GCRV-I capsid protein VP5 induces TRAP1 degradation via K48-linked ubiquitination for immune evasion and viral proliferation.

Grass carp hemorrhage disease, caused by the grass carp reovirus (GCRV), occurs frequently. Its high pathogenicity and infectivity pose significant challenges to grass carp culture in China. GCRV-873 is an early-identified type I GCRV (GCRV-I). However, its pathogenesis remains largely unknown. Current study elucidated the interaction mechansim between GCRV with its host, revealing that the main outer capsid protein VP5 specifically targets tumor necrosis factor receptor-associated protein 1 (CiTRAP1) to activate host apoptosis, thereby promoting viral proliferation. Specifically, overexpression of VP5 in CIK cells led to apoptosis and reduced cell viability. However, TRAP1 can mitigate VP5-induced apoptosis and GCRV-I proliferation. To elucidate the interplay between VP5 and TRAP1, we first demonstrated, through Western blot and immunoprecipitation, that VP5 promoted the degradation of TRAP1 via the proteasome pathway, thereby facilitating viral replication. Intriguingly, we found that VP5 specifically augmented K48-linked, but not K63-linked, polyubiquitination of TRAP1. Mutational analysis further indicated that mutation of lysine residues 123 and 195 (K123 and K195) on TRAP1 abolished K48-linked ubiquitination, pinpointing these two sites as specific targets of VP5-mediated ubiquitination. Collectively, our data suggest that TRAP1 functions as a cytoplasmic target for GCRV-I VP5, thereby ensuring the inhibition of the host immune system and the efficient proliferation of GCRV-I. This study offers new insights into the invasive mechanism of GCRV and also presents a new target for the development of antiviral drugs to combat GCRV infection.