title: Functional dependence on calcineurin by variants of the Saccharomyces cerevisiae vacuolar Ca2+/H+ exchanger Vcx1p.
abstract: The Ca(2+)-dependent protein phosphatase calcineurin is an important regulator of ion transporters from many organisms, including the Saccharomyces cerevisiae vacuolar Ca(2+)/H(+) exchanger Vcx1p. In yeast and plants, cation/H(+) exchangers are important in shaping cytosolic Ca(2+) levels involved in signal transduction and providing tolerance to potentially toxic concentrations of cations such as Ca(2+), Mn(2+) and Cd(2+). Previous genetic evidence suggested Vcx1p is negatively regulated by calcineurin. By utilizing direct transport measurements into vacuolar membrane vesicles, we demonstrate that Vcx1p is a low-affinity Ca(2+) transporter and may also function in Cd(2+) transport, but cannot transport Mn(2+). Furthermore, direct Ca(2+) transport by Vcx1p is calcineurin sensitive. Using a yeast growth assay, a mutant allele of VCX1 (VCX1-S204A/L208P), termed VCX1-M1, was previously found to confer strong Mn(2+) tolerance. Here we demonstrate that this Mn(2+) tolerance is independent of the Ca(2+)/Mn(2+)-ATPase Pmr1p and results from Mn(2+)-specific vacuolar transport activity of Vcx1-M1p. This Mn(2+) transport by Vcx1-M1p is calcineurin dependent, although the localization of Vcx1-M1p to the vacuole appears to be calcineurin independent. Additionally, we demonstrate that mutation of L208P alone is enough to confer calcineurin-dependent Mn(2+) tolerance. This study demonstrates that calcineurin can positively regulate the transport of cations by VCX1-M1p.
authors.affiliation: United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
authors.forename: Jon K
authors.initials: JK
authors.lastname: Pittman
authors.forename: Ning-Hui
authors.initials: NH
authors.lastname: Cheng
authors.forename: Toshiro
authors.initials: T
authors.lastname: Shigaki
authors.forename: Madhurababu
authors.initials: M
authors.lastname: Kunta
authors.forename: Kendal D
authors.initials: KD
authors.lastname: Hirschi
mesh_terms: D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002104:Cadmium / Q000378:metabolism; D019703:Calcineurin / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D017354:Point Mutation; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism
chemical_list: D017920:Antiporters; D018832:Molecular Chaperones; D020033:Protein Isoforms; C101767:SSC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C099946:VCX1 protein, S cerevisiae; D002104:Cadmium; D008345:Manganese; D019703:Calcineurin; D000252:Calcium-Transporting ATPases; D002118:Calcium