EcPSMB8 Contributes to Antiviral Immunity in Grouper by Modulating MHC I Signalling and Virus-Induced Autophagy

The PSMB8 gene belongs to the immunoproteasome β-subunit (PSMB) family and has been implicated in diverse physiological processes in mammals, including tumorigenesis, autophagy and apoptosis. However, its role in antiviral immunity in groupers remains largely unexplored. In this study, we cloned and characterised EcPSMB8, a homologue of PSMB8, from the orange-spotted grouper (Epinephelus coioides), and investigated its potential involvement in antiviral immune responses. EcPSMB8 encodes a conserved 275-amino-acid protein that is ubiquitously expressed in grouper tissues and predominantly localised in the cytoplasm. Functional analyses showed that EcPSMB8 overexpression was associated with reduced replication of both Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV). This antiviral effect was accompanied by suppression of basal and virus-induced autophagy, as indicated by decreased LC3-II accumulation and reduced expression of autophagy-related genes. Meanwhile, EcPSMB8 overexpression correlated with enhanced major histocompatibility complex class I (MHC I)-associated immune signalling, including increased promoter activities of MHC I-A, ISRE and IFN3, as well as upregulation of related cytokines. Together, these findings suggest that EcPSMB8 may contribute to grouper antiviral defence through coordinated modulation of immune signalling and autophagy. Importantly, a specific polyclonal antibody against EcPSMB8 was generated, providing a useful tool for protein-level analyses and supporting future studies on antiviral immune mechanisms in teleost fish.