Stefin A Regulation of Cathepsin B Expression and Localization in Cancerous and Non-Cancerous Cells.

Cathepsin B (CTSB), a lysosomal cysteine protease, plays pivotal roles in cellular homeostasis and pathology, including cancer progression. This study investigates the regulatory interplay between CTSB and Stefin A (STFA), an endogenous inhibitor of cysteine proteases, in renal and prostate cancer cells. Using plasmid-based overexpression and silencing systems, we demonstrated that overexpressing STFA significantly reduces CTSB activity and protein levels, while silencing STFA leads to elevated CTSB activity and expression in cancer cells but not in non-cancerous cells (embryonic kidney cells-Hek293T and endothelial cells-EA.hy926). Furthermore, STFA modulates the subcellular distribution of CTSB, with STFA overexpression reducing nuclear CTSB levels and silencing inducing cytoplasmic accumulation in cancer cells. Colocalization analysis confirms a direct interaction between STFA and CTSB, highlighting the spatial coordination necessary for effective protease inhibition. These findings underscore the critical role of the CTSB-STFA axis in maintaining proteolytic balance and suggest potential therapeutic strategies targeting this interaction in renal carcinoma and other cancers.