Avian encephalomyelitis virus induces apoptosis via major structural protein VP3.

Avian encephalomyelitis virus (AEV) strain L(2)Z was investigated for its apoptotic activity in specific-pathogen-free chick embryo brain tissue. DNA fragmentation analysis and electron microscopy observation demonstrated that AEV could induce apoptosis in chick embryo brain tissues characterized by chromatin condensation, plasma membrane blebbing, cell shrinkage, and nucleosomal DNA fragmentation after 4 days postinfection. AEV structural protein genes VP1, VP2, and VP3 were transfected into Cos-7 and chick embryo brain (CEB) cells, respectively. The results showed that only VP3 protein was an apoptotic inducer, as demonstrated by DNA fragmentation analysis and TUNEL assay at 24 and 48 h posttransfection. Furthermore, expression of VP3 protein resulted in the activation of caspase-3-like proteases in both cells, which could be inhibited by a caspase-3-like protease-specific inhibitor Ac-DEVD-CHO peptide, suggesting that AEV VP3 protein induces apoptosis through a caspase-3-like protease pathway. In addition, VP3 protein localized to mitochondria in the Cos-7 and CEB cells at 24 h posttransfection observed by confocal microscopy, indicating that mitochondria may play an important role in VP3-induced apoptosis. Taken together, our results show that AEV could induce apoptosis in chick embryo brain tissue, structural protein VP3 could serve as an apoptotic inducer resulting in apoptosis in cell culture through a caspase-3-like protease pathway, which may be related to its localization to mitochondria.