title: Human metastasis regulator protein H-prune is a short-chain exopolyphosphatase.
abstract: The DHH superfamily human protein h-prune, a binding partner of the metastasis suppressor nm23-H1, is frequently overexpressed in metastatic cancers. From an evolutionary perspective, h-prune is very close to eukaryotic exopolyphosphatases. Here, we show for the first time that h-prune efficiently hydrolyzes short-chain polyphosphates (k cat of 3-40 s (-1)), including inorganic tripoly- and tetrapolyphosphates and nucleoside 5'-tetraphosphates. Long-chain inorganic polyphosphates (>or=25 phosphate residues) are converted more slowly, whereas pyrophosphate and nucleoside triphosphates are not hydrolyzed. The reaction requires a divalent metal cofactor, such as Mg (2+), Co (2+), or Mn (2+), which activates both the enzyme and substrate. Notably, the exopolyphosphatase activity of h-prune is suppressed by nm23-H1, long-chain polyphosphates and pyrophosphate, which may be potential physiological regulators. Nucleoside triphosphates, diadenosine hexaphosphate, cAMP, and dipyridamole (inhibitor of phosphodiesterase) do not affect this activity. Mutation of seven single residues corresponding to those found in the active site of yeast exopolyphosphatase led to a severe decrease in h-prune activity, whereas one variant enzyme exhibited enhanced activity. Our results collectively suggest that prune is the missing exopolyphosphatase in animals and support the hypothesis that the metastatic effects of h-prune are modulated by inorganic polyphosphates, which are increasingly recognized as critical regulators in cells.
authors.affiliation: Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland.
authors.forename: Marko
authors.initials: M
authors.lastname: Tammenkoski
authors.forename: Katja
authors.initials: K
authors.lastname: Koivula
authors.forename: Emilio
authors.initials: E
authors.lastname: Cusanelli
authors.forename: Massimo
authors.initials: M
authors.lastname: Zollo
authors.forename: Clemens
authors.initials: C
authors.lastname: Steegborn
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Baykov
authors.forename: Reijo
authors.initials: R
authors.lastname: Lahti
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D003067:Coenzymes / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D043564:Inorganic Pyrophosphatase / Q000235:genetics / Q000378:metabolism; D008670:Metals / Q000378:metabolism; D009154:Mutation; D054778:NM23 Nucleoside Diphosphate Kinases / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000201:enzymology* / Q000235:genetics; D011122:Polyphosphates / Q000378:metabolism*
chemical_list: D003067:Coenzymes; D008670:Metals; D054778:NM23 Nucleoside Diphosphate Kinases; D009363:Neoplasm Proteins; D011122:Polyphosphates; C517938:NME1 protein, human; D017766:Acid Anhydride Hydrolases; D043564:Inorganic Pyrophosphatase; C020137:exopolyphosphatase