Opposite effects of apoptotic and necroptotic cellular pathways on rotavirus replication

Group A rotavirus (RVA), one of the leading pathogens causing severe acute gastroenteritis in children and a wide variety of young animals worldwide, induces apoptosis upon infecting cells. Though RVA-induced apoptosis mediated via the dual modulation of its NSP4 and NSP1 proteins is relatively well studied, the nature and signaling pathway(s) involved in RVA-induced necroptosis are yet to be fully elucidated. Here, we demonstrate the nature of RVA-induced necroptosis, the signaling cascade involved, and correlation with RVA-induced apoptosis. Infection with the bovine NCDV and human DS-1 RV strains was shown to activate receptor-interacting protein kinase 1 (RIPK1)/RIPK3/mixed lineage kinase domain-like protein (MLKL), the key necroptosis molecules in virus-infected cells. Using immunoprecipitation assay, RIPK1 was found to bind phosphorylated RIPK3 (pRIPK3) and pMLKL. pMLKL, the major executioner molecule in the necroptotic pathway, was translocated to the plasma membrane of RVA-infected cells to puncture the cell membrane. Interestingly, transfection of RVA NSP4 also induced necroptosis through the RIPK1/RIPK3/MLKL necroptosis pathway. Blockage of each key necroptosis molecule in the RVA-infected or NSP4-transfected cells resulted in decreased necroptosis but increased cell viability and apoptosis, thereby resulting in decreased viral yields in the RVA-infected cells. In contrast, suppression of RVA-induced apoptosis increased necroptosis and virus yields. Our findings suggest that RVA NSP4 also induces necroptosis via the RIPK1/RIPK3/MLKL necroptosis pathway. Moreover, necroptosis and apoptosis-which have proviral and antiviral effects, respectively-exhibited a crosstalk in RVA-infected cells. These findings significantly increase our understanding of the nature of RVA-induced necroptosis and the crosstalk between RVA-induced necroptosis and apoptosis. IMPORTANCE Viral infection usually culminates in cell death through apoptosis, necroptosis, and rarely, pyroptosis. Necroptosis is a form of programmed necrosis that is mediated by signaling complexes of the receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL). Although apoptosis induction by rotavirus and its NSP4 protein is well known, rotavirus-induced necroptosis is not fully understood. Here, we demonstrate that rotavirus and also its NSP4 protein can induce necroptosis in cultured cells through the activation of the RIPK1/RIPK3/MLKL necroptosis pathway. Moreover, rotavirus-induced necroptosis and apoptosis have opposite effects on viral yield, i.e., they function as proviral and antiviral processes, respectively, and counterbalance each other in rotavirus-infected cells. Our findings provide important insights for understanding the nature of rotavirus-induced necroptosis and the development of novel therapeutic strategies against infection with rotavirus and other RNA viruses.