Degradation of extracellular-matrix proteins by human cathepsin B from normal and tumour tissues

• Published in: Biochemical journal 1992-02, Vol.282 (1), p.273-278
• Main Authors: BUCK, M. R, KARUSTIS, D. G, DAY, N. A, HONN, K. V, SLOANE, B. F
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Biological and medical sciences; Breast Neoplasms - enzymology; Cathepsin B - isolation & purification; Cathepsin B - metabolism; Collagen - metabolism; Extracellular Matrix Proteins - metabolism; Fibronectins - metabolism; General aspects (metabolism, cell proliferation, established cell line...); Humans; Immunoblotting; Laminin - genetics; Laminin - metabolism; Liver - enzymology; Medical sciences; Mice; Molecular Sequence Data; Molecular Weight; Peptide Fragments - isolation & purification; Reference Values; Sequence Homology, Nucleic Acid; Tumor cell; Tumors
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj2820273

Our laboratory has previously demonstrated that increased malignancy of several histological types of human and animal tumours is associated with increases in their cathepsin B activity, particularly cathepsin B activity associated with plasma-membrane/endosomal vesicles or shed vesicles. Here we report that cathepsin B from normal or tumour tissues degrades purified extracellular-matrix components, type IV collagen, laminin and fibronectin, at both acid pH and neutral pH. The number and sizes of degradation products were analysed by SDS/PAGE. Cathepsin B from both sources exhibited similar activities towards, and similar patterns of cleavage of, the extracellular-matrix proteins. At neutral pH, cathepsin B from both sources appeared to undergo autodegradation, a process that was decreased in the presence of alternative substrates such as the extracellular-matrix proteins. Cathepsin B readily degraded type IV collagen at 25 degrees C, indicating activity towards native type IV collagen. Fibronectin degradation products of 100-200 kDa and of 18 and 22 kDa were observed. A single 70 kDa fragment was released from laminin under non-reducing conditions and multiple fragments ranging from 45 to 200 kDa under reducing conditions. These results suggest that cathepsin B at or near the surface of malignant tumour cells may play a functional role in the focal dissolution of extracellular matrices.