Elevated Ras/protein kinase A activity in Saccharomyces cerevisiae reduces proliferation rate and lifespan by two different reactive oxygen species-dependent routes. Aging Cell 7:148-157

Institute of Physiology, Czech Academy of Sciences, CZ-142 20 Prague, Czech Republic.
Aging cell (Impact Factor: 6.34). 04/2008; 7(2):148-57. DOI: 10.1111/j.1474-9726.2007.00361.x
Source: PubMed


Cells with overactive RAS/protein kinase A (PKA) signaling, such as RAS2(Val19) cells, exhibit reduced proliferation rates and accelerated replicative senescence. We show here that the extended generation time of RAS2(Val19)cells is the result of abrogated ATP/ADP carrier activity of the mitochondria. Both PKA-dependent and independent routes are responsible for inhibiting ATP/ADP exchange in the RAS-overactive cells. The reduced carrier activity is due, at least in part, to elevated levels of reactive oxygen species (ROS), which also cause a proteolysis-dependent fragmentation of the Aac2p carrier both in vivo and on isolated mitochondria. Attenuated carrier activity is suppressed by overproducing the superoxide dismutase, Sod1p, and this enhances both the proliferation rate and the replicative longevity of RAS2(Val19) cells. In contrast, overproducing functional Aac2p restored proliferation but not longevity of RAS2(Val19) cells. Thus, Ras signaling affects proliferation rate and replicative lifespan by two different, ROS-dependent, routes. While the reduction in generation time is linked to the inactivation, specifically, of the mitochondrial nucleotide carrier, longevity is affected by other, and hitherto unknown, target(s) of ROS attack.

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Available from: Lydie Plecitá-Hlavatá, Jan 19, 2015
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    • "Previous studies in yeast have established links between Ras signaling and mitochondrial function, via cAMP/PKA dependent and independent routes [16,17]. Within yeast Ras/cAMP/PKA signaling also controls cellular processes that include cell growth and proliferation and the induction of stress responses [18], making this pathway a good candidate to integrate environmental signaling with mitochondrial regulation. "
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    ABSTRACT: Appropriate control of mitochondrial function, morphology and biogenesis are crucial determinants of the general health of eukaryotic cells. It is therefore imperative that we understand the mechanisms that co-ordinate mitochondrial function with environmental signaling systems. The regulation of yeast mitochondrial function in response to nutritional change can be modulated by PKA activity. Unregulated PKA activity can lead to the production of mitochondria that are prone to the production of ROS, and an apoptotic form of cell death. We present evidence that mitochondria are sensitive to the level of cAMP/PKA signaling and can respond by modulating levels of respiratory activity or committing to self execution. The inappropriate activation of one of the yeast PKA catalytic subunits, Tpk3p, is sufficient to commit cells to an apoptotic death through transcriptional changes that promote the production of dysfunctional, ROS producing mitochondria. Our data implies that cAMP/PKA regulation of mitochondrial function that promotes apoptosis engages the function of multiple transcription factors, including HAP4, SOK2 and SCO1. We propose that in yeast, as is the case in mammalian cells, mitochondrial function and biogenesis are controlled in response to environmental change by the concerted regulation of multiple transcription factors. The visualization of cAMP/TPK3 induced cell death within yeast colonies supports a model that PKA regulation plays a physiological role in coordinating respiratory function and cell death with nutritional status in budding yeast.
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    • "Ras pathway activity is an important component in the regulation of cellular longevity in eukaryotic cells. The expression of a constitutively active form of Ras has been shown to result in the accumulation of reactive oxygen species (ROS) and a reduction in the life span in yeast and mammalian cells (Heeren et al., 2004; Hlavata et al., 2008; Serrano et al., 1997). The ability of the RascAMP-PKA pathway to regulate mitochondrial function and ROS production also appears to have been harnessed by a fungal apoptotic response. "
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    ABSTRACT: Elucidating the mechanisms by which eukaryotic cells coordinate environmental signals with intracellular ;fate' decisions, such as apoptosis, remains one of the important challenges facing cell biologists. It has recently emerged that the dynamic nature of the actin cytoskeleton is an important factor in the linkage of sensation of extracellular stimuli to signalling mechanisms that regulate programmed cell death. In yeast, actin has been shown to play a role in the regulation of apoptosis as cells prepare themselves for quiescence in the face of nutritional exhaustion, by facilitating the shutdown of Ras-cAMP-PKA pathway activity. Here, we demonstrate that the loss of Whi2p function, a protein known to influence cell cycle exit under conditions of nutritional stress, leads to cell death in yeast that displays the hallmarks of actin-mediated apoptosis. We show that actin-mediated apoptosis occurs as a result of inappropriate Ras-cAMP-PKA activity in Deltawhi2 cells. Cells lacking Whi2p function exhibit an aberrant accumulation of activated Ras2 at the mitochondria in response to nutritional depletion. This study provides evidence that the shutdown of cAMP-PKA signalling activity in wild-type cells involves Whi2p-dependent targeting of Ras2p to the vacuole for proteolysis. We also demonstrate for the first time that Whi2p-dependent regulation of cAMP-PKA signalling plays a physiological role in the differentiation of yeast colonies by facilitating elaboration of distinct zones of cell death.
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    • "Conversely, treating cells with hydrogen peroxide (H2O2) decreases the level of NAD+, decreases the activity of SIRT1, and lead to the accumulation of acetylated p53.48 While longevity genetic manipulations decrease the ROS level, short-lived mutants such as activated Ras2 increased the intracellular ROS level.49,50 Therefore, mathematically modeling the intracellular homeostasis of NAD/NADH, NADP/NADPH, GSH/GSSG, ROS, and calcium will highlight the contribution of involved proteins. "
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    ABSTRACT: Identification of genes involved in the aging process is critical for understanding the mechanisms of age-dependent diseases such as cancer and diabetes. Measuring the mutant gene lifespan, each missing one gene, is traditionally employed to identify longevity genes. While such screening is impractical for the whole genome due to the time-consuming nature of lifespan assays, it can be achieved by in silico genetic manipulations with systems biology approaches. In this review, we will introduce pilot explorations applying two approaches of systems biology in aging studies. One approach is to predict the role of a specific gene in the aging process by comparing its expression profile and protein-protein interaction pattern with those of known longevity genes (top-down systems biology). The other approach is to construct mathematical models from previous kinetics data and predict how a specific protein contributes to aging and antiaging processes (bottom-up systems biology). These approaches allow researchers to simulate the effect of each gene's product in aging by in silico genetic manipulations such as deletion or over-expression. Since simulation-based approaches are not as widely used as the other approaches, we will focus our review on this effort in more detail. A combination of hypothesis from data-mining, in silico experimentation from simulations, and wet laboratory validation will make the systematic identification of all longevity genes possible.
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