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Tumor-derived osteopontin is soluble, not matrix associated
Susan R Rittling1, Yanping Chen, Fei Feng
1Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, New Jersey 08854-8082, USA. rittling@mbcl.rutgers.edu
The Journal of Biological Chemistry
|December 14, 2001
Summary
Osteopontin (OPN) in tumors is mainly soluble, not extracellular matrix-associated. Soluble OPN does not support endothelial cell adhesion, proliferation, or prevent apoptosis without cell attachment.
Area of Science:
- Biochemistry
- Cell Biology
- Oncology
Background:
- Osteopontin (OPN) is a secreted phosphoprotein supporting endothelial cell adhesion and neovascularization.
- OPN synthesized by tumor cells is implicated in tumor growth, but its mechanism is unclear.
- The role of OPN's extracellular matrix (ECM) association in tumor biology is investigated.
Purpose of the Study:
- To determine if OPN in tumors is associated with the ECM.
- To investigate the functional role of soluble versus immobilized OPN in endothelial cell biology.
Main Methods:
- Biochemical fractionation of tumor tissue.
- Immunochemical analysis using laminin staining.
- Enzyme-linked immunosorbent assay (ELISA) for OPN-ECM interactions.
- In vitro cell adhesion and apoptosis assays with recombinant OPN.
Main Results:
- OPN is detectable in tumor extracts and serum, synthesized by tumor and host cells.
- OPN in tumors shows minimal association with the insoluble ECM and does not co-localize with laminin.
- Ras-transformed cells secrete OPN that does not bind ECM components in vitro.
- Immobilized OPN supports endothelial cell adhesion and survival, while soluble OPN does not.
Conclusions:
- Tumor-associated OPN is primarily soluble, not ECM-bound.
- Soluble OPN lacks the ability to support endothelial cell proliferation or prevent apoptosis independently of cell adhesion.