Mouse skin chemical carcinogenesis is inhibited by antizyme in promotion‐sensitive and promotion‐resistant genetic backgrounds

Abstract

Elevated polyamine content and increased ornithine decarboxylase (ODC) activity have been associated with neoplastic growth in numerous animal models and human tissues. Antizyme (AZ) is a negative regulator of polyamine metabolism that inhibits ODC activity, stimulates ODC degradation, and suppresses polyamine uptake. Preliminary evidence, obtained from transgenic mice with tissue specific overexpression of AZ indicates that tumor development can be suppressed by AZ. To extend these studies, we have examined the effect of keratin 5 (K5)- or K6-driven AZ transgenes on 7,12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) chemical carcinogenesis of the skin, in promotion-resistant C57BL/6 and promotion-sensitive DBA/2 mice. On both genetic backgrounds, K6-AZ mice showed a reduction in tumor multiplicity, with 85% fewer tumors than wild-type controls on the C57BL/6 background and 50% fewer tumors on the DBA/2 background. K5-AZ mice developed 50% fewer tumors than controls on both backgrounds. The percent of mice with tumors and tumor size were also reduced in the K5-AZ and K6-AZ groups. Tumor and TPA-treated skin sections from K6-AZ mice exhibited the strongest AZ expression, with localization mainly in suprabasal keratinocytes. K6-AZ mice also had slightly reduced cell proliferation rates in tumors and TPA-treated skin. The lack of a more pronounced effect on cell proliferation is probably explained by the observation that AZ staining did not colocalize with proliferating cell nuclear antigen (PCNA), a marker for the proliferative compartment. These studies demonstrate a tumor-suppressive effect of AZ in C57BL/6 and DBA/2 mice, and confirm the importance of ODC and polyamines in tumor development.

Mammalian polyamine metabolism and function

“…Although Odc heterozygosity did not influence induction of neuroblastomas by N-Myc (94), lymphoma development in response to an activated c-Myc was markedly delayed in Odc (+/−) transgenic mice (67), and substantially fewer skin papillomas developed in these mice when subjected to a two stage carcinogenesis protocol (141). Similarly, transgenic expression of AZ, producing a moderate reduction of ODC, blocked skin carcinogenesis in response to two stage carcinogenesis protocols (142), UV radiation (143), or overexpression of the MEK oncogene (144) and reduced tumor incidence in both N -nitrosomethylbenzylamine-induced forestomach tumor (145) and nitroquinoline- N -oxide-induced esophageal tumor models (145)(D. J. Feith, unpublished observations). These experiments provide a reasonable explanation for the remarkable efficacy of low doses of the ODC inhibitor DFMO in a recent human chemoprevention trial.…”

Targeted expression of tumor necrosis factor-related apoptosis-inducing ligand TRAIL in skin protects mice against chemical carcinogenesis

“…Indeed, mice from C57BL/6 background have previously been reported to be more resistant to tumor development and particularly to skin carcinogenesis, in contrast to mice having a DBA/2 genetic background which present a higher rate of tumors formation when subjected to the same protocol [41]. However, this resistance of benign tumors to progress to malignant lesions provided us with the opportunity to study the effect of high endogenous levels of TRAIL in skin on the early step of the skin tumorigenesis.…”

Characterization of transgenic mice with overexpression of spermidine synthase

“…Alternatively, the transgene was detected with a sense primer (5′-TTCGGCTTCTGGCGTGTGAC-3′) that binds in the β-actin promoter region and an antisense primer (5′-CTTACTGCGGAAGACGAGG-3′) that binds in the human SpdS coding region to amplify a 330 bp product. A second primer pair that yields a 520 bp product from the mouse antizyme 1 gene ( Oaz1 ) was also included in the reaction, which provides a positive control for successful PCR amplification for each genomic DNA sample (Feith et al 2007). …”