Release of elastase from monocytes adherent to a fibronectin-gelatin surface

Fibronectin (Fn) is a circulating and extracellular matrix glycoprotein that may serve to facilitate phagocytosis because of its ability to bind many inflammatory ligands and to a monocyte receptor. Fn fragments have been shown in many systems to have augmented properties over those of native Fn. We show in this report that although Fn fragments did not cause elastase release from monocytes in suspension, fragments did cause elastase release from monocytes that were first bound to Fn-gelatin surfaces. An amino-terminal 29-Kd and a 140-Kd integrin-binding fragment were half-maximally active at 100 nmol/L, whereas the Arg-Gly-Asp-Ser integrin-recognition peptide was half-maximally active at 100 mumol/L. Fluid-phase Fn was ineffective yet blocked the activity of the Fn fragments. Complexing of Fn with gelatin or with heparin partially removed the blocking effect of Fn. Similar results were obtained with U-937 cells. Substitution of the Fn-gelatin surface with bovine articular cartilage also promoted elastase release. Therefore, in conditions in vivo in which monocytes bind to tissue surface, a high ratio of Fn fragments to native Fn may upregulate certain monocyte activities such as protease release.