SAMHD1 depletion restricts SARS-CoV-2 infection by suppressing HNF1-dependent ACE2 expression in lung epithelial cells.

Sterile alpha motif and histidine-aspartate domain-containing protein 1 (SAMHD1) restricts a broad spectrum of viruses through multifaceted mechanisms. It also limits spontaneous- and virus-induced innate immune responses by suppressing proinflammatory cytokine and type-I interferon (IFN-I) production. Some viruses escape SAMHD1 restriction and utilize SAMHD1-mediated innate immune suppression to establish effective infection through IFN antagonism. Our previous studies showed that SAMHD1 is a proviral factor facilitating replication of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in human macrophages, monocytic THP-1 and epithelial-like HEK293T cell lines by suppressing IFN responses. However, it is unclear about the function of SAMHD1 in lung epithelial cells during SARS-CoV-2 infection. Here, we report that SAMHD1 knockout (KO) restricts SARS-CoV-2 replication in lung epithelial Calu-3 cells by suppressing endogenous expression of the viral receptor angiotensin-converting enzyme 2 (ACE2) via hepatocyte nuclear factor 1-alpha (HNF1α) and HNF1β. Using pseudotyped SARS-CoV-2 and lentiviral vectors, we found that SARS-CoV-2 spike protein-mediated viral entry was suppressed in SAMHD1 KO Calu-3 cells. SAMHD1 KO repressed ACE2 expression in Calu-3 cells at mRNA and protein levels. Functional analyses revealed that HNF1α and HNF1β were crucial for the endogenous ACE2 expression in Calu-3 cells. Additionally, SAMHD1 KO led to a reduction in the expression levels and ACE2-promoting function of HNF1α and HNF1β. Inhibition of IFN antiviral response by baricitinib, a Janus kinase 1 and 2 (JAK 1/2) inhibitor, did not revert the suppression of SARS-CoV-2 in SAMHD1 KO Calu-3 cells. SAMHD1 knock-in and deoxynucleoside supplementation experiments indicated that SAMHD1 expression and dNTP pool balance collectively regulated HNF1-mediated ACE2 expression in Calu-3 cells. Our findings demonstrate that SAMHD1 depletion hinders HNF1-mediated ACE2 expression and SARS-CoV-2 replication in Calu-3 cells via a novel mechanism beyond its IFN-suppressive function.