Decreases in phorbol ester-induced papilloma development in v-Ha-ras transgenic TG.AC mice during reduced gene dosage of bcl-2.

Abstract

We have demonstrated that induction of transgene expression in the v-Ha-ras-transgenic TG.AC mouse is a critical event in skin tumorigenesis and that cutaneous papillomas arise from follicular epidermis after treatment with chemical carcinogens. The sensitivity of TG.AC mice to skin tumorigenesis, coupled with their low incidence of spontaneous skin tumors, makes this strain a good model for identifying carcinogens and for investigating the roles that other genes may play in the development of skin neoplasia. To investigate the possible involvement of the bcl-2 gene in skin tumorigenesis in the TG.AC mouse, we crossed heterozygous bcl-2-knockout mice (C57BI/6, 129 background) with TG.AC mice (FVB/N background). Female mice were genotyped by using a neo cassette to identify bcl-2-deficient mice. In addition, homozygous TG.AC mice were bred with FVB/N mice to generate hemizygous TG.AC mice on an FVB/N background to serve as a gene-dosage control. The F1 progeny consisted of FVB/N(v-Ha-ras+/-):C57BI/6,129(bcl-2+/+),FVB/N(v-Ha-ra s+/-):C57BI/6,129(bcl-2+/-), and FVB/N(v-Ha-ras+/-,bcl-2+/+). Ten-week-old mice were dosed twice weekly for 10 wk with acetone, 1.25 microg of 7,12-tetradecanoylphorbol-13-acetate (TPA), or 2.5 microg of TPA, and papillomas were counted weekly. Papillomas were analyzed for ras transgene and bcl-2 expression by reverse transcription-polymerase chain reaction, v-Ha-ras expression by in situ hybridization, and proliferating cell nuclear antigen expression by immunohistochemical analysis. Fewer papillomas (P < 0.05) were observed at the low dose of TPA (1.25 microg) in mice carrying the bcl-2 knockout allele than in the wild-type mice, suggesting that reduction of the bcl-2 gene product affects the susceptibility of TG.AC mice to TPA-induced papillomas. However, at the high dose of TPA (2.5 microg), there was no difference in papilloma response between knockout and wild-type mice, regardless of strain background. This suggests that at the higher dose of TPA, the effect of reduction in bcl-2 gene product was obscured. These results support the hypothesis that bcl-2 plays a limited role in skin tumorigenesis in the TG.AC mouse.