A novel Bcl-2-like inhibitor of apoptosis is encoded by the parapoxvirus ORF virus.
Apoptotic cell death forms part of the host defense against virus infection. We tested orf virus, a member of the poxvirus family, for the ability to inhibit apoptosis and found that orf virus-infected cells were fully resistant to UV-induced changes in cell morphology, caspase activation, and DNA fragmentation. By using a library of vaccinia virus-orf virus recombinants, we identified an orf virus gene (ORFV125) whose presence was linked with the inhibition of apoptosis. The 173-amino-acid predicted protein had no clear homologs in public databases other than those encoded by other parapoxviruses. However, ORFV125 possessed a distinctive C-terminal domain which was necessary and sufficient to direct the protein to the mitochondria. We determined that ORFV125 alone could fully inhibit UV-induced DNA fragmentation, caspase activation, and cytochrome c release and that its mitochondrial localization was required for its antiapoptotic function. In contrast, ORFV125 did not prevent UV-induced activation of c-Jun NH2-terminal kinase, an event occurring upstream of the mitochondria. These features are comparable to the antiapoptotic properties of the mitochondrial regulator Bcl-2. Furthermore, bioinformatic analyses revealed sequence and secondary-structure similarities to Bcl-2 family members, including characteristic residues of all four Bcl-2 homology domains. Consistent with this, the viral protein inhibited the UV-induced activation of the proapoptotic Bcl-2 family members Bax and Bak. ORFV125 is the first parapoxvirus apoptosis inhibitor to be identified, and we propose that it is a new antiapoptotic member of the Bcl-2 family.
Westphal
Dana
D
Department of Microbiology and Immunology, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Ledgerwood
Elizabeth C
EC
Hibma
Merilyn H
MH
Fleming
Stephen B
SB
Whelan
Ellena M
EM
Mercer
Andrew A
AA
D017209:Apoptosis; D020169:Caspases / Q000378:metabolism; D053938:DNA Fragmentation / Q000528:radiation effects; D004474:Ecthyma, Contagious / Q000235:genetics* / Q000378:metabolism; D004789:Enzyme Activation / Q000235:genetics / Q000528:radiation effects; D006367:HeLa Cells; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics* / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D016366:Open Reading Frames; D009923:Orf virus / Q000235:genetics* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014466:Ultraviolet Rays; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
D051034:Inhibitor of Apoptosis Proteins; D014764:Viral Proteins; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D048031:JNK Mitogen-Activated Protein Kinases; D020169:Caspases