Characterization of cell-death pathways in Punta Toro virus-induced hepatocyte injury

Punta Toro virus (PTV; genus Phlebovirus, family Bunyaviridae) causes apoptosis of hepatocytes in vivo in experimentally infected hamsters and in vitro in cultured HepG2 cells. Screening for expression of apoptosis-related genes has shown alterations in the genes for tumour necrosis factor-α (TNF-α) and the TNF receptor family. This study examined the roles of the TNF receptor-related extrinsic pathway and the Bcl-2 family-associated mitochondrial pathway in PTV-induced cell death. The effects of caspase inhibitors (caspIs) and TNF on cellular viability, virus replication, and morphological and biochemical changes in apoptosis were examined in HepG2 cells at different time points after infection with PTV (Adames strain). The results showed that caspIs dampened the virus-induced reduction in cellular viability, partially suppressed and delayed viral titres and antigen expression, and partially decreased the expression of apoptotic genes, caspase activities and DNA fragmentation. TNF treatment further decreased cellular viability after PTV infection and increased the level of apoptosis, whilst caspIs partially inhibited these effects. These findings indicate that TNF, caspase-8 and caspase-9 contribute to PTV-induced hepatocytic apoptosis and that additional mediators are probably also involved in this process. These mediators from different pathways correlated with one another and may be interlinked.