A common drug-responsive element mediates the upregulation of the Candida albicans ABC transporters CDR1 and CDR2, two genes involved in antifungal drug resistance

Upregulation of the ATP-binding cassette (ABC) transporter genes CDR1 and CDR2 (Candida drug resistance 1 and 2) is a common mechanism observed in Candida albicans clinical isolates developing resistance to the class of azole antifungals. In this work, the regulatory elements of both genes were delimited using a reporter system in an azole-susceptible strain exposed to oestradiol, which allows transient induction of these genes. We found two regulatory elements in the CDR1 promoter: one responsible for basal expression (basal expression element; BEE) and the other required for oestradiol responsiveness (drug-responsive element 1; DREI). In the CDR2 promoter, a single regulatory element responsible for oestradiol responsiveness (DREII) was detected. Both DREs shared a consensus of 21 bp with the sequence 5'-CGGA(A/T)ATCGGATAT-MTTTT-3' having no equivalent to known eukaryotic regulatory sequence. Consistent with this finding, two other C. albicans genes identified by a search for the presence of in the C. albicans genome sequence database were responsive to oestradiol. Finally, the regulatory elements found in CDR1 and CDR2 were also functional in an azole-resistant strain with constitutive high expression of both transporters. These results suggest that, although CDR1 and CDR2 upregulation can be obtained by transient drug-induced and constitutive upregulation, these two processes converge to the same regulatory elements and probably mobilize the same trans-acting factors.