Expression Interplay Between Cathepsin B and Its Natural Inhibitor Stefin A in Cancer and Embryonic Cell Lines

Cathepsin B (CTSB) is a lysosomal protease that also operates outside the acidic environment of lysosomes. In healthy cells, CTSB plays a crucial role in processes such as apoptosis, autophagy, and the maintenance of cellular homeostasis. However, in cancer, it contributes significantly to disease progression by promoting invasion and metastasis. This study introduces a novel exploration of the relationship between CTSB and its natural inhibitor, Stefin A (STFA), renal cancer cells. For the first time, we demonstrated the precise regulatory influence of CTSB on STFA expression by investigating their expression in noncancerous embryonic renal cells (Hek293T), renal cancer cells (769p), and nonrenal cancer cells (Du145). This study highlights the intricate interplay between CTSB and its inhibitor, offering new insights into the CTSB/STFA balance that occurs in kidney cancer biology. In this study, we simultaneously examined the mRNA and protein expression of CTSB and STFA in various cancer cell lines by employing CTSB gain-of-function, loss-of-function, and biochemical inhibition approaches to understand the contributions of CTSB expression and activity in influencing STFA levels and their reciprocal subcellular localization. We found that cancer cells exhibited impaired regulation of CTSB and STFA gene expression. In particular, our results indicate that exogenous expression of CTSB significantly alters STFA levels, suggesting a feedback mechanism influenced by CTSB's enzymatic activity. Importantly, the relationship between CTSB and STFA is preserved at the protein level, indicating complex regulatory mechanisms mitigating transcriptional misbalances at the translational level. This study provides insight into the interplay between CTSB and STFA in cancer cells and compares it to their behavior in embryonic cells, highlighting how aberrant CTSB expression can influence its inhibitor and advancing our understanding of this balance in tumor progression.