Sindbis virus entry into cells triggers apoptosis by activating sphingomyelinase, leading to the release of ceramide

Sindbis virus (SV) causes acute encephalomyelitis by infecting and inducing the death of neurons. Induction of apoptosis occurs during virus entry and involves acid-induced conformational changes in the viral surface glycopro teins and sphingomyelin (SM)-dependent fusion of the virus envelope with th e endosomal membrane. We have studied neuroblastoma cells to determine how this entry process triggers cell death. Acidic sphingomyelinase was activat ed during entry followed by activation of neutral sphingomyelinase, SM degr adation, and a sustained increase in ceramide. Ceramide-induced apoptosis a nd SV-induced apoptosis could be inhibited by treatment with Z-VAD-fmk, a c aspase inhibitor, and by overexpression of Bcl-2, an antiapoptotic cellular protein. Acid ceramidase, expressed in a recombinant SV, decreased intrace llular ceramide and protected cells from apoptosis. The data suggest that a cid-induced SM-dependent virus fusion initiates the apoptotic cascade by in ducing SM degradation and ceramide release.