title: Rapid activation and down-regulation of protein kinase C alpha in 12-O-Tetradecanoylphorbol-13-acetate-induced differentiation of human rhabdomyosarcoma cells.
abstract: Human rhabdomyosarcoma RD cells express the myogenic regulatory factors MyoD and myogenin but differentiate spontaneously very poorly. Prolonged treatment of RD cells with the protein kinase C (PKC) activator 12-O-tetradecanoylphorbol-13-acetate (TPA) induces growth arrest and myogenic differentiation as shown by the accumulation of alpha-actin and myosin light and heavy chains, without affecting the expression of MyoD and myogenin. In this study, we show that short-term phorbol ester treatment of the cultures is sufficient to trigger myogenic differentiation but not growth arrest. Furthermore, PKC inhibitors, such as staurosporine or calphostin C, prevent TPA-induced differentiation but not cell growth arrest. These data suggest that the two events are mediated by different pathways; a possible interpretation is that the activation of one or more PKC isoforms mediates the induction of differentiation, whereas the down-regulation of the same or different isoforms mediates the growth arrest. To address the mechanism whereby TPA affects cell growth and differentiation in RD cells, we first analyzed PKC isoenzyme distribution. We found that RD cells express the alpha, beta 1, gamma, and sigma PKC isoenzymes. Only the alpha isoform is exclusively found in the soluble fraction, but it translocates to the membrane fraction within 5 min of TPA treatment and is completely down-regulated after 6 h. The other isoenzymes are found associated to both the soluble and the particulate fractions and are down-regulated after long-term TPA treatment. By immunofluorescence analysis, we show that the PKC alpha down-regulation is specific for those cells that respond to TPA by activating the muscle phenotype. We propose that TPA-induced differentiation in RD cells is mediated by the transient activation of PKC alpha, which activates some of the intracellular events that are necessary for MyoD and myogenin transacting activity and for the induction of terminal differentiation of RD cells. By contrast, the constitutively active beta 1 and sigma are responsible for the maintenance of cell growth, and their down-regulation is responsible for long-term TPA-induced cell growth arrest.
authors.affiliation: Institute of Histology and General Embryology, University of Rome La Sapienza, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Bouché
authors.forename: F
authors.initials: F
authors.lastname: Zappelli
authors.forename: M
authors.initials: M
authors.lastname: Polimeni
authors.forename: S
authors.initials: S
authors.lastname: Adamo
authors.forename: W C
authors.initials: WC
authors.lastname: Wetsel
authors.forename: M I
authors.initials: MI
authors.lastname: Senni
authors.forename: M
authors.initials: M
authors.lastname: Molinaro
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects; D004627:Embryonic Induction / Q000187:drug effects; D004789:Enzyme Activation; D005333:Fetus / Q000166:cytology; D006131:Growth Inhibitors / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000502:physiology*; D008969:Molecular Sequence Data; D011493:Protein Kinase C / Q000502:physiology*; D051571:Protein Kinase C-alpha; D012208:Rhabdomyosarcoma / Q000201:enzymology* / Q000473:pathology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D006131:Growth Inhibitors; D007527:Isoenzymes; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D013755:Tetradecanoylphorbol Acetate