CTSB

CTSB is the gene that encodes cathepsin B, a lysosomal cysteine protease of the papain family in humans. The enzyme participates in intracellular protein turnover under acidic lysosomal conditions and is synthesized as a preproenzyme containing a signal peptide and a propeptide; proteolytic processing yields the mature protease. In addition to its lysosomal role, cathepsin B can be secreted or released extracellularly, where it contributes to tissue remodeling and matrix degradation.

Cathepsin B participates in proteolysis, antigen processing for MHC class II presentation, and regulation of autophagy. It can activate other proteases and influence inflammatory signaling. Physiologically, it supports protein turnover and immune responses; pathologically, extracellular cathepsin B activity can promote invasion and metastasis by degrading extracellular matrix and activating proenzymes.

Dysregulation of CTSB expression or activity is linked to several diseases. Elevated cathepsin B levels are observed in various cancers and correlate with aggressiveness. In neurodegenerative disorders such as Alzheimer's disease, CTSB may influence amyloid precursor protein processing and amyloid-beta degradation, though its role is complex. It is also studied in inflammatory and pancreatobiliary diseases.

CTSB activity is regulated by endogenous inhibitors such as cystatins and by pharmacologic inhibitors like E-64. Therapeutic approaches include small-molecule inhibitors and antibodies aimed at modulating cathepsin B in cancer and inflammatory diseases.