Oxygen radicals are important components of metazoan apoptosis. We have found that apoptosis can be induced in the yeast Saccharomyces cerevisiae by depletion of glutathione or by low external doses of H2O2. Cycloheximide prevents apoptotic death revealing active participation of the cell. Yeast can also be triggered into apoptosis by a mutation in CDC48 or by expression of mammalian bax. In both cases, we show oxygen radicals to accumulate in the cell, whereas radical depletion or hypoxia prevents apoptosis. These results suggest that the generation of oxygen radicals is a key event in the ancestral apoptotic pathway and offer an explanation for the mechanism of bax-induced apoptosis in the absence of any established apoptotic gene in yeast.

Apoptosis is co-regulated by the conserved family of Bcl-2-related proteins, which includes both its agonists (Bax) and antagonists (Bcl-X v ). A mutant strain of the yeast Saccharomyces cerevisiae has been shown to express all morphological signs of apoptosis. Overexpression of Bax is lethal in S. cerevisiae, whereas simultaneous overexpression of Bcl-X v rescues the cells. We report that overexpression of mammalian Bax in a S. cerevisiae wild type strain triggers morphological changes similar to those of apoptotic metazoan cells: the loss of asymmetric distribution of plasma membrane phosphatidylserine, plasma membrane blebbing, chromatin condensation and margination, and DNA fragmentation. Simultaneous overexpression of Bcl-X v prevents these changes. We demonstrate that Bax triggers phenotypic alterations in yeast strongly resembling those it causes in metazoan apoptotic cells.z 1998 Federation of European Biochemical Societies.

We have identified the yeast gene STM1 in an overexpression screen for new proteasomal substrates. Stm1 is unstable in wild-type cells and stabilized in cells with defective proteasomal activity and thus a bona fide substrate of the proteasome. It is localized in the perinuclear region and is required for growth in the presence of mutagens. Overexpression in cells with impaired proteasomal degradation leads to cell death accompanied with cytological markers of apoptosis: loss of plasma membrane asymmetry, chromatin condensation, and DNA cleavage. Cells lacking Stm1 display deficiency in the apoptosis-like cell death process induced by treatment with low concentrations of H2O2. We suggest that Stm1 is involved in the control of the apoptosis-like cell death in yeast. Survival is increased when Stm1 is completely missing from the cells or when inhibition of Stm1 synthesis permits proteasomal degradation to decrease its amount in the cell. Conversely, Stm1 accumulation induces cell death. In addition we identified five other genes whose overexpression in proteasomal mutants caused similar apoptotic phenotypes.

ARA70 was first identified as a gene fused to the ret oncogene in thyroid carcinoma and subsequently as a co-activator for androgen receptor (AR). Two isoforms of ARA70 have been identified: a 70-kDa version called ARA70␣ and an internally spliced 35-kDa variant termed ARA70␤. We have previously reported that ARA70␣ expression is reduced in prostate cancer, and its overexpression inhibits proliferation of LNCaP prostate cancer cells. However, the function of the ARA70␤ isoform in prostate cancer is not understood. In this report we examined the effects of ARA70␤ on AR transcriptional regulation as well as prostate cancer cellular proliferation and invasion. Although both ARA70␣ and ARA70␤ functioned as transcriptional co-activators of AR in cell-based reporter assays, ARA70␤ overexpression, in contrast to ARA70␣, promoted prostate cancer cellular proliferation and invasion through Matrigel. Interestingly, genome-wide expression profiling of cells expressing ARA70␤ revealed an increase in the expression of genes involved in the control of cell division and adhesion, compatible with a role for ARA70␤ in proliferation and invasion. Consistent with its function in promoting cell growth and invasion, ARA70␤ expression was increased in prostate cancer. Our findings implicate ARA70␤ as a regulator of tumor cell growth and metastasis by affecting gene expression. The androgen receptor (AR) is a transcription factor that regulates prostate cell growth and differentiation.1 AR mediates transcription through a series of events including ligand binding, DNA binding to cognate androgen response elements (AREs), and interaction with various co-activators. This results in activation of the general transcriptional machinery. 2 Co-activators are components that are required for activator-dependent transcription but appear to be dispensable for basal transcription. AR co-activators are thought to facilitate AR-dependent transcription by linking the receptor to the basal transcription machinery or by modulating chromatin through methylation and acetylation.3,4 An increasing number of AR-interacting proteins have been identified, and several have been shown to function as AR co-activators in cellbased reporter assay. [5][6][7] Interestingly, a number of AR co-activators display diverse patterns of expression in prostate cancer. For example, the AR cofactors ARA24, PIAS1, 8 cyclinD1, 9 SRC1, 10 and FHL2 11 appear overexpressed, whereas ARA70 8 and ART-27 12 are reduced in human prostate cancers compared to adjacent benign tissue. In addition, although most co-factors are expressed in prostatic epithelium, ARA55 is expressed exclusively in prostatic stroma, with reduced expression in prostate cancer. These findings suggest that AR coactivators perform distinct functions in prostate growth.One of the earliest described AR co-activators is ARA70. It was initially identified as a gene fused to the ret oncogene 13,14 and subsequently characterized as an AR co-activator.15 ARA70 interacts with the AR ligand-binding domain (LBD) via an FXX...