The authors state that they have no conflicts of interest.
Negative Regulation by p70 S6 Kinase of FGF-2–Stimulated VEGF Release Through Stress-Activated Protein Kinase/c-Jun N-Terminal Kinase in Osteoblasts†
Article first published online: 18 DEC 2006
Copyright © 2007 ASBMR
Journal of Bone and Mineral Research
Volume 22, Issue 3, pages 337–346, March 2007
How to Cite
Takai, S., Tokuda, H., Hanai, Y., Harada, A., Yasuda, E., Matsushima-Nishiwaki, R., Kato, H., Ogura, S., Ohta, T. and Kozawa, O. (2007), Negative Regulation by p70 S6 Kinase of FGF-2–Stimulated VEGF Release Through Stress-Activated Protein Kinase/c-Jun N-Terminal Kinase in Osteoblasts. J Bone Miner Res, 22: 337–346. doi: 10.1359/jbmr.061209
- Issue published online: 4 DEC 2009
- Article first published online: 18 DEC 2006
- Manuscript Accepted: 15 DEC 2006
- Manuscript Revised: 20 NOV 2006
- Manuscript Received: 29 JUN 2006
- p70 S6 kinase;
- fibroblast growth factor-2;
- vascular endothelial growth factor;
- mitogen-activated protein kinase
To clarify the mechanism of VEGF release in osteoblasts, we studied whether p70 S6 kinase is involved in basic FGF-2–stimulated VEGF release in osteoblast-like MC3T3-E1 cells. In this study, we show that p70 S6 kinase activated by FGF-2 negatively regulates VEGF release through SAPK/JNK in osteoblasts.
Introduction: Vascular endothelial growth factor (VEGF) plays an important role in bone metabolism. We have previously reported that fibroblast growth factor-2 (FGF-2) stimulates the release of VEGF through p44/p42 mitogen-activated protein (MAP) kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells and that FGF-2–activated p38 MAP kinase negatively regulates VEGF release. However, the mechanism behind VEGF release in osteoblasts is not precisely known.
Materials and Methods: The levels of VEGF released from MC3T3-E1 cells were measured by enzyme immunoassay. The phosphorylation of each protein kinase was analyzed by Western blotting. To knock down p70 S6 kinase in MC3T3-E1 cells, the cells were transfected with siRNA to target p70 S6 kinase.
Results: FGF-2 time-dependently induced the phosphorylation of p70 S6 kinase. Rapamycin significantly enhanced the FGF-2–stimulated VEGF release and VEGF mRNA expression. The FGF-2–induced phosphorylation of p70 S6 kinase was suppressed by rapamycin. Rapamycin markedly enhanced the FGF-2–induced phosphorylation of SAPK/JNK without affecting the phosphorylation of p44/p42 MAP kinase or p38 MAP kinase. SP600125, a specific inhibitor of SAPK/JNK, suppressed the amplification by rapamycin of the FGF-2–stimulated VEGF release similar to the levels of FGF-2 with SP600125. Finally, downregulation of p70 S6 kinase by siRNA significantly enhanced the FGF-2–stimulated VEGF release and phosphorylation of SAPK/JNK.
Conclusions: These results strongly suggest that p70 S6 kinase limits FGF-2–stimulated VEGF release through self-regulation of SAPK/JNK, composing a negative feedback loop, in osteoblasts.