Cathepsin B

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Cathepsin B (CatB) is an enzymatic protein belonging to the peptidase (or protease) families. In humans, it is coded by the CTSB gene.

Function

The protein encoded by this gene is a lysosomal cysteine protease composed of a dimer of disulfide-linked heavy and light chains, both produced from a single protein precursor. It is a member of the peptidase C1 family. At least five transcript variants encoding the same protein have been found for this gene.

Clinical significance

A wide array of diseases result in elevated levels of cathepsin B, which causes numerous pathological processes including cell death, inflammation, and production of toxic peptides. Focusing on neurological diseases, cathepsin B gene knockout studies in an epileptic rodent model have shown cathepsin B causes a significant amount of the apoptotic cell death that occurs as a result of inducing epilepsy. Cathepsin B inhibitor treatment of rats in which a seizure was induced resulted in improved neurological scores, learning ability and much reduced neuronal cell death and pro-apoptotic cell death peptides. Similarly, cathepsin B gene knockout and cathepsin B inhibitor treatment studies in traumatic brain injury mouse models have shown cathepsin B to be key to causing the resulting neuromuscular dysfunction, memory loss, neuronal cell death and increased production of pro-necrotic and pro-apoptotic cell death peptides. In ischemic non-human primate and rodent models, cathepsin B inhibitor treatment prevented a significant loss of brain neurons, especially in the hippocampus. In a streptococcus pneumoniae meningitis rodent model, cathepsin B inhibitor treatment greatly improved the clinical course of the infection and reduced brain inflammation and inflammatory Interleukin-1beta (IL1-beta) and tumor necrosis factor-alpha (TNFalpha). In a transgenic Alzheimer's disease (AD) animal model expressing human amyloid precursor protein (APP) containing the wild-type beta-secretase site sequence found in most AD patients or in guinea pigs, which are a natural model of human wild-type APP processing, genetically deleting the cathepsin B gene or chemically inhibiting cathepsin B brain activity resulted in a significant improvement in the memory deficits that develop in such mice and reduces levels of neurotoxic full-length Abeta(1-40/42) and the particularly pernicious pyroglutamate Abeta(3-40/42), which are thought to cause the disease. In a non-transgenic senescence-accelerated mouse strain, which also has APP containing the wild-type beta-secretase site sequence, treatment with bilobalide, which is an extract of Ginko biloba leaves, also lowered brain Abeta by inhibiting cathepsin B. Moreover, siRNA silencing or chemically inhibiting cathepsin B in primary rodent hippocampal cells or bovine chromaffin cells, which have human wild-type beta-secretase activity, reduces secretion of Abeta by the regulated secretory pathway.

Mutations in the CTSB gene have been linked to tropical pancreatitis, a form of chronic pancreatitis.

Interactions

Cathepsin B has been shown to interact with:

• cystatin A, and
• cystatin B, and
• S100A10.

See also

• Cathepsins

External links

• The MEROPS online database for peptidases and their inhibitors: C01.060
• Cathepsin B at the US National Library of Medicine Medical Subject Headings (MeSH)