{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,4]],"date-time":"2026-06-04T05:00:51Z","timestamp":1780549251825,"version":"3.54.1"},"reference-count":36,"publisher":"American Society for Microbiology","issue":"3","license":[{"start":{"date-parts":[[2024,3,13]],"date-time":"2024-03-13T00:00:00Z","timestamp":1710288000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2024,3,13]],"date-time":"2024-03-13T00:00:00Z","timestamp":1710288000000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.asm.org\/non-commercial-tdm-license"}],"funder":[{"DOI":"10.13039\/100000062","name":"HHS | NIH | National Institute of Diabetes and Digestive and Kidney Diseases","doi-asserted-by":"crossref","award":["DK052574"],"award-info":[{"award-number":["DK052574"]}],"id":[{"id":"10.13039\/100000062","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/100000062","name":"HHS | NIH | National Institute of Diabetes and Digestive and Kidney Diseases","doi-asserted-by":"crossref","award":["DK007130"],"award-info":[{"award-number":["DK007130"]}],"id":[{"id":"10.13039\/100000062","id-type":"DOI","asserted-by":"crossref"}]},{"name":"HHS | National Institutes of Health","award":["AI167285"],"award-info":[{"award-number":["AI167285"]}]},{"DOI":"10.13039\/100004319","name":"Pfizer","doi-asserted-by":"crossref","award":["#61798927"],"award-info":[{"award-number":["#61798927"]}],"id":[{"id":"10.13039\/100004319","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":["journals.asm.org"],"crossmark-restriction":true},"short-container-title":["mBio"],"published-print":{"date-parts":[[2024,3,13]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n          <jats:sec>\n            <jats:title\/>\n            <jats:p>\n              Since the beginning of the coronavirus disease 2019 (COVID-19) pandemic, much effort has been dedicated to identifying effective antivirals against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A number of calpain inhibitors show excellent antiviral activities against SARS-CoV-2 by targeting the viral main protease (M\n              <jats:sup>pro<\/jats:sup>\n              ), which plays an essential role in processing viral polyproteins. In this study, we found that calpain inhibitors potently inhibited the infection of a chimeric vesicular stomatitis virus (VSV) encoding the SARS-CoV-2 spike protein but not M\n              <jats:sup>pro<\/jats:sup>\n              . In contrast, calpain inhibitors did not exhibit antiviral activities toward the wild-type VSV with its native glycoprotein. Genetic knockout of calpain-2 by CRISPR\/Cas9 conferred resistance of the host cells to the chimeric VSV-SARS-CoV-2 virus and a clinical isolate of wild-type SARS-CoV-2. Mechanistically, calpain-2 facilitates SARS-CoV-2 spike protein-mediated cell attachment by positively regulating the cell surface levels of ACE2. These results highlight an M\n              <jats:sup>pro<\/jats:sup>\n              -independent pathway targeted by calpain inhibitors for efficient viral inhibition. We also identify calpain-2 as a novel host factor and a potential therapeutic target responsible for SARS-CoV-2 infection at the entry step.\n            <\/jats:p>\n          <\/jats:sec>\n          <jats:sec>\n            <jats:title>IMPORTANCE<\/jats:title>\n            <jats:p>Many efforts in small-molecule screens have been made to counter SARS-CoV-2 infection by targeting the viral main protease, the major element that processes viral proteins after translation. Here, we discovered that calpain inhibitors further block SARS-CoV-2 infection in a main protease-independent manner. We identified the host cysteine protease calpain-2 as an important positive regulator of the cell surface levels of SARS-CoV-2 cellular receptor ACE2 and, thus, a facilitator of viral infection. By either pharmacological inhibition or genetic knockout of calpain-2, the SARS-CoV-2 binding to host cells is blocked and viral infection is decreased. Our findings highlight a novel mechanism of ACE2 regulation, which presents a potential new therapeutic target. Since calpain inhibitors also potently interfere with the viral main protease, our data also provide a mechanistic understanding of the potential use of calpain inhibitors as dual inhibitors (entry and replication) in the clinical setting of COVID-19 diseases. Our findings bring mechanistic insights into the cellular process of SARS-CoV-2 entry and offer a novel explanation to the mechanism of activities of calpain inhibitors.<\/jats:p>\n          <\/jats:sec>","DOI":"10.1128\/mbio.02287-23","type":"journal-article","created":{"date-parts":[[2024,2,13]],"date-time":"2024-02-13T14:02:30Z","timestamp":1707832950000},"update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":7,"title":["Calpain-2 mediates SARS-CoV-2 entry via regulating ACE2 levels"],"prefix":"10.1128","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3731-9950","authenticated-orcid":false,"given":"Qiru","family":"Zeng","sequence":"first","affiliation":[{"name":"Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, 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