Conspiracy of yeast killers: The fifth international meeting on yeast apoptosis in Prague, Czech Republic, 3–7 September, 2006
Year: 2007
Type: article
Abstract: It was a unique atmosphere when 60 birds of paradise from all over the world gathered in Kutna Hora, an old silver-digger town near Prague. No justifications, no explanations, no excuses regarding the decision to work on such an exotic topic were offered. Instead, the community, which is almost a family since a core group of people and a growing number of others meet regularly to offer advice and help with plasmids and strains, suddenly realized that a turning point in the field had been reached. Prior to this meeting, most publications had demonstrated that yeast apoptosis (Madeo, 1997) is comparable to mammalian apoptosis. Here, for the first time, the majority of groups presented results that provided new insights into apoptosis research as a whole and that could give new directions to research in other model organisms or cell-culture systems. Chronological ageing of yeast, defined as the lifespan of a postdiauxic but still metabolic active culture, has been used as a valuable model with which to study oxidative damage and molecularly conserved ageing pathways of postmitotic tissues in higher organisms. Replicative ageing, defined by the number of daughters born from a single mother, represents a model for asymmetrically dividing stem cells. Both replicative and chronological ageing of yeast cells have been demonstrated to culminate in cell death with an apoptotic phenotype (Laun, 2001; Fabrizio, 2004; Herker, 2004). It was Ian Dawes (Sydney, Australia) who opened the meeting with an introduction about how reactive oxygen species (ROS) contribute to ageing by damaging nucleic acids, proteins and lipids. In addition, he gave details of a study aiming to evaluate the influence of diverse antioxidants on replicative lifespan and discussed the correlation between oxidative stress and replicative ageing (Laun, 2001). On a more methodological level, David Goldfarb (Rochester, USA) presented the development and initial applications of a new assay for determining replicative lifespan (‘death of daughters’ assay). Here, a genetically engineered yeast strain is used in which the daughters of mother cells die under nonpermissive conditions limiting replicative lifespan to the initial population of mother cells (Jarolim, 2004). He reported on the use of the assay to identify new genes that are required for full lifespan. Gennaro D'Urso (Miami, USA) showed how the method of apoptosis induction by chronological ageing is transferable to fission yeast. Data from this method suggest that DNA replication stress under starvation conditions may be responsible for activation of the cell-death pathway. In a different ageing approach, Kai-Uwe Fröhlich and Christoph Ruckenstuhl (Graz, Austria) presented a new monocolony assay to monitor developmental cell death within whole colonies. Interestingly, mitochondria, the central death-regulating organelles, appear to play a crucial role for cell survival in yeast colonies. Stefan Woelfl and Ana Kitanovic (Heidelberg, Germany) focused on cellular adaptive responses to low doses of toxic substances. In their study, low concentrations of MMS, a DNA-alkylating and thus DNA-damaging agent, triggered an adaptive response induced by the onset of the general stress response mechanism, an increased ROS production, and an intensified metabolic rate. However, this defence response, although it leads to an effective DNA damage repair, also shortens the life-span of the cells. Kitanovic & Wolfl (2006) further demonstrated that regulation of the key enzyme of gluconeogenesis, FBP1, is essential for such a proper response to DNA damage and ageing. Furthermore, rapid ageing upon Fbp1p-overexpression and a requirement for Yca1p or Aif1p, two key players of yeast apoptosis (Madeo, 2002; Wissing, 2004), in this process were shown. Paola Fabrizio (Los Angeles, USA) described a cell death and ageing regulatory network connecting mutations in yeast orthologues of mammalian Ras, Akt and Tor with resistance to stress-induced and age-dependent cell death. These results are beginning to reveal the complexity of a network of proteins involved in the regulation of both ageing and age-dependent cell death conserved from yeast to higher eukaryotes. Peter Hauptmann (Regensburg, Germany) presented a new, Yca1p-independent protease involved in cell death induced by defective N-glycosylation and acetic acid. Although cell death induced by N-glycosylation defects was accompanied by caspase-like activity, this activity seemed to be independent of YCA1. Instead, deletion of the protease KEX1 decreased the caspase-like activity, inhibited ROS formation, and improved cell survival (Hauptmann, 2006). The influence of acetic acid on induced cell death was also reported by Paula Ludovico from Braga, Portugal (Ludovico, 2002). Tobias Eisenberg (Graz, Austria) showed that polyamines promote yeast longevity and could provide the first insights into the mechanism behind it. Daniela Ehehalt (Stuttgart, Germany) delineated perturbations in calcium and manganese homeostasis as inducers of ER stress and programmed cell death in yeast. Heat stress caused impaired degradation of ER-luminal malfolded glycoproteins and subsequent death in cells deleted in PMR1, an ion pump for Ca2+ and Mn2+ uptake, which could be suppressed by the addition of calcium but not of manganese. This ER-linked death program required yeast metacaspase YCA1 and was most pronounced in Δpmr1Δaif1 cells, documenting also the protective role of the yeast apoptosis-inducing factor AIF1. Autophagy is a major intracellular-degradation process that plays a crucial role in survival during starvation in organisms ranging from yeast to mammals. Although autophagy is generally considered to be a nonselective process, selective forms of it have been shown to be involved in the degradation of several organelles. Using lactate-grown yeast subjected to nitrogen starvation, Ingrid Kiššová (Bordeaux, France) was able to provide evidence for selective as well as nonselective mitochondrial autophagy in yeast. The early process of selective targetting of mitochondria was dependent on Uth1p, a mitochondrial outer membrane protein, whereas a late process of classical nonselective microautophagy (including that of mitochondria) was not altered upon deletion of UTH1 (Kissova, 2004). Maïka Deffieu (Bordeaux, France) presented data suggesting that oxidation events play a crucial role in the regulation of mitophagy. Nitrogen starvation to induce autophagy during stationary phase revealed that deletion of the UTH1 gene results in higher levels of mitochondrial protein oxidation, an increase in ROS accumulation and an alteration in fatty acid composition of phospholipids (Kissova, 2006). In recent years, yeast has been successfully established as a model with which to study the functions and mechanisms of various human pro and antiapoptotic proteins involved in cancer development, several neurodegenerative diseases, and AIDS. During this meeting, Peter Polčic (Bratislava, Slovak Republic) presented new insights into the mechanisms that underlie the interactions of Bcl-2 family members. Using yeast as a heterologous expression system to learn about ‘BH3-only’ proteins, he introduced representative ‘BH3-only’ members into yeast and was able to show that these proteins induce cell death in yeast when Bax is coexpressed, indicating that their function can be reconstituted in the yeast system. Stephén Manon (Bordeaux, France) delineated the molecular mechanisms underlying the interaction between Bax and mitochondria during apoptosis. The mobility of the two ends of the protein was demonstrated to be crucial for the conformational change needed in order for it to be targetted to and inserted in the outer mitochondrial membrane. The movement of the C- and N-terminal ends of Bax was shown to enable the protein to uncover the domain (the α1 helix) necessary for interaction with mitochondrial protein(s), thus facilitating its insertion in the mitochondrial outer membrane. In parallel, he was able to demonstrate that the insertion of the hydrophobic C-terminal helix á9 is not required for Bax-insertion. Additional data presented suggest that posttranslational modifications such as phosphorylation of certain residues have an important function in the regulation of the translocation and activation of Bax. In a screen of mammalian cDNA libraries for suppressors of the growth-inhibitory effect of Bax in yeast, Chamel M. Khoury (Montreal, Canada) had identified a novel human antiapoptotic gene product that suppresses Bax-induced yeast cell death independently of the ESCRT (endosomal sorting complex required for transport) pathway. He presented data showing that an alternatively spliced variant of the human VPS24 protein lacking the N-terminal lipid binding domain is not involved in the ESCRT pathway but does serve an antiapoptotic role upon Bax-expression. Using fission yeast as a model system with which to study apoptosis induced by HIV-1 viral protein R (Vpr), Richard Y. Zhao (Baltimore, USA) aimed to gain further insights into the molecular mechanisms underlying Vpr-induced apoptosis. He presented data showing that expression of vpr in fission yeast leads to rapid cell death accompanied by apoptotic chromatin condensation and phosphatidylserine externalization. In yeast, as in mammalian cells, Vpr interrupts the mitochondrial membrane potential in yeast. He further demonstrated that Vpr affects mitochondrial morphology by producing mitochondrial aggregates near the centre of the yeast cell, a phenomenon that could further link to apoptosis. Using the fission yeast model system, two novel antiapoptotic Vpr suppressors, hsp16 or ef2, were identified (Benko, 2004; Zelivianski, 2006). Expression of hsp16 or ef2 not only completely inhibited Vpr-induced cell death and changes of mitochondrial morphology in fission yeast but also suppressed Vpr-induced apoptosis in mammalian cells. Joris Winderickx (Leuven, Belgium) presented novel insights into á-Synuclein-induced toxicity and its effect on longevity and apoptosis in yeast. He showed that expression of synuclein dramatically reduces the chronological life span of yeast cells. Notably, this life-span reduction correlated with the formation of aggregates (Zabrocki, 2005). Frank Madeo (Graz, Austria) presented evidence that yeast Endonuclease G regulates caspase-independent apoptosis and elucidated the pathway necessary for yeast Endonuclease G-mediated cell death. Manuela Côrte-Real (Braga, Portugal) described the first evidence of the requirement of ATP/ADP carrier for mitochondrial outer membrane permeabilization and cytochrome c release in yeast committed to apoptosis. She also showed that DNA degradation, comparable to higher-order apoptotic DNA fragmentation in mammalian cells, is linked to yeast apoptosis (Ribeiro, 2006). She also examined the apoptotic modulation of Bcl-2 family proteins by individual mammalian protein kinase C (PKC) isoforms and the regulation of p53-dependent apoptosis by PKC. Karen Sapienza (Msida, Malta) presented data demonstrating the mitochondrial involvement in aspirin-induced apoptosis in yeast cells, a phenomenon of considerable pathophysiological impact (Sapienza & Balzan, 2005). The release of cytochrome c from mitochondria was shown to be an important part of the apoptotic mechanism of aspirin and to occur prior to the disruption of the mitochondrial membrane potential. Using proteomic and cell biological approaches, Paula Ludovico (Braga, Portugal) was able to demonstrate that the TOR pathway is necessary for acetic acid-induced apoptosis. Deletion of two key transcriptional regulators of amino acid synthesis was found to rescue acetic acid-induced yeast cell death. Sergio Giannattasio (Bari, Italy) further delineated yeast programmed cell death triggered by acetic acid. He could demonstrate that, upon acetic acid treatment, yeast follows either a faster YCA1-dependent or a slower YCA1-independent death pathway (Guaragnella, 2006). In addition, he investigated the time course of cytochrome c release into the cytoplasm, providing first insights into the mechanism of this pivotal process in yeast programmed cell death triggered by acetic acid. Birthe Fahrenkrog (Basel, Switzerland) showed that the proapoptotic activity of the nuclear HtrA/Omi-like serine protease Nma111p (Fahrenkrog, 2004) depends on its nuclear localization. She has now identified two nuclear localization signals (NLSs) and one nuclear export signal (NES), and has studied their influence on the ability of Nma111p to mediate yeast apoptosis. Whereas expression of intact Nma111p enhanced apoptotic cell death, a construct mutated in the NLSs showed no hallmarks of apoptosis after induction of cell death using H2O2. Deletion of the NES did not affect cell killing mediated by Nma111p. Campbell Gourlay (Sheffield, UK) presented a defined link between environmental sensing, actin remodelling and apoptosis in budding yeast. He demonstrated that stabilization of the actin cytoskeleton, caused by deletion of SLA1 or END1, induces hyperactivation of the Ras signalling pathway. The consequent rise in cAMP levels leads to the loss of mitochondrial membrane potential, accumulation of ROS and death, primarily through a subunit of protein kinase A (PKA). An artificial elevation of cAMP-levels was shown to directly mimic the apoptotic phenotype displayed in actin-stabilized cells. Moreover, he has established a mechanistic link between Ras signalling and actin, by demonstrating that ROS production in actin-stabilized cells is dependent on the G-actin binding region of the cyclase-associated protein Srv2p/CAP. Besides their role in cellular energy metabolism, mitochondria are established and recognized as key players in cell death. Their central role during apoptosis is marked by the release of proapoptotic factors such as cytochrome c and apoptosis-inducing factor (AIF). In yeast, where among others the orthologue of AIF (Wissing, 2004) and apoptotic scenarios such as cytochrome c release (Ludovico, 2002) can be found, mitochondria have advanced to be the main apoptotic organelles. Michael Breitenbach (Salzburg, Austria) introduced the latest advances in the involvement of mitochondria in yeast cell death by delineating the role of two mitochondrial proteins, YGR076cp and Mmi1p. YGR076p, a mitochondrial ribosomal protein, was shown to influence replicative lifespan and to be involved in the TOR pathway, while Mmi1p, the yeast member of the highly conserved eukaryotic gene family TCTP (translationally controlled tumor protein), was demonstrated to shuttle to mitochondria and to colocalize with Rpg1p in so-called stress granules when cells are treated with a mild oxidative stress to induce apoptosis (Rinnerthaler, 2006). Michal Jazwinski (New Orleans, USA) clarified the role of mitochondria in nuclear genome instability and illustrated its relationship with the retrograde response, an intracellular signalling pathway that compensates for age-related mitochondrial dysfunction by inducing the transcription of metabolic and stress-response genes. He also discussed the possibility of an association between age asymmetry and the retrograde response. The meeting was a unique one, not only from a scientific point of view but also on a personal level due to the nice and friendly temper of all participants. The organization by Alena Pichova was perfect, even turning into magic when she brought us into a deep forest near Kutná Hora where the exotic white deer with blue eyes live; they are few but growing in number. After the conference dinner in the empire chateau Kačina, Gennaro D'Urso, a former postdoctorate from Paul Nurse's laboratory, played guitar and sang melting love songs. In one of the conference rest periods we visited an old silver mine, and, seeing how people in Medieval times used to dig 600 m down into the Earth, we realized that the job of a scientist is not that bad, even when working on yeast death is involved. We all look forward to the next meeting, which will be organized by Joris Winderickx during Spring 2008 in the beautiful town of Leuven in Belgium.
Source: FEMS Yeast Research
Institution: University of Graz
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W1975474219