The Hsp90 Co-chaperones Sti1, Aha1, and P23 Regulate Adaptive Responses to Antifungal Azoles.

Xiaokui Gu,Yajing Yin,Xianyun Sun,Wei Xue,Shaojie Li,Hongwei Liu

doi:10.3389/fmicb.2016.01571

Abstract

Heat Shock Protein 90 (Hsp90) is essential for tumor progression in humans and drug resistance in fungi. However, the roles of its many co-chaperones in antifungal resistance are unknown. In this study, by susceptibility test of Neurospora crassa mutants lacking each of 18 Hsp90/Calcineurin system member genes (including 8 Hsp90 co-chaperone genes) to antifungal drugs and other stresses, we demonstrate that the Hsp90 co-chaperones Sti1 (Hop1 in yeast), Aha1, and P23 (Sba1 in yeast) were required for the basal resistance to antifungal azoles and heat stress. Deletion of any of them resulted in hypersensitivity to azoles and heat. Liquid chromatography–mass spectrometry (LC-MS) analysis showed that the toxic sterols eburicol and 14α-methyl-3,6-diol were significantly accumulated in the sti1 and p23 deletion mutants after ketoconazole treatment, which has been shown before to led to cell membrane stress. At the transcriptional level, Aha1, Sti1, and P23 positively regulate responses to ketoconazole stress by erg11 and erg6, key genes in the ergosterol biosynthetic pathway. Aha1, Sti1, and P23 are highly conserved in fungi, and sti1 and p23 deletion also increased the susceptibility to azoles in Fusarium verticillioides. These results indicate that Hsp90-cochaperones Aha1, Sti1, and P23 are critical for the basal azole resistance and could be potential targets for developing new antifungal agents.

Highlights

Invasive fungal diseases (IFDs), primarily caused by yeast-like fungi (e.g., Candida albicans and Cryptococcus neoformans) and filamentous fungi (e.g., Aspergillus fumigatus), are life-threatening infections with high morbidity and mortality in human, especially for immunocompromised patients, such as cancer patients undergoing chemotherapy and transplant recipients
By susceptibility test of N. crassa mutants lacking each of Heat Shock Protein 90 (Hsp90) orchestrates member genes [hsp80, hsp70-1, hsp70-2, hsp70-3, p23, aha1, sti1, cdc37, nup-17 (PPIase), nup-5 (PPIase B), nup-13 (PPIase H), and fkr-5 (PPIase FKBP-type)], calcineurin encoding genes, Hsp90/calcineurin-dependent stress responses genes and other heat shock protein family genes to antifungal drug ketoconazole, we found that the Hsp90 co-chaperones Sti1, Aha1, and P23 participated in adaptive responses to azoles
Calcineurin plays a pivotal role in the basal resistance to antifungal azoles in C. albicans, C. neoformans, and A. fumigatus (Juvvadi et al, 2016)

Summary

Introduction

Invasive fungal diseases (IFDs), primarily caused by yeast-like fungi (e.g., Candida albicans and Cryptococcus neoformans) and filamentous fungi (e.g., Aspergillus fumigatus), are life-threatening infections with high morbidity and mortality in human, especially for immunocompromised patients, such as cancer patients undergoing chemotherapy and transplant recipients. The most widely used antifungal agents, are still applied as the first-line therapy to treat patients suffering from IFDs because their side effects are lower than the “gold standard” polyenes such as Amphotericin B (AMB; Laniado-Laborín and Cabrales-Vargas, 2009). Azole-resistant pathogenic fungi have frequently been isolated (Sheehan et al, 1999; Snelders et al, 2008; Howard et al, 2009). Surveillance studies indicate that azole-resistant A. fumigatus has spread throughout Europe, Asia, and Africa and can be detected in environmental and clinical settings (Howard et al, 2009; Bueid et al, 2010; Denning and Perlin, 2011). The evolution of antifungal resistance could render first-line azole treatment obsolete.

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