title: Expression of the CDR1 efflux pump in clinical Candida albicans isolates is controlled by a negative regulatory element.
abstract: Resistance to azole antifungal drugs in clinical isolates of the human fungal pathogen Candida albicans is often caused by constitutive overexpression of the CDR1 gene, which encodes a multidrug efflux pump of the ABC transporter superfamily. To understand the relevance of a recently identified negative regulatory element (NRE) in the CDR1 promoter for the control of CDR1 expression in the clinical scenario, we investigated the effect of mutation or deletion of the NRE on CDR1 expression in two matched pairs of azole-sensitive and resistant clinical isolates of C. albicans. Expression of GFP or lacZ reporter genes from the wild type CDR1 promoter was much higher in the azole-resistant C. albicans isolates than in the azole-susceptible isolates, reflecting the known differences in CDR1 expression in these strains. Deletion or mutation of the NRE resulted in enhanced reporter gene expression in azole-sensitive strains, but did not further increase the already high CDR1 promoter activity in the azole-resistant strains. In agreement with these findings, electrophoretic mobility shift assays showed a reduced binding to the NRE of nuclear extracts from the resistant C. albicans isolates as compared with extracts from the sensitive isolates. These results demonstrate that the NRE is involved in maintaining CDR1 expression at basal levels and that this repression is overcome in azole-resistant clinical C. albicans isolates, resulting in constitutive CDR1 overexpression and concomitant drug resistance.
authors.affiliation: Membrane Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India.
authors.forename: Naseem Akhtar
authors.initials: NA
authors.lastname: Gaur
authors.forename: Raman
authors.initials: R
authors.lastname: Manoharlal
authors.forename: Preeti
authors.initials: P
authors.lastname: Saini
authors.forename: Tulika
authors.initials: T
authors.lastname: Prasad
authors.forename: Gauranga
authors.initials: G
authors.lastname: Mukhopadhyay
authors.forename: Milan
authors.initials: M
authors.lastname: Hoefer
authors.forename: Joachim
authors.initials: J
authors.lastname: Morschhäuser
authors.forename: Rajendra
authors.initials: R
authors.lastname: Prasad
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D001393:Azoles / Q000494:pharmacology; D002176:Candida albicans / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004351:Drug Resistance / Q000502:physiology; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects / Q000502:physiology*; D005809:Genes, Regulator / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D001393:Azoles; C094693:CDR1 protein, Candida albicans; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins