Regulation of ornithine decarboxylase gene expression in normal and transformed hamster embryo fibroblasts following stimulation by 12-O-tetradecanoylphorbol-13-acetate

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Abstract
We have compared the regulation of ornithine decarboxylase (ODC) gene expression in primary cultures of hamster embryo fibroblasts and in two independently transfonned hamster embryo cell lines. Previous studies have demonstrated that 12-O-tetradecanoylphorbol-13-acetate (TPA) can greatly potentiate the serum growth factor induction of ODC enzyme activity in transformed cells, but not in normal hamster embryo fibroblasts. Treatment of either normal or transformed cells with both TPA and serum yielded greater accumulations of ODC mRNA than with either treatment alone, which is consistent with changes at the protein level. However, treatment of the transformed cells with TPA and serum resulted in a greater increase in steady state levels of ODC mRNA than that observed using normal fibroblasts. The time course for the induction of ODC mRNA was similar for both normal and transformed cells with maximal accumulations 4–8 h after treatment. Studies with actinomycin D further suggests that ODC mRNA is comparatively long-lived in both normal and transformed cells. The accumulation of ODC mRNA after stimulation with TPA and serum is blocked by cycloheximide in normal hamster fibroblasts suggesting that this induction is dependent upon protein synthesis. In contrast, cydoheximide did not affect the accumulation of ODC mRNA under similar treatment conditions in transformed cells. This altered regulation of ODC gene expression in transformed hamster embryo fibroblasts cannot be explained by either gene rearrangement or the amplification of an ODC gene. These data suggest that transformation of hamster embryo cells results in a loss of cellular control over ODC gene regulation which includes an alteration in the requirement for protein synthesis for ODC mRNA accumulation.