Effect of Specific Fatty Acids on p53 Expression in Rat Mammary Tumor Cells

Abstract

In previous studies, we have demonstrated that, while dietary fats were not found to affect the frequency of ras mutation in rat mammary tumors induced by N-nitrosomethylurea (NMU), they did affect final incidence of tumors, supporting the idea that the diet mediates promotion-related changes. As altered p53 expression has been described in 45–55% of human breast cancers, we have used a rat mammary tumor cell line, NMU (ATCC CRL 1743) as a model to determine whether specific fatty acids might affect expression and, in turn, activity of the p53 tumor suppressor gene. Under standard growth conditions (10% FBS), NMU cells over-express p53. Metabolic pulse-chase labeling revealed p53 protein with a prolonged half-life of about 2 hours. To study the effects of specific fatty acids on p53 protein expression, NMU cells were exposed to medium containing high serum (10% FBS), low serum (1% FBS), or low serum plus 1 μg/ml linoleic acid (LA), oleic acid (OA), or docosahexaenoic acid (DHA)). Growth rates for NMU cells were reduced by 30% to 60% in 1% FBS compared with 10% FBS, while addition of LA resulted in an intermediate growth rate and no changes were observed after treatment with OA or DHA. After 3 days in the experimental medium, p53 expression was found to be higher in NMU cells maintained in low serum medium than in those grown in high serum. In the presence of low serum, LA was found to decrease p53 levels, an effect which was not seen with either OA or DHA. Increased p53 expression in cells grown in low serum correlated with their slower growth rate and, similarly, LA was able to decrease p53 expression as well as increasing the growth rate.