ABSTRACT
Several biological events including pathological ones, such as regulation of gene expression, cell proliferation, cell differentiation, cell migration, apoptosis, and formation of metastases, are dependent upon cell adhesion, and different types of adhesion receptors have been described in the literature, including cadherins, integrins, mucins, selectins (Engel, 1992; Hynes, 1992; Paulsson, 1992; Mercurio, 1995; Crocker and Feizi, 1996; Laflamme and Auer, 1996; Ruoslahti and Öbrink, 1996; Sanchez-Mateos et al., 1996; Penberthy et al., 1997; Aumailley and Gayraud, 1998; Pignatelli, 1998). The cell-extracellular matrix interaction is a multistep phenomenon including cell attachment to extracellular matrix components, such as laminin, collagen and fibronectin, via specific cell surface-receptors, followed by rearrangements of plasma membrane and cytoskeletal elements which trigger cell spreading. Most surface receptors are glycoproteins, and it is now clear that the carbohydrates carried by these receptors play a central role in cell-recognition processes (Hughes, 1992a; Olden, 1993). Carbohydrates can interact with other carbohydrates, as well as with certain proteins called lectins (Hakomori, 1992; Fukuda, 1995). The affinity of such interactions is low and may serve as regulatory mechanisms in cell-adhesion phenomena giving rise to transient, specific and reversible interactions, such as that observed during the rolling of leukocytes on endothelial cells or during the formation of cancer cell metastases. However, carbohydrates spaced closely together on a polypeptide chain might become packed tightly together when the molecule is folded, thereby forming a clustered carbohydrate patch and increasing the binding strength (Spillmann, 1994; Yi et al., 1998). Thus, cell adhesion is a dynamic phenomenon which implicates not only one receptor, but a variety of different receptors each of which is characterized by its affinity binding (more or less high) for a given cell type leading to the consolidation or not of the cell interactions.
