Coordinate induction of collagenase-1, stromelysin-1 and urokinase plasminogen activator (uPA) by the 120-kDa cell-binding fibronectin fragment in fibrocartilaginous cells: uPA contributes to activation of procollagenase-1

Specific fibronectin (Fn) fragments found in synovial fluid of arthritic jo ints potentially contribute to the loss of cartilage proteoglycans by induc ing matrix metalloproteinase (MMP) expression. However, whether or not the Fn fragment-modulated changes in expression of MMPs result in a net increas e in matrix-degradative activity through alterations in the balance between MMP activation and inhibition has not been established. To understand the mechanisms by which proteolytic Fn fragments may contribute to joint degene ration, conditioned medium from fibrocartilaginous cells exposed to Fn, its 30-kDa fragment containing the collagen/gelatin-binding domain, its 120-kD a fragment containing the central cell-binding domain, and the RGD peptide were assayed for MMPs, and MMP activators and inhibitors. We found that the 120-kDa fragment of Fn (but not intact Fn), the 30-kDa fragment, and the R GD peptide, dose-dependently induced procollagenase-1 and prostromelysin-1 and decreased levels of the tissue inhibitor of metalloproteinases (TIMPs) -1 and -2. The alpha5 beta1 integrin was implicated in the induction of col lagenase by the 120-kDa Fn fragment, since collagenase induction was abroga ted in the presence of blocking antibody to this integrin. Conditioned medi um from cells exposed to the 120-kDa Fn fragment also demonstrated increase d levels of the activated collagenase-1, which resulted in significantly el evated collagen degradative activity. That the urokinase plasminogen activa tor (uPA) was involved in the activation of procollagenase-1 was suggested by findings that the 120-kDa Fn fragment induced uPA coordinately with proc ollagenase-1, and the activation of procollagenase-1 was dose-dependently i nhibited in the presence of plasminogen activator inhibitor-1. These data d emonstrate that the 120-kDa cell-binding fragment of Fn induces a net incre ase in matrix-degradative activity in fibrocartilaginous cells by concomita ntly inducing MMPs and their activator, uPA, while decreasing TIMPs. (C) 20 00 Elsevier Science B.V. International Society of Matrix Biology. All right s reserved.