Degradation of extracellular-matrix proteins by human cathepsin B from normal and tumour tissues.
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.
Buck
M R
MR
Department of Pharmacology, Wayne State University, Detroit, MI 48201.
Karustis
D G
DG
Day
N A
NA
Honn
K V
KV
Sloane
B F
BF
D000595:Amino Acid Sequence; D000818:Animals; D001943:Breast Neoplasms / Q000201:enzymology*; D002401:Cathepsin B / Q000302:isolation & purification / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007797:Laminin / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000302:isolation & purification; D012016:Reference Values; D012689:Sequence Homology, Nucleic Acid
D016326:Extracellular Matrix Proteins; D005353:Fibronectins; D007797:Laminin; D010446:Peptide Fragments; D003094:Collagen; D002401:Cathepsin B