Calcium and phospholipid-dependent protein kinase activity in mouse epidermis cytosol. Stimulation by complete and incomplete tumor promoters and inhibition by various compounds.

Calcium- and phospholipid-dependent protein kinase (Ca, PL-PK) activity is detectable in mouse epidermis cytosol. It can be stimulated in vitro by complete and incomplete tumor promoters (12-0-tetradecanoylphorbol-13-acetate (TPA) and 12-0-retinoylphorbol-13-acetate (RPA], respectively. Effective inhibition of the enzyme activity is achieved with quercetin and phloretin, whereas the lipoxygenase and cyclooxygenase inhibitors nordihydroguaiaretic acid (NDGA) and esculetin show just weak or no inhibition. Quercetin inhibits the lipoxygenase and cyclooxygenase equally well as the Ca, PL-PK, whereas the strong Ca, PL-PK inhibitor phloretin is absolutely ineffective in inhibiting the lipoxygenase/cyclooxygenase. The application of these inhibitors in differentiating tumor promoter induced effects in vivo is proposed.