Effects of inhibitors of signal transduction pathways on transforming growth factor beta 1 and osteogenic protein-1-induced insulinlike growth factor binding protein-3 expression in human bone cells

Signal transduction initiated by TGF beta 1 and OP-l was studied in MG63 human osteosarcoma cells and in normal human bone cells (HBCs) in the presence of inhibitors of signal transduction events, using insulinlike growth factor binding protein-3 (IGFBP-3) production as an end point. Treatment of serum-tree MG63 cells and normal HBCs with TGF beta 1 increased IGFBP-3 protein level several fold in the conditioned medium. This effect of TCF beta 1 was mediated by increased de novo synthesis because mRNA level increased to the same extent as protein level and TCF beta 1 treatment had very little effect on IGFBP-3 protease activity, The stimulatory effect of TGF beta 1 on IGFBP-3 production was inhibited in a dose-dependent manner by pretreatment With staurosporine, a protein kinase C inhibitor, or with vanadate, a phosphotyrosyl protein phosphatase inhibitor in both MG63 cells and normal HBCs. In addition, pretreatment with okadoic acid, an inhibitor of serine/threonine protein phosphatase, counteracted TGF beta 1 induction of IGFBP-3 production. interestingly, pretreatment of MG63 cells or HBCs with staurosporine, vanadate, or okadoic acid augmented OP-l stimulation of IGFBP-3 production. Staurosporine-or vanadate-induced changes in IGFBP-3 protein levels in the presence of TGF beta 1 and OP-l were associated with corresponding changes in IGFBP-3 mRNA levels in MG63 cells. These findings are consistent with the hypothesis that TGF beta 1 and OP-l increase IGFBP-3 expression via distinct intracellular signal transduction pathways. (C) 1997 Wiley-Liss, Inc.