FBXO31 — F-box Protein 31

FBXO31 — F-box Protein 31

<div class="infobox infobox-gene">
| | |
|:---|:---|
| Gene Symbol | FBXO31 |
| Gene Name | F-box Protein 31 |
| Alternative Names | FBX31, Fbx31, M phase cyclin degradation protein 1 (Mcd1) |
| Chromosomal Location | 16q24.2 |
| NCBI Gene ID | 79791 |
| OMIM ID | 609102 |
| Ensembl ID | ENSG00000103265 |
| UniProt ID | Q8IFY6 |
| Protein Length | 483 amino acids |
| Protein Family | F-box family, SCF ubiquitin ligase complex |
</div>

Overview

FBXO31 (F-box Protein 31) encodes a substrate recognition component of the SCF (Skp1-Cul1-F-box) ubiquitin ligase complex, a critical component of the ubiquitin-proteasome system (UPS). The SCF complex is one of the largest families of E3 ubiquitin ligases, responsible for targeting specific proteins for ubiquitination and subsequent degradation by the 26S proteasome. FBXO31 serves as the substrate recognition module, binding to specific phosphorylation-dependent degrons on target proteins and facilitating their polyubiquitination. [@kumamoto2012]

FBXO31 — F-box Protein 31

<div class="infobox infobox-gene">
| | |
|:---|:---|
| Gene Symbol | FBXO31 |
| Gene Name | F-box Protein 31 |
| Alternative Names | FBX31, Fbx31, M phase cyclin degradation protein 1 (Mcd1) |
| Chromosomal Location | 16q24.2 |
| NCBI Gene ID | 79791 |
| OMIM ID | 609102 |
| Ensembl ID | ENSG00000103265 |
| UniProt ID | Q8IFY6 |
| Protein Length | 483 amino acids |
| Protein Family | F-box family, SCF ubiquitin ligase complex |
</div>

Overview

FBXO31 (F-box Protein 31) encodes a substrate recognition component of the SCF (Skp1-Cul1-F-box) ubiquitin ligase complex, a critical component of the ubiquitin-proteasome system (UPS). The SCF complex is one of the largest families of E3 ubiquitin ligases, responsible for targeting specific proteins for ubiquitination and subsequent degradation by the 26S proteasome. FBXO31 serves as the substrate recognition module, binding to specific phosphorylation-dependent degrons on target proteins and facilitating their polyubiquitination. [@kumamoto2012]

FBXO31 has emerged as an important regulator of multiple cellular processes including cell cycle progression, DNA damage response, cellular senescence, and neuronal survival. The gene has been extensively studied as a tumor suppressor, with decreased expression in various cancers. More recent research has revealed critical roles in neurodegeneration, where FBXO31 dysfunction contributes to protein aggregation, oxidative stress, and neuronal death in Alzheimer's disease (AD), Parkinson's disease (PD), and spinocerebellar ataxia (SCA). Mutations in FBXO31 have been identified as causative for a novel form of autosomal recessive spinocerebellar ataxia, establishing a direct link between FBXO31 and neurodegenerative disease. [@santosa2019]

Protein Structure and Function

Structural Features

The FBXO31 protein contains several key structural elements:

• F-box domain: The defining feature of F-box proteins, approximately 50 amino acids, mediates binding to Skp1
• Substrate-binding region: Variable region determining substrate specificity
• Phosphorylation recognition motif: Recognizes phosphorylated serine/threonine residues on substrates
• Dimerization domain: Enables formation of functional SCF complexes
• Nuclear localization signals: FBXO31 exhibits nuclear-cytoplasmic shuttling

SCF Complex Assembly

FBXO31 functions as part of the SCF ubiquitin ligase complex:

Substrate Specificity

FBXO31 recognizes specific substrates:

• Cyclin D1: Key cell cycle regulator, FBXO31 mediates its degradation
• p53: Tumor suppressor, FBXO31 regulates its stability
• Miz1: Transcription factor involved in cell cycle arrest
• Snail: Transcription repressor involved in epithelial-mesenchymal transition

Biological Functions

Cell Cycle Regulation

FBXO31 is a critical regulator of cell cycle progression:

The degradation of cyclin D1 by FBXO31 is phosphorylation-dependent, requiring prior phosphorylation by glycogen synthase kinase 3β (GSK3β). This creates a regulatory checkpoint linking cellular signaling to cell cycle progression. [@liu2021]

DNA Damage Response

FBXO31 plays important roles in the DNA damage response:

Following DNA damage, FBXO31 expression increases and contributes to p53-dependent cell cycle arrest and apoptosis. This tumor suppressor function is frequently lost in cancers. [@ghosh2020]

Protein Quality Control

As part of the ubiquitin-proteasome system:

The ubiquitin-proteasome system is critical for neuronal health, as neurons are particularly vulnerable to protein aggregation and require efficient quality control mechanisms. [@kumar2015]

Expression Pattern

Brain Expression

FBXO31 exhibits region-specific expression in the brain:

• Cerebellum: High expression in Purkinje cells, critical for motor coordination
• Cerebral cortex: Moderate expression in pyramidal neurons
• Hippocampus: Expression in CA1-CA3 pyramidal cells and dentate gyrus
• Substantia nigra: Expression in dopaminergic neurons
• Brainstem: Various nuclei show expression
• Spinal cord: Motor neurons express FBXO31

• Neurons: High expression, particularly in projection neurons
• Astrocytes: Lower expression
• Microglia: Moderate expression, increases with activation

Developmental Expression

FBXO31 expression is developmentally regulated:

• Embryonic development: Early expression in neural tube
• Postnatal brain: Increased expression during synaptic development
• Adult brain: Maintained expression with regional variation
• Aging: Altered expression patterns in aged brain

Role in Neurodegenerative Diseases

Alzheimer's Disease

FBXO31 dysfunction contributes to AD pathogenesis through multiple mechanisms:

Studies have reported reduced FBXO31 expression in AD brain tissue, particularly in regions affected by pathology. This reduction may contribute to the accumulation of damaged proteins and neuronal dysfunction. [@kumar2015]

Parkinson's Disease

Spinocerebellar Ataxia

Biallelic mutations in FBXO31 cause a novel form of autosomal recessive spinocerebellar ataxia:

The identification of FBXO31 mutations establishes direct causation between FBXO31 dysfunction and neurodegeneration, highlighting the critical importance of FBXO31 in neuronal health. [@santosa2019]

Other Neurodegenerative Conditions

• Amyotrophic Lateral Sclerosis (ALS): Altered expression of F-box proteins reported
• Huntington's Disease: FBXO31 may be involved in mutant huntingtin clearance
• Frontotemporal Dementia: Protein quality control impairment
• Aging: Age-related changes in FBXO31 expression

Signaling Pathways

p53 Pathway

FBXO31 interfaces with the p53 tumor suppressor pathway:

• p53 stabilization: FBXO31 helps maintain p53 levels
• Cell cycle arrest: Through p21 regulation
• Apoptosis: Modulates apoptotic responses
• Senescence: Contributes to cellular senescence programs

Cell Cycle Pathways

• Cyclin D1 degradation: Controls G1/S transition
• GSK3β signaling: Phosphorylation-dependent substrate recognition
• Rb signaling: Interactions with retinoblastoma pathway
• Checkpoint kinases: ATM/ATR-mediated regulation

Stress Response Pathways

• Oxidative stress: FBXO31 helps manage oxidative protein damage
• ER stress: Role in unfolded protein response
• DNA damage: Part of the DNA damage response network

Therapeutic Implications

Therapeutic Strategies

Targeting FBXO31 for neuroprotection:

Challenges

• Delivery: Achieving adequate brain delivery
• Specificity: Avoiding off-target effects
• Timing: Optimal intervention in disease progression
• Balance: Maintaining appropriate protein homeostasis

Research Directions

• Developing FBXO31-based therapeutics
• Understanding regulation of FBXO31 activity
• Identifying additional substrates
• Exploring combination therapies

Animal Models

Knockout Studies

• FBXO31 knockout mice: Embryonic lethal in some backgrounds
• Conditional knockouts: Brain-specific deletion models
• Heterozygous mice: Partial loss-of-function models

Disease Models

• AD models: Crossbreeding with APP/PS1 mice
• PD models: Alpha-synuclein overexpression with FBXO31 modulation

Clinical Relevance

Biomarkers

• FBXO31 expression: Potential tissue biomarker
• Genetic testing: For spinocerebellar ataxia diagnosis
• Protein levels: Potential peripheral biomarker

Diagnostics

• Genetic testing: For FBXO31-related ataxia
• Expression analysis: In patient tissue samples

Research Methods

• Gene expression: qPCR, RNA-seq
• Protein analysis: Western blot, immunohistochemistry
• Functional studies: Ubiquitination assays
• Animal models: Transgenic and knockout mice

See Also

• [F-box Protein 31 Protein](/proteins/fbxo31-protein)
• [Ubiquitin-Proteasome System in Neurodegeneration](/mechanisms/ubiquitin-proteasome-neurodegeneration)
• [Spinocerebellar Ataxia](/diseases/spinocerebellar-ataxia)
• [Alzheimer's Disease - Molecular Mechanisms](/diseases/alzheimers-disease)
• [Parkinson's Disease - Molecular Mechanisms](/diseases/parkinsons-disease)
• [Protein Quality Control in Neurodegeneration](/mechanisms/protein-quality-control)

External Links

• [NCBI Gene: FBXO31](https://www.ncbi.nlm.nih.gov/gene/79791)
• [UniProt: Q8IFY6](https://www.uniprot.org/uniprot/Q8IFY6)
• [Ensembl: ENSG00000103265](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000103265)
• [OMIM: 609102](https://www.omim.org/entry/609102)

Brain Atlas Resources

• [Allen Human Brain Atlas - FBXO31](https://human.brain-map.org/microarray/search/show?search_term=FBXO31)
• [BrainSpan Atlas - FBXO31 Expression](https://www.brainspan.org/search?gene=FBXO31)
• [Allen Mouse Brain Atlas](https://mouse.brain-map.org/search?query=FBXO31)

References