Binding sites for elastase on cultured human fibroblasts that do not mediate internalization

Abstract

The proteolytic actions of elastases have been implicated in extracellular matrix damage, which is characteristic of a variety of pathological conditions including emphysema and rheumatoid arthritis. In order to elucidate the molecular events involved in elastase interaction with connective tissue cells, the present study was designed to investigate the association of elastase with human fibroblasts at 4 degrees C. Elastase bound saturably to binding sites that were present on the surface of these cells. Analysis of cell-bound elastase by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of a high molecular weight complex (Mr 54,000) that was not formed with elastase whose catalytic site serine was derivatized with a diisopropylphosphate group. The complex did not represent elastase bound to either protease nexin or contaminating serum. The cellular component with which elastase formed a complex could not be detected in the cell culture medium. Unexpectedly, elastase that had been pre-bound at 4 degrees C was not internalized after cells were warmed to 37 degrees C. The elastase binding site described in this report is therefore distinct from high affinity binding sites involved in receptor-mediated endocytosis and intracellular degradation.

Neutrophil elastase and cathepsin G stimulate secretion from cultured bovine airway gland serous cells.

“…Specific binding of chymotrypsin to mast cells does not occur, implying that the activation by chymotrypsin does not involve a simple ligand-receptor binding (45). In contrast, low affinity binding sites for cathepsin G and elastase mediating endocytosis into macrophages and high affinity receptor binding sites for elastase on fibroblasts not mediating endocytosis have been described (51)(52)(53). Intracellular proteases have been shown to be required for exocytosis and other cellular functions in some cells such as mast cells (54)(55)(56)(57), so it is conceivable that exogenous proteases may mimic these endogenous proteases if they are endocytosed.…”