FLNC Protein

Filamin C (FLNC) Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">FLNC Protein</th>
</tr>
<tr>
<td class="label">Gene Name</td>
<td>FLNC</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q14315</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~291 kDa (single chain)</td>
</tr>
<tr>
<td class="label">Family</td>
<td>Filamin family</td>
</tr>
<tr>
<td class="label">Structure</td>
<td>24 Ig-like repeats + 2 hinge regions</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Skeletal muscle, heart, brain, endothelium</td>
</tr>
<tr>
<td class="label">Tissue Specificity</td>
<td>Highest in muscle, moderate in brain</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/myofibrillar-myopathy" style="color:#ef9a9a">Myofibrillar Myopathy</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">22 edges</a></td>
</tr>
</table>

Overview

Filamin C (FLNC) Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">FLNC Protein</th>
</tr>
<tr>
<td class="label">Gene Name</td>
<td>FLNC</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q14315</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~291 kDa (single chain)</td>
</tr>
<tr>
<td class="label">Family</td>
<td>Filamin family</td>
</tr>
<tr>
<td class="label">Structure</td>
<td>24 Ig-like repeats + 2 hinge regions</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Skeletal muscle, heart, brain, endothelium</td>
</tr>
<tr>
<td class="label">Tissue Specificity</td>
<td>Highest in muscle, moderate in brain</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/myofibrillar-myopathy" style="color:#ef9a9a">Myofibrillar Myopathy</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">22 edges</a></td>
</tr>
</table>

Overview

Filamin C (FLNC), also known as filamin-2 or ABP-L (actin-binding protein L), is a large actin-crosslinking protein that plays essential roles in cytoskeletal organization, cell signaling, and mechanical stability. As a member of the filamin family (which also includes FLNA/filamin A and FLNB/filamin B), FLNC is characterized by its unique ability to form flexible networks through repeated actin-binding domains and flexible hinge regions. FLNC is predominantly expressed in skeletal and cardiac muscle, where it localizes to Z-discs and the myotendinous junction, but is also expressed in non-muscle tissues including the brain[@van2001].

In [neurons](/entities/neurons) and other cell types, FLNC contributes to cytoskeletal organization, membrane receptor signaling, and cell migration. Mutations in FLNC are associated with myofibrillar myopathies and cardiomyopathies, highlighting its essential role in muscle integrity. In the central nervous system, FLNC is expressed in neurons where it participates in synaptic function and cytoskeletal dynamics. Its role in neurodegenerative diseases is an emerging area of research[@feng2004].

Protein Information

Molecular Structure

Domain Architecture

FLNC possesses an exceptionally large and modular architecture optimized for flexible crosslinking:

N-terminal Actin-Binding Domain (ABD):

• Comprises the first two immunoglobulin-like repeats (Ig1-Ig2)
• Binds to actin filaments with moderate affinity
• Enables crosslinking of actin filaments into networks
• Critical for cytoskeletal organization

• Contains 22 additional immunoglobulin-like repeats (Ig3-Ig24)
• Each repeat is ~100 amino acids with a β-sandwich fold
• Connected by flexible hinge regions (H1 between Ig15-Ig16, H2 between Ig23-Ig24)
• Provides flexibility for different crosslinking configurations

• Ig24 contains the dimerization interface
• Forms antiparallel homodimers
• Enables crosslinking of actin filaments at distant sites

Hinge Regions

FLNC contains two hinge regions:

Hinge 1 (between Ig15-Ig16):

• Enables large-angle bending
• Allows network formation with variable geometries
• Susceptible to protease cleavage

• More rigid than hinge 1
• Important for mechanical stability
• Site of binding for many partner proteins

Flexibility and Crosslinking

The filamin structure enables:

• Flexible angle crosslinking: Ig domains rotate freely, enabling variable crosslinking angles
• Mechanical buffering: Hinge regions absorb mechanical stress
• Protein platform: Multiple binding sites for diverse signaling molecules

Cellular Functions

Cytoskeletal Organization

FLNC organizes the actin cytoskeleton through:

Actin crosslinking: FLNC crosslinks actin filaments into orthogonal and parallel networks, providing mechanical strength and enabling cell shape maintenance[@shepts1999].

Membrane anchorage: Links actin cytoskeleton to membrane proteins and cell adhesion molecules.

Mechanical signaling: Acts as a mechanosensor, transmitting mechanical forces to signaling pathways.

Muscle-Specific Functions

In skeletal and cardiac muscle:

Z-disc integration: FLNC is a major component of Z-discs, where it links actin thin filaments to the membrane and coordinates sarcomere assembly.

Myotendinous junction: Concentrated at the muscle-tendon interface, where it connects the cytoskeleton to extracellular matrix proteins.

Mechanical stability: Provides structural integrity during muscle contraction and relaxation.

Neuronal Functions

In neurons, FLNC has emerging roles:

Synaptic organization: Associates with postsynaptic densities and may contribute to synaptic protein organization.

Axonal cytoskeleton: Contributes to axonal stability and may participate in transport processes.

Cell adhesion: Links membrane proteins to the neuronal cytoskeleton.

Cell Signaling

FLNC serves as a signaling platform:

• Integrin signaling: Binds to integrin cytoplasmic domains, modulating adhesion and migration
• Small GTPase signaling: Interacts with Rho family GTPases and their effectors
• Growth factor receptors: Associates with various receptor tyrosine kinases

Role in Neurodegeneration

Alzheimer's Disease

Emerging evidence links FLNC to AD pathogenesis:

Cytoskeletal integrity: FLNC contributes to neuronal cytoskeletal stability, and dysfunction may accelerate [tau](/proteins/tau) pathology and synaptic loss.

Synaptic function: As a component of postsynaptic densities, FLNC may be affected by early synaptic alterations in AD.

Protein aggregation: FLNC may co-localize with protein aggregates in disease states, though this is less characterized than for other cytoskeletal proteins.

Parkinson's Disease

FLNC may contribute to PD through:

Dopaminergic neuron function: The unique stress on dopaminergic neurons may involve cytoskeletal components like FLNC.

[Alpha-synuclein](/proteins/alpha-synuclein) interactions: Possible interactions between alpha-synuclein and cytoskeletal proteins.

Axonal transport: FLNC's role in transport processes may be relevant to the axonal pathology in PD.

Amyotrophic Lateral Sclerosis

FLNC involvement in ALS includes:

Motor neuron vulnerability: The extremely long axons of motor neurons require robust cytoskeletal support, in which FLNC participates.

Cytoskeletal defects: ALS is associated with cytoskeletal abnormalities, and FLNC may contribute to or be affected by these changes.

Protein aggregation: FLNC may be incorporated into ALS-related aggregates in some cases.

Myofibrillar Myopathy

Mutations in FLNC cause myofibrillar myopathy:

• Missense mutations: Lead to protein aggregation and muscle fiber degeneration
• Late-onset: Symptoms typically appear in adulthood
• Diverse phenotypes: Including cardiomyopathy and respiratory failure

Therapeutic Relevance

Small Molecule Approaches

Targeting FLNC therapeutically:

• Stabilizers: Compounds that protect FLNC from degradation
• Aggregation inhibitors: Prevent pathogenic FLNC aggregation in myopathy
• Anti-inflammatory: Reduce inflammatory components that exacerbate pathology

Gene Therapy

• Gene replacement: Viral delivery of wild-type FLNC for loss-of-function mutations
• Allele-specific silencing: For dominant-negative mutations
• Gene editing: CRISPR-based approaches to correct mutations

Biomarker Potential

FLNC as a biomarker:

• Muscle release: May be elevated in blood with muscle damage
• CSF levels: Changes may indicate neuronal involvement
• Mutation carriers: Useful for tracking disease progression

Research Methods

Biochemical Analysis

• Actin crosslinking assays: Measure FLNC bundling activity
• Protein interaction studies: Identify binding partners
• Protease sensitivity: Characterize hinge region flexibility

Cell Biological Methods

• Immunofluorescence: Localize FLNC in cells and tissues
• Live cell imaging: Study cytoskeletal dynamics
• Mechanical measurements: Assess cytoskeletal stiffness

Genetic Approaches

• Mouse models: Knockout and conditional deletion
• Patient-derived cells: Study mutation effects
• CRISPR: Generate cellular models

Structural Studies

• X-ray crystallography: High-resolution structure determination
• Cryo-EM: Visualize FLNC-actin complexes
• SAXS: Study solution conformation

Interactions and Binding Partners

Actin and Cytoskeletal Proteins

• F-actin: Primary binding partner
• α-actinin: May cooperate or compete in crosslinking
• Myosin: Interaction at Z-discs

Membrane Proteins

• Integrins: β1, β3, and β7 integrin cytoplasmic tails
• Glycoproteins: Various cell adhesion molecules

Signaling Proteins

• Rho GTPases: RalA, Rac1 effectors
• PIP5K: Phosphatidylinositol phosphate kinase
• MEK: MAP kinase kinase

Summary

Filamin C is a large actin-crosslinking protein essential for cytoskeletal organization in muscle and non-muscle cells. Its modular structure with 24 immunoglobulin-like repeats and flexible hinge regions enables flexible crosslinking of actin filaments into networks that provide mechanical stability and serve as signaling platforms. In muscle cells, FLNC is critical for Z-disc integrity and the myotendinous junction, while in neurons it participates in synaptic organization and axonal cytoskeleton maintenance. Mutations in FLNC cause myofibrillar myopathy and cardiomyopathies, while its role in neurodegenerative diseases is an emerging area of research. Understanding FLNC function may lead to therapeutic strategies for both muscle and neuronal pathologies.

See Also

• [Actin Cytoskeleton](/entities/actin-cytoskeleton)
• [Cytoskeletal Proteins](/entities/cytoskeletal-proteins)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [Skeletal Muscle](/cell-types/skeletal-muscle-cells)
• [Z-disc](/entities/z-disc)

External Links

• [UniProt FLNC](https://www.uniprot.org/uniprot/Q14315)
• [Human Protein Atlas](https://www.proteinatlas.org/)
• [OMIM: FLNC](https://www.omim.org/entry/102565)

References