Modulation of Aβ(42 )low-n oligomerization using a novel yeast reporter system

BACKGROUND: While traditional models of Alzheimer's disease focused on large fibrillar deposits of the Aβ(42 )amyloid peptide in the brain, recent work suggests that the major pathogenic effects may be attributed to SDS-stable oligomers of Aβ(42). These Aβ(42 )oligomers represent a rational target for therapeutic intervention, yet factors governing their assembly are poorly understood. RESULTS: We describe a new yeast model system focused on the initial stages of Aβ(42 )oligomerization. We show that the activity of a fusion of Aβ(42 )to a reporter protein is compromised in yeast by the formation of SDS-stable low-n oligomers. These oligomers are reminiscent of the low-n oligomers formed by the Aβ(42 )peptide in vitro, in mammalian cell culture, and in the human brain. Point mutations previously shown to inhibit Aβ(42 )aggregation in vitro, were made in the Aβ(42 )portion of the fusion protein. These mutations both inhibited oligomerization and restored activity to the fusion protein. Using this model system, we found that oligomerization of the fusion protein is stimulated by millimolar concentrations of the yeast prion curing agent guanidine. Surprisingly, deletion of the chaperone Hsp104 (a known target for guanidine) inhibited oligomerization of the fusion protein. Furthermore, we demonstrate that Hsp104 interacts with the Aβ(42)-fusion protein and appears to protect it from disaggregation and degradation. CONCLUSION: Previous models of Alzheimer's disease focused on unravelling compounds that inhibit fibrillization of Aβ(42), i.e. the last step of Aβ(42 )assembly. However, inhibition of fibrillization may lead to the accumulation of toxic oligomers of Aβ(42). The model described here can be used to search for and test proteinacious or chemical compounds for their ability to interfere with the initial steps of Aβ(42 )oligomerization. Our findings suggest that yeast contain guanidine-sensitive factor(s) that reduce the amount of low-n oligomers of Aβ(42). As many yeast proteins have human homologs, identification of these factors may help to uncover homologous proteins that affect Aβ(42 )oligomerization in mammals

Pharmacologically Reversible, Loss of Function Mutations in the tm2 and tm4 Inner Pore Helices of Trek-1 k2p Channels

A better understanding of the gating of TREK two pore domain potassium (K2P) channels and their activation by compounds such as the negatively charged activator, flufenamic acid (FFA) is critical in the search for more potent and selective activators of these channels. Currents through wild-type and mutated human K2P channels expressed in tsA201 cells were measured using whole-cell patch-clamp recordings in the presence and absence of FFA. Mutation of the TM2.6 residue of TREK-1 to a phenylalanine (G171F) and a similar mutation of TM4.6 (A286F) substantially reduced current through TREK-1 channels. In complementary experiments, replacing the natural F residues at the equivalent position in TRESK channels, significantly enhanced current. Known, gain of function mutations of TREK-1 (G137I, Y284A) recovered current through these mutated channels. This reduction in current could be also be reversed pharmacologically, by FFA. However, an appropriate length MTS (MethaneThioSulfonate) cross-linking reagent (MTS14) restricted the activation of TREK-1_A286C channels by repeated application of FFA. This suggests that the cross-linker stabilises the channel in a conformation which blunts FFA activation. Pharmacologically reversible mutations of TREK channels will help to clarify the importance of these channels in pathophysiological conditions such as pain and depression

[SWI+], the Prion Formed by the Chromatin Remodeling Factor Swi1, Is Highly Sensitive to Alterations in Hsp70 Chaperone System Activity

The yeast prion [SWI+], formed of heritable amyloid aggregates of the Swi1 protein, results in a partial loss of function of the SWI/SNF chromatin-remodeling complex, required for the regulation of a diverse set of genes. Our genetic analysis revealed that [SWI+] propagation is highly dependent upon the action of members of the Hsp70 molecular chaperone system, specifically the Hsp70 Ssa, two of its J-protein co-chaperones, Sis1 and Ydj1, and the nucleotide exchange factors of the Hsp110 family (Sse1/2). Notably, while all yeast prions tested thus far require Sis1, [SWI+] is the only one known to require the activity of Ydj1, the most abundant J-protein in yeast. The C-terminal region of Ydj1, which contains the client protein interaction domain, is required for [SWI+] propagation. However, Ydj1 is not unique in this regard, as another, closely related J-protein, Apj1, can substitute for it when expressed at a level approaching that of Ydj1. While dependent upon Ydj1 and Sis1 for propagation, [SWI+] is also highly sensitive to overexpression of both J-proteins. However, this increased prion-loss requires only the highly conserved 70 amino acid J-domain, which serves to stimulate the ATPase activity of Hsp70 and thus to stabilize its interaction with client protein. Overexpression of the J-domain from Sis1, Ydj1, or Apj1 is sufficient to destabilize [SWI+]. In addition, [SWI+] is lost upon overexpression of Sse nucleotide exchange factors, which act to destabilize Hsp70's interaction with client proteins. Given the plethora of genes affected by the activity of the SWI/SNF chromatin-remodeling complex, it is possible that this sensitivity of [SWI+] to the activity of Hsp70 chaperone machinery may serve a regulatory role, keeping this prion in an easily-lost, meta-stable state. Such sensitivity may provide a means to reach an optimal balance of phenotypic diversity within a cell population to better adapt to stressful environments

Amyloid-Mediated Sequestration of Essential Proteins Contributes to Mutant Huntingtin Toxicity in Yeast

BACKGROUND: Polyglutamine expansion is responsible for several neurodegenerative disorders, among which Huntington disease is the most well-known. Studies in the yeast model demonstrated that both aggregation and toxicity of a huntingtin (htt) protein with an expanded polyglutamine region strictly depend on the presence of the prion form of Rnq1 protein ([PIN+]), which has a glutamine/asparagine-rich domain. PRINCIPAL FINDINGS: Here, we showed that aggregation and toxicity of mutant htt depended on [PIN+] only quantitatively: the presence of [PIN+] elevated the toxicity and the levels of htt detergent-insoluble polymers. In cells lacking [PIN+], toxicity of mutant htt was due to the polymerization and inactivation of the essential glutamine/asparagine-rich Sup35 protein and related inactivation of another essential protein, Sup45, most probably via its sequestration into Sup35 aggregates. However, inhibition of growth of [PIN+] cells depended on Sup35/Sup45 depletion only partially, suggesting that there are other sources of mutant htt toxicity in yeast. CONCLUSIONS: The obtained data suggest that induced polymerization of essential glutamine/asparagine-rich proteins and related sequestration of other proteins which interact with these polymers represent an essential source of htt toxicity

Prion Formation and Polyglutamine Aggregation Are Controlled by Two Classes of Genes

Prions are self-perpetuating aggregated proteins that are not limited to mammalian systems but also exist in lower eukaryotes including yeast. While much work has focused around chaperones involved in prion maintenance, including Hsp104, little is known about factors involved in the appearance of prions. De novo appearance of the [PSI+] prion, which is the aggregated form of the Sup35 protein, is dramatically enhanced by transient overexpression of SUP35 in the presence of the prion form of the Rnq1 protein, [PIN+]. When fused to GFP and overexpressed in [ps−] [PIN+] cells, Sup35 forms fluorescent rings, and cells with these rings bud off [PSI+] daughters. We investigated the effects of over 400 gene deletions on this de novo induction of [PSI+]. Two classes of gene deletions were identified. Class I deletions (bug1Δ, bem1Δ, arf1Δ, and hog1Δ) reduced the efficiency of [PSI+] induction, but formed rings normally. Class II deletions (las17Δ, vps5Δ, and sac6Δ) inhibited both [PSI+] induction and ring formation. Furthermore, class II deletions reduced, while class I deletions enhanced, toxicity associated with the expanded glutamine repeats of the huntingtin protein exon 1 that causes Huntington's disease. This suggests that prion formation and polyglutamine aggregation involve a multi-phase process that can be inhibited at different steps.National Institutes of Health (U.S.) (grant GM56350)National Institutes of Health (U.S.) (NSRA F32 postdoctoral fellowship GM072340)National Institutes of Health (U.S.) (grant GM25874)Howard Hughes Medical Institut

Disease-Associated Mutant Ubiquitin Causes Proteasomal Impairment and Enhances the Toxicity of Protein Aggregates

Protein homeostasis is critical for cellular survival and its dysregulation has been implicated in Alzheimer's disease (AD) and other neurodegenerative disorders. Despite the growing appreciation of the pathogenic mechanisms involved in familial forms of AD, much less is known about the sporadic cases. Aggregates found in both familial and sporadic AD often include proteins other than those typically associated with the disease. One such protein is a mutant form of ubiquitin, UBB+1, a frameshift product generated by molecular misreading of a wild-type ubiquitin gene. UBB+1 has been associated with multiple disorders. UBB+1 cannot function as a ubiquitin molecule, and it is itself a substrate for degradation by the ubiquitin/proteasome system (UPS). Accumulation of UBB+1 impairs the proteasome system and enhances toxic protein aggregation, ultimately resulting in cell death. Here, we describe a novel model system to investigate how UBB+1 impairs UPS function and whether it plays a causal role in protein aggregation. We expressed a protein analogous to UBB+1 in yeast (Ubext) and demonstrated that it caused UPS impairment. Blocking ubiquitination of Ubext or weakening its interactions with other ubiquitin-processing proteins reduced the UPS impairment. Expression of Ubext altered the conjugation of wild-type ubiquitin to a UPS substrate. The expression of Ubext markedly enhanced cellular susceptibility to toxic protein aggregates but, surprisingly, did not induce or alter nontoxic protein aggregates in yeast. Taken together, these results suggest that Ubext interacts with more than one protein to elicit impairment of the UPS and affect protein aggregate toxicity. Furthermore, we suggest a model whereby chronic UPS impairment could inflict deleterious consequences on proper protein aggregate sequestration

Chondroprotection by urocortin involves blockade of the mechanosensitive ion channel Piezo1

Osteoarthritis (OA) is characterised by progressive destruction of articular cartilage and chondrocyte cell death. Here, we show the expression of the endogenous peptide urocortin1 (Ucn1) and two receptor subtypes, CRF-R1 and CRF-R2, in primary human articular chondrocytes (AC) and demonstrate its role as an autocrine/paracrine pro-survival factor. This effect could only be removed using the CRF-R1 selective antagonist CP-154526, suggesting Ucn1 acts through CRF-R1 when promoting chondrocyte survival. This cell death was characterised by an increase in p53 expression, and cleavage of caspase 9 and 3. Antagonism of CRF-R1 with CP-154526 caused an accumulation of intracellular calcium (Ca2+) over time and cell death. These effects could be prevented with the non-selective cation channel blocker Gadolinium (Gd3+). Therefore, opening of a non-selective cation channel causes cell death and Ucn1 maintains this channel in a closed conformation. This channel was identified to be the mechanosensitive channel Piezo1. We go on to determine that this channel inhibition by Ucn1 is mediated initially by an increase in cyclic adenosine monophosphate (cAMP) and a subsequent inactivation of phospholipase A2 (PLA2), whose metabolites are known to modulate ion channels. Knowledge of these novel pathways may present opportunities for interventions that could abrogate the progression of OA

Function of SSA Subfamily of Hsp70 Within and Across Species Varies Widely in Complementing Saccharomyces cerevisiae Cell Growth and Prion Propagation

BACKGROUND:The cytosol of most eukaryotic cells contains multiple highly conserved Hsp70 orthologs that differ mainly by their spatio-temporal expression patterns. Hsp70s play essential roles in protein folding, transport or degradation, and are major players of cellular quality control processes. However, while several reports suggest that specialized functions of Hsp70 orthologs were selected through evolution, few studies addressed systematically this issue. METHODOLOGY/PRINCIPAL FINDINGS:We compared the ability of Ssa1p-Ssa4p from Saccharomyces cerevisiae and Ssa5p-Ssa8p from the evolutionary distant yeast Yarrowia lipolytica to perform Hsp70-dependent tasks when expressed as the sole Hsp70 for S. cerevisiae in vivo. We show that Hsp70 isoforms (i) supported yeast viability yet with markedly different growth rates, (ii) influenced the propagation and stability of the [PSI(+)] and [URE3] prions, but iii) did not significantly affect the proteasomal degradation rate of CFTR. Additionally, we show that individual Hsp70 orthologs did not induce the formation of different prion strains, but rather influenced the aggregation properties of Sup35 in vivo. Finally, we show that [URE3] curing by the overexpression of Ydj1p is Hsp70-isoform dependent. CONCLUSION/SIGNIFICANCE:Despite very high homology and overlapping functions, the different Hsp70 orthologs have evolved to possess distinct activities that are required to cope with different types of substrates or stress situations. Yeast prions provide a very sensitive model to uncover this functional specialization and to explore the intricate network of chaperone/co-chaperone/substrates interactions

Potassium and Sodium Transport in Yeast

[EN] As the proper maintenance of intracellular potassium and sodium concentrations is vital for cell growth, all living organisms have developed a cohort of strategies to maintain proper monovalent cation homeostasis. In the model yeast Saccharomyces cerevisiae, potassium is accumulated to relatively high concentrations and is required for many aspects of cellular function, whereas high intracellular sodium/potassium ratios are detrimental to cell growth and survival. The fact that S. cerevisiae cells can grow in the presence of a broad range of concentrations of external potassium (10 M–2.5 M) and sodium (up to 1.5 M) indicates the existence of robust mechanisms that have evolved to maintain intracellular concentrations of these cations within appropriate limits. In this review, current knowledge regarding potassium and sodium transporters and their regulation will be summarized. The cellular responses to high sodium and potassium and potassium starvation will also be discussed, as well as applications of this knowledge to diverse fields, including antifungal treatments, bioethanol production and human disease.L.Y. is funded by grant BFU2011-30197-C03-03 from the Spanish Ministry of Science and Innovation (Madrid, Spain) and EUI2009-04147 [Systems Biology of Microorganisms (SysMo2) European Research Area-Network (ERA-NET)].Yenush, L. (2016). Potassium and Sodium Transport in Yeast. Advances in Experimental Medicine and Biology. 892:187-228. https://doi.org/10.1007/978-3-319-25304-6_8S187228892Ahmed A, Sesti F, Ilan N, Shih TM, Sturley SL et al (1999) A molecular target for viral killer toxin: TOK1 potassium channels. Cell 99:283–291Albert A, Yenush L, Gil-Mascarell MR, Rodriguez PL, Patel S et al (2000) X-ray structure of yeast Hal2p, a major target of lithium and sodium toxicity, and identification of framework interactions determining cation sensitivity. J Mol Biol 295:927–938Albertyn J, Hohmann S, Thevelein JM, Prior BA (1994) GPD1, which encodes glycerol-3-phosphate dehydrogenase, is essential for growth under osmotic stress in Saccharomyces cerevisiae, and its expression is regulated by the high-osmolarity glycerol response pathway. Mol Cell Biol 14:4135–4144Alepuz PM, Cunningham KW, Estruch F (1997) Glucose repression affects ion homeostasis in yeast through the regulation of the stress-activated ENA1 gene. Mol Microbiol 26:91–98Ali R, Brett CL, Mukherjee S, Rao R (2004) Inhibition of sodium/proton exchange by a Rab-GTPase-activating protein regulates endosomal traffic in yeast. J Biol Chem 279:4498–4506Alijo R, Ramos J (1993) Several routes of activation of the potassium uptake system of yeast. Biochim Biophys Acta 1179:224–228Anderson JA, Huprikar SS, Kochian LV, Lucas WJ, Gaber RF (1992) Functional expression of a probable Arabidopsis thaliana potassium channel in Saccharomyces cerevisiae. Proc Natl Acad Sci U S A 89:3736–3740Anderson JA, Nakamura RL, Gaber RF (1994) Heterologous expression of K+ channels in Saccharomyces cerevisiae: strategies for molecular analysis of structure and function. Symp Soc Exp Biol 48:85–97André B, Scherens B (1995) The yeast YBR235w gene encodes a homolog of the mammalian electroneutral Na(+)-(K+)-C1- cotransporter family. Biochem Biophys Res Commun 217:150–153Andrés MT, Viejo-Díaz M, Fierro JF (2008) Human lactoferrin induces apoptosis-like cell death in Candida albicans: critical role of K+-channel-mediated K+ efflux. Antimicrob Agents Chemother 52:4081–4088Anemaet IG, van Heusden GP (2014) Transcriptional response of Saccharomyces cerevisiae to potassium starvation. BMC Genomics 15:1040Arino J, Ramos J, Sychrova H (2010) Alkali metal cation transport and homeostasis in yeasts. Microbiol Mol Biol Rev 74:95–120Babazadeh R, Furukawa T, Hohmann S, Furukawa K (2014) Rewiring yeast osmostress signalling through the MAPK network reveals essential and non-essential roles of Hog1 in osmoadaptation. Sci Rep 4:4697Baev D, Rivetta A, Li XS, Vylkova S, Bashi E et al (2003) Killing of Candida albicans by human salivary histatin 5 is modulated, but not determined, by the potassium channel TOK1. Infect Immun 71:3251–3260Baev D, Rivetta A, Vylkova S, Sun JN, Zeng GF et al (2004) The TRK1 potassium transporter is the critical effector for killing of Candida albicans by the cationic protein, Histatin 5. J Biol Chem 279:55060–55072Bagriantsev SN, Ang KH, Gallardo-Godoy A, Clark KA, Arkin MR et al (2013) A high-throughput functional screen identifies small molecule regulators of temperature- and mechano-sensitive K2P channels. ACS Chem Biol 8:1841–1851Bañuelos MA, Sychrová H, Bleykasten-Grosshans C, Souciet JL, Potier S (1998) The Nha1 antiporter of Saccharomyces cerevisiae mediates sodium and potassium efflux. Microbiology 144(Pt 10):2749–2758Bañuelos MA, Ruiz MC, Jiménez A, Souciet JL, Potier S et al (2002) Role of the Nha1 antiporter in regulating K(+) influx in Saccharomyces cerevisiae. Yeast 19:9–15Barnett JA (2008) A history of research on yeasts 13. Active transport and the uptake of various metabolites. Yeast 25:689–731Barreto L, Canadell D, Petrezselyova S, Navarrete C, Maresova L et al (2011) A genomewide screen for tolerance to cationic drugs reveals genes important for potassium homeostasis in Saccharomyces cerevisiae. Eukaryot Cell 10:1241–1250Barreto L, Canadell D, Valverde-Saubí D, Casamayor A, Ariño J (2012) The short-term response of yeast to potassium starvation. Environ Microbiol 14:3026–3042Benito B, Moreno E, Lagunas R (1991) Half-life of the plasma membrane ATPase and its activating system in resting yeast cells. Biochim Biophys Acta 1063:265–268Benito B, Quintero FJ, Rodríguez-Navarro A (1997) Overexpression of the sodium ATPase of Saccharomyces cerevisiae: conditions for phosphorylation from ATP and Pi. Biochim Biophys Acta 1328:214–226Benito B, Garciadeblás B, Rodríguez-Navarro A (2002) Potassium- or sodium-efflux ATPase, a key enzyme in the evolution of fungi. Microbiology 148:933–941Benito B, Garciadeblás B, Schreier P, Rodríguez-Navarro A (2004) Novel p-type ATPases mediate high-affinity potassium or sodium uptake in fungi. Eukaryot Cell 3:359–368Bernardi P (1999) Mitochondrial transport of cations: channels, exchangers, and permeability transition. Physiol Rev 79:1127–1155Bertl A, Slayman CL, Gradmann D (1993) Gating and conductance in an outward-rectifying K+ channel from the plasma membrane of Saccharomyces cerevisiae. J Membr Biol 132:183–199Bertl A, Bihler H, Reid JD, Kettner C, Slayman CL (1998) Physiological characterization of the yeast plasma membrane outward rectifying K+ channel, DUK1 (TOK1), in situ. J Membr Biol 162:67–80Bertl A, Ramos J, Ludwig J, Lichtenberg-Fraté H, Reid J et al (2003) Characterization of potassium transport in wild-type and isogenic yeast strains carrying all combinations of trk1, trk2 and tok1 null mutations. Mol Microbiol 47:767–780Bihler H, Slayman CL, Bertl A (1998) NSC1: a novel high-current inward rectifier for cations in the plasma membrane of Saccharomyces cerevisiae. FEBS Lett 432:59–64Bihler H, Slayman CL, Bertl A (2002) Low-affinity potassium uptake by Saccharomyces cerevisiae is mediated by NSC1, a calcium-blocked non-specific cation channel. Biochim Biophys Acta 1558:109–118Blomberg A (1995) Global changes in protein synthesis during adaptation of the yeast Saccharomyces cerevisiae to 0.7 M NaCl. J Bacteriol 177:3563–3572Blomberg A (2000) Metabolic surprises in Saccharomyces cerevisiae during adaptation to saline conditions: questions, some answers and a model. FEMS Microbiol Lett 182:1–8Borst-Pauwels GW (1981) Ion transport in yeast. Biochim Biophys Acta 650:88–127Botstein D, Fink GR (2011) Yeast: an experimental organism for 21st Century biology. Genetics 189:695–704Bouillet LE, Cardoso AS, Perovano E, Pereira RR, Ribeiro EM et al (2012) The involvement of calcium carriers and of the vacuole in the glucose-induced calcium signaling and activation of the plasma membrane H(+)-ATPase in Saccharomyces cerevisiae cells. Cell Calcium 51:72–81Bowers K, Levi BP, Patel FI, Stevens TH (2000) The sodium/proton exchanger Nhx1p is required for endosomal protein trafficking in the yeast Saccharomyces cerevisiae. Mol Biol Cell 11:4277–4294Breinig F, Tipper DJ, Schmitt MJ (2002) Kre1p, the plasma membrane receptor for the yeast K1 viral toxin. Cell 108:395–405Brett CL, Tukaye DN, Mukherjee S, Rao R (2005) The yeast endosomal Na+K+/H+ exchanger Nhx1 regulates cellular pH to control vesicle trafficking. Mol Biol Cell 16:1396–1405Cagnac O, Leterrier M, Yeager M, Blumwald E (2007) Identification and characterization of Vnx1p, a novel type of vacuolar monovalent cation/H+ antiporter of Saccharomyces cerevisiae. J Biol Chem 282:24284–24293Cagnac O, Aranda-Sicilia MN, Leterrier M, Rodriguez-Rosales MP, Venema K (2010) Vacuolar cation/H+ antiporters of Saccharomyces cerevisiae. J Biol Chem 285:33914–33922Calahorra M, Lozano C, Sánchez NS, Peña A (2011) Ketoconazole and miconazole alter potassium homeostasis in Saccharomyces cerevisiae. Biochim Biophys Acta 1808:433–445Canadell D, González A, Casado C, Ariño J (2015) Functional interactions between potassium and phosphate homeostasis in Saccharomyces cerevisiae. Mol Microbiol 95:555–572Casado C, Yenush L, Melero C, del Carmen Ruiz M, Serrano R et al (2010) Regulation of Trk-dependent potassium transport by the calcineurin pathway involves the Hal5 kinase. FEBS Lett 584:2415–2420Causton HC, Ren B, Koh SS, Harbison CT, Kanin E et al (2001) Remodeling of yeast genome expression in response to environmental changes. Mol Biol Cell 12:323–337Clotet J, Posas F (2007) Control of cell cycle in response to osmostress: lessons from yeast. Methods Enzymol 428:63–76Cornet M, Gaillardin C (2014) pH signaling in human fungal pathogens: a new target for antifungal strategies. Eukaryot Cell 13:342–352Courchesne WE (2002) Characterization of a novel, broad-based fungicidal activity for the antiarrhythmic drug amiodarone. J Pharmacol Exp Ther 300:195–199Courchesne WE, Ozturk S (2003) Amiodarone induces a caffeine-inhibited, MID1-dependent rise in free cytoplasmic calcium in Saccharomyces cerevisiae. Mol Microbiol 47:223–234Crespo JL, Daicho K, Ushimaru T, Hall MN (2001) The GATA transcription factors GLN3 and GAT1 link TOR to salt stress in Saccharomyces cerevisiae. J Biol Chem 276:34441–34444Cunningham KW, Fink GR (1996) Calcineurin inhibits VCX1-dependent H+/Ca2+ exchange and induces Ca2+ ATPases in Saccharomyces cerevisiae. Mol Cell Biol 16:2226–2237Curto M, Valledor L, Navarrete C, Gutiérrez D, Sychrova H et al (2010) 2-DE based proteomic analysis of Saccharomyces cerevisiae wild and K+ transport-affected mutant (trk1,2) strains at the growth exponential and stationary phases. J Proteomics 73:2316–2335D’Avanzo N, Cheng WW, Xia X, Dong L, Savitsky P et al (2010) Expression and purification of recombinant human inward rectifier K+ (KCNJ) channels in Saccharomyces cerevisiae. Protein Expr Purif 71:115–121Daran-Lapujade P, Daran JM, Luttik MA, Almering MJ, Pronk JT et al (2009) An atypical PMR2 locus is responsible for hypersensitivity to sodium and lithium cations in the laboratory strain Saccharomyces cerevisiae CEN.PK113-7D. FEMS Yeast Res 9:789–792Davis DA (2009) How human pathogenic fungi sense and adapt to pH: the link to virulence. Curr Opin Microbiol 12:365–370de Nadal E, Posas F (2011) Elongating under stress. Genet Res Int 2011:326286de Nadal E, Clotet J, Posas F, Serrano R, Gomez N et al (1998) The yeast halotolerance determinant Hal3p is an inhibitory subunit of the Ppz1p Ser/Thr protein phosphatase. Proc Natl Acad Sci U S A 95:7357–7362de Nadal E, Calero F, Ramos J, Ariño J (1999) Biochemical and genetic analyses of the role of yeast casein kinase 2 in salt tolerance. J Bacteriol 181:6456–6462de Nadal E, Alepuz PM, Posas F (2002) Dealing with osmostress through MAP kinase activation. EMBO Rep 3:735–740De Nadal E, Zapater M, Alepuz PM, Sumoy L, Mas G et al (2004) The MAPK Hog1 recruits Rpd3 histone deacetylase to activate osmoresponsive genes. Nature 427:370–374Dimmer KS, Fritz S, Fuchs F, Messerschmitt M, Weinbach N et al (2002) Genetic basis of mitochondrial function and morphology in Saccharomyces cerevisiae. Mol Biol Cell 13:847–853Durell SR, Guy HR (1999) Structural models of the KtrB, TrkH, and Trk1,2 symporters based on the structure of the KcsA K(+) channel. Biophys J 77:789–807Eide DJ, Clark S, Nair TM, Gehl M, Gribskov M et al (2005) Characterization of the yeast ionome: a genome-wide analysis of nutrient mineral and trace element homeostasis in Saccharomyces cerevisiae. Genome Biol 6:R77Elicharova H, Sychrova H (2014) Fluconazole affects the alkali-metal-cation homeostasis and susceptibility to cationic toxic compounds of Candida glabrata. Microbiology 160:1705–1713Endele S, Fuhry M, Pak SJ, Zabel BU, Winterpacht A (1999) LETM1, a novel gene encoding a putative EF-hand Ca(2+)-binding protein, flanks the Wolf-Hirschhorn syndrome (WHS) critical region and is deleted in most WHS patients. Genomics 60:218–225Eraso P, Mazón MJ, Portillo F (2006) Yeast protein kinase Ptk2 localizes at the plasma membrane and phosphorylates in vitro the C-terminal peptide of the H+-ATPase. Biochim Biophys Acta 1758:164–170Erez O, Kahana C (2002) Deletions of SKY1 or PTK2 in the Saccharomyces cerevisiae trk1Deltatrk2Delta mutant cells exert dual effect on ion homeostasis. Biochem Biophys Res Commun 295:1142–1149Estrada E, Agostinis P, Vandenheede JR, Goris J, Merlevede W et al (1996) Phosphorylation of yeast plasma membrane H+-ATPase by casein kinase I. J Biol Chem 271:32064–32072Fairman C, Zhou X, Kung C (1999) Potassium uptake through the TOK1 K+ channel in the budding yeast. J Membr Biol 168:149–157Farnaud S, Evans RW (2003) Lactoferrin – a multifunctional protein with antimicrobial properties. Mol Immunol 40:395–405Fell GL, Munson AM, Croston MA, Rosenwald AG (2011) Identification of yeast genes involved in k homeostasis: loss of membrane traffic genes affects k uptake. G3 (Bethesda) 1:43–56Fernandes AR, Sá-Correia I (2003) Transcription patterns of PMA1 and PMA2 genes and activity of plasma membrane H+-ATPase in Saccharomyces cerevisiae during diauxic growth and stationary phase. Yeast 20:207–219Ferrando A, Kron SJ, Rios G, Fink GR, Serrano R (1995) Regulation of cation transport in Saccharomyces cerevisiae by the salt tolerance gene HAL3. Mol Cell Biol 15:5470–5481Ferrigno P, Posas F, Koepp D, Saito H, Silver PA (1998) Regulated nucleo/cytoplasmic exchange of HOG1 MAPK requires the importin beta homologs NMD5 and XPO1. EMBO J 17:5606–5614Flegelova H, Haguenauer-Tsapis R, Sychrova H (2006) Heterologous expression of mammalian Na/H antiporters in Saccharomyces cerevisiae. Biochim Biophys Acta 1760:504–516Flis K, Hinzpeter A, Edelman A, Kurlandzka A (2005) The functioning of mammalian ClC-2 chloride channel in Saccharomyces cerevisiae cells requires an increased level of Kha1p. Biochem J 390:655–664Forment J, Mulet JM, Vicente O, Serrano R (2002) The yeast SR protein kinase Sky1p modulates salt tolerance, membrane potential and the Trk1,2 potassium transporter. Biochim Biophys Acta 1565:36–40Froschauer E, Nowikovsky K, Schweyen RJ (2005) Electroneutral K+/H+ exchange in mitochondrial membrane vesicles involves Yol027/Letm1 proteins. Biochim Biophys Acta 1711:41–48Fukuda A, Nakamura A, Tagiri A, Tanaka H, Miyao A et al (2004) Function, intracellular localization and the importance in salt tolerance of a vacuolar Na(+)/H(+) antiporter from rice. Plant Cell Physiol 45:146–159Gaber RF (1992) Molecular genetics of yeast ion transport. Int Rev Cytol 137:299–353Gaber RF, Styles CA, Fink GR (1988) TRK1 encodes a plasma membrane protein required for high-affinity potassium transport in Saccharomyces cerevisiae. Mol Cell Biol 8:2848–2859Gaxiola RA, Rao R, Sherman A, Grisafi P, Alper SL et al (1999) The Arabidopsis thaliana proton transporters, AtNhx1 and Avp1, can function in cation detoxification in yeast. Proc Natl Acad Sci U S A 96:1480–1485Gelis S, Curto M, Valledor L, González A, Ariño J et al (2012) Adaptation to potassium starvation of wild-type and K(+)-transport mutant (trk1,2) of Saccharomyces cerevisiae: 2-dimensional gel electrophoresis-based proteomic approach. Microbiologyopen 1:182–193Gómez MJ, Luyten K, Ramos J (1996) The capacity to transport potassium influences sodium tolerance in Saccharomyces cerevisiae. FEMS Microbiol Lett 135:157–160González A, Casado C, Petrezsélyová S, Ruiz A, Ariño J (2013) Molecular analysis of a conditional hal3 vhs3 yeast mutant links potassium homeostasis with flocculation and invasiveness. Fungal Genet Biol 53:1–9Goossens A, de La Fuente N, Forment J, Serrano R, Portillo F (2000) Regulation of yeast H(+)-ATPase by protein kinases belonging to a family dedicated to activation of plasma membrane transporters. Mol Cell Biol 20:7654–7661Gupta SS, Canessa CM (2000) Heterologous expression of a mammalian epithelial sodium channel in yeast. FEBS Lett 481:77–80Gustin MC, Martinac B, Saimi Y, Culbertson MR, Kung C (1986) Ion channels in yeast. Science 233:1195–1197Haass FA, Jonikas M, Walter P, Weissman JS, Jan YN et al (2007) Identification of yeast proteins necessary for cell-surface function of a potassium channel. Proc Natl Acad Sci U S A 104:18079–18084Haro R, Rodríguez-Navarro A (2002) Molecular analysis of the mechanism of potassium uptake through the TRK1 transporter of Saccharomyces cerevisiae. Biochim Biophys Acta 1564:114–122Haro R, Rodríguez-Navarro A (2003) Functional analysis of the M2(D) helix of the TRK1 potassium transporter of Saccharomyces cerevisiae. Biochim Biophys Acta 1613:1–6Haro R, Garciadeblas B, Rodríguez-Navarro A (1991) A novel P-type ATPase from yeast involved in sodium transport. FEBS Lett 291:189–191Hasenbrink G, Schwarzer S, Kolacna L, Ludwig J, Sychrova H et al (2005) Analysis of the mKir2.1 channel activity in potassium influx defective Saccharomyces cerevisiae strains determined as changes in growth characteristics. FEBS Lett 579:1723–1731Herrera R, Álvarez MC, Gelis S, Ramos J (2013) Subcellular potassium and sodium distribution in Saccharomyces cerevisiae wild-type and vacuolar mutants. Biochem J 454:525–532Herrera R, Alvarez MC, Gelis S, Kodedová M, Sychrová H et al (2014) Role of Saccharomyces cerevisiae Trk1 in stabilization of intracellular potassium content upon changes in external potassium levels. Biochim Biophys Acta 1838:127–133Hess DC, Lu W, Rabinowitz JD, Botstein D (2006) Ammonium toxicity and potassium limitation in yeast. PLoS Biol 4:e351Hoeberichts FA, Perez-Valle J, Montesinos C, Mulet JM, Planes MD et al (2010) The role of K+ and H+ transport systems during glucose- and H2O2-induced cell death in Saccharomyces cerevisiae. Yeast 27:713–725Hohmann S (2002) Osmotic stress signaling and osmoadaptation in yeasts. Microbiol Mol Biol Rev 66:300–372Hohmann S, Krantz M, Nordlander B (2007) Yeast osmoregulation. Methods Enzymol 428:29–45Idnurm A, Walton FJ, Floyd A, Reedy JL, Heitman J (2009) Identification of ENA1 as a virulence gene of the human pathogenic fungus Cryptococcus neoformans through signature-tagged insertional mutagenesis. Eukaryot Cell 8:315–326Jung KW, Strain AK, Nielsen K, Jung KH, Bahn YS (2012) Two cation transporters Ena1 and Nha1 cooperatively modulate ion homeostasis, antifungal drug resistance, and virulence of Cryptococcus neoformans via the HOG pathway. Fungal Genet Biol 49:332–345Kafadar KA, Cyert MS (2004) Integration of stress responses: modulation of calcineurin signaling in Saccharomyces cerevisiae by protein kinase A. Eukaryot Cell 3:1147–1153Kahm M, Navarrete C, Llopis-Torregrosa V, Herrera R, Barreto L et al (2012) Potassium starvation in yeast: mechanisms of homeostasis revealed by mathematical modeling. PLoS Comput Biol 8:e1002548Kallay LM, Brett CL, Tukaye DN, Wemmer MA, Chyou A et al (2011) Endosomal Na+(K+)/H+ exchanger Nhx1/Vps44 functions independently and downstream of multivesicular body formation. J Biol Chem 286:44067–44077Kane PM (2007) The long physiological reach of the yeast vacuolar H+-ATPase. J Bioenerg Biomembr 39:415–421Kane PM (2012) Targeting reversible disassembly as a mechanism of controlling V-ATPase activity. Curr Protein Pept Sci 13:117–123Ke R, Ingram PJ, Haynes K (2013) An integrative model of ion regulation in yeast. PLoS Comput Biol 9:e1002879Ketchum KA, Joiner WJ, Sellers AJ, Kaczmarek LK, Goldstein SA (1995) A new family of outwardly rectifying potassium channel proteins with two pore domains in tandem. Nature 376:690–695Kinclová O, Ramos J, Potier S, Sychrová H (2001) Functional study of the Saccharomyces cerevisiae Nha1p C-terminus. Mol Microbiol 40:656–668Kinclova-Zimmermannova O, Sychrova H (2006) Functional study of the Nha1p C-terminus: involvement in cell response to changes in external osmolarity. Curr Genet 49:229–236Kinclová-Zimmermannová O, Flegelová H, Sychrová H (2004) Rice Na+/H+-antiporter Nhx1 partially complements the alkali-metal-cation sensitivity of yeast strains lacking three sodium transporters. Folia Microbiol (Praha) 49:519–525Kinclova-Zimmermannova O, Gaskova D, Sychrova H (2006) The Na+, K+/H+ -antiporter Nha1 influences the plasma membrane potential of Saccharomyces cerevisiae. FEMS Yeast Res 6:792–800Klee CB, Draetta GF, Hubbard MJ (1988) Calcineurin. Adv Enzymol Relat Areas Mol Biol 61:149–200Klipp E, Nordlander B, Krüger R, Gennemark P, Hohmann S (2005) Integrative model of the response of yeast to osmotic shock. Nat Biotechnol 23:975–982Ko CH, Gaber RF (1991) TRK1 and TRK2 encode structurally related K+ transporters in Saccharomyces cerevisiae. Mol Cell Biol 11:4266–4273Ko CH, Buckley AM, Gaber RF (1990) TRK2 is required for low affinity K+ transport in Saccharomyces cerevisiae. Genetics 125:305–312Ko CH, Liang H, Gaber RF (1993) Roles of multiple glucose transporters in Saccharomyces cerevisiae. Mol Cell Biol 13:638–648Kojima A, To