Genome-wide expression profile of steroid response in Saccharomyces cerevisiae

Differential carbohydrate-active enzymes and secondary metabolite production by the grapevine trunk pathogen Neofusicoccum parvum Bt-67 grown on host and non-host biomass

Neofusicoccum parvum is one of the most aggressive Botryosphaeriaceae species associated with grapevine trunk diseases. This species may secrete enzymes capable of overcoming the plant barriers, leading to wood colonization. In addition to their roles in pathogenicity, there is an interest in taking advantage of N. parvum carbohydrate-active enzymes (CAZymes), related to plant cell wall degradation, for lignocellulose biorefining. Furthermore, N. parvum produces toxic secondary metabolites that may contribute to its virulence. In order to increase knowledge on the mechanisms underlying pathogenicity and virulence, as well as the exploration of its metabolism and CAZymes for lignocellulose biorefining, we evaluated the N. parvum strain Bt-67 capacity in producing lignocellulolytic enzymes and secondary metabolites when grown in vitro with two lignocellulosic biomasses: grapevine canes (GP) and wheat straw (WS). For this purpose, a multiphasic study combining enzymology, transcriptomic, and metabolomic analyses was performed. Enzyme assays showed higher xylanase, xylosidase, arabinofuranosidase, and glucosidase activities when the fungus was grown with WS. Fourier transform infrared (FTIR) spectroscopy confirmed the lignocellulosic biomass degradation caused by the secreted enzymes. Transcriptomics indicated that the N. parvum Bt-67 gene expression profiles in the presence of both biomasses were similar. In total, 134 genes coding CAZymes were up-regulated, where 94 of them were expressed in both biomass growth conditions. Lytic polysaccharide monooxygenases (LPMOs), glucosidases, and endoglucanases were the most represented CAZymes and correlated with the enzymatic activities obtained. The secondary metabolite production, analyzed by high-performance liquid chromatography-ultraviolet/visible spectophotometry-mass spectrometry (HPLC-UV/Vis-MS), was variable depending on the carbon source. The diversity of differentially produced metabolites was higher when N. parvum Bt-67 was grown with GP. Overall, these results provide insight into the influence of lignocellulosic biomass on virulence factor expressions. Moreover, this study opens the possibility of optimizing the enzyme production from N. parvum with potential use for lignocellulose biorefining.

The Fungus Trichoderma Regulates Submerged Conidiation Using the Steroid Pregnenolone

In previous work, we evolved a population of Trichoderma citrinoviride in liquid cultures to speed up its asexual development cycle. The evolved population, called T-6, formed conidia 3 times sooner and in >1000-fold greater numbers. Here, we identify the steroid pregnenolone as a molecular signal for this different behavior. Media in which the ancestral T. citrinoviride population was grown (called ancestral spent media) contained a submerged conidiation inhibitor. Growing the evolved population T-6 in ancestral spent media eliminated the abundant formation of conidia. This inhibition depended on the amount and age of the ancestral spent medium and the time that the ancestral spent medium was added to the T-6 culture. Fractionation of the ancestral spent medium identified a hydrophobic inhibiting compound with a molecular weight less than 2000 g/mol. A combination of GC-MS, ELISA, and reaction with cholesterol oxidase identified it as pregnenolone. The addition of pregnenolone to cultures of T-6 inhibited submerged conidiation by inhibiting formation of conidiophores, while 10 other analogous steroids did not. Pregnenolone also inhibited submerged conidiation of Fusarium graminearum PH-1, a plant pathogen that causes head blight in wheat and barley. This identification of steroids as signal molecules in fungi creates opportunities to disrupt this signaling to control fungal behavior.

Mycologic Endocrinology

The interactions of fungi and chemical messenger molecules, hormones or pheromones, are addressed in this chapter. These interactions include mammalian fungal pathogens, also plant pathogens, or non-pathogenic fungi, which can result in functional responses in receptor- or non-receptor-mediated fashions. Endogenous ligands in the fungi have been demonstrated to be important for mating in a number of systems. Mammalian hormones have been demonstrated to have stimulatory or inhibitory effects on growth for organisms such as Candida albicans, Paracoccidioides brasiliensis, Saccharomyces cerevisiae, Rhizopus nigricans, Aspergillus fumigatus, Coccidioides, and dermatophytic fungi. A number of fungi have been shown to have specific binding proteins for corticosteroid, estrogen and progesterone that are stereo-specific and high affinity. In some instances, the interactions of a mammalian hormone with the organism, in vivo, affects pathogenesis. Genome expression profiles of C. albicans in the presence of estradiol or progesterone, and S. cerevisiae with progesterone, indicate major up-regulation of various drug resistance pumps, like CDR1, and CDR2, can affect antifungal susceptibility. Azole antifungal interactions occur with fungal hormone binding proteins. Azoles also can block mammalian steroidogenesis. The finding of interactions of mammalian hormones with fungi and subsequent functional responses by the fungi, suggest that hormonal interactions with fungal systems has been conserved throughout evolution and have an important role in fungal pathogenesis, as well as in the overall biology of the organisms.

Novel Regulatory Mechanisms of Pathogenicity and Virulence to Combat MDR in Candida albicans

Continuous deployment of antifungals in treating infections caused by dimorphic opportunistic pathogen Candida albicans has led to the emergence of drug resistance resulting in cross-resistance to many unrelated drugs, a phenomenon termed multidrug resistance (MDR). Despite the current understanding of major factors which contribute to MDR mechanisms, there are many lines of evidence suggesting that it is a complex interplay of multiple factors which may be contributed by still unknown mechanisms. Coincidentally with the increased usage of antifungal drugs, the number of reports for antifungal drug resistance has also increased which further highlights the need for understanding novel molecular mechanisms which can be explored to combat MDR, namely, ROS, iron, hypoxia, lipids, morphogenesis, and transcriptional and signaling networks. Considering the worrying evolution of MDR and significance of C. albicans being the most prevalent human fungal pathogen, this review summarizes these new regulatory mechanisms which could be exploited to prevent MDR development in C. albicans as established from recent studies.

Steroid toxicity and detoxification in ascomycetous fungi

In the last couple of decades fungal infections have become a significant clinical problem. A major interest into fungal steroid action has been provoked since research has proven that steroid hormones are toxic to fungi and affect the host/fungus relationship. Steroid hormones were found to differ in their antifungal activity in ascomycetous fungi Hortaea werneckii, Saccharomyces cerevisiae and Aspergillus oryzae. Dehydroepiandrosterone was shown to be the strongest inhibitor of growth in all three varieties of fungi followed by androstenedione and testosterone. For their protection, fungi use several mechanisms to lower the toxic effects of steroids. The efficiency of biotransformation in detoxification depended on the microorganism and steroid substrate used. Biotransformation was a relatively slow process as it also depended on the growth phase of the fungus. In addition to biotransformation, steroid extrusion out of the cells contributed to the lowering of the active intracellular steroid concentration. Plasma membrane Pdr5 transporter was found to be the most effective, followed by Snq2 transporter and vacuolar transporters Ybt1 and Ycf1. Proteins Aus1 and Dan1 were not found to be involved in steroid import. The research of possible targets of steroid hormone action in fungi suggests that steroid hormones inhibit ergosterol biosynthesis in S. cerevisiae and H. werneckii. Results of this inhibition caused changes in the sterol content of the cellular membrane. The presence of steroid hormones most probably causes the degradation of the Tat2 permease and impairment of tryptophan import.

Characterization and ligand identification of a membrane progesterone receptor in fungi: existence of a novel PAQR in Sporothrix schenckii

Background

Adaptive responses in fungi result from the interaction of membrane receptors and extracellular ligands. Many different classes of receptors have been described in eukaryotic cells. Recently a new family of receptors classified as belonging to the progesterone-adiponectin receptor (PAQR) family has been identified. These receptors have the seven transmembrane domains characteristic of G-protein coupled receptors, but their activity has not been associated directly to G proteins. They share sequence similarity to the eubacterial hemolysin III proteins.

Results

A new receptor, SsPAQR1 (Sporothrixschenckiiprogesterone-adiponectinQ receptor1), was identified as interacting with Sporothrix schenckii G protein alpha subunit SSG-2 in a yeast two-hybrid assay. The receptor was identified as a member of the PAQR family. The cDNA sequence revealed a predicted ORF of 1542 bp encoding a 514 amino acids protein with a calculated molecular weight of 57.8 kDa. Protein domain analysis of SsPAQR1 showed the 7 transmembrane domains (TM) characteristic of G protein coupled receptors and the presence of the distinctive motifs that characterize PAQRs. A yeast-based assay specific for PAQRs identified progesterone as the agonist. S. schenckii yeast cells exposed to progesterone (0.50 mM) showed an increase in intracellular levels of 3^′, 5^′ cyclic adenosine monophosphate (cAMP) within the first min of incubation with the hormone. Different progesterone concentrations were tested for their effect on the growth of the fungus. Cultures incubated at 35°C did not grow at concentrations of progesterone of 0.05 mM or higher. Cultures incubated at 25°C grew at all concentrations tested (0.01 mM-0.50 mM) with growth decreasing gradually with the increase in progesterone concentration.

Conclusion

This work describes a receptor associated with a G protein alpha subunit in S. schenckii belonging to the PAQR family. Progesterone was identified as the ligand. Exposure to progesterone increased the levels of cAMP in fungal yeast cells within the first min of incubation suggesting the connection of this receptor to the cAMP signalling pathway. Progesterone inhibited the growth of both the yeast and mycelium forms of the fungus, with the yeast form being the most affected by the hormone.

Response of pathogenic and non-pathogenic yeasts to steroids

Steroids are known to induce pleiotropic drug resistance states in hemiascomycetes, with tremendous potential consequences on human fungal infections. The proteins capable of binding to steroids such as progesterone binding protein (PBP), estradiol binding proteins (ESP) are found in yeasts, however, the well known receptor mediated signaling present in higher eukaryotic cells is absent in yeasts and fungi. Steroids are perceived as stress by yeast cells which triggers general stress response leading to activation of heat shock proteins, cell cycle regulators, MDR transporters, etc. In this article, we review the response of yeast to human steroid hormones which affects its cell growth, morphology and virulence. We discuss that a fairly conserved response to steroids at the level of transcription and translation exists between pathogenic and non-pathogenic yeasts. Article from a special issue on steroids and microorganisms.

Aspects of the progesterone response in Hortaea werneckii: Steroid detoxification, protein induction and remodelling of the cell wall

Progesterone in sublethal concentrations temporarily inhibits growth of Hortaea werneckii. This study investigates some of the compensatory mechanisms which are activated in the presence of progesterone and are most probably contributing to escape from growth inhibition. These mechanisms lead on the one hand to progesterone biotransformation/detoxification but, on the other, are suggested to increase the resistance of H. werneckii to the steroid. Biotransformation can detoxify progesterone efficiently in the early logarithmic phase, with mostly inducible steroid transforming enzymes, while progesterone biotransformation/detoxification in the late logarithmic and stationary phases of growth is not very efficient. The relative contribution of constitutive steroid transforming enzymes to progesterone biotransformation is increased in these latter phases of growth. In the presence of progesterone, activation of the cell wall integrity pathway is suggested by the overexpression of Pck2 which was detected in the stationary as well as the logarithmic phase of growth of the yeast. Progesterone treated H. werneckii cells were found to be more resistant to cell lysis than mock treated cells, indicating for the first time changes in the yeast cell wall as a result of treatment with progesterone.

Heterologous expression of human mPRalpha, mPRbeta and mPRgamma in yeast confirms their ability to function as membrane progesterone receptors

The nuclear progesterone receptor (nPR) mediates many of the physiological effects of progesterone by regulating the expression of genes, however, progesterone also exerts non-transcriptional (non-genomic) effects that have been proposed to rely on a receptor that is distinct from nPR. Several members of the progestin and AdipoQ-Receptor (PAQR) family were recently identified as potential mediators of these non-genomic effects. Membranes from cells expressing these proteins, called mPRalpha, mPRbeta and mPRgamma, were shown to specifically bind progesterone and have G-protein coupled receptor (GPCR) characteristics, although other studies dispute these findings. To clarify the role of these mPRs in non-genomic progesterone signaling, we established an assay for PAQR functional evaluation using heterologous expression in Saccharomyces cerevisiae. Using this assay, we demonstrate unequivocally that mPRalpha, mPRbeta and mPRgamma can sense and respond to progesterone with EC(50) values that are physiologically relevant. Agonist profiles also show that mPRalpha, mPRbeta and mPRgamma are activated by ligands, such as 17alpha-hydroxyprogesterone, that are known to activate non-genomic pathways but not nPR. These results strongly suggest that these receptors may indeed function as the long-sought-after membrane progesterone receptors. Additionally, we show that two uncharacterized PAQRs, PAQR6 and PAQR9, are also capable of responding to progesterone. These mPR-like PAQRs have been renamed as mPRdelta (PAQR6) and mPRvarepsilon (PAQR9). Additional characterization of mPRgamma and mPRalpha indicates that their progesterone-dependent signaling in yeast does not require heterotrimeric G-proteins, thus calling into question the characterization of the mPRs as a novel class of G-protein coupled receptor.

Responses of pathogenic and nonpathogenic yeast species to steroids reveal the functioning and evolution of multidrug resistance transcriptional networks

Steroids are known to induce pleiotropic drug resistance states in hemiascomycetes, with tremendous potential consequences for human fungal infections. Our analysis of gene expression in Saccharomyces cerevisiae and Candida albicans cells subjected to three different concentrations of progesterone revealed that their pleiotropic drug resistance (PDR) networks were strikingly sensitive to steroids. In S. cerevisiae, 20 of the Pdr1p/Pdr3p target genes, including PDR3 itself, were rapidly induced by progesterone, which mimics the effects of PDR1 gain-of-function alleles. This unique property allowed us to decipher the respective roles of Pdr1p and Pdr3p in PDR induction and to define functional modules among their target genes. Although the expression profiles of the major PDR transporters encoding genes ScPDR5 and CaCDR1 were similar, the S. cerevisiae global PDR response to progesterone was only partly conserved in C. albicans. In particular, the role of Tac1p, the main C. albicans PDR regulator, in the progesterone response was apparently restricted to five genes. These results suggest that the C. albicans and S. cerevisiae PDR networks, although sharing a conserved core regarding the regulation of membrane properties, have different structures and properties. Additionally, our data indicate that other as yet undiscovered regulators may second Tac1p in the C. albicans drug response.

A genome-wide steroid response study of the major human fungal pathogen Candida albicans

In the absence of steroid receptors and any known mechanism of gene regulation by steroid hormones in Candida albicans, we did a genome-wide analysis of C. albicans cells treated with progesterone using Eurogentec cDNA microarrays to find the complete repertoire of steroid responsive genes. Northern blotting analysis was employed to validate the genes that were differentially regulated by progesterone in the microarray experiments. A total of 99 genes were found to be significantly regulated by progesterone, among them 60 were up-regulated and 39 were down-regulated. It was observed that progesterone considerably enhanced the expression of multi-drug resistance (MDR) genes belonging to ATP Binding Cassette (CDR1 and CDR2) super-family of multidrug transporters, suggesting a possible relationship between steroid stress and MDR genes. Several genes associated with hyphal induction and the establishment of pathogenesis were also found up-regulated. In silico search for various transcription factor (TF) binding sites in the promoter of the affected genes revealed that EFG1, CPH1, NRG1, TUP1, MIG1 and AP-1 regulated genes are responsive to progesterone. The stress responsive elements (STRE; AG(4) or C(4)T) were also found in the promoters of several responsive genes. Our data sheds new light on the regulation of gene expression in C. albicans by human steroids, and its correlation with drug resistance, virulence, morphogenesis and general stress response. A comparison with drug induced stress response has also been discussed.

Screening of target-specific stress-responsive genes for the development of cell-based biosensors using a DNA microarray

In this study, we describe a straightforward strategy to develop whole cell-based biosensors using fusions of the bacterial bioluminescence genes and the promoters from chemically responsive genes within Escherichia coli, in which chemical target-responsive genes were screened by using the information of gene expression data obtained from DNA microarray analysis. Paraquat was used as a model chemical to trigger gene expression changes of E. coli and to show the DNA microarray-assisted development of whole cell-based biosensors. Gene expression data from the DNA microarray were obtained by time course analysis (10, 30, and 60 min) after exposure to paraquat. After clustering gene expression data obtained by time course analysis, a group of highly expressed genes over the all time courses could be classified. Within this group, three genes expressed highly for overall time points were selected and promoters of these genes were used as fusion partners with reporter genes, lux CDABE, to construct whole cell-based biosensors. The constructed biosensors recognized the presence of model inducer, paraquat, and structural analogue chemicals of paraquat with a high specificity, and the results were reconfirmed by using DNA microarray experiments for those structural analogues. This strategy to develop whole cell-based biosensors assisted by DNA microarray information should be useful in general for constructing chemical-specific or stress-specific biosensors with a high-throughput manner.

Cigarette smoke extract induces changes in growth and gene expression of Saccharomyces cerevisiae

The response of Saccharomyces cerevisiae cells to an aqueous extract of cigarette smoke was studied. Exposure to cigarette smoke extract inhibits yeast growth and results in global changes in gene expression spanning many functional classes of genes. Genes involved in response to oxidative stress are upregulated after a brief exposure to cigarette smoke extract. The effects of cigarette smoke extract on yeast growth can be reversed by treatment with anti-oxidants. Mutants lacking superoxide dismutase gene were hypersensitive to cigarette smoke exposure. YAP1 is a central transcriptional regulator of oxidative stress in yeast. YAP1 dependent expression of beta-galactosidase was enhanced following exposure to cigarette smoke. The overall agreement between our observations and the recently reported effects of cigarette smoke on gene expression in rodent and human cells suggests that yeast can be used as a model system in toxicogenomics studies for monitoring toxic agents and studying the cellular and molecular consequences of exposure to potentially toxic agents.

Global Analysis of the Hortaea werneckii Proteome: Studying Steroid Response in Yeast

The response of the halophilic black yeast Hortaea werneckii to the steroid hormone progesterone has been studied at the protein level using fluorescent two-dimensional differential gel electrophoresis (2D-DIGE) technology in combination with mass spectrometry. Data on protein identification from this study reveal molecular mechanisms of the response to progesterone. In particular, the overexpression of Pck2 and Pac2 in the stimulated cells indicates the interactions of progesterone with the cell growth and reproduction signaling pathways.

In vitro bioactivity of 17alpha-estradiol

A miniaturised short-term in vitro assay based on the activation of the human estrogen receptor alpha and genetically modified yeast (Saccharomyces cerevisiae) cells was performed to explore the capacity of this system to monitor the bioactivity of estrogenic compounds, particularly 17alpha- and 17beta-estradiol. Together with the human estrogen receptor (hER)-alpha plasmid, the reporter plasmid containing a yeast-optimised version of the green fluorescent protein (yEGFP) linked to three repeats of the cis-acting estrogen hormone-responsive element (ERE) were expressed in a strain being deleted in the pleiotropic drug resistance transporters Pdr5, Snq2 and Yor1, known to facilitate efflux of organic compounds including steroids and chemotherapeutics. Agonists that bind to hER in vitro trigger estrogen receptor-mediated transcriptional activation of the GFP reporter gene monitored by fluorescence emission at 535 nm. The sensitivity of the assay was tested with various 17alpha- and 17beta-estradiol concentrations, yielding a detection limit of 5 pg/ml (0.018 nM) for the agonist 17beta-E2 in solvent and in human charcoal-stripped serum using a S. cerevisiae pdr5, snq2 and yor1 mutant strain. For 17alpha-estradiol only, at approximately 1500 pg/ml a similar fluorescence response compared to 100 pg/ml 17beta-E2 was observed implicating a much weaker potency of this stereoisomer. The specificity of the system was tested by expression of a truncated hER lacking the ligand-binding domain E and by administration of the androgen, 4-androsten 3,17 dione. Both controls did not yield an increase in fluorescence emission. This fluorescence emission assay enables detection of estrogenic biological activity induced by direct agonists, such as 17beta-E2 at concentrations similar to those found in human sera or by estrogen-like chemicals.