The protein acid protease active in intracellular protein breakdown and involved in the pathogenesis of several diseases such as breast cancer and possibly Alzheimer disease. It is specificity similar to; but narrower than; that of pepsin A and it does not cleave the 4-Gln-|-His-5 bond in B chain of insulin. It consists of a light chain and a heavy chain and expressed in the aorta extrcellular space. The Val-58 allele is significantly overrepresented in demented patients (11.8%) compared with non-demented controls (4.9%). Carriers of the Val-58 allele have a 3.1-fold increased risk for developing AD than non-carriers.It belongs to the peptidase A1 family
Cathepsin D (CTSD); a well known lysosomal aspartyl protease and belongs to the peptidase C1 family; which is a normal and major component of lysosomes; and is found in almost all cells and tissues of mammals. Its mostly described function is intracellular catabolism in lysosomal compartments; other physiological effect include hormone and antigen processing. Cathepsin D has a specificity similar to but narrower than that of pepsin A. Cathepsin D plays an important role in the degradation of proteins; the generation of bioactive proteins; antigen processing; etc. Among different role in cell physiology; a new function of this enzyme is examined. Cathepsin D is an important regulator of apoptotic pathways in cells. It acts at different stage of intrinsic and extrinsic pathway of apoptosis. In addition; CTSD secreted from human prostate carcinoma cells are responsible for the generation of angiostatin; a potent endogenous inhibitor of angiogenesis; suggesting its contribution to the prevention of tumor growth and angiogenesis-dependent growth of metastases.
Cathepsin E (CTSE) is a gastric aspartyl protease that functions as a disulfide-linked homodimer. It is a member of the Peptidase C1 family, and has a specificity similar to that of Pepsin A and Cathepsin D. CTSE is localized to the endoplasmic reticulum and Golgi apparatus, while the mature enzyme is localized to the endosome. It is expressed abundantly in the stomach, the Clara cells of the lung and activated B-lymphocytes, and at lower levels in lymph nodes, skin and spleen. CTSE is an intracellular proteinase that have a role in immune function, activation-induced lymphocyte depletion in the thymus, neuronal degeneration and glial cell activation in the brain. Futhermore, it probably involved in the processing of antigenic peptides during MHC class II-mediated antigen presentation.
Cathepsin L2 belongs to the Peptidase C1 family. Cathepsin L2 can be autocatalytically convertedto the mature form as a proenzyme in lysosomes at pH=7.0. Cathepsin L2 cannot be expressed in normal mammary gland, colon and peritumoral tissue, but it can be expressed in breast carcinomas and colorectal tissues. These suggeats Cathepsin L2 may play a role in tumor processes. Cathepsin L2 is specifically expressed in the testis, thymus, and corneal epithelium.
Cathepsin V (CTSV), also known as Cathepsin L2, CTSL2, and CATL2, is a member of the peptidase C1 family. It is predominantly expressed in the thymus and testis. Cathepsin V is also expressed in corneal epithelium, and to a lesser extent in conjuctival epithelium and skin. It is a lysosomal cysteine proteinase that may play an important role in corneal physiology. It has about 75% protein sequence identity to murine cathepsin L. The fold of this enzyme is similar to the fold adopted by other members of the papain superfamily of cysteine proteases. Cathepsin V has been recently described as highly homologous to Cathepsin L and exclusively expressed in human thymus and testis. Cathepsin V is the dominant cysteine protease in cortical human thymic epithelial cells, while Cathepsin L and Cathepsin S seem to be restricted to dendritic and macrophage-like cells. Active Cathepsin V in thymic lysosomal preparations was demonstrated by active-site labeling. Recombinant Cathepsin V was capable of converting Ii into CLIP efficiently, suggesting that it is the protease that controls the generation of alphabeta-CLIP complexes in the human thymus. Cathepsin V is the third elastolytic cysteine protease which exhibits the most potent elastase activity yet described among human proteases and that it is present in atherosclerotic plaque specimens. Cathepsin L2 may play a specialized role in the thymus and testis. Expression analysis of cathepsin L2 in human tumors revealed a widespread expression in colorectal and breast carcinomas but not in normal colon or mammary gland or in peritumoral tissues.
Cathepsin L is a lysosomal cysteine protease that plays a major role in intracellular protein catabolism, and is potent in degrading collagen, laminin, elastin, as well as alpha-1 protease inhibitor and other structural proteins of basement membranes. Like many proteases, Cathepsin L is synthesized as an inactive preproenzyme, and cleavage of the 96-residue proregion is necessary to generate the fully active 221-residue mature enzyme. Studies have demonstrated that cleavage of the proregion occur autocatalytically under acidic conditions. The enzyme takes part in nutrient acquisition by catabolizing host proteins to absorbable peptides, facilitates the migration of the parasite through the host intestine and liver by cleaving interstitial matrix proteins such as fibronectin, laminin and native collagen and is implicated in the inactivation of host immune defenses by cleaving immunoglobulins. Recently, Cathepsin L has been shown to suppress Th1 immune response in infected laboratory animals making them susceptible to concurrent bacterial infections. Cathepsin L is synthesized in large amounts and secreted by many malignantly transformed cells, and induced by growth factors and tumor promoters. In addition to its role in protein degradation, evidence has accumulated for the participation of Cathepsin L in various physiological and pathological processes, such as tumor invasion and metastasis, bone resorption, spermatogenesis, and arthritis. Accordingly, Cathepsin L may prove useful as a diagnostic or prognostic marker of human tumor malignancy.
Cathepsin L is an enzyme. Cathepsin L, a lysosomal endopeptidase expressed in most eukaryotic cells, is a member of the papain-like family of cysteine proteinases. Cathepsin L plays a major role in antigen processing, tumor invasion and metastasis, bone resorption, and turnover of intracellular and secreted proteins involved in growth regulation. Unlike the precursor forms of other papain family members, the 43 kDa pro-cathepsin L itself is secreted from various cells. Pro-cathepsin L is the major excreted protein of malignantly transformed mouse fibroblasts and is also one of the major acidic cysteine proteases in mammalian cells.
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