Effects of food factors on signal transduction pathways

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Abstract
Consumption of plant‐derived foods, especially fruits and vegetables, has been linked to decreased risk of cancer. Laboratory studies with animals and cells in culture have shown cancer preventive activity of chemicals isolated from soy, tea, rice and many green, yellow and orange fruits and vegetables. Using cell culture, transgenic mice and knockout mice models to examine the anti‐cancer effects of these dietary factors at the molecular level, we found that (1) (‐)‐epigallocatechin gallate (EGCG), the major active polyphenol in green tea, and theaflavins, the major active components in black tea, inhibit epidermal growth factor (EGF)‐ or 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA)‐induced JB6 cell transformation. At the same dose range that inhibited cell transformation, EGCG and theaflavins inhibited activator protein‐1 (AP‐1) activation. These compounds also inhibited ultraviolet B (UVB)‐induced AP‐1 and nuclear factor kappa B (NFκB)‐dependent transcriptional activation; (2) resveratrol, found at high levels in grapes, inhibited cell transformation through the induction of apoptosis, mediated through JNK and p53‐dependent pathways; (3) inositol hexaphosphate (InsP6), an active compound from rice and other grains, inhibited TPA‐ or EGF‐induced transformation and signal transduction through its effects on phosphatidylinositol‐3 kinase (PI‐3) kinase; (4) phenethyl isothiocyanate (PEITC), which occurs as a conjugate in certain cruciferous vegetables, inhibited cell transformation corresponding with the induction of apoptosis. An elevation of p53 is required for PEITC‐induced apoptosis. Our studies indicated that the chemopreventive effect of these food factors may be mediated by their effects on different signal transduction pathways; (5) retinoids (vitamin A and its metabolites) inhibited tumor promoter‐induced cell transformation and tumor promotion in transgenic mice through the inhibition of AP‐1 action but not through the activation of retinoic acid response element (RARE).