DIFFERENTIAL REGULATION BY ANTI-TUMOR-PROMOTING 12-DEOXYPHORBOL-13-PHENYLACETATE REVEALS DISTINCT ROLES OF THE CLASSICAL AND NOVEL PROTEIN-KINASE-C ISOZYMES IN BIOLOGICAL RESPONSES OF PRIMARY MOUSE KERATINOCYTES

12-Deoxyphorbol-13-phenylacetate (dPP) is the prototype for a new clas s of phorbol derivatives that function as protein kinase C (PKC) activ ators with potent anti-tumor-promoting activity. To explore the mechan ism of action of dPP, we have conducted detailed analyses of the trans location and down-regulation patterns of individual PKC isozymes in mo use primary keratinocytes upon dPP treatment. PKC-alpha, -delta, and - epsilon were very quickly (within 2-5 min) translocated from the solub le fraction to the Triton X-100-soluble particulate fraction. PKC-delt a and -epsilon were translocated with 2 orders of magnitude higher pot ency than was PKC-alpha. After translocation, PKC-alpha, -delta, -eta, and -epsilon were down-regulated; the down-regulation of PKC-E contra sts with its retention after phorbol-12-myristate-13-acetate or bryost atin treatment. As was the case with translocation, dPP down-regulated the novel PKC isozymes (delta, epsilon, and eta) with 2 orders of mag nitude higher potency (ED(50), about 1-2 nM), compared with PKC-alpha (ED(50), about 100 nM). dPP induced transglutaminase activity, ornithi ne decarboxylase activity, and cornification with potencies similar to that for PKC-alpha translocation. On the other hand, dPP caused inhib ition of EGF binding with a potency similar to that for the translocat ion of the novel PKC isozymes. Although the generality of its selectiv ity in different cell types remains to be determined, at least in kera tinocytes dPP is a powerful tool for dissecting the involvement of the classical and novel PKC isozymes in biological responses. The unique regulatory pattern of PKC-epsilon could contribute to the anti-tumor-p romoting activity of dPP.