Modulatory role of tumor necrosis factor receptor type 1-associated death domain protein (TRADD) in innate antiviral immune responses and apoptosis in red-spotted grouper (Epinephelus akaara).

Tumor necrosis factor receptor type 1-associated death domain protein (TRADD) is a unique adaptor molecule involved in multiple receptor-mediated signaling pathways that regulate cell survival and apoptosis in a context-dependent manner. Despite extensive studies on TRADD in mammals, its functional role in teleosts remains poorly understood. To address this gap, the present study characterized a TRADD homolog from red-spotted grouper (Epinephelus akaara, EaTRADD) to determine its function in teleosts. The predicted EaTRADD encoded a putative protein of 291 amino acids, comprising an N-terminal domain and a C-terminal death domain. Structural analysis confirmed that EaTRADD shared a conserved domain architecture across diverse organisms. Spatial expression analysis under normal physiological conditions revealed that EaTRADD was ubiquitously expressed across all examined tissues, with the highest level observed in the spleen. Following immune stimulation, EaTRADD expression was significantly upregulated in the spleen and blood in the early stages. Subcellular localization analysis demonstrated that EaTRADD was predominantly localized in the cytoplasm. EaTRADD overexpression in fathead minnow cells significantly suppressed viral replication, accompanied by increased transcription of interferon-related genes and pro-inflammatory cytokines, providing compelling evidence of its antiviral properties. Additionally, dual-luciferase reporter gene assays revealed that EaTRADD activates the NF-κB signaling pathway following viral infection. Furthermore, EaTRADD overexpression significantly increased apoptotic activity under basal conditions and in response to oxidative stress, accompanied by activation of caspase-3, -8, and -9. Overall, our findings demonstrate that EaTRADD is a key modulator of innate antiviral immune responses and apoptosis in red-spotted grouper.