Inducible and Constitutive Activation of Two Polymorphic Promoter Alleles of the Candida albicans Multidrug Efflux Pump MDR1

Abstract

Overexpression of the multidrug efflux pump MDR1 confers resistance to the antifungal drug fluconazole on Candida albicans. It has been reported that two types of MDR1 promoters exist in C. albicans and that homozygosity for the allele with higher activity may promote fluconazole resistance. We found that the two MDR1 promoter alleles in strain SC5314 were equally well activated by inducing chemicals or hyperactive forms of the transcription factors Mrr1 and Cap1, which control MDR1 expression. In addition, no loss of heterozygosity at the MDR1 locus was observed in MDR1-overexpressing clinical C. albicans strains that developed fluconazole resistance during therapy. Infections by the fungal pathogen Candida albicans are commonly treated with fluconazole, an antifungal drug that inhibits ergosterol biosynthesis. C. albicans can develop resistance to fluconazole during therapy by various mechanisms, including mutations in the ERG11 gene, which encodes the drug target enzyme; overexpression of ERG11; or upregulation of multidrug efflux pumps that transport fluconazole out of the cell (16). The constitutive overexpression of efflux pumps in fluconazole-resistant strains is caused by gain-of-function mutations in the transcriptional regulators Mrr1 and Tac1, which control the expression of the major facilitator MDR1 and the ABC transporters CDR1 and CDR2, respectively (17). As C. albicans is a diploid organism, resistance mutations first occur in one of the two alleles of a gene. This is frequently followed by loss of heterozygosity, which further increases the drug resistance of the resulting homozygous strains. Indeed, loss of heterozygosity has been observed in many fluconazole-resistant clinical isolates containing mutations in ERG11, MRR1,14,18,29). Similarly, loss of heterozygosity has also been found in a fluconazole-resistant strain with a gainof-function mutation in Upc2, the transcriptional regulator of ERG11 and other ergosterol biosynthesis genes (9).The diploid genome of C. albicans exhibits a high degree of heterozygosity (12). In a given strain, the two alleles of a gene usually are not identical but differ from one another to various degrees. It has been recently reported that two types of MDR1 alleles exist in C. albicans which can be distinguished by specific polymorphic nucleotides in the promoter region (2). One of these promoter alleles was found to confer higher MDR1 expression than the other allele. Many clinical isolates contained two alleles of the higher-activity type, whereas strains containing only the less active allele were rare, and it was suggested that the higher-activity alleles of the MDR1 promoter could promote the development of drug resistance (2). These observations indicated that in strains containing both types of MDR1 alleles, loss of heterozygosity would be an additional mechanism of increased drug resistance.In most C. albicans strains, including reference strain SC5314, MDR1 is not significantly expressed under standard growth conditions, but it is induced in the presence...

Research of Mrr1, Cap1 and MDR1 in Candida albicans resistant to azole medications

“…Furthermore, it has been reported that Spt-Ada-Gcn5-acetyltransferase complex subunit Ada2 promotes Cap1-mediated upregulation of the multidrug efflux pump MDR1 in fluconazole-resistant C. albicans ( 11 ). Additionally, a study by Sasse et al ( 12 ) demonstrated that two polymorphic promoter alleles in MDR1 may be associated with the development of fluconazole resistance. A study by Wang et al ( 13 ) identified mutations in the EGR11 gene in azole-resistant C. albicans .…”

Mutations in transcription factor Mrr2p contribute to fluconazole resistance in clinical isolates of Candida albicans

“…Several mechanisms that contribute to fluconazole resistance in C. albicans have been elucidated, including increased drug efflux and mutations or overexpression of the ERG11 gene, which encodes lanosterol 14␣-demethylase [4][5][6]. Point mutations in ERG11 contribute to decreased binding affinity of azoles for their target enzyme Erg11p and increased azole resistance.…”

Broad sensitivity ofCandida aurisstrains to quinolones and mechanisms of resistance

“…Cap1 is a transcriptional regulator. In C. albicans, it promotes expression of the major facilitator superfamily (MFS) drug transporter MDR1, and it has been reported that C-terminal truncations of CAP1, like those we isolated from our drug-resistance screen, cause a hyperactive phenotype which increases MDR1 expression and thereby increases fluconazole resistance (61)(62)(63)(64). To test whether this is also the case with our resistant C. auris CAP1 mutants, we used RT-qPCR to examine the levels of MDR1 expression along with two other drug transporters: CDR1 and CDR2.…”