THE ROLE OF THE ARGININE-GLYCINE-ASPARTIC ACID-DIRECTED CELLULAR-BINDING TO TYPE-I COLLAGEN AND RAT MESENCHYMAL CELLS IN COLORECTAL TUMOR DIFFERENTIATION

The relationship between the adhesion of five human colorectal carcinoma cell lines to extracellular matrix (ECM) proteins, namely type I collagen, type IV collagen, fibronectin, laminin and basement membrane extract (Matrigel), and the ability of these cells to express morphological differentiation when grown in a basement membrane extract (Matrigel) or on normal rat mesenchymal cells has been examined. Two cell lines, SW1222 and HRA-19, organised into glandular structures, with well-defined polarity when cultured on both substrata as well as in three-dimensional (3D) collagen gel culture as previously shown [27,36]. The remaining three cell lines (SW620, SW480 and HT29) grew as loose aggregates or as they would normally grow on tissue culture plastic. Addition to the culture medium of a hexapeptide, containing the cell-matrix recognition sequence arginine-glycine-aspartic acid (RGD), inhibited attachment and glandular formation of SW1222 and HRA-19 when these cells were grown on living mesenchymal cells, but not in Matrigel. The morphological differentiation of HRA-19 cells in 3D-collagen was also inhibited by the same RGD-containing peptide, as previously shown for SW1222 cells [36]. Attachment of the remaining three cell lines was inhibited on mesenchyme but not in Matrigel, further supporting the specificity of the peptide effect on epithelial-mesenchymal binding. In conclusion we have shown that colorectal tumor cells are able to bind ECM proteins and that the cellular binding is an essential step in the induction of the morphological differentiation seen on living mesenchymal cells, in basement membrane extracts and in type I collagen gel. In addition these data further confirm that the interaction of colorectal tumor cells with mesenchymal cells, as well as type I collagen and fibronectin, is mediated by an RGD-directed receptor whereas their interaction with basement membrane proteins, such as type IV collagen and laminin, is RGD-independent. These data suggest that colorectal tumour cells express a multitude of ECM receptors with different adhesion properties and binding specificity.