EFFECT OF ENFORCED EXPRESSION OF HUMAN BCL-2 ON JAPANESE ENCEPHALITISVIRUS-INDUCED APOPTOSIS IN CULTURED-CELLS

Infection by Japanese encephalitis virus (JEV), a mosquito-borne flavi virus, causes acute encephalitis in humans and induces severe cytopath ic effects in different types of cultured cells. This study attempted to determine whether apoptosis contributes to virus-induced cell death in a culture system by characterizing JEV lytic infection in baby ham ster kidney BHK-21 cells, murine neuroblastoma N18 cells, and human ne uronal progenitor NT2 cells. According to our results, the replication of JEV, and not the UV-inactivated virions per se, triggered apoptosi s in these cell lines, as evidenced by nuclear condensation, DNA fragm entation ladder, and in situ end labeling of DNA strand breaks with te rminal transferase (terminal deoxynucleotidyltransferase-mediated dUTP -biotin nick end labeling assay). Different strains of JEV, regardless of whether they are neurovirulent to mice, could induce apoptosis of the infected cells. In addition, enforced expression of the human prot ooncogene bcl-2 in BHK-21 cells, which did not influence virus product ion, appeared to delay the process of JEV-induced apoptosis, despite t he fact that most infected cells were inevitably killed after prolonge d cultures. However, Bcl-2 proteins ex-pressed in N18 cells failed to block JEV-induced apoptosis, although they did prevent Sindbis virus-i nduced apoptosis from occurring in the same tells. This finding sugges ts that these two viruses may utilize similar but not identical mechan isms to kill their infected cells. The results presented here thus dem onstrate that apoptosis can be a general mechanism for JEV-induced cel l death and that enforced bcl-2 expression may be inadequate in protec ting all cell types from JEV-induced apoptosis in cell cultures.