Inactive cathepsin B-like enzyme in human melanoma culture medium

Proteases in cutaneous malignant melanoma: relevance as biomarker and therapeutic target

Cutaneous malignant melanoma is the most aggressive skin cancer. It is also the most rapidly spreading cancer in terms of worldwide incidence. Although it is detected by simple inspection and can be relatively easily removed or treated, differential diagnosis to other melanocytic lesions, lack of prognostic markers, and no efficient treatment of advanced melanoma pose problems. Detection and targeting of proteases may represent a useful tool since they play a role in tumor cell metabolism, invasion, angiogenesis and metastasis. This review gives an overview of the role of proteases in development and progression of cutaneous malignant melanoma. In addition, regulation, activation, and interaction of proteases and their inhibitors are explained for tumors in general. The potential use of proteases as differential markers for melanoma mimicking melanocytic lesions, as biomarkers in tissues, and as prognostic serum markers is discussed. Current and future possibilities to target tumor proteases in therapy are presented.

Molecular regulation, membrane association and secretion of tumor cathepsin B

Upregulation, membrane association and secretion of cathepsin B have been shown to occur in many types of tumors and to correlate positively with their invasive and metastatic capabilities. To further understand changes in cathepsin B activity and localization, we have been examining its regulation at many levels including transcription and trafficking. Our studies indicate that there may be three promoter regions in the cathepsin B gene. Of these, continued examination of the promoter upstream of exon 1 has indicated possible control by several regulatory factors including E-box and Sp-1 binding elements. Upregulation of cathepsin B at this level may account for some of the secretion of cathepsin B found in tumors. We have also gathered evidence that endo- and exocytosis of cathepsin B may be regulated by ras and ras-related proteins in addition to previously described trafficking systems. There is also evidence that several populations of lysosomes may exist and that trafficking to different populations may determine whether cathepsin B is secreted from the tumor cell or remains intracellular. Our results indicate that membrane association and secretion of cathepsin B is not a random process in the tumor cell, but rather part of a tightly controlled system.

Elevations in cathepsin B protein content and enzyme activity occur independently of glycosylation during colorectal tumor progression

Western blots, enzyme assays, protein glycosylation studies, and immunohistochemical staining were used to characterize cathepsin B expression at successive stages of colorectal tumor progression. In normal colon mucosa and premalignant adenomas, cathepsin B expression was predominantly due to mature two-chain protein detected on Western blots as the nonglycosylated 27-kDa form, with overexpression of this protein occurring in only 4 of 18 adenomas. Overexpression increased significantly in Dukes A and B carcinomas (26 of 37 cases), with cathepsin B protein generally detectable in carcinomas as a combination of both 27-kDa nonglycosylated and 28-kDa glycosylated mature two-chain forms. Glycosylated cathepsin B protein in carcinoma extracts was sensitive to PNGase F but resistant to Endo H, indicating a pattern consistent with complex rather than high mannose type glycosylation. When sorted by advancing tumor stage, peak expression of cathepsin B protein occurred in carcinomas involved in local invasion compared with adenomas or metastatic cancers. At all stages, cathepsin B activity correlated significantly with the levels of heavy chain mature cathepsin B protein (r = 0.6682, p < 0.0001) irrespective of glycosylation. Immunohistochemical staining of cathepsin B protein revealed fine diffuse cytoplasmic staining in both adenomas and carcinomas compared with coarse granular cytoplasmic staining (typical of lysosomes) seen in matched normal mucosa. Our results demonstrate several sequential, apparently independent changes in cathepsin B expression during colorectal tumor progression including early changes in subcellular localization, up-regulation of cathepsin B protein and activity in invasive cancers, and altered protein glycosylation detected in malignant tumors at all stages.

Role of cysteine endopeptidases in cancerogenesis

Role of cysteine endopeptidases in cancerogenesis steps: neoplastic transformation, invasion and metastasis is reviewed and discussed. Positive correlation between tumor invasiveness, as well as its metastatic potential and secretion of cysteine endopeptidase (particularly cathepsins B and L) has been documented well in literature. Based on our recent results we postulate that serum endopeptidase-like activity could be used as a marker of cancer aggressiveness in diagnostic procedures in oncology. We also propose that the cysteine endopeptidase inhibitor levels (total, active and latent) could be useful factors for recognising the activation of the organism self-defence mechanisms against cancer. In addition, our idea of use of urinary cysteine peptidase inhibitors (UCPI) as potential anticancer agents is presented and discussed.

Different roles for plasminogen activators and metalloproteinases in melanoma metastasis

Malignant human melanoma cells produce many matrix-degrading enzymes, including plasminogen activators and matrix metalloproteinases. These enzymes have substrate specificity for different components of ECM and most of them have been demonstrated to contribute to melanoma cell-mediated dissolution of matrices and to melanoma cell invasion. The degradation of complex matrices in vitro requires the cooperation of proteases with specificity for glycoproteins and collagens. The contribution of proteases to spontaneous melanoma metastasis was studied by overexpressing specific protease inhibitors in human melanoma cells. Overexpression of PAI-2 inhibited the spread of distant metastasis indicating a role for uPA/plasmin in melanoma invasion. Overexpression of TIMP-2, in contrast, reduced the growth rate of subcutaneous tumors, but did not inhibit metastasis, indicating that MMP activities promote melanoma growth in the skin and may not be required for metastatic dissemination. Thus, uPA and MMP activities are involved in different processes, but they both contribute to melanoma malignancy.