Cathepsin B activity in human lung tumor cell lines: ultrastructural localization, pH sensitivity, and inhibitor status at the cellular level

• Published in: The Journal of histochemistry and cytochemistry Vol. 42; no. 7; pp. 917 - 929
• Main Authors: Spiess, E, Bruning, A, Gack, S, Ulbricht, B, Spring, H, Trefz, G, Ebert, W
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Los Angeles, CA Histochemical Soc 01.07.1994; SAGE Publications; Histochemical Society
• Subjects: Air breathing; Amino Acid Sequence; Biological and medical sciences; Carcinoma, Non-Small-Cell Lung - enzymology; Cathepsin B - antagonists & inhibitors; Cathepsin B - metabolism; Cells, Cultured; Cystatin B; Cystatins - metabolism; Cysteine Proteinase Inhibitors - metabolism; Fundamental and applied biological sciences. Psychology; Humans; Hydrogen-Ion Concentration; Kinetics; Lung - enzymology; Lung Neoplasms - enzymology; Lung Neoplasms - ultrastructure; Microscopy - methods; Microscopy, Electron; Molecular Sequence Data; Respiratory system: anatomy, metabolism, gas exchange, ventilatory mechanics, respiratory hemodynamics; Tumor Cells, Cultured; Vertebrates: respiratory system; Human; Enzyme; Cysteine endopeptidases; Lung; Respiratory system; Plasma membrane; Cathepsin B; Hydrolases; Inhibition; Localization; Proteinases; Endoplasmic reticulum; Tumor cell
• ISSN: 0022-1554; 1551-5044
• DOI: 10.1177/42.7.8014475

We investigated the appearance and activity of the cysteine proteinase cathepsin B and its physiological inhibitors, stefins A and B, at the cellular level in human tumor cell lines HS-24, derived from a primary lung tumor (squamous cell), and SB-3, derived from a metastasis (lung adenocarcinoma). In addition to cathepsin B, these tumor cells also expressed the immunologically and functionally related cathepsin L, but not cathepsin H. Stefin A was found in HS-24 but not in SB-3 cells; stefin B was found in both cell types. Using a specific fluorogenic cytochemical assay, the intracellular activity of the enzyme was localized and quantified. Thus, the cellular cathepsin B kinetics for the synthetic substrates Z-Arg-Arg-4M beta NA and Z-Val-Lys-Lys-Arg-4M beta NA, its pH dependence and inhibition by E64, stefins A and B, and cystatin C could be determined. From these measurements it appeared that the enzyme exhibited different cleavage rates for these substrates in the different cell types, showed considerable cleavage activity at neutral pH, which was stable under these conditions for extended time periods, and was highly sensitive to the inhibitors E64 and cystatin C but was considerably less sensitive to stefins, particularly stefin A. By conventional light microscopy, confocal laser scanning microscopy, and electron microscopy the enzymatic activity was localized in lysosomes, as expected, but also in the endoplasmic reticulum, nuclear membrane, and plasma membrane. The endoplasmic reticulum is a site at which only pre-mature enzyme forms exist, which are usually not active. The appearance of enzymatic activity at the plasma membrane confirms earlier biochemical and immunofluorescence microscopic investigations. The different sites of localization within the cells make it likely that different forms of the enzyme are expressed simultaneously, which follow alternate ways of processing and sorting. Taken together, the results support an involvement of the enzyme under extracellular conditions in degradative processes.