Mechanism of transforming growth factor-β1-induced expression of vascular endothelial growth factor in murine osteoblastic MC3T3-E1 cells

Transforming growth factor-beta 1 (TGF-beta 1), an abundant growth factor in bone matrix, has been shown to be involved in bone formation and fracture healing. The mechanism of action of the osteogenic effect of TGF-beta 1 is not clearly understood. In this study, we found that the addition of TGF-beta 1 to murine osteoblastic MC3T3-E1 cells induced vascular endothelial growth factor (VEGF) mRNA production. VEGF mRNA levels reached a plateau within 2 h after the addition of TGF-beta 1. The induction was superinduced by cycloheximide and blocked by actinomycin D. Ro 31-8220, a protein kinase C inhibitor, abrogated the induction. In addition, curcumin, an inhibitor for transcription factor AP-1, also blocked the induction. Electrophoretic mobility shift assay revealed an enhanced binding of transcription factors AP-1 and NF-kappa B. Transient transfection experiment showed that VEGF promoter activity increased 3.6-fold upon TGF-beta 1 stimulation. Immunoblot analysis showed that the amount of secreted VEGF was elevated in the medium 4 h after TGF-beta 1 stimulation. Our results therefore suggest that at least part of the osteogenic activity of TGF-beta 1 may be attributed to the production of VEGF. (C) 2000 Elsevier Science B.V. All rights reserved.