Integrin activation is an essential component of SARS-CoV-2 infection

Peter Simons, Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
Derek A. Rinaldi, Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
Virginie Bondu, Molecular Genetics and Microbiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
Alison M. Kell, Molecular Genetics and Microbiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USACenter for Infectious Diseases and Immunity, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
Steven Bradfute, Department of Internal Medicine, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA. 4Center for Infectious Diseases and Immunity, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
Diane Lidke, Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA, Comprehensive Cancer Center, University of New Mexico Health Sciences Center, Albuquerque, NM 87131
Tione Buranda, Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA, Center for Infectious Diseases and Immunity, University of New Mexico School of Medicine, Albuquerque, NM 87131

Abstract

SARS-CoV-2 infection depends on binding its spike (S) protein to angiotensin-converting enzyme 2 (ACE2). The S protein expresses an RGD motif, suggesting that integrins may be co-receptors. Here, we UV-inactivated SARS-CoV-2 and fluorescently labeled the envelope membrane with octadecyl rhodamine B (R18) to explore the role of integrin activation in mediating cell entry and productive infection. We used flow cytometry and confocal microscopy to show that SARS-CoV-2^R18 particles engage basal-state integrins. Furthermore, we demonstrate that Mn²⁺, which induces integrin extension, enhances cell entry of SARS-CoV-2^R18. We also show that one class of integrin antagonist, which binds to the αI MIDAS site and stabilizes the inactive, closed conformation, selectively inhibits the engagement of SARS-CoV-2^R18 with basal state integrins, but is ineffective against Mn²⁺-activated integrins. RGD-integrin antagonists inhibited SARS-CoV-2^R18 binding regardless of integrin activation status. Integrins transmit signals bidirectionally: 'inside-out' signaling primes the ligand-binding function of integrins via a talin-dependent mechanism, and 'outside-in' signaling occurs downstream of integrin binding to macromolecular ligands. Outside-in signaling is mediated by Gα₁₃. Using cell-permeable peptide inhibitors of talin and Gα₁₃ binding to the cytoplasmic tail of an integrin's β subunit, we demonstrate that talin-mediated signaling is essential for productive infection.