Modulation of phorbol ester receptors in mouse skin by application of quercetin

The topical application of quercetin, an anti-tumor promoter, to mouse skin reduced the number of phorbol ester receptors, although quercetin did not inhibit specific ^3H12-O-tetradecanoylphorbol-13-acetate binding to a mouse skin particulate fraction. Quercetin, morin, kaempferol and luteolin inhibited activation of protein kinase C by teleocidin, and caused half-maximal activation at 25μM (+)-Catechin, which has been reported not to inhibit tumor-promoting activity, did not have any effect on these reactions. The modulation of phorbol ester receptors and inhibition of activation of protein kinase C are considered to be involved in the anti-tumor-pro-moting effect of quercetin in mouse skin. Diet containing 4% or 1% quercetin did not influence the action of teleocidin on mouse skin in a two-stage carcinogenesis experi-ment.