Regulation of the CgPdr1 Transcription Factor from the Pathogen Candida glabrata
ABSTRACTCandida glabratais an opportunistic human pathogen that is increasingly associated with candidemia, owing in part to the intrinsic and acquired high tolerance the organism exhibits for the important clinical antifungal drug fluconazole. This elevated fluconazole resistance often develops through gain-of-function mutations in the zinc cluster-containing transcriptional regulatorC. glabrataPdr1 (CgPdr1). CgPdr1 induces the expression of an ATP-binding cassette (ABC) transporter-encoding gene, CgCDR1.Saccharomyces cerevisiaehas two CgPdr1 homologues called ScPdr1 and ScPdr3. These factors control the expression of an ABC transporter-encoding gene called ScPDR5, which encodes a homologue of CgCDR1. Loss of the mitochondrial genome (ρ0cell) or overexpression of the mitochondrial enzyme ScPsd1 induces ScPDR5expression in a strictly ScPdr3-dependent fashion. ScPdr3 requires the presence of a transcriptional Mediator subunit called Gal11 (Med15) to fully induce ScPDR5transcription in response to ρ0signaling. ScPdr1 does not respond to either ρ0signals or ScPsd1 overproduction. In this study, we employed transcriptional fusions between CgPdr1 target promoters, like CgCDR1, to demonstrate that CgPdr1 stimulates gene expression via binding to elements called pleiotropic drug response elements (PDREs). Deletion mapping and electrophoretic mobility shift assays demonstrated that a single PDRE in the CgCDR1promoter was capable of supporting ρ0-induced gene expression. Removal of one of the two ScGal11 homologues fromC. glabratacaused a major defect in drug-induced expression of CgCDR1but had a quantitatively minor effect on ρ0-stimulated transcription. These data demonstrate that CgPdr1 appears to combine features of ScPdr1 and ScPdr3 to produce a transcription factor with chimeric regulatory properties.