Affinage

CASP9

Caspase-9 · UniProt P55211

Length
416 aa
Mass
46.3 kDa
Annotated
2026-06-09
58 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CASP9 (caspase-9) is an initiator cysteine protease of the intrinsic apoptotic pathway that, once proteolytically activated, cleaves downstream death substrates including poly(ADP-ribose) polymerase (PARP) (PMID:8663294). It is processed and activated by the cytotoxic lymphocyte protease granzyme B and operates within a protease cascade in which mature caspase-3/CPP32 cleaves pro-CASP9 preferentially at Asp330 to liberate its catalytic subunits, placing CASP9 downstream of caspase-3 in granzyme B-mediated death (PMID:8663294, PMID:8900201). Apoptosome-dependent activation of CASP9 requires assembly with APAF-1 and cytochrome c, a step positively regulated by histone H1.2 following UV-induced DNA damage (PMID:17618626). CASP9 expression is transcriptionally amplified by NF-κB, which directly binds the CASP9 promoter while repressing the CASP9-targeting miR-1276 in a coherent feed-forward loop that potentiates TNFα/doxorubicin-induced apoptosis (PMID:32225068). Beyond apoptosis, CASP9 has distinct non-apoptotic roles: it maintains mitochondrial homeostasis and is required for autophagosome membrane sealing and maturation through proper ATG3 function and Atg8-family (GABARAPL1) lipidation (PMID:31818185), and it acts non-catalytically at endosomal membranes to facilitate retrograde IGF2R/CI-MPR transport from endosomes to the trans-Golgi network via interactions with the retromer subunit VPS35, SNX-BAR dimers (SNX1-SNX5, SNX2-SNX6), ESCRT-0 (HGS), and clathrin heavy chain (PMID:32397873). Loss-of-function CASP9 variants that attenuate intrinsic apoptosis are associated with neural tube defects, including a folate-dependent gene-environment interaction (PMID:29365368).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1996 High

    Established CASP9 as a death protease by showing it is activated by granzyme B and cleaves a canonical apoptotic substrate, defining its place in cytotoxic-lymphocyte-triggered apoptosis.

    Evidence In vitro granzyme B cleavage assay, overexpression in MCF7 cells, and PARP cleavage readout

    PMID:8663294

    Open questions at the time
    • Did not resolve the physiological upstream activator versus granzyme B
    • Apoptosome requirement for activation not yet defined
    • No structural basis for the divergent QACGG active site
  2. 1996 High

    Defined the precise activating cleavage site (Asp330) and ordered the cascade, placing CASP9 downstream of caspase-3/CPP32 in granzyme B-mediated apoptosis.

    Evidence In vitro cleavage with site-directed Asp330 mutagenesis and SDS-PAGE analysis of subunit products

    PMID:8900201

    Open questions at the time
    • Hierarchy between CASP9 and caspase-3 in other death stimuli not addressed
    • In-cell relevance of each cleavage site not quantified
  3. 2007 Medium

    Identified a DNA-damage-linked positive regulator of apoptosome activation, showing histone H1.2 promotes APAF-1/CASP9/cytochrome c assembly and downstream caspase-3/7 activation.

    Evidence Affinity labeling, mass spectrometry, and cell-free caspase activation assay after UV irradiation

    PMID:17618626

    Open questions at the time
    • Stoichiometry and direct binding interface within the apoptosome unstructured
    • In vivo contribution of H1.2 to apoptosis not established
    • Single-lab finding without independent replication in the corpus
  4. 2014 Medium

    Revealed a function for CASP9 in restraining ER-stress responses, where its loss prolongs UPR and autophagy and confers resistance to ER-stress-induced death.

    Evidence Comparison of isogenic casp9+/+ and casp9-/- MEFs under ER stress with UPR, autophagy, and viability readouts

    PMID:25086361

    Open questions at the time
    • Molecular mechanism linking CASP9 to UPR resolution unknown
    • Whether catalytic activity is required not tested
    • Nature of the non-canonical death mode undefined
  5. 2018 Medium

    Connected CASP9 to human disease by showing loss-of-function variants attenuate intrinsic apoptosis, including a folate-dependent gene-environment interaction relevant to neural tube defects.

    Evidence Sequencing of NTD cohorts plus functional apoptosis/caspase assays in neuroepithelial and HEK293T cells under complete and low-folate conditions

    PMID:29365368

    Open questions at the time
    • Causality in NTD pathogenesis not established beyond cell-based assays
    • Mechanism of the R191G folate-conditional effect unknown
  6. 2018 Medium

    Showed a pro-survival, non-apoptotic role for the CASP9 prodomain at late endosomal/pre-lysosomal membranes in drug-tolerant KRAS-mutant cancer cells.

    Evidence HSP90 inhibitor treatment, prodomain expression analysis, immunofluorescence localization, and cell survival assays

    PMID:29561705

    Open questions at the time
    • Mechanistic basis of prodomain-driven survival not defined
    • ATG7-independence only partially characterized
    • Limited mechanistic detail available
  7. 2019 High

    Established a non-apoptotic requirement for CASP9 in autophagosome maturation and mitochondrial homeostasis, separating its role in membrane sealing/ATG3-Atg8 lipidation from its mitochondrial regulatory function.

    Evidence CRISPR knockout with re-expression rescue, super-resolution microscopy, ATG3/LC3 lipidation blots, and mitochondrial membrane potential assays with H2O2 rescue

    PMID:31818185

    Open questions at the time
    • Whether the maturation role requires catalytic activity not fully resolved here
    • Direct molecular target of CASP9 in ATG3 activation unidentified
    • Mechanism coupling mitochondrial ROS to ATG3 stability unclear
  8. 2020 High

    Defined a catalytically independent scaffolding role for CASP9 in endosome-to-TGN retrograde transport, with rescue by a non-catalytic mutant confirming proteolysis-independent function.

    Evidence CASP9 KO/knockdown, reciprocal co-immunoprecipitation of retromer/SNX-BAR/ESCRT-0/clathrin partners, non-catalytic mutant rescue, fractionation, and IGF2R degradation assays

    PMID:32397873

    Open questions at the time
    • Direct versus indirect nature of each partner interaction not fully dissected
    • Structural basis of endosomal membrane recruitment unknown
  9. 2020 Medium

    Mapped transcriptional control of CASP9 by showing NF-κB directly activates the promoter while repressing miR-1276 in a feed-forward loop that amplifies CASP9-dependent apoptosis.

    Evidence ChIP and luciferase reporter assays plus CASP9 activation blots and pharmacological CASP9 inhibition in TNFα/doxorubicin-treated HeLa and HepG2 cells

    PMID:32225068

    Open questions at the time
    • Generality of the loop across cell types/stimuli untested
    • Quantitative contribution of miR-1276 versus direct activation unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How CASP9 switches between its catalytic apoptotic role and its non-catalytic membrane-trafficking and autophagy functions, and what governs its differential localization, remains unresolved.
  • No structural model distinguishing apoptotic versus scaffolding conformations
  • Signals directing CASP9 to endosomal versus mitochondrial/apoptosome pools unknown
  • Direct molecular substrates/effectors in autophagy maturation unidentified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 2 GO:0016787 hydrolase activity 1 GO:0060090 molecular adaptor activity 1
Localization
GO:0005768 endosome 2 GO:0005739 mitochondrion 1 GO:0005829 cytosol 1
Pathway
R-HSA-5357801 Programmed Cell Death 4 R-HSA-5653656 Vesicle-mediated transport 1 R-HSA-9612973 Autophagy 1
Partners
APAF1CLTCCYCSHGSHIST1H1CSNX1SNX5VPS35
Complex memberships
apoptosome (APAF-1/cytochrome c/CASP9)

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1996 ICE-LAP6 (CASP9) is proteolytically processed and activated by granzyme B, a cytotoxic T cell protease. Once activated, ICE-LAP6 cleaves the death substrate poly(ADP-ribose) polymerase (PARP) into signature apoptotic fragments. ICE-LAP6 contains an active site QACGG pentapeptide (rather than QACRG shared by other family members) and overexpression induces apoptosis. In vitro cleavage assay with granzyme B, overexpression in MCF7 cells, PARP cleavage assay The Journal of biological chemistry High 8663294
1996 Pro-Mch6 (pro-CASP9) is a substrate for mature CPP32 (caspase-3), which processes it preferentially at Asp330 to generate 37 kDa and 10 kDa subunits. Granzyme B can also process pro-Mch6 but at a site N-terminal to that cleaved by CPP32. This established a protease cascade: granzyme B → CPP32 → Mch6, placing CASP9 downstream of CPP32 in granzyme B-mediated apoptosis. In vitro cleavage assay, site-directed mutagenesis at Asp330, SDS-PAGE analysis of processing products The Journal of biological chemistry High 8900201
2007 Upon UV irradiation, histone H1.2 forms a protein complex with APAF-1, CASP9, and cytochrome c (CYT c). In cell-free systems, histone H1.2 triggers activation of CASP-3 and CASP-7 via APAF-1 and CASP-9, establishing histone H1.2 as a positive regulator of apoptosome formation. Affinity labeling, mass spectrometry, cell-free caspase activation assay FEBS letters Medium 17618626
2019 CASP9 (caspase 9) has a non-apoptotic function required for autophagosome maturation. In CASP9 knockout cells, phagophore initiation and elongation are normal but membrane sealing and autophagosome maturation are impaired, ATG3 accumulates in inactive form, and lipidation of Atg8-family members (especially GABARAPL1) is decreased. CASP9 also maintains mitochondrial homeostasis (membrane potential, ROS production, fusion-fission protein levels). Exogenous H2O2 can rescue ATG3 levels and autophagy flux but not mitochondrial defects, indicating separate CASP9-dependent mitochondrial regulatory function. CASP9 knockout (CRISPR), ectopic re-expression rescue, pharmacological inhibition, super-resolution microscopy, western blot for ATG3 and LC3 lipidation, mitochondrial membrane potential assay Autophagy High 31818185
2020 CASP9 localizes to endosomal membranes and facilitates retrograde transport of IGF2R/CI-MPR from endosomes to the trans-Golgi network via a non-apoptotic, non-catalytic mechanism. CASP9-deficient cells show missorted CTSD and other acid hydrolases, late endosome accumulation, and reduced lysosomal protein degradation. Rescue by a non-catalytic CASP9 mutant confirms the effect is independent of proteolytic activity. CASP9 interacts with retromer components VPS35, SNX1-SNX5 and SNX2-SNX6 dimers, as well as HGS/HRS/ESCRT-0 and clathrin heavy chain (CLTC). CASP9 KO and knockdown, co-immunoprecipitation of endosomal transport complexes, rescue with non-catalytic mutant, subcellular fractionation, immunofluorescence, IGF2R degradation assay Autophagy High 32397873
2018 In KRAS-mutant NSCLC cells surviving HSP90 inhibition, elevated CASP9 prodomain expression at late endosomal/pre-lysosomal membranes serves as a cell survival mechanism that does not involve CASP9 apoptotic activity and is largely ATG7-independent. HSP90 inhibitor treatment, CASP9 expression analysis, subcellular localization by immunofluorescence, functional cell survival assays Autophagy Medium 29561705
2018 NTD-specific missense variant p.Y251C in CASP9 attenuates apoptosis by reducing CASP9 protein expression and decreasing intrinsic apoptosis pathway activity (loss-of-function). A recurrent p.R191G variant does not affect intrinsic apoptosis under normal conditions but completely inhibits apoptosis induced by low folic acid medium, demonstrating gene-environment interaction. High-throughput sequencing of NTD cases and controls, functional apoptosis assays in transiently transfected neuroepithelial cells and HEK293T cells, caspase activity assays under complete and low-FA conditions CNS neuroscience & therapeutics Medium 29365368
2020 NF-κB directly binds to the CASP9 promoter and upregulates CASP9 expression in TNFα-treated HeLa and HepG2 cells. NF-κB simultaneously downregulates miR-1276, which itself represses CASP9, forming a coherent feed-forward loop that amplifies CASP9 upregulation. CASP9 is subsequently activated and mediates TNFα-promoted apoptosis induced by doxorubicin; a CASP9 activation inhibitor significantly represses this pro-apoptotic effect. ChIP (NF-κB binding to CASP9 and miR-1276 promoters), luciferase reporter, western blot for CASP9 activation, pharmacological inhibition of CASP9 International journal of molecular sciences Medium 32225068
2014 CASP9-deficient MEFs (casp9-/-) show prolonged activation of the unfolded protein response (UPR) and autophagy compared to casp9+/+ MEFs under ER stress, which display only transient UPR/autophagy activation. Casp9-/- MEFs are resistant to ER stress-induced cell death, but prolonged exposure leads to activation of a non-canonical, caspase-mediated mode of cell death. Comparative analysis of casp9+/+ vs casp9-/- mouse embryonic fibroblasts under ER stress, UPR markers, autophagy markers, cell viability assays Biochemical and biophysical research communications Medium 25086361

Source papers

Stage 0 corpus · 58 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
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 284 8663294
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 269 8900201
2011 Assessment of template based protein structure predictions in CASP9. Proteins 135 22002823
2011 Automated protein structure modeling in CASP9 by I-TASSER pipeline combined with QUARK-based ab initio folding and FG-MD-based structure refinement. Proteins 118 22069036
2007 Melatonin maintains mitochondrial membrane potential and attenuates activation of initiator (casp-9) and effector caspases (casp-3/casp-7) and PARP in UVR-exposed HaCaT keratinocytes. Journal of pineal research 103 18086147
2011 Assessment of protein structure refinement in CASP9. Proteins 80 22069034
2011 CASP9 assessment of free modeling target predictions. Proteins 75 21997521
2019 CASP9 (caspase 9) is essential for autophagosome maturation through regulation of mitochondrial homeostasis. Autophagy 68 31818185
2011 Evaluation of model quality predictions in CASP9. Proteins 65 21997462
2022 Exosome-transmitted miR-769-5p confers cisplatin resistance and progression in gastric cancer by targeting CASP9 and promoting the ubiquitination degradation of p53. Clinical and translational medicine 57 35522909
2011 CASP9 target classification. Proteins 57 21997778
2017 Apoptosis-inducing and antiproliferative effect by inhibition of miR-182-5p through the regulation of CASP9 expression in human breast cancer. Cancer gene therapy 52 28084318
2002 Analyses of apoptotic regulators CASP9 and DFFA at 1P36.2, reveal rare allele variants in human neuroblastoma tumours. British journal of cancer 34 11870543
2018 HSP90 inhibition targets autophagy and induces a CASP9-dependent resistance mechanism in NSCLC. Autophagy 32 29561705
2013 Analysis of association between IL-1β, CASP-9, and GDF5 variants and low-back pain in Chinese male soldier: clinical article. Journal of neurosurgery. Spine 29 23725396
2011 Activity of selenium on cell proliferation, cytotoxicity, and apoptosis and on the expression of CASP9, BCL-XL and APC in intestinal adenocarcinoma cells. Mutation research 29 21763329
2007 Proapoptotic histone H1.2 induces CASP-3 and -7 activation by forming a protein complex with CYT c, APAF-1 and CASP-9. FEBS letters 27 17618626
2011 An automatic method for CASP9 free modeling structure prediction assessment. Bioinformatics (Oxford, England) 20 21994223
2013 Effects of β-glucan extracted from Agaricus blazei on the expression of ERCC5, CASP9, and CYP1A1 genes and metabolic profile in HepG2 cells. Human & experimental toxicology 19 23424205
2020 Upregulation of CASP9 through NF-κB and Its Target MiR-1276 Contributed to TNFα-promoted Apoptosis of Cancer Cells Induced by Doxorubicin. International journal of molecular sciences 18 32225068
2020 Involvement of CASP9 (caspase 9) in IGF2R/CI-MPR endosomal transport. Autophagy 18 32397873
2012 Expression of c-Jun, p73, Casp9, and N-ras in thymic epithelial tumors: relationship with the current WHO classification systems. Diagnostic pathology 18 22974165
2013 Influence of survivin (BIRC5) and caspase-9 (CASP9) functional polymorphisms in renal cell carcinoma development: a study in a southern European population. Molecular biology reports 17 23645041
2011 Target highlights in CASP9: Experimental target structures for the critical assessment of techniques for protein structure prediction. Proteins 17 22020785
2019 Analysis of the expression of BAX, BCL2, BIRC6, CASP3, CASP9 apoptosis genes during the first episode of schizophrenia. Psychiatria polska 16 32017818
2017 Genetic Susceptibility in Acute Pancreatitis: Genotyping of GSTM1, GSTT1, GSTP1, CASP7, CASP8, CASP9, CASP10, LTA, TNFRSF1B, and TP53 Gene Variants. Pancreas 14 27984487
2021 Annona muricata silver nanoparticles exhibit strong anticancer activities against cervical and prostate adenocarcinomas through regulation of CASP9 and the CXCL1/CXCR2 genes axis. Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine 13 33935122
2009 CASP-9: A susceptibility locus for multiple sclerosis in Italy. Journal of neuroimmunology 13 19359048
2001 The potential tumour suppressor role for caspase-9 (CASP9) in the childhood malignancy, neuroblastoma. European journal of cancer (Oxford, England : 1990) 13 11677110
2021 Relationship Between CASP9 and CASP10 Gene Polymorphisms and Cancer Susceptibility: Evidence from an Updated Meta-analysis. Applied biochemistry and biotechnology 12 34463927
2019 Immune genes, IL1β and Casp9, show sexual dimorphic methylation patterns in zebrafish gonads. Fish & shellfish immunology 12 31830572
2017 CASP9 germline mutation in a family with multiple brain tumors. Brain pathology (Zurich, Switzerland) 12 27935156
2021 Long non-coding RNA LINC00607 silencing exerts antioncogenic effects on thyroid cancer through the CASP9 Promoter methylation. Journal of cellular and molecular medicine 11 34232553
2017 GSTP1 c.313A>G, XPD c.934G>A, XPF c.2505T>C and CASP9 c.-1339A>G Polymorphisms and Severity of Vomiting in Head and Neck Cancer Patients treated with Cisplatin Chemoradiation. Basic & clinical pharmacology & toxicology 11 28686330
2007 [A study on the expression of CASP9 gene and its polymorphism distribution in non-small cell lung cancer]. Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 11 17285546
2018 Genetic screening and functional analysis of CASP9 mutations in a Chinese cohort with neural tube defects. CNS neuroscience & therapeutics 10 29365368
2017 Inducing cell proliferative prevention in human acute promyelocytic leukemia by miR-182 inhibition through modulation of CASP9 expression. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie 10 28298075
2013 KAT5 silencing induces apoptosis of GBC-SD cells through p38MAPK-mediated upregulation of cleaved Casp9. International journal of clinical and experimental pathology 10 24427328
2017 Association Between a Polymorphism in CASP3 and CASP9 Genes and Ischemic Stroke. Annals of rehabilitation medicine 8 28503451
2013 CASP-9 gene functional polymorphisms and cancer risk: a large-scale association study plus meta-analysis. Genetics and molecular research : GMR 8 23479167
2018 FOXA1 knock-out via CRISPR/Cas9 altered Casp-9, Bax, CCND1, CDK4, and fibronectin expressions in LNCaP cells. Experimental biology and medicine (Maywood, N.J.) 7 30043639
2001 Two novel single-nucleotide polymorphisms of the Caspase-9 (CASP9) gene in the Japanese population. Genes and immunity 7 11393657
2013 Association of CASP9, CASP10 gene polymorphisms and tea drinking with colorectal cancer risk in the Han Chinese population. Journal of Zhejiang University. Science. B 6 23303631
2012 Recursive protein modeling: a divide and conquer strategy for Protein Structure Prediction and its case study in CASP9. Journal of bioinformatics and computational biology 6 22809379
2019 CASP9 c.-1339A>G and CASP3 c.-1191A>G polymorphisms alter susceptibility and clinical aspects of head and neck squamous cell carcinoma. Head & neck 5 30903678
2011 [Association of CASP3 and CASP9 polymorphisms with genetic susceptibility to stomach cancer]. Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 5 21644232
2012 Role of the CASP-9 Ex5+32 G>A polymorphism in susceptibility to cancer: A meta-analysis. Experimental and therapeutic medicine 4 23251262
2025 Novel strategy for hair regeneration: Exosomes and collagenous sequences of human a1(XVII) chain enhance hair follicle stem cell activity by regulating the hsa-novel-238a-CASP9 axis. Experimental cell research 3 40010561
2025 USP6NL knockdown suppresses colorectal cancer progression by inducing CASP9-Mediated apoptosis and disrupting FOXC2/SNAI1-Driven EMT and angiogenesis. Functional & integrative genomics 3 40643716
2016 [Clinical and Functional Importance of Selected CASP8 and CASP9 Polymorphisms in Breast Carcinoma]. Klinicka onkologie : casopis Ceske a Slovenske onkologicke spolecnosti 3 27951722
2011 Unsupervised Integration of Multiple Protein Disorder Predictors: The Method and Evaluation on CASP7, CASP8 and CASP9 Data. Proteome science 3 22166115
2023 Variants of the CASP9 gene as candidate markers for primary response to anti-TNF therapy in Crohn's disease patients. Journal of applied genetics 2 37658984
2014 ER stress responses in the absence of apoptosome: a comparative study in CASP9 proficient vs deficient mouse embryonic fibroblasts. Biochemical and biophysical research communications 2 25086361
2025 Antineoplastic potential of Kushneria avicenniae pigments via modulation of the BAX/BCL-2 axis and CASP-9 pathway in inducing G2/M arrest and apoptosis in liver and breast cancer. Medical oncology (Northwood, London, England) 1 40753129
2020 Influence of CASP9 c.-1339A>G and CASP3 c.-1191A>G variants in outcome of patients with head and neck squamous cell carcinoma. Journal of oral pathology & medicine : official publication of the International Association of Oral Pathologists and the American Academy of Oral Pathology 1 32816327
2025 Transcriptome analysis and molecular docking reveal the activation of FOXO4, TNFSF15 and CASP9 in HeLa cells treated with DCM fraction from Clinacanthus nutans (C. nutans). Journal of Asian natural products research 0 40094535
2025 Overexpression of CASP-3, CASP-8, CASP-9 and P53 in HT-29 Cancer Cells after Co-Treatment of New Strain of Lactobacillus Crispatus Extract and Doxorobixin and Complementary Docking Study. Current microbiology 0 41320686
2017 Transcript expression and genetic variability analysis of caspases in breast carcinomas suggests CASP9 as the most interesting target. Clinical chemistry and laboratory medicine 0 27327132

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