Elastonectin and the elastin receptor.

Two different types of interactions were described between cells and elastin: 1) the adhesion of cells to insoluble fibrous elastin and 2) the binding of soluble elastin derived peptides by cells. We could show that these are two different mechanisms underlying those two types of interactions. The adhesion of cells to elastin fibers is mediated by a cell-membrane complex with a 120 kD protein as the main adhesive compound which we proposed to designate elastonectin. Three other proteins (67, 60 and 45 kD) were coisolated with elastonectin. Adhesion of insoluble elastin to mesenchymal cells (fibroblasts, smooth muscle cells) is inducible with soluble elastin peptides. Highly metastatic Lewis lung carcinoma cells and human melanoma cells also exhibited the adhesion mechanism, but without a lag phase (constitutive adhesion). Binding curve (Scatchard plots) obtained with radiolabelled elastin peptides indicated the presence of high affinity elastin receptors on mesenchymal cells and human white blood cells (monocytes and PMNs) with Kd-s in the nanomolar range. The binding of elastin peptides triggers several cellular reactions such as chemotaxis, Ca++ influx (increase of Ca++i) and with mononuclear blood cells release of lytic enzymes and oxygen radicals. All these cells which exhibited elastin receptor function also exhibited adhesion although the two processes could be inhibited selectively. The receptor action is mediated by a G-protein-phospholipase-IP3 mechanism, involved in the increase of intracellular Ca++. It appears that this action also triggers the biosynthesis and membrane localization of elastonectin. The coupling of these 2 mechanisms between receptor and adhesion appears to be modified in transformed cells.