(-)-Epigallocatechin gallate suppresses endothelin-1-induced interleukin-6 synthesis in osteoblasts: inhibition of p44/p42 MAP kinase activation.
We previously showed that endothelin-1 (ET-1) stimulates the synthesis of interleukin-6 (IL-6), a potent bone resorptive agent, in osteoblast-like MC3T3-E1 cells, and that protein kinase C (PKC)-dependent p44/p42 mitogen-activated protein (MAP) kinase plays a part in the IL-6 synthesis. In the present study, we investigated the effect of (-)-epigallocatechin gallate (EGCG), one of the major flavonoids containing in green tea, on ET-1-induced IL-6 synthesis in osteoblasts and the underlying mechanism. EGCG significantly reduced the synthesis of IL-6 stimulated by ET-1 in MC3T3-E1 cells as well primary cultured mouse osteoblasts. SB203580, a specific inhibitor of p38 MAP kinase, but not SP600125, a specific SAPK/JNK inhibitor, suppressed ET-1-stimulated IL-6 synthesis. ET-1-induced phosphorylation of p38 MAP kinase was not affected by EGCG. On the other hand, EGCG suppressed the phosphorylation of p44/p42 MAP kinase induced by ET-1. Both the IL-6 synthesis and the phosphorylation of p44/p42 MAP kinase stimulated by 12-O-tetradecanoylphorbol 13-acetate (TPA), a direct activator of PKC, were markedly suppressed by EGCG. The phosphorylation of MEK1/2 and Raf-1 induced by ET-1 or TPA were also inhibited by EGCG. These results strongly suggest that EGCG inhibits ET-1-stimulated synthesis of IL-6 via suppression of p44/p42 MAP kinase pathway in osteoblasts, and the inhibitory effect is exerted at a point between PKC and Raf-1 in the ET-1 signaling cascade.
Tokuda
Haruhiko
H
Department of Clinical Laboratory, National Hospital for Geriatric Medicine, National Center for Geriatrics and Gerontology, Obu 474-8511, Japan. tokuda@ncgg.go.jp
Takai
Shinji
S
Hanai
Yoshiteru
Y
Matsushima-Nishiwaki
Rie
R
Hosoi
Takayuki
T
Harada
Atsushi
A
Ohta
Toshiki
T
Kozawa
Osamu
O
D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002478:Cells, Cultured; D019332:Endothelin-1 / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D015850:Interleukin-6 / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects* / Q000201:enzymology; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000093242:Interleukin-6 Inhibitors
D000873:Anthracenes; D002392:Catechin; D019332:Endothelin-1; D005419:Flavonoids; D007093:Imidazoles; D015850:Interleukin-6; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D011493:Protein Kinase C; D019908:Proto-Oncogene Proteins c-raf; D011725:Pyridines; D013755:Tetradecanoylphorbol Acetate; D048051:p38 Mitogen-Activated Protein Kinases; D000093242:Interleukin-6 Inhibitors; C432165:pyrazolanthrone; C045651:epigallocatechin gallate; C093642:SB 203580