The yeast stress response. Role of the Yap family of b-ZIP transcription factors. The PABMB Lecture delivered on 30 June 2004 at the 29th FEBS Congress in Warsaw

YeastYeast 2010; 27: 245–258.Published online 10 February 2010 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/yea.1752

Review

The Yap family and its role in stress responseClaudina Rodrigues-Pousada*, Regina A. Menezes and Catarina PimentelGenomics and Stress Laboratory, Instituto de Tecnologia Quımica e Biologica, Avenida da Republica, 2780-157 Oeiras, Portugal

*Correspondence to:Claudina Rodrigues-Pousada,Genomics and Stress Laboratory,Instituto de Tecnologia Quımicae Biologica, Av. da Republica,Apt. 127, 2780-157Oeiras, Portugal.E-mail: [email protected]

Received: 6 November 2009Accepted: 20 December 2009

AbstractThe budding yeast Saccharomyces cerevisiae possesses a very flexible and complexprogramme of gene expression when exposed to several environmental challenges.Homeostasis is achieved through a highly coordinated mechanism of transcriptionregulation involving several transcription factors, each one acting singly or incombination to perform specific functions. Here, we review our current knowledgeof the function of the Yap transcription factors in stress response. They belongto b-ZIP proteins comprising eight members with specificity at the DNA-bindingdomain distinct from that of the conventional yeast AP-1 factor, Gcn4. We finishwith new insights into the links of transcriptional networks controlling several cellularprocesses. The data reviewed in this article illustrate how much our comprehensionof the biology of Yap family involved in stress response has advanced, and how muchresearch is still needed to unravel the complexity of the role of these transcriptionalfactors. The complexities of these regulatory interactions, as well as the dynamicsof these processes, are important to understand in order to elucidate the control ofstress response, a highly conserved process in eukaryotes. Copyright 2010 JohnWiley & Sons, Ltd.

Keywords: Yap transcription factors; H2O2; cadmium; osmotic; iron; arsenicstresses

Contents

IntroductionThe Yap family of transcriptional regulatorsYap1, the major oxidative stress regulatorYap2 in cadmium stressYap4 and Yap6 in osmotic stressYap1 and Yap5 in iron metabolismYap1 and Yap8 in detoxification of arseniccompoundsYap3 and Yap7 of unknown functionInterplay between the transcriptional regulatorsConcluding remarksAcknowledgementsReferences

Introduction

Biological structures as well as their buildingblocks are quite flexible and they are the basis for

their functions and their efficiency in adaptationto highly divergent metabolic and environmentalchanges. The capacity for adaptation to changesin intra- and extracellular conditions is a universalprerequisite for an organism’s survival and evo-lution. The existence of molecular mechanismsresponsible for response, repair and adaptation,many of which are greatly conserved across nature,endows the cell with the plasticity it requires toadjust to its ever-changing environment, a homeo-static event that is termed the stress response.

The budding yeast Saccharomyces cerevisiaepossesses a complex programme of gene expres-sion when exposed to a plethora of environmentalcues. Yeast cell homeostasis is achieved througha highly coordinated mechanism of transcriptionregulation, involving several transcription factors,each one acting singly or in combination to per-form specific functions. Through the sensing and

Copyright 2010 John Wiley & Sons, Ltd.

246 C. Rodrigues-Pousada, R. A. Menezes and C. Pimentel

transduction of the stress signal, a genetic repro-gramming occurs that leads, on the one hand, to atransient arrest of normal cellular processes, such asa decrease in the expression of housekeeping genesand protein synthesis, and on the other hand to anincrease of the expression of genes encoding stressproteins. These proteins include molecular chap-erones responsible for maintaining protein fold-ing, transcription factors that further modulate geneexpression and a diverse network of players, suchas membrane transporters and proteins involvedin repair, degradation and detoxification pathways,nutrient metabolism and osmolyte production. Sur-vival and growth resumption necessarily impliessuccessful cellular adaptation to the new conditionsas well as the repair of damage suffered by thecell that would otherwise compromise its viabil-ity. Although specific stress conditions trigger dis-tinct cellular responses, underlying gene expressionprogrammes common to all environmental stressresponse are at play. The stress response, tailoredto the intensity of the insult, represents a gradedcombination of both specific and general mecha-nisms that must be employed with precision, soas to ensure successful adaptation without compro-mising cell viability. Specific forms of stress, suchas heat-shock and some forms of oxidative stress,demand the activation of the heat-shock factor(HSF), a modular protein consisting of an α-helixclass of DNA-binding domain (DBD), a leucinezipper domain required for trimerization and aC-terminal transcription activation domain. TheHSF is a pre-existing transcription activator thatbinds to an array of a 5 bp heat-shock ele-ment (HSE; nGAAn), present in the promot-ers of all heat-shock genes. HSF targets arealso activated by diamide, nitrogen starvation andstationary phase transition [1]. HSF-independentmechanisms also exist in the yeast S. cere-visiae, viz. the environmental stress response,largely mediated by the two zinc-finger tran-scription factors, Msn2 and Msn4 [2]. AnotherHSF-independent mechanism is that played byb-ZIP transcription factors, the Yap family.

The Yap family of transcriptionalregulators

The yeast activator protein (Yap) family of b-ZIPproteins comprises eight members, with significant

sequence similarity to the conventional yeast AP-1protein, Gcn4, at the DNA-binding domain. How-ever, common to all members of this family are keyresidues that give to these factors distinct DNA-binding properties.

Yap1, the first member of the Yap family tobe described, was initially identified by its abil-ity to bind and activate the SV-40 AP-1 recogni-tion element (ARE: TGACTAA) [3]. Based on thisARE-binding capacity, this factor was purified as a90 kDa protein and the corresponding gene, clonedby screening a λgt11 library with a monoclonalantibody raised against Yap1. Subsequently, thisgene was also found in multicopy transformantsresistant to the iron chelators 1,10-phenantrolineand 1-nitroso-2-naphtol, as well as to a varietyof drugs, including cycloheximide, the locus beinghistorically designated PAR1/SNQ3/PDR4. BesidesYAP1, a second gene, YAP2, conferring resistanceto 1,10-phenantroline in transformed cells overex-pressing a yeast library was also described [4]. Thisgene encodes a 45 kDa protein that also binds AREcis-acting elements. Sequence homologies identi-fied it as CAD1, so-named due to the acquisitionof cadmium resistance in cells overexpressing thisgene. The sequencing of YAP1 and YAP2 genesrevealed the presence of a bZIP-domain in theN-terminus homologous to that in Gcn4 and c-Jun,its mammalian counterpart, as well as in regionsof similarity, one at the C-terminus and one at aninternal region adjacent to the bZIP-domain (forreview see [5]).

The Gcn4–DNA complex was defined by bio-chemical and crystallographic analyses and theoptimal AP-1 site as TGACTCA [6,7]. In theGcn4 basic domain, five residues (Asn235, Ala238,Ala239, Ser242 and Arg243) required for the base-specific contacts in Gcn4 and Jun/Fos are mosthighly conserved [8–10]. Using a degenerate motifbased on the sequences of a large number of basicregions in b-ZIP proteins from various organisms,several b-ZIP proteins were identified in S. cere-visiae genome. The search revealed 14 proteins,including Gcn4, Yap1, Yap2, Met28 [11], Sko1 [12]and Hac1 [13], probably representing the completeset of budding yeast b-ZIP proteins [5]. Align-ment of these sequences revealed a family of sixnewly identified proteins, Yap3–Yap8, containingconserved amino acid residues similar to thosepresent in Yap1 and Yap2. The characteristics thatdistinguish the members of Yap family from Gcn4

Copyright 2010 John Wiley & Sons, Ltd. Yeast 2010; 27: 245–258.DOI: 10.1002/yea

Yap family 247

are precisely the amino acids contacting with theDNA. Indeed, Ala239 is replaced by a glutamineand Ser242 is replaced by phenylalanine or tyro-sine. Furthermore, there are two family-specificresidues, Gln234 and Ala241. Thus, the Yap fam-ily binding site was characterized as TTAC/GTAAfor Yap1–Yap5 and termed the ‘Yap site’ or ‘Yapresponse element’ (YRE). So far, only the corre-sponding binding site for Yap6–Yap7 has not beencharacterized and, although Yap8 binds to the vari-ant TTAATAA [14], the existence of other bind-ing sequences cannot be excluded. The cis-elementrecognized by Yap8 slightly differs from the canon-ical YRE TTAC/GTAA. Both Yap1 and Yap8 bindto the sequence GATTTAATAATCA, in whichthe bases flanking the core sequence (underlined)are essential for Yap8 recognition [15]. The keyresidues in the Yap8 bZIP domain were mutated inorder to identify those that are essential for DNArecognition. It was found that mutations K21A,R22A, A23T, R27A, K35E, R36A and Q25A com-promises the ability of Yap8 to recognize its targetsequence (Amaral et al., unpublished). The leadersequences of YAP1 and YAP2 mRNAs contain,respectively, one (uORF) and two upstream open-ing reading frames. The latter is involved in YAP2mRNA turnover via termination-dependent decay[16]. Indeed, the YAP1-type uORF allows scanning40S subunits to proceed via leaky scanning and re-initiation to the major ORF, whereas the YAP2-typeacts to block ribosomal scanning by promoting effi-cient termination [16].

Orthologues of several Yap family membershave been found in several organisms, includingSchizosaccharomyces pombe Pap1 [17], Candidaalbicans Cap1 and Fcr3, Candida glabrata withall the members except Yap8, and Kluveromyceslactis with all the members [18,19].

Yap1, the major oxidative stressregulator

Cells have to keep intracellular concentrations ofperoxides [H2O2 and organic peroxides, reactiveoxygen species (ROS)] at very low levels by regu-lating their concentration through tightly controlledmechanisms. This control will allow cells to facethe permanent endogenous production of ROS thatresults from their aerobic respiration and fromalterations of their environment.

Microorganisms, including the eukaryotic Sac-charomyces cerevisiae, possess sensors that detectvery low levels of H2O2 and in consequence theoxidant-scavengers are induced to prevent cellulardamage triggered by oxidative stress. Under theseconditions, yeast cells activate the glutathione andthioredoxin pathways, which in turn activate Yap1(anti-oxidant and redox signalling [20]). Yap1 wascharacterized through the observation that the dele-tion mutant is hypersensitive to the oxidants H2O2and t-BOOH, as well as to chemicals that generatesuperoxide anion radicals [5]. Parallel yap1 mutantstudies further indicated sensitivity to methylgly-oxal, cadmium [5,21] and cycloheximide, amongstothers. Kuge et al. [22] provided the first and clearclue towards the role of Yap1 in this responsemechanism, through the identification of the Yap1target TRX2, showing that its induction by H2O2,t-BOOH, diamide and diethylmaleate (DEM) isYap1-dependent and mediated by two YREs inits promoter [22]. The identification of the secondYap1 target, GSH1, also established its role in cad-mium detoxification pathways [21]. Subsequently,several other Yap1-dependent genes involved incadmium tolerance have been identified [5]. Stud-ies by global analysis have also added a growingnumber of different Yap1 targets involved in thedetoxification of ROS [2,23]. Among the proteinsencoded by these genes can be found most cellu-lar antioxidants as well as those involved in thiolredox control (for details, see [20]).

Although several reports have pointed to aninduction of YAP1 upon exposure to stress, the con-trol over Yap1-mediated gene regulation is mainlyaccomplished through its subcellular localization.Kuge et al. demonstrated that nuclear retentionof Yap1 is mediated by the cysteine-rich domainlocated at the C-terminus of the protein (c-CRD)[22]. Removal of this region generates a consti-tutively nuclear and active protein. In addition,three conserved cysteine residues (Cys598, Cys620and Cys629) were identified as being importantfor this post-translational regulation (see Figure 1).Yan et al. demonstrated that nuclear export ofYap1 is mediated by the exportin Crm1 (alsoknown as Xpo1) binding to the Yap1 NES, whichoverlaps the c-CRD [24]. Delaunay et al. [25,26]showed in vivo that two cysteines, Cys303 inthe N-terminal CRD (n-CRD) and Cys598 in thec-CRD, are oxidized in response to H2O2 and form



Figure 1. Structural features of the Yap family. In the upper part of the figure, the sequences of the eight Yap bZIPdomains are compared with the equivalent region of Gcn4, the classical yeast AP-1 factor. In the lower part, a schemedepicts the position of the relevant structural domains, the cysteine-rich domains (n-CRD and c-CRD) and the nuclearexport signal (NES). The numbers of the cysteine residues are indicated under the corresponding domains. The sequenceof the NES motifs was assigned by comparison with Yap1 sequence (Yap2, Yap3 and Yap8) or by means of NetNES1.1software (http://www.cbs.dtu.dk/services/NetNES/)

an intramolecular disulphide bond that compro-mises the binding of Crm1 to the NES, leadingto Yap1 nuclear retention. In vitro studies per-formed by Wood et al. [27] have revealed that anadditional intramolecular disulphide bond betweenCys310 and Cys629 is formed between the n- andc-CRD upon H2O2 exposure. Activation of Yap1by H2O2 also requires multistep bond formationof disulphide bonds that are important for trans-duction of the H2O2 stress signal to induce theappropriate duration of transcription duration [28].However, Yap1 is not oxidized directly by H2O2.Rather, the oxidant receptor peroxidase 1 (Orp1,also known as Gpx3 or Hyr1) acts as the sen-sor, together with the Yap1-binding protein (Ybp1)[29]. Orp1 has peroxidase activity in vitro and pos-sesses two cysteine residues, Cys36 and Cys82,

that are part of its catalytic site and are involvedin the disulphide bond formation. Orp1 is a per-oxidase, different from the classical ones, that issubsequently reduced by thioredoxin (Trx). Oxi-dized Yap1 is recycled by thioredoxin and thesignal transduced to Yap1 is performed throughthe creation of an intermolecular disulphide bondbetween Cys36 of Orp1 and Yap1 Cys598, whichis then resolved into the previously described Yap1Cys303–Cys598 intramolecular bridge [29]. TheCys82 of Orp1 is only required for the peroxida-tive reaction, as observed by the fact that the Orp1mutant in Cys82 does not possess any phenotype.It is not abundant in the cells and its function asa sensor requires very low levels of this protein(for details, see [20]). Ybp1 is also required forYap1 redox sensing, both forming a cytoplasmic


Yap family 249

precomplex that in turn is recognized by Orp1. Inthe fission yeast Schizosaccharomyces pombe, theYap1 orthologue Pap1 regulates the activation ofgene transcription only in response to low concen-trations of H2O2, whereas the MAP kinase Sty1pathway is activated at high pro-oxidant concen-trations [30,31]. Analogous to the sensing mecha-nism of S. cerevisiae, the S. pombe peroxiredoxin,Tpx1, has been shown to transfer the redox signalto Pap1 under low oxidant concentrations. How-ever, at high concentrations this redox signal isinhibited through the oxidation of the Tpx1 cat-alytic cysteine to a sulphinic acid. This oxidationcan be reversed by the sulphiredoxin Srx1, whoseexpression is tightly regulated by the Sty1 pathway[32]. In contrast, the Yap1 response to diamide isOrp1/Gpx3-independent and does not involve then-CRD [25,33]. This is consistent with the notionthat it possesses two redox centres [34]. Indeed,the electrophile N -ethylmaleimide (NEM) and thequinone menadione, both an electrophile and asuperoxide anion generator, have been shown tomodify c-CRD cysteines independently of Gpx3and leading to Yap1 nuclear accumulation. Massspectrometry analyses further revealed that NEM,and possibly menadione, bind directly to the Yap1c-CRD, thus occluding the NES [34].

Yap2 in cadmium stress

Yap2/Cad1 is the family member that shares thehighest homology with Yap1 [4,35]. When overex-pressed, Yap2 confers resistance to several stressagents, suggesting a role for this transcription fac-tor in the response to toxic compounds, althoughyap2 mutant strains are not hypersensitive to cad-mium or to other forms of stress. However, theYap2 transactivation domain is stimulated upontreatment with cadmium [5], and domain-swappingexperiments between the Yap1 and Yap2 c-CRDsrevealed that the latter promotes cadmium ratherthan H2O2 regulation [36]. The C-terminus of Yap2contains Cys356, Cys378, Cys387 and Cys391,which, except for Cys378, are required for Yap2function. Curiously, Yap2 also contains, in then-CRD region, Cys256, Cys259, Cys287, Cys291,Cys395, Cys301 and Cys308, whose functions havenot yet been investigated (Figure 1). Also, cad-mium binds directly these residues, as shown usingthe high molecular mass alkylating agent, AMS,

which produces cysteine derivatization [36]. Thebinding of Cd to these residues abolishes the recog-nition of Yap2 nuclear export by Crm1, a mecha-nism similar to that of Yap1. Replacement of theYap1cCRD by the homologous Yap2 domain pre-serves the response to cadmium but not to H2O2,confirming the equivalency of cCRDs domains inCd-sensing functions and demonstrating that thebuilt-in specificity of the Yap1 c-CRD towardsH2O2 is not conserved in the homologous Yap2domain. What could be the role of this Yap2 Cd-sensing and regulatory mechanism with regard tothe lack of a Cd phenotype of YAP2 deleted strains?The nature of target genes should help to deci-pher this question, but up to now such clarificationhas been lacking. By proteomic analysis after Cdtreatment only, one Yap2-target gene, FRM2, wasidentified as being highly induced upon Cd treat-ment [36]. FRM2 was initially identified in a screenfor mutants defective in OLE1 repression by unsat-urated fatty acids [37] and, based on the sensitivityof the frm2 mutant to arachidonic acid, it was sug-gested that it participates in lipid metabolism [38].Given that cadmium is known to exert its toxicityby promoting lipid peroxidation cascades [39], it ispossible that Yap2 is regulating lipid metabolism inresponse to cadmium. FRM2 also encodes a pro-tein with strong homology to nitroreductase but itsrole in cadmium detoxification pathways remainsto be deciphered.

Microarray analyses indicate that Yap2 mayregulate a set of genes encoding proteins involvedin stabilization and folding proteins in an oxidativeenvironment [40]. Yap2 was also shown to bind thekinase Rck1 under conditions of oxidative stress,although the nature of the physiological relevanceof this interaction remains to be determined [5]. Sofar, Yap2’s function remains elusive.

Yap4 and Yap6 in osmotic stress

The fourth member of the family, YAP4 (CIN5/HAL6), was initially characterized as a chromo-some instability mutant [5] and encodes a 33 kDaprotein. Yap6 is a 44 kDa protein sharing almost20% identity with Yap4 along the protein length,making these the closest-related Yap family mem-bers. Overexpression studies in the ena1 mutant(lacking the Na+/Li+ extrusion ATPase) subse-quently identified both YAP4 (HAL6) and YAP6



Figure 2. YAP4 and YAP6 contain several stress-associated cis-elements in their promoter regions

(HAL7) as genes that confer salt tolerance througha mechanism unrelated to the Na+/Li+ extrusionATPase [41]. Resistance associated with multicopyYAP4/6 expression has also been described, includ-ing resistance to the antimalarial drugs chloro-quine, quinine and mefloquine [42] and to thechemotherapeutic agent cis-platinum [43]. In con-trast to YAP1, YAP2 and YAP8, their subcellu-lar localization was shown to be constitutivelynuclear. However, in a recent report it was shown,through the isolation of nuclei, that Yap4 is onlyin the nucleus in quinone-stressed yeast cells. Inthis paper the authors also found that Yap4 isbound to the complex formed by dimeric quinonereductase (Lot6) and the 20S proteasome [44].Their data suggest that the redox state of theflavin cofactor controls the recruitment of Yap4to the 20S proteasome. They propose that the sta-bility and localization of the transcription factorYap4 is under direct redox control of the quinonereductase-proteasome system, which is crucial forthe response to oxidative stress. This interpreta-tion is, however, not supported by results obtainedin other laboratories that found Yap4 constitu-tively nuclear localized [43]. Pereira et al., usingYap4–GFP constructs, found that this protein isalways in the nucleus, in either the presence orthe absence of the stress [45]. Also, these authors,when studying the role of Yap4 phosphorylation,showed that the nuclear localization is not affectedby the phosphorylation state of Yap4. Besides,Yap4 is not involved in oxidative stress but, asdescribed in Nevitt et al., is induced by severalstresses, including oxidative stress, osmotic stress,heat-shock and metals, among others [46]. Pereira

and colleagues also showed that Yap4 phospho-rylation is driven by the protein kinases PKAand GSK3, which affect its stability, as the non-phosphorylated form has a shorter half-life than thephosphorylated form. Using site-directed mutagen-esis, the T192 and S196 residues were found to bephosphorylated [45].

Global genomic approaches indicate a clearinduction of YAP4 and YAP6 under several stressconditions, including oxidative and osmotic stress,heat and stationary phase [2,47,48]. Indeed, thepromoter region of these two genes is particularlyrich in regulatory stress-associated cis-elementsthat undoubtedly contribute to their induction bymultiple signalling pathways (Figure 2).

The regulation of YAP4 under conditions ofhigh external osmolarity is mediated by Msn2in a Hog1-dependent manner via two STREsin the upstream promoter, whilst under oxida-tive conditions, YAP4 induction is co-regulatedby Msn2 and Yap1 through the STRE and YRE,respectively [46,49]. Transcriptional profiling ofthe mutant under mild conditions of hyperosmo-larity has revealed a large set of genes that arepotentially regulated by this transcription factor(Nevitt et al., unpublished results). Indeed, over100 genes show a two-fold or more decreasein expression in the yap4 mutant strain. Theseinclude genes that play a role in the synthesisand accumulation of the osmolytes glycerol andtrehalose, those that encode products with protec-tive functions or chaperone activity, componentsof signal transduction pathways as well as regu-lators of gene expression. As these genes belongto several functional classes, this hints towards a


Yap family 251

general role for Yap4 in the yeast stress response.Indeed, subsequent validation experiments haverevealed genes whose expression is decreased inthe yap4 mutant strain, including: DCS2, encod-ing a homologue of the mRNA-decapping enzymeencoded by DCS1; GPP2, encoding one of tworedundant glycerol phosphatases [46]; as well asgenes displaying altered induction kinetics, suchas the GPD1-encoded glycerol-3-phosphate dehy-drogenase, the cytoplasmic glutaredoxin encodedby TTR1 and the YAK1 kinase (Nevitt et al.,unpublished results). Although considerably lessis known about YAP6 regulation and function, itappears to be regulated by Msn2 and Yap4 underconditions of hyperosmolarity and is very stronglyinduced under heat stress (Nevitt et al., unpub-lished data).

Li Ni and colleagues have also examined glob-ally, in detail, the temporal order of binding ofseveral key factors to their targets involved in yeastunder osmotic stress [50]. Among these factorsthey studied Yap4, Yap6 and Sko1. They showedthat multiple binding patterns exist for Yap4 andSko1, suggesting the requirement of additional fac-tors likely mediating their binding. They also founda correlation between Yap4 and Yap6, as 73–86%of the Yap6 targets overlap with Yap4. Many Yap4constitutively bound genes were also bound bySko1 and Yap6, at both 0 and 30 min after saltinduction. They showed that Yap6 and Sko1 binda significant number of salt-induced Yap4-bindingtargets at 30 min that are not bound at 0 min. Inconclusion, it is clear from their data that the tran-scription factors can act individually but also inassociation, and therefore they regulate differentset of genes. Indeed, Yap4, Yap6 and Sko1 asso-ciate to regulate transporters. The fact that differ-ent factors are acting synergistically may lead tounderstanding of their function in the cell. This isvital information to decipher the regulatory codein eukaryotes that, subjected to different environ-mental challenges, lead to many cellular changes.The mapping of the various targets regulated by alarge number of transcription factors will allow theunderstanding of these complex processes and howthe set of events occurs in cells under stress.

Yap1 and Yap5 in iron metabolism

Almost every organism on earth needs iron as anessential nutrient that is a widely utilized cofactor

in key redox reactions involved in many cen-tral biochemical processes. Abnormal iron accu-mulation, in either excessive or insufficient lev-els, underlies several human diseases, includinghereditary haemochromatosis, Friedreich’s ataxia,and iron-deficiency anaemia [51–53]. Although thesecond most abundant metal in the Earth’s crust, itsbioavailability is very low, owing to the fact thatiron is rapidly oxidized in an aerobic environmentto the ferric form, Fe(III), which has a poor solu-bility in water at neutral pH and forms precipitatesof oxyhydroxides [54]. Microorganisms, however,have the capacity to scavenge iron from these pre-cipitates by secreting and taking up siderophores,which are low molecular weight compounds bind-ing to Fe(III) with very high affinity and speci-ficity. Budding and fission yeasts appear to be anexception; they neither synthesize nor secrete thesecompounds [55]. Saccharomyces cerevisiae, how-ever, can recognize and take up iron from a varietyof structurally distinct siderophores [56–58].

Iron-dependent regulation in Saccharomycescerevisiae is mediated by two transcription fac-tors, Aft1 and Aft2 (standing for activation ofFe(II) transport), which activate gene expressionwhen iron is scarce, and consequently the strainslacking both factors exhibit a reduced expressionof iron regulon [59]. Whereas the aft1 mutantexhibits a clear phenotype under low-iron con-ditions, the aft2-null strain does not exhibit anyphenotype. The aft1aft2 double mutant is, how-ever, more sensitive to low iron growth than asingle aft1 null strain, which is consistent with thefunctional similarity of these factors. Interestingly,overexpression of AFT2 complements an aft1-nullstrain, revealing its partial functional redundancy[60,61]. Transcription control is therefore highlyexerted when cells cope with iron deficiency, andthe existence of a post-transcriptional control wasshown by Thiele’s group, who demonstrated thatthe Cth1 gene is a direct target of Aft1/2 transcrip-tion factors that are induced rapidly and transientlyin response to Fe deficiency, having also demon-strated that the mRNA-binding proteins, Cth1 andits paralogue Cth2, play important roles in targetingspecific functional classes of mRNAs for degra-dation in response to Fe deficiency. It was alsoshown that Yap1, the sensor of oxidative stress,is involved in iron metabolism [5,62]. In order togive the cells their iron homeostasis control, they



possess not only the ability to regulate iron acqui-sition but also to store iron once it is absorbed. Itwas recently shown that Yap5 is involved in ironstorage by regulating the expression of the vacuo-lar iron transporter, Ccc1 [63]. It was shown byKaplan’s group that Yap5 is constitutively local-ized in the nucleus. Like Yap1, Yap2 and Yap8,this factor contains, in its C-terminus, the amino-terminal and the carboxyl- terminal domains. Asshown in Figure 1, each domain contains four Cysresidues that, when mutated, give rise to a completeabrogation of transcriptional activity affecting thefunction of Yap5 in preventing high-iron toxicity[63]. Although Li and colleagues did not find anynuclear export signal (NES), by using the programNetNES v1.1 we found a canonic NES near thebZIP domain (Figure 1).

Yap1 and Yap8 in detoxificationof arsenic compounds

The highly toxic arsenic is the most potent humancarcinogen. This widespread compound enters thebiosphere primarily by leaching from geologicalformations, although human activities, such as theuse of pesticides, also contribute to its accumula-tion in the environment [64]. Arsenic poisoning isconsidered to be the greatest single cause of ill-health worldwide. Chronic exposure causes manyadverse health effects, including cancer, black footdisease, diabetes mellitus and cardiovascular dis-eases. However, despite its toxicity, it can alsobring benefits to human health. Arsenic trioxide(ATO) is successfully used in tandem with all-trans-retinoic acid to treat acute promyelocyticleukaemia (APL) [65], due to its property to selec-tively kill these cells, and arsenic-containing drugshave been used to treat parasitic infections, such asAfrican sleeping sickness and leishmaniasis [66].Although they have controversial impact, eitheras poison or treatment, the mechanisms underly-ing arsenic tolerance are still far from being deci-phered.

In Saccharomyces cerevisiae, Yap8 (Acr1) [5]plays a pivotal role in arsenic stress responses.Yap8 is the master regulator of this response,mediating transcriptional activation of ACR2 andACR3, encoding the arsenate-reductase and theplasma membrane arsenite-efflux protein, respec-tively [67,68]. Both proteins constitute a first-line

defence, since they facilitate the extrusion of arsen-ite molecules from the cytoplasm. Yap1 contributesto arsenic stress responses to a lesser extent thanYap8 at at least three different levels: (a) regulatingYCF1 expression, which corresponds to a paral-lel arsenite detoxification system by catalysing theATP-driven uptake of arsenite (AsIII)–GSH con-jugates into the vacuole; (b) contributing to reg-ulated expression of ACR2 and ACR3 (18); and(c) maintaining the redox homeostasis disturbed byarsenic compounds, as we have recently shown[69]. In the absence of Yap1, cells accumulateincreased levels of lipid peroxidation, intracellu-lar oxidation and protein carbonylation when cellsare subjected to arsenic treatment. Also, underthese conditions, the ratio of oxidized : reduced glu-tathione is drastically disturbed in cells bearingyap1 mutations. In the mutant yap8, which accu-mulates high levels of As(III), the well-knownYap1 target genes TRX2, GSH1 and SOD1 areeven more induced compared to the wild-typestrain, suggesting that arsenite retention in the cyto-plasm triggers a more severe antioxidant response.Thus, Yap1 is essential to promote cell adapta-tion by preventing the accumulation of the verytoxic reactive oxygen species (ROS) generated byarsenic compounds (Figure 3) [67]. The upregula-tion of cell antioxidant defences by arsenic com-pounds is strongly corroborated by high-throughputarsenite/arsenate-triggered changes in transcrip-tional profiling ( [67,70]; Amaral et al., unpub-lished work).

Similarly to what happens with Yap1, regu-lation of Yap8 occurs primarily at the level ofnuclear localization. Under physiological condi-tions, the chimeras GFP–Yap1 and GFP–Yap8shuttle between the nucleus and the cytoplasm,rapidly accumulating in the nucleus after exposureto arsenic [67]. Subcellular compartmentalizationof both proteins is mediated through the binding ofCrm1 to the nuclear export signal (NES) domainunder physiological growth. Under stress condi-tions, As(III) modifies the sulphydryl groups ofspecific cysteine on both proteins (our unpublisheddata), masking the NES and preventing recogni-tion by the exportin Crm1. Arsenic modification ofYap8 involves Cys132, 137 and 274, whereas Yap1modification occurs in the Cys residues located inthe c-CRD (Figure 1) [67]. In contrast to this view,it was described [68] that Yap8 is a nuclear-residentprotein and that Cys132 and 274 do not affect


Yap family 253

Figure 3. Arsenic adaptation in Saccharomyces cerevisiae. Arsenate is taken up by phosphate transporters that are reducedin the cytoplasm by the arsenate reductase Acr2. Arsenite can also enter into the cells through the aquaglyceroporin Fps1and hexose transporters. Arsenite detoxification is primarily facilitated by the plasma membrane arsenite efflux proteinAcr3, but As(III)–glutathione conjugates are also sequestered by Ycf1 into the vacuole. Yap8 and Yap1 are the masterregulators of Acr2/Acr3 and Ycf1, respectively, and their activity is essential to the efficient removal of arsenite from thecytoplasm. Additionally, Yap1 is important to the maintenance of the redox homeostasis disturbed by arsenic compounds(adapted from Menezes et al., 2008)

its localization. The discrepancy in these resultsmay be due to methodological reasons and theuse of different strains. A further level of Yap8control lies in a regulated transactivation functionwhich is enhanced up to 10-fold in the presenceof As(V) [67]. Yap8 seems also to be target ofregulated degradation. Indeed, Di and Tamas [71]proposed a model in which Yap8 is degraded bythe ubiquitin–proteasome pathway under physio-logical conditions in a mechanism dependent onthe ubiquitin-conjugating enzyme Ubc4.

Although Yap8-controlled arsenic detoxificationand Yap1-mediated redox homeostasis appear tobe the major players, there are additional path-ways contributing to full arsenic tolerance. Thetranscriptional regulator Met4, together with Yap1,controls the assimilation of sulphur into glutathionebiosynthesis [72] to compensate for its continu-ous oxidation during the detoxification process.The nitrogen-activated protein kinase Hog1 is alsoimplicated in arsenic resistance, being required for

full activation of Acr3 and Ycf1 [73] and to controlthe uptake of As(III) through phosphorylation ofthe aquaglyceroporin Fps1 [74].

Interestingly, it was also shown by transcrip-tional arrays that arsenate compounds produce animbalance of iron. Indeed, the activation of manygenes implicated in protein biosynthesis containingiron and copper is observed (Batista-Nascimento,unpublished), suggesting that arsenate may producea decrease of iron content in the cells.

Yap3 and Yap7 of unknown function

Very little is known about Yap3 and Yap7 mem-bers. In fact, Yap3 shows virtually no response atthe level of genomic microarray analyses to themultiple forms of environmental insults and cellu-lar stress studied so far. However, Candida albi-cans Yap3 orthologues, FCR3 gene, was shownto confer, when over-expressed, high resistance to



Figure 4. Potential interplay between members of the Yap family

fluconazole and 4-nitroquinoline 1-oxide (4-NQO)in a pdr1pdr3 double mutant strain of S. cere-visiae [75]. Yap3, like Yap1, Yap2, Yap5 and Yap8,contains two CRDs located respectively in the N-and the C-terminus; the NES is located near thec-CRD, as illustrated in Figure 1. The role of Yap7in the yeast stress response was also not estab-lished. However, it was shown to be constitutivelylocated in the nucleus [76], a fact that can beexplained by the absence of a NES and of cys-teine residues (Figure 1). ChIP-chip data chartedits putative binding site [77]. Microarray analysisunder arsenic stress revealed that its expressionincreases upon stress in a Yap1-dependent way(Batista-Nascimento et al., unpublished results).

Interplay between the transcriptionalregulators

The existing data have so far revealed manyinteractions between the different stress responseregulators. Indeed, Lee and colleagues performedgenome-wide location analyses for each of the 106yeast strains expressing an epitope-tagged regula-tor [78]. Nearly 4000 interactions between regula-tors and promoter regions were identified. Further-more, it was determined that the promoter regionof 2343 of the total of 6270 genes was boundby one or more transcriptional regulators in yeastcells growing in rich medium. Although the bind-ing of promoters by multiple transcriptional reg-ulators has been characterized as a specific fea-ture of higher eukaryotes, many yeast genes werefound in simultaneous association with several

transcription factors. In this context, Yap4 has beenshown to be regulated either by Msn2, under con-ditions of osmotic stress, or by Msn2 and Yap1under oxidative stress [46,49]. Using computa-tional approaches, transcriptional regulatory net-works were derived that were shown to control sev-eral cellular processes, such as the cell cycle, envi-ronmental stress, development and metabolism. Itwas also predicted, through mathematical mod-elling, that Yap4 interacts with Yap6 [78]. Usingseveral biochemical approaches, it has indeed beendemonstrated that this interaction does occur exper-imentally (Nevitt et al., unpublished results). Sev-eral studies have shown that the Yap family mem-bers appear to have a degree of functional overlapas well as distinct physiological roles. It was indeedshown that it is possible to distinguish betweenthe functions of Yap1 and Yap2 by using DNAmicroarrays [40]. These two transcription factors,although having overlapping functions, both acti-vate non-overlapping gene sets. It was also demon-strated by the same authors that the two proteinsmay function as repressors as well as activators.One possible model put forward to describe the Yapnetwork demonstrates that, during oxidative stress,the Yap1 and Yap2 homodimers activate distinctregulons, whereas Yap1/Yap2 heterodimers collab-orate to repress a separate regulon [40].

Similarly, the yap8 yap1 strain has increasedmetalloid sensitivity relative to either single mutant[67]. The expression of the Yap8 target genes,ACR2 and ACR3, is also significantly regulated byYap1 and both strains have been shown to bind theYRE variant, TGATTAATAATCA (Amaral et al.,


Yap family 255

unpublished results). The putative interactions ofYap transcription factors are shown in Figure 4.

The transcription factors Msn2/4 and HSF1are examples of other transcription factors cross-talking with respect to the regulation of expres-sion of several stress genes. Amoros and Estruchhave indeed shown that, in Saccharomyces cere-visiae, HSF1 and Msn2/4 cooperate in the expres-sion of HSP26 and HSP104 [79]. Moreover, theinterplay between these transcription factors wasshown to be dependent on both gene and stressconditions. These data were further strengthenedby Grably et al. [80], who showed that the HSP104gene is regulated either exclusively or coopera-tively via HSF1 and Msn2/4. These authors alsoprovided evidence that the Ras pathway affects theHSP104 promoter primarily through the STREs.The HSP104 promoter seems to be activateddepending on the imposed stress conditions. It iswell known that the main HSF1 targets are theheat-shock proteins (HSP) functioning as molecularchaperones in protein folding, stabilization, activa-tion, targeting and degradation.

However, genome-wide approaches haverevealed other targets, including RPN4, whichencodes a transcription factor that directly activatesthe expression of a number of genes coding for pro-teasome subunits [1,78]. More recently, Hahn andcolleagues have shown the existence of a networkoperating together with HSF1, Pdr3 and Rpn4.Indeed, these authors demonstrated that HSF1 acti-vates the expression of RPN4, either directly orthrough Pdr3, a transcription factor involved inpleiotropic drug resistance. Indeed, the RPN4 pro-moter contains several regulatory elements for thebinding and action of at least three transcriptionfactors, HSF1, Pdr1/Pdr3 and Yap1 (see above)[81].

It was also shown, using system approaches,that a transcriptional networking involving Yap1,Yap2/Cad1, Yap4/Cin5, Yap5, Yap6 and HSF1,among others, takes place under conditions ofDNA damage [77,82]. It is necessary, however, toconfirm whether these interactions happen in vivo.Many other cooperative ways of transcription fac-tors controlling the cell cycle were also predictedby Banerjee and Zhang [83]. This cooperativitysuggests essential cross-talk that allows the coordi-nation of different functions.

Accumulating evidence indicates, therefore, thatdifferent transcription factors bind promoters,

activating several genes that, in turn, activate sev-eral regulatory networks. Recent data from Sny-der’s group have shown that, under osmotic stress,there exists a network of transcription factorsinvolving Yap4, Yap6 and Sko1 [50]. Indeed, thereare many circuits in which specific combinations oftranscription factors are responsible for the coordi-nate expression of a collection of different genesthat endow cells with the ability to respond toimportant biological processes, such as environ-mental challenges and development.

Concluding remarks

Data obtained in the last decade have shown thatgene expression regulation under stress conditionsdoes not involve a single transcription factor butcooperation between several such factors. Indeed,the studies carried so far reinforce the hypothesisthat the response to stress is not a linear sequenceof discrete events, but rather an orchestrated phe-nomenon that puts into play a diverse networkof pathways and response elements that, throughcondition- and gene-specific cross-talk events, leadto a precise response and adaptation to the newenvironment.

In this review we have therefore highlighted theYap transcription factors, which mediate the yeaststress response. The challenge we now face is tounderstand how the coordination of these regulatorsis achieved and to identify the signals triggeringthis coordination, as well as its integration withmetabolic pathways. Genomic approaches, togetherwith ChIP-chip analysis, should, as it is beginningto emerge, largely contribute to answering thesequestions.

Acknowledgements

This study was supported by grants from Fundacao paraa Ciencia e Tecnologia (FCT) to CR-P (No. PTDC/BIA-MIC/108747/2008) and fellowships to RAM (No. SFRH/BPD/26506/2006) and to CP (No. SFRH/BPD/35052/2007).

References

1. Hahn JS, Hu Z, Thiele DJ, Iyer VR. 2004. Genome-wideanalysis of the biology of stress responses through heat shocktranscription factor. Mol Cell Biol 24: 5249–5256.



2. Gasch AP, Spellman PT, Kao CM, et al. 2000. Genomicexpression programs in the response of yeast cells toenvironmental changes. Mol Biol Cell 11: 4241–4257.

3. Moye-Rowley WS, Harshman KD, Parker CS. 1989. YeastYAP1 encodes a novel form of the jun family of transcriptionalactivator proteins. Genes Dev 3: 283–292.

4. Bossier P, Fernandes L, Rocha D, Rodrigues-Pousada C.1993. Overexpression of YAP2, coding for a new yAP protein,and YAP1 in Saccharomyces cerevisiae alleviates growthinhibition caused by 1,10-phenanthroline. J Biol Chem 268:23640–23645.

5. Rodrigues-Pousada CA, Nevitt T, Menezes R, et al. 2004.Yeast activator proteins and stress response: an overview.FEBS Lett. 567: 80–85.

6. Kim J, Tzamarias D, Ellenberger T, et al. 1993. Adaptabilityat the protein–DNA interface is an important aspect ofsequence recognition by bZIP proteins. Proc Natl Acad SciUSA 90: 4513–4517.

7. Oliphant AR, Brandl CJ, Struhl K. 1989. Defining thesequence specificity of DNA-binding proteins by selectingbinding sites from random-sequence oligonucleotides: analysisof yeast GCN4 protein. Mol Cell Biol 9: 2944–2949.

8. Ellenberger TE, Brandl CJ, Struhl K, Harrison SC. 1992. TheGCN4 basic region leucine zipper binds DNA as a dimer ofuninterrupted α-helices: crystal structure of the protein–DNAcomplex. Cell 71: 1223–1237.

9. Glover JN, Harrison SC. 1995. Crystal structure of theheterodimeric bZIP transcription factor c-Fos–c-Jun bound toDNA. Nature 373: 257–261.

10. Konig P, Richmond TJ. 1993. The X-ray structure of theGCN4-bZIP bound to ATF/CREB site DNA shows thecomplex depends on DNA flexibility. J Mol Biol 233:139–154.

11. Kuras L, Cherest H, Surdin-Kerjan Y, Thomas D. 1996. Aheteromeric complex containing the centromere bindingfactor 1 and two basic leucine zipper factors, Met4 andMet28, mediates the transcription activation of yeast sulfurmetabolism. EMBO J 15: 2519–2529.

12. Nehlin JO, Carlberg M, Ronne H. 1992. Yeast SKO1 geneencodes a bZIP protein that binds to the CRE motif and acts asa repressor of transcription. Nucleic Acids Res 20: 5271–5278.

13. Nojima H, Kimura I, Kimura M. 1994. The evidence ofaccelerative interaction between cAMP-dependent proteinkinase and external calcium for the desensitization of nicotinicacetylcholine receptor channel in mouse skeletal muscle cells.Neurosci Lett 167: 113–116.

14. Wysocki R, Clemens S, Augustyniak D, et al. 2003. Metalloidtolerance based on phytochelatins is not functionallyequivalent to the arsenite transporter Acr3p. Biochem BiophysRes Commun 304: 293–300.

15. Ilina Y, Sloma E, Maciaszczyk-Dziubinska E, et al. 2008.Characterization of the DNA-binding motif of the arsenic-responsive transcription factor Yap8p. Biochem J 415:467–475.

16. Vilela C, Ramirez CV, Linz B, et al. 1999. Post-terminationribosome interactions with the 5′ UTR modulate yeast mRNAstability. EMBO J 18: 3139–3152.

17. Toda T, Shimanuki M, Yanagida M. 1991. Fission yeast genesthat confer resistance to staurosporine encode an AP-1-like transcription factor and a protein kinase related to the

mammalian ERK1/MAP2 and budding yeast FUS3 and KSS1kinases. Genes Dev 5: 60–73.

18. Billard P, Dumond H, Bolotin-Fukuhara M. 1997. Character-ization of an AP-1-like transcription factor that mediates anoxidative stress response in Kluyveromyces lactis . Mol GenGenet 257: 62–70.

19. Bussereau F, Casaregola S, Lafay JF, Bolotin-Fukuhara M.2006. The Kluyveromyces lactis repertoire of transcriptionalregulators. FEMS Yeast Res 6: 325–335.

20. Toledano MB, Delaunay A, Monceau L, Tacnet F. 2004.Microbial H2O2 sensors as archetypical redox signalingmodules. Trends Biochem Sci 29: 351–357.

21. Wu AL, Moye-Rowley WS. 1994. GSH1, which encodesγ -glutamylcysteine synthetase, is a target gene for yAP-1transcriptional regulation. Mol Cell Biol 14: 5832–5839.

22. Kuge S, Jones N, Nomoto A. 1997. Regulation of yAP-1nuclear localization in response to oxidative stress. EMBO J16: 1710–1720.

23. Lee J, Godon C, Lagniel G, et al. 1999. Yap1 and Skn7control two specialized oxidative stress response regulons inyeast. J Biol Chem 274: 16040–16046.

24. Yan C, Lee LH, Davis LI. 1998. Crm1p mediates regulatednuclear export of a yeast AP-1-like transcription factor. EMBOJ. 17: 7416–7429.

25. Delaunay A, Isnard AD, Toledano MB. 2000. H2O2 sensingthrough oxidation of the Yap1 transcription factor. EMBO J19: 5157–5166.

26. Delaunay A, Pflieger D, Barrault MB, et al. 2002. A thiolperoxidase is an H2O2 receptor and redox-transducer in geneactivation. Cell 111: 471–481.

27. Wood MJ, Andrade EC, Storz G. 2003. The redox domain ofthe Yap1p transcription factor contains two disulfide bonds.Biochemistry 42: 11982–11991.

28. Okazaki S, Tachibana T, Naganuma A, et al. 2007. Multistepdisulfide bond formation in Yap1 is required for sensing andtransduction of H2O2 stress signal. Mol Cell 27: 675–688.

29. Veal EA, Ross SJ, Malakasi P, et al. 2003. Ybp1 is requiredfor the hydrogen peroxide-induced oxidation of the Yap1transcription factor. J Biol Chem 278: 30896–30904.

30. Quinn J, Findlay VJ, Dawson K, et al. 2002. Distinctregulatory proteins control the graded transcriptionalresponse to increasing H2O2 levels in fission yeastSchizosaccharomyces pombe. Mol Biol Cell 13: 805–816.

31. Toone WM, Kuge S, Samuels M, et al. 1998. Regulation ofthe fission yeast transcription factor Pap1 by oxidative stress:requirement for the nuclear export factor Crm1 (Exportin) andthe stress-activated MAP kinase Sty1/Spc1. Genes Dev 12:1453–1463.

32. Vivancos AP, Castillo EA, Biteau B, et al. 2005. A cys-teine–sulfinic acid in peroxiredoxin regulates H2O2-sensingby the antioxidant Pap1 pathway. Proc Natl Acad Sci USA102: 8875–8880.

33. Kuge S, Arita M, Murayama A, et al. 2001. Regulation of theyeast Yap1p nuclear export signal is mediated by redox signal-induced reversible disulfide bond formation. Mol Cell Biol 21:6139–6150.

34. Azevedo D, Tacnet F, Delaunay A, et al. 2003. Two redoxcenters within Yap1 for H2O2 and thiol-reactive chemicalssignaling. Free Radic Biol Med 35: 889–900.


Yap family 257

35. Wu A, Wemmie JA, Edgington NP, et al. 1993. Yeast bZipproteins mediate pleiotropic drug and metal resistance. J BiolChem 268: 18850–18858.

36. Azevedo D, Nascimento L, Labarre J, et al. 2007. TheS. cerevisiae Yap1 and Yap2 transcription factors share acommon cadmium-sensing domain. FEBS Lett 581: 187–195.

37. McHale MW, Kroening KD, Bernlohr DA. 1996. Identifica-tion of a class of Saccharomyces cerevisiae mutants defectivein fatty acid repression of gene transcription and analysis ofthe frm2 gene. Yeast 12: 319–331.

38. Ball CA, Dolinski K, Dwight SS, et al. 2000. Integratingfunctional genomic information into the Saccharomycesgenome database. Nucleic Acids Res 28: 77–80.

39. Reiser V, Ruis H, Ammerer G. 1999. Kinase activity-dependent nuclear export opposes stress-induced nuclearaccumulation and retention of Hog1 mitogen-activated proteinkinase in the budding yeast Saccharomyces cerevisiae. MolBiol Cell 10: 1147–1161.

40. Cohen BA, Pilpel Y, Mitra RD, Church GM. 2002. Discrimi-nation between paralogs using microarray analysis: applicationto the Yap1p and Yap2p transcriptional networks. Mol BiolCell 13: 1608–1614.

41. Mendizabal I, Rios G, Mulet JM, et al. 1998. Yeast putativetranscription factors involved in salt tolerance. FEBS Lett 425:323–328.

42. Delling U, Raymond M, Schurr E. 1998. Identification ofSaccharomyces cerevisiae genes conferring resistance toquinoline ring-containing antimalarial drugs. AntimicrobAgents Chemother 42: 1034–1041.

43. Furuchi T, Ishikawa H, Miura N, et al. 2001. Two nuclearproteins, Cin5 and Ydr259c, confer resistance to cisplatin inSaccharomyces cerevisiae. Mol Pharmacol 59: 470–474.

44. Sollner S, Schober M, Wagner A, et al. 2009. Quinonereductase acts as a redox switch of the 20S yeast proteasome.EMBO Rep 10: 65–70.

45. Pereira J, Pimentel C, Amaral C, et al. 2009. Yap4 PKA- andGSK3-dependent phosphorylation affects its stability but notits nuclear localization. Yeast 26: 641–653.

46. Nevitt T, Pereira J, Rodrigues-Pousada C. 2004. YAP4 geneexpression is induced in response to several forms of stress inSaccharomyces cerevisiae. Yeast 21: 1365–1374.

47. Posas F, Chambers JR, Heyman JA, et al. 2000. Thetranscriptional response of yeast to saline stress. J Biol Chem275: 17249–17255.

48. Rep M, Krantz M, Thevelein JM, Hohmann S. 2000. Thetranscriptional response of Saccharomyces cerevisiae toosmotic shock. Hot1p and Msn2p/Msn4p are required for theinduction of subsets of high osmolarity glycerol pathway-dependent genes. J Biol Chem 275: 8290–8300.

49. Nevitt T, Pereira J, Azevedo D, et al. 2004. Expression ofYAP4 in Saccharomyces cerevisiae under osmotic stress.Biochem J 379: 367–374.

50. Ni L, Bruce C, Hart C, et al. 2009. Dynamic and complextranscription factor binding during an inducible response inyeast. Genes Dev 23: 1351–1363.

51. Dunn LL, Rahmanto YS, Richardson DR. 2007. Iron uptakeand metabolism in the new millennium. Trends Cell Biol 17:93–100.

52. Hentze MW, Muckenthaler MU, Andrews NC. 2004. Balanc-ing acts: molecular control of mammalian iron metabolism.Cell 117: 285–297.

53. Rouault TA. 2006. The role of iron regulatory proteins inmammalian iron homeostasis and disease. Nat Chem Biol 2:406–414.

54. Yun CW, Bauler M, Moore RE, et al. 2001. The role of theFRE family of plasma membrane reductases in the uptake ofsiderophore-iron in Saccharomyces cerevisiae. J Biol Chem276: 10218–10223.

55. Neilands JB. 1995. Siderophores: structure and function ofmicrobial iron transport compounds. J Biol Chem 270:26723–26726.

56. Askwith CC, de Silva D, Kaplan J. 1996. Molecular biologyof iron acquisition in Saccharomyces cerevisiae. MolMicrobiol 20: 27–34.

57. Heymann P, Ernst JF, Winkelmann G. 1999. Identificationof a fungal triacetylfusarinine C siderophore transport gene(TAF1 ) in Saccharomyces cerevisiae as a member of the majorfacilitator superfamily. Biometals 12: 301–306.

58. Yun CW, Tiedeman JS, Moore RE, Philpott CC. 2000.Siderophore-iron uptake in Saccharomyces cerevisiae. Identifi-cation of ferrichrome and fusarinine transporters. J Biol Chem275: 16354–16359.

59. Blaiseau PL, Lesuisse E, Camadro JM. 2001. Aft2p, a noveliron-regulated transcription activator that modulates, withAft1p, intracellular iron use and resistance to oxidative stressin yeast. J Biol Chem 276: 34221–34226.

60. Rutherford JC, Bird AJ. 2004. Metal-responsive transcriptionfactors that regulate iron, zinc, and copper homeostasis ineukaryotic cells. Eukaryot Cell 3: 1–13.

61. Yamaguchi-Iwai Y, Dancis A, Klausner RD. 1995. AFT1:a mediator of iron regulated transcriptional control inSaccharomyces cerevisiae. EMBO J 14: 1231–1239.

62. Lesuisse E, Raguzzi F, Crichton RR. 1987. Iron uptake by theyeast Saccharomyces cerevisiae: involvement of a reductionstep. J Gen Microbiol 133: 3229–3236.

63. Li L, Bagley D, Ward DM, Kaplan J. 2008. Yap5 is an iron-responsive transcriptional activator that regulates vacuolar ironstorage in yeast. Mol Cell Biol 28: 1326–1337.

64. Rosen BP. 2002. Transport and detoxification systems fortransition metals, heavy metals and metalloids in eukaryoticand prokaryotic microbes. Comp Biochem Physiol A MolIntegr Physiol 133: 689–693.

65. Hu J, Liu YF, Wu CF, et al. 2009. Long-term efficacy andsafety of all-trans retinoic acid/arsenic trioxide-based therapyin newly diagnosed acute promyelocytic leukemia. Proc NatlAcad Sci USA 106: 3342–3347.

66. Borst P, Ouellette M. 1995. New mechanisms of drugresistance in parasitic protozoa. Annu Rev Microbiol 49:427–460.

67. Menezes RA, Amaral C, Delaunay A, et al. 2004. Yap8pactivation in Saccharomyces cerevisiae under arsenicconditions. FEBS Lett. 566: 141–146.

68. Wysocki R, Fortier PK, Maciaszczyk E, et al. 2004. Tran-scriptional activation of metalloid tolerance genes in Saccha-romyces cerevisiae requires the AP-1-like proteins Yap1p andYap8p. Mol Biol Cell 15: 2049–2060.

69. Menezes RA, Amaral C, Batista-Nascimento L, et al. 2008.Contribution of Yap1 towards Saccharomyces cerevisiaeadaptation to arsenic-mediated oxidative stress. Biochem J414: 301–311.



70. Haugen AC, Kelley R, Collins JB, et al. 2004. Integratingphenotypic and expression profiles to map arsenic-responsenetworks. Genome Biol 5: R95.

71. Di Y, Tamas MJ. 2007. Regulation of the arsenic-responsivetranscription factor Yap8p involves the ubiquitin–proteasomepathway. J Cell Sci 120: 256–264.

72. Thorsen M, Lagniel G, Kristiansson E, et al. 2007. Quantita-tive transcriptome, proteome, and sulfur metabolite profilingof the Saccharomyces cerevisiae response to arsenite. PhysiolGenom 30: 35–43.

73. Sotelo J, Rodriguez-Gabriel MA. 2006. Mitogen-activatedprotein kinase Hog1 is essential for the response to arsenite inSaccharomyces cerevisiae. Eukaryot Cell 5: 1826–1830.

74. Thorsen M, Di Y, Tangemo C, et al. 2006. The MAPK Hog1pmodulates Fps1p-dependent arsenite uptake and tolerance inyeast. Mol Biol Cell 17: 4400–4410.

75. Yang X, Talibi D, Weber S, et al. 2001. Functional isolationof the Candida albicans FCR3 gene encoding a bZiptranscription factor homologous to Saccharomyces cerevisiaeYap3p. Yeast 18: 1217–1225.

76. Huh WK, Falvo JV, Gerke LC, et al. 2003. Global analysis ofprotein localization in budding yeast. Nature 425: 686–691.

77. Tan K, Feizi H, Luo C, et al. 2008. A systems approach todelineate functions of paralogous transcription factors: role of

the Yap family in the DNA damage response. Proc Natl AcadSci USA 105: 2934–2939.

78. Lee TI, Rinaldi NJ, Robert F, et al. 2002. Transcriptionalregulatory networks in Saccharomyces cerevisiae. Science298: 799–804.

79. Amoros M, Estruch F. 2001. Hsf1p and Msn2/4p cooperatein the expression of Saccharomyces cerevisiae genes HSP26and HSP104 in a gene- and stress type-dependent manner.Mol Microbiol 39: 1523–1532.

80. Grably MR, Stanhill A, Tell O, Engelberg D. 2002. HSF andMsn2/4p can exclusively or cooperatively activate the yeastHSP104 gene. Mol Microbiol 44: 21–35.

81. Hahn JS, Neef DW, Thiele DJ. 2006. A stress regulatorynetwork for co-ordinated activation of proteasome expressionmediated by yeast heat shock transcription factor. MolMicrobiol 60: 240–251.

82. Workman CT, Mak HC, McCuine S, et al. 2006. A systemsapproach to mapping DNA damage response pathways.Science 312: 1054–1059.

83. Banerjee N, Zhang MQ. 2003. Identifying cooperativityamong transcription factors controlling the cell cycle in yeast.Nucleic Acids Res 31: 7024–7031.


Documents

The yeast stress response. Role of the Yap family of b-ZIP transcription factors. The PABMB Lecture delivered on 30 June 2004 at the 29th FEBS Congress in Warsaw