Candidiasis is the most common fungal infection, with an estimated 63,000 episodes of invasive candidiasis per year occurring in the United States, with a cost estimated at $2-4 billion. Although a diverse selection of pathogenic fungi have been isolated from clinical samples, the yeast species of the genus Candida are the predominant cause of opportunistic fungal infections, with Candida albicans the prevalent pathogen, causing an estimated 40% of cases of fungemia. For the last decade, Candida infections have been effectively treated with caspofungin, a major antifungal of the echinocandin class that interferes with cell wall synthesis. As antici- pated based on increased use of this drug, the number of reports of infections with caspofungin-resistant strains has increased, from 0.5% in 2001 to 3.1% in 2009, and so caspofungin resistance is expected to be- come a major concern in the near future. However, in contrast to the numerous and well-understood mecha- nisms of C. albicans resistance to fluconazole, little is known regarding the mechanism(s) of resistance to cas- pofungin. There is one recognized mechanism of caspofungin clinical resistance that involves point mutations in the FKS1 (orf19.2929) gene encoding a subunit of 1,3-?-D-glucan synthase required for normal synthesis of glucan, a major component of the cell wall. Formation of FKS1 mutations is always associated with therapeutic failure. Many other isolates from patients contain remodeled cell wall and show increase of resistance to cas- pofungin in laboratory experiments. This co-called cell wall salvage mechanism is associated with reversible alterations that strengthen the cell wall, particularly increased chitin. Our own data show that laboratory resistance to caspofungin can be attained via multiple molecular mech- anisms. When culturing C. albicans in the presence of caspofungin, we have observed the emergence of re- sistant strains monosomic for Ch5, indicating that negative regulators of resistance are resident on this chro- mosome. Monosomic Ch5 leads to decreased glucan and increased chitin in the cell wall. Cloning and charac- terization of the Ch5-linked genes involved in this regulator mechanism will help elucidate key molecular pathways of caspofungin resistance. Moreover, in preliminary studies, we have obtained evidence that Ch5 monosomy involves two-fold downregulation of the FKS1 (see above) or GSL2 genes, residing on Ch1 and ChR, respectively, and required for normal synthesis of cell wall glucan. Based on our findings, we hypothesize that Ch5 carries multiple genes required for normal synthesis of cell wall components. Loss of one Ch5 leads to increased laboratory resistance to drugs of the echinocandin class. In support of this hypothesis, our initial analyses have revealed two candidate genes on Ch5 that are likely to be involved in the mechanism of caspofungin resistance in monosomic strains. Here, we propose to initiate the study of the genes that encode negative regulators of caspofungin resistance. Our findings will be of high significance to clinicians and researchers investigating the phenomenon of drug resistance in C. albicans.

Public Health Relevance

Genetic factors determining Candida albicans resistance to an important antifungal caspofungin are poorly understood. We propose to initiate a study of network of factors that are uncovered by manipulating the copy number of chromosome 5. These factors control the components of cell wall and subsequently the laboratory resistance to caspofungin. Resistance associated with this control includes uncharacterized pathways that are distinct from previously recognized mechanisms for cell wall remodeling.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI110764-02
Application #
8903703
Study Section
Drug Discovery and Mechanisms of Antimicrobial Resistance Study Section (DDR)
Program Officer
Duncan, Rory A
Project Start
2014-08-15
Project End
2017-07-31
Budget Start
2015-08-01
Budget End
2016-07-31
Support Year
2
Fiscal Year
2015
Total Cost
Indirect Cost
Name
University of Rochester
Department
Biochemistry
Type
School of Medicine & Dentistry
DUNS #
041294109
City
Rochester
State
NY
Country
United States
Zip Code
14627
Suwunnakorn, Sumanun; Wakabayashi, Hironao; Kordalewska, Milena et al. (2018) FKS2 and FKS3 Genes of Opportunistic Human Pathogen Candida albicans Influence Echinocandin Susceptibility. Antimicrob Agents Chemother 62:
Tucker, Christopher; Bhattacharya, Soumyaroop; Wakabayashi, Hironao et al. (2018) Transcriptional Regulation on Aneuploid Chromosomes in Divers Candida albicans Mutants. Sci Rep 8:1630
Wakabayashi, Hironao; Tucker, Christopher; Bethlendy, Gabor et al. (2017) NuA4 histone acetyltransferase activity is required for H4 acetylation on a dosage-compensated monosomic chromosome that confers resistance to fungal toxins. Epigenetics Chromatin 10:49
Yang, Feng; Zhang, Lulu; Wakabayashi, Hironao et al. (2017) Tolerance to Caspofungin in Candida albicans Is Associated with at Least Three Distinctive Mechanisms That Govern Expression of FKS Genes and Cell Wall Remodeling. Antimicrob Agents Chemother 61:
Suwunnakorn, Sumanun; Wakabayashi, Hironao; Rustchenko, Elena (2016) Chromosome 5 of Human Pathogen Candida albicans Carries Multiple Genes for Negative Control of Caspofungin and Anidulafungin Susceptibility. Antimicrob Agents Chemother 60:7457-7467