Submitted on July 8, 2002
Accepted on February 19, 2003
p38 MAP kinase regulates BMP-4-stimulated VEGF synthesis via p70 S6 kinase in osteoblasts
Haruhiko Tokuda1, Daijiro Hatakeyama2, Toshiyuki Shibata2, Shigeru Akamatsu2, Yutaka Oiso3, and Osamu Kozawa2*
1 Department of Internal Medicine, Chubu National Hospital: National Institute for Longitivity Science, Obu, Aichi, Japan
2 Department of Pharmacology, Department of Oral and Maxillofacial Surgery, and Department of Critical Care Medicine, Gifu University School of Medicine, Gifu, Gifu, Japan
3 First Department of Internal Medicine, Nagoya University School of Medicine, Nagoya, Aichi, Japan
* To whom correspondence should be addressed. E-mail: okozawa{at}cc.gifu-u.ac.jp.
We previously reported that p70 S6 kinase takes part in bone morphogenetic protein-4 (BMP-4)-stimulated vascular endothelial growth factor (VEGF) synthesis in osteoblast-like MC3T3-E1 cells. Recently, we showed that BMP-4-induced osteocalcin synthesis is regulated by p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase in these cells. In the present study, we investigated whether the MAP kinases are involved in the BMP-4-stimulated synthesis of VEGF in MC3T3-E1 cells. PD98059 and U0126, inhibitors of upstream kinase of p44/p42 MAP kinase, failed to affect the BMP-4-stimulated VEGF synthesis. SB203580 and PD169316, inhibitors of p38 MAP kinase, significantly reduced the VEGF synthesis while SB202474, a negative control for p38 MAP kinase inhibitor, had little effect on the VEGF synthesis. The BMP-4-stimulated phosphorylation of p38 MAP kinase was not affect by rapamycin, an inhibitor of p70 S6 kinase. On the contrary, SB203580 and PD169316 reduced the BMP-4-stimulated phosphorylation of p70 S6 kinase. In addition, anisomycin, an activator of p38 MAP kinase, phosphorylates p70 S6 kinase and the phosphorylation was suppressed by SB203580. LY294002, an inhibitor of phosphatidylinositol 3-kinase, failed to suppress the phosphorylation of p38 MAP kinase induced by BMP-4. Not BMP-4 but anisomycin weakly induced the phosphorylation of PDK-1. However, anisomycin had little effect on those of either Akt or mTOR. Taken together, our results suggest that p38 MAP kinase functions in BMP-4-stimulated VEGF synthesis as a positive regulator at a point upstream from p70 S6 kinase in osteoblasts.
