Technical Abstract: Strawberries (Fragaria x ananassa Duch.) antioxidant enzymes and the potential inhibitory effects on tetradecanoylphorbol-13-acetate (TPA) or ultraviolet-B (UVB) induced activator protein-1 (AP-1) and Nuclear factor-kappaB (NF-'B) activities, and the inhibitory effect on proliferation and transformation of human and mouse cancer cells were evaluated. Strawberries had high activities of glutathione-peroxidase (GSH-POD), superoxide dismutase (SOD), guaiacol peroxidase (G-POD), ascorbate peroxidase (AsA-POD), and glutathione reductase (GR). Strawberry extracts inhibited the proliferation of human lung epithelial cancer cell line A549 and decreased TPA-induced neoplastic transformation of JB6 P+ mouse epidermal cells. Pretreatment of JB6 P+ mouse epidermal cells with strawberry extract resulted in the inhibition of both UVB- and TPA-induced AP-1 and NF-'B transactivation. Furthermore, strawberry extract also blocked TPA induced phosphorylation of ERKs and UVB-induced phosphorylation of ERKs and JNK kinase in JB6 P+ mouse epidermal cell culture. These results suggest that the ability of strawberries for blocking of UVB-and TPA-induced AP-1- and NF-'B- activation may be due to its antioxidant properties and their ability to reduce oxidative stress. The oxidative events that regulate AP-1- and NF-'B transactivation can be important molecular targets for cancer prevention. The strawberries may be highly effective as a chemopreventive agent that acts by targeting the down-regulation of AP-1 and NF-'B activities, blocking MAPK signaling, and suppression of cancer cell proliferation and transformation.