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

Dunkel, Nico; Liu, Teresa T.; Barker, Katherine S.; Homayouni, Ramin; Morschhäuser, Joachim; Rogers, P. David

doi:10.1128/ec.00103-08

Cited by 206 publications

(185 citation statements)

References 51 publications

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“…Tac1p was also shown to activate the transcription of CDR1 and CDR2 upon cell treatment with different compounds such as fluphenazine (FPZ) and steroids (estrogen, progesterone) (6), but the mechanisms by which these compounds trigger Tac1p activity are still unknown. Similarly, gain-of-function mutations in two other zinc cluster transcription factors, Mrr1p and Upc2p, have recently been shown to be responsible for the constitutive upregulation of Mdr1p and Erg11p, respectively, in clinical A r isolates (10,22). These data confirmed the involvement of different transcriptional pathways in the upregulation of the CDR1/CDR2, MDR1, and ERG11 genes in A r isolates.…”

supporting

confidence: 73%

Relative Contributions of the Candida albicans ABC Transporters Cdr1p and Cdr2p to Clinical Azole Resistance

Tsao

Rahkhoodaee

Raymond

2009

Antimicrob Agents Chemother

111

101

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Candida albicans frequently develops resistance to treatment with azole drugs due to the acquisition of gain-of-function mutations in the transcription factor Tac1p. Tac1p hyperactivation in azole-resistant isolates results in the constitutive overexpression of several genes, including CDR1 and CDR2, which encode two homologous transporters of the ATP-binding cassette family. Functional studies of Cdr1p and Cdr2p have been carried out so far by heterologous expression in the budding yeast Saccharomyces cerevisiae and by gene deletion or overexpression in azole-sensitive C. albicans strains in which CDR1 expression is low and CDR2 expression is undetectable. Thus, the direct demonstration that CDR1 and CDR2 overexpression causes azole resistance in clinical strains is still lacking, as is our knowledge of the relative contribution of each transporter to clinical azole resistance. In the present study, we used the SAT1 flipper system to delete the CDR1 and CDR2 genes from clinical isolate 5674. This strain is resistant to several azole derivatives due to a strong hyperactive mutation in Tac1p and expresses high levels of Cdr1p and Cdr2p. We found that deleting CDR1 had a major effect, reducing resistance to fluconazole (FLC), ketoconazole (KTC), and itraconazole (ITC) by 6-, 4-, and 8-fold, respectively. Deleting CDR2 had a much weaker effect, reducing FLC or KTC resistance by 1.5-fold, and had no effect on ITC resistance. These results demonstrate that Cdr1p is a major determinant of azole resistance in strain 5674 and potentially in other clinical strains overexpressing Cdr1p and Cdr2p, while Cdr2p plays a more minor role.Candida albicans is one of the leading causes of fungal infections affecting immunocompromised individuals. Candida infections range from chronic superficial infections of the skin and mucosal surfaces to invasive, life-threatening systemic infections (21, 38). Many antifungal drugs used to treat Candida infections target the biosynthesis of ergosterol, the major sterol in the fungal cell membranes (24). Polyenes, such as amphotericin B (AMB), directly bind to ergosterol and form pores in the cell membrane, resulting in low selectivity and high toxicity (24). Azoles, a class of well-tolerated antifungal drugs that includes fluconazole (FLC), ketoconazole (KTC), itraconazole (ITC), and new-generation derivatives such as voriconazole and posaconazole, target the enzyme lanosterol 14␣-demethylase (Erg11p), which is involved in ergosterol biosynthesis, blocking the production of ergosterol and causing the accumulation of toxic intermediate sterol species (24). As a consequence, the fluidity and permeability of the fungal cell membrane are changed and the activity of membrane-bound proteins, such as enzymes involved in cell wall synthesis, is altered (24).However, the fungistatic rather than fungicidal action of azole drugs leads to the frequent emergence of azole-resistant (A r ) C. albicans strains (1, 44). One mechanism of azole resistance consists of increased levels of ERG11 RNA, resulting in i...

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supporting

confidence: 73%

Relative Contributions of the Candida albicans ABC Transporters Cdr1p and Cdr2p to Clinical Azole Resistance

Tsao

Rahkhoodaee

Raymond

2009

Antimicrob Agents Chemother

111

101

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“…Upc2 also binds to two distinct regions in its own promoter to autoregulate expression during azole exposure (229). Furthermore, G648D and G643A point mutations in Upc2 cause a hyperactivation of the transcription factor, resulting in the overexpression of ergosterol biosynthesis genes and increased fluconazole resistance (164,223). These mutations have been identified in C. albicans clinical isolates (223).…”

Section: Alteration Of the Drug Targetmentioning

confidence: 99%

Regulatory Circuitry Governing Fungal Development, Drug Resistance, and Disease

Shapiro

Robbins

Cowen

2011

Microbiol Mol Biol Rev

492

547

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SUMMARY Pathogenic fungi have become a leading cause of human mortality due to the increasing frequency of fungal infections in immunocompromised populations and the limited armamentarium of clinically useful antifungal drugs. Candida albicans , Cryptococcus neoformans , and Aspergillus fumigatus are the leading causes of opportunistic fungal infections. In these diverse pathogenic fungi, complex signal transduction cascades are critical for sensing environmental changes and mediating appropriate cellular responses. For C. albicans , several environmental cues regulate a morphogenetic switch from yeast to filamentous growth, a reversible transition important for virulence. Many of the signaling cascades regulating morphogenesis are also required for cells to adapt and survive the cellular stresses imposed by antifungal drugs. Many of these signaling networks are conserved in C. neoformans and A. fumigatus , which undergo distinct morphogenetic programs during specific phases of their life cycles. Furthermore, the key mechanisms of fungal drug resistance, including alterations of the drug target, overexpression of drug efflux transporters, and alteration of cellular stress responses, are conserved between these species. This review focuses on the circuitry regulating fungal morphogenesis and drug resistance and the impact of these pathways on virulence. Although the three human-pathogenic fungi highlighted in this review are those most frequently encountered in the clinic, they represent a minute fraction of fungal diversity. Exploration of the conservation and divergence of core signal transduction pathways across C. albicans , C. neoformans , and A. fumigatus provides a foundation for the study of a broader diversity of pathogenic fungi and a platform for the development of new therapeutic strategies for fungal disease.

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“…Resistance to azole drugs is partly due to the alteration of the ergosterol biosynthetic pathway. Many gain-offunction mutations in Upc2 that contribute to the drug resistance were identified in clinical isolates 8 . Mutations in the C-terminal domain (CTD) of Upc2 (A643V, A643T or G648D in C. albicans Upc2) result in the constitutive activation of the transcription factor (TF), resulting in the upregulation of ergosterol synthesis pathway and sterol uptake, which leads to a decreased susceptibility of the strains to azole drugs 9,10 .…”

mentioning

confidence: 99%

“…Candida albicans is responsible for a large proportion of infections in immunocompromised individuals and the emergence of drug-resistant strains is of medical concern 8 . Resistance to azole drugs is partly due to the alteration of the ergosterol biosynthetic pathway.…”

mentioning

confidence: 99%

Structural mechanism of ergosterol regulation by fungal sterol transcription factor Upc2

et al. 2015

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Transcriptional regulation of ergosterol biosynthesis in fungi is crucial for sterol homeostasis and for resistance to azole drugs. In Saccharomyces cerevisiae, the Upc2 transcription factor activates the expression of related genes in response to sterol depletion by poorly understood mechanisms. We have determined the structure of the C-terminal domain (CTD) of Upc2, which displays a novel a-helical fold with a deep hydrophobic pocket. We discovered that the conserved CTD is a ligand-binding domain and senses the ergosterol level in the cell. Ergosterol binding represses its transcription activity, while dissociation of the ligand leads to relocalization of Upc2 from cytosol to nucleus for transcriptional activation. The C-terminal activation loop is essential for ligand binding and for transcriptional regulation. Our findings highlight that Upc2 represents a novel class of fungal zinc cluster transcription factors, which can serve as a target for the developments of antifungal therapeutics.

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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

Cited by 206 publications

References 51 publications

Relative Contributions of the Candida albicans ABC Transporters Cdr1p and Cdr2p to Clinical Azole Resistance

Relative Contributions of the Candida albicans ABC Transporters Cdr1p and Cdr2p to Clinical Azole Resistance

Regulatory Circuitry Governing Fungal Development, Drug Resistance, and Disease

Structural mechanism of ergosterol regulation by fungal sterol transcription factor Upc2

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