Function of Candida glabrata ABC transporter gene, PDH1

The rapid increase in azole resistance during treatment of patients infected with Candida glabrata may be due to increased azole efflux mediated by ABC transporters, as occurs with increased expression of PDR5 in Saccharomyces cerevisiae. Two known C. glabrata homologues of PDR5 influencing azole susceptibility are PDH1 (CgCDR2) and CgCDR1. Disruption of PDH1 in a cgcdr1::ura3 strain increased susceptibility to rhodamine 6G, cycloheximide and chloramphenicol, and also increased rhodamine 6G accumulation, all properties of pdr5 null mutants. Overexpression of PDH1 in S. cerevisiae complemented the pdr5 mutation by reversing susceptibility to rhodamine 6G, chloramphenicol and cycloheximide, as well as by decreasing rhodamine 6G intracellular concentration. Expression of PDH1 in a C. glabrata cgcdr1::ura3 pdh1Delta::ura3 mutant using a multicopy plasmid almost completely restored the wild-type phenotype, showing that PDH1 at higher levels of expression can replace CgCDR1. Because PDH1 and CgCDR1 have both been reported to have upstream sequences similar to the Pdr1p- and Pdr3p-binding elements of PDR5, we sought similarities in regulation between the three genes. Abundance of PDH1 and CgCDR1 mRNA in C. glabrata was increased by rhodamine 6G, cycloheximide and oligomycin, properties in common with PDR5. PDH1, CgCDR1 and PDR5 have striking similarities in function and regulation.