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Eukaryotic Cell doi:10.1128/EC.00103-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A Gain-of-function Mutation in the Transcription Factor Upc2p Causes Upregulation of Ergosterol Biosynthesis Genes and Increased Fluconazole Resistance in a Clinical Candida albicans Isolate

Institut für Molekulare Infektionsbiologie, Universität Würzburg, Röntgenring 11, D-97070 Würzburg, Germany; Departments of Clinical Pharmacy, Pharmaceutical Sciences, Molecular Sciences, and Pediatrics, University of Tennessee Health Science Center, Memphis, Tennessee, 38163; Children's Foundation Research Center of Memphis, Le Bonheur Children's Medical Center, Memphis, Tennessee 38103; Bioinformatics Program, University of Memphis, Memphis, Tennessee 38152; Department of Biology, University of Memphis, Memphis, Tennessee 38152

^* To whom correspondence should be addressed. Email: joachim.morschhaeuser{at}mail.uni-wuerzburg.de. drogers{at}utmem.edu.

	Abstract

In the pathogenic yeast Candida albicans, the zinc cluster transcription factor Upc2p has been shown to regulate expression of ERG11 and other genes involved in ergosterol biosynthesis upon exposure to azole antifungals. ERG11 encodes lanosterol demethylase, the target enzyme of this antifungal class. Over-expression of UPC2 reduces azole susceptibility, whereas its disruption results in hypersusceptibility to azoles and reduced accumulation of exogenous sterols. Over-expression of ERG11 leads to increased production of lanosterol demethylase, which contributes to azole resistance in clinical isolates of C. albicans, but the mechanism for this has yet to be determined. Using genome-wide gene expression profiling, we found UPC2 and other genes involved in ergosterol biosynthesis to be coordinately up-regulated with ERG11 in a fluconazole-resistant clinical isolate as compared with a matched susceptible isolate from the same patient. Sequence analysis of the UPC2 alleles of these isolates revealed that the resistant isolate contained a single nucleotide substitution in one UPC2 allele that resulted in a G648D exchange in the encoded protein. Introduction of the mutated allele into a drug susceptible strain resulted in constitutive up-regulation of ERG11 and increased resistance to fluconazole. By comparing the gene expression profiles of the fluconazole-resistant isolate and of strains carrying wild-type and mutated UPC2 alleles, we identified target genes that are controlled by Upc2p. Here we show for the first time that a gain-of-function mutation in UPC2 leads to increased expression of ERG11 and imparts resistance to fluconazole in clinical isolates of C. albicans.