ABSTRACT
Apoptosis, an intrinsic cellular pathway that eliminates unwanted cells from multicellular organisms, represents an important mechanism for protection against viral infections. When cells infected by viruses get recognized by immune cells, apoptosis is triggered in the infected cells. Among the many regulators of apoptosis involved in this process, a family of proteins homologous to oncogene Bcl-2 plays a central role. Their concerted activities converge to permeabilization of mitochondrial membranes and activation of apoptotic pathways in the presence of diverse apoptotic signals, including virus infection. In the genomes of many viruses, genes encoding for homologues of antiapoptotic proteins of Bcl-2 family can be found. These proteins, collectively referred to as vBcl-2 proteins, inhibit apoptosis in infected cells at the different stages of virus life cycle to enable the virus to complete its replication and to spread.
Subject(s)
Proto-Oncogene Proteins c-bcl-2/genetics , Viral Proteins/genetics , Animals , Apoptosis/genetics , Humans , Virus Diseases/genetics , Virus Replication/genetics , Viruses/geneticsABSTRACT
The mitochondrial ADP/ATP carrier in Saccharomyces cerevisiae is encoded by three genes that are differentially expressed under different physiological conditions. We investigated the transcriptional control of AAC3, an oxygen-repressed isoform. By deletion analysis, DNA electrophoretic mobility-shift assays, DNase I footprinting and site-directed mutagenesis, we have identified a promoter region (upstream repressing sequence 1, URS(1)) involved in a carbon-source-dependent repression of AAC3. It is different from the previously characterized oxygen-dependent ROX1 (regulation by oxygen 1) repressor-binding region (URS(2)). The complex character of URS(1) includes the presence of two different cis-acting sequences: (i) a RAP1 (repressor activator protein 1)-binding site that is capable of binding the RAP1 protein in vitro and (ii) two putative ethanol-repression sequences, the modification of which derepresses the AAC3 gene. These findings demonstrate that the hypoxic AAC3 gene is regulated by two upstream repressor sites; one controlled by oxygen and haem, the other by the carbon source. Both sites function to completely switch off the expression of the AAC3 isoform when ATP is made by oxidative phosphorylation, and they modulate AAC3 expression when import of glycolytic ATP into mitochondria is required.
Subject(s)
Carbon/pharmacology , Gene Expression Regulation, Fungal/drug effects , Mitochondrial ADP, ATP Translocases/genetics , Response Elements/genetics , Saccharomyces cerevisiae/genetics , Base Sequence , Binding Sites , DNA Footprinting , DNA, Fungal/genetics , DNA, Fungal/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , DNA-Binding Proteins/physiology , Deoxyribonuclease I/metabolism , Ethanol/metabolism , Ethanol/pharmacology , Fungal Proteins/metabolism , Genes, Fungal/genetics , Genes, Reporter/genetics , Isoenzymes/genetics , Mitochondria/enzymology , Mutation/genetics , Promoter Regions, Genetic/genetics , Protein Binding , Repressor Proteins/genetics , Repressor Proteins/physiology , Saccharomyces cerevisiae/drug effects , Saccharomyces cerevisiae/enzymology , Saccharomyces cerevisiae ProteinsABSTRACT
The effect of the expression of murine Bax protein on growth and vitality was examined in Saccharomyces cerevisiae and compared with the effect of Bax in mutant cells lacking functional mitochondria. The cytotoxic effect of Bax on yeast does not require functional oxidative phosphorylation, respiration, or mitochondrial proteins (ADP/ATP carriers) implicated in the formation of the permeability transition pore in mammalian mitochondria. In the wild type S. cerevisiae the expression of Bax does not result in a severe effect on mitochondrial membrane potential and respiration. On the basis of Bax induced differences in the fluorescence of green fluorescent protein fused to mitochondrial proteins, it is proposed that Bax may interfere with one essential cellular process in yeast: the mitochondrial protein import pathway that is specific for the proteins of the mitochondrial carrier family.
Subject(s)
Mitochondria/metabolism , Mitochondrial ADP, ATP Translocases/metabolism , Proto-Oncogene Proteins c-bcl-2 , Proto-Oncogene Proteins/pharmacology , Saccharomyces cerevisiae/drug effects , Biological Transport , Cell Division/drug effects , Colony-Forming Units Assay , Membrane Potentials/drug effects , Mitochondria/drug effects , Oxygen Consumption , Proto-Oncogene Proteins/metabolism , Saccharomyces cerevisiae/metabolism , bcl-2-Associated X ProteinABSTRACT
The mitochondrial ADP/ATP carrier in Saccharomyces cerevisiae is encoded by three independent genes. AAC1, AAC2, and AAC3. In this work, we analysed the 5' upstream region of AAC1 by sequencing and by mapping the transcription initiation site of the gene. By monitoring the level of AAC1 mRNA and the beta-galactosidase activity of AAC1-lacZ fusion constructs, we showed that expression of AAC1 is subjected to regulation by oxygen. In contrast to the other two AAC genes, the effect of oxygen on AAC1 is not mediated by heme and heme-dependent transcription factors. The AAC1 expression was reduced eightfold in anaerobically grown cells compared to expression in cells grown aerobically, but it was not affected by the nature of carbon source used for growth. The data presented show that AAC1 expression, while constitutive under all aerobic conditions tested, is repressed during anaerobiosis in a heme-independent manner.
