Abstract
5-Flucytosine is currently used as an antifungal drug in combination therapy, but fungal pathogens are rapidly able to develop resistance against this drug, compromising its therapeutic action. The understanding of the underlying resistance mechanisms is crucial to deal with this problem. In this work, the S. cerevisiae deletion mutant collection was screened for increased resistance to flucytosine. Through this chemogenomics analysis, 183 genes were found to confer resistance to this antifungal agent. Consistent with its known effect in DNA, RNA and protein synthesis, the most significant Gene Ontology terms over-represented in the list of 5-flucytosine resistance determinants are related to DNA repair, RNA and protein metabolism. Additional functional classes include carbohydrate and nitrogen—particularly arginine—metabolism, lipid metabolism and cell wall remodeling. Based on the results obtained for S. cerevisiae as a model system, further studies were conducted in the pathogenic yeast Candida glabrata. Arginine supplementation was found to relieve the inhibitory effect exerted by 5-flucytosine in C. glabrata. Lyticase susceptibility was found to increase within the first 30min of 5-flucytosine exposure, suggesting this antifungal drug to act as a cell wall damaging agent. Upon exponential growth resumption in the presence of 5-flucytosine, the cell wall exhibited higher resistance to lyticase, suggesting that cell wall remodeling occurs in response to 5-flucytosine. Additionally, the aquaglyceroporin encoding genes CgFPS1 and CgFPS2, from C. glabrata, were identified as determinants of 5-flucytosine resistance. CgFPS1 and CgFPS2 were found to mediate 5-flucytosine resistance, by decreasing 5-flucytosine accumulation in C. glabrata cells.
Highlights
Systemic fungal infections are a problem of increasing clinical significance, in particular for immunocompromised patients, and especially since the extensive use of antifungal drugs, both as treatment and prophylaxis, has led to an increase in the number of infections withPLOS ONE | DOI:10.1371/journal.pone.0135110 August 12, 2015Genome-Wide Flucytosine Resistance in Yeast intrinsically resistant fungal pathogens [1,2]
Since CgFps1 is predicted to be an integral membrane protein, these results strongly suggest a plasma membrane localization, similar to what was observed for its S. cerevisiae homolog Fps1
The deletion of CgFPS1 was found to exert a stronger effect in flucytosine accumulation than that of CgFPS2, which appears to be consistent with the effect of the deletion of each gene in the susceptibility to this antifungal drug. These results strongly suggests that CgFps1 and CgFps2 activities increase C. glabrata resistance towards 5-flucytosine by reducing its accumulation within yeast cells
Summary
Systemic fungal infections are a problem of increasing clinical significance, in particular for immunocompromised patients, and especially since the extensive use of antifungal drugs, both as treatment and prophylaxis, has led to an increase in the number of infections withPLOS ONE | DOI:10.1371/journal.pone.0135110 August 12, 2015Genome-Wide Flucytosine Resistance in Yeast intrinsically resistant fungal pathogens [1,2]. The antifungal drug 5-flucytosine is a fluorinated pyrimidine which enters fungal cells through one or more permeases [3,4,5] and is converted, by cytosine deaminase, to its metabolically active form 5-fluorouracil (5-FU) [3,4,6]. This antifungal drug acts by inhibiting transcription, DNA replication and protein synthesis [3,6]. Despite these side-effects, 5-flucytosine it is still used in clinical treatments, mostly in combination with azoles, such as fluconazole, or amphotericin B, for the treatment of Cryptoccoci infections [6]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
