The antifungal azoles (e.g., miconazole, fluconazole, and itraconazole) are widely used in the treatment of candidiasis and a variety of other fungal infections. Their use is increasingly compromised, however, by the innate resistance of certain fungi (e.g., Aspergillus and Candida glabrata) and acquired resistance in Candida albicans. Recent studies suggest that azole resistance in C. albicans is primarily mediated by overexpression of multi-drug resistance (MDR) efflux proteins, specifically ATP-binding cassette transporters (ABCT) and major facilitator superfamily transporters (MFST). We have used Saccharomyces cerevisiae as a genetic model to study MDR-mediated azole resistance and its regulation. Disruption of the S. cerevisiae ABCT gene PDR5 resulted in azole hypersensitivity. Previous studies suggest that the PDR5 gene is regulated by the related transcriptional activators PDR1 and PDR3. Consistent with this, a PDR1/PDR3 disruptant was also azole hypersensitive. Hybridization studies revealed that brief treatment of S. cerevisiae cultures with the azoles miconazole or clotrimazole resulted in a 5 to 10-fold induction of RNA specific to PDR5 and the related ABCT gene SNQ2. Similarly, transcription of the MFST gene FLR1 (but not the related ATR1) was induced by these azoles. Recent studies have shown that a second pair of transcriptional activators, YAP1 and YAP2, regulate the FLR1 and ATR1 genes, and overexpression of FLR1 confers fluconazole resistance. Consequently, we examined RNA induction by azoles in cultures of PDR1/PDR3 and YAP1/YAP2-disrupted S. cerevisiae. YAP1/YAP2 disruption decreased constitutive and azole induced expression of FLR1, but had no effect on the ABCT genes. PDR1/PDR3 disruption, on the other hand, blocked constitutive and induced expression of FLR1, PDR5, and SNQ2, demonstrating their central role in regulation of multidrug resistance. While YAP1/YAP2 homologs have been cloned from C. albicans and other fungi, a PDR1/PDR3 homolog has not as yet been identified outside of S. cerevisiae.
Full conference title:
38th Interscience Conference on Antimicrobial Agents and Chemotherapy
- ICAAC 38th