title: Overexpression of glutamine synthetase is associated with beta-catenin-mutations in mouse liver tumors during promotion of hepatocarcinogenesis by phenobarbital.
abstract: Phenobarbital (PB) is an antiepileptic drug that promotes hepatocarcinogenesis in rodents when administered subsequent to an initiating carcinogen like N-nitrosodiethylamine (DEN). In the mouse, the promotional effect of PB on liver tumor development results from a selective stimulation of clonal outgrowth of hepatocytes harboring activating mutations in the beta-catenin gene. Because glutamine synthetase (GS) has recently been shown to be a putative transcriptional target of beta-catenin, expression of GS during PB-mediated promotion of mouse hepatocarcinogenesis was investigated. Preneoplastic and neoplastic liver lesions were induced in 6-week-old male mice by a single injection of 90 micro g/g body weight of DEN, and groups of mice were subsequently kept on PB-containing (0.05%) or control diet for 39 weeks. In PB-treated mice, 46 of 51 lesions ( approximately 90%) were GS-positive in contrast to only 16 of 46 ( approximately 35%) in mice not treated with PB. Approximately 33% of liver was occupied by neoplastic tissue in PB-treated mice, of which >80% was GS positive. By contrast, only approximately 3.5% of liver consisted of neoplastic tissue in mice treated with DEN only, and approximately 25% of this was GS positive. We have previously shown that beta-catenin mutations are present in approximately 80% of liver tumors from PB-treated mice but are absent in liver tumors from mice treated with DEN only. By analyzing a panel of larger liver tumors, we now observed that tumors harboring beta-catenin mutations were GS positive, whereas tumors without beta-catenin mutations were GS negative. Similarly, tumors from an additional mouse carcinogenicity experiment where PB inhibited rather than promoted hepatocarcinogenesis were mostly GS negative. These data suggest that promotion of hepatocarcinogenesis by PB confers beta-catenin-mutated tumor cells with a selective advantage by up-regulation of GS expression.
authors.affiliation: Institut für Toxikologie, Universität Tübingen, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Loeppen
authors.forename: Daniela
authors.initials: D
authors.lastname: Schneider
authors.forename: Frank
authors.initials: F
authors.lastname: Gaunitz
authors.forename: Rolf
authors.initials: R
authors.lastname: Gebhardt
authors.forename: Raffael
authors.initials: R
authors.lastname: Kurek
authors.forename: Albrecht
authors.initials: A
authors.lastname: Buchmann
authors.forename: Michael
authors.initials: M
authors.lastname: Schwarz
mesh_terms: D000818:Animals; D003598:Cytoskeletal Proteins / Q000235:genetics*; D004052:Diethylnitrosamine / Q000633:toxicity; D005974:Glutamate-Ammonia Ligase / Q000096:biosynthesis* / Q000235:genetics; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000201:enzymology / Q000235:genetics; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation; D010634:Phenobarbital / Q000633:toxicity*; D015534:Trans-Activators / Q000235:genetics*; D015533:Transcriptional Activation / Q000187:drug effects; D015854:Up-Regulation; D051176:beta Catenin
chemical_list: C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D015534:Trans-Activators; D051176:beta Catenin; D004052:Diethylnitrosamine; D005974:Glutamate-Ammonia Ligase; D010634:Phenobarbital