Matrix sialoprotein of developing bone

Using nondegradative isolation procedures, we purified and characterized a glycoprotein from fetal calf bone that is rich in sialic acid. This bone sialoprotein (BSP) has an apparent Mr = 70,000-80,000 and stains with Alcian blue and Stains All on sodium dodecyl sulfate gels but does not stain with Coomassie blue without prior treatment with neuraminidase. This glycoprotein contains 50% protein, 12% sialic acid, 7% glucosamine, and 6% galactosamine. Fetal calf BSP is rich in glutamate (19%), aspartate (15.4%), and glycine (11.8%) but, in contrast to osteonectin and the bone proteoglycan, has relatively low amounts of leucine (4.3%). Antisera raised against fetal calf BSP localized the glycoprotein by indirect immunofluorescence to developing bone trabeculae with an overall tissue distribution identical with that of osteonectin. On competition enzyme-linked immunosorbent assay analysis, BSP was 11.5% (+/-2.4%, S.E.) of mineral-bound (guanidine-EDTA-soluble) calf bone protein. Immunoreplicas (Western blots) of calf bone extracts suggest that more than 95% of the antigenicity resided in the Mr = 70,000-80,000 region with the remaining cross-reactivity in Alcian blue positive, Mr = approximately 20,000 and approximately 30,000 bands. Brief treatment of the Mr = 70,000-80,000 species with trypsin produced lower molecular weight, Alcian blue-staining products of similar size. No BSP was detected in guanidine extracts of various soft or unmineralized connective tissues, but dentin contained small amounts (0.4%) of the protein. Rat and fetal human bone were also observed to contain a sialoprotein with similar properties and a certain degree of cross-reactivity with the bovine BSP.     

Keratan sulfate proteoglycan in rabbit compact bone is bone sialoprotein II

A keratan sulfate proteoglycan was isolated under denaturing conditions from the mineral compartment of rabbit cortical bone. This small proteoglycan (Kd = 0.39 on Superose 6, Mr approximately 20,000 on sodium dodecyl sulfate gels) contained small keratan sulfate chains that were distinctly bimodal in size. The keratanase and endo-beta-galactosidase digestible glycosaminoglycan chains were O-linked to a core protein of Mr approximately 80,000. This core protein had several properties in common with the bone sialoprotein II molecule of bovine and human bone including: a closely spaced doublet band on sodium dodecyl sulfate electrophoresis gels; a high staining intensity with Stains All that was greatly diminished by neuraminidase; a significant amount of small O-linked oligosaccharides; and an amino-terminal amino acid sequence that was nearly identical to human bone sialoprotein II. (In contrast, bone sialoprotein II in human, bovine, and rat bone does not appear to have any keratan sulfate chains.) Antiserum made against the keratan sulfate proteoglycan reacted with its core protein on electrotransfers from sodium dodecyl sulfate-polyacrylamide gels.     

Identification of a bone sialoprotein receptor in osteosarcoma cells

Bone sialoprotein (BSP) is an extracellular matrix glycoprotein associated with the mineral bone matrix. The amino acid sequence of BSP contains an Arg-Gly-Asp (RGD) sequence which confers to the protein cell binding properties (Oldberg, A., Franzén, A., and Heineg?rd, D. (1988) J. Biol. Chem. 263, 19430-19432). When BSP was used as an affinity matrix to isolate a cell surface receptor from rat osteosarcoma cells, a protein composed of polypeptides similar in size to those of a previously characterized vitronectin receptor was obtained. This putative BSP receptor, like the vitronectin receptor, bound also to an affinity matrix made of an RGD-containing heptapeptide. Moreover, similar patterns of inhibition of cell attachment to BSP and vitronectin was obtained with variant RGD-containing peptides, with BSP and with vitronectin. Finally, an anti-vitronectin receptor antiserum immunoprecipitated a receptor identical in size to the receptor bound to a BSP affinity matrix. These results show that BSP is recognized by an RGD-directed receptor and that both vitronectin and BSP can bind to this receptor.     

Neoplastic odontogenic epithelial cells express bone sialoprotein

Bone sialoprotein (BSP) is synthesized and secreted by bone-, dentine- and cementum-forming cells and has been implicated in de novo bone formation and mineralization. In this study, we used histological sections of odontogenic neoplasms and performed immunohi stochemical and in situ hybridization analyses. In ameloblastoma, BSP mRNA signals were seen in the neoplastic epithelial cells forming nests, strips and islands. BSP deposition was also seen in the stellate reticulum of the tumour masses revealed by immunohistochemistry using human BSP antibodies. In calcifying epithelial odontogenic tumour, the calcified masses demonstrated positive immunoreactivity to the human BSP antibodies, and the hybridization signals for BSP were located in the cells near the calcified particles. In the calcifying odontogenic cyst, strong BSP signals were seen in cells surrounding the characteristic nests of ghost cells, which often calcify subsequently. BSP protein was also found in these cells by immunohistochemistry. The active expression of BSP in the epithelial elements of the odontogenic tumours of adult patients suggests the activation of this matrix protein gene in the neoplastic process, and that BSP may play an important role in tumour formation and differentiation with respect to pathological calcification. © Chapman & Hall     

Delineation of the hydroxyapatite-nucleating domains of bone sialoprotein

Bone sialoprotein (BSP) is a highly modified, anionic phosphoprotein that is expressed almost exclusively in mineralizing connective tissues and has been shown to be a potent nucleator of hydroxyapatite (HA). Two polyglutamic acid (poly[E]) regions, predicted to be in an alpha-helical conformation and located in the amino-terminal half of the molecule, are believed to be responsible for this activity. Using a prokaryotic expression system, full-length rat BSP was expressed and tested for HA nucleating activity in a steady-state agarose gel system. The unmodified protein is less potent than native bone BSP, indicating a role for the post-translational modifications in HA nucleation. Site-directed mutagenesis of the poly[E] regions in full-length BSP was performed, replacing the poly[E] with either polyaspartic acid (poly[D]) or polyalanine (poly[A]) to examine role of charge and conformation, respectively, in HA nucleation. Replacement of single domains with either poly[A] or poly[D] did not alter nucleating activity nor did replacement of both domains with poly[D]. Replacement of both domains with poly[A], however, significantly decreased nucleating activity. In addition, two recombinant peptides, each encompassing one of the two poly[E] domains, were expressed and tested for nucleating activity. Whereas the peptide encompassing the second poly[E] domain was capable of nucleating HA, the first domain peptide showed no activity. The conformation of the wild-type and mutated proteins and peptides were studied by circular dichroism and small angle x-ray scattering, and no secondary structure was evident. These results demonstrate that a sequence of at least eight contiguous glutamic acid residues is required for the nucleation of HA by BSP and that this nucleating "site" is not alpha-helical in conformation.     

The primary structure of a cell-binding bone sialoprotein

We have determined the amino acid sequence of rat bone sialoprotein (BSP). The sequence deduced from a 1974-base pair cDNA encodes a protein of 320 residues, including a 16-residues long signal peptide. The mature BSP has a molecular mass of 33,600 and contains predominantly glutamic acid and glycine residues, which constitute 32% of all residues. The glutamic acid residues are typically distributed in clusters of up to 10 consecutive residues. The tissue distribution of BSP mRNA suggests that the protein may be a unique product of cells in bone tissue. BSP contains an Arg-Gly-Asp sequence, which presumably is responsible for its cell binding properties (Oldberg, A., Franzén, A., Heineg?rd, D., Pierschbacher, M., and Ruoslahti, E. (1988) J. Biol. Chem. 263, 19433-19436).     

Quantitative immunogold labeling of bone sialoprotein and osteopontin in methylmethacrylate-embedded rat bone.

Methylmethacrylate (MMA) embedding of undecalcified bone is routinely employed for histomorphometric analyses. Although MMA-embedded bone has been used for immunolabeling at the light microscopic level after removal of the resin, there are no such reports for electron microscopy. The aim of the present study was to determine whether MMA embedding can be used for ultrastructural immunolabeling and how it compares to LR White (LRW), an acrylic resin frequently used for immunocytochemistry of bone. Rat tibiae were fixed by vascular perfusion with aldehyde and embedded either in MMA or LRW resin. Thin sections were processed for postembedding protein A-gold immunolabeling with antibodies to rat bone sialoprotein (BSP) and osteopontin (OPN). The density of gold particles over bone was quantified. The density and distribution of immunolabeling for BSP and OPN respectively, were comparable between MMA and LRW. These results indicate that MMA performs as well as LRW for the ultrastructural immunolabeling of noncollagenous bone matrix proteins.     

Ethical issues in transgenics

The arguments of critics and concerns of the public on generating transgenic cloned animals are analyzed for the absence or presence of logical structure. Critics' arguments are symbolically compared with "genetic trespassing," "genetic speeding," or "going the wrong way," and responses are provided to these arguments. Scientists will be empowered to participate in the public discussion and to engage the critics on these issues as they consider thoughtful, plausible responses to their concerns. Temporary moratoriums are recognized as a plausible approach to dealing with possible concerns of new scientific advancements.     

Some studies on the composition of bovine cortical-bone sialoprotein

1. An analysis of bovine bone sialoprotein, a homogeneous glycoprotein isolated from cortical bone, is presented. 2. Analytical results agree with earlier physical measurements indicating a molecular weight of about 23000. 3. Mild acid hydrolysis and treatment with neuraminidase showed that fucose and sialic acid occupy terminal positions on oligosaccharide chains. 4. Treatment of the sialic acid-free glycoprotein with beta-galactosidase showed that much of the galactose occupies a sub-terminal location in the intact glycoprotein. 5. The polypeptide chain is rich in aspartic acid, glutamic acid, serine, threonine and glycine, and has no detectable free terminal amino group. 6. Glycopeptides were studied after proteolytic digestion. 7. It is considered that the carbohydrate moiety is highly branched and is probably linked by an acid- and alkali-stable glycosylamine bond involving aspartic acid.