The ABC transporter Pdr5p mediates the efflux of nonsteroidal ecdysone agonists in Saccharomyces cerevisiae

We have previously shown that the synthetic nonsteroidal ecdysone agonist tebufenozide (RH-5992) is actively excluded by resistant cells of insects. To identify the transporter that could be involved in the efflux of RH-5992, the role of three ATP binding cassette transporters, Pdr5p, Snq2p and Ycf1p, has been studied using transporter-deletion mutants of yeast Saccharomyces cerevisiae. PDR5 (pleiotropic drug resistance 5) deletion mutants (Δpdr5 and Δpdr5Δsnq2) retained significantly higher levels of ¹⁴C-radiolabeled RH-5992 within the cells when compared to wild-type strain or single deletion mutants of SNQ2 (Δsnq2) and YCF1 (Δycf1). Introduction of an expression vector containing the PDR5 gene into the PDR5 single deletion mutant reversed the effect, resulting in the active exclusion of [¹⁴C]RH-5992 from these cells as efficiently as the wild-type cells. These results demonstrated that the ABC transporter Pdr5p but not Snq2p or Ycf1p was responsible for the active exclusion of [¹⁴C]RH-5992 in yeast. This exclusion was temperature-dependent and was blocked by the ATPase inhibitors oligomycin and vanadate, indicating that the efflux was an active process. The mutants with the PDR5 deletion can also selectively accumulate [¹⁴C]RH-0345 and [¹⁴C]RH-2485, but not [¹⁴C]RH-5849, indicating that these three compounds share the same transporter Pdr5p for efflux.