Some physiological alteration associated with pleiotropic cross resistance and collateral sensitivity in Saccharomyces cerevisiae

Attenuated apoptotic BAX expression as a xenobiotic reporter in Saccharomyces cerevisiae

Fungal infections are a major challenge to medicine and agriculture. Repeated and prophylactic use of antifungals can lead to pathogen cross-resistance to different classes of drugs. The early development of multidrug resistance in pathogenic fungi includes drug tolerance mediated by drug-dependent activation of drug efflux. In Saccharomyces cerevisiae and the fungal pathogen Candida glabrata, xenobiotic sensing motifs in transcription factors upregulate expression of several ATP-binding cassette (ABC) drug efflux pumps. We have therefore considered how drug candidates that trigger or prevent drug resistance could be identified and evaluated during drug discovery. We report a robust and sensitive, S. cerevisiae-based xenobiotic sensing system using the Pdr1 protein as a sensor and an attenuated version of the apoptotic murine BCL2-associated X (BAX) gene as a reporter. A molecular mechanism of attenuation that involves frameshift reversal may be associated with translation coupling and requires further investigation.

Multidrug resistance in fungi: regulation of transporter-encoding gene expression

A critical risk to the continued success of antifungal chemotherapy is the acquisition of resistance; a risk exacerbated by the few classes of effective antifungal drugs. Predictably, as the use of these drugs increases in the clinic, more resistant organisms can be isolated from patients. A particularly problematic form of drug resistance that routinely emerges in the major fungal pathogens is known as multidrug resistance. Multidrug resistance refers to the simultaneous acquisition of tolerance to a range of drugs via a limited or even single genetic change. This review will focus on recent progress in understanding pathways of multidrug resistance in fungi including those of most medical relevance. Analyses of multidrug resistance in Saccharomyces cerevisiae have provided the most detailed outline of multidrug resistance in a eukaryotic microorganism. Multidrug resistant isolates of S. cerevisiae typically result from changes in the activity of a pair of related transcription factors that in turn elicit overproduction of several target genes. Chief among these is the ATP-binding cassette (ABC)-encoding gene PDR5. Interestingly, in the medically important Candida species, very similar pathways are involved in acquisition of multidrug resistance. In both C. albicans and C. glabrata, changes in the activity of transcriptional activator proteins elicits overproduction of a protein closely related to S. cerevisiae Pdr5 called Cdr1. The major filamentous fungal pathogen, Aspergillus fumigatus, was previously thought to acquire resistance to azole compounds (the principal antifungal drug class) via alterations in the azole drug target-encoding gene cyp51A. More recent data indicate that pathways in addition to changes in the cyp51A gene are important determinants in A. fumigatus azole resistance. We will discuss findings that suggest azole resistance in A. fumigatus and Candida species may share more mechanistic similarities than previously thought.

Yeast ABC proteins involved in multidrug resistance

Pleiotropic drug resistance is a complex phenomenon that involves many proteins that together create a network. One of the common mechanisms of multidrug resistance in eukaryotic cells is the active efflux of a broad range of xenobiotics through ATP-binding cassette (ABC) transporters. Saccharomyces cerevisiae is often used as a model to study such activity because of the functional and structural similarities of its ABC transporters to mammalian ones. Numerous ABC transporters are found in humans and some are associated with the resistance of tumors to chemotherapeutics. Efflux pump modulators that change the activity of ABC proteins are the most promising candidate drugs to overcome such resistance. These modulators can be chemically synthesized or isolated from natural sources (e.g., plant alkaloids) and might also be used in the treatment of fungal infections. There are several generations of synthetic modulators that differ in specificity, toxicity and effectiveness, and are often used for other clinical effects.

Novel target genes of the yeast regulator Pdr1p: a contribution of the TPO1 gene in resistance to quinidine and other drugs

The yeast transcription factor Pdr1p regulates the expression of a number of genes, several of which encode ATP-driven transport proteins involved in multiple drug resistance. Among 20 genes containing binding consensus sequences for the transcription factor Pdr1p in their promoter, we studied more particularly the regulation and function of PDR16 (involved in phospholipid synthesis), TPO1 (involved in vacuolar transport of polyamines), YAL061W (homologous to polyol dehydrogenases) and YLR346C (unknown function). We found that the regulation of these four genes depends on Pdr1p, since promoter activities studied by lacZ fusion analysis and mRNA levels studied by Northern blotting analysis changed upon deletion or hyperactivation by the pdr1-3 mutant of this transcription factor. The drug sensitivity of the strains deleted for these genes revealed that TPO1, a gene previously found to be involved in spermidine resistance and vacuolar polyamine transport, is a determinant of multidrug transporter since it also mediates growth resistance to cycloheximide and quinidine. This resistance pattern overlapped with that of YOR273C, a homolog of TPO1. These two homologous transporters are thus bona fide members of the phylogenetic subfamily DHA1 (drug/proton antiport TC 2.A.1. 2) of the major facilitator superfamily. Both YOR273C and TPO1 as well as at least one other determinant involved in the yeast pleiotropic drug resistance network contribute to resistance to a quinoline-containing antimalarial drug.

Cross-talk between transcriptional regulators of multidrug resistance in Saccharomyces cerevisiae

Multiple or pleiotropic drug resistance often arises in the yeast Saccharomyces cerevisiae due to genetic alterations of the functional state of the Cys(6)-Zn(II)(2) transcription factors Pdr1p and Pdr3p. Single amino acid substitutions give rise to hyperactive forms of these regulatory proteins, which in turn cause overproduction of downstream target genes that directly mediate multidrug resistance. Previous work has identified a novel Cys(6)-Zn(II)(2) transcription factor designated Yrr1p as mutant forms of this protein confer high level resistance to the cell cycle inhibitor reveromycin A and DNA damaging agent 4-nitroquinoline-N-oxide. In the present study, we demonstrate that Yrr1p also mediates oligomycin resistance through activation of the ATP-binding cassette transporter-encoding gene YOR1. Additionally, insertion of triplicated copies of the hemagglutinin epitope in the C-terminal region of Yrr1p causes the protein to behave as a hyperactive regulator of transcription. We have found that YRR1 expression is both controlled in a Pdr1p/Pdr3p-dependent manner and autoregulated. Chromatin immunoprecipitation experiments also show that Yrr1p associates with target promoters in vivo. Together these data argue that the signal generated by activation of Pdr1p and/or Pdr3p can be amplified through the action of these transcriptional regulatory proteins on downstream target genes, like YRR1, that also encode transcription factors.

Hyperactive forms of the Pdr1p transcription factor fail to respond to positive regulation by the hsp70 protein Pdr13p

Multidrug resistance in Saccharomyces cerevisiae is commonly associated with the overproduction of ATP-binding cassette transporter proteins such as Pdr5p or Yor1p. The Cys6-Zn(II)2 cluster-containing transcription factors Pdr1p and Pdr3p are key regulators of expression of these pleiotropic drug resistance (PDR) loci. Previous experiments have demonstrated that the Hsp70 protein encoded by the PDR13 gene is a positive regulator of Pdr1p function. We have examined the mechanism underlying the control of Pdr1p by Pdr13p. Expression of deletion, insertion and amino acid substitution mutant variants of Pdr1p suggest that the centre region of the transcription factor is the target for Pdr13p-mediated positive regulation. Immunological and fusion protein analyses demonstrate that Pdr13p is located in the cytoplasm, while Pdr1p is found in the nucleus. Biochemical fractionation experiments indicate that Pdr13p is associated with a high-molecular-weight complex and suggest the association of some fraction of Pdr13p with ribosomes.

In vivo characterization of the drug resistance profile of the major ABC transporters and other components of the yeast pleiotropic drug resistance network

Multidrug resistance (MDR) mediated by broad specificity transporters is one of the most important strategies used by pathogens, including cancer cells, to evade chemotherapy. In the yeast Saccharomyces cerevisiae, a complex pleiotropic drug resistance (PDR) network of genes involved in MDR is composed of the transcriptional regulators Pdr1p and Pdr3p, which activate expression of the ATP-binding cassette (ABC) MDR transporters-encoding genes PDR5, SNQ2, and YOR1 as well as other not yet identified genes. We have screened 349 toxic compounds in isogenic S. cerevisiae strains deleted of PDRS, SNQ2, or YOR1 in different combinations as well as both PDR1 and PDR3. The screen revealed extremely promiscuous, yet limited, and to a large extent overlapping but distinct drug resistance profiles of Pdr5p, Snq2p, and Yor1p. These ABC-MDR transporters mediated resistance to most currently available classes of clinically and agriculturally important fungicides and also to many antibiotics, herbicides, and others. Several classes of compounds were identified for the first time in the drug resistance spectrum of MDR transporters. These are fungicides, such as anilinopyrimidines, benzimidazoles, benzenedicarbonitriles, dithiocarbamates, guanidines, imidothiazoles, polyenes, pyrimidynyl carbinols, and strobilurine analogues; the urea derivative and anilide herbicides; flavonoids, several membrane lipids resembling detergents; and newly synthesized lysosomotropic aminoesters; as well as many others. Identification of compounds showing Pdr1p, Pdr3p-dependent, but Pdr5p-, Snq2p-, and Yor1p-independent toxicity, reflected in the case of rhodamine 6G, by efflux alterations, suggests the involvement of new drug resistance genes and is a first step toward their identification. The highly increased toxicity of bile acids toward the PDR1, PDR3 double disruptant together with the decreased level of BAT1 promoter dependent beta-galactosidase activity suggest that the Bat1p ABC transporter is a new member of the PDR network. Our results may contribute to a better understanding of the mechanism of MDR, in particular in the pathogenic yeast Candida albicans. They also provide and indication of the physiological function of MDR transporters and suggest new approaches for the cloning of the mammalian bile acid transporters.

Regulation of pleiotropic drug resistance in yeast

This review focuses on the molecular mechanisms involved in the regulation of multiple drug resistance in the model yeast Saccharomyces cerevisiae and the pathogenic fungus Candida albicans. Recent developments in the study of the transcription factors Pdr1p, Pdr3p and Yap1p are reported. Understanding the molecular basis leading to multiple drug resistance is a prerequisite for the development of new antifungal therapeutics. Copyright 1999 Harcourt Publishers Ltd.

PDR16 and PDR17, two homologous genes of Saccharomyces cerevisiae, affect lipid biosynthesis and resistance to multiple drugs

The Saccharomyces cerevisiae open reading frame YNL231C was recently found to be controlled by the multiple drug resistance regulator Pdr1p. Here we characterize YNL231C (PDR16) and its homologue YNL264C (PDR17). Deletion of PDR16 resulted in hypersensitivity of yeast to azole inhibitors of ergosterol biosynthesis. While no increase in drug sensitivity was found upon deletion of PDR17 alone, a Deltapdr16,Deltapdr17 double mutant was hypersensitive to a broad range of drugs. Both mutations caused significant changes of the lipid composition of plasma membrane and total cell extracts. Deletion of PDR16 had pronounced effects on the sterol composition, whereas PDR17 deletion mainly affected the phospholipid composition. Thus, Pdr16p and Pdr17p may regulate yeast lipid synthesis like their distant homologue, Sec14p. The azole sensitivity of the PDR16-deleted strain may be the result of imbalanced ergosterol synthesis. Impaired plasma membrane barrier function resulting from a change in the lipid composition appears to cause the increased drug sensitivity of the double mutant strain Deltapdr16,Deltapdr17. The uptake rate of rhodamine-6-G into de-energized cells was shown to be almost 2-fold increased in a Deltapdr16,Deltapdr17 strain as compared with wild-type and Deltapdr5 strains. Collectively, our results indicate that PDR16 and PDR17 control levels of various lipids in various compartments of the cell and thereby provide a mechanism for multidrug resistance unrecognized so far.

Identification and characterization of SNQ2, a new multidrug ATP binding cassette transporter of the yeast plasma membrane

The SNQ2 gene of Saccharomyces cerevisiae, which encodes an ATP binding cassette protein responsible for resistance to the mutagen 4-nitroquinoline oxide, is regulated by the DNA-binding proteins PDR1 and PDR3. In a plasma membrane-enriched fraction from a pdr1 mutant, the SNQ2 protein is found in the 160-kDa over-expressed band, together with PDR5. The SNQ2 protein was solubilized with n-dodecyl beta-D-maltoside from the plasma membranes of a PDR5-deleted strain and separated from the PMA1 H(+/-)ATPase by sucrose gradient centrifugation. The enzyme shows a nucleoside triphosphatase activity that differs biochemically from that of PDR5 (Decottignies, A., Kolaczkowski, M., Balzi, E., and Goffeau, A. (1994) J. Biol. Chem. 269, 12797-12803) and is sensitive to vanadate, erythrosine B, and Triton X-100 but not to oligomycin, which inhibits the PDR5 activity only. Disruption of both PDR5 and SNQ2 in a pdr1 mutant decreases the cell growth rate and reveals the presence of at least two other ATP binding cassette proteins in the 160-kDa overexpressed band that have been identified by amino-terminal microsequencing.

Yeast multidrug resistance: the PDR network

This minireview describes a network of genes involved in multiple drug resistance of the yeast S. cerevisiae. The transcription regulators, PDR1, PDR3, PDR7, and PDR9 control the expression of the gene PDR5, encoding a membrane protein of the ATP-binding-cassette superfamily and functioning as a drug extrusion pump. Next to PDR5, several other target genes, encoding membrane pumps of the ABC type, such as SNQ2, STE6, PDR10, PDR11, YOR1, but also other membrane-associated (such as GAS1, D4405) or soluble proteins (such as G3PD), involved or not in multidrug resistance, are found to be controlled by PDR1. On another side, the PDR3 regulator participates with its homolog PDR1 to co- and auto-regulation circuits of yeast multidrug resistance.

Genetic mapping of nuclear mucidin resistance mutations in Saccharomyces cerevisiae. A new pdr locus on chromosome II

In the yeast Saccharomyces cerevisiae, two nuclear pleiotropic drug resistance mutations pdr3-1 (former designation mucPR) and pdr3-2 (former designation DRI9/T7) have been selected as resistant to mucidin and as resistant to chloramphenicol plus cycloheximide, respectively. The pdr3 mutations were found not to affect the plasma membrane ATPase activity measured in a crude membrane fraction. Meiotic mapping using strains with standard genetic markers revealed that mutation pdr3-1 is centromere linked on the left arm of chromosome II at a distance of 5.9 +/- 3.3 cM from its centromere and 11.6 +/- 3.1 cM from the marker pet9. The centromere linked pdr3-2 mutation exhibited also genetic linkage to pet9 with a map distance of 9.8 +/- 3.2 cM. These results indicate that pdr3-1 and pdr3-2 are alleles of the same pleiotropic drug resistance locus PDR3 which is involved in the control of the plasma membrane permeability in yeast.

Characterization of Saccharomyces cerevisiae mutants supersensitive to aminoglycoside antibiotics

We describe mutants of Saccharomyces cerevisiae that are more sensitive than the wild type to the aminoglycoside antibiotics G418, hygromycin B, destomycin A, and gentamicin X2. In addition, the mutants are sensitive to apramycin, kanamycin B, lividomycin A, neamine, neomycin, paromomycin, and tobramycin--antibiotics which do not inhibit wild-type strains. Mapping studies suggest that supersensitivity is caused by mutations in at least three genes, denoted AGS1, AGS2, and AGS3 (for aminoglycoside antibiotic sensitivity). Mutations in all three genes are required for highest antibiotic sensitivity; ags1 ags2 double mutants have intermediate antibiotic sensitivity. AGS1 was mapped 8 centimorgans distal from LEU2 on chromosome III. Analyses of yeast strains transformed with vectors carrying antibiotic resistance genes revealed that G418, gentamicin X2, kanamycin B, lividomycin A, neamine, and paromomycin are inactivated by the Tn903 phosphotransferase and that destomycin A is inactivated by the hygromycin B phosphotransferase. ags strains are improved host strains for vectors carrying the phosphotransferase genes because a wide spectrum of aminoglycoside antibiotics can be used to select for plasmid maintenance.

Multiple drug resistance in the fission yeast Schizosaccharomyces pombe: evidence for the existence of pleiotropic mutations affecting dependent transport systems

The uptake of L-tyrosine into wild type and antibiotic resistant strains of Schizosaccharomyces pombe requires an energy source, is initially linear with respect to time, is inhibited by 2,4-dinitrophenol and sodium azide and is saturable. However the initial uptake rates and the amount of L-tyrosine accummulated by antibiotic resistant strains are much less than wild type. Comparison of the kinetic constants of uptake shows that mutant strains have a reduced maximum velocity of uptake compared to wild type and a larger Km. Since the three mutant strains possess a permeability barrier to L-tyrosine as well as being drug resistant this is an indication that antibiotic resistance may be caused by a decrease in plasma membrane permeability.

Nuclear inheritance of resistance to antimycin A in Saccharomyces cerevisiae

A group of 30 independent mutants of Saccharomyces cerevisiae, resistant to the respiratory inhibitor antimycin A, was investigated from a genetical and biochemical point of view. All the mutants can be grouped into two nuclear loci: AMY1 maps on the VII chromosome, between leu 1 and trp 5; AMY2 is close to its centromere on either chromosome XVIII or XIX. Both genes do not affect mitochondrial structures or functions.

Inheritance of multiple drug resistance in Saccharomyces cerevisiae: linkage to leu1 and analyses of 2 micron DNA in partial revertants

The inheritance and phenotype of multiple drug resistance in independent multiple drug resistant mutants, two isolated in this laboratory (GR359 and 2-20), and two (DRI 9/T7 and DRI 9/T8) reported by Guerineau et al. (Biochem. Biophys. Res. Commun. 61,462), was investigated. Comparison of resistance to 12 selected drugs showed that the resistance phenotypes of all mutants were similar, although some differences in levels of resistance of each mutant was observed with certain drugs. Mapping of the resistance loci in GR359 and 2-20 revealed tight linkage of both resistance genes to the centromere linked gene leul. 2 micron DNA was analysed by hybridization of 2 micron RNA to EcoRI fragments of a total DNA extract. Eight partial revertants of 2-20, which had been chosen as having a phenotype similar to the 2 micron DNA deficient [cir degrees] isolate DRI 9/T7, revealed the presence of 2 micron DNA. The lack of detectable 2 micron DNA in DRI 9/T7 was confirmed.

Nuclear-extranuclear interactions affecting oligomycin resistance in Aspergillus nidulans

The extranuclear mitochondrial oligomycin-resistant mutation of Aspergillus nidulans, (oliA1), was transferred asexually into four nuclear oligomycin-resistant strains of different phenotypes. In all four cases, the possession of the nuclear plus extranuclear mutation led to an increase in the in vivo level of oligomycin resistance. In two cases, the altered cytochrome spectrum and impaired growth ability determined by (oliA1) were suppressed by the nuclear mutations. In the third case, the in vitro oligomycin resistance of the double mutant ATPase was dramatically increased above that of either of the component single mutant strains, indicating a synergystic interaction between the nuclear and extranuclear gene products. In the fourth case, the double mutant became cold-sensitive. A new extranuclear mitochondrial oligomycin-resistant mutation (oliB332) is described. This mutant is phenotypically similar to, though not identical with, (oliA1) but is separable by recombination. A range of nuclear oligomycin-resistant mutants have been mapped. Despite presenting five distinctly different phenotypes, they all map at the same locus.

Single gene alteration of plasma and mitochondrial membrane function in Saccharomyces cerevisiae

Some physiological properties of a multiple-drug-resistant mutant with a permeability barrier to chloramphenicol and its isogenic parental strain were compared. The ATPase specific activity of plasma and mitochondrial membranes isolated from the mutant strain was approximately 20% lower (P less than 0.001, Tables 1 and 2) than that of membranes isolated from the isogenic parental strain. Additional evidence of altered mitochondrial function was: (i) the enhanced growth of the parental strain was eliminted by the [rho-] state (Table 3); (ii) the mutant strain had a greater resistance to petite induction by ethidium bromide (Table 4); (iii) the mutant strain was unable to use a nonfermentable energy source for respiratory adaptation (Table 5). It is proposed that a single gene mutation has resulted in an alteration of some physiological properties of the plasma and mitochondrial membranes.