title: 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.
abstract: In the pathogenic yeast Candida albicans, the zinc cluster transcription factor Upc2p has been shown to regulate the 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. Overexpression of UPC2 reduces azole susceptibility, whereas its disruption results in hypersusceptibility to azoles and reduced accumulation of exogenous sterols. Overexpression of ERG11 leads to the 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 upregulated with ERG11 in a fluconazole-resistant clinical isolate 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 upregulation 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 the increased expression of ERG11 and imparts resistance to fluconazole in clinical isolates of C. albicans.
authors.affiliation: Institut für Molekulare Infektionsbiologie, Universität Würzburg, Röntgenring 11, D-97070 Würzburg, Germany.
authors.forename: Nico
authors.initials: N
authors.lastname: Dunkel
authors.forename: Teresa T
authors.initials: TT
authors.lastname: Liu
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Barker
authors.forename: Ramin
authors.initials: R
authors.lastname: Homayouni
authors.forename: Joachim
authors.initials: J
authors.lastname: Morschhäuser
authors.forename: P David
authors.initials: PD
authors.lastname: Rogers
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology; D002176:Candida albicans / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D002177:Candidiasis / Q000382:microbiology*; D018389:Codon, Nonsense; D025141:Drug Resistance, Fungal; D004875:Ergosterol / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D015725:Fluconazole / Q000494:pharmacology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006801:Humans; D009154:Mutation; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D000935:Antifungal Agents; D018389:Codon, Nonsense; D005656:Fungal Proteins; D014157:Transcription Factors; D015725:Fluconazole; D004875:Ergosterol