Laminin receptors and laminin-binding proteins during tumor invasion and metastasis

Interactions between cancer cells and laminin, a major component of basement membranes, play a critical role at several steps of the complex process of tumor invasion and metastasis. These interactions are mediated through a large variety of cell surface proteins designated as laminin receptors and/or laminin-binding proteins. The growing number of identified laminin binding proteins and domains of this glycoprotein that are biologically active illustrate the complexity of cellular interactions with laminin. The 67-kD laminin receptor (67 LR) was the first protein identified in 1983 as a high-affinity laminin receptor, and its expression is dramatically increased in a large variety of cancer cells. The 67 LR is the subject of several controversies and confusion generated mainly by two events. First, the identification of several new laminin-binding proteins has raised the difficult task of attributing specific functions to specific receptors in contrast to initial beliefs that all cellular laminin-driven biological activities were mediated through the 67 LR. The second source of controversy is the large molecular-weight discrepancy between the 37-kD polypeptide encoded by the 67 LR cDNA clone and the mature 67 LR. In this manuscript, a critical and extensive review of the data accumulated on the 67 LR is presented regarding both its molecular structure and its role during tumor invasion and metastasis. A hypothetical model of the 67 LR is also proposed. Since the first identification of the 67 LR, at least 14 other cell surface molecules have been reported to be potential laminin receptors or laminin-binding proteins. These include members of the beta-galactoside-binding lectin family, seven members of the integrin family, the galactosyltransferase and some not yet fully characterized cell surface molecules. These laminin receptors and laminin-binding proteins are also described and their functions are also discussed with a particular emphasis on their participation in the constitution of the invasive phenotype.