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The study examined the timing of modulation of activator protein 1(AP-1):DNA binding and production of AP-1 constituent proteins by ultraviolet B (UVB) radiation and effect of dietary energy restriction [DER, 40% calorie reduction from fat and carbohydrate compared to control ad-libitum (AL) diet] in SKH-1 mouse epidermis. AP-1:DNA binding by electromobility shift assay (EMSA) was increased in a biphasic manner after treatment with a tumor promoting suberythemal dose (750mJ/cm 2 ) of UVB light (311-313nm) with peaks at 3 and 18 hours post irradiation. DER overall reduced AP-1:DNA binding in mock-treated and UVB treated skin at 3 and 18 hours after UVB treatment. The timing of modulation of production of AP-1 constituent proteins by western blot analysis was examined at 0hr (mock treatment), 3hr, 9hr, 18hr, and 24hr. We found that c-jun (9 hr), jun-B (9 and 18hrs), phosphorylated c-jun (3hr), and fra-1 (18hr) protein levels were increased after UVB treatment compared to mock controls. In a follow-up diet experiment, animals were placed on DER or AL diet for 10-12 weeks and treated with UVB as before. DER was found to completely block the UVB induced increase in phosphorylated c-jun protein levels and decrease in fra-2 protein levels at 18hr. In addition, DER enhanced UVB-induced increase in jun-B levels and lowered basal levels of c-fos seen 18 hours after UVB. These data suggest that DER may be able to assist in the prevention of UVB induced skin carcinogenesis by modulating AP-1:DNA binding and AP-1 constituent protein levels.

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