Multiple cis-acting sequences mediate upregulation of the MDR1 efflux pump in a fluconazole-resistant clinical Candida albicans isolate.

Overexpression of the MDR1 gene, which encodes a multidrug efflux pump of the major facilitator superfamily, is a frequent cause of resistance to the antimycotic agent fluconazole and other metabolic inhibitors in clinical Candida albicans strains. Constitutive MDR1 overexpression in such strains is caused by mutations in as yet unknown trans-regulatory factors. In order to identify the cis-acting sequences in the MDR1 regulatory region that mediate constitutive MDR1 upregulation, we performed a promoter deletion analysis in the genetic background of an MDR1-overexpressing clinical C. albicans isolate. We found that several different regions in the MDR1 promoter can mediate MDR1 overexpression in this isolate. In contrast, deletion of one of these regions abolished benomyl-induced MDR1 expression in a C. albicans laboratory strain. These results suggest that multiple transcription factors control expression of the MDR1 efflux pump in C. albicans and that the mutation(s) that causes constitutive MDR1 overexpression and drug resistance in clinical C. albicans isolates affects the activities of several of these transcription factors.