AP1-mediated Multidrug Resistance in Saccharomyces cerevisiae Requires FLR1 Encoding a Transporter of the Major Facilitator Superfamily

Abstract We have isolated a Candida albicansgene that confers resistance to the azole derivative fluconazole (FCZ) when overexpressed in Saccharomyces cerevisiae. This gene encodes a protein highly homologous to S. cerevisiae yAP-1, a bZip transcription factor known to mediate cellular resistance to toxicants such as cycloheximide (CYH), 4-nitroquinolineN-oxide (4-NQO), cadmium, and hydrogen peroxide. The gene was named CAP1, for C. albicansAP-1 . Cap1 and yAP-1 are functional homologues, since CAP1 expression in a yap1mutant strain partially restores the ability of the cells to grow on toxic concentrations of cadmium or hydrogen peroxide. We have found that the expression of YBR008c, an open reading frame identified in the yeast genome sequencing project and predicted to code for a multidrug transporter of the major facilitator superfamily, is dramatically induced in S. cerevisiae cells overexpressingCAP1. Overexpression of either CAP1 orYAP1 in a wild-type strain results in resistance to FCZ, CYH, and 4-NQO, whereas such resistance is completely abrogated (FCZ and CYH) or strongly reduced (4-NQO) in a ybr008c deletion mutant, demonstrating that YBR008c is involved inYAP1- and CAP1-mediated multidrug resistance.YBR008c has been renamed FLR1, forfluconazole resistance 1. The expression of an FLR1-lacZ reporter construct is strongly induced by the overexpression of either CAP1 orYAP1, indicating that the FLR1 gene is transcriptionally regulated by the Cap1 and yAP-1 proteins. Taken collectively, our results demonstrate that FLR1 represents a new YAP1-controlled multidrug resistance molecular determinant in S. cerevisiae. A similar detoxification pathway is also likely to operate in C. albicans.