Fungal pathogens are a leading cause of human mortality, at least in part due to their ability to thwart therapeutic regimens by rapidly evolving resistance to antifungal drugs, and as a consequence of the increasing frequency of immunocompromised individuals most vulnerable to
fungal infection. Candida albicans, the leading human fungal pathogen, has evolved an elegant repertoire of mechanisms to survive the cellular stress exerted by the azoles, which are the most
widely deployed class of antifungals and inhibit ergosterol biosynthesis, inducing cell membrane stress. The evolution and maintenance of diverse resistance phenotypes is contingent upon cellular stress response circuitry, including that regulated by the molecular chaperone Hsp90 and its client protein calcineurin. My doctoral research focuses on three aspects of the role of fungal stress responses in regulation of azole resistance. First, I establish a novel role for nutrients and nutrient signalling in azole resistance of C. albicans and the model yeast Saccharomyces cerevisiae. Compromising a global regulator that couples growth to environmental cues, Tor
kinase, provides a powerful strategy to abrogate fungal drug resistance with broad therapeutic potential. Second, I implicate the molecular chaperone Hsp90 as a key regulator of biofilm drug resistance in C. albicans. Compromising Hsp90 function transforms the azoles from ineffective to highly efficacious at eradicating biofilms in vitro and in vivo. Depletion of Hsp90 leads to reduction of client proteins’ calcineurin and Mkc1 in planktonic but not biofilm conditions, suggesting that Hsp90 regulates drug resistance through different mechanisms in these distinct
cellular states. Third, I establish that inhibition of lysine deacetylases (KDACs) blocks the emergence and maintenance of Hsp90-dependent azole resistance in C. albicans and S. cerevisiae. S. cerevisiae Hsp90 is acetylated on lysine 27 and 270, and key KDACs for drug
resistance are Hda1 and Rpd3. Compromising KDACs alters stability and function of Hsp90 client proteins, including drug resistance regulator calcineurin. Overall, this work provides novel insight into the mechanisms by which cellular stress responses mediate azole resistance, and establishes acetylation as a novel mechanism of post-translational control of Hsp90 function in fungi; ultimately, this unveils numerous targets that could be exploited for therapeutic benefit in the treatment of fungal disease.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/35941 |
| Date | 09 August 2013 |
| Creators | Robbins, Nicole |
| Contributors | Cowen, Leah |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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