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The activities'of the lysosomal cysteine proteinases cathepsin B and L are regulated by their endogenous inhibitors, stefins A and B, and cystatin C, and their imbalance may be associated with increased invasiveness and development of the malignant cell phenotype. The aim of this study was to investigate mRNA, protein and activity levels of the above proteins in relation to in vitro invasiveness and to the reported in vivo tumorigenicity of four human breast tumor cell lines: the spontaneously immortalized cell line MCF10A, its c-Ha-ras transfectant MCF10AT, and two tumorigenic derivative cell lines, MCF10AT-Ca1a and MCF10AT-Ca1d. Invasiveness did not correlate with tumorigenicity, since the MCF10AT cell was the most invasive and the remaining three were at about half of its level. Cathepsin B expression paralleled the in vitro invasiveness through matrigel at all levels of expression, but cathepsin L did not. Stefin levels were elevated several-fold in the tumorigenic cell lines, but not in MCF10AT. The hypothesis that cathepsin B plays an active role in the invasion of breast cancer cell lines was confirmed by the fact that synthetic cysteine proteinase inhibitors, particularly those selective for cathepsin B, significantly reduced the invasion of the MCF10AT cells.

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Cysteine protease cathepsin B (CatB) and its endogenous inhibitor stefin A (StA) play an important role in tumor progression. Increase of CatB expression and lower levels of its inhibitors were associated with tumor malignancy in brain tumors. In this study of 100 patients, CatB was localized by immunostaining to both, tumor and endothelial cells of primary brain tissue. Significant correlation with poor prognosis was found by univariate Cox's regression model. Intense overall immunostaining and immunostaining in endothelial cells alone were prognostic for survival (p=0.003 in both). When comparing CatB expression at mRNA level, we found considerable differences between center and periphery of a tumor as well as between different tumor samples. StA mRNA was only detected in benign, but not in malignant tissues. We suggest that screening of cysteine-protease genes expression can be applied in clinical prognosis of brain tumors.