title: Drosophila ABC transporter, DmHMT-1, confers tolerance to cadmium. DmHMT-1 and its yeast homolog, SpHMT-1, are not essential for vacuolar phytochelatin sequestration.
abstract: Half-molecule ATP-binding cassette transporters of the HMT-1 (heavy metal tolerance factor 1) subfamily are required for Cd2+ tolerance in Schizosaccharomyces pombe, Caenorhabditis elegans, and Chlamydomonas reinhardtii. Based on studies of S. pombe, it has been proposed that SpHMT-1 transports heavy metal.phytochelatin (PC) complexes into the vacuolysosomal compartment. PCs are glutathione derivatives synthesized by PC synthases (PCS) in plants, fungi, and C. elegans in response to heavy metals. Our previous studies in C. elegans, however, suggested that HMT-1 and PCS-1 do not necessarily act in concert in metal detoxification. To further explore this inconsistency, we have gone on to test whether DmHMT-1, an HMT-1 from a new source, Drosophila, whose genome lacks PCS homologs, functions in heavy metal detoxification. In so doing, we show that heterologously expressed DmHMT-1 suppresses the Cd2+ hypersensitivity of S. pombe hmt-1 mutants and localizes to the vacuolar membrane but does not transport Cd.PC complexes. Crucially, similar analyses of S. pombe hmt-1 mutants extend this finding to show that SpHMT-1 itself either does not transport Cd.PC complexes or is not the principal Cd.PC/apoPC transporter. Consistent with this discovery and with our previous suggestion that HMT-1 and PCS-1 do not operate in a simple linear metal detoxification pathway, we demonstrate that, unlike PCS-deficient cells, which are hypersensitive to several heavy metals, SpHMT-1-deficient cells are hypersensitive to Cd2+, but not to Hg2+ or As3+. These findings significantly change our current understanding of the function of HMT-1 proteins and invoke a PC-independent role for these transporters in Cd2+ detoxification.
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Thanwalee
authors.initials: T
authors.lastname: Sooksa-Nguan
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Bakhtiyor
authors.initials: B
authors.lastname: Yakubov
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Volodymyr I
authors.initials: VI
authors.lastname: Kozlovskyy
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Caitlin M
authors.initials: CM
authors.lastname: Barkume
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Howe
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Theodore W
authors.initials: TW
authors.lastname: Thannhauser
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Rutzke
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Hart
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Leon V
authors.initials: LV
authors.lastname: Kochian
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Rea
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, the Robert W. Holley Center for Agriculture and Health, United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, New York 14853, and the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104. Electronic address: okv2@cornell.edu.
authors.forename: Olena K
authors.initials: OK
authors.lastname: Vatamaniuk
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D019881:Aminoacyltransferases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002104:Cadmium / Q000494:pharmacology*; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D025141:Drug Resistance, Fungal / Q000187:drug effects / Q000502:physiology*; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D054811:Phytochelatins / Q000235:genetics / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000235:genetics / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D029721:Drosophila Proteins; C489670:hmt1 protein, S pombe; D002104:Cadmium; D054811:Phytochelatins; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase