PubMed · 6675149
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T M Saba. 1983. Current knowledge on fibronectin.. https://doi.org/10.1007/bf02918426
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Fibronectins and plasminogen activators, both tissue and urokinase types, are involved in the physiopathological degradation of the extracellular matrix. Previous reports indicate that fibronectin can be degraded by urokinase without plasminogen. Also, we have shown that tissue-type plasminogen activator can cleave fibronectin, without plasminogen, generating fragments of 30 and 220-250 kDa detectable by immunoblotting analysis. A comparison with urokinase-induced degradation indicates that the cleavage sites are the same for both plasminogen activators. One is close to the carboxyl-terminal, disrupting the fibronectin dimeric structure, and one is near the amino-terminal, generating a 30 kDa fragment. In solution, the activity of tissue-type plasminogen activator was prevalent on the amino-terminal site, while urokinase activity was prevalent on the carboxyl-terminal site. On fibronectin immobilized onto a gelatin coated surface, only the 30 kDa fragment was released when treated with both plasminogen activators. Plasminogen activators also were active on fibronectin assembled into the extracellular matrix of cultured fibroblasts. Urokinase caused the complete disappearance of extracellular matrix fibronectin, together with the release of the 30 and the 220-250 kDa fibronectin fragments, but left a flat morphology, while tissue-type plasminogen activator induced the release of the 30 kDa fragment associated with changes in cellular morphology. The plasminogen-independent fibronectin degradation exerted by tissue-type plasminogen activator and urokinase is 100 times lower than that exerted by plasmin. This may provide a mechanism for localized and limited degradation of fibronectin preventing the generalized proteolysis associated with plasminogen activation.
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The amino-terminal domain of fibronectin has a fibrin binding site and a site for covalent cross-linking to fibrin. This fibrin binding domain was isolated from human recombinant fibronectin and labeled with In-111; the final molecular weight was 12 kD. It was applied to a pilot study of 62 patients; 30 who were thought to have deep vein thrombosis and 32 controls. All 30 patients had either impedance plethysmography, duplex ultrasound, contrast venography, or various combinations of the three. Eight disagreements in the 30 patients suspected of having deep vein thrombosis were registered between fibrin binding domain imaging and the other examinations. Three of the patients with negative scan results had clots that were 1 week old or older, and this may be a limitation of the technique. In three other patients who had negative scan results, but positive alternative studies, there was a history of previous episodes of deep vein thrombosis and this could be a cause of false-positive results in the other modalities. There was one documented false-negative scan in a fresh clot. Normal scans were obtained in the lower extremities of the control patients, except in two who demonstrated uptake at the sites of insulin injections. The initial results of this feasibility study are encouraging and warrant further investigation.