Novel role for the Saccharomyces cerevisiae oligopeptide transporter Opt2 in drug detoxification

Saccharomyces cerevisiae Opt2 is a member of the oligopeptide transporter family that was initially identified to transport tetra- and pentapeptides. Mutants deleted for the OPT2 gene exhibit no growth defects under normal culture conditions. We identified OPT2 from a high-throughput screen that when deleted results in mutants that displayed sensitivity to the anticancer agent bleomycin. The opt2Δ mutant was also reisolated in two additional genome-wide screens designed to identify mutants that are sensitive to the immunosuppressant rapamycin and the divalent metal ion zinc. However, t he role of Opt2 in protecting cells against these agents was not investigated. Herein, we show that opt2A mutants are also sensitive to a wide variety of toxic agents that are typically detoxified by the vacuoles. Mutants lacking two other related oligop eptide transporters, Opt1 and Yg1114w, showed no significant sensitivities to these drugs, indicating a specific role for Opt2 in drug detoxification. The sensitivities of the opt2Δ mutants were not related to an increased drug uptake but rather to the presence of several small vesicles instead of a functional large vacuole. We propose that Opt2 has a novel function involving the fusion of vesicles to form a mature vacuole. Key words: bleomycin, polyamines, divalent ions, sensitivity, vital dye, vacuolar morphology. Resume: Chez Saccaromyces cerevisiae, Opt2 est un membre de la famille des transporteurs d'oligopeptides d'abord identifie dans le transport des tetra- et des pentapeptides. Les mutants de deletion du gene OPT2 ne presentent pas de defauts de croissance en conditions de culture normales. Nous avons identifie OPT2 lors d'un criblage a haut debit qui, lorsque supprime, produit des mutants sensibles a la bleomycine, un agent anticancereux. Le mutant opt2Δ a aussi ete isole de nouveau, lors de deux criblages additionnels sur tout le genome ayant pour but d'identifier des mutants sensibles a l'immunosuppresseur rapamycine et au zinc, un ion metallique divalent. Cependant, le role de Opt2 dans la protection des cellules contre ces agents n'avait pas ete examine. Nous montrons ici que les mutants opt2Δ sont aussi sensibles a une grande variete d'agents toxiques typiquement detoxiques par les vacuoles. Les mutants deficients en deux autres transporteurs d'oligopeptides, Opt1 et Yg1114w, ne montraient aucune sensibilite significative envers ces drogues, indiquant que Opt2 joue un role specifique dans la detoxication des drogues. La sensibilite des mutants opt2Δ n'etait pas reliee a une augmentation de la captation de ces drogues, mais a la presence de plusieurs petites vesicules a la place d'une grande vacuole fonctionn elle. Nous proposons que Opt2 possede une nouvelle fonction impliquant la fusion des vesicules pour former une vacuole mature. Mots-cles : bleomycine, polyamines, ions divalents, sensibilite, colorant vital, morphologie vacuolaire. [Traduit par la Redaction]
Introduction All organisms have devised a mechanism involving cytoplasmic membrane transporters to specifically take up small peptides in the range of two to six amino acid residues (Hauser et al. [...]