Biological roles of the non-integrin elastin/laminin receptor.

The 67-kDa protein identical to the enzymatically inactive spliced variant of beta-galactosidase is a major component of the non-integrin cell surface receptor expressed on fibroblasts, smooth muscle cells, chondroblasts, leukocytes, and certain cancer cell types. It recognizes several non-identical hydrophobic domains on elastin, laminin, and type IV collagen, provided they form a similar secondary conformation. The 67-kDa protein is not a transmembrane molecule, but immobilizes on the cell surface by an association with two other proteins, the 61-kDa neuraminidase and the 55-kDa 'protective protein'. The 67-kDa protein binds to matrix ligands in a calcium independent manner and only in the absence of galactosugars. Binding of these carbohydrate-bearing moieties causes such conformational changes of the 67-kDa protein that it loses the ability to bind its principal matrix ligands and separates from the cell surface. Galactosugars which inactivate this unique cell surface receptor may therefore modulate cell-matrix interactions, especially in such processes as SMC migration during vascular thickening, tumor cell metastasis, or tissue infiltration by the leukocytes. In elastin-producing cells, the 67-kDa protein associates with tropoelastin and serves as a molecular chaperone which facilitates its intracellular transport and extracellular assembly.