The Effects Of RACK1on Apoptosis Induced By Interaction Of IBDV VP5with VDAC2in Host Cells

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease in young chickens that occurs across the world. Its causative agent IBD virus (IBDV) destroys its target cells, the B-lymphocyte precursors. IBDV infection may cause mortality in naive chickens and very high mortality in chickens with low levels of neutralizing antibodies or no mortality at all but a high degree of immunosuppression. The survival chickens suffer from a severe immunosuppression which leads to an increased susceptibility to other pathogens. Our previous report indicates that IBDV VP5induces apoptosis via interaction with the voltage-dependent anion channel2(VDAC2). However, the underlying molecular mechanism is still unclear. Here we showed the critical role of RACK1during IBDV infection.In this study, we used VDAC2as bait in the yeast two-hybrid system to screen a cDNA library generated from the chicken bursa of Fabricius. Among the positive clones, Receptor of activated protein kinase C1(RACK1) was identified as the interacting partner with VDAC2in yeast. The interaction between VDAC2and RACK1was further verified with a Colony-lift Filter assay. Then we showed that RACK1interacts with both VDAC2and VP5in host cells and they form a complex in IBDV-infected cells by co-immunoprecipitation assay. Further study showed that RACK1colocalized with VDAC2or IBDV VPS in the cytoplasm of host cells and they were all located in the mitochondria as shown by confocal laser scanning microscopy assay. Importantly, we found that over-expression of RACK1inhibited IBDV-induced apoptosis and enhanced IBDV growth in DF-1and Primary chicken embryo fibroblast (CEF) cells and that knockdown of RACK1by small interfering RNA induced apoptosis associated with activation of caspases9and3, and suppressed IBDV growth.These results indicate that RACK1plays an anti-apoptotic role during IBDV infection via interaction with VDAC2and VP5, suggesting that VP5sequesters RACK1and VDAC2in the apoptosis-inducing process.