Infection with Langat flavivirus or expression of the envelope protein induces apoptotic cell death

Langat (LGT) flavivirus, derived from infectious full-length cDNA clone 636 , was investigated for its apoptotic activities in mouse neuroblastoma (Neu ro-2a) and simian kidney (Vero and LLC-MK2) cells. The hallmark of apoptosi s, cleavage of cellular DNA, was observed 48 h after infection of Vero, LLC -MK2, and Neuro-2a cells by electrophoresis analysis. Apoptosis in infected cells was also confirmed by TUNEL assay. LGT-infected Neuro-2a cells showe d an increase in caspase-3-like protease (DEVDase) activity. Expression of the major envelope glycoprotein (E) alone reduced cell viability in both Ve ro and Neuro-2a cells, and the baculovirus P35 protein, which inhibits mult iple caspases, completely blocked this effect Cleavage of cellular DNA was observed in E gene-transfected Vero cells by TUNEL assay, Expression of E p rotein or caspase-9 resulted in activation of caspase-3-like proteases in N euro-2a cells. The caspase-3-like protease specific inhibitor, Ac-DEVD-CHO peptide, partially inhibited E protein- or caspase-9-induced apoptosis in N euro-2a cells. These observations indicate that infection of cells with LGT virus or expression of LGT virus E protein induces apoptosis through a cas pase-3-like protease pathway.