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Results for “Receptors, Vitronectin”

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At least 19 recordsLinked to original sources

PubMed1993

[Expression of fibronectin receptor and vitronectin receptor in diseased human kidneys].

Expression of fibronectin and vitronectin receptors was studied in normal human kidney tissues and renal tissue biopsies from patients with several types of glomerulonephritis. Immunofluorescent staining of the normal kidneys showed that fibronectin receptor was present along the glomerular capillary walls, and that vitronectin receptor was present in the vessel walls, but was almost absent from the glomerulus. In kidney tissues biopsied from patients with various renal diseases, expression of fibronectin and vitronectin receptors was correlated with increase in the mesangial expansion. Expression of these receptors was decreased in the sclerosed area and hyalinized glomeruli compared with normal tissues. Fibronectin and vitronectin receptors were occasionally colocalized in the glomeruli with fibronectin and vitronectin, respectively. In situ hybridization showed that fibronectin receptor mRNA and vitronectin receptor mRNA were expressed in the diseased glomeruli. These findings indicate that expression of fibronectin and vitronectin receptors was altered in human glomerulonephritis, and that integrin expression may be important in cell-matrix interaction in the diseased glomeruli.

Glomerulonephritis↗

PubMed1990

Integrin (alpha v beta 3)-ligand interaction. Identification of a heterodimeric RGD binding site on the vitronectin receptor.

The vitronectin receptor mediates cell adhesion to the extracellular matrix proteins vitronectin, fibrinogen, von Willebrand factor, and thrombospondin in an RGD-dependent manner. We previously demonstrated the direct interaction between the vitronectin receptor and an RGD-containing peptide by photoaffinity labeling the receptor with 125I-sulfosuccinimidyl-2-(p-azido-salicylamido)-1,3'-dithioprop ion ate (SASD)-GRGDSPK (Smith, J. W., and Cheresh, D. A. (1988) J. Biol. Chem. 263, 18726-18731). In that report, we identified amino acid residues 61-203 of the beta-subunit as proximal to the ligand binding site. Here we demonstrate that 125I-SASD-GRGDSPK affinity labels the alpha-subunit of the receptor at least two distinct sites within the region encompassing residues 139-349. Both of these regions are within the putative divalent cation binding region of the alpha-subunit. Collectively, our results suggest that discrete amino-terminal domains of both subunits of the receptor contribute to the structure of the ligand binding domain and furthermore that the ligand and divalent cation binding domains are spatially and functionally linked.

Affinity Labels↗

PubMed1989

Biogenesis of the vitronectin receptor in human endothelial cell: evidence that the vitronectin receptor and GPIIb-IIIa are synthesized by a common mechanism.

Human endothelial cells express a membrane glycoprotein alpha beta heterodimer similar to the human platelet glycoprotein IIb-IIIa complex (GPIIb-IIIa). This noncovalently associated complex is the vitronectin receptor (VNR). These two receptors belong to the cytoadhesin family and share the same beta subunit. They express different recognition specificities: platelet GPIIb-IIIa is a receptor for fibrinogen, fibronectin, and von Willebrand factor (vWF), whereas VNR is a receptor for vitronectin, and is possibly a receptor for fibrinogen and vWF. We analyzed the biosynthesis of the endothelial cell VNR. Our data show that VNR alpha is a two-chain protein which is biosynthesized as a single-chain precursor: the pro-VNR alpha. Pro-VNR alpha forms a complex with VNR beta, and this association occurs prior to the Golgi-mediated processing of the oligosaccharide side chains. Mature VNR beta is glycosylated by not fully processed oligosaccharide side chains because it remains endoglycosidase H (endo H) sensitive, even when the complex is expressed on the cell surface. This characteristic appears as a common feature for the members of the cytoadhesin family. These results indicate that although VNR and GPIIb-IIIa are biosynthesized in different cells, their expression is controlled by similar mechanisms, providing further support for the concept that the cytoadhesin family constitutes a distinct group of adhesion receptors.

Cells, Cultured↗

PubMed1990

The integrin beta 1 subunit associates with the vitronectin receptor alpha v subunit to form a novel vitronectin receptor in a human embryonic kidney cell line.

We describe a novel integrin heterodimer on the surface of the human embryonic kidney cell line 293. This receptor is comprised of alpha v and beta 1 subunits, each of which has been previously found in association with other integrin subunits. This alpha v.beta 1 complex was identified as the predominant vitronectin receptor (VnR) on the surface of 293 cells by immunoprecipitation with antibodies raised against the alpha v subunit. Polymerase chain reaction analysis detected mRNAs for alpha v and beta 1 subunits while no evidence was obtained for beta 2, beta 3, or alpha IIb integrin subunit mRNA. Immunoprecipitation of surface-iodinated proteins with antibodies to alpha v gave bands of 150 and 120 kDa. The 120-kDa band reacted with antibodies to beta 1 in immunoblotting experiments. 293 cells adhere to vitronectin, fibronectin, laminin, and collagen IV, while von Willebrand factor and fibrinogen, known ligands of the VnR (alpha v.beta 3), did not support adhesion. A polyclonal antibody directed against both subunits of the VnR (alpha v, beta 3) inhibits attachment of 293 cells to vitronectin but not to other adhesive proteins. A beta 1-specific monoclonal inhibited attachment to fibronectin, laminin, and collagen IV, known ligands of beta 1 integrins, as well as vitronectin. This novel (alpha v. beta 1) VnR thus appears to mediate cell adhesion exclusively to vitronectin, in contrast to previously described VnRs which have multiple ligands.

Antibodies↗

PubMed1989

Regulation of cell adhesion receptors by transforming growth factor-beta. Regulation of vitronectin receptor and LFA-1.

We have examined the ability of transforming growth factor-beta 1 (TGF-beta 1) to regulate the expression of members of the alpha beta 2 and alpha beta 3 families of integrins. TGF-beta 1 elevates the expression of vitronectin receptors (alpha v beta 3 integrin) in all cells examined including WI-38 human lung fibroblasts, 3T3-L1 mouse fibroblasts, and MG-63 human osteogenic sarcoma cells. TGF-beta 1 action increases the level of mRNA and the synthesis of vitronectin receptor subunits with t1/2 o 3-4 h and 6 h, respectively. TGF-beta 1 up-regulates expression of the intercellular adhesion receptor, LFA-1 (alpha L beta 2), in THP-1 human monocytic leukemia cells by increasing the synthesis of alpha L subunit but not beta 2 subunit. The increase in alpha L synthesis and assembly into LFA-1 complexes induced by TGF-beta 1 occurs in parallel with elevated fibronectin receptor synthesis in THP-1 cells. These responses to TGF-beta 1 are lost upon phorbol ester-induced differentiation of THP-1 cells into the macrophage phenotype. The results suggest a role of TGF-beta in the regulation of cell-matrix interactions mediated by vitronectin receptors and cell-cell interactions mediated by LFA-1 in the immune system.

Animals↗

PubMed1987

Comparison of cDNA-derived protein sequences of the human fibronectin and vitronectin receptor alpha-subunits and platelet glycoprotein IIb.

The fibronectin receptor (FnR), the vitronectin receptor (VnR), and the platelet membrane glycoprotein (GP) IIb-IIIa complex are members of a family of cell adhesion receptors, which consist of noncovalently associated alpha- and beta-subunits. The present study was designed to compare the cDNA-derived protein sequences of the alpha-subunits of human FnR, VnR, and platelet GP IIb. cDNA clones for the alpha-subunit of the FnR (FnR alpha) were obtained from a human umbilical vein endothelial (HUVE) cell library by using an oligonucleotide probe designed from a peptide sequence of platelet GP IIb. cDNA clones for platelet GP IIb were isolated from a cDNA expression library of human erythroleukemia cells by using antibodies. cDNA clones of the VnR alpha-subunit (VnR alpha) were obtained from the HUVE cell library by using an oligonucleotide probe from the partial cDNA sequence for the VnR alpha. Translation of these sequences showed that the FNR alpha, the VnR alpha, and GP IIb are composed of disulfide-linked large (858-871 amino acids) and small (137-158 amino acids) chains that are posttranslationally processed from a single mRNA. A single hydrophobic segment located near the carboxyl terminus of each small chain appears to be a transmembrane domain. The large chains appear to be entirely extracellular, and each contains four repeated putative Ca2+-binding domains of about 30 amino acids that have sequence similarities to other Ca2+-binding proteins. The identity among the protein sequences of the three receptor alpha-subunits ranges from 36.1% to 44.5%, with the Ca2+-binding domains having the greatest homology. These proteins apparently evolved by a process of gene duplication.

Amino Acid Sequence↗

PubMed1987

Amino acid sequence of the vitronectin receptor alpha subunit and comparative expression of adhesion receptor mRNAs.

The amino acid sequence of the vitronectin receptor alpha subunit deduced from cDNA is presented. The sequence defines a 1047-amino-acid polypeptide precursor with a putative signal sequence, a large extracellular domain with several sites homologous to calcium binding sites in other proteins, a transmembrane domain, and a 32-amino-acid cytoplasmic domain. The 7-kilobase vitronectin receptor alpha subunit mRNA was found to be expressed in all cell lines examined, including endothelial cells, K562 and HEL leukemia cells, and osteosarcoma cells. In the two leukemia cell lines, the expression of the vitronectin receptor mRNA, as well as that of the fibronectin receptor, was enhanced in the presence of phorbol ester, a treatment known to increase the adhesiveness of these cells. The HEL cells were the only ones among the cell lines tested that also contained the mRNA of the platelet adhesion receptor alpha subunit, glycoprotein IIb. The expression of glycoprotein IIb was slightly enhanced by treatment of the cells with phorbol ester. These results complete the partial cDNA sequence of the vitronectin receptor alpha subunit published previously (Suzuki, S., Argraves, W. S., Pytela, R., Arai, H., Krusius, T., Pierschbacher, M. D., and Ruoslahti, E. (1986) Proc. Natl. Acad. Sci. U.S.A., 83, 8614-8618), confirm that the vitronectin receptor, and not IIb, is expressed in endothelial cells, and show that changes in the level of its expression correlate with changes in cell adhesiveness.

Amino Acid Sequence↗

PubMed1988

Cell surface distribution of fibronectin and vitronectin receptors depends on substrate composition and extracellular matrix accumulation.

We used antibodies against the alpha subunits of the human fibronectin receptor (FNR) and vitronectin receptor (VNR) to localize simultaneously FNR and VNR at major substrate adhesion sites of fibroblasts and melanoma cells with double-label immunofluorescence microscopy. In early (2-6-h) serum-containing cultures, both FNR and VNR coaccumulated in focal contacts detected by interference reflection microscopy. Under higher resolution immunoscanning electron microscopy, FNR and VNR were also observed to be distributed randomly on the dorsal cell surface. As fibronectin-containing extracellular matrix fibers accumulated beneath the cells at 24 h, FNR became concentrated at contacts with these fibers and was no longer detected at focal contacts. VNR was not observed at matrix contacts but remained strikingly localized in focal contacts of the 24-h cells. Since focal contacts represent the sites of strongest cell-to-substrate adhesion, these results suggest that FNR and VNR together play critical roles in the maintenance of stable contacts between the cell and its substrate. In addition, the accumulation of FNR at extracellular matrix contacts implies that this receptor might also function in the process of cellular migration along fibronectin-containing matrix cables. To define the factors governing accumulation of FNR and VNR at focal contacts, fibroblasts in serum-free media were plated on substrates coated with purified ligands. Fibronectin-coated surfaces fostered accumulation of FNR but not VNR at focal contacts. On vitronectin-coated surfaces, or substrata derivatized with a tridecapeptide containing the cell attachment sequence Arg-Gly-Asp, both FNR and VNR became concentrated at focal contacts. These observations suggest that the availability of ligand is critical to the accumulation of FNR and VNR at focal contacts, and that FNR might also recognize substrate-bound vitronectin.

Cell Adhesion↗

PubMed1994

Immunohistochemical studies of vitronectin, C5b-9, and vitronectin receptor in membranous nephropathy.

To investigate the involvement of vitronectin, the terminal complement complex (C5b-9), and the vitronectin receptor in the pathogenesis of membranous nephropathy, the immunohistochemical localization of these antigens in the kidney was determined using the immunoperoxidase method and monoclonal antibodies: antivitronectin, anti-SC5b-9 (neoantigen), and antivitronectin receptor (specific for alpha v beta 3 and alpha v). The subjects were 6 patients with membranous nephropathy, and the controls were 2 patients with minimal-change nephrotic syndrome. In membranous nephropathy, vitronectin was localized in subepithelial deposits and in epithelial cell foot processes and was intensely positive in the foot processes adjacent to subepithelial deposits. C5b-9 showed a similar pattern of localization to vitronectin. Both alpha v beta 3 and alpha v were localized in the basal portions of the foot processes of visceral epithelial cells as well as along the borders of these cells adjacent to the urinary space. Deposition at the former site was heavier than at the latter, and localization was especially prominent adjacent to the subepithelial deposits. In addition, alpha v was localized around and within some of the electron-lucent subepithelial deposits in the basement membrane. In contrast, the deposition of vitronectin, C5b-9, alpha v beta 3, and alpha v was always less intense in minimal-change nephrotic syndrome than in membranous nephropathy. Vitronectin and C5b-9 were localized to small parts of mesangium and glomerular basement membrane, while alpha v beta 3 and alpha v deposits showed no difference in intensity between the basal portions of the foot processes and the urinary border of the visceral epithelial cells. Thus, membranous nephropathy featured increased localization of vitronectin, C5b-9, and vitronectin receptors both within and around the subepithelial deposits, suggesting that the mechanism of immune complex disposal via the vitronectin receptor and the vitronectin-C5b-9 complex, associated with complement activation due to subepithelial immune complex formation, may also be active.

Adult↗

PubMed1991

Adhesive properties of the beta 3 integrins: comparison of GP IIb-IIIa and the vitronectin receptor individually expressed in human melanoma cells.

Glycoprotein IIb-IIIa (alpha IIb beta 3) and the vitronectin receptor (alpha v beta 3), two integrins that share the common beta 3 subunit, have been reported to function as promiscuous receptors for the RGD-containing adhesive proteins fibrinogen, vitronectin, fibronectin, von Willebrand factor, and thrombospondin. The present study was designed to establish a cell system for the expression of either GP IIb-IIIa or the vitronectin receptor in an otherwise identical cellular environment and to compare the adhesive properties of these two integrins with those of native GP IIb-IIIa and the vitronectin receptor constitutively expressed in HEL cells or platelets. M21 human melanoma cells lack GP IIb-IIIa and use the vitronectin receptor to attach to vitronectin, fibrinogen, fibronectin, and von Willebrand factor. To study the functional properties of GP IIb-IIIa in these cells, we transfected GP IIb into M21-L cells, a variant of M21 cells (Cheresh, D.A., and R.C. Spiro. 1987. J. Biol. Chem. 262:17703-17711), which lack the expression of functional alpha v and are therefore unable to attach to vitronectin, fibrinogen, and von Willebrand factor. Transfectants expressing GP IIb were isolated by immunomagnetic beads and surface expression of the GP IIb-IIIa complex was documented by FACS analysis and immunoprecipitation experiments performed with 125I-labeled M21-L/GP IIb cells. Comparative functional studies demonstrated that GP IIb-IIIa expressed in M21-L/GPIIb cells as well as native GP IIb-IIIa constitutively expressed in HEL-5J20 cells (an HEL variant lacking alpha v beta 3) mediated cell attachment to immobilized fibrinogen, but not to vitronectin or von Willebrand factor, whereas the vitronectin receptor expressed in M21 cells and HEL-AD1 cells (an HEL variant expressing alpha v beta 3) mediated cell attachment to fibrinogen, vitronectin, and von Willebrand factor. Similarly, PGl2-treated resting platelets attached to immobilized fibrinogen but not to vitronectin or von Willebrand factor, and this attachment could be inhibited by mAb A2A9 (directed against a functional site on the GP IIb-IIIa complex). However, in contrast to platelets, which adhered to vitronectin and von Willebrand factor after stimulation by thrombin or PMA, activation of the protein kinase C pathway in M21-L/GP IIb or HEL cells did not induce cell adhesion to vitronectin or von Willebrand factor.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Platelets↗

PubMed1996

Expressions of very late antigen-6 and vitronectin receptor, and their interactions to laminin and vitronectin during tonsillar B-cell activation.

This study examined the expressions of a-subunits of very late antigen-6 (VLA-6; alpha 6) and vitronectin receptor (VNR; alpha V) on tonsillar B cells and interactions between those integrins and their respective ligands, laminin (LM) and vitronectin (VN). alpha 6 and alpha V were expressed on about 30 to 40% of tonsillar B cells. When purified tonsillar B cells were separated by a discontinuous Percoll gradient, the number of alpha 6- and alpha V-positive cells decreased as the cell density went down, while the number of activated cells went up. After in vitro activation of tonsillar B cells by Staphylococcus aureus Cowan I strain (SAC), the expressions of alpha 6 and alpha V and their adhesiveness to LM or VN decreased significantly. Increased proliferation of B cells was observed when tonsillar B cells were cultured with immobilized LM or VN. The results of immunohistological staining showed VLA-6, VNR, LM and VN in the follicular area. These results suggest that the expressions of VLA-6 and VNR on tonsillar B cells may be decreased during B cell activation, and the interaction between VLA-6, VNR, and LM, VN may give a costimulatory effect on B cell activation in the follicular area of the tonsil.

Antibodies, Monoclonal↗

PubMed1992

Up-regulated biosynthesis and expression of endothelial cell vitronectin receptor enhances cancer cell adhesion.

Extravasation of circulating cancer cells during metastasis is thought to involve adhesion to the vascular endothelium. To characterize this process, we measured the attachment of A549 human lung carcinoma cells to monolayers of cultured human umbilical vein endothelial cells. Pretreatment of the endothelial cells with 10 ng/ml interleukin 1 alpha (IL-1) for 4 h increased cancer cell attachment 2-5-fold. This increase was blocked by 100 microM glycyl-arginyl-glycyl-aspartyl-serine peptide and was decreased 60 +/- 10% (SD) by a vitronectin receptor polyclonal antiserum or 56 +/- 8% by a vitronectin receptor monoclonal antibody, LM609. Glycyl-arginyl-glycyl-aspartyl-serine or the vitronectin receptor antibodies did not inhibit cancer cell attachment to untreated endothelial cells. A fibronectin receptor antiserum had no effect on attachment to untreated or IL-1-treated endothelial cells. Pretreatment of endothelial cells with IL-1 increased their adhesion to fibronectin and vitronectin and increased the expression of vitronectin receptor and fibronectin receptor as detected by immunofluorescence flow cytometry, quantitative antibody binding, and immunoprecipitation of [35S]methionine-labeled cell extracts. IL-1 pretreatment also increased beta 1, beta 3, and alpha, integrin mRNA. The A549 cells did not express vitronectin receptor, since LM609 did not inhibit A549 adhesion to vitronectin or bind to A549 cells in flow cytometry, and vitronectin receptor antisera failed to immunoprecipitate vitronectin receptor from A549 cells. Furthermore, the beta 3 complementary DNA probe failed to hybridize to A549 RNA. A549 cells did express fibronectin receptor, which was increased by IL-1 treatment. We conclude that IL-1 induces the expression of both vitronectin receptor and fibronectin receptor on endothelial cells and that vitronectin receptor, in turn, facilitates A549 cell adhesion to endothelial cells.

Antibodies↗

PubMed1997

The alpha v beta 3 integrin "vitronectin receptor".

The alpha v beta 3 "vitronectin receptor" is a member of the integrin superfamily of adhesion molecules. As such, this 160/85 kDa heterodimeric protein exhibits many of the typical structural and functional features of integrins. It mediates cell adhesion to extracellular matrix by recognizing the conserved arg-gly-asp (RGD) sequence of several plasma and matrix proteins. Recently, it has also been shown that alpha v beta 3 is involved in signal transduction and cell to cell interactions. alpha v beta 3 is highly expressed in bone resorbing cells, osteoclasts, and upregulated in response to vascular damage, during angiogenesis and in certain types of malignancy. Antagonists of alpha v beta 3 are being developed for use in a variety of diseases associated with altered receptor function or level.

Animals↗

PubMed1996

Temporal and spatial regulation of integrin vitronectin receptor mRNAs in the embryonic chick retina.

PURPOSE: To identify integrin vitronectin receptor subunit mRNAs in the developing avian retina and to track their expression. METHODS: Reverse transcription-polymerase chain reaction was used to identify integrin vitronectin receptor subunit mRNAs expressed in embryonic chick retina. cDNA clones encoding the beta 5 subunit were isolated and sequenced. Expression patterns of mRNAs encoding alpha v, beta 3, and beta 5 subunits were analyzed using northern analysis and in situ hybridization. RESULTS: Integrin beta 1, beta 3, and beta 5 subunit mRNA were identified in embryonic day 6 chick retina. The sequence of chicken beta 5 was 77% identical to that of human beta 5, and sequences with known signaling functions were highly conserved. Integrin alpha v, beta 3, and beta 5 mRNAs were expressed throughout the development of the embryonic retina, with the highest levels per retina observed around the embryonic day 9. In situ hybridization showed that both beta 3 and beta 5 were expressed throughout the developing retina, particularly in undifferentiated neuroepithelial precursor cells. At later times, beta 3 was expressed uniformly throughout the retina, whereas beta 5 expression was highest in a band throughout the central retina. CONCLUSIONS: The strong conservation of sequences with known signaling functions in chicken beta 5 suggests that it functions in a manner similar to human beta 5. Spatial expression patterns of vitronectin receptor subunits at early times of development point to a range of possible functions beyond axon outgrowth, including retinoblast proliferation, adhesion, and migration.

Amino Acid Sequence↗

PubMed1990

The vitronectin receptor alpha v beta 3 binds fibronectin and acts in concert with alpha 5 beta 1 in promoting cellular attachment and spreading on fibronectin.

The vitronectin receptor (alpha v beta 3) is a member of the integrin superfamily of adhesive protein receptors that mediate a wide spectrum of adhesive cellular interactions, including attachment to vitronectin, von Willebrand factor, fibrinogen, and thrombospondin. We have studied the binding of fibronectin to the purified vitronectin receptor, and the role of this receptor in the attachment of cells to fibronectin. A solid-phase microtiter assay was developed to investigate the binding properties of the vitronectin receptor. Purified alpha v beta 3 bound fibronectin with high affinity in a saturable, divalent cation-dependent manner. Binding was inhibited by soluble vitronectin, by RGD-containing peptides, and by LM609, a monoclonal antibody against the vitronectin receptor known to inhibit the binding of adhesive proteins to alpha v beta 3. Immunoinhibition experiments showed that M21 human melanoma cells, which express the fibronectin receptor, alpha 5 beta 1, as well as alpha v beta 3, used both of these integrins to attach and spread on fibronectin. In support of this finding, M21-L cells, a variant cell line that specifically lacks alpha v beta 3 but expresses alpha v beta 1, attached and spread poorly on fibronectin. In addition, alpha v beta 3 from surface-labeled M21 cells was retained, and selectively eluted by RGDS from a fibronectin affinity column. These results indicate that alpha v beta 3 acts in concert with alpha 5 beta 1 in promoting fibronectin recognition by these cells. We conclude that fibronectin binds to the alpha v beta 3 vitronectin receptor specifically and with high affinity, and that this interaction is biologically relevant in supporting cell adhesion to matrix proteins.

Antibodies, Monoclonal↗

PubMed1991

Platelet vitronectin receptor expression differentiates Iraqi-Jewish from Arab patients with Glanzmann thrombasthenia in Israel.

Glanzmann thrombasthenia is a rare, inherited disorder of the platelet glycoprotein IIb/IIIa (GP IIb/IIIa) complex. We previously identified two distinct populations with this disorder in Israel, Iraqi-Jews and Arabs. The groups are indistinguishable in hemorrhagic symptoms and platelet GP IIB/IIIa receptor deficiency, but they differ in their platelet immunodetectable GP IIIa (beta 3), with the Iraqi-Jewish population expressing no detectable GP IIIa and the Arab population expressing small amounts. We have now examined the platelets of these two populations as well as normal platelets for the alpha v beta 3 vitronectin receptor. Normal platelets contained between approximately 50 to 100 alpha v beta 3 vitronectin receptors as judged by the binding of antibodies to both alpha v (LM142) and the intact alpha v beta 3 vitronectin receptor complex (LM609). In addition, normal platelets bound to immobilized vitronectin in the presence of 1 mmol/LMnCl2; the adhesion was mediated predominantly through GP IIb/IIIa, but with a distinct contribution by the alpha v beta 3 vitronectin receptor, as determined by monoclonal antibody inhibition studies. Iraqi-Jewish patients' platelets had a profound decrease in immunodetectable alpha v beta 3 vitronectin receptors, and their platelets did not adhere well to vitronectin. In contrast, Arab patients' platelets had normal or increased numbers of platelet alpha v beta 3 vitronectin receptors, and these receptors functioned well in the vitronectin adhesion assay, taking over much of the adhesion mediated by GP IIb/IIIa in normal platelets. These studies define further the heterogeneity of the molecular basis of Glanzmann thrombasthenia; they also have more widespread implications for understanding the synthesis and function of the beta 3 family of integrin receptors.

Blood Platelets↗

PubMed1991

Arg-Gly-Asp (RGD) peptides and the anti-vitronectin receptor antibody 23C6 inhibit dentine resorption and cell spreading by osteoclasts.

Studies with a range of monoclonal and polyclonal antisera to components of the human, rat, and chick vitronectin receptor, alpha V beta 3, and the VLA beta 1 chain show that chick and rat osteoclasts express similar integrin receptors to those described in man. Biochemical analysis with monoclonal antibody 23C6 confirmed the presence on chick osteoclasts of a vitronectin receptor heterodimer of similar size (110/95 kDa reduced) to that immunoprecipitated from human osteoclastoma giant cells. The synthetic peptide GRGDSP, corresponding to the cell adhesion sequence in fibronectin, but not GRGESP peptide, induced significant (P less than 0.005) osteoclast retraction in chick and rat osteoclasts at IC50s (+/- SEM) of 210.0 +/- 14.4 and 191.4 +/- 13.7 microM, respectively; monoclonal anti-vitronectin receptor alpha V beta 3 complex antibody, 23C6, produced similar changes in chick osteoclasts (IC50 = 1.45 +/- 0.22 microM). Antibody 23C6 inhibited the number of pits resorbed in dentine by chick osteoclasts over a concentration range of 4.4 to 88 micrograms/ml; a significant 76% reduction (P = 0.03) was observed at a final concentration of 88 micrograms/ml (6 microM). The effect of peptides upon dentine resorption was less dramatic. No consistent inhibition was seen using chick osteoclasts. Inhibitory effects on resorption by rat osteoclasts were, however, observed; significant reduction in resorption occurred with both GRGDSP (78%; P less than 0.01) and GRGESP (67%; P = 0.02) peptides at 400 microM peptide concentration. These data demonstrate that osteoclast function can be disrupted by low concentrations of the anti-vitronectin receptor antibody, 23C6. The inhibitory effects of the peptides used in this study produced effects on dentine resorption which were generally weaker and variable, although osteoclast cell adhesion was consistently inhibited in an Arg-Gly-Asp (RGD)-dependent manner. We conclude that the vitronectin receptor may play an important role in effecting resorption of mineralized tissues by osteoclasts.

Amino Acid Sequence↗

PubMed1991

Vitronectin receptor has a role in bone resorption but does not mediate tight sealing zone attachment of osteoclasts to the bone surface.

During bone resorption, osteoclasts form a tight attachment, the sealing zone, around resorption lacunae. Vitronectin receptor has previously been shown to be expressed in osteoclasts and it has been suggested that it mediates the tight attachment at the sealing zone. In this study we have shown that glycine-arginine-glycine-aspartic acid-serine pentapeptide inhibits bone resorption by isolated osteoclasts and drastically changes the morphology of the osteoclasts. When the vitronectin receptor was localized by immunofluorescence in rat and chicken osteoclasts cultured on bone slices, it was found to be distributed throughout the osteoclast cell membrane except in the sealing zone areas. Immunoperoxidase staining of rat bone sections at the light microscopical level also revealed intense staining of the cell membrane with occasional small unstained areas, probably corresponding to the sealing zones. Immunoelectron microscopy confirmed the results obtained by light microscopy showing specific labeling only at the ruffled borders and basolateral membranes (0.82 and 2.43 gold particles/microns of membrane, respectively), but not at the sealing zone areas (0.06 gold particles/microns of membrane). Both alpha v and beta 3 subunits of the vitronectin receptor were similarly localized. These results strongly suggest that, although the vitronectin receptor is important in the function of osteoclasts, it is not mediating the final sealing zone attachment of the osteoclasts to the mineralized bone surface.

Animals↗