CASP9 (caspase 9, apoptosis-related cysteine peptidase)

2006-12-01   Sabrina Di Bartolomeo , Francesco Cecconi 

Department of Biology, Via della Ricerca Scientifica, 00133, Rome, Italy





The human caspase-9 gene contains 9 exons and 8 introns and was predicted to span over approximately 35 kb of the genomic DNA.


Three mRNA isoforms have been identified in Homo sapiens.
Caspase-9S, also classified as caspase-9b or caspase-9beta, is a small variant of caspase-9 lacking exons 3-6, which contain the catalytic domain. Caspase-9S functions as an endogenous dominant-negative isoform of full-length caspase-9 by binding to the Apaf-1 protein thus hampering its binding and processing of the full-length procaspase-9.
Recently, it has been cloned and characterized a novel caspase-9 splice variant, named caspase9-gamma. Caspase9-gamma is generated from an alternative splicing of the fourth exon of caspase-9 gene, that results in a 58 nucleotide-long insertion, absent in caspase-9 full length. As the inserted fragment introduces a stop codon, the resulting RNA sequence is prematurely terminated and translated in a 154 aminoacids protein corresponding to only the CARD domain of the caspase-9 full length. Caspase9-gamma does not contain small and large catalytic subunits and cannot promote apoptosis, but like caspase-S, it can function as an apoptosis inhibitor by interferring with the CARD-CARD interaction between procaspase-9 and Apaf-1.



Like for other caspase genes, caspase-9 mRNA is translated in a precursor protein, the procaspase, that is subsequently converted to the active enzyme. The procaspase-9 consists of 416 amino acids corresponding to a molecular weight of 46281 Da. Cleavages at Asp315 and Asp330 by granzyme B and CPP32 (caspase-3), respectively, generate two active peptides. The active caspase-9 is, in fact, constituted by an heterodimer of a 35kDa (p35) and a 10 kDa (p10) subunit. It belongs to the peptidase C14 family and contains three major domains: a prodomain (in which a CARD domain is located), a large subunit catalytic domain (LSCD) and a small subunit catalytic domain (SSCD).


Caspase-9 expression is ubiquitous, with highest expression in the heart and a moderate expression in liver, skeletal muscle, and pancreas.


Mainly cytosolic, but both proenzyme and active caspase-9 have been also observed in the mitochondria and in the nucleus.


Caspase-9 is a member of the cysteine aspartic acid protease, or caspase, family. The procaspase-9 is activated in apoptotic conditions and it is involved in the activation of the caspase cascade responsible for apoptosis execution. The procaspase-9 and Apaf-1 interact each other through their CARD domains generating, in presence of cytochrome c and ATP, the protein complex named "apoptosome". The latter one, in turn, cleaves and activates the effector caspases such the caspase-3.
Caspase-9 plays an essential role in apoptosis during normal development. The majority of homozygous CASP-9 null mice die perinatally with an enlarged and malformed cerebrum caused by a reduced apoptosis during brain development.


CASP9 (Canis familiaris, Pan troglodytes, Gallus gallus), Casp9 (Rattus norvegicus, Mus musculus), Casp9-A (Xenopous Laevis), Dr.16035 (Danio Rerio).



Not known in Homo sapiens


Three different somatic mutations have been detected in two colorectal carcinomas and in one gastric carcinoma among 353 cancer specimen analyzed, including 180 gastric, 104 colorectal and 69 lung adenocarcinomas. However, all these mutations were silent mutation, thus not contributing to the pathogenesis of these cancers.

Implicated in

Entity name
Lung cancer
CASP-9 promoter polymorphisms influence the promoter activity and are associated with the risk of developing lung cancer.
It has been examined the association of four CASP-9 promoter polymorphisms with the risk of lung cancer in a Korean population comprising 432 lung cancer patients and 432 healthy controls. The -1263 GG genotype was associated with a significantly decreased risk of lung cancer compared with -1263 AA or combined -1263 AA + AG. Moreover, individuals with at least one -712T allele had a significantly increased risk of lung cancer compared with those carrying the -712 CC genotype. In brief, the polymorphisms that result in an higher promoter activity seem to be associated with a decreased risk to develop lung cancer. Polymorphisms in CASP-9 promoter can then be useful markers for determining genetic susceptibility to this cancer. However, the association between CASP-9 polymorphisms and risk of lung cancer seem to be influenced by tobacco smoking, no association being present in never-smoker patients. Moreover, as polymorphisms can show ethnic variations, the observations should be extended to diverse ethnic groups.
Colon cancer
Caspase-9 was shown to be downregulated in colon cancer samples in comparison with normal mucosa tissues. Immunohistochemical analysis reveals that the expression of caspase-9 is variable in the healthy enterocytes. However, in the enterocytic component of 12 among 26 cancer samples analyzed, a decrease in caspase-9 immunostaining intensity has been observed: a profile similar, but to a smaller extent, to that observed for caspase 7.
Entity name
Head and neck squamous cell carcinoma
In a certain type of head and neck squamous cell carcinoma cells (HNSCCs), the inhibition of caspase-9 activity and Apaf-1 expression may represent a mechanism of acquired cisplatin resistance. It has been reported that cisplatin induced caspase-9 activation and apoptosis in cisplatin-sensitive HNSCCs in vitro. On the contrary, the cisplatin-resistant HNSCCs analyzed were not able to activate caspase-9 following cisplatin treatment, thus not responding to the therapy.
Entity name
Testicular germ cell cancer
Similarly to head and neck squamous cell carcinama cells, failure of activation of caspase-9 induces cisplatin resistance in testicular cancer cells in vitro. Testicular germ cell cancer is a tumor highly responsive to cisplatin-based chemotherpy, but in a few cases a phenomenon of chemoresistence can occour leading to an unfavourable prognosis. In in vitro experiments, it has been shown that a cisplatin-resistant human testicular germ cell cancer cell line (1411HP) failed to activate caspase-9 and apoptosis after cisplatin treatment in comparison with two cisplatin-sensitive human testicular germ cell cancer cell line (2102EP and H12.1). In the resistant cell line, however, it was possible induce a caspase-9 independent apoptosis using a 3.3-fold higher cisplatin dose.
By using biopsy specimens of primary diffuse large B-cell lymphoma (DLBCL) it has been demonstrated that a cellular profile consistent with inhibition of the caspase-9 pathway is associated with poor response to chemotherapy and fatal outcome. On the contrary, a cellular profile consistent with caspase-8 pathway inhibition is associated with an excellent response to chemotherapy. Identifying the functional status of caspase-9 and caspase-8 in patients may have implications for the outcome prediction and for development of alternative therapeutics strategies.
Entity name
Gastric cancer
Seven cell lines derived from human gastric cancers were used to investigate the involvement of caspases in chemoresistance mechanisms. Among those examined, the cell line most resistant to apoptotic stimuli expressed the highest levels of the caspase-9 isoform beta, thus confirming the role of caspase-9 in promoting apoptosis in treated cancer cells.


Pubmed IDLast YearTitleAuthors
103840551999Genomic organization of the human caspase-9 gene on Chromosome 1p36. 1-p36.3.Hadano S et al
146343351999Identification of an alternative form of caspase-9 in human gastric cancer cell lines: a role of a caspase-9 variant in apoptosis resistance.Izawa M et al
151923242004Caspase-9 regulation: an update.Johnson CR et al
106879482000Caspase-9.Kuida K et al
125431672003Inhibition of caspase-9 activity and Apaf-1 expression in cisplatin-resistant head and neck squamous cell carcinoma cells.Kuwahara D et al
125438102003Failure of activation of caspase-9 induces a higher threshold for apoptosis and cisplatin resistance in testicular cancer.Mueller T et al
155764772005Immunohistochemical profiling of caspase signaling pathways predicts clinical response to chemotherapy in primary nodal diffuse large B-cell lymphomas.Muris JJ et al
158768722005Inhibition of caspase 9 and not caspase 8 mediated apoptosis may determine clinical response to chemotherapy in primary nodal diffuse large B-cell lymphomas.Oudejans JJ et al
113813622001Caspase 7 downregulation as an immunohistochemical marker of colonic carcinoma.Palmerini F et al
166874422006Caspase 9 promoter polymorphisms and risk of primary lung cancer.Park JY et al
152736592004Caspases and cancer: mechanisms of inactivation and new treatment modalities.Philchenkov A et al
108879672000Nuclear localization of procaspase-9 and processing by a caspase-3-like activity in mammary epithelial cells.Ritter PM et al
98909661999A caspase-9 variant missing the catalytic site is an endogenous inhibitor of apoptosis.Seol DW et al
156166062005Antiangiogenic gene therapy: disruption of neovascular networks mediated by inducible caspase-9 delivered with a transcriptionally targeted adenoviral vector.Song W et al
166898292006Mutational analysis of proapoptotic caspase-9 gene in common human carcinomas.Soung YH et al
100709541999Identification of an endogenous dominant-negative short isoform of caspase-9 that can regulate apoptosis.Srinivasula SM et al
98926201999Mitochondrial release of caspase-2 and -9 during the apoptotic process.Susin SA et al
167808932006Cloning of a novel human caspase-9 splice variant containing only the CARD domain.Wang P et al

Other Information

Locus ID:

NCBI: 842
MIM: 602234
HGNC: 1511
Ensembl: ENSG00000132906


dbSNP: 842
ClinVar: 842
TCGA: ENSG00000132906


Gene IDTranscript IDUniprot

Expression (GTEx)



PathwaySourceExternal ID
p53 signaling pathwayKEGGko04115
VEGF signaling pathwayKEGGko04370
Alzheimer's diseaseKEGGko05010
Amyotrophic lateral sclerosis (ALS)KEGGko05014
Huntington's diseaseKEGGko05016
Colorectal cancerKEGGko05210
Pancreatic cancerKEGGko05212
Endometrial cancerKEGGko05213
Prostate cancerKEGGko05215
Small cell lung cancerKEGGko05222
Non-small cell lung cancerKEGGko05223
p53 signaling pathwayKEGGhsa04115
VEGF signaling pathwayKEGGhsa04370
Alzheimer's diseaseKEGGhsa05010
Parkinson's diseaseKEGGhsa05012
Amyotrophic lateral sclerosis (ALS)KEGGhsa05014
Huntington's diseaseKEGGhsa05016
Pathways in cancerKEGGhsa05200
Colorectal cancerKEGGhsa05210
Pancreatic cancerKEGGhsa05212
Endometrial cancerKEGGhsa05213
Prostate cancerKEGGhsa05215
Small cell lung cancerKEGGhsa05222
Non-small cell lung cancerKEGGhsa05223
Viral myocarditisKEGGhsa05416
Influenza AKEGGko05164
Influenza AKEGGhsa05164
PI3K-Akt signaling pathwayKEGGhsa04151
PI3K-Akt signaling pathwayKEGGko04151
Hepatitis BKEGGhsa05161
Thyroid hormone signaling pathwayKEGGhsa04919
Apoptotic machineryKEGGhsa_M00685
Apoptotic machineryKEGGM00685
Diseases of signal transductionREACTOMER-HSA-5663202
PI3K/AKT Signaling in CancerREACTOMER-HSA-2219528
Constitutive Signaling by AKT1 E17K in CancerREACTOMER-HSA-5674400
Immune SystemREACTOMER-HSA-168256
Adaptive Immune SystemREACTOMER-HSA-1280218
Signaling by the B Cell Receptor (BCR)REACTOMER-HSA-983705
Downstream signaling events of B Cell Receptor (BCR)REACTOMER-HSA-1168372
PIP3 activates AKT signalingREACTOMER-HSA-1257604
AKT phosphorylates targets in the cytosolREACTOMER-HSA-198323
Innate Immune SystemREACTOMER-HSA-168249
Nucleotide-binding domain, leucine rich repeat containing receptor (NLR) signaling pathwaysREACTOMER-HSA-168643
NOD1/2 Signaling PathwayREACTOMER-HSA-168638
DAP12 interactionsREACTOMER-HSA-2172127
DAP12 signalingREACTOMER-HSA-2424491
Fc epsilon receptor (FCERI) signalingREACTOMER-HSA-2454202
Role of LAT2/NTAL/LAB on calcium mobilizationREACTOMER-HSA-2730905
Signal TransductionREACTOMER-HSA-162582
Signaling by EGFRREACTOMER-HSA-177929
GAB1 signalosomeREACTOMER-HSA-180292
Signalling by NGFREACTOMER-HSA-166520
NGF signalling via TRKA from the plasma membraneREACTOMER-HSA-187037
PI3K/AKT activationREACTOMER-HSA-198203
Signaling by PDGFREACTOMER-HSA-186797
Downstream signal transductionREACTOMER-HSA-186763
Signaling by SCF-KITREACTOMER-HSA-1433557
Programmed Cell DeathREACTOMER-HSA-5357801
Caspase activation via extrinsic apoptotic signalling pathwayREACTOMER-HSA-5357769
Ligand-independent caspase activation via DCCREACTOMER-HSA-418889
Intrinsic Pathway for ApoptosisREACTOMER-HSA-109606
Apoptotic factor-mediated responseREACTOMER-HSA-111471
Cytochrome c-mediated apoptotic responseREACTOMER-HSA-111461
Formation of apoptosomeREACTOMER-HSA-111458
Activation of caspases through apoptosome-mediated cleavageREACTOMER-HSA-111459
SMAC-mediated apoptotic responseREACTOMER-HSA-111469
SMAC binds to IAPsREACTOMER-HSA-111463
SMAC-mediated dissociation of IAP:caspase complexesREACTOMER-HSA-111464
Apoptosis - multiple speciesKEGGko04215
Apoptosis - multiple speciesKEGGhsa04215
Platinum drug resistanceKEGGko01524
Platinum drug resistanceKEGGhsa01524

Protein levels (Protein atlas)

Not detected


Entity IDNameTypeEvidenceAssociationPKPDPMIDs


Pubmed IDYearTitleCitations
126202392003A unified model for apical caspase activation.295
187236802008Executioner caspase-3 and caspase-7 are functionally distinct proteases.155
118016022002De novo ceramide regulates the alternative splicing of caspase 9 and Bcl-x in A549 lung adenocarcinoma cells. Dependence on protein phosphatase-1.107
243467022014Cas9 effector-mediated regulation of transcription and differentiation in human pluripotent stem cells.103
217245512011In vitro and in vivo selective antitumor activity of a novel orally bioavailable proteasome inhibitor MLN9708 against multiple myeloma cells.94
174666302007Phosphorylation of caspase-9 by CDK1/cyclin B1 protects mitotic cells against apoptosis.85
199131212009Gene-centric association signals for lipids and apolipoproteins identified via the HumanCVD BeadChip.85
153002552004Apollon ubiquitinates SMAC and caspase-9, and has an essential cytoprotection function.73
202273712010tRNA binds to cytochrome c and inhibits caspase activation.73
203796142010Personalized smoking cessation: interactions between nicotine dose, dependence and quit-success genotype score.62


Sabrina Di Bartolomeo ; Francesco Cecconi

CASP9 (caspase 9, apoptosis-related cysteine peptidase)

Atlas Genet Cytogenet Oncol Haematol. 2006-12-01

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