Journal Article

Overexpression of a dominant-negative ornithine decarboxylase in mouse skin: effect on enzyme activity and papilloma formation

Lisa M. Shantz, Yongjun Guo, Janet A. Sawicki, Anthony E. Pegg and Thomas G. O'Brien

in Carcinogenesis

Volume 23, issue 4, pages 657-664
Published in print April 2002 | ISSN: 0143-3334
Published online April 2002 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/23.4.657
Overexpression of a dominant-negative ornithine decarboxylase in mouse skin: effect on enzyme activity and papilloma formation

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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.

Keywords: DFMO, α-difluoromethylornithine; DMBA, 7,12-dimethylbenz[a]anthracene; K6, keratin 6; ODC, ornithine decarboxylase; ORS, outer root sheath; TPA, tetradecanoyl phorbol acetate.

Journal Article.  6708 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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