Novocastra Cathepsin B
Cathepsin B is one member of a family of proteolytic enzymes and is expressed in cytoplasmic lysosomes in different types of normal and neoplastic tissues. It is a cysteine protease and like most cathepsins is involved in cellular metabolism such as protein degradation.
Immunohistochemical studies have detected expression in bowel mucosa, skin, prostate and thyroid. Staining for cathepsin B, in common with other cathepsins, may be so intense that it appears to be nuclear in some cells. A proportion of endothelial cells are positive in many tissues. This has been reported previously where it has been described as sprouting endothelial cells. In tissues containing tumors this is thought to be related to tumor progression. Cathepsin B is an important matrix-degrading protease in several human cancers including lung adenocarcinomas, squamous cell carcinomas, rectal and breast carcinomas. Cathepsin B is reported to be overexpressed in squamous cell carcinoma where undifferentiated cells are strongly positive and the more differentiated cells in tumor islands are either weakly positive or negative. The expression of cathepsin B has also been reported in melanomas where the upregulation of this enzyme was found to be a characteristic of a more invasive tumor phenotype.