IN-VITRO STUDY OF BASEMENT-MEMBRANE DEGRADATION BY THE CYSTEINE PROTEINASES, CATHEPSINS B, B-LIKE AND L - DIGESTION OF COLLAGEN-IV, LAMININ, FIBRONECTIN, AND RELEASE OF GELATINASE ACTIVITIES FROM BASEMENT-MEMBRANE FIBRONECTIN

We have studied the soluble fragments obtained from bovine lens capsul es after digestion by the cysteine proteinases cathepsins B, B-like an d L. These proteinases liberated collagen IV, laminin and fibronectin fragments, as shown by immunoblotting. Sodium dodecyl sulfate treatmen t of digested capsules gave a soluble material used for subsequent fra ctionation and immunochemical study. Comparison of both results demons trate the ability of these cathepsins to degrade a basement membrane a t near neutral pH values. The differences observed in the size and the number of fragments suggest that the three proteinases exhibit simila r specificities in basement membrane digestion, as shown previously. N evertheless, cathepsin L seems to be more effective than cathepsins B and B-like. From this study, cysteine proteinases could be associated to basement membrane destruction. Soluble cysteine proteinase digests of bovine lens capsules showed several bands of gelatinolytic activity by gelatin zymography. Three major bands of 77, 60 and 45 kDa were se en whatever the cysteine proteinase used. These bands were identified as fibronectin fragments. Thus cysteine proteinases can activate the l atent proteinase fibronectin from basement membrane leading to a new ' 'metastatic cascade''. This would be an important factor in the ''in v ivo'' basement membrane dissolution observed during tumor invasion.