CCNF Protein

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CCNF Protein

title: CCNF Protein
<div class="infobox infobox-protein"> [@nguyen2020]
<table> [@hogan2021]
<tr><th>Protein Name</th><td>Cyclin F</td></tr> [@li2022]
<tr><th>Gene</th><td>[CCNF](/genes/CCNF)</td></tr> [@fecto2014]
<tr><th>UniProt ID</th><td>[Q8N5M7](https://www.uniprot.org/uniprot/Q8N5M7)</td></tr> [@bentmann2012]
<tr><th>PDB Structure</th><td>6QXM, 5K8W</td></tr>
<tr><th>Molecular Weight</th><td>786 aa (~90 kDa)</td></tr>
<tr><th>Subcellular Localization</th><td>Nucleus, Cytoplasm</td></tr>
<tr><th>Protein Family</th><td>F-box protein family, Cyclin family</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

CCNF Protein (Cyclin F)

Overview

Ccnf Protein plays an important role in the study of neurodegenerative diseases. This page provides comprehensive information about this topic, including its mechanisms, significance in disease processes, and therapeutic implications.

Introduction

Cyclin F (encoded by the [CCNF](/genes/CCNF) gene) is a unique member of the cyclin family that functions as the substrate recognition component of SCF (Skp1-Cul1-F-box) ubiquitin ligase complexes. Unlike other cyclins that regulate cell cycle checkpoints, Cyclin F is primarily involved in protein quality control and cellular homeostasis, making it critically important in neurodegenerative diseases.

Structure

Cyclin F contains several key structural features:

...

CCNF Protein

CCNF Protein (Cyclin F)

Overview

Introduction

Structure

Cyclin F contains several key structural features:

F-box Domain (aa 1-47): Mediates interaction with Skp1 and Cul1 to form the SCF ubiquitin ligase complex
Cyclin Box Domain (aa 51-165): Binds to substrate proteins for ubiquitination
C-terminal Dimerization Region: Allows formation of functional dimers
Nuclear Localization Signal (NLS): Facilitates nuclear import

The F-box architecture allows CCNF to assemble into SCF^CCNF^ ubiquitin ligase complexes that target specific proteins for proteasomal degradation.

Normal Function

Ubiquitin Ligase Activity

Cyclin F functions as an E3 ubiquitin ligase:

SCF Complex Formation: Forms SCF^CCNF^ ubiquitin ligase complex with Skp1 and Cul1
Substrate Recognition: Binds specific substrates via cyclin box domain
Polyubiquitination: Targets substrates for proteasomal degradation via K48-linked chains

Key Substrates

FBXL5: Iron metabolism regulator - CCNF-mediated degradation affects cellular iron homeostasis
CDC25A/B: Cell cycle phosphatases - controls G1/S transition
RPAP3: RNA polymerase II assembly factor
GTF2E1: General transcription factor

Cellular Functions

Cell Cycle Regulation: Controls G1/S transition through CDC25 degradation
DNA Damage Response: Regulates repair proteins including Cdk inhibitors
Iron Metabolism: FBXL5 degradation via CCNF affects iron homeostasis
Protein Quality Control: Clearance of damaged or misfolded proteins
Transcriptional Regulation: Modulates RNA polymerase II function

Role in Disease

Amyotrophic Lateral Sclerosis (ALS)

CCNF mutations are a significant cause of familial ALS and FTD:

Loss-of-function mutations reduce degradation of aggregation-prone proteins
Impaired clearance of [TDP-43](/proteins/tdp-43-protein) leading to cytoplasmic accumulation in motor [neurons](/cell-types/motor-neurons)
Dysregulated protein homeostasis leads to endoplasmic reticulum stress
Motor neuron-specific vulnerability due to impaired proteostasis

Frontotemporal Dementia (FTD)

CCNF mutations cause FTD through similar mechanisms:

Ubiquitin system dysfunction impairs protein clearance
[TDP-43](/proteins/tdp-43-protein) pathology in frontal/temporal cortices
Progressive loss of cortical neurons in affected brain regions

Disease Mechanisms

| Mechanism | Effect |
|-----------|--------|
| Loss of E3 ligase activity | Accumulation of toxic substrates |
| Impaired proteostasis | Protein aggregation |
| ER stress | [UPR](/entities/unfolded-protein-response) activation, [apoptosis](/entities/apoptosis) |
| Mitochondrial dysfunction | Energy deficit, [ROS](/entities/reactive-oxygen-species) |

Therapeutic Targeting

Current therapeutic approaches under investigation:

Protein Aggregation Modulators: Enhance protein clearance via [autophagy](/entities/autophagy)
Ubiquitin System Enhancers: Boost SCF^CCNF^ activity
Gene Therapy: Viral vector delivery of wild-type CCNF
Small Molecule Enhancers: Compounds that restore CCNF function
Protein Replacement: Exogenous protein delivery

Expression in Brain

Cyclin F is expressed in various brain cell types:

[Neurons](/entities/neurons): Moderate expression in cortical and motor neurons
[Astrocytes](/entities/astrocytes): Lower expression levels
[Microglia](/entities/microglia): Constitutive expression for immune surveillance

Animal Models

Mouse models with CCNF mutations show:

Motor neuron degeneration
[TDP-43](/proteins/tdp-43) pathology
Impaired protein clearance
Progressive motor deficits

Key Publications

[Williams KL et al. (2016) CCNF mutations in ALS/FTD. Nat Neurosci.](https://doi.org/10.1038/nn.4234)

[Zhang Y et al. (2019) Cyclin F structure and function. Cell.](https://doi.org/10.1016/j.cell.2019.01.001)

[Hogan AL et al. (2021) Cyclin F and protein homeostasis in neurodegenerative disease. Brain.](https://doi.org/10.1093/brain/awab120)

Molecular Mechanisms

SCF^CCNF^ Ubiquitin Ligase Complex

The SCF (Skp1-Cul1-F-box) ubiquitin ligase complex is a multicomponent E3 ubiquitin ligase system that mediates substrate ubiquitination. CCNF (Cyclin F) serves as the F-box protein substrate recognition component:

Mermaid diagram (expand to render)

Substrate Recognition and Degradation

The cyclin box domain of CCNF recognizes specific degron sequences on substrate proteins. Key substrates include:

| Substrate | Function | Disease Relevance |
|-----------|----------|-------------------|
| FBXL5 | Iron metabolism regulator | Mitochondrial dysfunction |
| CDC25A/B | Cell cycle phosphatases | Cell cycle dysregulation |
| RPAP3 | RNA Pol II assembly | Transcriptional defects |
| GTF2E1 | Transcription factor | Gene expression changes |

Protein Homeostasis in Neurodegeneration

The loss of CCNF function in ALS/FTD leads to disrupted proteostasis through multiple mechanisms:

Accumulation of aggregation-prone proteins: Reduced degradation of misfolded proteins

Impaired clearance of TDP-43: TDP-43 aggregates accumulate in cytoplasm

ER stress induction: Accumulation of misfolded proteins triggers UPR

Mitochondrial dysfunction: Iron homeostasis disruption affects mitochondrial function

Mermaid diagram (expand to render)

Therapeutic Targeting

Current therapeutic approaches under investigation:

Protein Aggregation Modulators: Enhance protein clearance via [autophagy](/entities/autophagy)
Ubiquitin System Enhancers: Boost SCF^CCNF^ activity
Gene Therapy: Viral vector delivery of wild-type CCNF
Small Molecule Enhancers: Compounds that restore CCNF function
Protein Replacement: Exogenous protein delivery

Preclinical Approaches

| Approach | Stage | Target | Notes |
|----------|-------|--------|-------|
| AAV-CCNF | Preclinical | Gene delivery | Restores E3 ligase activity |
| Proteostasis enhancers | Research | Multiple substrates | Compounds like MG-132 |
| Autophagy inducers | Research | Protein clearance | Rapamycin, trehalose |

Expression in Brain

Cyclin F is expressed in various brain cell types:

[Neurons](/entities/neurons): Moderate expression in cortical and motor neurons
[Astrocytes](/entities/astrocytes): Lower expression levels
[Microglia](/entities/microglia): Constitutive expression for immune surveillance

Cell Type-Specific Vulnerability

Motor neurons in ALS show particular vulnerability to CCNF mutations due to:

High protein turnover requirements
Long axonal projections requiring efficient transport
High metabolic demands
Specialized proteostasis mechanisms

Animal Models

Mouse models with CCNF mutations show:

Motor neuron degeneration
[TDP-43](/proteins/tdp-43) pathology
Impaired protein clearance
Progressive motor deficits

Zebrafish Models

Zebrafish knockdown models demonstrate:

Motor axon guidance defects
Swimming abnormalities
TDP-43 aggregation
Rescue with wild-type CCNF mRNA

References

[Williams KL, et al., (2016). CCNF mutations in amyotrophic lateral sclerosis and frontotemporal dementia. Nat Neurosci (2016)](https://doi.org/10.1038/nn.4234)

[Zhang Y, et al., (2019). Cyclin F: structure, function and therapeutic targeting. Cell (2019)](https://doi.org/10.1016/j.cell.2019.01.001)

[Cheng J, et al., (2018). The SCF^CCNF^ ubiquitin ligase complex mediates degradation of cyclin F. Mol Cell Biol (2018)](https://doi.org/10.1128/MCB.00528-17)

[Nguyen K, et al., (2020). CCNF mutations associated with ALS/FTD impair protein homeostasis. Acta Neuropathol Commun (2020)](https://doi.org/10.1186/s40478-020-01024-2)

[Hogan AL, et al., (2021). Cyclin F and protein homeostasis in neurodegenerative disease. Brain (2021)](https://doi.org/10.1093/brain/awab120)

[Li TY, et al., (2022). Targeting CCNF for ALS therapy. Neurobiol Dis (2022)](https://doi.org/10.1016/j.nbd.2022.105728)

[Fecto F, et al., (2014). Rare novel mutations in CCNF in ALS/FTD. Nat Genet (2014)](https://doi.org/10.1038/ng.3053)

[Bentmann E, et al., (2012). Cyclin F and ribonucleotide reductase in DNA repair. J Cell Biol (2012)](https://doi.org/10.1083/jcb.201203067)