The biological processes that occur at the cell surface have profound effects on the behaviour of cells and organisms. Today, cell surface phenomena mediated by adhesion receptors are major areas of research in all disciplines of modern biology, ranging from physiology and development to immunology, neurobiology and cancerology. The past 10 years have witnessed tremendous progress in our knowledge of adhesion molecules and their functions. Cell adhesion receptors include different families of proteins such as integrins, cadherins, molecules of the Ig superfamily (also referred as to CAMs), syndecans and Eph receptors. These molecules represent an integrated sensory system for transducing positional information of crucial importance in controlling the correct organization of the body plan during development and several patho-physiological processes in adult organisms. Adhesion molecules act as genuine surface receptors which convey biochemical signals inside the cells regulating tyrosine kinases/phosphatases, GTPases, lipid metabolisms, intracellular ionic concentrations.
Although the basic molecular events flowing from single activated adhesion receptors have been partially described, new questions arise from this work that will represent major research topics in the next few years. It is clear that signalling pathways by adhesion receptors do not function separately, but are highly integrated with that of other surface receptors and the underlying cytoskeleton. A paradigmatic example of such integration is the absolute requirement of cell adhesion for proliferative response to mitogens. It is, thus, crucial to elucidate the structural basis of adhesive receptors cross-talk with other cell surface molecules such as cytokine, growth factor receptors, and other adhesion receptors. On the other hand, it is now clear that adhesion receptors can affect gene expression and identification of the genes whose expression is specifically regulated by adhesion is now becoming a central issue. The third crucial issue concerns the identification of the receptor-proximal molecular events connecting adhesive receptors to the intracellular signalling machinery.