SF3B1

SF3B1

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">sf3b1</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>SF3B1</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Splicing Factor 3b Subunit 1</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>2q33.1</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>6762</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000115523</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>O75533</td>
</tr>
<tr>
<td class="label">Gene Type</td>
<td>Protein coding</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>Myelodysplastic syndromes, Chronic lymphocytic leukemia, ALS, Alzheimer's disease, Parkinson's disease</td>
</tr>
<tr>
<td class="label">Agent</td>
<td>Target</td>
</tr>
<tr>
<td class="label">H3B-8800</td>
<td>SF3B1</td>
</tr>
<tr>
<td class="label">E7107</td>
<td>Spliceosome</td>
</tr>
<tr>
<td class="label">PLS-001</td>
<td>SF3B1</td>
</tr>
<tr>
<td class="label">Various ASOs</td>
<td>Specific splicing</td>
</tr>
</table>

Introduction

SF3B1

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">sf3b1</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>SF3B1</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Splicing Factor 3b Subunit 1</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>2q33.1</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>6762</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000115523</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>O75533</td>
</tr>
<tr>
<td class="label">Gene Type</td>
<td>Protein coding</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>Myelodysplastic syndromes, Chronic lymphocytic leukemia, ALS, Alzheimer's disease, Parkinson's disease</td>
</tr>
<tr>
<td class="label">Agent</td>
<td>Target</td>
</tr>
<tr>
<td class="label">H3B-8800</td>
<td>SF3B1</td>
</tr>
<tr>
<td class="label">E7107</td>
<td>Spliceosome</td>
</tr>
<tr>
<td class="label">PLS-001</td>
<td>SF3B1</td>
</tr>
<tr>
<td class="label">Various ASOs</td>
<td>Specific splicing</td>
</tr>
</table>

Introduction

SF3B1 (Splicing Factor 3b Subunit 1) is a gene located on chromosome 2q33.1 that encodes a key component of the U2 small nuclear ribonucleoprotein (snRNP) complex. SF3B1 is essential for pre-mRNA splicing and is one of the most frequently mutated genes in certain cancers, particularly myelodysplastic syndromes (MDS) and chronic lymphocytic leukemia (CLL). The protein plays a critical role in spliceosome assembly and 3' splice site recognition. [@papaemmanuil2011]

Beyond its well-established role in cancer, emerging research has revealed important connections between SF3B1 dysfunction and neurodegenerative diseases. Alterations in splicing factor expression and spliceosome function have been documented in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS), and various tauopathies. [@quednow2022]

Gene Information

The SF3B1 gene spans approximately 52 kb and consists of 25 exons encoding a 1308 amino acid protein. The protein is a core component of the U2 snRNP, which is essential for recognizing the branch point sequence during pre-mRNA splicing.

Protein Structure and Function

Structure

SF3B1 is a large protein consisting of multiple domains:

• N-terminal domain: Contains HEAT repeats that mediate protein-protein interactions
• C-terminal domain: Contains the SF3b core that directly contacts the pre-mRNA branch point
• PHAT domain: Present in some isoforms, involved in RNA binding

Splicing Mechanism

SF3B1 participates in the spliceosome assembly through multiple mechanisms:

Expression Pattern

Normal Tissue Expression

• Ubiquitous expression: SF3B1 is expressed in all cell types at moderate to high levels
• Nuclear localization: The protein localizes to the nucleus, particularly the nucleolus
• High turnover: SF3B1 protein has a relatively short half-life, allowing dynamic regulation

Brain Expression

In the central nervous system:

• Neuronal expression: High expression in pyramidal neurons and interneurons
• Glial expression: Present in astrocytes and oligodendrocytes
• Developmentally regulated: Expression patterns change during brain development

Disease Associations

Myelodysplastic Syndromes (MDS)

SF3B1 is one of the most frequently mutated genes in MDS:

Mutation patterns:

• Hotspot mutations at K700E (most common), K666E/N/T, and other residues
• Mutations occur in approximately 20-30% of MDS cases
• Particularly common in ring sideroblast MDS (up to 70%)

• Altered 3' splice site recognition
• Aberrant splicing of genes involved in iron metabolism
• Hematopoietic differentiation defects

• SF3B1 mutations are associated with better prognosis in MDS
• Predicts response to specific therapies
• May influence disease progression

Amyotrophic Lateral Sclerosis (ALS)

Growing evidence links SF3B1 to ALS:

Genetic associations:

• Rare SF3B1 variants identified in familial ALS cases
• Altered expression of SF3B1 in ALS motor cortex
• Dysregulated splicing of transcripts critical for neuronal survival

• Defective RNA splicing affects survival motor neuron (SMN) function
• Altered splicing of TDP-43 target transcripts
• Disrupted spliceosome function in motor neurons

• Knockdown of SF3B1 in motor neurons causes neurodegeneration
• ALS-associated mutations impair spliceosome assembly
• Motor neurons show increased sensitivity to spliceosome disruption

Alzheimer's Disease

SF3B1 dysfunction contributes to AD pathogenesis:

Evidence:

• Altered SF3B1 expression in AD brain
• Aberrant splicing of tau exon 10 in tauopathies
• Impaired spliceosome function in AD neurons
• Changes in alternative splicing of amyloid processing genes

• TDP-43 pathology affects SF3B1 function
• Reduced SF3B1 protein levels in vulnerable neurons
• Splicing changes in transcripts related to synaptic function

Parkinson's Disease

SF3B1 connections to PD:

• Altered splicing patterns in PD substantia nigra
• Changes in SF3B1 expression in Lewy body disease
• Splicing dysregulation of mitochondrial transcripts
• Connections to alpha-synuclein pathology

Other Neurodegenerative Disorders

• Frontotemporal dementia: SF3B1 splicing changes
• Tauopathies: Altered branch point recognition in tau exon 10
• Spinocerebellar ataxia: Some SCA subtypes involve spliceosome dysfunction

Molecular Mechanisms in Neurodegeneration

Spliceosome Dysfunction

The spliceosome is increasingly recognized as a nexus of neurodegeneration:

RNA Binding Protein Dysregulation

SF3B1 interacts with multiple RNA binding proteins implicated in neurodegeneration:

• TDP-43: ALS/FTD protein that regulates SF3B1 splicing targets
• FUS: Another ALS protein affecting spliceosome function
• hnRNP proteins: Altered in various neurodegenerative conditions

Therapeutic Implications

Targeting the spliceosome is an emerging therapeutic strategy:

• Spliceosome modulators: Small molecules that normalize splicing
• Antisense oligonucleotides: Targeted correction of aberrant splicing
• Gene therapy: Restoring SF3B1 expression levels

Research Methods

Experimental Approaches

• RNA-seq: Genome-wide splicing analysis
• CLIP-seq: Mapping SF3B1 binding sites on RNA
• Proteomics: Interaction network analysis
• CRISPR: Genetic manipulation in cellular models

Model Systems

• Cell lines: Neuronal and non-neuronal cell cultures
• iPSC-derived neurons: Patient-specific models
• Animal models: Transgenic and knockout mice
• Organoids: Three-dimensional brain models

Key Publications

See Also

• [genes/srsf2](/genes/srsf2)
• [genes/u2af1](/genes/u2af1)
• [diseases/amyotrophic-lateral-sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [diseases/alzheimers-disease](/diseases/alzheimers-disease)
• [mechanisms/rna-splicing-neurodegeneration](/mechanisms/rna-splicing-neurodegeneration)

External Links

• [NCBI Gene: SF3B1](https://www.ncbi.nlm.nih.gov/gene/6762)
• [UniProt: O75533](https://www.uniprot.org/uniprotkb/O75533)
• [Ensembl: SF3B1](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000115523)
• [GeneCards: SF3B1](https://www.genecards.org/cgi-bin/carddisp.pl?gene=SF3B1)
• [OMIM: 605590](https://www.omim.org/entry/605590)

References

Spliceosome Assembly and Function

The SF3b Complex in Detail

The SF3b complex is a critical component of the U2 small nuclear ribonucleoprotein (snRNP) and plays essential roles in spliceosome assembly and function. This multiprotein complex directly contacts the pre-mRNA branch point sequence and is essential for the early stages of spliceosome assembly.

Complex Composition:

• SF3B1: The largest subunit, directly binds branch point adenosine
• SF3A1, SF3A2, SF3A3: Additional core components
• SF3B2, SF3B3, SF3B4, SF3B5: Supporting subunits
• SF3B14: Associated factor with regulatory functions

Molecular Mechanism of Action

SF3B1 recognizes the branch point sequence (BPS), which is typically located 18-40 nucleotides upstream of the 3' splice site. The branch point adenosine serves as the nucleophile in the first transesterification reaction of splicing. SF3B1 binding stabilizes the U2 snRNP-pre-mRNA interaction and facilitates the recruitment of the U4/U5/U6 tri-snRNP complex.

The protein contains multiple HEAT repeat domains that form a flexible scaffold for protein-protein interactions. These repeats allow SF3B1 to simultaneously interact with the pre-mRNA, U2 snRNA, and other SF3b components, creating a stable platform for spliceosome assembly.

Alternative Splicing Regulation

Beyond its essential role in constitutive splicing, SF3B1 influences alternative splicing decisions through:

Cellular and Systemic Functions

Role in Cellular Homeostasis

SF3B1 is essential for cellular viability through its central role in RNA processing:

mRNA Maturation:

• Processing of all pre-mRNAs in the nucleus
• Generation of diverse protein isoforms through alternative splicing
• Quality control of splicing through nonsense-mediated decay coupling

• Global effects on transcript diversity
• Tissue-specific isoform expression
• Response to cellular stress through regulated splicing

Implications for Neuronal Function

Neurons are particularly dependent on accurate splicing due to:

• Complex alternative splicing patterns in the brain
• High demand for specific protein isoforms at synapses
• Long axonal projections requiring precise localization of transcripts

• Altered splicing of synaptic proteins
• Impaired axonal transport of transcripts
• Disrupted synaptic plasticity mechanisms

Clinical and Therapeutic Perspectives

Diagnostic Applications

SF3B1 mutation testing has become standard in hematological diagnostics:

Testing Methods:

• Targeted NGS panels for splicing factor mutations
• Sanger sequencing for validation
• RNA-seq for splicing pattern analysis

• Initial workup of suspected MDS
• Prognostic assessment in CLL
• Risk stratification in AML

Therapeutic Targeting

The spliceosome represents a novel therapeutic target:

Spliceosome Modulators:

• H3B-8800: SF3B1-targeting compound in clinical trials
• E7107: Pladienolide derivative showing activity in early trials
• Natural products like spliceostatin A

• Splice-switching oligonucleotides for specific splicing corrections
• ASOs targeting aberrant splice products
• Delivery strategies for CNS penetration being developed

• Combining spliceosome modulators with standard chemotherapy
• Sequential treatment approaches
• Personalized approaches based on SF3B1 mutation status

Research Frontiers

Emerging Questions

Several critical questions remain:

Model Systems and Approaches

Advanced Models:

• CRISPR-edited iPSC lines with SF3B1 mutations
• Cerebral organoids for brain-specific studies
• Single-cell RNA-seq to examine cell-type specificity

• Long-read sequencing for full-length isoform detection
• Ribosome profiling to assess translation consequences
• Proteomics to identify downstream effects

Evolution and Conservation

Species Conservation

SF3B1 is highly conserved across eukaryotes:

• Yeast ortholog (Hsh155) maintains core functions
• Drosophila SF3B1 essential for viability
• Zebrafish knockout causes developmental defects
• Mouse knockout results in embryonic lethality

Functional Divergence

While core functions are preserved, evolutionary changes include:

• Increased complexity of the SF3b complex in higher eukaryotes
• Additional regulatory domains and post-translational modification sites
• Tissue-specific splice variants through alternative splicing

Summary

SF3B1 encodes a core component of the U2 snRNP complex essential for pre-mRNA splicing. Mutations in SF3B1 are among the most common genetic alterations in myelodysplastic syndromes and chronic lymphocytic leukemia, where they are associated with distinct clinical features and generally favorable prognosis. Beyond its well-established role in cancer, emerging evidence demonstrates connections between SF3B1 dysfunction and neurodegenerative diseases including ALS, Alzheimer's disease, and Parkinson's disease. The protein plays a critical role in spliceosome assembly, branch point recognition, and alternative splicing regulation. SF3B1 dysfunction may contribute to neurodegeneration through alterations in neuronal RNA processing, impaired spliceosome function, and interactions with other RNA-binding proteins affected in neurodegenerative conditions. The spliceosome represents an attractive therapeutic target, with several splicing modulators currently in clinical development for cancer and increasingly for neurodegenerative diseases.

SF3B1 in the Context of Neurodegenerative Disease Mechanisms

Interaction with Other Disease Proteins

SF3B1 does not operate in isolation but interacts with multiple RNA-binding proteins implicated in neurodegenerative diseases:

TDP-43 (TARDBP):

• TDP-43 regulates splicing of SF3B1 target transcripts
• In ALS/FTD, TDP-43 pathology disrupts SF3B1 function
• Shared target transcripts affected by both proteins

• FUS interacts with SF3B1 in the spliceosome
• ALS-causing FUS mutations alter splicing patterns
• Both proteins involved in stress response

• hnRNPA1, hnRNPA2B1 implicated in ALS
• Coordinate with SF3B1 for proper splicing
• Mutations affect splicing fidelity

Connection to Protein Aggregation

SF3B1 dysfunction may contribute to protein aggregation:

Mitochondrial Implications

SF3B1 mutations particularly affect mitochondrial function:

• Aberrant splicing of iron-sulfur cluster assembly genes
• Impaired mitochondrial respiration
• Increased oxidative stress
• Links to neurodegeneration through energy failure

Synaptic Function Effects

Neuronal SF3B1 dysfunction impacts synaptic biology:

• Altered splicing of synaptic receptor transcripts
• Changes in ion channel isoform expression
• Impaired synaptic plasticity mechanisms
• Disrupted activity-dependent splicing responses

Therapeutic Development Landscape

Current Clinical Trials

Several clinical trials target splicing in disease:

Challenges and Opportunities

Challenges:

• Delivery to the central nervous system
• Achieving adequate brain penetration
• Balancing efficacy with toxicity
• Selecting appropriate patient populations

• Biomarker development for patient selection
• Combination approaches with existing therapies
• Personalized medicine based on splicing patterns
• Repurposing cancer splicing drugs for neurodegeneration

Future Research Directions

Outstanding Questions

Key questions driving the field:

Emerging Technologies

New tools enabling progress:

• Single-cell RNA-seq to examine cell-type specificity
• Long-read sequencing for complete isoform characterization
• CRISPR screening to identify genetic modifiers
• Proteomics to map interaction networks

Translational Priorities

Near-term research priorities:

• Developing brain-penetrant splicing modulators
• Creating better model systems for neurodegeneration
• Identifying predictive biomarkers
• Designing clinical trials for neurodegenerative indications

Pathway Diagram

The following diagram shows the key molecular relationships involving sf3b1 discovered through SciDEX knowledge graph analysis:

Pathway Diagram

The following diagram shows the key molecular relationships involving SF3B1 discovered through SciDEX knowledge graph analysis: