cDNA array analysis of the differential expression change in virulence-related genes during the development of resistance in Candida albicans

A semisynthetic borrelidin analogue BN-3b exerts potent antifungal activity against Candida albicans through ROS-mediated oxidative damage

In the process of investigating the antifungal structure-activity relationships (SAR) of borrelidin and discovering antifungal leads, a semisynthetic borrelidin analogue, BN-3b with antifungal activity against Candida albicans, was achieved. In this study, we found that oxidative damage induced by endogenous reactive oxygen species (ROS) plays an important role in the antifungal activity of BN-3b. Further investigation indicated that BN-3b stimulated ROS accumulation, increased malondialdehyde (MDA) levels, and decreased reduced/oxidized glutathione (GSH/GSSG) ratio. Moreover, BN-3b decreased mitochondrial membrane potential (MMP) and ATP generation. Ultrastructure analysis revealed that BN-3b severely damaged the cell membrane of C. albicans. Quantitative PCR (RT-qPCR) analysis revealed that virulence factors of C. albicans SAPs, PLB1, PLB2, HWP1, ALSs, and LIPs were all down-regulated after BN-3b exposure. We also found that BN-3b markedly inhibited the hyphal formation of C. albicans. In addition, in vivo studies revealed that BN-3b significantly prolonged survival and decreased fungal burden in mouse model of disseminated candidiasis.

Non-steroidal anti-inflammatory drugs may modulate the protease activity of Candida albicans

The phenotypic pressure exerted by non-steroidal anti-inflammatory drugs (NSAIDs) on autochthonous and pathogenic microbiota remains sparsely known. In this study, we investigated if some NSAIDs increment or diminish the secretion of aspartyl-proteases (Sap) by Candida albicans grown under different phenotypes and oxygen availability using a set of SAP knock-out mutants and other set for genes (EFG1 and CPH1) that codify transcription factors involved in filamentation and protease secretion. Pre-conditioned cells were grown under planktonic and biofilm phenotypes, in normoxia and anoxia, in the presence of plasma concentrations of acetylsalicylic acid, diclofenac, indomethacin, nimesulide, piroxicam, ibuprofen, and acetaminophen. For diclofenac, indomethacin, nimesulide, and piroxicam the secretion rates of Sap by SAP1-6, EFG1, and CPH1 mutants were similar or, even, inferior to parental wild-type strain. This suggests that neither Sap 1-6 isoenzymes nor Efg1/Cph1 pathways may be entirely responsible for protease release when exposed to these NSAIDs. Ibuprofen and acetaminophen enhanced Sap secretion rates in three environmental conditions (normoxic biofilm, normoxic planktonic and anoxic planktonic). In other hand, aspirin seems to reduce the Sap-related pathogenic behavior of candidal biofilms. Modulation of Sap activity may occur according to candidal phenotypic state, oxygen availability, and type of NSAID to which the cells are exposed.

Roles of the Snf1-activating kinases during nitrogen limitation and pseudohyphal differentiation in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, Snf1 protein kinase is important for growth on carbon sources that are less preferred than glucose. When glucose becomes limiting, Snf1 undergoes catalytic activation, which requires phosphorylation of its T-loop threonine (Thr210). Thr210 phosphorylation can be performed by any of three Snf1-activating kinases: Sak1, Tos3, and Elm1. These kinases are redundant in that all three must be eliminated to confer snf1Delta-like growth defects on nonpreferred carbon sources. We previously showed that in addition to glucose signaling, Snf1 also participates in nitrogen signaling and is required for diploid pseudohyphal differentiation, a filamentous-growth response to nitrogen limitation. Here, we addressed the roles of the Snf1-activating kinases in this process. Loss of Sak1 caused a defect in pseudohyphal differentiation, whereas Tos3 and Elm1 were dispensable. Sak1 was also required for increased Thr210 phosphorylation of Snf1 under nitrogen-limiting conditions. Expression of a catalytically hyperactive version of Snf1 restored pseudohyphal differentiation in the sak1Delta/sak1Delta mutant. Thus, while the Snf1-activating kinases exhibit redundancy for growth on nonpreferred carbon sources, the loss of Sak1 alone produced a significant defect in a nitrogen-regulated phenotype, and this defect resulted from deficient Snf1 activation rather than from disruption of another pathway. Our results suggest that Sak1 is involved in nitrogen signaling upstream of Snf1.

Detection of endogenous Snf1 and its activation state: application to Saccharomyces and Candida species

The stress-response Snf1 protein kinase of Saccharomyces cerevisiae serves as a powerful model for studies of the eukaryotic Snf1/AMP-activated protein kinase (AMPK) family. Central to studies of Snf1 are methods that determine its activation state under various physiological and genetic conditions. Here, we have developed a convenient and sensitive method for immunoblot analysis of endogenous yeast Snf1 and its activation-loop threonine (Thr210) phosphorylation. The method employs readily obtainable reagents and yields results that faithfully reflect the environmental and genetic conditions tested. Using our method, we have obtained evidence that Snf1 remains stress-regulated in reg1 Delta cells, revealing the existence of a Snf1 signalling mechanism(s) that is independent of Reg1-PP1 phosphatase. In addition to strains of common laboratory S. cerevisiae backgrounds, we have applied the method to two pathogenic Candida species, C. glabrata and C. albicans. We have detected proteins whose gel mobilities, immune properties and regulation patterns are consistent with those expected for the corresponding Snf1 homologues. Because Snf1 activation is a sensitive marker of several types of stress, including artifactual stresses associated with common cell harvesting and protein extraction procedures, the convenient and efficient protein extraction method described here should be advantageous for SDS-PAGE and immunoblot analyses of stress-regulated and other proteins from various yeast species.

DNA microarray analysis of fluconazole resistance in a laboratory Candida albicans strain

Several mechanisms are responsible for the acquired fluconazole (FLC) resistance in Candida albicans. In this study, we developed a FLC-resistant C. albicans strain through serial cultures of a FLC-susceptible C. albicans strain with inhibitory concentrations of FLC. Complimentary DNA microarray analysis and real-time reverse transcription-polymerase chain reaction were used to investigate gene expression changes during the acquisition of azole resistance in the susceptible parental strain and the resistant daughter strain. The differentially expressed genes represented functions as diverse as transporters (e.g. CDR1, PDR17), ergosterol biosynthesis (e.g. ERG2, ERG9), sterol metabolism (e.g. ARE2, IPF6464), energy metabolism (e.g. ADH3, AOX2) and transcription factors (e.g. FCR1, ECM22). Functional analysis revealed that energy-dependent efflux activity of membrane transporters increased and that ergosterol content decreased with the accumulation of sterol intermediates in the resistant strain as compared with the susceptible strain. We found that a point mutation (N977K) in transcription factor TAC1 that resulted in hyperactivity of Tac1 could be the reason for overexpression of CDR1, CDR2, and PDR17 in the resistant strain. Furthermore, a single amino acid difference (D19E) in ERG3 that led to the inactivation of Erg3 could account for both sterol precursor accumulation and the changes in the expression of ergosterol biosynthesis genes in this resistant strain. These findings expand the understanding of potential novel molecular targets of FLC resistance in clinical C. albicans isolates.

Candida albicans THI13 disruption affects production of monocytic cytokines

INTRODUCTION

The Candida albicansTHI13 gene was identified by its homology to the Candida tropicalis CtNMT1 gene, which is involved in pyrimidine precursor biosynthesis.

METHODS

Disruption of THI13 revealed that this gene played a minor role in thiamin biosynthesis in C. albicans. Purified human monocytes were incubated with C. albicans at the optimal Candida: monocyte ratio of 0.5 and cytokines in the supernatants were measured by enzyme-linked immunosorbent assay.

RESULTS AND DISCUSSION

This experiment showed that the wild-type strain significantly induced interleukin-10 (IL-10) production but had little effect on IL-12 production, and that THI13 mutants had no significant effect on IL-10 production, though the IL-12 level was increased in the supernatants. These results suggest that THI13 is involved in the host effective immune response by regulating IL-10 and IL-12 production.

CaIPF7817 is involved in the regulation of redox homeostasis in Candida albicans

CaIPF7817, a functionally unknown gene in Candida albicans, was suggested to be involved in the redox system previously, but its exact role is unknown. In this study, ipf7817 null mutant was generated with the URA-blaster method. After the deletion of CaIPF7817, intracellular levels of reactive oxygen species were significantly increased; mitochondrial membrane potential, a direct indicator of mitochondrial function, was elevated; some important redox-related genes, including GLR1, SOD2, and TRR1, were up-regulated; and the GSH/GSSG ratio was raised. These changes indicated that CaIPF7817 played important roles in the regulation of redox homeostasis in C. albicans.

Barrier activity in Candida albicans mediates pheromone degradation and promotes mating

Mating in Candida albicans and Saccharomyces cerevisiae is regulated by the secretion of peptide pheromones that initiate the mating process. An important regulator of pheromone activity in S. cerevisiae is barrier activity, involving an extracellular aspartyl protease encoded by the BAR1 gene that degrades the alpha pheromone. We have characterized an equivalent barrier activity in C. albicans and demonstrate that the loss of C. albicans BAR1 activity results in opaque a cells exhibiting hypersensitivity to alpha pheromone. Hypersensitivity to pheromone is clearly seen in halo assays; in response to alpha pheromone, a lawn of C. albicans Deltabar1 mutant cells produces a marked zone in which cell growth is inhibited, whereas wild-type strains fail to show halo formation. C. albicans mutants lacking BAR1 also exhibit a striking mating defect in a cells, but not in alpha cells, due to overstimulation of the response to alpha pheromone. The block to mating occurs prior to cell fusion, as very few mating zygotes were observed in mixes of Deltabar1 a and alpha cells. Finally, in a barrier assay using a highly pheromone-sensitive strain, we were able to demonstrate that barrier activity in C. albicans is dependent on Bar1p. These studies reveal that a barrier activity to alpha pheromone exists in C. albicans and that the activity is analogous to that caused by Bar1p in S. cerevisiae.

cDNA microarray analysis of differential gene expression and regulation in clinically drug-resistant isolates of Candida albicans from bone marrow transplanted patients

Fungi have emerged as the fourth most common pathogens isolated in nosocomial bloodstream infections, and Candida albicans is the most common human fungal pathogen. Only a few antibiotics are effective in the treatment of fungal infections. In addition, the repetition and lengthy duration of fluconazole therapy has led to an increased incidence of azole resistance and treatment failure associated with C. albicans. To investigate the mechanism of drug resistance and explore new targets to treat clinically resistant fungal pathogens, we examined the large-scale gene expression profile of two sets of matched fluconazole-susceptible and -resistant bloodstream C. albicans isolates from bone marrow transplanted (BMT) patients for the first time by microarray analysis. More than 198 differentially expressed genes were identified and they were confirmed and validated by RT-PCR independently. Not surprisingly, the resistant phenotype is associated with increased expression of CDR mRNA, as well as some common genes involved in drug resistance such as CaIFU5, CaRTA2 and CaIFD6. Meanwhile, some special functional groups of genes, including ATP binding cassette (ABC) transporter genes (IPF7530, CaYOR1, CaPXA1), oxidative stress response genes (CaALD5, CaGRP1, CaSOD2, IPF10565), copper transport and iron mobilization-related genes (CaCRD1/2, CaCTR1/2, CaCCC2, CaFET3) were found to be differentially expressed in the resistant isolates. Furthermore, among these differentially expressed genes, some co-regulated with CaCDR1, CaCDR2 and CaIFU5, such as CaPDR16 and CaIFD6, have a DRE-like element and may interact with TAC1 in the promoter region. These findings may shed light on mechanisms of azole resistance in C. albicans and clinical antifungal therapy.