title: Altered expression of the 100 kDa subunit of the Dictyostelium vacuolar proton pump impairs enzyme assembly, endocytic function and cytosolic pH regulation.
abstract: The vacuolar proton pump (V-ATPase) appears to be essential for viability of Dictyostelium cells. To investigate the function of VatM, the 100 kDa transmembrane V-ATPase subunit, we altered its level. By means of homologous recombination, the promoter for the chromosomal vatM gene was replaced with the promoter for the act6 gene, yielding the mutant strain VatMpr. The act6 promoter is much more active in cells growing axenically than on bacteria. Thus, transformants were selected under axenic growth conditions, then shifted to bacteria to determine the consequences of reduced vatM expression. When VatMpr cells were grown on bacteria, the level of the 100 kDa V-ATPase subunit dropped, cell growth slowed, and the A subunit, a component of the peripheral catalytic domain of the V-ATPase, became mislocalized. These defects were complemented by transformation of the mutant cells with a plasmid expressing vatM under the control of its own promoter. Although the principal locus of vacuolar proton pumps in Dictyostelium is membranes of the contractile vacuole system, mutant cells did not manifest osmoregulatory defects. However, bacterially grown VatMpr cells did exhibit substantially reduced rates of phagocytosis and a prolonged endosomal transit time. In addition, mutant cells manifested alterations in the dynamic regulation of cytosolic pH that are characteristic of normal cells grown in acid media, which suggested that the V-ATPase also plays a role in cytosolic pH regulation.
authors.affiliation: Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, 825 N.E. 13th Street, Oklahoma City, OK 73104, USA.
authors.forename: Tongyao
authors.initials: T
authors.lastname: Liu
authors.forename: Christian
authors.initials: C
authors.lastname: Mirschberger
authors.forename: Lilian
authors.initials: L
authors.lastname: Chooback
authors.forename: Quyen
authors.initials: Q
authors.lastname: Arana
authors.forename: Zeno
authors.initials: Z
authors.lastname: Dal Sacco
authors.forename: Harry
authors.initials: H
authors.lastname: MacWilliams
authors.forename: Margaret
authors.initials: M
authors.lastname: Clarke
mesh_terms: D000818:Animals; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D003470:Culture Media / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology*; D004023:Dictyostelium / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004705:Endocytosis / Q000235:genetics*; D011992:Endosomes / Q000201:enzymology / Q000648:ultrastructure; D004798:Enzymes / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D005822:Genetic Vectors / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000201:enzymology / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D017494:Proton Pumps / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000172:deficiency* / Q000235:genetics; D014617:Vacuoles / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D003470:Culture Media; D004798:Enzymes; D017494:Proton Pumps; D011993:Recombinant Fusion Proteins; D025262:Vacuolar Proton-Translocating ATPases