A novel Bcl-2-like inhibitor of apoptosis is encoded by the parapoxvirus ORF virus

J Virol. 2007 Jul;81(13):7178-88. doi: 10.1128/JVI.00404-07. Epub 2007 May 2.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis
  • Caspases / metabolism
  • DNA Fragmentation / radiation effects
  • Ecthyma, Contagious / genetics*
  • Ecthyma, Contagious / metabolism
  • Enzyme Activation / genetics
  • Enzyme Activation / radiation effects
  • HeLa Cells
  • Humans
  • Inhibitor of Apoptosis Proteins / genetics*
  • Inhibitor of Apoptosis Proteins / metabolism
  • JNK Mitogen-Activated Protein Kinases / metabolism
  • Mitochondria / metabolism
  • Open Reading Frames*
  • Orf virus / genetics*
  • Orf virus / metabolism
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Ultraviolet Rays
  • Viral Proteins / genetics*
  • Viral Proteins / metabolism
  • bcl-2 Homologous Antagonist-Killer Protein / genetics
  • bcl-2 Homologous Antagonist-Killer Protein / metabolism
  • bcl-2-Associated X Protein / genetics
  • bcl-2-Associated X Protein / metabolism


  • Inhibitor of Apoptosis Proteins
  • Viral Proteins
  • bcl-2 Homologous Antagonist-Killer Protein
  • bcl-2-Associated X Protein
  • JNK Mitogen-Activated Protein Kinases
  • Caspases