Candida species are the fourth most common cause of hospital-acquired blood-stream infections in the United States with mortality rates approaching 50%. Treatment of candidiasis is hampered by the limited number of antifungal drugs whose efficacy is compromised by host toxicity, fungistatic activity, and the emergence of drug resistance. I established a new role for the essential molecular chaperone Hsp90 and the protein phosphatase calcineurin in regulating resistance to cell wall stress exerted by the echinocandins, the only new class of antifungal drug to reach the clinic in decades, in both Candida albicans and Candida glabrata, the two leading causes of candidiasis. Through reciprocal co-immunoprecipitation studies, calcineurin activation studies, and protein stability assays, I established calcineurin as the first client protein of Hsp90 in C. albicans. I found that the calcineurin downstream effector Crz1 plays only a partial role in mediating tolerance to the echinocandins in C. albicans, implicating additional downstream effectors. Complementary studies in the model organism Saccharomyces cerevisiae revealed a divergence in the requirement of Hsp90 and calcineurin in this species’ ability to tolerate echinocandins despite a conserved functional relationship
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between Hsp90 and calcineurin. I also provided the first global view of mutations that accompany the evolution of fungal drug resistance in a human host. I found an association of mutations in CDC6 and MOH1 with echinocandin resistance in unrelated C. glabrata clinical isolates, genes previously not implicated in echinocandin resistance. I propose a new model by which Hsp90 and calcineurin regulate echinocandin resistance by controlling expression of the resistance determinant FKS2. Taken together, my research reveals new mechanisms mediating antifungal drug resistance and suggests new therapeutic strategies to save human lives.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/32891 |
| Date | 31 August 2012 |
| Creators | Singh, Sheena |
| Contributors | Cowen, Leah |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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