Candida glabrata Drug:H+Antiporter CgQdr2 Confers Imidazole Drug Resistance, Being Activated by Transcription Factor CgPdr1

Abstract

ABSTRACTThe widespread emergence of antifungal drug resistance poses a severe clinical problem. Though predicted to play a role in this phenomenon, the drug:H+antiporters (DHA) of the major facilitator superfamily have largely escaped characterization in pathogenic yeasts. This work describes the first DHA from the pathogenic yeastCandida glabratareported to be involved in antifungal drug resistance, theC. glabrata QDR2(CgQDR2) gene (ORFCAGL0G08624g). The expression ofCgQDR2inC. glabratawas found to confer resistance to the antifungal drugs miconazole, tioconazole, clotrimazole, and ketoconazole. By use of a green fluorescent protein (GFP) fusion, the CgQdr2 protein was found to be targeted to the plasma membrane inC. glabrata. In agreement with these observations,CgQDR2expression was found to decrease the intracellular accumulation of radiolabeled clotrimazole inC. glabrataand to play a role in the extrusion of this antifungal from preloaded cells. Interestingly, the functional heterologous expression ofCgQDR2in the model yeastSaccharomyces cerevisiaefurther confirmed the role of this gene as a multidrug resistance determinant: its expression was able to complement the susceptibility phenotype exhibited by itsS. cerevisiaehomologue,QDR2, in the presence of imidazoles and of the antimalarial and antiarrhythmic drug quinidine. In contrast to the findings reported for Qdr2, CgQdr2 expression does not contribute to the ability of yeast to grow under K+-limiting conditions. Interestingly,CgQDR2transcript levels were seen to be upregulated inC. glabratacells challenged with clotrimazole or quinidine. This upregulation was found to depend directly on the transcription factor CgPdr1, the major regulator of multidrug resistance in this pathogenic yeast, which has also been found to be a determinant of quinidine and clotrimazole resistance inC. glabrata.