SPARC (BM-40, Osteonectin) Inhibits the Mitogenic Effect of Vascular Endothelial Growth Factor on Microvascular Endothelial Cells*
- From the Department of Biological Structure, University of Washington School of Medicine, Seattle, Washington 98195-7420
Abstract
SPARC (secreted protein, acidic and rich in cysteine) is a matricellular protein that modulates cell adhesion and proliferation and is thought to function in tissue remodeling and angiogenesis. In this study, we demonstrate that SPARC inhibits DNA synthesis by >90% in human microvascular endothelial cells (HMEC) stimulated by the endothelial cell mitogen vascular endothelial growth factor (VEGF). Peptides derived from SPARC domain IV, which contains a disulfide-bonded EF-hand sequence and binds to endothelial cells, mimicked the effect of native SPARC. The inhibition was also observed with a peptide from the follistatin-like domain II, whereas peptides from SPARC domains I and III had no effect on VEGF-stimulated DNA synthesis. The inhibition of HMEC proliferation was mediated in part by the binding of VEGF to SPARC. The binding of125I-VEGF to HMEC was reduced by SPARC and SPARC peptides from domain IV in a concentration-dependent manner. In a radioimmune precipitation assay, peptides from SPARC domains II and IV each competed with native SPARC for its binding to VEGF. It has been reported that VEGF stimulates the tyrosine phosphorylation and activation of mitogen-activated protein kinases Erk1 and Erk2. We now show that SPARC reduces this phosphorylation in VEGF-stimulated HMEC to levels of unstimulated controls. SPARC thus modulates the mitogenic activity of VEGF through a direct binding interaction and reduces the association of VEGF with its cell-surface receptors. Moreover, an additional diminution of VEGF activity by SPARC is accomplished through a reduction in the tyrosine phosphorylation of mitogen-activated protein kinases.
Footnotes
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↵* This work was supported in part by National Institutes of Health Grants GM 40711 and HL 18645 (to E. H. S.), Grant Ku 1076/1-1 from the Deutsche Forschungsgemeinschaft (to C. K.), and Grant 91-020-06-IRG from the American Cancer Society (to K. M.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Present address: Humboldt-University, Franz-Volhard-Klinik Berlin-Buch, Wiltbergstrasse 50, D-13125 Berlin.
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↵§ To whom correspondence should be addressed. Tel.: 206-685-1192; Fax: 206-543-1524.
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↵2 T. Quinn, personal communication.
- Abbreviations:
- ECM
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extracellular matrix
- BSA
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bovine serum albumin
- HMEC
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human microvascular endothelial cell(s)
- MAPK
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mitogen-activated protein kinase
- PBS
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phosphate-buffered saline
- PDGF
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platelet-derived growth factor
- bFGF
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basic fibroblast growth factor
- VEGF
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vascular endothelial growth factor
- PAGE
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polyacrylamide gel electrophoresis.
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- Received June 12, 1998.
- Revision received August 11, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
