Receptor-mediated binding of leukocyte elastase by chondrocytes

Studies on the effect of leukocyte elastase on the metabolism of chondrocytes in culture have demonstrated that these cells possess a specific cell surface receptor for leukocyte-derived elastase. Purified elastase from rabbit and human leukocytes is capable of modulating the metabolism of the cell by causing a marked decrease in both proteoglycan and protein biosynthesis. Addition of 125I-labeled elastase to chondrocytes maintained in suspension culture has shown that binding occurs, and that it is saturable and is inhibited by the addition of unlabeled enzyme. We ascertained that the active site of the enzyme was necessary for binding to the chondrocyte, since phenylmethylsulfonyl fluoride-inactivated leukocyte elastase failed to bind. Pancreatic elastase had only a slight affinity for the receptor, whereas trypsin and bovine serum albumin failed to bind to any significant extent. Autoradiographic studies and the use of inhibitors of endocytosis, such as dansyl cadaverine, confirmed that endocytosis of elastase was the secondary event after cell binding.