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A Novel Bcl-2-Like Inhibitor of Apoptosis Is Encoded by the Parapoxvirus Orf Virus

Department of Microbiology and Immunology,¹ Department of Biochemistry, University of Otago, Dunedin, New Zealand²

Received 25 February 2007/ Accepted 23 April 2007

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.

Published ahead of print on 2 May 2007.

This article has been cited by other articles:

• Banadyga, L., Gerig, J., Stewart, T., Barry, M. (2007). Fowlpox Virus Encodes a Bcl-2 Homologue That Protects Cells from Apoptotic Death through Interaction with the Proapoptotic Protein Bak. J. Virol. 81: 11032-11045 [Abstract] [Full Text]