Cathepsin B
Protein-coding gene in the species Homo sapiens
From Wikipedia, the free encyclopedia
Cathepsin B belongs to a family of lysosomal cysteine proteases known as the cysteine cathepsins and plays an important role in intracellular proteolysis.[5] In humans, cathepsin B is encoded by the CTSB gene.[6][7] Cathepsin B is upregulated in certain cancers, in pre-malignant lesions, and in various other pathological conditions.[8][9][10][11]
Structure
Gene
The CTSB gene is located at chromosome 8p22, consisting of 13 exons. The promoter of CTSB gene contains a GC-rich region including many SP1 sites, which is similar to housekeeping genes.[12] At least five transcript variants encoding the same protein have been found for this gene.[13]
Protein
Cathepsin B is synthesized on the rough endoplasmic reticulum as a preproenzyme of 339 amino acids with a signal peptide of 17 amino acids.[14][15] Procathepsin B of 43/46 kDa is then transported to the Golgi apparatus, where cathepsin B is formed. Mature cathepsin B is composed of a heavy chain of 25-26 kDa and a light chain of 5kDa, which are linked by a dimer of disulfide.
Function
Cathepsin B may enhance the activity of other proteases, including matrix metalloproteinase, urokinase (serine protease urokinase plasminogen activator), and cathepsin D,[16][17] and thus it has an essential position for the proteolysis of extracellular matrix components, intercellular communication disruption, and reduced protease inhibitor expression.[11]
Cells may become carcinogenic when cathepsin B is unregulated.[18]
Potential in disease
Cathepsin B has been proposed as a potentially effective biomarker for a variety of cancers.[16][19] Overexpression of cathepsin B is correlated with invasive and metastatic cancers.[20]
Cathepsin B has been shown to be involved in the pathogenesis of pancreatitis, by prematurely activating the digestive enzyme trypsinogen within the pancreas, leading to autodigestion of acinar cells.[21][22][23]
