| Abstract: | Phorbol ester TPA has been previously shown to induce a rapid translocation, followed by a progressive decline of protein kinase C activity in MCF-7 cells (J.M. Darbon et al, 1986, Biochem. Biophys. Res. Comm. 137: 1159-1166). We show now a parallel TPA-induced movement of phorbol ester binding sites from the cytosolic to the particulate fraction with no change in the binding affinities for the (3H) PDBu probe (KD congruent to 2 nM). The subcellular redistribution process is followed by a rapid decrease of the phorbol ester binding capacity at the membrane level. The concomitant decline in both phorbol ester binding and protein kinase C activities that we observed during the course of TPA treatment strongly argues for a real down-regulation of the enzyme in phorbol ester-treated MCF-7 cells. The molecular mechanisms of these events and their relations to the inhibition of cell growth remain to be clarified. |
