A novel screening for inhibitors of a pleiotropic drug resistant pump, Pdr5, in Saccharomyces cerevisiae

Yeast is an excellent model system of eukaryotes for the study of molecular mechanisms of ATP-binding cassette transporters. Pdr5 protein is a yeast S accharomyces cerevisiae ATP-binding cassette transporter conferring resista nce to several unrelated drugs. Here, we described a novel drug screening s ystem designated to detect compounds that inhibit the function of Pdr5. An indicator strain with increased drug sensitivity was constructed with an er gosterol-deficient background (Delta syr1/erg3 null mutation). The sensitiv ity of the indicator strain (Delta syr1/erg3 Delta pdr5 Delta snq2) to the Pdr5 substrates, cycloheximide and cerulenin, was increased 16-fold and 4-f old against wild type, respectively. The screening system is mainly based o n the growth inhibition of the PDR5-overexpressed indicator strain with the combination of a sample and cycloheximide or cerulenin. The effect of an m dr inhibitor, FK506 on the screening system was clearly detected even at a low concentration (similar to0.5 mug/ml). In addition, accumulation of rhod amine 6G in the cells was detected as a result of Pdr5 inhibition by FK506. These results indicated that the screening system is useful for a sensitiv e screening of Pdr5-specific inhibitors with low toxicity.