Adhesion of osteosarcoma cells to the 70-kDa core region of thrombospondin-1 is mediated by the alpha 4 beta 1 integrin.
Thrombospondin-1 (TSP-1) is an extracellular glycoprotein that is involved in a variety of physiological processes such as tumor cell adhesion, invasion, and metastasis. It has been hypothesized that TSP-1 provides an adhesive matrix for osteosarcoma cells. Here we present data showing that TSP-1 can promote cell substrate adhesion to U2OS and SAOS cells through the alpha 4 beta 1 integrin. The dose-dependent adhesion to TSP-1 was inhibited by anti-integrin antibodies directed against the alpha 4 or beta 1 subunit, but not by control antibodies against other integrins. To localize the potential alpha 4 beta 1-binding site within the TSP-1 molecule, the protein was subjected to limited proteolysis with chymotrypsin in the absence of calcium. The stable 70-kDa core fragment produced under these conditions promoted alpha 4 beta 1-dependent osteosarcoma cell adhesion in a manner similar to that of the intact protein. Moreover adhesion experiments with neutralizing antibodies revealed that the adhesion was totally dependent on the alpha 4 beta 1 interaction. Further blocking experiments with potential inhibitory peptides revealed that the alpha 4 beta 1-mediated adhesion was not influenced by peptides containing the RGD sequence. Attachment to the 70-kDa fragment was strongly inhibited by the CS-1 peptide, which represents the most active recognition domain for alpha 4 beta 1 integrin in fibronectin. The present data provide evidence that TSP-1 contains an alpha 4 beta 1 integrin-binding site within the 70-kDa core region.
Decker
Stephan
S
Department of Paediatric Haematology and Oncology, University of Münster, Domagkstrasse 3, D-48149 Münster, Germany.
van Valen
Frans
F
Vischer
Peter
P
D001859:Bone Neoplasms; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000502:physiology*; D012516:Osteosarcoma; D010446:Peptide Fragments / Q000494:pharmacology; D016201:Receptors, Lymphocyte Homing / Q000502:physiology*; D019700:Thrombospondin 1 / Q000494:pharmacology / Q000502:physiology*; D014407:Tumor Cells, Cultured
D039041:Integrin alpha4beta1; D016023:Integrins; D010446:Peptide Fragments; D016201:Receptors, Lymphocyte Homing; D019700:Thrombospondin 1