Yap1: a DNA damage responder in Saccharomyces cerevisiae

Molecular Mechanisms of Resistance to Ionizing Radiation in S. cerevisiae and Its Relationship with Aging, Oxidative Stress, and Antioxidant Activity

The repair of the damage produced to the genome and proteome by the action of ionizing radiation, oxidizing agents, and during aging is important to maintain cellular homeostasis. Many of the metabolic pathways influence multiple processes. In this way, this work aims to study the relationship between resistance/response to ionizing radiation, cellular aging, and the response mechanisms to oxidative stress, free radicals, reactive oxygen species (ROS), and antioxidant activity in the yeast S. cerevisiae. Systems biology allows us to use tools that reveal the molecular mechanisms common to different cellular response phenomena. The results found indicate that homologous recombination, non-homologous end joining, and base excision repair pathways are the most important common processes necessary to maintain cellular homeostasis. The metabolic routes of longevity regulation are those that jointly contribute to the three phenomena studied. This study proposes eleven common biomarkers for response/resistance to ionizing radiation and aging (EXO1, MEC1, MRE11, RAD27, RAD50, RAD51, RAD52, RAD55, RAD9, SGS1, YKU70) and two biomarkers for response/resistance to radiation and oxidative stress, free radicals, ROS, and antioxidant activity (NTG1, OGG1). In addition, it is important to highlight that the HSP104 protein could be a good biomarker common to the three phenomena studied.

Manganese Stress Tolerance Depends on Yap1 and Stress-Activated MAP Kinases

Understanding which intracellular signaling pathways are activated by manganese stress is crucial to decipher how metal overload compromise cellular integrity. Here, we unveil a role for oxidative and cell wall stress signaling in the response to manganese stress in yeast. We find that the oxidative stress transcription factor Yap1 protects cells against manganese toxicity. Conversely, extracellular manganese addition causes a rapid decay in Yap1 protein levels. In addition, manganese stress activates the MAPKs Hog1 and Slt2 (Mpk1) and leads to an up-regulation of the Slt2 downstream transcription factor target Rlm1. Importantly, Yap1 and Slt2 are both required to protect cells from oxidative stress in mutants impaired in manganese detoxification. Under such circumstances, Slt2 activation is enhanced upon Yap1 depletion suggesting an interplay between different stress signaling nodes to optimize cellular stress responses and manganese tolerance.

Knowledge base and emerging trends in YAP1 research

Yes-associated protein 1 (YAP1) is a transcriptional coactivator that mediates the Hippo signaling pathway, which participates in the development and growth of the body; it plays key roles in tumorigenesis, metastasis, and therapy resistance. However, the pathophysiological mechanism of YAP1 has not been fully elucidated. Therefore, we explored the status and evolutionary trend in YAP1 research via bibliometric analysis. A total of 2,928 publications were downloaded from Web of Science Core Collection (WOSCC). The co-citation network map was drawn via CiteSpace and VOSviewer software. We analyzed the co-authorship networks among countries, journals, and authors, as well as co-occurrence of co-cited references, citation bursts, and keywords in YAP1 research, in order to predict its literature development. The present research evaluates the annual publication trends of YAP1 literature, and the following results were established: research on YAP1 are of steady increase; China present the highest co-citation; the Journal of Biological Chemistry (J Biol Chem) was the most productive journal, while Cell press received the most citations from co-cited references; Among the authors in the overall citations Bin Zhao is the most promising collaborator for emerging scholars in this field; and lastly, co-occurrence keyword analysis indicated that the emerging trends in YAP1 research were mainly focused on cancer therapy. We established that projects on YAP1 research is presently in its rapid developmental stage with active global collaboration. In addition, the mechanism and clinical significance of YAP1 in cancer was established as the potential trend of future studies.

AaTAS1 and AaMFS1 Genes for Biosynthesis or Efflux Transport of Tenuazonic Acid and Pathogenicity of Alternaria alternata

Taking tenuazonic acid (TeA) synthetase 1 (TAS1) in Pyricularia oryzae as a reference, the homolog AaTAS1 was first anchored in Alternaria alternata via de novo sequencing. Subsequently, AaMFS1, as a major facilitator superfamily (MFS) protein-encoding gene in the adjacent upstream region, was followed with interest. As hypothesized, AaTAS1 is required for TeA biosynthesis, while AaMFS1 is an efflux pump for the transmembrane transport of TeA. Comparatively, the TeA yield of ΔAaTAS1 and ΔAaMFS1 dropped significantly compared with that of the wild-type strain. Specifically, the A domain of AaTAS1 catalyzed the start of TeA biosynthesis in vitro. Simultaneously, the pathogenicity of ΔAaTAS1 was also significantly decreased. Transcriptome analysis confirmed the abovementioned consistency between the TeA-producing phenotypes and related gene expression. Moreover, the proteins AaTAS1 and AaMFS1 were found present in the cytoplasm, plasma membrane, and intracellular membrane system, respectively, by fluorescence localization. Namely, AaTAS1 was responsible for the biosynthesis of TeA, and AaMFS1 was responsible for the efflux transport of TeA. Certainly, AaTAS1 indirectly regulated the expression of AaMFS1 through the level of synthetic TeA. Overall, data on the novel AaTAS1 and AaMFS1 genes mainly contribute to theoretical advances in mycotoxin biosynthesis and the pathogenicity of phytopathogens to agricultural foods.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Genetically induced redox stress occurs in a yeast model for Roberts syndrome

Roberts syndrome (RBS) is a multispectrum developmental disorder characterized by severe limb, craniofacial, and organ abnormalities and often intellectual disabilities. The genetic basis of RBS is rooted in loss-of-function mutations in the essential N-acetyltransferase ESCO2 which is conserved from yeast (Eco1/Ctf7) to humans. ESCO2/Eco1 regulate many cellular processes that impact chromatin structure, chromosome transmission, gene expression, and repair of the genome. The etiology of RBS remains contentious with current models that include transcriptional dysregulation or mitotic failure. Here, we report evidence that supports an emerging model rooted in defective DNA damage responses. First, the results reveal that redox stress is elevated in both eco1 and cohesion factor Saccharomyces cerevisiae mutant cells. Second, we provide evidence that Eco1 and cohesion factors are required for the repair of oxidative DNA damage such that ECO1 and cohesin gene mutations result in reduced cell viability and hyperactivation of DNA damage checkpoints that occur in response to oxidative stress. Moreover, we show that mutation of ECO1 is solely sufficient to induce endogenous redox stress and sensitizes mutant cells to exogenous genotoxic challenges. Remarkably, antioxidant treatment desensitizes eco1 mutant cells to a range of DNA damaging agents, raising the possibility that modulating the cellular redox state may represent an important avenue of treatment for RBS and tumors that bear ESCO2 mutations.

An innovative targeted therapy for fluoroscopy-induced chronic radiation dermatitis

Fluoroscopy-induced chronic radiation dermatitis (FICRD) is a complication of fluoroscopy-guided intervention. Unlike acute radiation dermatitis, FICRD is different as delayed onset and usually appears without preexisting acute dermatitis. Unfortunately, the chronic and progressive pathology of FICRD makes it difficult to treat, and some patients need to receive wide excision and reconstruction surgery. Due to lack of standard treatment, investigating underlying mechanism is needed in order to develop an effective therapy. Herein, the Hippo pathway is specifically identified using an RNA-seq analysis in mild damaged skin specimens of patients with FICRD. Furthermore, specific increase of the Yes-associated protein (YAP1), an effector of the Hippo pathway, in skin region with mild damage plays a protective role for keratinocytes via positively regulating the numerous downstream genes involved in different biological processes. Interestingly, irradiated-keratinocytes inhibit activation of fibroblasts under TGF-β1 treatment via remote control by an exosome containing YAP1. More importantly, targeting one of YAP1 downstream genes, nuclear receptor subfamily 3 group C member 1 (NR3C1), which encodes glucocorticoid receptor, has revealed its therapeutic potential to treat FICRD by inhibiting fibroblasts activation in vitro and preventing formation of radiation ulcers in a mouse model and in patients with FICRD. Taken together, this translational research demonstrates the critical role of YAP1 in FICRD and identification of a feasible, effective therapy for patients with FICRD. KEY MESSAGES: • YAP1 overexpression in skin specimens of radiation dermatitis from FICRD patient. • Radiation-induced YAP1 expression plays protective roles by promoting DNA damage repair and inhibiting fibrosis via remote control of exosomal YAP1. • YAP1 positively regulates NR3C1 which encodes glucocorticoid receptor expression. • Targeting glucocorticoid receptor by prednisolone has therapeutic potential for FICRD patient.

Hydroxyurea-The Good, the Bad and the Ugly

Hydroxyurea (HU) is mostly referred to as an inhibitor of ribonucleotide reductase (RNR) and as the agent that is commonly used to arrest cells in the S-phase of the cycle by inducing replication stress. It is a well-known and widely used drug, one which has proved to be effective in treating chronic myeloproliferative disorders and which is considered a staple agent in sickle anemia therapy and—recently—a promising factor in preventing cognitive decline in Alzheimer’s disease. The reversibility of HU-induced replication inhibition also makes it a common laboratory ingredient used to synchronize cell cycles. On the other hand, prolonged treatment or higher dosage of hydroxyurea causes cell death due to accumulation of DNA damage and oxidative stress. Hydroxyurea treatments are also still far from perfect and it has been suggested that it facilitates skin cancer progression. Also, recent studies have shown that hydroxyurea may affect a larger number of enzymes due to its less specific interaction mechanism, which may contribute to further as-yet unspecified factors affecting cell response. In this review, we examine the actual state of knowledge about hydroxyurea and the mechanisms behind its cytotoxic effects. The practical applications of the recent findings may prove to enhance the already existing use of the drug in new and promising ways.

Molecular Tools for the Yeast Papiliotrema terrestris LS28 and Identification of Yap1 as a Transcription Factor Involved in Biocontrol Activity

Fungal attacks on stored fruit and vegetables are responsible for losses of products. There is an active research field to develop alternative strategies for postharvest disease management, and the use of biocontrol agents represents a promising approach. Understanding the molecular bases of the biocontrol activity of these agents is crucial to potentiate their effectiveness. The yeast Papiliotrema terrestris is a biocontrol agent against postharvest pathogens. Phenotypic studies suggest that it exerts its antagonistic activity through competition for nutrients and space, which relies on its resistance to oxidative and other cellular stresses. In this study, we developed tools for genetic manipulation in P. terrestris to perform targeted gene replacement and functional complementation of the transcription factors Yap1 and Rim101. In vitro phenotypic analyses revealed a conserved role of Yap1 and Rim101 in broad resistance to oxidative stress and alkaline pH sensing, respectively. In vivo analyses revealed that P. terrestris yap1Δ and rim101Δ mutants display decreased ability to colonize wounded fruit compared to that of the parental wild-type (WT) strain; the yap1Δ mutant also displays reduced biocontrol activity against the postharvest pathogens Penicillium expansum and Monilinia fructigena, indicating an important role for resistance to oxidative stress in timely wound colonization and biocontrol activity of P. terrestris In conclusion, the availability of molecular tools developed in the present study provides a foundation to elucidate the genetic mechanisms underlying biocontrol activity of P. terrestris, with the goal of enhancing this activity for the practical use of P. terrestris in pest management programs based on biological and integrated control.IMPORTANCE The use of fungicides represents the most effective and widely used strategy for controlling postharvest diseases. However, their extensive use has raised several concerns, such as the emergence of plant pathogens' resistance as well as the health risks associated with the persistence of chemical residues in fruit, in vegetables, and in the environment. These factors have brought attention to alternative methods for controlling postharvest diseases, such as the utilization of biocontrol agents. In the present study, we developed genetic resources to investigate at the molecular level the mechanisms involved in the biocontrol activity of Papiliotrema terrestris, a basidiomycete yeast that is an effective biocontrol agent against widespread fungal pathogens, including Penicillium expansum, the etiological agent of blue mold disease of pome fruits. A deeper understanding of how postharvest biocontrol agents operate is the basic requirement to promote the utilization of biological (and integrated) control for the reduction of chemical fungicides.

DNA damage induces Yap5-dependent transcription of ECO1/CTF7 in Saccharomyces cerevisiae

Yeast Eco1 (ESCO2 in humans) acetyltransferase converts chromatin-bound cohesins to a DNA tethering state, thereby establishing sister chromatid cohesion. Eco1 establishes cohesion during DNA replication, after which Eco1 is targeted for degradation by SCF E3 ubiquitin ligase. SCF E3 ligase, and sequential phosphorylations that promote Eco1 ubiquitination and degradation, remain active throughout the M phase. In this way, Eco1 protein levels are high during S phase, but remain low throughout the remaining cell cycle. In response to DNA damage during M phase, however, Eco1 activity increases-providing for a new wave of cohesion establishment (termed Damage-Induced Cohesion, or DIC) which is critical for efficient DNA repair. To date, little evidence exists as to the mechanism through which Eco1 activity increases during M phase in response to DNA damage. Possibilities include that either the kinases or E3 ligase, that target Eco1 for degradation, are inhibited in response to DNA damage. Our results reveal instead that the degradation machinery remains fully active during M phase, despite the presence of DNA damage. In testing alternate models through which Eco1 activity increases in response to DNA damage, the results reveal that DNA damage induces new transcription of ECO1 and at a rate that exceeds the rate of Eco1 turnover, providing for rapid accumulation of Eco1 protein. We further show that DNA damage induction of ECO1 transcription is in part regulated by Yap5-a stress-induced transcription factor. Given the role for mutated ESCO2 (homolog of ECO1) in human birth defects, this study highlights the complex nature through which mutation of ESCO2, and defects in ESCO2 regulation, may promote developmental abnormalities and contribute to various diseases including cancer.

Role of Blood Oxygen Saturation During Post-Natal Human Cardiomyocyte Cell Cycle Activities

Blood oxygen saturation (SaO₂) is one of the most important environmental factors in clinical heart protection. This study used human heart samples and human induced pluripotent stem cell-cardiomyocytes (iPSC-CMs) to assess how SaO₂ affects human CM cell cycle activities. The results showed that there were significantly more cell cycle markers in the moderate hypoxia group (SaO₂: 75% to 85%) than in the other 2 groups (SaO₂ <75% or >85%). In iPSC-CMs 15% and 10% oxygen (O₂) treatment increased cell cycle markers, whereas 5% and rapid change of O₂ decreased the markers. Moderate hypoxia is beneficial to the cell cycle activities of post-natal human CMs.

Lack of superoxide dismutase in a rad51 mutant exacerbates genomic instability and oxidative stress-mediated cytotoxicity in Saccharomyces cerevisiae

A genetic analysis of synthetic lethal interactions in yeast revealed that the mutation of SOD1, encoding an antioxidant enzyme that scavenges superoxide anion radical, impaired the growth of a set of mutants defective in homologous recombination (HR) pathway. Hence, SOD1 inhibition has been proposed as a promising approach for the selective killing of HR-deficient cancer cells. However, we show that the deletion of RAD51 and SOD1 is not synthetic lethal but displays considerably slow growth and synergistic sensitivity to both reactive oxygen species (ROS)- and DNA double-strand break (DSB)-generating drugs in the budding yeast Saccharomyces cerevisiae. The function of Sod1 in regard to Rad51 is dependent on Ccs1, a copper chaperone for Sod1. Sod1 deficiency aggravates genomic instability in conjunction with the absence of Rad51 by inducing DSBs and an elevated mutation frequency. Inversely, lack of Rad51 causes a Sod1 deficiency-derived increase of intracellular ROS levels. Taken together, our results indicate that there is a significant and specific crosstalk between two major cellular damage response pathways, ROS signaling and DSB repair, for cell survival.

Light treatments of nail fungal infections

Nail fungal infections are notoriously persistent and difficult to treat which can lead to severe health impacts, particularly in the immunocompromized. Current antifungal treatments, including systemic and topical drugs, are prolonged and do not effectively provide a complete cure. Severe side effects are also associated with systemic antifungals, such as hepatotoxicity. Light treatments of onychomycosis are an emerging therapy that has localized photodynamic, photothermal or photoablative action. These treatments have shown to be an effective alternative to traditional antifungal remedies with comparable or better cure rates achieved in shorter times and without systemic side effects. This report reviews significant clinical and experimental studies in the field, highlighting mechanisms of action and major effects related to light therapy; in particular, the impact of light on fungal genetics.

Unraveling new functions of superoxide dismutase using yeast model system: Beyond its conventional role in superoxide radical scavenging

To deal with chemically reactive oxygen molecules constantly threatening aerobic life, cells are readily equipped with elaborate biological antioxidant systems. Superoxide dismutase is a metalloenzyme catalytically eliminating superoxide radical as a first-line defense mechanism against oxidative stress. Multiple different SOD isoforms have been developed throughout evolution to play distinct roles in separate subcellular compartments. SOD is not essential for viability of most aerobic organisms and intriguingly found even in strictly anaerobic bacteria. Sod1 has recently been known to play important roles as a nuclear transcription factor, an RNA binding protein, a synthetic lethal interactor, and a signal modulator in glucose metabolism, most of which are independent of its canonical function as an antioxidant enzyme. In this review, recent advances in understanding the unconventional role of Sod1 are highlighted and discussed with an emphasis on its genetic crosstalk with DNA damage repair/checkpoint pathways. The budding yeast Saccharomyces cerevisiae has been successfully used as an efficient tool and a model organism to investigate a number of novel functions of Sod1.

Yap1 and Skn7 genetically interact with Rad51 in response to oxidative stress and DNA double-strand break in Saccharomyces cerevisiae

Reactive oxygen species (ROS)-mediated DNA adducts as well as DNA strand breaks are highly mutagenic leading to genomic instability and tumorigenesis. DNA damage repair pathways and oxidative stress response signaling have been proposed to be highly associated, but the underlying interaction remains unknown. In this study, we employed mutant strains lacking Rad51, the homolog of E. coli RecA recombinase, and Yap1 or Skn7, two major transcription factors responsive to ROS, to examine genetic interactions between double-strand break (DSB) repair proteins and cellular redox regulators in budding yeast Saccharomyces cerevisiae. Abnormal expression of YAP1 or SKN7 aggravated the mutation rate of rad51 mutants and their sensitivity to DSB- or ROS-generating reagents. Rad51 deficiency exacerbated genome instability in the presence of increased levels of ROS, and the accumulation of DSB lesions resulted in elevated intracellular ROS levels. Our findings suggest that evident crosstalk between DSB repair pathways and ROS signaling proteins contributes to cell survival and maintenance of genome integrity in response to genotoxic stress.

Hydroxyurea Induces Cytokinesis Arrest in Cells Expressing a Mutated Sterol-14α-Demethylase in the Ergosterol Biosynthesis Pathway

Hydroxyurea (HU) has been used for the treatment of multiple diseases, such as cancer. The therapeutic effect is generally believed to be due to the suppression of ribonucleotide reductase (RNR), which slows DNA polymerase movement at replication forks and induces an S phase cell cycle arrest in proliferating cells. Although aberrant mitosis and DNA damage generated at collapsed forks are the likely causes of cell death in the mutants with defects in replication stress response, the mechanism underlying the cytotoxicity of HU in wild-type cells remains poorly understood. While screening for new fission yeast mutants that are sensitive to replication stress, we identified a novel mutation in the erg11 gene encoding the enzyme sterol-14α-demethylase in the ergosterol biosynthesis pathway that dramatically sensitizes the cells to chronic HU treatment. Surprisingly, HU mainly arrests the erg11 mutant cells in cytokinesis, not in S phase. Unlike the reversible S phase arrest in wild-type cells, the cytokinesis arrest induced by HU is relatively stable and occurs at low doses of the drug, which likely explains the remarkable sensitivity of the mutant to HU. We also show that the mutation causes sterol deficiency, which may predispose the cells to the cytokinesis arrest and lead to cell death. We hypothesize that in addition to the RNR, HU may have a secondary unknown target(s) inside cells. Identification of such a target(s) may greatly improve the chemotherapies that employ HU or help to expand the clinical usage of this drug for additional pathological conditions.

Inner nuclear membrane protein Lem2 facilitates Rad3-mediated checkpoint signaling under replication stress induced by nucleotide depletion in fission yeast

DNA replication checkpoint is a highly conserved cellular signaling pathway critical for maintaining genome integrity in eukaryotes. It is activated when DNA replication is perturbed. In Schizosaccharomyces pombe, perturbed replication forks activate the sensor kinase Rad3 (ATR/Mec1), which works cooperatively with mediator Mrc1 and the 9-1-1 checkpoint clamp to phosphorylate the effector kinase Cds1 (CHK2/Rad53). Phosphorylation of Cds1 promotes autoactivation of the kinase. Activated Cds1 diffuses away from the forks and stimulates most of the checkpoint responses under replication stress. Although this signaling pathway has been well understood in fission yeast, how the signaling is initiated and thus regulated remains incompletely understood. Previous studies have shown that deletion of lem2(+) sensitizes cells to the inhibitor of ribonucleotide reductase, hydroxyurea. However, the underlying mechanism is still not well understood. This study shows that in the presence of hydroxyurea, Lem2 facilitates Rad3-mediated checkpoint signaling for Cds1 activation. Without Lem2, all known Rad3-dependent phosphorylations critical for replication checkpoint signaling are seriously compromised, which likely causes the aberrant mitosis and drug sensitivity observed in this mutant. Interestingly, the mutant is not very sensitive to DNA damage and the DNA damage checkpoint remains largely intact, suggesting that the main function of Lem2 is to facilitate checkpoint signaling in response to replication stress. Since Lem2 is an inner nuclear membrane protein, these results also suggest that the replication checkpoint may be spatially regulated inside the nucleus, a previously unknown mechanism.

The current state of eukaryotic DNA base damage and repair

DNA damage is a natural hazard of life. The most common DNA lesions are base, sugar, and single-strand break damage resulting from oxidation, alkylation, deamination, and spontaneous hydrolysis. If left unrepaired, such lesions can become fixed in the genome as permanent mutations. Thus, evolution has led to the creation of several highly conserved, partially redundant pathways to repair or mitigate the effects of DNA base damage. The biochemical mechanisms of these pathways have been well characterized and the impact of this work was recently highlighted by the selection of Tomas Lindahl, Aziz Sancar and Paul Modrich as the recipients of the 2015 Nobel Prize in Chemistry for their seminal work in defining DNA repair pathways. However, how these repair pathways are regulated and interconnected is still being elucidated. This review focuses on the classical base excision repair and strand incision pathways in eukaryotes, considering both Saccharomyces cerevisiae and humans, and extends to some important questions and challenges facing the field of DNA base damage repair.

Important role of catalase in the cellular response of the budding yeast Saccharomyces cerevisiae exposed to ionizing radiation

Ionizing radiation indirectly causes oxidative stress in cells via reactive oxygen species (ROS), such as hydroxyl radicals (OH(-)) generated by the radiolysis of water. We investigated how the catalase function was affected by ionizing radiation and analyzed the phenotype of mutants with a disrupted catalase gene in Saccharomyces cerevisiae exposed to radiation. The wild-type yeast strain and isogenic mutants with disrupted catalase genes were exposed to various doses of (60)Co gamma-rays. There was no difference between the wild-type strain and the cta1 disruption mutant following exposure to gamma-ray irradiation. In contrast, there was a significant decrease in the ctt1 disruption mutant, suggesting that this strain exhibited decreased survival on gamma-ray exposure compared with other strains. In all three strains, stationary phase cells were more tolerant to the exposure of gamma-rays than exponential phase cells, whereas the catalase activity in the wild-type strain and cta1 disruption mutant was higher in the stationary phase than in the exponential phase. These data suggest a correlation between catalase activity and survival following gamma-ray exposure. However, this correlation was not clear in the ctt1 disruption mutant, suggesting that other factors are involved in the tolerance to ROS induced by irradiation.

Opposite roles for p38MAPK-driven responses and reactive oxygen species in the persistence and resolution of radiation-induced genomic instability

We report the functional and temporal relationship between cellular phenotypes such as oxidative stress, p38MAPK-dependent responses and genomic instability persisting in the progeny of cells exposed to sparsely ionizing low-Linear Energy Transfer (LET) radiation such as X-rays or high-charge and high-energy (HZE) particle high-LET radiation such as ⁵⁶Fe ions. We found that exposure to low and high-LET radiation increased reactive oxygen species (ROS) levels as a threshold-like response induced independently of radiation quality and dose. This response was sustained for two weeks, which is the period of time when genomic instability is evidenced by increased micronucleus formation frequency and DNA damage associated foci. Indicators for another persisting response sharing phenotypes with stress-induced senescence, including beta galactosidase induction, increased nuclear size, p38MAPK activation and IL-8 production, were induced in the absence of cell proliferation arrest during the first, but not the second week following exposure to high-LET radiation. This response was driven by a p38MAPK-dependent mechanism and was affected by radiation quality and dose. This stress response and elevation of ROS affected genomic instability by distinct pathways. Through interference with p38MAPK activity, we show that radiation-induced stress phenotypes promote genomic instability. In contrast, exposure to physiologically relevant doses of hydrogen peroxide or increasing endogenous ROS levels with a catalase inhibitor reduced the level of genomic instability. Our results implicate persistently elevated ROS following exposure to radiation as a factor contributing to genome stabilization.

The MFS-type efflux pump Flr1 induced by Yap1 promotes canthin-6-one resistance in yeast

Screening for suppressors of canthin-6-one toxicity in yeast identified Yap1, a transcription factor involved in cell response to a broad range of injuries. Although canthin-6-one did not promote a significant oxidative stress, overexpression of YAP1 gene clearly increased resistance to this drug. We demonstrated that Yap1-mediated resistance involves the plasma membrane major-facilitator-superfamily efflux pump Flr1 but not the vacuolar ATP-binding-cassette transporter Ycf1. FLR1 overexpression was sufficient to reduce sensitivity to the drug, but strictly dependent on a functional YAP1 gene.

Genome-wide single-cell-level screen for protein abundance and localization changes in response to DNA damage in S. cerevisiae

An effective response to DNA damaging agents involves modulating numerous facets of cellular homeostasis in addition to DNA repair and cell-cycle checkpoint pathways. Fluorescence microscopy-based imaging offers the opportunity to simultaneously interrogate changes in both protein level and subcellular localization in response to DNA damaging agents at the single-cell level. We report here results from screening the yeast Green Fluorescent Protein (GFP)-fusion library to investigate global cellular protein reorganization on exposure to the alkylating agent methyl methanesulfonate (MMS). Broad groups of induced, repressed, nucleus- and cytoplasm-enriched proteins were identified. Gene Ontology and interactome analyses revealed the underlying cellular processes. Transcription factor (TF) analysis identified principal regulators of the response, and targets of all major stress-responsive TFs were enriched amongst the induced proteins. An unexpected partitioning of biological function according to the number of TFs targeting individual genes was revealed. Finally, differential modulation of ribosomal proteins depending on methyl methanesulfonate dose was shown to correlate with cell growth and with the translocation of the Sfp1 TF. We conclude that cellular responses can navigate different routes according to the extent of damage, relying on both expression and localization changes of specific proteins.