The cell survival signal Akt is differentially activated by PDGF-BB, EGF, and FGF-2 in osteoblastic cells.
Stimulation of osteoblast survival signals may be an important mechanism of regulating bone anabolism. Protein kinase B (PKB/Akt), a serine-threonine protein kinase, is a critical regulator of normal cell growth, cell cycle progression, and cell survival. In this study we have investigated the signaling pathways activated by growth factors PDGF-BB, EGF, and FGF-2 and determined whether PDGF-BB, EGF, and FGF-2 activated Akt in human or mouse osteoblastic cells. The results demonstrated that both ERK1 and ERK2 were activated by FGF-2 and PDGF-BB. Activation of ERK1 and ERK2 by PDGF-BB and FGF-2 was inhibited by PD 098059 (100 microM), a specific inhibitor of MEK. Wortmannin (500 nM), a specific inhibitor of phosphatidylinositol 3-kinase ( PI 3-K), inhibited the activation of ERK1 and ERK2 by PDGF-BB but not by FGF-2 suggesting that PI 3-K mediated the activation of ERK MAPK pathway by PDGF-BB but not by FGF-2. Rapamycin, an inhibitor of p70 S6 protein kinase and a downstream target of ERK1/2 and PI 3-K, did not affect the activation of ERK1 and ERK2 by the growth factors. Furthermore, our results demonstrated that Akt, a downstream target of PI 3-K, was activated by PDGF-BB but not by FGF-2. Akt activation by PDGF-BB was inhibited by PI 3-kinase inhibitor LY294002. Rapamycin had no effect on Akt activation. Epidermal growth factor (EGF) also activated Akt in osteoblastic cells which was inhibited by LY294002 but not by rapamycin. Taken together, our data for the first time revealed that the activation of ERK1/2 by PDGF-BB is mediated by PI 3-K, and secondly, Akt is activated by PDGF-BB and EGF but not by FGF-2 in human and mouse osteoblastic cells. These results are of critical importance in understanding the role of these growth factors in apoptosis and cell survival. PDGF-BB and EGF but not FGF-2 may stimulate osteoblast cell survival.
Renal Division, Department of Internal Medicine, Washington University School of Medicine at Barnes-Jewish Hospital North, St. Louis, Missauri 63110, USA.
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D016475:3T3 Cells; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000077214:Becaplermin; D015153:Blotting, Western; D002455:Cell Division; D002470:Cell Survival; D002478:Cells, Cultured; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism*; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010006:Osteoblasts / Q000201:enzymology* / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010982:Platelet-Derived Growth Factor / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D020574:Proto-Oncogene Proteins c-sis; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors; D012272:Ribs / Q000166:cytology; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D020574:Proto-Oncogene Proteins c-sis; D016222:Fibroblast Growth Factor 2; D000077214:Becaplermin; D004815:Epidermal Growth Factor; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus; D000077191:Wortmannin