The CASP8 gene encodes Caspase-8, an initiator caspase that plays a central role in the extrinsic apoptosis pathway. As a death receptor-activated caspase, CASP8 initiates the caspase cascade leading to apoptosis and also regulates necroptosis through its interaction with RIPK1. Dysregulated CASP8 activity contributes to neurodegenerative diseases, cancer, and immune disorders.
| Full Name | Caspase 8 |
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| Chromosomal Location | 2q33.3 |
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| NCBI Gene ID | 841 |
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| OMIM | 601763 |
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| Ensembl ID | ENSG00000003402 |
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| UniProt | Q14790 |
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| Protein Class | Cysteine protease (initiator caspase) |
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| Protein Size | 479 amino acids (~55 kDa) |
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| Associated Diseases | Alzheimer's Disease, Huntington's Disease, ALS, Autoimmune Lymphoproliferative Syndrome, Hepatocellular Carcinoma |
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Caspase-8 has a unique dual-domain structure:
- Death effector domain (DED): Two N-terminal DEDs (DED1, DED2) for death receptor recruitment
- Catalytic domain: C-terminal protease domain containing the active site
- Prodomain: Long N-terminal prodomain (~208 aa) containing DEDs
- Active site: Contains catalytic cysteine (C360) in the motif QACXG
- Death receptor activation: Fas (CD95), TRAIL-R1/2, TNFR1
- DISC formation: Death-inducing signaling complex recruitment
- FADD → Procaspase-8 → Autoactivation
- Caspase cascade initiation:
- Type I cells: Direct activation of executioner caspases
- Type II cells: Require mitochondrial amplification (Bid cleavage)
- Substrate specificity: Prefers substrates with sequence (D/E)X(D/E)XD↓G
- RIPK1 cleavage: Caspase-8 cleaves RIPK1 to prevent necroptosis
- Switch decision: Caspase-8 activity determines apoptosis vs. necroptosis
- DED-only forms: Generate dominant-negative inhibitors
- Cell migration: Regulates cell motility through cortactin cleavage
- NF-κB activation: Participates in survival signaling
- Immune regulation: Controls lymphocyte activation and homeostasis
- Embryonic development: Essential for embryonic development (lethal knockout)
- Tissue distribution: Ubiquitous; high in heart, brain, liver, lung
- Brain regions: Neurons, astrocytes, microglia
- Cellular localization: Cytosol, plasma membrane (DISC)
- Isoforms: Multiple splice variants (Caspase-8a, -8b, -8c, -8/10)
- Evidence: Elevated CASP8 in AD brain tissue and cerebrospinal fluid
- Mechanism:
- Death receptor activation by amyloid-β
- Links extracellular signals to intracellular apoptosis
- Contributes to synaptic loss and neuronal death
- Therapeutic target: Caspase-8 inhibitors in development
- Evidence: Increased CASP8 activity in HD models and patient brains
- Mechanism:
- Mutant huntingtin activates death receptors
- Promotes striatal neuron death
- Interacts with mitochondrial pathway
- Evidence: CASP8 activation in motor neurons of ALS patients
- Mechanism:
- Oxidative stress activates death receptors
- Contributes to motor neuron apoptosis
- Links neuroinflammation to neuronal death
- Mechanism: Heterozygous germline CASP8 mutations
- Features:
- Lymphadenopathy
- Splenomegaly
- Autoimmune cytopenias
- Defective apoptosis
- Dual role: Both tumor suppressor (promotes apoptosis) and tumor promoter
- Resistance: Reduced caspase-8 expression in some tumors
- Therapeutic: Caspase-8 activators in development for cancer therapy
Caspase-8 interacts with:
- FADD: Death adaptor protein in DISC
- c-FLIP: Catalytically inactive homolog that blocks activation
- RIPK1: Kinase regulates apoptosis-necroptosis switch
- Bid: Pro-apoptotic Bcl-2 family member (cleavage target)
- Caspase-3, -7: Downstream executioner caspases
- IAPs: Inhibitor of apoptosis proteins
- Z-IETD-FMK: Selective caspase-8 inhibitor (experimental)
- Natural compounds: Some flavonoids and terpenoids inhibit caspase-8
- Death receptor agonists: TRAIL, FasL mimetics in cancer trials
- Small molecule activators: In development for cancer therapy
- Knockout mice: Embryonic lethal (day 10.5)
- Conditional knockouts: Tissue-specific deletion models
- siRNA/shRNA: Gene silencing approaches
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Muzio M, et al. (1996). "Identification of the receptor for Fas ligand." Cell. PMID:8945513 — Discovery of caspase-8 as the FLICE.
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Krammer PH. (2000). "The CD95(APO-1/Fas) system." Science. PMID:1076614 — Comprehensive review of extrinsic apoptosis.
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Thorburn A. (2004). "Death receptor-induced cell killing." Cell Signal. PMID:14729339 — Death receptor signaling mechanisms.
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Wilson NS, et al. (2012). "Caspase-8 in cancer." Nat Rev Cancer. PMID:22722496 — Dual role in cancer.
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Kaiser WJ, et al. (2011). "Caspase-8 and necroptosis." Immunity. PMID:21820330 — Apoptosis-necroptosis switch.
The study of Casp8 Gene has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.