caspase-8-protein

Caspase-8 Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">caspase-8-protein</th>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Caspase-8</td>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>CASP8</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q14790</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>MACH, FLICE, CAP4</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~55 kDa (proenzyme), ~41 kDa (active subunits)</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>479 amino acids</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>2q33.3</td>
</tr>
<tr>
<td class="label">Subcellular Location</td>
<td>Cytoplasm, plasma membrane</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Caspase family, Initiator caspases</td>
</tr>
<tr>
<td class="label">Strategy</td>
<td>Compound</td>
</tr>
<tr>
<td class="label">Direct inhibitors</td>
<td>Z-IETD-FMK</td>
</tr>
<tr>
<td class="label">Peptide derivatives</td>
<td>CASP8-targeted peptides</td>
</tr>
<tr>
<td class="label">Allosteric inhibitors</td>
<td>Various</td>
</tr>
<tr>
<td class="label">Gene therapy</td>
<td>siRNA/shRNA</td>
</tr>
<tr>
<td class="label">Optimal pH</td>
<td>7.2-7.6</td>
</tr>
<tr>
<td class="label">Substrate specificity</td>
<td>IETD sequence (P1)</td>
</tr>
<tr>
<td class="label">Km for subst

Caspase-8 Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">caspase-8-protein</th>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Caspase-8</td>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>CASP8</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q14790</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>MACH, FLICE, CAP4</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~55 kDa (proenzyme), ~41 kDa (active subunits)</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>479 amino acids</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>2q33.3</td>
</tr>
<tr>
<td class="label">Subcellular Location</td>
<td>Cytoplasm, plasma membrane</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Caspase family, Initiator caspases</td>
</tr>
<tr>
<td class="label">Strategy</td>
<td>Compound</td>
</tr>
<tr>
<td class="label">Direct inhibitors</td>
<td>Z-IETD-FMK</td>
</tr>
<tr>
<td class="label">Peptide derivatives</td>
<td>CASP8-targeted peptides</td>
</tr>
<tr>
<td class="label">Allosteric inhibitors</td>
<td>Various</td>
</tr>
<tr>
<td class="label">Gene therapy</td>
<td>siRNA/shRNA</td>
</tr>
<tr>
<td class="label">Optimal pH</td>
<td>7.2-7.6</td>
</tr>
<tr>
<td class="label">Substrate specificity</td>
<td>IETD sequence (P1)</td>
</tr>
<tr>
<td class="label">Km for substrates</td>
<td>~10-50 μM</td>
</tr>
<tr>
<td class="label">Turnover number</td>
<td>~1-5 s⁻¹</td>
</tr>
<tr>
<td class="label">Inhibition</td>
<td>Z-VAD-FMK (broad), Z-IETD-FMK (selective)</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

Overview

Caspase-8 (CASP8) is a cysteine protease that plays a central role in regulating cell death pathways, particularly extrinsic apoptosis initiated by death receptors. As an initiator caspase, caspase-8 sits at the apex of the caspase cascade, activated by death receptor engagement and then cleaving downstream executioner caspases to carry out programmed cell death[@kumar2019].

Beyond its well-established role in apoptosis, caspase-8 has emerged as a critical regulator of necroptosis, a form of programmed necrotic cell death, through its ability to cleave and inactivate RIPK1[@tummers2019]. This dual function as both a pro-apoptotic enzyme and a necroptosis inhibitor makes caspase-8 a crucial node in cell death decisions. In the context of neurodegeneration, caspase-8 dysregulation contributes to excessive neuronal death in Alzheimer's disease, Parkinson's disease, stroke, and traumatic brain injury, making it both a potential biomarker and therapeutic target[@neghta2021].

The protein is encoded by the CASP8 gene located on chromosome 2q33-34 in humans. Alternative splicing produces multiple isoforms, with the full-length caspase-8 (p55/p53) being the predominant form in most tissues. The zymogen exists as an inactive procaspase that requires proteolytic processing for activation.

Protein Information

Structure and Activation

Domain Architecture

Caspase-8 possesses a characteristic caspase structure:

N-Terminal Regions:

• DED1 (Death Effector Domain 1): N-terminal domain involved in protein-protein interactions with adaptor proteins like FADD
• DED2 (Death Effector Domain 2): Second DED, also participates in death receptor complex formation
• These DEDs allow caspase-8 to be recruited to the DISC (Death-Inducing Signaling Complex)

• Large subunit (p20): Contains the active site cysteine residue and substrate-binding pocket
• Small subunit (p10): Completes the catalytic site
• The proenzyme contains an interdomain linker that must be cleaved for activation

Activation Mechanisms

Caspase-8 is activated through two primary pathways[@tummers2019]:

1. Receptor-Mediated Activation (Extrinsic Pathway):

• Death ligands (FasL, TNF, TRAIL) bind their respective receptors
• Receptor oligomerization recruits adaptor proteins (FADD)
• Procaspase-8 is recruited to the DISC via DED-DED interactions
• High local concentration promotes autocatalytic cleavage
• Cleavage releases the active p18/p10 heterotetramer

• Caspase-8 can be activated by caspase-3 (amplification loop)
• Can be activated by caspase-6 in some contexts
• Mitochondrial pathway can feed into caspase-8 activation

Normal Cellular Functions

Extrinsic Apoptosis

The primary function of caspase-8 is initiating extrinsic apoptosis[@kumar2019]:

Necroptosis Regulation

Caspase-8 critically regulates necroptosis through RIPK1 cleavage[@oberst2011][@hullbrand2020]:

• RIPK1 Phosphorylation: RIPK1 can be phosphorylated by RIPK3 in necroptosis
• Caspase-8 Cleavage: Active caspase-8 cleaves RIPK1 at D324
• Inhibition: Cleaved RIPK1 cannot form the necrosome
• Dual Role: Prevents both apoptosis and necroptosis depending on context

Alternative Cell Death

Caspase-8 also participates in other cell death modalities:

pyroptosis: Can activate in response to inflammasome signals

• Can cleave gasdermin D in some contexts
• Links extrinsic death pathways to inflammatory cell death

• NF-κB activation in some contexts
• Cell proliferation and differentiation signals

Role in Neurodegeneration

Alzheimer's Disease

Caspase-8 contributes to AD pathogenesis through multiple mechanisms[@sanchez2022]:

Amyloid-beta-induced Apoptosis:

• Aβ oligomers activate caspase-8 in neurons
• Caspase-8 activation leads to downstream executioner caspase activation
• Neuronal apoptosis in affected brain regions
• Synaptic loss involves caspase-8-mediated mechanisms

• Caspase-8 can cleave tau, generating truncated forms
• Caspase-8 activation correlates with tau pathology progression
• Truncated tau may be more aggregation-prone

• Caspase-8 inhibitors show neuroprotective effects in AD models
• Must balance anti-apoptotic effects with potential necroptosis risks

Parkinson's Disease

In PD, caspase-8 participates in dopaminergic neuron death[@engler2022]:

Death Receptor Activation:

• Parkin mutations sensitize neurons to caspase-8 activation
• Environmental toxins activate caspase-8 pathway
• TNF-α levels elevated in PD brains promote caspase-8 activation

• Cross-talk between intrinsic and extrinsic pathways
• Caspase-8 can amplify mitochondrial apoptosis signals

• Caspase-8 inhibition protects dopaminergic neurons
• Death receptor blockade shows promise in models

Stroke and Traumatic Brain Injury

Caspase-8 is a major contributor to secondary brain injury:

Ischemic Injury:

• Ischemia activates death receptor pathways
• Caspase-8 contributes to both apoptotic and necrotic cell death
• Inhibition reduces infarct size in animal models

• Mechanical injury activates caspase-8
• Contributes to progressive neuronal loss
• Therapeutic window for intervention

Neuroinflammation

Caspase-8 regulates inflammatory responses in the brain[@dumont2020]:

• Controls microglial activation states
• Affects cytokine production
• Links cell death to inflammation
• May have context-dependent pro-inflammatory effects

Therapeutic Approaches

Caspase-8 Inhibitors

Several strategies for caspase-8 inhibition have been explored[@festjens2007][@zheng2023]:

Challenges

Alternative Strategies

• Death receptor blockade: Targeting upstream activators
• RIPK1 inhibitors: Downstream of caspase-8
• Combination approaches: Multi-target strategies

Biochemical Properties

Cross-Linking Relationships

Related Proteins

• [FADD](/proteins/fadd-protein) — Adaptor protein in DISC
• [Caspase-3](/proteins/caspase-3-protein) — Executioner caspase
• [RIPK1](/proteins/ripk1-protein) — Substrate regulating necroptosis
• [Caspase-10](/proteins/caspase-10-protein) — Related executor

Related Pathways

• [Extrinsic Apoptosis](/mechanisms/extrinsic-apoptosis) — Primary pathway
• [Necroptosis](/mechanisms/necroptosis) — Inhibited by caspase-8
• [Death Receptor Signaling](/mechanisms/death-receptor-signaling) — Activation mechanism
• [TNF Signaling](/mechanisms/tnf-signaling) — Major activator

Disease Associations

• [Alzheimer's Disease](/diseases/alzheimers-disease) — Neuronal death
• [Parkinson's Disease](/diseases/parkinsons-disease) — Dopaminergic loss
• [Stroke](/diseases/stroke) — Ischemic injury
• [Traumatic Brain Injury](/diseases/traumatic-brain-injury) — Secondary damage

See Also

• [Caspase Family](/entities/caspase-proteins)
• [Apoptosis Pathways](/mechanisms/apoptosis)
• [Fas/FasL Signaling](/mechanisms/fas-signaling)
• [Alzheimer's Disease Mechanisms](/mechanisms/alzheimers-pathogenesis)
• [Parkinson's Disease Mechanisms](/mechanisms/parkinsons-pathogenesis)
• [Neuroprotection Strategies](/therapeutics/neuroprotective-agents)

External Links

• [UniProt: Q14790](https://www.uniprot.org/uniprot/Q14790)
• [NCBI Gene: CASP8](https://www.ncbi.nlm.nih.gov/gene/841)
• [BML-UNi: Caspase-8](https://bml-u.org/caspase-8)
• [R&D Systems: Caspase-8](https://www.rndsystems.com/caspase-8)

Research Directions

Current Questions

Emerging Research Areas

• Targeted delivery: Nanoparticle-based inhibitor delivery
• Combination therapies: Multi-pathway targeting
• Biomarkers: Caspase-8 activity as biomarker
• Gene therapy: CRISPR-based approaches

References