title: A GTP-binding protein in rat liver nuclei serving as the specific substrate of pertussis toxin-catalyzed ADP-ribosylation.
abstract: The ADP-ribosyl moiety of NAD was transferred to a 40-kDa protein when rat liver nuclei were incubated with pertussis toxin. The 40-kDa substrate in the nuclei displayed unique properties as follows, some of which were apparently distinct from those observed with the toxin-substrate GTP-binding protein (Gi) in the liver plasma membranes. 1) The nuclear 40-kDa protein was recognized with antibodies reacting with the alpha-subunits (alpha i-1 and alpha i-2) of Gi, but not with anti-Go-alpha-subunit antibody. 2) The nuclear protein had a higher mobility than alpha-subunit of the plasma membrane-bound Gi upon electrophoresis with a urea/sodium dodecyl sulfate-containing polyacrylamide gel. 3) The nuclear protein was not extracted from the nuclei with 1% Triton X-100, whereas Gi was easily solubilized from the plasma membranes. 4) There was a beta gamma-subunit-like activity in the nuclei, which was assayed by an ability to support pertussis toxin-catalyzed ADP-ribosylation of a purified alpha-subunit of Gi. Moreover, a 36-kDa protein in the nuclei was recognized with antibody raised against purified beta-subunits of Gi. 5) Pertussis toxin-induced ADP-ribosylation of the nuclear protein was selectively inhibited by the addition of a nonhydrolyzable GTP analogue, and its inhibitory action was competitively blocked by the simultaneous addition of GDP or its analogues, as had been observed with plasma membrane-bound Gi. It thus appeared that a novel form of alpha beta gamma-trimeric GTP-binding protein serving as the substrate of pertussis toxin was present in rat liver nuclei. In order to examine a possible role of the nuclear GTP-binding protein, rats were injected with carbon tetrachloride, a necrosis inducer of hepatocytes. There was a marked increase in the nuclear substrate activity from 3-6 days after the injection, without a significant change in the activity of Gi in the plasma membranes. The time course of the increase corresponded with a recovering stage from the hepatocyte necrosis. These results suggested that the nuclear GTP-binding protein found in the present study might be involved at some stages in the hepatocyte growth.
authors.affiliation: Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Takei
authors.forename: H
authors.initials: H
authors.lastname: Kurosu
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.forename: T
authors.initials: T
authors.lastname: Katada
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000818:Animals; D002251:Carbon Tetrachloride / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D046911:Macromolecular Substances; D008297:Male; D037342:Pertussis Toxin; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
chemical_list: D006150:Guanine Nucleotides; D046911:Macromolecular Substances; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002251:Carbon Tetrachloride; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins