Caspase-9
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Location (UCSC) | Chr 1: 15.49 – 15.53 Mb | Chr 4: 141.52 – 141.54 Mb | |||||||
PubMed search | [3] | [4] |
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Caspase-9 is an
Caspase-9 belongs to a family of caspases, cysteine-aspartic proteases involved in
Correct caspase-9 function is required for apoptosis, leading to the normal development of the
Different protein isoforms of caspase-9 are produced due to alternative splicing.[10]
Structure
Similar to other caspases, caspase-9 has three domains: N-terminal pro-domain, large subunit, and a small subunit.
The caspase-9 monomer consists of one large and one small subunit, both comprising the catalytic domain.[13] Differing from the normally conserved active site motif QACRG in other caspases, caspase-9 has the motif QACGG.[14][12]
When dimerized, caspase-9 has two different active site conformations within each dimer.[13] One site closely resembles the catalytic site of other caspases, whereas the second has no 'activation loop', disrupting the catalytic machinery in that particular active site.[13] Surface loops around the active site are short, giving rise to broad substrate specificity as the substrate-binding cleft is more open.[15] Within caspase-9's active site, in order for catalytic activity to occur there has to be specific amino acids in the right position. Amino acid Asp at position P1 is essential, with a preference for amino acid His at position P2.[16]
Localization
Within the cell, caspase-9 in humans is found in the mitochondria, cytosol, and nucleus.[17]
Protein expression
Caspase-9 in humans is expressed in fetus and adult tissues.[14][12] Tissue expression of caspase-9 is ubiquitous with the highest expression in the brain and heart, specifically at the developmental stage of an adult in the heart's muscle cells.[18] The liver, pancreas, and skeletal muscle express this enzyme at a moderate level, and all other tissues express caspase-9 at low levels.[18]
Mechanism
Active caspase-9 works as an initiating caspase by cleaving, thus activating downstream executioner caspases, initiating apoptosis.[19] Once activated, caspase-9 goes on to cleave caspase-3, -6, and -7, initiating the caspase cascade as they cleave several other cellular targets.[8]
When caspase-9 is inactive, it exists in the cytosol as a zymogen, in its monomer form.[13][20] It is then recruited and activated by the CARDs in apaf-1, recognizing the CARDs in caspase-9.[21]
Processing
Before activation can occur, caspase-9 has to be processed.[22] Initially, caspase-9 is made as an inactive single-chain zymogen.[22] Processing occurs when the apoptosome binds to pro-caspase-9 as apaf-1 assists in the autoproteolytic processing of the zymogen.[22] The processed caspase-9 stays bound to the apoptosome complex, forming a holoenzyme.[23]
Activation
Activation occurs when caspase-9 dimerizes, and there are two different ways for which this can occur:
- Caspase-9 is auto-activated when it binds to apaf-1(apoptosome), as apaf-1 oligomerizes the precursor molecules of pro-caspase-9.[17]
- Previously activated caspases can cleave caspase-9, causing its dimerization.[24]
Catalytic activity
Caspase-9 has a preferred cleavage sequence of Leu-Gly-His-Asp-(cut)-X.[16]
Regulation
Negative regulation of caspase-9 occurs through phosphorylation.[8] This is done by a serine-threonine kinase, Akt, on serine-196 which inhibits the activation and protease activity of caspase-9, suppressing caspase-9 and further activation of apoptosis.[25] Akt acts as an allosteric inhibitor of caspase-9 because the site of phosphorylation of serine-196 is far from the catalytic site.[25] The inhibitor affects the dimerization of caspase-9 and causes a conformational change that affects the substrate-binding cleft of caspase-9.[25]
Akt can act on both processed and unprocessed caspase-9 in-vitro, where phosphorylation on processed caspase-9 occurs on the large subunit.[26]
Deficiencies and mutations
A deficiency in caspase-9 largely affects the brain and its development.[27] The effects of having a mutation or deficiency in this caspase compared to others is detrimental.[27] The initiating role caspase-9 plays in apoptosis is the cause for the severe effects seen in those with an atypical caspase-9.
Mice with insufficient caspase-9 have a main phenotype of an affected or abnormal brain.[8] Larger brains due to a decrease in apoptosis, resulting in an increase of extra neurons is an example of a phenotype seen in caspase-9 deficient mice.[28] Those homozygous for no caspase-9 die perinatally as a result of an abnormally developed cerebrum.[8]
In humans, expression of caspase-9 varies from tissue to tissue, and the different levels have a physiological role.
Clinical significance
The effects of abnormal caspase-9 levels or function impacts the clinical world. The impact caspase-9 has on the brain can lead to future work in inhibition through targeted therapy, specifically with diseases associated with the brain as this enzyme may take part in the developmental pathways of neuronal disorders.[8]
The introduction of caspases may also have medical benefits.[19] In the context of graft versus host disease, caspase-9 can be introduced as an inducible switch.[31] In the presence of a small molecule, it will dimerize and trigger apoptosis, eliminating lymphocytes.[31]
iCasp9
iCasp9 (inducible caspase-9) is a type of control system for
If therapy with CAR T cells results in severe side effects, iCasp9 can be used to halt treatment. Administering a small-molecule drug such as
Alternative transcripts
Through alternative splicing, four difference caspase-9 variants are produced.
Caspase-9α (9L)
This variant is used as the reference sequence, and it has full cysteine protease activity.[11][34]
Caspase-9β (9S)
Isoform 2 doesn't include exons 3, 4, 5, and 6; it is missing amino acids 140-289.[11][34] Caspase-9S doesn't have central catalytic domain, therefore it functions as an inhibitor of caspase-9α by attaching to the apoptosome, suppressing the caspase enzyme cascade and apoptosis.[11][35] Caspase-9β is referred to as the endogenous dominant-negative isoform.
Caspase-9γ
This variant is missing amino acids 155-416, and for amino acids 152-154, the sequence AYI is changed to TVL.[34]
Isoform 4
In comparison with the reference sequence, it is missing amino acids 1-83.[34]
Interactions
Caspase-9 has been shown to
See also
References
- ^ a b c GRCh38: Ensembl release 89: ENSG00000132906 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000028914 – Ensembl, May 2017
- ^ "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.
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- ^ "HomoloGene - NCBI". www.ncbi.nlm.nih.gov. Retrieved 2017-12-01.
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- ^ "CASP9 caspase 9 [Homo sapiens (human)] - Gene - NCBI". www.ncbi.nlm.nih.gov. Retrieved 2017-11-30.
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- ^ a b c "Definition of autologous iCASP9-CD19-expressing T lymphocytes". National Cancer Institute. Retrieved 2 July 2020.
- ^ a b c d "CASP9 - Caspase-9 precursor - Homo sapiens (Human) - CASP9 gene & protein". www.uniprot.org. Retrieved 2017-12-01.
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Further reading
- Cohen GM (August 1997). "Caspases: the executioners of apoptosis". The Biochemical Journal. 326 (Pt 1): 1–16. PMID 9337844.
- Deveraux QL, Reed JC (February 1999). "IAP family proteins--suppressors of apoptosis". Genes & Development. 13 (3): 239–52. PMID 9990849.
- Zhao LJ, Zhu H (December 2004). "Structure and function of HIV-1 auxiliary regulatory protein Vpr: novel clues to drug design". Current Drug Targets. Immune, Endocrine and Metabolic Disorders. 4 (4): 265–75. PMID 15578977.
- Le Rouzic E, Benichou S (February 2005). "The Vpr protein from HIV-1: distinct roles along the viral life cycle". Retrovirology. 2: 11. PMID 15725353.
- Moon HS, Yang JS (February 2006). "Role of HIV Vpr as a regulator of apoptosis and an effector on bystander cells". Molecules and Cells. 21 (1): 7–20. PMID 16511342.
- Kopp S (September 1976). "Reproducibility of response to a questionnaire on symptoms of masticatory dysfunction". Community Dentistry and Oral Epidemiology. 4 (5): 205–9. PMID 1067155.
- Fernandes-Alnemri T, Litwack G, Alnemri ES (December 1994). "CPP32, a novel human apoptotic protein with homology to Caenorhabditis elegans cell death protein Ced-3 and mammalian interleukin-1 beta-converting enzyme". The Journal of Biological Chemistry. 269 (49): 30761–4. PMID 7983002.
- Duan H, Orth K, Chinnaiyan AM, Poirier GG, Froelich CJ, He WW, Dixit VM (July 1996). "ICE-LAP6, a novel member of the ICE/Ced-3 gene family, is activated by the cytotoxic T cell protease granzyme B". The Journal of Biological Chemistry. 271 (28): 16720–4. PMID 8663294.
- Srinivasula SM, Fernandes-Alnemri T, Zangrilli J, Robertson N, Armstrong RC, Wang L, Trapani JA, Tomaselli KJ, Litwack G, Alnemri ES (October 1996). "The Ced-3/interleukin 1beta converting enzyme-like homolog Mch6 and the lamin-cleaving enzyme Mch2alpha are substrates for the apoptotic mediator CPP32". The Journal of Biological Chemistry. 271 (43): 27099–106. PMID 8900201.
- Srinivasula SM, Ahmad M, Fernandes-Alnemri T, Litwack G, Alnemri ES (December 1996). "Molecular ordering of the Fas-apoptotic pathway: the Fas/APO-1 protease Mch5 is a CrmA-inhibitable protease that activates multiple Ced-3/ICE-like cysteine proteases". Proceedings of the National Academy of Sciences of the United States of America. 93 (25): 14486–91. PMID 8962078.
- Kothakota S, Azuma T, Reinhard C, Klippel A, Tang J, Chu K, McGarry TJ, Kirschner MW, Koths K, Kwiatkowski DJ, Williams LT (October 1997). "Caspase-3-generated fragment of gelsolin: effector of morphological change in apoptosis". Science. 278 (5336): 294–8. PMID 9323209.
- Li P, Nijhawan D, Budihardjo I, Srinivasula SM, Ahmad M, Alnemri ES, Wang X (November 1997). "Cytochrome c and dATP-dependent formation of Apaf-1/caspase-9 complex initiates an apoptotic protease cascade". Cell. 91 (4): 479–89. S2CID 14321446.
- Pan G, O'Rourke K, Dixit VM (March 1998). "Caspase-9, Bcl-XL, and Apaf-1 form a ternary complex". The Journal of Biological Chemistry. 273 (10): 5841–5. PMID 9488720.
- Hu Y, Benedict MA, Wu D, Inohara N, Núñez G (April 1998). "Bcl-XL interacts with Apaf-1 and inhibits Apaf-1-dependent caspase-9 activation". Proceedings of the National Academy of Sciences of the United States of America. 95 (8): 4386–91. PMID 9539746.
- Deveraux QL, Roy N, Stennicke HR, Van Arsdale T, Zhou Q, Srinivasula SM, Alnemri ES, Salvesen GS, Reed JC (April 1998). "IAPs block apoptotic events induced by caspase-8 and cytochrome c by direct inhibition of distinct caspases". The EMBO Journal. 17 (8): 2215–23. PMID 9545235.
- Srinivasula SM, Ahmad M, Fernandes-Alnemri T, Alnemri ES (June 1998). "Autoactivation of procaspase-9 by Apaf-1-mediated oligomerization". Molecular Cell. 1 (7): 949–57. PMID 9651578.
- Kamada S, Kusano H, Fujita H, Ohtsu M, Koya RC, Kuzumaki N, Tsujimoto Y (July 1998). "A cloning method for caspase substrates that uses the yeast two-hybrid system: cloning of the antiapoptotic gene gelsolin". Proceedings of the National Academy of Sciences of the United States of America. 95 (15): 8532–7. PMID 9671712.
- Cardone MH, Roy N, Stennicke HR, Salvesen GS, Franke TF, Stanbridge E, Frisch S, Reed JC (November 1998). "Regulation of cell death protease caspase-9 by phosphorylation". Science. 282 (5392): 1318–21. PMID 9812896.
- Hu Y, Ding L, Spencer DM, Núñez G (December 1998). "WD-40 repeat region regulates Apaf-1 self-association and procaspase-9 activation". The Journal of Biological Chemistry. 273 (50): 33489–94. PMID 9837928.
- Lei K, Nimnual A, Zong WX, Kennedy NJ, Flavell RA, Thompson CB, Bar-Sagi D, Davis RJ (July 2002). "The Bax subfamily of Bcl2-related proteins is essential for apoptotic signal transduction by c-Jun NH(2)-terminal kinase". Molecular and Cellular Biology. 22 (13): 4929–42. PMID 12052897.
- Earnshaw WC, Martins LM, Kaufmann SH (1999). "Mammalian caspases: structure, activation, substrates, and functions during apoptosis". Annual Review of Biochemistry. 68: 383–424. PMID 10872455.
External links
- The MEROPS online database for peptidases and their inhibitors: C14.010[permanent dead link]