title: The vaccinia virus F1L protein interacts with the proapoptotic protein Bak and inhibits Bak activation.
abstract: Many viruses have evolved strategies to counteract cellular immune responses, including apoptosis. Vaccinia virus, a member of the poxvirus family, encodes an antiapoptotic protein, F1L. F1L localizes to mitochondria and inhibits apoptosis by preventing the release of cytochrome c by an undetermined mechanism (S. T. Wasilenko, T. L. Stewart, A. F. Meyers, and M. Barry, Proc. Natl. Acad. Sci. USA 100:14345-14350, 2003; T. L. Stewart, S. T. Wasilenko, and M. Barry, J. Virol. 79:1084-1098, 2005). Here, we show that in the absence of an apoptotic stimulus, F1L associates with Bak, a proapoptotic member of the Bcl-2 family that plays a pivotal role in the release of cytochrome c. Cells infected with vaccinia virus were resistant to Bak oligomerization and the initial N-terminal exposure of Bak following the induction of apoptosis with staurosporine. A mutant vaccinia virus missing F1L was no longer able to inhibit apoptosis or Bak activation. In addition, the expression of F1L was essential to inhibit tBid-induced cytochrome c release in both wild-type murine embryonic fibroblasts (MEFs) and Bax-deficient MEFs, indicating that F1L could inhibit apoptosis in the presence and absence of Bax. tBid-induced Bak oligomerization and N-terminal exposure of Bak in Bax-deficient MEFs were inhibited during virus infection, as assessed by cross-linking and limited trypsin proteolysis. Infection with the F1L deletion virus no longer provided protection from tBid-induced Bak activation and apoptosis. Additionally, infection of Jurkat cells with the F1L deletion virus resulted in cellular apoptosis, as measured by loss of the inner mitochondrial membrane potential, caspase 3 activation, and cytochrome c release, indicating that the presence of F1L was pivotal for inhibiting vaccinia virus-induced apoptosis. Our data indicate that F1L expression during infection inhibits apoptosis and interferes with the activation of Bak.
authors.affiliation: Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Canada.
authors.forename: Shawn T
authors.initials: ST
authors.lastname: Wasilenko
authors.forename: Logan
authors.initials: L
authors.lastname: Banadyga
authors.forename: David
authors.initials: D
authors.lastname: Bond
authors.forename: Michele
authors.initials: M
authors.lastname: Barry
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001483:Base Sequence; D017931:DNA Primers; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes; D019169:Jurkat Cells; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000502:physiology / Q000821:virology; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D014616:Vaccinia virus / Q000502:physiology*; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D017931:DNA Primers; C507356:F1L protein, vaccinia virus; D011994:Recombinant Proteins; D014764:Viral Proteins; D019311:Staurosporine