High expression of cathepsin B in transitional bladder carcinoma correlates with tumor invasion

Abstract BACKGROUND Cathepsin B (CB) is a lysosomal cysteine proteinase synthesized as a zymogen of 39–47 kilodaltons (kD), which is subsequently converted into an active single‐ chain form of 33 kD (CB 33 ) and, by additional processing, into the active 2‐chain form containing a heavy chain of 27–29 kD (CB 27‐29 ) and a light chain of 4–6 kD. Increased or altered CB expression has been documented in a variety of tumor cells, but to the authors' knowledge only one study published to date has reported clinicopathologic significance for CB in transitional cell carcinoma (TCC) of the bladder. METHODS In this work, CB expression was determined by Western blot analysis in TCC bladder tissue from 30 patients. Nontumor bladder tissue was also analyzed for CB expression. RESULTS The study results demonstrate higher expression of CB in TCC invasive tumors than in superficial bladder carcinoma. Furthermore, whereas normal bladder only expressed the 29‐kD CB protein, tumor and peritumoral tissue demonstrated the 27‐ to 29‐kD CB form. Immunohistochemical staining did not evidence changes in CB localization between tumor and nontumor tissue. CONCLUSIONS According to the results of the current study, bladder tumor progression appears to be associated with quantitative changes in CB protein expression, as well as with qualitative changes related to the type of CB expressed. Cancer 2003;98:262–8. © 2003 American Cancer Society. DOI 10.1002/cncr.11493