CHOP Protein (DDIT3)

CHOP Protein — DNA Damage Inducible Transcript 3

Overview

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">CHOP (GADD153)</th></tr>
<tr><td><strong>Protein Name</strong></td><td>DNA Damage Inducible Transcript 3</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>[DDIT3](/genes/DDIT3)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9UHS1](https://www.uniprot.org/uniprot/Q9UHS1)</td></tr>
<tr><td><strong>Alternative Names</strong></td><td>CHOP, GADD153, CEBPZ</td></tr>
<tr><td><strong>Protein Family</strong></td><td>C/EBP transcription factor family</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>19 kDa (169 amino acids)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Nucleus, Cytoplasm</td></tr>
<tr><td><strong>Brain Expression</strong></td><td>[Neurons](/entities/neurons), [Astrocytes](/entities/astrocytes), [Microglia](/cell-types/microglia-neuroinflammation)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ad" style="color:#ef9a9a">AD</a>, <a href="/wiki/ali" style="color:#ef9a9a">ALI</a>, <a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">497 edges</a></td>
</tr>
</table>
</div>

CHOP Protein — DNA Damage Inducible Transcript 3

Overview

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">CHOP (GADD153)</th></tr>
<tr><td><strong>Protein Name</strong></td><td>DNA Damage Inducible Transcript 3</td></tr>
<tr><td><strong>Gene Symbol</strong></td><td>[DDIT3](/genes/DDIT3)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9UHS1](https://www.uniprot.org/uniprot/Q9UHS1)</td></tr>
<tr><td><strong>Alternative Names</strong></td><td>CHOP, GADD153, CEBPZ</td></tr>
<tr><td><strong>Protein Family</strong></td><td>C/EBP transcription factor family</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>19 kDa (169 amino acids)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Nucleus, Cytoplasm</td></tr>
<tr><td><strong>Brain Expression</strong></td><td>[Neurons](/entities/neurons), [Astrocytes](/entities/astrocytes), [Microglia](/cell-types/microglia-neuroinflammation)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ad" style="color:#ef9a9a">AD</a>, <a href="/wiki/ali" style="color:#ef9a9a">ALI</a>, <a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">497 edges</a></td>
</tr>
</table>
</div>

CHOP (C/EBP Homologous Protein), encoded by the [DDIT3](/genes/DDIT3) gene and also known as GADD153, is a 19 kDa (169 amino acid) transcription factor that serves as a central mediator of endoplasmic reticulum (ER) stress-induced [apoptosis](/entities/apoptosis). CHOP is the primary pro-apoptotic effector of the [unfolded protein response](/mechanisms/er-stress-unfolded-protein-response) (UPR), and its sustained activation drives neuronal cell death across Alzheimer's disease, Parkinson's disease, ALS, and other neurodegenerative disorders[@oyadomari2004][@huang2021].

Unlike classical anti-apoptotic proteins, CHOP does not directly trigger cell death through pore formation or cytochrome c release. Instead, it reprograms gene expression to tilt the cellular balance toward death by downregulating anti-apoptotic factors, upregulating pro-death proteins, and disrupting calcium homeostasis[@szegezdi2006]. This transcriptional remodeling makes CHOP a critical decision point between survival and death under ER stress conditions.

CHOP is induced by multiple cellular stresses including nutrient deprivation, oxidative stress, proteasome inhibition, and accumulation of misfolded proteins. In the context of neurodegeneration, chronic ER stress leads to sustained CHOP expression, which contributes to neuronal apoptosis in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS), and other neurological disorders[@huang2021]. The protein functions as a dominant-negative inhibitor of other C/EBP transcription factors, altering gene expression patterns that ultimately lead to cell death.

Structure

CHOP possesses a simple modular architecture:

• N-terminal regulatory region: Contains serine residues (Ser30, Ser31) that can be phosphorylated by p38 MAPK, modulating transcriptional activity without altering DNA binding. The N-terminal regulatory domain also contains serine residues that can be phosphorylated to modulate protein activity.
• Basic DNA-binding domain: Located centrally, contacts C/EBP consensus sites (TGTTNNNA) in target gene promoters
• Leucine zipper (bZIP) domain: At the C-terminus, mediates dimerization with other C/EBP family members (C/EBP-alpha, C/EBP-beta) and with itself[@ron1992]. The leucine zipper motif consists of heptad repeats of leucine residues that form the dimerization interface. The basic region adjacent to the leucine zipper contacts DNA at specific response elements.

Normal Function

ER Stress Response and the Unfolded Protein Response

CHOP is a key node in the UPR, a three-arm cellular stress response to misfolded protein accumulation in the ER:

PERK-ATF4-CHOP axis:

ATF6 pathway:

• ATF6 (Activating Transcription Factor 6) is cleaved in the Golgi under ER stress, and its cytosolic fragment translocates to the nucleus where it can induce CHOP expression

• While IRE1 primarily activates XBP1, cross-talk between pathways ensures CHOP induction even when IRE1 is activated alone

Pro-apoptotic Functions

CHOP executes apoptosis through multiple transcriptional programs:

Non-apoptotic Functions

Beyond apoptosis, CHOP participates in:

• Necroptosis: CHOP can promote receptor-interacting protein kinase 3 (RIPK3)-mediated necroptosis under certain conditions[@wang2022]
• Pyroptosis: CHOP induces gasdermin D expression and caspase-1 activation
• Metabolic reprogramming: CHOP represses genes involved in lipid synthesis and glucose metabolism
• Autophagy: CHOP can either promote or inhibit autophagy depending on context

Role in Neurodegeneration

Alzheimer's Disease

CHOP is a major contributor to neuronal death in AD:

Amyloid-beta toxicity: [Aβ](/proteins/amyloid-beta) oligomers trigger ER stress in neurons, leading to PERK activation, eIF2-alpha phosphorylation, and robust CHOP induction[@sokka2007]. Aβ-induced CHOP expression is observed in both cell culture and post-mortem AD brain tissue.

Tau pathology connection: [Hyperphosphorylated tau](/proteins/tau) also induces ER stress, further amplifying CHOP activation. The PERK-eIF2-alpha-CHOP pathway is chronically activated in AD brain regions vulnerable to neurodegeneration.

Synaptic dysfunction: CHOP-mediated apoptosis contributes to early synaptic loss, the strongest pathological correlate of cognitive decline. CHOP deletion in APP/PS1 AD mouse models reduces neuronal death and preserves cognitive function.

Therapeutic angle: CHOP knockout or knockdown is neuroprotective in multiple AD models, making it a high-priority therapeutic target.

Parkinson's Disease

In PD, CHOP mediates dopaminergic neuron vulnerability in the [substantia nigra pars compacta](/brain-regions/substantia-nigra):

Alpha-synuclein toxicity: Misfolded [α-synuclein](/proteins/alpha-synuclein) aggregates induce ER stress, activating the PERK-CHOP pathway in dopaminergic neurons.

Toxin models: MPTP, 6-OHDA, and rotenone all activate CHOP in dopaminergic neurons. CHOP knockout mice are significantly more resistant to MPTP toxicity[@kikuchi2010].

LRRK2 and GBA connections: Mutations in [LRRK2](/genes/LRRK2) and [GBA](/genes/GBA) (linked to familial PD) increase ER stress and CHOP activation.

Vulnerable population: Dopaminergic neurons in the substantia nigra have high baseline ER activity due to their high protein synthesis rate and dopamine metabolism, making them particularly sensitive to CHOP-mediated apoptosis.

Amyotrophic Lateral Sclerosis

CHOP plays a critical role in motor neuron degeneration:

SOD1 mutations: Mutant [SOD1](/genes/SOD1) (causing familial ALS) causes severe ER stress and persistent CHOP activation. CHOP deletion significantly delays disease onset and extends survival in SOD1 G93A mice.

TDP-43 pathology: TDP-43 aggregation, the hallmark pathology of most ALS cases, disrupts ER homeostasis and activates the UPR, including CHOP induction.

C9orf72 hexanucleotide repeats: Repeat-associated non-AUG translation and dipeptide repeat proteins cause ER stress and CHOP activation.

Stroke and Traumatic Brain Injury

Ischemic injury: Cerebral ischemia rapidly induces CHOP in affected brain regions. CHOP mediates both apoptotic and necroptotic cell death following stroke[@wang2022].

Therapeutic window: CHOP inhibition (via siRNA, small molecules, or genetic deletion) reduces infarct size and improves functional outcomes when administered post-ischemia.

Therapeutic Targeting

Small Molecule Inhibitors

| Compound | Mechanism | Development Stage | Notes |
|----------|-----------|-------------------|-------|
| Salubrinal | Inhibits GADD34, maintains eIF2-alpha phosphorylation, reduces CHOP indirectly | Research | Also inhibits global protein synthesis |
| TUDCA (Tauroursodeoxycholic acid) | Chemical chaperone, reduces ER stress | Phase II trials (liver), preclinical for CNS | Shows neuroprotection in ALS models[@martinez2017] |
| Guanabenz | eIF2-alpha phosphatase inhibitor (via GADD34) | Research | Reduces CHOP while preserving adaptive UPR |
| ISRIB | eIF2-alpha phosphorylation pathway activator | Research | Enhances adaptive stress response |
| ER stress modulators | Broader UPR modulators | Various | May reduce CHOP as downstream effect |

Genetic Approaches

• RNAi knockdown: siRNA or shRNA targeting DDIT3 reduces CHOP expression
• CRISPRi: Epigenetic silencing of DDIT3 promoter
• Dominant-negative CHOP: Expressing truncated CHOP that can't dimerize

Neuroprotective Strategies

• BCL-2 agonists: Counteract CHOP's repression of BCL-2
• BIM inhibitors: Block the pro-apoptotic effector downstream of CHOP
• Calcium stabilizers: Prevent CHOP-driven calcium release from ER
• Antioxidants: Reduce oxidative stress that synergizes with ER stress to activate CHOP

See Also

• [DDIT3 Gene](/genes/DDIT3) — The gene encoding CHOP
• [Unfolded Protein Response](/mechanisms/er-stress-unfolded-protein-response) — ER stress pathways
• [Endoplasmic Reticulum Stress](/mechanisms/er-stress-neurodegeneration) — ER stress in neurodegeneration
• [Alzheimer's Disease](/diseases/alzheimers-disease) — AD and ER stress
• [Parkinson's Disease](/diseases/parkinsons-disease) — PD pathogenesis
• [ALS](/diseases/amyotrophic-lateral-sclerosis) — ALS mechanisms
• [Apoptosis Pathways](/mechanisms/apoptosis-neuronal) — Neuronal cell death

References