Release of biologically active fragments from human plasma-fibronectin by murine T cell-specific proteinase 1 (TSP-1)

We have studied the proteolytic activity of TSP-1, a tissue-specific serine proteinase expressed by activated murine T cells, on human plasma fibronectin and have investigated by affinity chromatography the biological activity of the polypeptides released after limited proteolysis. A Mr approximately 2.9 x 10(4) peptide bound to denatured collagen (gelatine) but not to heparin, a Mr approximately 3.0 x 10(4) fragment contained heparin-binding but not collagen-binding sites and a third Mr approximately 3.5 x 10(4) peptide did not express either of the two activities. All larger fragments - an array of five to six polypeptides with relative molecular masses between 15 x 10(4) and 19 x 10(4) - were bound to heparin-Sepharose but not to gelatine-Sepharose and could be eluted with high salt concentration. These data confirm recent results suggesting multiple, proteinase-resistant domains with discrete biological functions within fibronectins. The release of small, biologically active fibronectin fragments by TSP-1, an enzyme specifically released by activated T cells upon contact with antigen, suggests a role for this enzyme in the numerous cellular functions elicited by T lymphocytes in vivo.