CATHEPSIN-B, THIOLS AND CYSTEINE PROTEASE INHIBITORS IN SQUAMOUS-CELLLUNG-CANCER

We investigated activities of the cysteine protease cathepsin B (CB; E C 3.4.22.1), the levels of reduced glutathione (GSH) and cysteine and the activity of gamma-glutamyltransferase (gamma-GT; EC 2.3.2.2.) in s quamous-cell lung carcinoma (SQCLC) and the lung parenchyma specimens from surgically treated patients. The basal CB activity, assayed in ti ssue extracts in the absence of exogenous activators, was significantl y higher in SQCLC compared to the lung. The residual CB activity, rema ining in tissue extracts after preincubation at 37 degrees C, was not any longer significantly different in SQCLC and the lungs. The inhibit ed CB activity, calculated as the difference between the basal and res idual CB activities, was significantly higher in SQCLC compared to the lung. In the case of the cysteine protease cathepsin C (CC; EC 3.4.14 .1), neither the basal nor the residual nor the inhibited CC activitie s in SQCLC and the lung were significantly different. Compared to CC, the powerfulness of endogenous cysteine protease inhibitors to inhibit CB was much higher in both SQCLC and the lung. The cysteine protease inhibitors from SQCLC and the lung which effectively inhibited CB coul d be related to the inhibitors with an apparent M-r ranging from 10 00 0 to 30 000. Isoelectric focusing studies indicated significant differ ences in the progress of inhibition of the activity of CB isoforms in SQCLC and lung parenchyma extracts. The levels of both GSH and Cys wer e significantly higher in SQCLC compared to the lung and the level of GSH was significantly higher in Stage III tumors compared to Stage I t umors. The activity of gamma-GT was not significantly different in SQC LC and the lung but it was significantly higher in Stage I tumors comp ared to Stage III tumors and showed a significant negative correlation with GSH level in SQCLC, Dithiothreitol did not increase the basal ac tivity of CB from SQCLC and the lung which indicates that reversibly o xidized forms of CB do not accumulate in the tumors and the lungs. The basal activity of CB from SQCLC and the lung was competitively inhibi ted by Cys, Moreover, increasing Cys concentrations had a modulatory e ffect on the basal activity of CB from SQCLC and the lung which was fe atured by Cys-induced inhibition of CB activity and by subsequent Cys- effected recovery of CB activity from its previous inhibition by Cys.