Proteinase species secreted by 10 human gastric carcinoma cell lines were analyzed by gelatin zymography and immunoblotting. These cell lines were classified into the following three groups with respect to proteinase secretion: cell lines secreting mainly gelatinases A and/or B; those secreting multiple types of serine proteinases; and those scarcely secreting these enzymes. Two cell lines of the second group, STKM-1 and MKN28, hardly secreted metalloproteinases but secreted the following four types of serine proteinases: (a) two trypsin-like enzymes (Mr 26,000 and 24,000 in proenzyme forms); (b) a tissue kallikrein-like enzyme (Mr 150,000 in a complex form); (c) a plasmin-like enzyme (Mr 70,000); and (d) a plasminogen activator (urokinase-type, Mr 57,000, from STKM-1 and tissue-type, Mr 70,000, from MKN28). The Mr 70,000 plasmin-like enzyme was also detected at lower levels in the conditioned media of four other cell lines (MKN1, MKN45, NUGC-3, and KATO III). The Mr 24,000 proenzyme of the trypsin-like enzyme was purified from the serum-free conditioned medium of STKM-1. The proenzyme was activated by enterokinase treatment or autolytically by incubation at neutral pH, decreasing its apparent molecular weight from 24,000 to 23,000 on nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The activated enzyme extensively degraded fibronectin, laminin, and gelatins and to lesser extents type I, III, IV, and V collagens at 30°C. These results suggest that the matrix serine proteinases may play a major role in the matrix degradation by some kinds of human cancer cells.

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This work was supported by a Grant-in-Aid from the Special Coordination Funds of the Science and Technology Agency of Japan.

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