# MYO1F Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- MYO1F encodes a monomeric class I myosin motor essential for actin-dependent cellular processes including phagocytosis, immune synapse assembly, and membrane trafficking, predominantly in hematopoietic and immune cell lineages.
- The gene's promoter is regulated by epigenetic mechanisms, specifically tissue-specific DNA methylation, and transcription factors like PU.1 and C/EBPα, enabling restricted expression in immune cells.
- Pathogenic alterations include MLL-MYO1F and VAV1-MYO1F gene fusions in acute myeloid leukemia and peripheral T-cell lymphoma, respectively, leading to oncogenic transcriptional dysregulation and constitutive signaling.
- MYO1F plays a critical role in innate immunity, particularly antifungal defense, by promoting microtubule acetylation via interaction with ATAT1 and sequestration of HDAC6, which is essential for phagosome maturation.
- Dysregulation of MYO1F is implicated in various pathologies, including thyroid cancer (R554C missense mutation causing mitochondrial dysfunction), and it serves as a potential biomarker in coronary artery disease and renal cell carcinoma.
- Therapeutic strategies are being explored targeting MYO1F's motor domain (ATP-binding pocket inhibitors) or tail domain (disrupting protein-protein interactions), with potential applications in cancer immunotherapy and infectious diseases.

---

## Executive Summary & Key Metadata

MYO1F encodes an unconventional class I myosin, a monomeric actin-based molecular motor expressed predominantly in hematopoietic and immune cell lineages. Unlike conventional myosins that form filaments, MYO1F functions as a single-headed motor that translocates cargo along actin filaments, orchestrating membrane dynamics, phagocytosis, podosome formation, and immune synapse assembly. The protein integrates cytoskeletal mechanics with metabolic and transcriptional programs through its capacity to scaffold signaling complexes and regulate post-translational modifications of key metabolic enzymes.

| Attribute | Detail |
|---|---|
| **HGNC Symbol** | MYO1F |
| **UniProt Accession** | O00160 |
| **Representative PDB ID** | True (homology models; experimental structures pending) |
| **Chromosomal Locus** | 19p13.2 (GRCh38: chr19:8,520,000–8,570,000) |
| **Primary Molecular Function** | Actin-dependent ATPase motor; intracellular transport; membrane trafficking; immune cell effector functions |
| **Disease & Pathology Associations** | Nonsyndromic deafness (DFNB15 candidate); acute myeloid leukemia (MLL fusions); peripheral T-cell lymphoma (VAV1 fusions); thyroid cancer; inflammatory and autoimmune conditions |
| **Expression Pattern** | Hematopoietic cells (macrophages, neutrophils, T cells, NK cells); microglia; cochlear hair cells |
| **Protein Length** | 1,098 amino acids (canonical isoform) |
| **Molecular Weight** | ~124 kDa |

The clinical significance of MYO1F spans a remarkable breadth—from monogenic hearing loss to somatically acquired oncogenic fusions in aggressive hematologic malignancies. The gene's product operates at the interface of cytoskeletal dynamics and immune signaling, making it an attractive but challenging therapeutic target. This reference manual provides a comprehensive analysis of MYO1F's genomic architecture, structural biology, signaling networks, pathogenic mutations, and therapeutic relevance.

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## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Gene Structure

MYO1F is located on the short arm of chromosome 19 at cytogenetic band 19p13.2. The gene spans approximately 50 kilobases of genomic DNA and is oriented on the minus strand (reverse orientation) relative to the chromosome's p-arm telomere. The precise coordinates in GRCh38 are chr19:8,520,000–8,570,000, with the transcriptional start site positioned near the centromeric boundary of this interval.

The genomic organization of MYO1F comprises 27 exons, with exon sizes ranging from 57 base pairs (exon 5) to over 300 base pairs (exon 27, which contains the 3' untranslated region). The intronic regions vary considerably in size, with intron 1 being the largest at approximately 8.5 kilobases. This intron contains multiple regulatory elements, including a CpG island that extends from the promoter region into the first intron—a feature common to genes with broad expression plasticity in immune cells.

### 1.2 Promoter Architecture and Regulatory Elements

The core promoter of MYO1F lacks a canonical TATA box but contains a high-density CpG island spanning approximately 1.2 kilobases surrounding the transcription start site. This CpG-rich promoter is characteristic of housekeeping-like genes but is subject to tissue-specific methylation patterns that restrict expression to hematopoietic lineages. DNA methylation analysis has revealed that the MYO1F promoter is hypomethylated in peripheral blood mononuclear cells and microglia but hypermethylated in non-hematopoietic tissues, providing an epigenetic gatekeeper for cell-type-specific expression.

Multiple transcription factor binding sites have been identified within the proximal promoter region:

- **PU.1 (SPI1)**: A critical hematopoietic master regulator that binds at positions -180 to -165 relative to the TSS. PU.1 occupancy is essential for MYO1F expression in myeloid cells.
- **C/EBPα**: Binds at -320 to -305 and cooperates with PU.1 to drive macrophage-specific expression.
- **GATA-1**: Occupies a site at -450 to -435 in erythroid precursors, though MYO1F expression in these cells is transient.
- **NF-κB**: Multiple consensus sites within the first intron respond to inflammatory stimuli, enabling rapid transcriptional upregulation during macrophage activation.

Enhancer elements have been mapped using chromatin conformation capture techniques. A distal enhancer located approximately 40 kilobases upstream of the TSS (at chr19:8,480,000) shows strong H3K27ac marks in macrophages and microglia. This enhancer physically loops to the MYO1F promoter in a PU.1-dependent manner, and its deletion in model systems reduces MYO1F expression by approximately 70%.

### 1.3 Alternative Splicing and Isoform Diversity

Alternative splicing generates multiple MYO1F transcript variants, though the functional significance of most isoforms remains incompletely characterized. The canonical transcript (ENST00000301234.10) encodes a 1,098-amino acid protein and is the dominant isoform in all expressing tissues.

| Isoform | Exon Composition | Protein Length | Expression Context |
|---|---|---|---|
| Canonical (v1) | All 27 exons | 1,098 aa | Ubiquitous in immune cells |
| v2 | Skips exon 18 (57 bp) | 1,079 aa | Detected in microglia; altered tail domain |
| v3 | Skips exons 18 and 22 | 1,051 aa | Low abundance; detected in T cells |
| v4 | Alternative 5' UTR (exon 1b) | 1,098 aa | Macrophage-specific; distinct translational regulation |

Exon 18 skipping (isoform v2) removes a proline-rich segment within the neck domain, potentially altering the protein's stiffness and cargo-binding capacity. Isoform v4 utilizes an alternative first exon located approximately 15 kilobases upstream of the canonical exon 1, generating a distinct 5' UTR that contains an upstream open reading frame (uORF) implicated in translational control during macrophage polarization.

### 1.4 Phylogenetic Conservation

MYO1F belongs to the class I myosin family, which diversified early in eukaryotic evolution. Orthologs are present in all vertebrates, and the gene structure is highly conserved from fish to mammals. The zebrafish ortholog (myo1f) shares 78% amino acid identity with human MYO1F and has been instrumental in functional studies, particularly regarding mitochondrial dynamics and tumor proliferation. The amoeba *Dictyostelium discoideum* expresses multiple class I myosins that share the core motor domain architecture, though the tail domains have diverged substantially.

---

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Domain Organization Overview

The MYO1F protein adopts the tripartite architecture characteristic of unconventional myosins: an N-terminal motor domain (head), a regulatory neck region containing IQ motifs, and a C-terminal tail domain that confers cargo specificity. The protein spans 1,098 amino acids with the following domain boundaries:

| Domain | Residues | Function |
|---|---|---|
| Motor domain (head) | 1–720 | Actin binding; ATP hydrolysis; force generation |
| IQ motif 1 | 730–750 | Calmodulin/light chain binding |
| IQ motif 2 | 755–775 | Calmodulin/light chain binding |
| IQ motif 3 | 780–800 | Calmodulin/light chain binding |
| Proline-rich region | 810–860 | SH3 domain interaction site |
| MyTH4 domain | 870–980 | Microtubule interaction; cargo binding |
| SH3 domain | 990–1050 | Protein-protein interactions |
| C-terminal extension | 1050–1098 | Membrane binding; regulatory |

### 2.2 Motor Domain (Residues 1–720)

The motor domain is the catalytic engine of MYO1F, containing the actin-binding interface and the ATP hydrolysis site. The domain folds into a seven-stranded β-sheet surrounded by α-helices, with the nucleotide-binding pocket located at the apex of the structure. Key structural elements include:

- **P-loop (residues 170–180)**: The phosphate-binding loop coordinates the β- and γ-phosphates of ATP. The consensus sequence GESGAGKT contains the invariant lysine (K175) essential for nucleotide binding.
- **Switch I (residues 230–245)**: This region undergoes conformational changes upon ATP hydrolysis, communicating nucleotide state to the actin-binding interface.
- **Switch II (residues 450–470)**: Contains the catalytic glutamic acid (E460) that activates the water molecule for nucleophilic attack on the γ-phosphate.
- **Actin-binding interface**: Formed by loop 2 (residues 620–650) and loop 4 (residues 400–420), which make electrostatic contacts with the actin filament. Loop 2 in MYO1F is notably longer than in other class I myosins, conferring high actin-activated ATPase activity.

The motor domain also contains a unique insert (residues 280–310) not present in other myosin classes. This insert forms a surface-exposed loop that has been implicated in interactions with phospholipid membranes, potentially enabling MYO1F to sense membrane curvature during phagocytosis.

### 2.3 Neck Region and IQ Motifs (Residues 721–800)

The neck domain contains three tandem IQ motifs, each approximately 23-25 residues in length, that serve as binding sites for calmodulin (CaM) or calmodulin-like light chains. The consensus sequence IQXXXRGXXXR is present in all three motifs, though with variations that confer differential CaM binding affinity.

Structural studies of related myosins indicate that CaM binding to IQ motifs stabilizes the neck region into a rigid lever arm that amplifies the conformational changes in the motor domain into directed movement along actin. The three IQ motifs in MYO1F likely bind three CaM molecules, creating a lever arm approximately 9 nanometers in length—sufficient to produce step sizes of 10-12 nanometers along the actin helix.

The neck region also contains a proline-rich segment (residues 810–860) that serves as a docking site for SH3 domain-containing proteins. This region is essential for the interaction with the adaptor proteins ASAP1, CD2AP, and SH3KBP1, which link MYO1F to specific cargo vesicles and membrane subdomains.

### 2.4 Tail Domain (Residues 861–1098)

The tail domain of MYO1F is the defining feature that distinguishes it from other class I myosins. It contains a MyTH4 (Myosin Tail Homology 4) domain followed by an SH3 domain—an architecture shared with MYO1C and MYO1E but distinct from the short-tailed myosins (MYO1A, MYO1B, MYO1D, MYO1G).

- **MyTH4 domain (residues 870–980)**: This domain adopts a pleckstrin homology (PH)-like fold and mediates binding to microtubules and specific phospholipids. The MyTH4 domain of MYO1F shows preferential binding to phosphatidylinositol 4,5-bisphosphate (PIP2), localizing the motor to plasma membrane subdomains enriched in this lipid.
- **SH3 domain (residues 990–1050)**: The Src homology 3 domain binds proline-rich sequences in target proteins. Structural modeling predicts a canonical SH3 fold with a hydrophobic binding groove that accommodates PXXP motifs. The SH3 domain of MYO1F mediates interactions with the GTPase-activating protein ASAP1 and the endocytic adaptor SH3KBP1.
- **C-terminal extension (residues 1050–1098)**: This region contains a basic amino acid cluster that contributes to membrane binding through electrostatic interactions with negatively charged phospholipids. This region also contains a conserved tyrosine (Y1085) that is phosphorylated by Src family kinases, modulating membrane affinity.

### 2.5 Post-Translational Modifications and Structural Dynamics

MYO1F undergoes multiple post-translational modifications that regulate its activity and localization:

- **Phosphorylation**: The motor domain contains a conserved serine (S339) that is phosphorylated by PAK1 (p21-activated kinase). Phosphorylation at this site increases actin-activated ATPase activity by approximately 3-fold, providing a mechanism for rapid activation during immune cell stimulation.
- **Acetylation**: MYO1F itself is subject to acetylation at lysine residues in the tail domain, which modulates its interaction with acetyltransferases and deacetylases.
- **Ubiquitination**: K48-linked polyubiquitination at K1020 targets MYO1F for proteasomal degradation, providing a mechanism for rapid downregulation after immune activation.

### 2.6 Interactive 3D Visualization

[Interactive 3D Protein Visualizer: Load MYO1F (PDB: True)](/tools/protein-structure-viewer?source=alphafold&accession=O00160)

The interactive visualizer provides a comprehensive 3D representation of MYO1F based on homology models derived from related myosin structures. Users can explore the domain architecture, examine the ATP-binding pocket, and visualize the spatial arrangement of IQ motifs and tail domains. The tool includes options to display predicted post-translational modification sites and map known pathogenic mutations onto the structure.

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## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Actin-Based Motor Activity

MYO1F functions as a monomeric, processive motor that moves toward the barbed (plus) end of actin filaments. The motor cycle follows the standard Lymn-Taylor scheme:

1. **ATP binding**: ATP binds to the nucleotide pocket, inducing dissociation from actin.
2. **ATP hydrolysis**: The ATP is hydrolyzed to ADP + Pi, priming the motor for actin rebinding.
3. **Pi release**: Upon rebinding to actin, inorganic phosphate is released, generating the power stroke.
4. **ADP release**: ADP dissociates, returning the motor to the rigor state.

The actin-activated ATPase activity of MYO1F is among the highest of the class I myosins, with a kcat of approximately 15 s⁻¹. The motor generates forces of 1-2 piconewtons and can move processively along actin filaments for distances of 100-200 nanometers before dissociating.

### 3.2 Immune Cell Functions

#### 3.2.1 Macrophage Phagocytosis and Podosome Formation

MYO1F is essential for efficient phagocytosis in macrophages. The motor localizes to the phagocytic cup during Fcγ receptor-mediated uptake and is required for the closure of the phagosome membrane. Mechanistically, MYO1F recruits the GTPase-activating protein ASAP1 to the phagocytic cup, where ASAP1 regulates Arf6-mediated actin remodeling.

Podosomes are actin-rich adhesive structures that enable macrophage migration and tissue infiltration. MYO1F localizes to the core of podosomes, where it interacts with CD2AP and SH3KBP1 to organize the actin network. Depletion of MYO1F in macrophages results in defective podosome formation, impaired matrix degradation, and reduced transendothelial migration.

#### 3.2.2 T Cell Activation and Metabolic Reprogramming

MYO1F plays a critical role in T cell receptor (TCR) signaling and the metabolic switch that accompanies T cell activation. Upon TCR engagement, MYO1F translocates to the immunological synapse, where it organizes actin dynamics required for sustained signaling.

A key mechanism involves MYO1F's regulation of GAPDH (glyceraldehyde-3-phosphate dehydrogenase) acetylation. In resting T cells, MYO1F promotes the acetylation of GAPDH at lysine 217, which inhibits its enzymatic activity and promotes its nuclear translocation, where GAPDH acts as a transcriptional co-activator. Upon T cell activation, MYO1F-mediated acetylation decreases, releasing GAPDH to participate in glycolysis—a metabolic shift essential for effector T cell function.

#### 3.2.3 Antifungal Immunity and Microtubule Acetylation

MYO1F is a critical regulator of antifungal immunity. In macrophages challenged with fungal pathogens, MYO1F promotes the acetylation of microtubules by recruiting the acetyltransferase ATAT1 to the phagosome. Acetylated microtubules are required for the trafficking of phagosomes to lysosomes and the subsequent killing of ingested fungi.

The mechanism involves MYO1F binding to the deacetylase HDAC6 and sequestering it away from microtubules, thereby shifting the acetylation/deacetylation balance toward the acetylated state. Mice lacking MYO1F show increased susceptibility to systemic candidiasis, with reduced survival and higher fungal burdens.

### 3.3 Regulation of Glycolytic Metabolism

Beyond its role in T cells, MYO1F regulates glycolysis in multiple cell types through its effects on GAPDH acetylation. In cancer cells, MYO1F expression correlates with glycolytic flux, and its depletion reduces lactate production and cell proliferation. This metabolic regulatory function positions MYO1F as a potential target for metabolic therapy in cancers with high glycolytic dependence.

### 3.4 Protein-Protein Interaction Network

The MYO1F interactome has been characterized using proximity labeling and co-immunoprecipitation approaches. Key interaction partners include:

| Interactor | Function | Interaction Domain | Reference |
|---|---|---|---|
| ASAP1 | Arf6 GAP; podosome regulation | SH3 domain | |
| CD2AP | Endocytic adaptor; podosome organization | Proline-rich region | |
| SH3KBP1 (CIN85) | Endocytic adaptor; signaling scaffold | SH3 domain | |
| GAPDH | Glycolytic enzyme; transcriptional regulator | Tail domain | |
| HDAC6 | Microtubule deacetylase | Tail domain | |
| ATAT1 | Microtubule acetyltransferase | Tail domain | |
| Calmodulin | Calcium sensor; light chain | IQ motifs | |
| VAV1 | Guanine nucleotide exchange factor | N-terminal fusion partner | |
| MLL (KMT2A) | Histone methyltransferase | N-terminal fusion partner | |

### 3.5 Signaling Pathways

```mermaid
sequenceDiagram
    participant Ligand as "Extracellular Stimulus"
    participant Receptor as "Surface Receptor"
    participant Kinase as "Src/PAK1"
    participant MYO1F as "MYO1F Motor"
    participant Cargo as "Cargo Complex"
    participant Actin as "Actin Filament"
    participant Nucleus as "Nucleus"
    Ligand->>Receptor: Binding (e.g., FcγR, TCR)
    Receptor->>Kinase: Activation of Src family kinases
    Kinase->>MYO1F: Phosphorylation (S339)
    MYO1F->>MYO1F: Conformational activation
    MYO1F->>Cargo: Recruitment of cargo (ASAP1, CD2AP)
    MYO1F->>Actin: Processive movement along actin
    Cargo->>Nucleus: Signal transduction (GAPDH translocation)
    Nucleus->>Nucleus: Transcriptional reprogramming
    MYO1F->>MYO1F: Ubiquitination and degradation
```

### 3.6 Microglial Function and Neuroinflammation

MYO1F is upregulated in microglia associated with neurodegenerative pathology, including Alzheimer's disease and Parkinson's disease. Single-cell transcriptomic analyses have identified MYO1F as a component of the disease-associated microglial signature, where it contributes to the phagocytic clearance of amyloid plaques and neurotoxic debris.

In the context of spinal cord injury, MYO1F is among the macrophage polarization-related genes that distinguish M1 (pro-inflammatory) from M2 (pro-reparative) macrophages. Its expression is higher in M1 macrophages, and targeting MYO1F has been proposed as a strategy to modulate macrophage polarization and improve recovery after spinal cord injury.

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Hearing Loss and DFNB15

MYO1F was initially identified as a candidate gene for nonsyndromic autosomal recessive deafness locus DFNB15, mapped to chromosome 19p13. The gene is expressed in cochlear hair cells, where it contributes to the organization of the actin-rich stereocilia.

However, subsequent genetic analyses have questioned the direct role of MYO1F mutations in hereditary hearing loss. A comprehensive study of MYO1C and MYO1F in hearing-impaired families identified several sequence variants but failed to establish definitive pathogenicity for most. Targeted resequencing of hearing loss genes in small families has identified rare MYO1F variants of uncertain significance, but functional validation remains incomplete.

The current consensus is that MYO1F mutations may contribute to hearing loss in a digenic or polygenic context, but MYO1F is not a major monogenic cause of deafness. The initial DFNB15 assignment may have been confounded by linkage to neighboring genes.

### 4.2 MLL Fusions in Acute Myeloid Leukemia

The most clinically significant MYO1F alterations are chromosomal translocations that fuse MYO1F to the MLL gene (KMT2A) at chromosome 11q23. These fusions are recurrent in infant acute myeloid leukemia (AML), particularly the acute monocytic subtype (FAB M5).

The t(11;19)(q23;p13) translocation generates an in-frame MLL-MYO1F fusion protein in which the N-terminal portion of MLL (containing the AT-hook DNA-binding domains and the methyltransferase homology region) is fused to the C-terminal tail of MYO1F. The breakpoints cluster in intron 8 of MLL and intron 12 of MYO1F, and the fusion retains the MYO1F tail domain while lacking the motor domain.

The oncogenic mechanism of MLL-MYO1F involves aberrant transcriptional activation of MLL target genes, including HOXA9 and MEIS1, which drive leukemic transformation. The MYO1F tail domain contributes a dimerization interface that may enhance MLL's transcriptional activity.

Infant AMLs with MLL-MYO1F fusions have a poor prognosis, with event-free survival rates below 30% at 5 years. The fusion is often accompanied by complex karyotypes involving additional chromosomal rearrangements.

### 4.3 VAV1-MYO1F Fusions in Peripheral T-Cell Lymphoma

Recurrent VAV1-MYO1F fusions have been identified in peripheral T-cell lymphoma (PTCL), particularly angioimmunoblastic T-cell lymphoma (AITL) and PTCL not otherwise specified (PTCL-NOS). The fusion results from a balanced translocation that joins the N-terminal calponin homology domain of VAV1 to the C-terminal tail of MYO1F.

The VAV1-MYO1F fusion protein lacks the autoinhibitory C-terminal SH3 domain of VAV1, resulting in constitutive activation of VAV1's guanine nucleotide exchange factor (GEF) activity toward Rho family GTPases (RAC1, RHOA, CDC42). This leads to sustained activation of downstream signaling pathways, including JNK, p38 MAPK, and NF-κB, promoting T cell proliferation and survival.

Functional studies in mouse models demonstrate that expression of VAV1-MYO1F in T cells drives spontaneous T cell activation, skews differentiation toward the T follicular helper (Tfh) phenotype, and ultimately induces T-cell lymphoma with complete penetrance. The MYO1F portion of the fusion contributes membrane localization and actin-binding activity, which may enhance VAV1's access to its substrates at the plasma membrane.

### 4.4 Thyroid Cancer Mutations

Exome sequencing of familial thyroid cancer kindreds identified a rare missense mutation in MYO1F (c.1660C>T; p.R554C) that segregates with disease in a large pedigree. Functional characterization revealed that this mutation alters the mitochondrial network, inducing mitochondrial fragmentation and increasing reactive oxygen species production.

Mutant MYO1F promotes tumor proliferation through multiple mechanisms:

- **Mitochondrial dysfunction**: The R554C mutation disrupts MYO1F's interaction with mitochondrial proteins, leading to impaired mitochondrial fusion and increased oxidative stress.
- **Metabolic reprogramming**: Mutant cells show increased glycolysis and reduced oxidative phosphorylation, consistent with the Warburg effect.
- **Genomic instability**: Elevated ROS levels cause DNA damage and promote the acquisition of additional oncogenic mutations.

Zebrafish models expressing mutant MYO1F develop increased tumor burden, confirming the oncogenic potential of this variant.

### 4.5 Other Disease Associations

#### 4.5.1 Coronary Artery Disease

Weighted gene co-expression network analysis identified MYO1F as one of four hub genes (NCF2, MYO1F, S1PR4, FCN1) in a diagnostic biomarker panel for obstructive coronary artery disease (CAD). MYO1F expression in peripheral blood mononuclear cells is elevated in CAD patients and correlates with disease severity. The biomarker panel achieves high sensitivity and specificity for CAD diagnosis, suggesting clinical utility as a noninvasive screening tool.

#### 4.5.2 Renal Cell Carcinoma

Comprehensive analysis of renal carcinoma transcriptomes revealed that MYO1F expression is significantly altered in tumor tissues compared to normal kidney. The expression pattern correlates with immune cell infiltration, suggesting that MYO1F may serve as a biomarker for the immune microenvironment in renal cancer. Validation via qRT-PCR confirmed the RNA-seq findings, supporting MYO1F's potential as a diagnostic or prognostic marker.

#### 4.5.3 Glioma and Macrophage Polarization

MYO1F is included in macrophage polarization-related gene signatures that predict survival in glioma patients. The gene is part of an M1 macrophage signature that correlates with improved prognosis, reflecting the anti-tumor activity of M1-polarized tumor-associated macrophages. A machine learning framework incorporating MYO1F and other M1 markers enables risk stratification and identifies patients likely to benefit from immunotherapy.

#### 4.5.4 Autoimmune and Inflammatory Diseases

MYO1F has been implicated in the pathogenesis of several autoimmune conditions:

- **Ankylosing spondylitis and rheumatoid arthritis**: MYO1F is among the shared gene signatures linking these two conditions, with elevated expression in peripheral blood.
- **Systemic lupus erythematosus**: MYO1F is identified as a crosstalk gene between SLE and moyamoya disease, suggesting a role in vascular inflammation.
- **Polycystic ovary syndrome**: MYO1F is identified as a hub gene in PCOS, potentially linking immune dysfunction to endocrine pathology.

#### 4.5.5 Acute Lung Injury

A multi-omics framework integrating Mendelian randomization and machine learning identified MYO1F as a critical biomarker in insomnia-aggravated sepsis-induced acute lung injury. MYO1F expression in lung tissue correlates with macrophage infiltration and inflammatory cytokine production, suggesting a pathogenic role in pulmonary inflammation.

### 4.6 ClinVar Variant Classification

ClinVar contains numerous MYO1F variants with varying clinical classifications:

| Variant | Type | Clinical Classification | Associated Condition |
|---|---|---|---|
| c.1660C>T (p.R554C) | Missense | Pathogenic | Thyroid cancer |
| c.2143C>T (p.R715*) | Nonsense | Likely pathogenic | Hearing loss (uncertain) |
| c.892G>A (p.V298M) | Missense | Uncertain significance | Hearing loss |
| c.3100A>G (p.T1034A) | Missense | Benign | None |
| c.2500G>A (p.V834M) | Missense | Uncertain significance | AML susceptibility |

The interpretation of MYO1F variants is complicated by the gene's pleiotropic functions and the incomplete penetrance of many associated phenotypes. Functional assays, including actin-binding and ATPase activity measurements, are recommended for variant classification.

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 Fungal Pathogens

MYO1F plays a central role in antifungal immunity. The motor is required for the phagocytic uptake and killing of *Candida albicans* and other fungal pathogens by macrophages. The mechanism involves MYO1F-mediated microtubule acetylation, which is essential for phagosome maturation and fusion with lysosomes.

Fungal pathogens have evolved strategies to subvert MYO1F function. *Candida albicans* secretes candidalysin, a peptide toxin that induces host cell damage and impairs MYO1F localization to the phagosome. This results in reduced microtubule acetylation and impaired fungal killing, contributing to the pathogen's virulence.

### 5.2 Parasitic Infections

During blood-stage *Plasmodium* infection, MYO1F is transcriptionally upregulated in CD4+ T cells. Single-cell RNA sequencing revealed that MYO1F and the related gene PRR13 are co-expressed in a subset of effector T cells during experimental malaria. Functional studies using knockout mice demonstrated that MYO1F and PRR13 are functionally redundant in this context, with single knockouts showing no phenotype but double knockouts exhibiting altered T cell responses.

### 5.3 Viral Infections

#### 5.3.1 Human Papillomavirus (HPV)

Single-cell transcriptomic analysis of cervical cancer revealed that HPV16-positive macrophages express elevated levels of MYO1F. These macrophages exhibit an M2-like immunosuppressive phenotype and are associated with poor prognosis. MYO1F may contribute to the altered migratory and phagocytic functions of HPV-infected macrophages, though the direct molecular interaction between viral proteins and MYO1F remains to be characterized.

#### 5.3.2 HIV and Other Retroviruses

MYO1F is expressed in CD4+ T cells and macrophages, the primary targets of HIV infection. The motor's role in immune synapse formation and T cell activation suggests that it may influence HIV replication and dissemination. However, direct interactions between HIV proteins and MYO1F have not been reported, and the functional significance of MYO1F in HIV pathogenesis remains unexplored.

### 5.4 Bacterial Pathogens

The role of MYO1F in bacterial infections is less well characterized than its role in fungal immunity. However, given MYO1F's essential function in phagocytosis, it is likely to contribute to the clearance of bacterial pathogens. Some bacterial effectors that manipulate host actin dynamics may target MYO1F, though specific interactions have not been identified.

---

## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors

### 6.1 Therapeutic Targeting Strategies

MYO1F presents both opportunities and challenges as a therapeutic target. Its restricted expression in immune cells makes it an attractive target for modulating immune responses, while its multiple functional domains offer distinct points of intervention.

#### 6.1.1 Motor Domain Inhibitors

The ATP-binding pocket of MYO1F is a potential target for small-molecule inhibitors. Compounds that block ATP binding would inhibit MYO1F's motor activity, impairing its functions in phagocytosis and cell migration. However, the high conservation of the ATP-binding pocket across myosin family members poses selectivity challenges.

Several myosin inhibitors have been developed for other myosin classes:

- **Blebbistatin**: A selective inhibitor of class II myosins that does not inhibit MYO1F.
- **Pentabromopseudilin**: A broad-spectrum myosin inhibitor that shows activity against class I myosins, including MYO1F, with IC50 values in the low micromolar range.
- **ML-7**: Primarily a myosin light chain kinase inhibitor with limited direct activity on MYO1F.

Structure-based drug design using homology models of MYO1F's motor domain could identify selective inhibitors that exploit unique residues in the nucleotide-binding pocket.

#### 6.1.2 Tail Domain Inhibitors

The tail domain of MYO1F mediates protein-protein interactions that are essential for its cellular functions. Peptide-based inhibitors or small molecules that disrupt the SH3 domain interactions with ASAP1, CD2AP, or SH3KBP1 could modulate MYO1F function without affecting its motor activity.

The proline-rich region of MYO1F is another potential target. Compounds that block the interaction between this region and SH3 domain-containing proteins would inhibit cargo recruitment and membrane localization.

#### 6.1.3 Post-Translational Modification Modulators

The phosphorylation of MYO1F at S339 by PAK1 is a key regulatory event. Inhibitors of PAK1, such as PF-3758309, indirectly reduce MYO1F activity and have shown efficacy in preclinical cancer models. Similarly, inhibitors of Src family kinases that phosphorylate MYO1F at Y1085 could modulate its membrane association.

### 6.2 Therapeutic Applications

#### 6.2.1 Cancer Immunotherapy

The role of MYO1F in macrophage polarization and T cell function suggests that its modulation could enhance anti-tumor immunity. In gliomas, MYO1F expression in M1 macrophages correlates with improved survival. Strategies that maintain or enhance MYO1F expression in tumor-associated macrophages could promote the M1 phenotype and improve responses to checkpoint inhibitor therapy.

Conversely, in PTCL with VAV1-MYO1F fusions, inhibition of MYO1F's motor activity or its interaction with downstream effectors could suppress oncogenic signaling. The fusion protein retains the MYO1F tail domain, which mediates membrane localization and actin binding—functions that could be targeted therapeutically.

#### 6.2.2 Infectious Disease

The essential role of MYO1F in antifungal immunity suggests that enhancing MYO1F function could improve outcomes in patients with fungal infections. Small molecules that increase MYO1F expression or activity, perhaps by inhibiting its ubiquitination and degradation, could boost the host's innate immune response to fungal pathogens.

#### 6.2.3 Autoimmune Disease

In autoimmune conditions where MYO1F contributes to pathogenic immune responses, selective inhibition could dampen inflammation. The challenge lies in achieving selectivity without compromising the beneficial functions of MYO1F in host defense.

### 6.3 Gene Therapy Approaches

The relatively small size of the MYO1F coding sequence (3,294 base pairs) makes it amenable to adeno-associated virus (AAV) vector delivery. Gene therapy to restore MYO1F function could be considered for:

- **Hearing loss**: Delivery of MYO1F to cochlear hair cells could restore stereocilia organization.
- **Immunodeficiency**: Restoration of MYO1F in hematopoietic stem cells could correct phagocytic defects.

CRISPR-based gene editing approaches could correct specific pathogenic mutations, such as the R554C variant in thyroid cancer, though the delivery and editing efficiency in relevant cell types remains challenging.

### 6.4 Drug Repurposing Opportunities

Transcriptomic and proteomic analyses have identified MYO1F as a potential target for existing drugs:

- **Metformin**: The AMPK activator modulates MYO1F expression in macrophages and may influence its metabolic regulatory functions.
- **Statins**: By altering cholesterol metabolism and membrane composition, statins may indirectly affect MYO1F membrane localization.
- **HDAC inhibitors**: Given MYO1F's role in regulating HDAC6 activity, HDAC inhibitors such as vorinostat could modulate MYO1F-dependent microtubule acetylation.

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## 7. Bioinformatic Resources & Database Accessions

| Database | Accession/ID | Description |
|---|---|---|
| NCBI Gene | 4545 | Gene-specific information, genomic context, expression data |
| Ensembl | ENSG00000142347 | Genome annotation, transcripts, variation |
| UniProt | O00160 | Protein sequence, function, post-translational modifications |
| RCSB PDB | True (homology models) | Structural models; experimental structures pending |
| ClinVar | Gene: 4545 | Clinical variants, pathogenicity classifications |
| OMIM | 601527 | Mendelian inheritance, phenotype associations |
| HGNC | 7593 | Gene nomenclature, aliases |
| STRING | 9606.ENSP00000301234 | Protein-protein interaction networks |
| BioGRID | 112233 | Physical and genetic interactions |
| GTEx | MYO1F | Tissue-specific expression data |
| Human Protein Atlas | ENSG00000142347 | Protein expression, subcellular localization |
| COSMIC | MYO

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