EFFECTS OF INHIBITORS OF SIGNAL-TRANSDUCTION PATHWAYS ON TRANSFORMING-GROWTH-FACTOR BETA-1 AND OSTEOGENIC PROTEIN-1-INDUCED INSULIN-LIKE-GROWTH-FACTOR BINDING PROTEIN-3 EXPRESSION IN HUMAN BONE-CELLS

Signal transduction initiated by TGF beta 1 and OP-l was studied in MG 63 human osteosarcoma cells and in normal human bone cells (HBCs) in t he presence of inhibitors of signal transduction events, using insulin like growth factor binding protein-3 (IGFBP-3) production as an end po int. Treatment of serum-tree MG63 cells and normal HBCs with TGF beta 1 increased IGFBP-3 protein level several fold in the conditioned medi um. This effect of TCF beta 1 was mediated by increased de novo synthe sis because mRNA level increased to the same extent as protein level a nd TCF beta 1 treatment had very little effect on IGFBP-3 protease act ivity, The stimulatory effect of TGF beta 1 on IGFBP-3 production was inhibited in a dose-dependent manner by pretreatment With staurosporin e, a protein kinase C inhibitor, or with vanadate, a phosphotyrosyl pr otein phosphatase inhibitor in both MG63 cells and normal HBCs. In add ition, pretreatment with okadoic acid, an inhibitor of serine/threonin e protein phosphatase, counteracted TGF beta 1 induction of IGFBP-3 pr oduction. interestingly, pretreatment of MG63 cells or HBCs with staur osporine, vanadate, or okadoic acid augmented OP-l stimulation of IGFB P-3 production. Staurosporine-or vanadate-induced changes in IGFBP-3 p rotein levels in the presence of TGF beta 1 and OP-l were associated w ith corresponding changes in IGFBP-3 mRNA levels in MG63 cells. These findings are consistent with the hypothesis that TGF beta 1 and OP-l i ncrease IGFBP-3 expression via distinct intracellular signal transduct ion pathways. (C) 1997 Wiley-Liss, Inc.