HSV-1-induced PAD-mediated Citrullination as a New Target for Antiviral Therapy

Herpes simplex virus 1 (HSV-1) is a neuroinvasive and neurotoxic virus capable of entering the brain via peripheral nerves. Like other members of the Herpesvirus family, HSV-1 has developed different strategies, such as the exploitation of post-translational modification (PTM) of proteins, to ensure efficient viral replication and persistent infection. Citrullination is a PTM catalyzed by peptidyl-arginine deiminases (PADs), that convert peptidyl-arginine into peptidyl-citrulline. Here we show that HSV-1 infection triggers PAD-mediated citrullination through transcriptional activation of three PAD isoforms: PAD2, PAD3, and PAD4. Interestingly, the pan-PAD inhibitors, Cl-amidine and BB-Cl-amidine, and the PAD3-specific inhibitor, HF4, dramatically suppress HSV-1 replication. Finally, citrullinome analysis reveals significant changes in several host and viral proteins, with interferon (IFN)-inducible proteins IFIT1 and IFIT2 being among the most heavily deiminated ones. As genetic depletion of IFIT1 and IFIT2 strongly enhances HSV-1 growth, we propose the viral-induced IFIT1-2 citrullination as an HSV-1 evasion mechanism from host antiviral resistance. Altogether, these findings highlight the pivotal role of citrullination in subverting cellular responses to viral infection and demonstrate that PAD inhibitors efficiently suppress HSV-1 replication, suggesting their potential repurposing as HSV-1 antiviral drugs.