Genetic Alterations Cooperate with v-Ha-ras to Accelerate Multistage Carcinogenesis in TG.AC Transgenic Mouse Skin1

TG.AC transgenic mice harbor a v-Ha-ras transgene and retain two normal c-Ha-ras alÃ-elesand are susceptible to skin tumor formation by 12-O-tetradecanoylphorbol-13-acetate (TPA). To determine whether nor mal c-Ha-ras antagonizes the oncogenic potential of the v-Ha-ras transgene and/or whether additional non-Ha-ra.v 7,12-dimethylhenz(a (anthra cene (DMBA) initiation target genes exist in mouse skin, which could cooperate with v-Ha-ras to increase the frequency of initiation, rate of promotion, or risk of malignant conversion, we treated T(ì.ACmouse skin with a single subthreshold dose of DMBA. This was followed by limited TPA or diacylglycerol promotion to select for cells with additional genetic alterations over those cells containing the v-Ha-ras transgene only. DMBA-treatedyTPA-promoted TG.AC mice demonstrated a 10-fold in crease in the average number of papillomas per mouse, a greater incidence of papilloma bearing-mice, and an increased papilloma growth rate when compared to acetone-treated/TPA-promoted TG.AC mice. These pro found changes in papilloma frequency and growth occurred in the absence of the characteristic DMBA-induced A'*2-»T mutation in c-Ha-ras and immunohistochemical nuclear staining for p53 protein. DMBA-treated/ acetone-promoted TG.AC mice did not develop any tumors. Limited promotion with the model diacylglycerol, sn-l,2-didecanoylglycerol, sim ilarly produced an average of 10-fold more papillomas in DMBA-treated mice than in acetone-treated/sn-l,2-didecanoylglycerol-promoted TG.AC mice. DMBA-treated/TPA-promoted TG.AC mice developed their first malignancy by 16 weeks, and by 30 weeks, 50% of the mice developed malignancies, whereas no malignancies were observed in acetone-treated/ TPA-promoted TG.AC mice. These results indicate that there exist uni dentified DMBA initiation target genes in TG.AC mouse skin that coop erate with mutant Ha-ra.v to increase papilloma frequency, growth, and malignant conversion, and that promoter treatment can influence malig nant conversion by selecting for cells with multiple genetic alterations.