Hepatocyte growth factor (HGF), also known as scatter factor, is a powerful motogen, mitogen, and morphogen produced by cells of mesodermal origin, acting on epithelial and endothelial cells. Its receptor is the tyrosine kinase encoded by the c-MET protooncogene. We show that the HGF receptor is expressed by human primary osteoclasts, by osteoclast-like cell lines, and by osteoblasts. In both cell lineages, HGF stimulation triggers the receptor kinase activity and autophosphorylation. In osteoclasts, HGF receptor activation is followed by increase in intracellular Ca2+ concentration and by activation of the pp6Oc-src kinase. HGF induces changes in osteoclast shape and stimulates chemotactic migration and DNA replication. Osteoblasts respond to HGF by entering the cell cycle, as indicated by stimulation of DNA synthesis. Interestingly, osteoclasts were found to synthesize and secrete biologically active HGF. These data strongly suggest the possibility of an autocrine regulation of the osteoclast by HGF and a paracrine regulation of the osteoblast by the HGF produced by the osteoclast.Hepatocyte growth factor (HGF) (1, 2), also known as scatter factor (3), is secreted by cells of mesodermal origin and has mitogenic, motogenic, and morphogenic activity on epithelial and endothelial cells. The protein is a disulfide-linked heterodimer of two subunits of 60 and 32 kDa (4, 5). HGF is secreted as a biologically inactive single-chain precursor of 92 kDa (pro-HGF) that is activated into the mature form by urokinase in the extracellular environment (6) and by a factor XII related protease in serum (7). HGF induces pleiotropic effects on target cells, promoting proliferation, migration, and invasion of extracellular matrices (8, 9). In epithelial and endothelial cells, HGF induces cell polarization and stimulates the formation of three-dimensional tubular structures (10,11).The HGF receptor is the tyrosine kinase encoded by the MET protooncogene (12, 13). The receptor is a 190 kDa heterodimer consisting of an extracellular 50 kDa (a) chain disulfide linked to a transmembrane 145 kDa (13) chain, both derived from a single-chain 170 kDa precursor (14). The HGF receptor, originally detected in epithelial cells and often overexpressed in epithelial cancers (15), has also been found in hemopoietic cell lineages (16,17). Interestingly, we and others have recently shown that osteogenic sarcomas overexpress the MET protooncogene, and that bone giant cell tumors contain HGF (18). These data prompted us to study cell populations of skeletal origin, namely osteoblasts, whose progenitors belong to the bone marrow stromal lineage (19), and osteoclasts, deriving from monocyte-macrophage precursors (20).In this work, we show that both osteoblasts and osteoclasts express functional HGF receptors, and that osteoclasts also secrete HGF, suggesting an autocrine-paracrine control of osteoblast/osteoclast functions in vitro. MATERIALS AND METHODSCell Cultures. Primary human osteoclasts were obtained as described (21) by mechanical disa...

Abstract. Osteocalcin, also called Bone Gla Protein (BGP), is the most abundant of the non-collagenous proteins of bone produced by osteoblasts. It consists of a single chain of 46-50 amino acids, according to the species, and contains three vitamin K-dependent gamma-carboxyglutamic acid residues (GLA), involved in its binding to calcium and hydroxylapatite. Accumulating evidences suggest its involvement in bone remodeling, its physiological role, however, is still unclear. In this study the adhesion properties and the biological effects of osteocalcin on osteoclasts have been analyzed using as an experimental model, human osteoclast-like cells derived from giant cell tumors of bone (GCT). Osteocalcin promoted adhesion and spreading of these cells, triggering the release of bone sialoprotein (BSP), osteopontin (OPN) and fibronectin (FN), that in turn induced the clustering in focal adhesions of fl~ and/33 integrin chains. Spreading was dependent upon the synthesis of these proteins. In fact, when the cells were incubated in the presence of monensin during the adhesion assay, they still adhered but spreading did not occur, focal adhesions disappeared and BSP, OPN, and FN were accumulated in intracellular granules. Furthermore osteocalcin induced chemotaxis in a dose-dependent manner. The action of BGP on osteoclasts was mediated by an intracellular calcium increase due to release from thapsigargin-sensitive stores. These results provide evidences that BGP exerts a role in the resorption process, inducing intracellular signaling, migration and adhesion, followed by synthesis and secretion of endogenous proteins. STEOCALCIN, alSO called Bone Gla Protein (BGP), ~is the most abundant of the non-collagenous proteins of bone produced by osteoblasts, and has several interesting features. It consists of a single chain of 46-50 amino acids, according to the species, and contains three vitamin K-dependent gamma-carboxyglutamic acid residues (GLA), involved in its binding to calcium and hydroxylapatite (19,33). So far, BGP has been considered highly specific for bone, secreted by mature osteoblasts, and incorporated into the extracellular matrix. Recently, it has been demonstrated that the mouse genome contains an osteocalcin cluster composed of three genes (34, 13). The first two, named OG1 and OG2, are expressed only in bone, while the third

The covalent attachment of an Arg-Gly-Asp (RGD) containing peptide to polypyrrole(PPy)-coated titanium substrates has been investigated in order to develop a bioactive material of potential use in orthopedic fields. Polypyrrole has been employed as the coating polymer because of its suitability to be electrochemically grown directly onto metallic substrates of different shapes, leading to remarkably adherent films. The synthetic peptide Cys-Gly-(Arg-Gly-Asp)-Ser-Pro-Lys, containing the cell-adhesive region of fibronectin (RGD), has been grafted to the polymer substrate via the cysteine residue using a procedure recently developed in the authors laboratory. The effectiveness of grafting was monitored by X-ray photoelectron spectroscopy (XPS), which assessed the presence of the peptide grafted onto the polymer surface exploiting the cysteine sulfur as target element. Neonatal rat calvarial osteoblasts were attached to RGD-modified PPy-coated Ti substrates at levels significantly greater than on unmodified PPy-coated Ti and glass coverslip substrates.

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