Zap1 is required for Candida glabrata response to fluconazole

The increasing prevalence of fluconazole-resistant clinical isolates of Candida spp. strongly hinders the widespread use of the drug. To tackle this problem, great efforts have been made to fully understand the fungal response to fluconazole. In this work, we show that the role of Zap1 in Candida glabrata goes beyond regulating yeast adaptation to zinc deficiency. In line with our previous observation that deletion of ZAP1 makes yeast cells more sensitive to fluconazole, we found that the mutant CgΔzap1 accumulates higher levels of the drug, which correlates well with its lower levels of ergosterol. Surprisingly, Zap1 is a negative regulator of the drug efflux transporter gene CDR1 and of its regulator, PDR1. The apparent paradox of drug accumulation in cells where genes encoding transporters relevant for drug extrusion are being overexpressed led us to postulate that their activity could be impaired. In agreement, Zap1-depleted cells present, in addition to decreased ergosterol levels, an altered composition of membrane phospholipids, which together should impact membrane function and impair the detoxification of fluconazole. Overall, our study brings to light Zap1 as an important hub in Candida glabrata response to fluconazole.

Copper overload in Paracoccidioides lutzii results in the accumulation of ergosterol and melanin

Paracoccidioidomycosis is a highly prevalent systemic mycosis in Latin America, caused by fungi of the genus Paracoccidioides. Copper is essential for eukaryotes and bacteria. This micronutrient is used in many vital biochemical processes, although metal excess levels can be toxic for organisms. Pathways underlying copper overload are poorly understood in members of the Paracoccidioides complex. The responses of Paracoccidioides lutzii yeast cells to copper overload were here evaluated. The results showed that under copper overload, cells presented a dark brown pigment, identified as melanin. Proteomic analyses identified mainly the accumulation of proteins related to amino acids metabolism, ergosterol synthesis and melanin production, suggesting that P. lutzii responds to copper overload by changing aspects of its metabolism and also plasma membrane and cell wall remodeling. Proteomic data were confirmed by biochemical analysis.

Monovalent cation transporters at the plasma membrane in yeasts

Maintenance of proper intracellular concentrations of monovalent cations, mainly sodium and potassium, is a requirement for survival of any cell. In the budding yeast Saccharomyces cerevisiae, monovalent cation homeostasis is determined by the active extrusion of protons through the Pma1 H⁺ -ATPase (reviewed in another chapter of this issue), the influx and efflux of these cations through the plasma membrane transporters (reviewed in this chapter), and the sequestration of toxic cations into the vacuoles. Here, we will describe the structure, function, and regulation of the plasma membrane transporters Trk1, Trk2, Tok1, Nha1, and Ena1, which play a key role in maintaining physiological intracellular concentrations of Na⁺ , K⁺ , and H⁺ , both under normal growth conditions and in response to stress.

Influence of phenothiazines, phenazines and phenoxazine on cation transport in Candida albicans

AIMS

(i) To analyse the increase in calcium ion uptake caused by several cationic dyes on Candida albicans, (ii) to postulate a mechanism, (iii) to define the effects of Zn ions on the phenomenon, and (iv) to propose the use of the dyes or their derivatives against C. albicans.

METHODS AND RESULTS

Cells were grown in yeast peptone dextrose medium and starved. We measured the hydrophobic solvent/water partition coefficients and the dyes uptake by the cells and found no correlation with their hydrophobicity. Most of the dyes caused an increase in K+ efflux (in correlation with a decrease in 86 Rb+ uptake), and a raise in Ca2+ uptake except for those used as Zn salts, but not of their HCl salts. Respiration and acidification of the medium were modified only with few dyes and interestingly, when exposing cultures to nile blue, neutral red and toluidine blue ZnCl2 a decrease in C. albicans growth was observed.

CONCLUSIONS

We propose a general mechanism for the stimulation of Ca2+ uptake by the dyes used. Some of the dyes tested might be used as agents against C. albicans, probably combined with other agents. Moreover, the effects of Zn ions on Ca2+ uptake and on cell growth open possibilities of further studies, not only of their effects, but also of the mechanism of Ca2+ transport in C. albicans and other yeasts.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study, in conjunction with previously published results, contribute to the basic research regarding ion transport in C. albicans and the role of zinc in this process. Besides, suggests the additional use of dyes, along with other antifungals agents, as combined therapy against candidiasis. Derived dyes from those used also might be possible therapeutic agents against this disease.

Potassium Uptake Mediated by Trk1 Is Crucial for Candida glabrata Growth and Fitness

The maintenance of potassium homeostasis is crucial for all types of cells, including Candida glabrata. Three types of plasma-membrane systems mediating potassium influx with different transport mechanisms have been described in yeasts: the Trk1 uniporter, the Hak cation-proton symporter and the Acu ATPase. The C. glabrata genome contains only one gene encoding putative system for potassium uptake, the Trk1 uniporter. Therefore, its importance in maintaining adequate levels of intracellular potassium appears to be critical for C. glabrata cells. In this study, we first confirmed the potassium-uptake activity of the identified gene’s product by heterologous expression in a suitable S. cerevisiae mutant, further we generated a corresponding deletion mutant in C. glabrata and analysed its phenotype in detail. The obtained results show a pleiotropic effect on the cell physiology when CgTRK1 is deleted, affecting not only the ability of trk1Δ to grow at low potassium concentrations, but also the tolerance to toxic alkali-metal cations and cationic drugs, as well as the membrane potential and intracellular pH. Taken together, our results find the sole potassium uptake system in C. glabrata cells to be a promising target in the search for its specific inhibitors and in developing new antifungal drugs.

Tfp1 is required for ion homeostasis, fluconazole resistance and N-Acetylglucosamine utilization in Candida albicans

The vacuolar-type H+-ATPase (V-ATPase) is crucial for the maintenance of ion homeostasis. Dysregulation of ion homeostasis affects various aspects of cellular processes. However, the importance of V-ATPase in Candida albicans is not totally clear. In this study, we demonstrated the essential roles of V-ATPase through Tfp1, a putative V-ATPase subunit. Deletion of TFP1 led to generation of an iron starvation signal and reduced total iron content, which was associated with mislocalization of Fet34p that was finally due to disorders in copper homeostasis. Furthermore, the tfp1∆/∆ mutant exhibited weaker growth and lower aconitase activity on nonfermentable carbon sources, and iron or copper addition partially rescued the growth defect. In addition, the tfp1∆/∆ mutant also showed elevated cytosolic calcium levels in normal or low calcium medium that were relevant to calcium release from vacuole. Kinetics of cytosolic calcium response to an alkaline pulse and VCX1 (VCX1 encodes a putative vacuolar Ca2+/H+ exchanger) overexpression assays indicated that the cytosolic calcium status was in relation to Vcx1 activity. Spot assay and concentration-kill curve demonstrated that the tfp1∆/∆ mutant was hypersensitive to fluconazole, which was attributed to reduced ergosterol biosynthesis and CDR1 efflux pump activity, and iron/calcium dysregulation. Interestingly, carbon source utilization tests found the tfp1∆/∆ mutant was defective for growth on N-Acetylglucosamine (GlcNAc) plate, which was associated with ATP depletion due to the decreased ability to catabolize GlcNAc. Taken together, our study gives new insights into functions of Tfp1, and provides the potential to better exploit V-ATPase as an antifungal target.

Stress response and expression of fluconazole resistance associated genes in the pathogenic yeast Candida glabrata deleted in the CgPDR16 gene

In yeasts, the PDR16 gene encodes a phosphatidylinositol transfer protein which belongs to the Sec14 homologue (SFH) family and localizes to lipid droplets, microsomes and at the cell periphery. The loss of its function alters the lipid droplet metabolism and plasma membrane properties, and renders yeast cells more sensitive to azole antimycotics. In this study, the entire chromosomal CgPDR16 ORF was replaced by the ScURA3 gene both in azole sensitive and azole resistant strains of Candida glabrata bearing a gain-of-function mutation in the CgPDR1 gene, and their responses to different stresses were assessed. The CgPDR16 deletion was found to sensitize the mutant strains to azole antifungals without changes in their osmo- and halotolerance. Fluconazole treated pdr16Δ mutant strains displayed a reduced expression of several genes involved in azole tolerance. The gain-of-function CgPDR1 allele as well as the cycloheximide and hydrogen peroxide treatments of cells enhanced the expression of the CgPDR16 gene. The results indicate that CgPDR16 belongs to genes whose expression is induced by chemical and oxidative stresses. The loss of its function can attenuate the expression of drug efflux pump encoding genes that might also contribute to the decreased azole tolerance in pdr16Δ mutant cells.