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Differential modulation of cell adhesion by interaction between adhesive and counter-adhesive proteins: characterization of the binding of vitronectin to osteonectin (BM40, SPARC).

ABSTRACT: Heparin-binding forms of vitronectin, a multifunctional adhesive glycoprotein, are associated with the extracellular matrix (ECM) at different locations in the body and serve to promote cell adhesion and the regulation of pericellular proteolysis at sites of angiogenesis. In the present study we characterized the interactions of vitronectin with the counter-adhesive protein osteonectin (also termed SPARC or BM40). Osteonectin and vitronectin were both found associated with the ECM of cultured endothelial cells and were localized in vessel wall sections of kidney tissue. In vitro, the heparin-binding multimeric isoform of vitronectin bound to immobilized osteonectin in a saturable manner with half-maximal binding at 30-40 nM. Preincubation of plasma vitronectin with plasminogen activator inhibitor 1 (PAI-1), which provoked multimer formation, induced the binding of vitronectin to osteonectin. Binding was optimal at physiological ionic strength, and binary complexes were stabilized by tissue transglutaminase-mediated cross-linking. In a concentration-dependent fashion, PAI-1, CaCl2, heparin and heparan sulphate, but not other glycosaminoglycans, interfered with the binding of vitronectin to osteonectin. Using vitronectin-derived synthetic peptides as well as mutant forms of recombinant osteonectin, we found that the heparin-binding region of vitronectin interacted with the C-terminal region of osteonectin that contains a high-affinity Ca2+-binding site with counter-adhesive properties. Adhesion of cultured endothelial cells was partly abrogated by osteonectin and was correspondingly reversed by vitronectin in a concentration-dependent manner. These results indicate that specific interactions between vitronectin and osteonectin modulate cell adhesion and might thereby regulate endothelial cell function during angiogenesis.

SUBMITTER: Rosenblatt S

PROVIDER: S-EPMC1218432 | biostudies-other | 1997 May

REPOSITORIES: biostudies-other

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Project description:Barrett's oesophagus (BE) is the precursor lesion to adenocarcinoma of the oesophagus. Understanding of the molecular alterations in this multistage process may contribute to improved diagnosis and treatment. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that modulates cell adhesion and growth. Alterations in SPARC expression have been observed in a variety of solid tumours. The aim of this study was to assess the prevalence and timing of SPARC mRNA expression in Barrett's multistage disease and to investigate the impact of SPARC alterations on the development and progression of this disease. SPARC mRNA expression was measured using a quantitative real-time RT-PCR method in 108 specimens from 19 patients with BE without carcinoma, 20 patients with Barrett's-associated adenocarcinoma (EA), and a control group (CG) of 10 patients without evidence of gastro-oesophageal reflux disease. The median SPARC mRNA expression was significantly upregulated in BE tissues compared to paired normal oesophagus (NE) tissues for the BE group (P=0.004) and for the EA group (P<0.001). The SPARC mRNA expression was significantly higher in adenocarcinoma of the oesophagus compared to matching NE tissue and compared to Barrett's tissues in the EA group (P<0.001). Furthermore, SPARC expression values were significantly different between metaplastic and dysplastic Barrett's tissues (P=0.014). In histologically normal squamous oesophagus tissues obtained from carcinoma patients (EA group), the SPARC mRNA expression was significantly higher compared to NE mucosa from the BE group and the CG group (P=0.03). These findings suggest that the upregulation of SPARC mRNA expression is an early event in the development and progression of BE and EA, and that high SPARC expression may be a clinically useful biomarker for the detection of occult adenocarcinoma, and that a widespread 'field effect' is present in the NE of patients with oesophageal adenocarcinoma.

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Differential modulation of cell adhesion by interaction between adhesive and counter-adhesive proteins: characterization of the binding of vitronectin to osteonectin (BM40, SPARC).

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