would be essential for the prevention and especially treatment of COVID-19 patients. Here, using a dual luciferase reporter assay for hypoxia-response element (HRE), we initially identified SARS-CoV-2 nonstructural protein 5 (NSP5), NSP16, and open reading frame 3a (ORF3a) to upregulate hypoxia-inducible factor-1α (HIF-1α) signaling. Further experiments showed NSP16 to have the most prominent effect on HIF-1α, thus contributing to the induction of COVID-19 associated pro-inflammatory response. We demonstrate that NSP16 interrupts von Hippel-Lindau (VHL) protein interaction with HIF-1α, thereby inhibiting ubiquitin-dependent degradation of HIF-1α and allowing it to bind HRE region in the IL-6 promoter region. Taken together, the findings imply that SARS-CoV-2 NSP16 induces HIF-1α expression, which in turn exacerbates the production of IL-6.