DIFFERENTIAL BINDING OF TRANSFORMING GROWTH FACTOR-BETA-1, FACTOR-BETA-2, AND FACTOR-BETA-3 BY FIBROBLASTS AND EPITHELIAL-CELLS MEASURED BY AFFINITY CROSS-LINKING OF CELL-SURFACE RECEPTORS

A murine fibroblast cell line (AKR-2B clone 84A) and an epithelial cell line (BALB/MK) were compared for their ability to bind different transforming growth factor-beta (TGF-beta) species. The results of competitive binding assays indicated that the epithelial cells had a higher affinity for TGF-beta than the fibroblats. This difference may be the basis for the sensitivity of epithelial cells to much lower concentrations of TGF-beta than fibroblasts. Affinity cross-linking studies showed that both cell types express the three cell surface TGF-beta-binding molecules that have been previously described for a variety of cell types. The complexity of these cell surface binding proteins was further evaluated using all possible combinations of radiolabeled ligands in competition with each of the three unlabeled TGF-beta-species. Differences in the ability of specific TGF-beta-types to compete with radiolabeled TGF-beta-2 for binding to the type I and II receptors were observed, with TGF-beta-1 being more potent for epithelial cells, and TGF-beta-2 being more potent for fibroblasts. In addition, a difference in the ability of different TGF-beta-species to compete the [I-125]TGF-beta-3 from epithelial cell surface receptors was apparent. TGF-beta-2 was not able to compete with [I-125]TGF-beta-3 for binding to the type II receptor at any concentration tested, while TGF-beta-1 and TGF-beta-3 were about equally potent in competition for this receptor type. These differences in cell surface receptor binding of structurally and biologically similar molecules may reflect different functions for these molecules.