ABSTRACT
BH3-only proteins of the Bcl-2 family regulate programmed cell death in mammals through activation of multidomain proapoptotic proteins Bax and Bak in response to various proapoptotic stimuli by mechanism that remains under dispute. Here, we report that the cell death-promoting activity of BH3-only proteins Bik, Bmf, Noxa, and tBid can only be reconstituted in yeast when both multidomain proapoptotic and antiapoptotic Bcl-2 family proteins are present. Inability of these proteins to induce cell death in the absence of antiapoptotic proteins suggests that all tested BH3-only proteins likely activate Bax and Bak indirectly by inhibiting antiapoptotic proteins.
Subject(s)
Proto-Oncogene Proteins c-bcl-2/metabolism , Saccharomyces cerevisiae/metabolism , bcl-2 Homologous Antagonist-Killer Protein/metabolism , bcl-2-Associated X Protein/metabolism , Apoptosis/genetics , BH3 Interacting Domain Death Agonist Protein/genetics , BH3 Interacting Domain Death Agonist Protein/metabolism , Gene Expression , Proto-Oncogene Proteins c-bcl-2/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/growth & development , bcl-2 Homologous Antagonist-Killer Protein/genetics , bcl-2-Associated X Protein/geneticsABSTRACT
Proteins of the Bcl-2 family regulate programmed cell death in mammals by promoting the release of cytochrome c from mitochondria in response to various proapoptotic stimuli. The mechanism by which BH3-only members of the family activate multidomain proapoptotic proteins Bax and Bak to form a pore in mitochondrial membranes remains under dispute. We report that cell death promoting activity of BH3-only protein Bim can be reconstituted in yeast when both Bax and antiapoptotic protein Bcl-X(L) are present, suggesting that Bim likely activates Bax indirectly by inhibiting antiapoptotic proteins.
Subject(s)
Apoptosis Regulatory Proteins/metabolism , Membrane Proteins/metabolism , Proto-Oncogene Proteins/metabolism , bcl-2 Homologous Antagonist-Killer Protein/metabolism , bcl-2-Associated X Protein/metabolism , Animals , Apoptosis/genetics , Apoptosis/physiology , Apoptosis Regulatory Proteins/genetics , Bcl-2-Like Protein 11 , Cell Fractionation , Immunoblotting , Membrane Proteins/genetics , Mice , Mitochondrial Membranes/metabolism , Permeability , Proto-Oncogene Proteins/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/metabolism , bcl-2 Homologous Antagonist-Killer Protein/genetics , bcl-2-Associated X Protein/genetics , bcl-X Protein/genetics , bcl-X Protein/metabolismABSTRACT
One of the mechanisms of defense against viral infection is induction of apoptosis in infected cells. To escape this line of protection, genomes of many viruses encode for proteins that inhibit apoptosis. Murid herpesvirus 4 gene M11 encodes for homologue of cellular Bcl-2 proteins that inhibits apoptosis and autophagy in infected cell. To study a role of M11 in regulation of apoptosis we have established a yeast model system in which the action of M11 together with proapoptotic proteins Bax, Bak and Bid can be studied. When expressed in yeast, M11 did not inhibit autophagic pathway, so only effects of expression of M11 on activity of coexpressed proapoptotic proteins could be observed. In this experimental setting M11 potently inhibited both proapoptotic multidomain proteins Bax and Bak. The antiapoptotic activity of M11 was suppressed by coexpression of proapoptotic BH3-only protein tBid, indicating that M11 inhibits apoptosis likely by the same mechanism as cellular antiapoptotic proteins Bcl-2 or Bcl-XL.
