Cathepsins in basal cell carcinomas: activity, immunoreactivity and mRNA staining of cathepsins B, D, H and L.

In the majority of neoplasms invasion is inevitably linked to metastasis and even small tumors have the dormant potential for metastasis. In basal cell carcinoma (BCC) invasion can be evaluated separately because local invasion but no metastasis occurs. Important proteases in invasion and metastasis are the cathepsins. Their activity and regulation has not yet been evaluated in BCC. We determined the activities, immunoreactivities and mRNA of cathepsins B, L and H in sections of different subtypes of BCC. BCC cells and peritumoral cells contained activities for cathepsins B and L. In all parts of the tumor, the reaction with cathepsin B and L substrate was stronger than in normal skin. The immunoreactive protein and mRNA for these proteases, in contrast, was elevated only occasionally in small tumor nodules. Immunoreactive protein and mRNA of cathepsin D was detected predominantly in the center of tumor nodules. Cathepsin H activities, immunoreactivities and mRNA in most BCCs were higher than in normal skin, and the reactive cells were located between and around tumor nodules, but not in the tumor nests. The results indicate that cathepsins B and L are involved in invasion of BCC cells. Cathepsin H of the peritumoral cells may either promote invasion of the tumor cells by degradation of the extracellular matrix or may reflect an elevated activity of the surrounding immunological cells. The pattern of cathepsin staining markedly differs from that observed in melanomas and may characterize locally invading non-metastatic tumors.