title: Overexpression of a dominant-negative ornithine decarboxylase in mouse skin: effect on enzyme activity and papilloma formation.
abstract: A transgenic mouse line expressing a truncated form of the ornithine decarboxylase (ODC) dominant-negative mutant K69A/C360A under the control of the keratin 6 promoter has been established (K6/ODCdn mice). These mice were backcrossed onto both the DBA/2J and C57BL/6J backgrounds for subsequent tumorigenesis experiments utilizing an initiation/promotion protocol. In short-term experiments, expression of the ODCdn protein product was induced in the epidermis within 24 h after application of the tumor promoter tetradecanoyl phorbol acetate (TPA) to the skin, and ODC activity in the epidermis of K6/ODCdn mice was reduced by at least 75% compared with littermate controls. However, in tumorigenesis experiments utilizing a variety of initiator (7,12-dimethylbenz[a]anthracene; DMBA) and promoter (TPA) concentrations, K6/ODCdn mice formed at least as many tumors as their littermate controls regardless of background strain. In experiments utilizing chrysarobin, a tumor promoter with a different mechanism of action than TPA, again there was no significant difference in tumor formation between K6/ODCdn mice and littermate controls. Similarly, when K6/ODCdn mice were crossed with K5/ODC mice, a transgenic line described previously which forms tumors without application of a promoting agent, double transgenic mice formed as many tumors as mice expressing the K5/ODC transgene alone. Analysis of epidermis following multiple TPA applications revealed a dramatic spike in ODC activity in both K6/ODCdn mice and non-transgenic mice after six applications, and western blot analysis suggested a stabilization of endogenous wild-type ODC in K6/ODCdn transgenic mice. ODC activity, endogenous protein and polyamines were also elevated in tumors from K6/ODCdn mice. The accumulation of endogenous ODC protein is most probably the result of competition from the transgene-derived ODCdn protein for binding of antizyme, which is known to regulate ODC activity by stimulating degradation of the ODC protein.
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA. lms17@psu.edu
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Shantz
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Guo
authors.forename: Janet A
authors.initials: JA
authors.lastname: Sawicki
authors.forename: Anthony E
authors.initials: AE
authors.lastname: Pegg
authors.forename: Thomas G
authors.initials: TG
authors.lastname: O'Brien
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D015153:Blotting, Western; D002273:Carcinogens; D005799:Genes, Dominant; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008822:Mice, Transgenic; D009154:Mutation; D009368:Neoplasm Transplantation; D009955:Ornithine Decarboxylase / Q000096:biosynthesis* / Q000235:genetics*; D010212:Papilloma / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D012867:Skin / Q000201:enzymology*; D013755:Tetradecanoylphorbol Acetate; D013997:Time Factors
chemical_list: D000873:Anthracenes; D002273:Carcinogens; C013883:chrysarobin; D009955:Ornithine Decarboxylase; D013755:Tetradecanoylphorbol Acetate