Inhibition of the Cellular Deubiquitinase UCHL1 Suppresses SARS-CoV-2 Replication

Anti-SARS-CoV-2 Small Molecule Targeting of Oxysterol-Binding Protein (OSBP) Activates Cellular Antiviral Innate Immunity

Human oxysterol-binding protein (OSBP) is a potentially druggable mediator in the replication of a broad spectrum of positive-sense (+) single-stranded RNA (ssRNA) viruses, including members of the Picornaviridae, Flaviviridae, and Coronaviridae. OSBP is a cytoplasmic lipid transporting protein capable of moving cholesterol and phosphoinositides between the endoplasmic reticulum (ER) and Golgi, and the ER and lysosome. Several structurally diverse antiviral compounds have been reported to function through targeting OSBP, including the natural product compound OSW-1. Our prior work shows that transient OSW-1 treatment induces a reduction in OSBP protein levels over multiple successive cell generations (i.e., multigenerational), with no apparent cellular toxicity, and the OSW-1-induced reduction of OSBP has antiviral activity against multiple (+)ssRNA viruses. This study extends these findings and establishes that OSW-1 has in vitro antiviral activity against multiple pathogenic (+)ssRNA viruses, including human rhinovirus (HRV1B), the feline coronavirus peritonitis virus (FIPV), human coronavirus 229E (HCoV-229E), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We also demonstrate that OSW-1 treatment in human airway epithelial cells alters the expression of multiple antiviral innate immune mediators, including the interferon (IFN) related genes IFNB1, IFNL3, CXCL10, ISG15, and MX1. Furthermore, OSW-1 enhances the induction of specific components of type I and III IFN antiviral responses triggered by the RNA viral mimetic polyinosinic-polycytidylic acid (Poly IC). In summary, this study further demonstrates the importance of OSBP in (+)ssRNA virus replication and presents OSBP as a potential regulator of cellular antiviral innate immune responses.

Ubiquitin-specific proteinase 1 stabilizes PRRSV nonstructural protein Nsp1β to promote viral replication by regulating K48 ubiquitination

The porcine reproductive and respiratory syndrome virus (PRRSV) can lead to severe reproductive problems in sows, pneumonia in weaned piglets, and increased mortality, significantly negatively impacting the economy. Post-translational changes are essential for the host-dependent replication and long-term infection of PRRSV. Uncertainty surrounds the function of the ubiquitin network in PRRSV infection. Here, we screened 10 deubiquitinating enzyme inhibitors and found that the ubiquitin-specific proteinase 1 (USP1) inhibitor ML323 significantly inhibited PRRSV replication in vitro. Importantly, we found that USP1 interacts with nonstructural protein 1β (Nsp1β) and deubiquitinates its K48 to increase protein stability, thereby improving PRRSV replication and viral titer. Among them, lysine at position 45 is essential for Nsp1β protein stability. In addition, deficiency of USP1 significantly reduced viral replication. Moreover, ML323 loses antagonism to PRRSV rSD16-K45R. This study reveals the mechanism by which PRRSV recruits the host factor USP1 to promote viral replication, providing a new target for PRRSV defense.IMPORTANCEDeubiquitinating enzymes are critical factors in regulating host innate immunity. The porcine reproductive and respiratory syndrome virus (PRRSV) nonstructural protein 1β (Nsp1β) is essential for producing viral subgenomic mRNA and controlling the host immune system. The host inhibits PRRSV proliferation by ubiquitinating Nsp1β, and conversely, PRRSV recruits the host protein ubiquitin-specific proteinase 1 (USP1) to remove this restriction. Our results demonstrate the binding of USP1 to Nsp1β, revealing a balance of antagonism between PRRSV and the host. Our research identifies a brand-new PRRSV escape mechanism from the immune response.