title: Phorbol esters induce both intracellular translocation and down-regulation of protein kinase C in MCF-7 cells.
abstract: Exposure of MCF-7 human breast cancer cells to phorbol ester 12-O-tetradecanoyl-13-acetate (TPA) results in a complete inhibition of cell proliferation. We investigated the effects of TPA on protein kinase C activity when cells were exposed to phorbol ester for various lengths of time. TPA induces within 5 min a drastic dose-dependent decrease of the cytosolic protein kinase C activity. The enzyme apparently lost at the cytosolic level was only partially recovered in the particulate fraction. The apparent down-regulation of the translocated enzyme which was only 34% after 1 min reached 72% and 84% after respectively 10 min and 15 min. Moreover, when cells are treated with TPA for longer periods of time, the particulate protein kinase C activity continues to decrease, dropping below control after 1 hour. This progressive decline leads to an almost complete disappearance of protein kinase C activity in MCF-7 cells after 45 hours of TPA treatment. The apparent loss of protein kinase C activity upon short- as well as long-exposure of cells to TPA was not accompanied by a concomitant increase of Ca, PL-independent protein kinase activity. We discuss the implication of these biochemical events in the inhibition of cell proliferation with regard to the respective short- and long-term effects of TPA on protein kinase C activity.
mesh_terms: D001692:Biological Transport; D002451:Cell Compartmentation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007700:Kinetics; D010704:Phorbols / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D012995:Solubility; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D010704:Phorbols; D011494:Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate