Similarities and Distinctions in the Activation of the Pdr1 Regulatory Pathway by Azole and Non-azole Drugs

Incidences of fluconazole (FLC) resistance among clinical isolates is a growing issue in clinics. The pleiotropic drug response (PDR) network in . confers azole resistance and is defined primarily by the ZnCys zinc cluster-containing transcription factor Pdr1 and target genes such as , that encodes an ATP-binding cassette transporter protein thought to act as a FLC efflux pump. Mutations in the gene that render the transcription factor hyperactive are the most common cause of fluconazole resistance among clinical isolates. The phenothiazine class drug fluphenazine and a molecular derivative, CWHM-974, which both exhibit antifungal properties, have been shown to induce the expression of Cdr1 in spp. We have used a firefly luciferase reporter gene driven by the promoter to demonstrate two distinct patterns of promoter activation kinetics: gradual promoter activation kinetics that occur in response to ergosterol limitations imposed by exposure to azole and polyene class antifungals and a robust and rapid induction occurring in response to the stress imposed by fluphenazines. We can attribute these different patterns of induction as proceeding through the promoter region of this gene since this is the only segment of the gene included in the luciferase reporter construct. Genetic analysis indicates that the signaling pathways responsible for phenothiazine and azole induction of overlap but are not identical. The short time course of phenothiazine induction suggests that these compounds may act more directly on the Pdr1 protein to stimulate its activity.