Platelet-derived growth factor-BB amplifies PGF(2)(alpha)-stimulated VEGF synthesis in osteoblasts: Function of phosphatidylinositol 3-kinase.

摘要

We have reported that prostaglandin F(2)(alpha) (PGF(2)(alpha)) stimulates the synthesis of vascular endothelial growth factor (VEGF) via p44/p42 mitogen-activated protein (MAP) kinase in osteoblast-like MC3T3-E1 cells. In addition, we recently showed that phosphatidylinositol 3 (PI3)-kinase activated by platelet-derived growth factor-BB (PDGF-BB) negatively regulates the interleukin-6 synthesis in these cells. In the present study, we investigated the effect of PDGF-BB on the PGF(2)(alpha)-induced VEGF synthesis in MC3T3-E1 cells. PDGF-BB, which alone did not affect the levels of VEGF, significantly enhanced the PGF(2)(alpha)-stimulated VEGF synthesis. The amplifying effect of PDGF-BB was dose dependent in the range between 10 and 70ng/ml. LY294002 or wortmannin, specific inhibitors of PI3-kinase, which by itself failed to affect the PGF(2)(alpha)-stimulated VEGF synthesis, significantly suppressed the amplification by PDGF-BB. PD98059, a specific inhibitor of MEK1/2, suppressed the amplification by PDGF-BB of the PGF(2)(alpha)-stimulated VEGF synthesis similar to the levels of PGF(2)(alpha) with PD98059. PDGF-BB itself induced the phosphorylation of p44/p42 MAP kinase in these cells, and the effects of PDGF-BB and PGF(2)(alpha) on the phosphorylation of p44/p42 MAP kinase were additive. Moreover, LY294002 had little effect on the phosphorylation of p44/p42 MAP kinase induced by PGF(2)(alpha) with PDGF-BB. These results strongly suggest that PGF(2)(alpha)-stimulated VEGF synthesis is amplified by PI3-kinase-mediating PDGF-BB signaling in osteoblasts, and that the effect is exerted at a point downstream from p44/p42 MAP kinase.