Cathepsin B belongs to a family of lysosomalcysteine proteases known as the cysteine cathepsins and plays an important role in intracellular proteolysis.[5] In humans, cathepsin B is encoded by the CTSBgene.[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]
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]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Sloane BF (April 1990). "Cathepsin B and cystatins: evidence for a role in cancer progression". Seminars in Cancer Biology. 1 (2): 137–52. PMID2103490.
^Qian F, Frankfater A, Chan SJ, Steiner DF (April 1991). "The structure of the mouse cathepsin B gene and its putative promoter". DNA and Cell Biology. 10 (3): 159–68. doi:10.1089/dna.1991.10.159. PMID2012677.
^Vigneswaran N, Zhao W, Dassanayake A, Muller S, Miller DM, Zacharias W (August 2000). "Variable expression of cathepsin B and D correlates with highly invasive and metastatic phenotype of oral cancer". Human Pathology. 31 (8): 931–7. doi:10.1053/hupa.2000.9035. PMID10987253.
^ abPavlova A, Björk I (September 2003). "Grafting of features of cystatins C or B into the N-terminal region or second binding loop of cystatin A (stefin A) substantially enhances inhibition of cysteine proteinases". Biochemistry. 42 (38): 11326–33. doi:10.1021/bi030119v. PMID14503883.
^Estrada S, Nycander M, Hill NJ, Craven CJ, Waltho JP, Björk I (May 1998). "The role of Gly-4 of human cystatin A (stefin A) in the binding of target proteinases. Characterization by kinetic and equilibrium methods of the interactions of cystatin A Gly-4 mutants with papain, cathepsin B, and cathepsin L". Biochemistry. 37 (20): 7551–60. doi:10.1021/bi980026r. PMID9585570.