EXPRESSION OF THE NUCLEOSIDE TRIPHOSPHATE PYROPHOSPHOHYDROLASE PC-1 IS INDUCED BY BASIC FIBROBLAST GROWTH-FACTOR (BFGF) AND MODULATED BY ACTIVATION OF THE PROTEIN-KINASE-A AND PROTEIN-KINASE-C PATHWAYS IN OSTEOBLAST-LIKE OSTEOSARCOMA CELLS

The closely related cytokines bFGF and aFGF regulate the function of b one cells and mineralization, Osteoblasts express PPi-generating nucle oside triphosphate pyrophosphohydrolase (NTPPPH)/nucleotide phosphodie sterase I activity, bFGF and aFGF (10 ng/ml) up-regulated NTPPPH in hu man SaOS-2 and U2OS osteosarcoma cells, which express osteoblast-like features in culture, The induction was selective as alkaline phosphata se activity was down-regulated and specific as insulin-like growth fac tor-1 (IGF-1) and interleukin-1 beta (IL-1 beta) were not active, Furt hermore, IL-1 beta but not IGF-1 inhibited bFGF-induced up-regulation of NTPPPH. The induced NTPPPH remained predominantly associated with c ells, bFGF can induce signaling through pathways including protein kin ase A (PKA) and protein kinase C (PKC)-mediated transduction, An activ ator of the PKA pathway (8-bromo cyclic adenosine monophosphate [cAMP] ) induced NTPPPH. Furthermore, pretreatment with the PKC activator pho rbol myristate acetate (PMA) (80 nM) markedly increased subsequent NTP PPH induction by both bFGF and cAMP, The PMA effect,vas associated wit h morphologic changes characterized by long, thin intercellular extens ions. PKC desensitization also potentially contributed to this effect because the PKC inhibitors staurosporine and H-7 enhanced bFGF-induced and cAMP-induced NTPPPH expression in the absence of morphologic chan ges, We observed that bFGF induced expression of PC-1, a member of the NTPPPH gene family. The majority of NTPPPH activity was depleted by i mmunoadsorption using a monoclonal antibody to native human PC-1, bFGF - and aFGF-induced production of PC-1/NTPPPH in osteoblastoid cells ma y contribute to the effects of FGFs on bone metabolism.