sirolimus and pirinixic-acid

Effect of peroxisome proliferator-activated receptor alpha (PPARalpha) agonists, WY-14,643 (WY) and/or clofibrate, on the leucine-induced phosphorylation of translational targets in C2C12 myoblasts was studied. C2C12 cells were treated with WY or clofibrate for 24 h prior to stimulation with leucine. Western blot analyses revealed that the leucine-induced phosphorylation of p70 S6 kinase (p70S6K), a key regulator of translation initiation, was significantly higher in WY-treated cells than in control and clofibrate-treated cells. Phosphorylation of extracellular-regulated kinase (ERK1/2) was higher in WY-treated cells. WY treatment also increased the leucine-induced phosphorylation of ribosomal protein S6 and eukaryotic initiation factor 4B. In contrast, eukaryotic elongation factor 2, a marker for peptide chain elongation process, was significantly activated (dephosphorylated) only in leucine-stimulated control cells. Pre-treatment of the cells with PD98059 (ERK1/2 kinase inhibitor) prevented the phosphorylation of ERK1/2 and decreased the leucine-induced phosphorylation of p70S6K. It is concluded that WY increased the leucine-induced phosphorylation of target proteins involving in translation initiation via ERK/p70S6K pathway, but impaired the signaling for elongation process, suggesting that p70S6K phosphorylation may be essential, but not sufficient for the activation of entire targets for protein translation in WY-treated cells.

Topics: Adaptor Proteins, Signal Transducing; AMP-Activated Protein Kinases; Animals; Carrier Proteins; Cell Cycle Proteins; Cell Line; Clofibrate; Elongation Factor 2 Kinase; Eukaryotic Initiation Factors; Flavonoids; Leucine; Mice; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Multienzyme Complexes; p38 Mitogen-Activated Protein Kinases; Phosphoproteins; Phosphorylation; PPAR alpha; Protein Biosynthesis; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Pyrimidines; Ribosomal Protein S6; Ribosomal Protein S6 Kinases, 70-kDa; Sirolimus

WY-14,643, a potent hepatic peroxisome proliferator, decreased gap junctional intercellular communication when used at low and intermediate concentrations (1 nM to 10 microM) in the V79 Chinese hamster fibroblast cell line. It did not decrease intercellular communication in early passage Syrian hamster embryo fibroblasts. The mechanism of WY-14,643-induced suppression of intercellular communication was studied by preexposure of V79 cells to inhibitors of protein kinase C, mitogen-activated protein kinases, phosphatidylinositol 3-kinase, or mammalian target-of-rapamycin before addition of WY-14,643. Only protein kinase C, particularly the delta isoform, appeared involved in the inhibition of communication by WY-14,643. Also clofibrate-induced suppression of GJIC in V79 cells appeared to involve protein kinase Cdelta. Furthermore, WY-14,643 did not cause any activation of the mitogen-activated protein kinases p44/42, p38, or Jun N-terminal kinase. When WY-14,643 was used at a higher concentration (100 microM), intercellular communication was increased both in V79 and Syrian hamster embryo cells. This effect was inhibited by preexposure of V79 cells to brefeldin A. Thus, there may be a pool of connexins in the Golgi complex that could be recruited to the plasma membrane upon exposure to high concentrations of WY-14,643.

Topics: Acetophenones; Androstadienes; Animals; Benzopyrans; Brefeldin A; Butadienes; Cell Communication; Cells, Cultured; Cricetinae; Cricetulus; Enzyme Inhibitors; Flavonoids; Gap Junctions; Imidazoles; Indoles; Maleimides; Mesocricetus; Mitogen-Activated Protein Kinases; Nitriles; Peroxisome Proliferators; Protein Kinase C; Protein Synthesis Inhibitors; Pyridines; Pyrimidines; Signal Transduction; Sirolimus; Wortmannin