title: Regulation of purified hepatic PC-1 (phosphodiesterase-I/nucleotide pyrophosphatase) by threonine auto(de)phosphorylation and by binding of acidic fibroblast growth factor.
abstract: The plasma cell differentiation antigen PC-1 was purified to homogeneity from rat liver membranes. Denaturing electrophoresis revealed polypeptides of 118 and 128 kDa, which were both recognized by antibodies against recombinant murine PC-1. During gel filtration PC-1 migrated as a protein of about 500 kDa, suggesting a tetrameric structure. Purified PC-1 displayed a phosphodiesterase-I/nucleotide pyrophosphatase activity that could be completely blocked by EDTA, dithiothreitol and acidic fibroblast growth factor (extrapolated Ki = 1.3 nM). Purified PC-1 was also capable of threonine autophosphorylation and of phosphorylation of histone IIa. The autophosphorylation of PC-1 was inhibited by addition of histone IIa, and it was blocked by phosphodiesterase-I inhibitors (acidic fibroblast growth factor, dithiothreitol), by nucleotides (ATP, ADP, AMP), and by vanadate. When added to autophosphorylated PC-1, these compounds caused a prompt dephosphorylation. However, the same agents did not affect the (de)phosphorylation of histone IIa, which is not a substrate for the PC-1 phosphatase. These data indicate that phosphodiesterase-I inhibitors, nucleotides and vanadate affect the (de)phosphorylation of PC-1 by stimulating the PC-1 phosphatase and/or by shielding the autophosphorylation site from the PC-1 kinase. The rate of dephosphorylation of PC-1 was independent of the dilution, suggesting an autocatalytic intramolecular process. We propose that the autophosphorylation of PC-1 serves to block its nucleotide pyrophosphatase activity when extracellular ATP becomes scarce.
authors.affiliation: Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Uriarte
authors.forename: W
authors.initials: W
authors.lastname: Stalmans
authors.forename: S
authors.initials: S
authors.lastname: Hickman
authors.forename: M
authors.initials: M
authors.lastname: Bollen
mesh_terms: D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry; D002850:Chromatography, Gel; D004229:Dithiothreitol / Q000494:pharmacology; D016220:Fibroblast Growth Factor 1 / Q000378:metabolism* / Q000494:pharmacology; D006657:Histones / Q000378:metabolism / Q000494:pharmacology; D006706:Homeostasis; D008099:Liver / Q000737:chemistry; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009711:Nucleotides / Q000494:pharmacology; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism*; D011755:Pyrophosphatases / Q000378:metabolism*; D051381:Rats; D014638:Vanadates / Q000494:pharmacology
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D006657:Histones; D008562:Membrane Glycoproteins; D009711:Nucleotides; D016220:Fibroblast Growth Factor 1; D010769:Phosphothreonine; D014638:Vanadates; D010727:Phosphoric Diester Hydrolases; D043264:Phosphodiesterase I; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases; C021899:nucleotide pyrophosphatase; D004229:Dithiothreitol