Coxsackievirus B3 proteases 2A and 3C induce apoptotic cell death through mitochondrial injury and cleavage of eIF4GI but not DAP5/p97/NAT1

By transfection of Coxsackievirus B3 (CVB3) individual protease gene into HeLa cells, we demonstrated that 2Apro and 3Cpro induced apoptosis through multiple converging pathways. Firstly, both 2Apro and 3Cpro induced caspase-8-mediated activation of caspase-3 and dramatically reduced cell viability. Secondly, they both activated the intrinsic mitochondria-mediated apoptosis pathway leading to cytochrome c release from mitochondria and activation of caspase-9. However, 3Cpro induced these events via both up-regulation of Bax and cleavage of Bid, and 2Apro induced these events via cleavage of Bid only. Nevertheless, neither altered Bcl-2 expression. Thirdly, both proteases induced cell death through cleavage or down regulation of cellular factors for translation and transcription: both 2Apro and 3Cpro cleaved eukaryotic translation initiation factor 4GI but their cleavage products are different, indicating different cleavage sites; further, both 2Apro and 3Cpro down-regulated cyclic AMP responsive element binding protein, a transcription factor, with 2Apro exhibiting a stronger effect than 3Cpro. Surprisingly, neither could cleave DAP5/p97/NAT1, a translation regulator, although this cleavage was observed during CVB3 infection and could not be blocked by caspase inhibitor z-VAD-fmk. Taken together, these data suggest that 2Apro and 3Cpro induce apoptosis through both activation of proapoptotic mediators and suppression of translation and transcription.