Molecular cloning and expression analysis of the Ajuba gene of grass carp (Ctenopharyngodon idella) involved in cellular response to viral infection

TNF-α is involved in apoptosis triggered by grass carp reovirus infection in vitro

Grass carp reovirus (GCRV) infection causes apoptosis in Ctenopharyngodon idella kidney cells (CIK). However, the cause of GCRV-induced apoptosis and its signaling pathways remain unknown. This study investigated the role of TNF-α-induced capase-8 pathways in mediating GCRV-induced apoptosis in the grass carp (Ctenopharyngodon idella). Recombinant TNF-α was expressed and purified from Escherichia. coli. The western blot assay indicated that TNF-α expression level in kidney and spleen was higher than that in liver. In apoptosis assay, recombinant TNF-α triggered significant apoptosis in CIK cells, which was characterized by increased mRNA levels of TNF-α, TRADD or caspase-8, and enhanced caspase-8 activity in CIK cells. To confirm the biological activity of TNF-α during GCRV infection, significant apoptosis in CIK cells was induced by GCRV correlating with enhanced caspase-8 activity, increased mRNA level of TNF-α, TRADD or caspase-8, increased protein level of TNF-α in CIK cells and cell supernatant, suggesting that TNF-α-induced capase-8 pathways might be involved in GCRV-triggered apoptosis. Furthermore, treatment with an anti-TNF-α polyclonal antibody significantly decreased the degree of apoptosis in infected CIK cells compared with cells treated with a control antibody, which confirmed that TNF-α was a key mediator involved in GCRV-induced apoptosis. Taken together, these results indicated that GCRV might trigger apoptosis via TNF-α induced capase-8 pathways in CIK cells.

Grass carp reovirus NS26 interacts with cellular lipopolysaccharide-induced tumor necrosis factor-alpha factor, LITAF

The nonstructural protein NS26 of grass carp reovirus (GCRV) is encoded by the 11th genomic dsRNA segment, homolog of which is not found in orthoreoviruses. The role of NS26 in GCRV pathogenesis is still unclear. Previously, grass carp LITAF/SIMPLE protein was identified as a putative binding partner for NS26 in a yeast two-hybrid screen. Here, we further characterized the association between NS26 and LITAF using in vivo and in vitro protein interaction assays. Soluble GST-NS26 and His₆-LITAF were expressed and purified from E. coli; recombinant NS26 tagged with myc and LITAF tagged with GFP were expressed in Ctenopharyngon idellus kidney cells (CIK) by transient transfection experiments. A GST pulldown assay demonstrated that GST-tagged NS26 efficiently bound to His₆-LITAF. Co-immunoprecipitation assays demonstrated that GCRV NS26 reciprocally precipitated endogenous LITAF in CIK cells. Double-immunofluorescent analyses revealed myc-NS26 colocalized with GFP-LITAF in CIK cells. Taken together, the current in vitro and in vivo data demonstrated the interaction between cellular LITAF and GCRV NS26.