| Protein Name | Cyclin F |
|---|---|
| Gene | [CCNF](/genes/ccnf) |
| UniProt ID | [Q96VD8](https://www.uniprot.org/uniprot/Q96VD8) |
| PDB Structure | 6QXM, 5K8W, 5HRS |
| Molecular Weight | 786 aa (~89.5 kDa) |
| Subcellular Localization | Nucleus, Cytoplasm |
| Protein Family | F-box protein family, Cyclin family |
| Aliases | FBXO1, CycF |
Ccnf Protein (Cyclin F) 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.
Cyclin F (encoded by the CCNF gene) is a unique member of the cyclin family that functions as the substrate recognition component of the SCF (Skp1-Cul1-F-box) ubiquitin ligase complex[^1]. Unlike conventional cyclins, Cyclin F does not regulate cyclin-dependent kinases (CDKs) but instead plays a critical role in ubiquitin-mediated protein degradation. Pathogenic variants in CCNF have been firmly linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), making it a protein of significant interest in neurodegenerative disease research[^2].
Cyclin F possesses a distinctive domain organization that enables its functions as an E3 ubiquitin ligase:
F-box Domain (residues 43-93): This conserved domain mediates binding to the Skp1 adaptor protein, incorporating CCNF into the SCF ubiquitin ligase complex[^3]. The F-box serves as the critical link between the substrate recognition module and the Cul1 scaffold.
Leucine-Rich Repeats (LRRs) (residues 124-280): The LRR domain provides the structural basis for substrate recognition. These repeats form a curved solenoid structure that recognizes specific degron motifs in target proteins[^4].
N-terminal Domain: Contains regulatory elements including phosphorylation sites that modulate protein-protein interactions and substrate binding affinity.
C-terminal Regions: House additional protein interaction motifs and post-translational modification sites.
Cyclin F activity is regulated by several post-translational modifications:
Phosphorylation: Multiple serine/threonine phosphorylation sites regulate substrate binding and SCF complex assembly. Casein kinase 2 (CK2) phosphorylation enhances CCNF activity[^5].
Ubiquitination: As an E3 ligase, CCNF itself can be ubiquitinated, leading to proteasomal degradation in a feedback regulatory mechanism.
Sumoylation: SUMO modification influences nuclear-cytoplasmic trafficking and protein stability.
Cyclin F functions as the substrate recognition component of the SCF^CCNF ubiquitin ligase complex, which catalyzes the attachment of ubiquitin chains to target proteins, marking them for proteasomal degradation[^6]. This process is essential for:
SCF^CCNF targets diverse substrate classes:
CCNF is expressed in most tissues, with highest expression in:
CCNF mutations were first identified as causative in familial ALS in 2016, with subsequent studies confirming its role in both familial and sporadic forms[^7]. The disease mechanisms include:
Loss of Ubiquitination Function: Mutations in the LRR domain impair substrate recognition, reducing the degradation of neurotoxic proteins. This leads to:
Gain of Toxic Function: Some mutations may confer novel toxic properties:
Exacerbating Factors:
CCNF is classified as a causal gene for FTD, particularly the FTD-ALS spectrum[^8]:
The role of CCNF in protein aggregation involves:
TDP-43 Pathology: SCF^CCNF normally ubiquitinates TDP-43. Loss of function leads to TDP-43 accumulation[^9].
Aggregate Sequestration: Mutant CCNF can be incorporated into stress granules and aggregates, further disrupting cellular proteostasis.
Interplay with Other ALS/FTD Genes: CCNF interacts genetically and functionally with:
CCNF Mutation → Impaired substrate recognition → Reduced ubiquitination
↓
Accumulation of neurotoxic proteins (TDP-43, etc.)
↓
Protein aggregate formation
↓
Neuronal dysfunction and death
Given the central role of impaired protein degradation in CCNF-related disease:
| Approach | Stage | Challenges |
|---|---|---|
| ASOs | Preclinical | Delivery to CNS |
| Proteasome enhancers | Early clinical | Specificity |
| Gene therapy | Preclinical | Safety |
The seminal study by Williams et al. (2016) identified CCNF as an ALS/FTD causative gene through exome sequencing of familial cases[^2]. This finding was subsequently validated in multiple cohorts worldwide.
Laboratory studies have demonstrated that SCF^CCNF directly ubiquitinates TDP-43, providing a mechanistic link between CCNF dysfunction and the hallmark protein aggregates of ALS/FTD[^9].
Transgenic mouse models expressing mutant CCNF show:
CCNF interacts with several key cellular pathways:
Ccnf Protein (Cyclin F) 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.
The study of Ccnf Protein (Cyclin F) 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.