Requirement for ergosterol in V-ATPase function underlies antifungal activity of azole drugs

• Published in: PLoS pathogens 2010-06, Vol.6 (6), p.e1000939
• Main Authors: Zhang, Yong-Qiang, Gamarra, Soledad, Garcia-Effron, Guillermo, Park, Steven, Perlin, David S, Rao, Rajini
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatase; Amiodarone - pharmacology; Animals; Antifungal Agents - pharmacology; Azoles (Class of compounds); Biochemistry/Membrane Proteins and Energy Transduction; Biosynthesis; Candida albicans - drug effects; Candida albicans - enzymology; Cell cycle; Drug dosages; Drug Synergism; Drug therapy; Enzyme Inhibitors - pharmacology; Ergosterol; Ergosterol - pharmacology; Female; Fluconazole - pharmacology; Fungal infections; Fungi; Health aspects; Homeostasis; Infectious Diseases/Antimicrobials and Drug Resistance; Mice; Mice, Inbred BALB C; Microbiology/Medical Microbiology; Mycoses; Pharmacology; Physiological aspects; Protons; Saccharomyces cerevisiae - drug effects; Saccharomyces cerevisiae - enzymology; Sterols; Vacuolar Proton-Translocating ATPases - antagonists & inhibitors; Vacuolar Proton-Translocating ATPases - metabolism; Vacuoles - enzymology
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1000939

Ergosterol is an important constituent of fungal membranes. Azoles inhibit ergosterol biosynthesis, although the cellular basis for their antifungal activity is not understood. We used multiple approaches to demonstrate a critical requirement for ergosterol in vacuolar H(+)-ATPase function, which is known to be essential for fungal virulence. Ergosterol biosynthesis mutants of S. cerevisiae failed to acidify the vacuole and exhibited multiple vma(-) phenotypes. Extraction of ergosterol from vacuolar membranes also inactivated V-ATPase without disrupting membrane association of its subdomains. In both S. cerevisiae and the fungal pathogen C. albicans, fluconazole impaired vacuolar acidification, whereas concomitant ergosterol feeding restored V-ATPase function and cell growth. Furthermore, fluconazole exacerbated cytosolic Ca(2+) and H(+) surges triggered by the antimicrobial agent amiodarone, and impaired Ca(2+) sequestration in purified vacuolar vesicles. These findings provide a mechanistic basis for the synergy between azoles and amiodarone observed in vitro. Moreover, we show the clinical potential of this synergy in treatment of systemic fungal infections using a murine model of Candidiasis. In summary, we demonstrate a new regulatory component in fungal V-ATPase function, a novel role for ergosterol in vacuolar ion homeostasis, a plausible cellular mechanism for azole toxicity in fungi, and preliminary in vivo evidence for synergism between two antifungal agents. New insights into the cellular basis of azole toxicity in fungi may broaden therapeutic regimens for patient populations afflicted with systemic fungal infections.