Dietary energy restriction and fat modulation of protein kinase C isoenzymes and phorbol ester binding in Sencar mouse epidermis.

The purpose of our research is to understand the biochemical basis for dietary enhancement of phorbol ester induced tumor promotion in mice fed high-fat (HF) diet, and the inhibition of promotion in mice fed diets restricted in energy from fat and carbohydrate (ER). The present study assessed the presence of protein kinase C (PKC) isoenzymes in the Sencar mouse epidermis by Western blot and determined the influence of diet on the isoenzymes found. Mice were fed control, HF (24.5% corn oil) or ER (60% of control energy) diets for 6-29 weeks. Our initial studies assessed the immunoreactive levels of PKC alpha, beta, gamma, delta, epsilon and zeta and PKC alpha beta gamma using an antibody to a shared epitope. We detected PKC alpha, epsilon, delta and zeta in sufficient quantity for dietary studies. Dietary fat and energy did not significantly modify the presence of PKC epsilon or delta. We observed a 30% and 40% reduction in PKC alpha in comparison with control diet in cytosolic and particulate fractions respectively, from mice pre-fed ER diet. Reductions of 72% and 82% in cytosolic and particulate PKC were observed respectively with the alpha beta gamma antibody. ER diet reduced the overall amount of PKC zeta in cytosol and particulate by 42% and 59% respectively, with the cytosolic reduction being greater in mice pre-fed the restricted diets for 21-29 weeks. HF diet did not modify the protein levels of the PKC isoenzymes studied. The level of phorbol-12,13-dibutyrate binding to epidermal cells was assessed to determine if the reduction in PKC protein in the epidermis of ER mice would result in altered phorbol binding. Phorbol binding in cells isolated from mice fed ER diet was reduced in mice pre-fed the ER diet for 20-22 weeks in comparison with binding to cells from mice fed control diet. These results suggest that ER diet reduces specific PKC isoenzymes and the binding of phorbol esters in epidermis of mice. These observations may account for the inhibition of phorbol ester promotion of skin tumors in ER mice.