title: A member of the aldoketo reductase family confers methotrexate resistance in Leishmania.
abstract: Methotrexate (MTX)-resistant mutants of the parasitic protozoan Leishmania have been used as models for the mechanism and genetic basis of drug resistance in trypanosomatids and other cells. Three resistance mechanisms to MTX, a dihydrofolate reductase inhibitor, have been described in Leishmania: decreased uptake and accumulation of MTX via the folate/MTX transporter, amplification and overexpression of the dihydrofolate reductase-thymidylate synthase gene, and extrachromosomal amplification of H region DNA. We have now identified hmtxr as the H region gene conferring MTX resistance using a transfection-based approach. Data base searches show that the predicted HMTXr protein is related to members of the polyol dehydrogenase/carbonyl reductase family of aldoketo reductases, whose substrates include polyols, quinones, steroids, prostaglandins, fatty acids, and pterins. We therefore propose that HMTXr is also an oxidoreductase and suggest several biochemical mechanisms of resistance in Leishmania that could be exploited in the design of parasite-specific inhibitors.
authors.affiliation: Harvard Medical School, Department of Biological Chemistry and Molecular Pharmacology, Boston, Massachusetts 02115.
authors.forename: H L
authors.initials: HL
authors.lastname: Callahan
authors.forename: S M
authors.initials: SM
authors.lastname: Beverley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D004351:Drug Resistance / Q000235:genetics*; D006801:Humans; D007891:Leishmania / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D008727:Methotrexate / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D016366:Open Reading Frames; D010088:Oxidoreductases / Q000235:genetics*; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D013940:Thymidylate Synthase / Q000235:genetics*; D014162:Transfection
chemical_list: D009838:Oligodeoxyribonucleotides; D004247:DNA; D010088:Oxidoreductases; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase; D008727:Methotrexate