Cyprinid herpesvirus 2 (CyHV-2) ORF53 inhibits NF-κB signalling by targeting p65 degradation

Cyprinid herpesvirus 2 (CyHV-2) is the pathogen responsible for herpesviral disease in cyprinid fish, inflicting substantial economic losses on the carp aquaculture industry. At present, the immune evasion mechanism of CyHV-2 has not been fully elucidated. In the present study, the open reading frame 53 (ORF53) of CyHV-2 was functionally screened as a negative regulator of the NF-κB signalling pathway from 19 predicted non-membrane protein ORFs. Overexpression of ORF53 suppressed the activation of NF-κB promoter mediated by CyHV-2 infection and poly(dG:dC) stimulation, as well as by overexpression of TRAF6, IKKβ and p65. Co-immunoprecipitation (Co-IP) assays confirmed that the ORF53 protein interacted with NF-κB subunit p65 through immunoglobulin-like fold domain (IPT) of p65. Furthermore, ORF53 enhanced viral gene expression of CyHV-2 and reduced the transcription level of immune cytokines, such as type I interferon (IFN), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), through autophagic degradation of p65. In summary, this study uncovers a new molecular mechanism underlying CyHV-2-mediated immune evasion and provides a theoretical reference for elucidating the pathogenic mechanism of herpesviral hematopoietic necrosis.