Journal Article

<i>S</i>-adenosylmethionine decarboxylase overexpression inhibits mouse skin tumor promotion

Chenxu Shi, Timothy K. Cooper, Diane E. McCloskey, Adam B. Glick, Lisa M. Shantz and David J. Feith

in Carcinogenesis

Volume 33, issue 7, pages 1310-1318
Published in print July 2012 | ISSN: 0143-3334
Published online May 2012 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgs184

S-adenosylmethionine decarboxylase overexpression inhibits mouse skin tumor promotion

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Neoplastic growth is associated with increased polyamine biosynthetic activity and content. Tumor promoter treatment induces the rate-limiting enzymes in polyamine biosynthesis, ornithine decarboxylase (ODC), and S-adenosylmethionine decarboxylase (AdoMetDC), and targeted ODC overexpression is sufficient for tumor promotion in initiated mouse skin. We generated a mouse model with doxycycline (Dox)-regulated AdoMetDC expression to determine the impact of this second rate-limiting enzyme on epithelial carcinogenesis. TetO–AdoMetDC (TAMD) transgenic founders were crossed with transgenic mice (K5-tTA) that express the tetracycline-regulated transcriptional activator within basal keratinocytes of the skin. Transgene expression in TAMD/K5-tTA mice was restricted to keratin 5 (K5) target tissues and silenced upon Dox treatment. AdoMetDC activity and its product, decarboxylated AdoMet, both increased approximately 8-fold in the skin. This enabled a redistribution of the polyamines that led to reduced putrescine, increased spermine, and an elevated spermine:spermidine ratio. Given the positive association between polyamine biosynthetic capacity and neoplastic growth, it was somewhat surprising to find that TAMD/K5-tTA mice developed significantly fewer tumors than controls in response to 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate chemical carcinogenesis. Importantly, tumor counts in TAMD/K5-tTA mice rebounded to nearly equal the levels in the control group upon Dox-mediated transgene silencing at a late stage of tumor promotion, which indicates that latent viable initiated cells remain in AdoMetDC-expressing skin. These results underscore the complexity of polyamine modulation of tumor development and emphasize the critical role of putrescine in tumor promotion. AdoMetDC-expressing mice will enable more refined spatial and temporal manipulation of polyamine biosynthesis during tumorigenesis and in other models of human disease.

Journal Article.  6992 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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