Specific effects of fibronectin-releasing peptides on the extracellular matrices of cultured human fibroblasts.

Fibronectin-releasing activity has recently been found in concentrated serum-free culture media of the established human fibrosarcoma cell line, 8387. We used these M.W. 10,000 fibronectin-releasing polypeptides (10K peptides) to study their effects on the cell-free matrices of cultured diploid human lung fibroblasts. Metabolically labeled cultures of fibroblasts were extracted with sodium deoxycholate and hypotonic buffer to prepare the matrices. The isolated matrices contained fibronectin and procollagen as their major radiolabeled proteins, and some as yet unidentified polypeptides were also detected. the matrices that were attached on the culture dishes were exposed to increasing concentrations of the 10K peptides in serum-free medium, and the changes in the radiolabeled polypeptides were studied. As a result of this treatment, there was a massive release of both fibronectin and procollagen from the matrices. No major cleavages of either released protein could be seen. After digestion of the matrix-associated collagen with collagenase, the 10K peptides released only fibronectin. Collagenase treatment, on the contrary, did not affect matrix-associated fibronectin. On the other hand, a M.W. 66,000 matrix-associated protein was constantly cleaved to a M.W. 62,000 form that remained in the matrix as a result of the incubation of the matrices with the 10K peptides. The 10K peptides did not affect the other radiolabeled polypeptides present in the matrix. the results indicate that the fibronectin-releasing peptide behaves as a specific protease on the matrices of cultured human fibroblasts.