P70 S6 kinase negatively regulates fibroblast growth factor 2-stimulated interleukin-6 synthesis in osteoblasts: function at a point downstream from protein kinase C.
We have previously reported that protein kinase C negatively regulates basic fibroblast growth factor (FGF-2)-stimulated synthesis of interleukin-6 (IL-6), a potent bone resorptive agent, in osteoblast-like MC3T3-E1 cells. To further clarify the mechanism underlying the synthesis of IL-6 in osteoblasts, we investigated whether p70 S6 kinase is involved in the FGF-2-stimulated IL-6 synthesis in these cells. Rapamycin, an inhibitor of p70 S6 kinase, significantly enhanced the FGF-2-stimulated IL-6 synthesis in a dose-dependent manner. Downregulation of p70 S6 kinase by siRNA markedly amplified the FGF-2-stimulated IL-6 synthesis. 12-O-Tetradecanoylphorbol-13-acetate (TPA), a direct activator of protein kinase C, induced the phosphorylation of p70 S6 kinase. Go6976 and bisindolylmaleimide I, inhibitors of protein kinase C, suppressed the TPA-stimulated phosphorylation of p70 S6 kinase. Additionally, protein kinase C inhibitors markedly reduced the phosphorylation of p70 S6 kinase induced by FGF-2. These results strongly suggest that p70 S6 kinase functions at a point downstream of protein kinase C and limits the FGF-2-stimulated IL-6 synthesis in osteoblasts.
Takai
S
S
Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
Hanai
Y
Y
Matsushima-Nishiwaki
R
R
Minamitani
C
C
Otsuka
T
T
Tokuda
H
H
Kozawa
O
O
D000818:Animals; D002227:Carbazoles / Q000494:pharmacology; D002478:Cells, Cultured; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology; D015850:Interleukin-6 / Q000096:biosynthesis*; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate
D002227:Carbazoles; D007211:Indoles; D015850:Interleukin-6; D008301:Maleimides; D016222:Fibroblast Growth Factor 2; C081021:Go 6976; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate; D020123:Sirolimus