Altered ISGylation drives aberrant macrophage-dependent immune responses during SARS-CoV-2 infection.

Munnur, Deeksha; Teo, Qiwen; Eggermont, Denzel; Lee, Horace H Y; Thery, Fabien; Ho, Julian; van Leur, Sophie Wilhelmina; Ng, Wilson W S; Siu, Lewis Y L; Beling, Antje; Ploegh, Hidde; Pinto-Fernandez, Adan; Damianou, Andreas; Kessler, Benedikt; Impens, Francis; Mok, Chris Ka Pun; Sanyal, Sumana

Ubiquitin-like protein ISG15 (interferon-stimulated gene 15) (ISG15) is a ubiquitin-like modifier induced during infections and involved in host defense mechanisms. Not surprisingly, many viruses encode deISGylating activities to antagonize its effect. Here we show that infection by Zika, SARS-CoV-2 and influenza viruses induce ISG15-modifying enzymes. While influenza and Zika viruses induce ISGylation, SARS-CoV-2 triggers deISGylation instead to generate free ISG15. The ratio of free versus conjugated ISG15 driven by the papain-like protease (PLpro) enzyme of SARS-CoV-2 correlates with macrophage polarization toward a pro-inflammatory phenotype and attenuated antigen presentation. In vitro characterization of purified wild-type and mutant PLpro revealed its strong deISGylating over deubiquitylating activity. Quantitative proteomic analyses of PLpro substrates and secretome from SARS-CoV-2-infected macrophages revealed several glycolytic enzymes previously implicated in the expression of inflammatory genes and pro-inflammatory cytokines, respectively. Collectively, our results indicate that altered free versus conjugated ISG15 dysregulates macrophage responses and probably contributes to the cytokine storms triggered by SARS-CoV-2.