CD209L/L-SIGN and CD209/DC-SIGN Act as Receptors for SARS-CoV-2

Abstract

As the COVID-19 pandemic continues to spread, investigating the processes underlying the interactions between SARS-CoV-2 and its hosts is of high importance. Here, we report the identification of CD209L/L-SIGN and the related protein CD209/DC-SIGN as receptors capable of mediating SARS-CoV-2 entry into human cells. Immunofluorescence staining of human tissues revealed prominent expression of CD209L in the lung and kidney epithelia and endothelia. Multiple biochemical assays using a purified recombinant SARS-CoV-2 spike receptor-binding domain (S-RBD) or S1 encompassing both N termal domain and RBD and ectopically expressed CD209L and CD209 revealed that CD209L and CD209 interact with S-RBD. CD209L contains two N -glycosylation sequons, at sites N92 and N361, but we determined that only site N92 is occupied. Removal of the N -glycosylation at this site enhances the binding of S-RBD with CD209L. CD209L also interacts with ACE2, suggesting a role for heterodimerization of CD209L and ACE2 in SARS-CoV-2 entry and infection in cell types where both are present. Furthermore, we demonstrate that human endothelial cells are permissive to SARS-CoV-2 infection, and interference with CD209L activity by a knockdown strategy or with soluble CD209L inhibits virus entry. Our observations demonstrate that CD209L and CD209 serve as alternative receptors for SARS-CoV-2 in disease-relevant cell types, including the vascular system. This property is particularly important in tissues where ACE2 has low expression or is absent and may have implications for antiviral drug development.

SARS-CoV-2 S glycoprotein binding to multiple host receptors enables cell entry and infection

“…Interaction of SARS-CoV-2 S glycoprotein with additional receptors could emphasize severe inflammation and cytokine release (leading to cytokine storm). While Amraie et al [ 22 ] suggested CLRs could serve as alternative receptors to hACE2 in non-susceptible cells, this hasn’t been confirmed by Thépaut et al [ 41 ]. Detailed trans-infection mechanism and SARS-CoV-2 fate after interaction with CLRs remain an open question.…”

“…On the other hand, mannose receptor (MR) and MGL were expressed at a higher level, especially in lung and upper airway cells, and mostly restricted to macrophages and dendritic cells (DCs), which also produce DC-SIGN but to a lower extent. L-SIGN is mostly expressed in epithelial alveolar cells, lymphatic tissues in the ileum, endothelial cells in the pancreas and liver, and at lower levels in immune cells [ 10 , 22 ]. Expression levels of MGL and DC-SIGN were increased in severe COVID-19 patients with an elevated amount of proinflammatory monocyte-derived macrophages and inflammatory cytokines and chemokines (including IL-6, IL-1B, TNF, CXCL10, CXCL8, CCL2, and CCL3) [ 10 ].…”

“…In the same study, it was determined that ACE2 had the highest binding affinity for SARS-CoV-2, followed by DC-SIGN, while L-SIGN had a lower affinity for SARS-CoV-2 [ 10 ]. Amraei et al showed that L-SIGN binds to the RBD of SARS-CoV-2 to mediate cell entry as well as interacts with ACE2, when both are present, suggesting that heterodimerization of L-SIGN and ACE2 has a role in SARS-CoV-2 cell entry and infection [ 22 ]. Furthermore, soluble L-SIGN-Fc neutralized viral entry by 48%, while overexpression of L-SIGN in HEK293 cells increased SARS-CoV-2 viral replication [ 22 ].…”

“…Although ACE2 is broadly expressed in different mammalian tissues [ 15 , 16 ] and has been recognized as the main host cell receptor for SARS-CoV-2 cell entry [ 17 – 19 ], some studies have reported low expression of ACE2 in the respiratory system [ 15 , 20 , 21 ] indicating that S glycoprotein could interact with other receptors to enter the host cells causing systemic infection [ 10 , 22 ]. Recent NMR studies showed that N-glycans of the RBD at glycosylation sites N331 and N343 bind to macrophage galactose lectin (MGL), human lectins galectin-3, -7 and -8, sialic acid-binding immunoglobulin-type lectin (Siglec)-10 and dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) [ 23 ].…”

Cyclosporin A: A Repurposable Drug in the Treatment of COVID-19?

“…During the early infection process, the trimeric SARS-CoV-2 S1 spike first binds to the N-terminal portion of the angiotensin I-converting enzyme 2 (ACE2) which acts as viral receptor at the surface of susceptible cells ( 10 ). In addition to ACE2, molecules such as neuropilin-1 ( 11 ), chaperone GRP78 ( 12 ), and CD209/DC-SIGN ( 13 ) can act as SARS-CoV-2 receptors or co-receptors. Furthermore, the cellular transmembrane protease serine 2 (TMPRSS2) contributes to enhance the S-protein-driven viral entry ( 14 ).…”