(-)-Epigallocatechin gallate attenuates the induction of HSP27 stimulated by sphingosine 1-phosphate via suppression of phosphatidylinositol 3-kinase/Akt pathway in osteoblasts.
We previously reported that sphingosine 1-phosphate stimulates the induction of heat shock protein 27 (HSP27) through p38 mitogen-activated protein (MAP) kinase and phosphatidylinositol 3-kinase/Akt in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether (-)-epigallocatechin gallate (EGCG), the major polyphenol found in green tea, affects the induction of HSP27 in these cells and its mechanism, since it was previously reported that catechin, including EGCG, suppresses bone resorption. EGCG significantly reduced the induction of HSP27 stimulated by sphingosine 1-phosphate in a dose-dependent manner between 10 and 30 microM. Immunofluorescence microscopy studies revealed that sphingosine 1-phosphate certainly stimulated the induction of HSP27 in the cytosol of these cells, and that EGCG clearly suppressed its induction. However, sphingosine 1-phosphate-stimulated phosphorylation of p38 MAP kinase or MAPKAP-2 was not affected by EGCG. By contrast, EGCG markedly suppressed the phosphorylations of both Akt and glycogen synthase kinase-3beta stimulated by sphingosine 1-phosphate. These results strongly suggest that EGCG suppresses the induction of HSP27 stimulated by sphingosine 1-phosphate via attenuation of, not the p38 MAP kinase pathway, but of the phosphatidylinositol 3-kinase/Akt pathway in osteoblasts.
Natsume
Hideo
H
Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
Adachi
Seiji
S
Takai
Shinji
S
Tokuda
Haruhiko
H
Matsushima-Nishiwaki
Rie
R
Minamitani
Chiho
C
Yamauchi
Junichi
J
Kato
Kanefusa
K
Mizutani
Jun
J
Kozawa
Osamu
O
Otsuka
Takanobu
T
D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D055551:HSP27 Heat-Shock Proteins / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008246:Lysophospholipids / Q000494:pharmacology*; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D000099190:MAP-Kinase-Activated Kinase 2
D002392:Catechin; D055551:HSP27 Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008246:Lysophospholipids; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D013110:Sphingosine; D048051:p38 Mitogen-Activated Protein Kinases; D000099190:MAP-Kinase-Activated Kinase 2; C060506:sphingosine 1-phosphate; C045651:epigallocatechin gallate