ORAI1 limits SARS-CoV-2 infection by regulating tonic type I interferon signaling

ORAI1 and STIM1 are the critical mediators of store-operated Ca 2+ entry by acting as the pore subunit and an endoplasmic reticulum-resident signaling molecule, respectively. In addition to Ca 2+ signaling, STIM1 is also involved in regulation of the type I interferon (IFN-I) response. To examine their potential role in SARS-CoV-2 infection, we generated ORAI1 and STIM1 knockout human HEK293-ACE2 cells and checked their responses. STIM1 knockout cells showed strong resistance to SARS-CoV-2 infection due to enhanced type I interferon response. On the contrary, ORAI1 deletion induced high susceptibility to SARS-CoV-2 infection. Mechanistically, ORAI1 knockout cells showed reduced homeostatic cytoplasmic Ca 2+ concentration and severe impairment in tonic IFN-I signaling. Transcriptome analysis showed downregulation of multiple antiviral signaling pathways in ORAI1 knockout cells, likely, due to reduced expression of the Ca 2+ -dependent transcription factors of the activator protein 1 (AP-1) family and MEF2C . Accordingly, modulation of homeostatic Ca 2+ concentration by pre-treatment with ORAI1 blocker or agonist could influence baseline IFNB expression and resistance to SARS-CoV-2 infection in a human lung epithelial cell line. Our results identify a novel role of ORAI1-mediated Ca 2+ signaling in regulating the tonic type I interferon levels, which determine host resistance to SARS-CoV-2 infection.