Increased activity of the protease cathepsin B has been demonstrated in many tumor cells. A correlation of cathepsin B activity and metastatic potential of melanoma has been well established.
METHODS.
The cathepsins B, D, H, and L were evaluated in normal skin, nevi, and melanoma samples to obtain information about their role and their regulation in melanoma. The authors localized specific proteolytic activity with histochemistry, cathepsin protein immunohistochemistry, and mRNA with in situ hybridization.
RESULTS.
Activities and immunoreactivities of the cathepsins B and L were found to be increased in all melanocytic lesions. However, the staining for the corresponding mRNA levels was elevated only in melanomas. Cathepsin D protein and mRNA were expressed to a higher degree only in the dysplastic nevus and in melanomas. The increase was due to tumor cells and cells of the surrounding tissue. Cathepsin H activity, immunoreactivity, and mRNA appeared to be correlated inversely with the invasive potential of the lesion.
CONCLUSIONS.
It may be relevant for the malignant potential of the lesion whether the increase in activity is accompanied by an increase in the mRNA level. Two different mechanisms-the existence of different mRNAs and the higher transcription rate of the cathepsin gene-have been proposed for the regulation of cathepsin B activity in tumor cells. The current data suggest that, depending on the thickness of the melanoma, cathepsin activity is regulated by different mechanisms. The up-regulation of cathepsin gene transcription appears to be characteristic for more invasive tumor cells.