Apoptosis induced by Semliki Forest virus is RNA replication dependent and mediated via Bak.
The RNA alphavirus Semliki Forest (SFV) triggers apoptosis in various mammalian cells, but it has remained controversial at what infection stage and by which signalling pathways host cells are killed. Both RNA synthesis-dependent and -independent initiation processes and mitochondrial as well as death receptor signalling pathways have been implicated. Here, we show that SFV-induced apoptosis is initiated at the level of RNA replication or thereafter. Moreover, by expressing antiapoptotic genes from recombinant SFV (replicons) and by using neutralizing reagents and gene-knockout cells, we provide clear evidence that SFV does not require CD95L-, TRAIL (tumor necrosis factor-related apoptosis-inducing ligand)- or tumor necrosis factor-mediated signalling but mitochondrial Bak to trigger cytochrome c release, the fall in the mitochondrial membrane potential, apoptotic protease-activating factor-1/caspase-9 apoptosome formation and caspase-3/-7 activation. Of seven BH3-only proteins tested, only Bid contributed to effective SFV-induced apoptosis. However, caspase-8 activation and Bid cleavage occurred downstream of Bax/Bak, indicating that truncated Bid formation serves to amplify rather than trigger SFV-induced apoptosis. Our data show that SFV sequentially activates a mitochondrial, Bak-mediated, caspase-8-dependent and Bid-mediated death signalling pathway that can be accurately dissected with gene-knockout cells and SFV replicons carrying antiapoptotic genes.
Urban
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C
Institute of Molecular Medicine and Cell Research, Center for Biochemistry and Molecular Cell Research (ZBMZ), Albert Ludwigs University Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany.
Rhême
C
C
Maerz
S
S
Berg
B
B
Pick
R
R
Nitschke
R
R
Borner
C
C
D000330:Aedes / Q000166:cytology; D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics; D051023:BH3 Interacting Domain Death Agonist Protein / Q000502:physiology; D053181:Caspase 8 / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D016679:Genome, Viral; D008928:Mitochondria / Q000378:metabolism; D012367:RNA, Viral / Q000096:biosynthesis*; D012093:Replicon; D012672:Semliki forest virus / Q000235:genetics*; D015398:Signal Transduction; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D012367:RNA, Viral; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; D053181:Caspase 8; D020169:Caspases