ORAI1 Limits SARS-CoV-2 Infection by Regulating Tonic Type I IFN Signaling

Abstract

ORAI1 and stromal interaction molecule 1 (STIM1) are the critical mediators of store-operated Ca²⁺ entry by acting as the pore subunit and an endoplasmic reticulum-resident signaling molecule, respectively. In addition to Ca²⁺ signaling, STIM1 is also involved in regulation of the type I IFN (IFN-I) response. To examine their potential role in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, we generated <i>ORAI1</i> and <i>STIM1</i> knockout human HEK293-angiotensin-converting enzyme 2 cells and checked their responses. <i>STIM1</i> knockout cells showed strong resistance to SARS-CoV-2 infection as a result of enhanced IFN-I response. On the contrary, <i>ORAI1</i> deletion induced high susceptibility to SARS-CoV-2 infection. Mechanistically, <i>ORAI1</i> knockout cells showed reduced homeostatic cytoplasmic Ca²⁺ concentration and severe impairment in tonic IFN-I signaling. Transcriptome analysis showed downregulation of multiple antiviral signaling pathways in <i>ORAI1</i> knockout cells, likely because of reduced expression of the Ca²⁺-dependent transcription factors of the AP-1 family and <i>MEF2C</i> Accordingly, modulation of homeostatic Ca²⁺ concentration by pretreatment with ORAI1 blocker or agonist could influence baseline <i>IFNB</i> expression and resistance to SARS-CoV-2 infection in a human lung epithelial cell line. Our results identify a novel role of ORAI1-mediated Ca²⁺ signaling in regulating the tonic IFN-I levels, which determine host resistance to SARS-CoV-2 infection.