DEGRADATION OF HUMAN PLASMA AND EXTRACELLULAR-MATRIX FIBRONECTIN BY TISSUE-TYPE PLASMINOGEN-ACTIVATOR AND UROKINASE

Fibronectins and plasminogen activators, both tissue and urokinase typ es, are involved in the physiopathological degradation of the extracel lular matrix, Previous reports indicate that fibronectin can be degrad ed by urokinase without plasminogen, Also, we have shown that tissue-t ype plasminogen activator can cleave fibronectin, without plasminogen, generating fragments of 30 and 220-250 kDa detectable by immunoblotti ng 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 dim eric structure, and one is near the amino-terminal, generating a 30 kD a fragment, In solution, the activity of tissue-type plasminogen activ ator was prevalent on the amino-terminal site, while urokinase activit y was prevalent on the carboxyl-terminal site, On fibronectin immobili zed onto a gelatin coated surface, only the 30 kDa fragment was releas ed when treated with both plasminogen activators, Plasminogen activato rs also were active on fibronectin assembled into the extracellular ma trix of cultured fibroblasts. Urokinase caused the complete disappeara nce of extracellular matrix fibronectin, together with the release of the 30 and the 220-250 kDa fibronectin fragments, but left a flat morp hology, while tissue-type plasminogen activator induced the release of the 30 kDa fragment associated with changes in cellular morphology, T he plasminogen-independent fibronectin degradation exerted by tissue-t ype plasminogen activator and urokinase is 100 time's lower than that exerted by plasmin, This may provide a mechanism for localized and lim ited degradation of fibronectin preventing the generalized proteolysis associated with plasminogen activation. Copyright (C) 1996 Elsevier S cience Ltd