DISSOCIATION OF PHORBOL ESTERS LEADS TO IMMEDIATE REDISTRIBUTION TO THE CYTOSOL OF PROTEIN-KINASES C-ALPHA AND C-DELTA IN MOUSE KERATINOCYTES

We have measured the dissociation rate of phorbol 12-myristate 13-acet ate (PMA), a potent tumor promoter, phorbol 12,13-dibutyrate (PDBu), a weak tumor promoter, and 12-deoxyphorbol 13-phenylacetate (dPP), an a ntitumor promoter, from intact mouse keratinocytes. PDBu and dPP showe d a very rapid release from the cells (t(1/2) = 1 min), whereas PMA sh owed a slower release (t(1/2) = 9 min). Western blot analysis of the a mounts of protein kinase C alpha (PKC alpha) and PHC delta in the solu ble fraction and the Triton X-100-soluble particulate fraction reveale d that translocation of both isozymes from the soluble to the particul ate fraction was reversible when the phorbol esters were washed off. W ashes of 5-15 min resulted in complete redistribution of the PKC isozy mes when the cells were previously treated with 1 mu M dPP or 1 mu M P DBu for 5 min. In the case of treatment with 100 or 10 nar PMA, the re distribution required a longer time; nevertheless, the PHC isozymes re turned to the soluble fraction within 60 min. Longer initial treatment s with PMA dPP, and PDBu (up to 60 min) translocated PHC in a very sim ilar, completely reversible fashion. We conclude that in this cell lin e phorbol esters do not induce the conversion of PHC isozymes to an in tegral membrane state.