The yeast plasma membrane
protein Agp2 belongs to the family of
amino acid transporters. It acts as a regulator that controls the expression of several uptake transporter genes such as DUR3 and SAM3 encoding two high-affinity
polyamine permeases. agp2Δ mutants display extreme resistance to several cationic compounds including
polyamines, the
anticancer agent bleomycin, and cationic antifungal
peptides. We propose that Agp2 might be involved in regulating the uptake of other cationic anticancer drugs. To date, an uptake transporter has not been reported for
anthracyclines, a family of chemotherapeutic agents that are used for treating adult patients with
acute myeloid leukemia. Herein, we develop assay conditions to monitor the uptake of the
anthracycline doxorubicin into yeast cells and demonstrate for the first time that Agp2 is required for the
drug uptake. Deletion of both the DUR3 and SAM3 genes reduced
doxorubicin uptake, but not the deletion of either gene alone, while the agp2Δ mutant was severely compromised, suggesting that Agp2 controls the
drug uptake via Dur3 and Sam3 and at least one additional transporter. Overexpression of DUR3 or SAM3 from the endogenous promoter rescued
doxorubicin uptake into the sam3Δdur3Δ double mutant, consistent with a role for these transporters in the uptake of
anthracyclines. We further show by cross-species complementation analysis that expression of the Caenorhabditis elegans oct-1 gene encoding an organic
cation transporter restored full
doxorubicin uptake in the agp2Δ mutant. Four separate variants of CeOCT-1 derived by substituting the
amino acid residues Gln15, Cys31, Gln109 and Lys300 with
alanine were stably expressed, but did not mediate
doxorubicin uptake into the agp2Δ mutant. Moreover, we show that overexpression of CeOCT-1 sensitized parent yeast cells to
doxorubicin, suggesting that CeOCT-1 related members might be key transporters to facilitate entry of
anthracyclines into human cells.