Cellular proteasome subunit beta type-7 interacts with grass carp reovirus non-structural protein 12 (NS12)

Ctenopharyngodon idella is one of the main freshwater aquaculture fishes in China, with an annual output of more than 5 million tons, which is widely distributed throughout China. Grass carp reovirus (GCRV) is a member of the Aquareovirus genus of the family Reoviridae, a large family of double-stranded RNA (dsRNA) viruses infecting plants, insects, fishes and mammals. Proteasome subunit beta type-7 (PSMB7) is one of the major components of the 20S core proteasome complex and displays a trypsin-like activity. Capsid protein VP7 of GCRV has been shown to interact with PSMB7 both in vitro and in vivo. To investigate the interaction between GCRV non-structural protein 12 (NS12) and C. idella host protein PSMB7 and the effect of PSMB7 on the expression of ns12 during GCRV infection, yeast two-hybrid experiment, GST pull-down experiment and Real time PCR detection of ns12 transcription level after GCRV infection of grass carp ovarian cells (GCO) overexpressing PSMB7 were conducted in this research. The results of yeast two-hybrid experiments showed that PSMB7 and GCRV-encoded membrane-associated non-structural protein NS12 also had potential interactions; The results of Western blot showed that PSMB7 interacted with the membrane-related non-structural protein NS12 encoded by GCRV; The overexpression of PSMB7 by about 60 times can up-regulate the expression level of ns12 during viral infection by about three times; Western blot verified that NS12 was not sensitive to protein degradation. Previous studies in our laboratory have verified that PSMB7 expression is constant during viral infection. In summary, these results revealed that GCRV NS12 had an intermolecular interaction with PSMB7, but it did not act as a substrate for PSMB7. This indicates that the function of NS12 induced by PSMB7 may be positively correlated with the replication of GCRV in host cells, revealing that NS12 may participate in the early replication cycle of GCRV virus in host cells and avoid degradation of viral proteins by competitively recruiting PSMB7. The interference of viral proteins with the accumulation of intracellular PSMB7 of the proteasome complex may be a viral strategy to escape from proteasome-mediated innate immunity.