# PDGFRB Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- The *PDGFRB* gene encodes a receptor tyrosine kinase critical for mesenchymal cell biology, vascular development, and tissue homeostasis, mediating pleiotropic effects on cell proliferation, migration, and survival.
- Germline and somatic alterations in *PDGFRB*, including activating mutations (e.g., p.Arg561Cys in infantile myofibromatosis) and gene fusions (e.g., ETV6::PDGFRB in myeloid/lymphoid neoplasms), drive a spectrum of developmental syndromes and hematological malignancies.
- PDGFRβ signaling is activated by PDGF-BB and PDGF-DD, initiating downstream cascades including RAS-MAPK, PI3K-AKT, and JAK-STAT pathways, which are crucial for cell growth, survival, and differentiation.
- The kinase domain of PDGFRβ is a validated therapeutic target, with tyrosine kinase inhibitors (TKIs) such as imatinib mesylate demonstrating significant efficacy in PDGFRB-rearranged hematological neoplasms and certain solid tumors.
- Specific mutations in *PDGFRB*, such as p.Tyr562Cys in intracranial aneurysms, highlight its role in vascular pathology, while loss-of-function mutations (e.g., in primary familial brain calcification) underscore its importance in neurodevelopment and barrier integrity.
- Alternative splicing can generate functional isoforms, including a soluble decoy receptor (sPDGFRB) that negatively regulates PDGF signaling, and kinase-dead variants that exert dominant-negative effects.

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## Executive Summary & Key Metadata

The platelet-derived growth factor receptor beta (PDGFRB) gene encodes a class III receptor tyrosine kinase (RTK) that is fundamental to mesenchymal cell biology, vascular development, and tissue homeostasis. PDGFRB is a critical mediator of platelet-derived growth factor (PDGF) signaling, particularly the PDGF-BB and PDGF-DD isoforms, and exerts pleiotropic effects on cell proliferation, migration, survival, and differentiation across multiple lineages, including pericytes, smooth muscle cells, fibroblasts, and glial cells. Germline and somatic alterations in PDGFRB underlie a spectrum of diseases ranging from developmental syndromes (e.g., Kosaki overgrowth syndrome, primary familial brain calcification, infantile myofibromatosis) to hematological malignancies driven by gene fusions and solid tumors with activating mutations or copy number alterations. The receptor's kinase domain is a validated therapeutic target, with imatinib mesylate and other tyrosine kinase inhibitors (TKIs) demonstrating remarkable efficacy in PDGFRB-rearranged myeloid/lymphoid neoplasms.

| Attribute | Value |
|---|---|
| **HGNC Symbol** | PDGFRB |
| **UniProt Accession** | P09619 |
| **Representative PDB ID** | true (multiple structures available; e.g., 3MJG for kinase domain) |
| **Chromosomal Locus** | 5q32 (GRCh38: chr5:150,113,839-150,155,845) |
| **Primary Molecular Function** | Receptor tyrosine kinase; signal transduction for PDGF-BB/DD; regulation of cell proliferation, migration, survival, pericyte recruitment, and vascular maturation |
| **Disease & Pathology Associations** | Myeloid/lymphoid neoplasms with eosinophilia and PDGFRB rearrangement; Ph-like acute lymphoblastic leukemia; infantile myofibromatosis; Kosaki overgrowth syndrome; Penttinen premature aging syndrome; primary familial brain calcification; fusiform intracranial aneurysms; various solid tumors (mesothelioma, sarcoma, gastric cancer, bladder cancer) |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Gene Structure

The *PDGFRB* gene is located on the long arm of chromosome 5 at band q32 (5q32), a genomic region of significant interest in oncology due to its frequent involvement in chromosomal translocations and deletions. The gene spans approximately 42.5 kilobases (kb) of genomic DNA on the plus strand, oriented from centromere to telomere. The reference genome assembly (GRCh38) places the gene between coordinates 150,113,839 and 150,155,845. The gene comprises 23 exons, with the translation initiation codon located in exon 1 and the stop codon in exon 23. The coding sequence is 3,366 nucleotides in length, encoding a precursor protein of 1,106 amino acids, which undergoes signal peptide cleavage to yield the mature 1,074-amino-acid receptor.

The genomic architecture of *PDGFRB* is notable for its large intronic regions, particularly intron 1 (~10 kb) and intron 10 (~8 kb), which harbor regulatory elements and potential sites for chromosomal breakage. The 5' untranslated region (UTR) is relatively short (~200 bp) but contains multiple transcription start sites (TSS) as identified by Cap Analysis of Gene Expression (CAGE) data, suggesting alternative promoter usage. The 3' UTR is extensive (~2.5 kb) and contains multiple AU-rich elements (AREs) that mediate mRNA instability, as well as binding sites for microRNAs including miR-140, miR-199a, and miR-455, which post-transcriptionally regulate PDGFRB expression.

### 1.2 Promoter Architecture and Transcriptional Regulation

The core promoter of *PDGFRB* lacks a canonical TATA box but contains a GC-rich region with multiple Sp1 binding sites, consistent with a housekeeping-like promoter that is nonetheless subject to cell-type-specific regulation. Functional promoter analysis has identified several critical cis-regulatory elements within the first 500 bp upstream of the TSS:

- **Sp1/Sp3 binding sites** (-50 to -450 bp): These GC-box elements are essential for basal transcription. Sp1 recruits TFIID and Mediator complexes, facilitating RNA Polymerase II pre-initiation complex assembly. In vascular smooth muscle cells (VSMCs), Sp1 binding is enhanced by PDGF-BB stimulation, creating a positive autoregulatory loop.
- **E-box elements** (-200 to -300 bp): Bound by basic helix-loop-helix (bHLH) transcription factors such as USF1/USF2. These elements mediate responsiveness to cellular stress and hypoxia.
- **NF-κB binding site** (-350 bp): A functional NF-κB response element confers inducibility by inflammatory cytokines (TNF-α, IL-1β). This is particularly relevant in vascular pathology, where inflammation drives PDGFRB upregulation in atherosclerotic lesions and aneurysms.
- **GATA motifs** (-150 bp): Recognized by GATA-2 and GATA-3, contributing to endothelial and hematopoietic expression.

### 1.3 Enhancer Elements and Chromatin Architecture

Chromatin conformation capture studies (Hi-C, ChIA-PET) have identified several distal enhancer elements that interact with the *PDGFRB* promoter in a cell-type-specific manner. A prominent enhancer cluster located approximately 50 kb downstream of the gene (within intron of the neighboring *CDKAL1* gene) shows strong H3K27ac and H3K4me1 marks in pericytes and VSMCs. This enhancer region contains binding sites for MEF2C, SRF, and MYOCD, transcription factors central to the myogenic program. In embryonic stem cells, the *PDGFRB* locus is maintained in a poised state marked by H3K4me1 and H3K27me3 (bivalent domain), which resolves to an active state upon mesodermal differentiation.

The *PDGFRB* locus also contains a differentially methylated region (DMR) in its promoter. DNA methylation at CpG dinucleotides within the Sp1 binding sites correlates inversely with gene expression. Hypermethylation of this DMR has been reported in gastric cancer, where it silences PDGFRB expression and is associated with poor prognosis. Conversely, hypomethylation of the *NRP1* gene, which is co-expressed with PDGFRB, has been linked to poor overall survival in gastric cancer, suggesting coordinated epigenetic regulation of the PDGF signaling axis.

### 1.4 Alternative Splicing and Isoforms

Alternative splicing of *PDGFRB* generates multiple transcript variants, although the functional significance of most remains incompletely characterized. The major transcript (ENST00000261799) encodes the full-length receptor. However, several minor isoforms have been documented:

- **Soluble PDGFRB (sPDGFRB)**: Generated by alternative splicing that skips exon 11, which encodes the transmembrane domain. This produces a secreted protein comprising the extracellular ligand-binding domain. sPDGFRB acts as a decoy receptor, sequestering PDGF-BB and PDGF-DD and thereby negatively regulating PDGF signaling. Elevated serum levels of sPDGFRB have been reported in patients with systemic sclerosis and certain malignancies.
- **Kinase-dead isoform**: A splice variant lacking exon 15, which encodes part of the ATP-binding pocket of the kinase domain. This isoform, when co-expressed with the full-length receptor, exerts a dominant-negative effect, reducing downstream signaling.
- **Intronic retention isoforms**: RNA-seq data from GTEx reveal low-abundance transcripts with retained introns (e.g., intron 12 retention), which are predicted to undergo nonsense-mediated decay (NMD). These may represent a regulatory mechanism for fine-tuning receptor levels.

The 5' UTR also exhibits alternative splicing, with some transcripts containing an additional upstream exon (exon 1a) that introduces a short upstream open reading frame (uORF). This uORF represses translation of the main ORF, providing a mechanism for translational control of PDGFRB expression.

---

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

### 2.1 Primary Structure and Domain Organization

The PDGFRβ protein (UniProt P09619) is a single-pass type I transmembrane receptor tyrosine kinase. The mature protein (after signal peptide cleavage) of 1,074 amino acids is organized into distinct functional domains, each with specific structural and biochemical properties:

| Domain | Residues (mature protein) | Structural Features | Function |
|---|---|---|---|
| **Signal Peptide** | 1-32 (precursor) | Hydrophobic α-helix | Directs co-translational translocation to ER |
| **Extracellular Domain (ECD)** | 33-529 | 5 immunoglobulin-like (Ig-like) domains (D1-D5) | Ligand binding (D1-D3), receptor dimerization (D4-D5) |
| **Transmembrane Domain (TM)** | 530-550 | Single α-helix (23 residues) | Membrane anchoring, signal transduction across lipid bilayer |
| **Juxtamembrane Domain (JM)** | 551-570 | Flexible, partially α-helical | Autoinhibitory function; phosphorylation sites (Y557, Y562) |
| **Kinase Domain (KD)** | 571-930 | Bilobal kinase fold (N-lobe, C-lobe) | ATP binding, phosphotransferase activity |
| **Kinase Insert Domain (KID)** | 740-800 | Loop structure within KD | Docking site for signaling proteins (e.g., PI3K, PLCγ) |
| **C-terminal Tail** | 931-1074 | Flexible, unstructured | Regulatory phosphorylation sites (Y1009, Y1021); ubiquitination sites |

### 2.2 Extracellular Domain: Immunoglobulin-Like Repeats

The extracellular region consists of five immunoglobulin (Ig)-like domains, each adopting the characteristic Ig fold: a sandwich of two β-sheets composed of 7-9 antiparallel β-strands. The domains are arranged in a tandem, slightly bent conformation, with flexible linkers between D1-D2 and D2-D3 that allow conformational changes upon ligand binding.

- **D1-D3 (Ligand-binding domains)**: These domains form the primary binding site for PDGF-BB and PDGF-DD. The crystal structure of PDGF-BB in complex with PDGFRβ D1-D3 (determined by Shim et al., 2010) reveals that the ligand dimer binds asymmetrically, with one PDGF-BB monomer contacting D1 of one receptor molecule and D3 of the other. Key residues involved in ligand binding include Arg-155, Arg-156, and Lys-158 in D1, and Asn-204, Arg-207, and His-210 in D3. The binding interface is predominantly electrostatic, with complementary charged surfaces on ligand and receptor.
- **D4-D5 (Dimerization domains)**: These domains do not contact the ligand directly but mediate receptor-receptor interactions that stabilize the signaling-competent dimer. The D4 domain contains a conserved "dimerization arm" - a loop that inserts into a hydrophobic pocket on the opposing receptor monomer. This interaction is critical for the formation of the 2:2 (ligand:receptor) signaling complex. Mutations in D4 that disrupt dimerization (e.g., W366R) abolish receptor activation.

### 2.3 Transmembrane and Juxtamembrane Domains

The single transmembrane α-helix (residues 530-550) anchors the receptor in the plasma membrane. The JM domain (residues 551-570) is a critical regulatory region. In the inactive state, the JM domain adopts a conformation that inserts into the kinase domain, stabilizing the autoinhibited conformation. Specifically, the JM domain forms a short α-helix that packs against the N-lobe of the kinase domain, preventing ATP binding and catalytic activity. Two tyrosine residues within the JM domain (Tyr-557 and Tyr-562) are phosphorylated upon receptor activation; phosphorylation disrupts the autoinhibitory interaction and stabilizes the active conformation.

### 2.4 Kinase Domain: Catalytic Machinery

The kinase domain (residues 571-930) adopts the canonical bilobal protein kinase fold:

- **N-lobe** (residues 571-740): Composed of a five-stranded antiparallel β-sheet (β1-β5) and a single α-helix (αC). The N-lobe contains the glycine-rich loop (GxGxxG motif, residues 634-639) that coordinates the phosphate groups of ATP. The αC helix is a key regulatory element; its inward rotation is required for the formation of the active kinase conformation.
- **C-lobe** (residues 741-930): Predominantly α-helical, containing the catalytic loop (HRDLAARN, residues 810-817), the activation loop (A-loop, residues 840-865), and the DFG motif (Asp-840, Phe-841, Gly-842). The catalytic loop contains the essential Asp-811, which acts as the catalytic base in the phosphotransfer reaction.

The kinase insert domain (KID, residues 740-800) is a unique feature of type III RTKs. This ~60-residue loop protrudes from the C-lobe and contains multiple tyrosine phosphorylation sites (Tyr-740, Tyr-751, Tyr-763, Tyr-771) that serve as docking sites for downstream signaling proteins. The KID is largely unstructured in the apo state but becomes ordered upon phosphorylation and binding of effector proteins.

### 2.5 Autoinhibition and Activation Mechanism

In the basal state, PDGFRβ exists as an inactive monomer in the plasma membrane. The kinase domain is maintained in an autoinhibited conformation through two key interactions:

1. **JM domain-mediated inhibition**: The JM domain (residues 551-570) inserts into the kinase domain, with Tyr-562 forming a hydrogen bond with Asp-844 in the activation loop. This interaction stabilizes the A-loop in a "closed" conformation that blocks substrate access.
2. **A-loop conformation**: The activation loop adopts a folded conformation that positions Phe-841 (of the DFG motif) in a "DFG-out" orientation, preventing ATP binding.

Ligand-induced dimerization triggers a conformational change: the JM domain is displaced from the kinase domain, allowing the A-loop to flip to the "DFG-in" conformation. This transition is accompanied by autophosphorylation of JM tyrosines (Tyr-557, Tyr-562), which stabilizes the active state. Subsequent trans-autophosphorylation of KID tyrosines and C-terminal tyrosines creates docking sites for SH2-domain-containing proteins.

### 2.6 Structural Basis of Pathogenic Mutations

The three-dimensional structure of PDGFRβ provides a framework for understanding the functional consequences of disease-associated mutations:

- **Activating mutations in the JM domain** (e.g., p.Arg561Cys, p.Tyr562Cys): These mutations disrupt the autoinhibitory interaction between the JM domain and the kinase domain, leading to constitutive receptor activation. The p.Tyr562Cys mutation, identified in fusiform intracranial aneurysms and infantile myofibromatosis, replaces a key hydrogen-bonding residue with a cysteine, abolishing the JM-A-loop interaction.
- **Activation loop mutations** (e.g., p.Asp844Val, p.Asp850Val): These mutations destabilize the inactive conformation of the A-loop, promoting the active state. The p.Asp850Val mutation has been identified in high-grade sarcomas with myogenic differentiation.
- **Kinase domain mutations conferring TKI resistance** (e.g., p.Thr681Ile, p.Val824Ala): These mutations, identified in patients with PDGFRB-rearranged neoplasms who relapse on imatinib, alter the ATP-binding pocket and reduce drug affinity.

> **Interactive 3D Protein Visualizer: Load PDGFRB (PDB: true)**
> [Interactive 3D Protein Visualizer: Load PDGFRB (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=P09619)
>
> This visualizer loads the experimentally determined structure of the PDGFRβ kinase domain (PDB: 3MJG) in complex with a small-molecule inhibitor. Users can explore the ATP-binding pocket, the activation loop, and the juxtamembrane domain. The tool also allows overlay of pathogenic mutation sites (e.g., p.Tyr562Cys, p.Asp850Val) to visualize their structural context.

---

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Ligand Binding and Receptor Activation

PDGFRβ is activated by PDGF-BB (homodimer of PDGF-B chains) and PDGF-DD (homodimer of PDGF-D chains). PDGF-BB binds with high affinity (Kd ~0.1 nM) to PDGFRβ, while PDGF-DD shows slightly lower affinity. The ligands are disulfide-linked homodimers, each monomer containing a conserved growth factor domain with a cystine-knot fold. Ligand binding induces receptor dimerization through a two-step mechanism:

1. **Initial binding**: One PDGF-BB monomer binds to the D1-D3 domains of one PDGFRβ molecule.
2. **Dimer stabilization**: The second PDGF-BB monomer recruits a second PDGFRβ molecule, and the D4 domains of the two receptors interact to stabilize the dimer.

This 2:2 complex brings the two kinase domains into close proximity, enabling trans-autophosphorylation. The initial phosphorylation events occur on JM domain tyrosines (Tyr-557, Tyr-562), which relieves autoinhibition. Subsequent phosphorylation of KID tyrosines (Tyr-740, Tyr-751, Tyr-763, Tyr-771) and C-terminal tyrosines (Tyr-1009, Tyr-1021) creates docking sites for downstream effectors.

### 3.2 Downstream Signaling Cascades

Upon activation, PDGFRβ recruits and activates multiple signaling pathways through SH2-domain-mediated interactions:

#### 3.2.1 RAS-MAPK Pathway
The adaptor protein GRB2 binds to phosphorylated Tyr-716 (via its SH2 domain) and recruits the guanine nucleotide exchange factor SOS to the membrane. SOS activates RAS (HRAS, NRAS, KRAS), which initiates the RAF-MEK-ERK cascade. ERK1/2 translocates to the nucleus and phosphorylates transcription factors (ELK1, MYC, FOS), driving cell proliferation. The RAS-MAPK pathway is a major mediator of PDGFRβ-induced mitogenesis.

#### 3.2.2 PI3K-AKT Pathway
The p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3K) binds to phosphorylated Tyr-740 and Tyr-751 in the KID. PI3K generates PIP3 at the plasma membrane, recruiting AKT via its PH domain. AKT is activated by PDK1 and mTORC2, and phosphorylates multiple substrates including FOXO transcription factors, GSK3β, and BAD, promoting cell survival and metabolism. The PI3K-AKT pathway is particularly important for PDGFRβ-mediated cell survival and resistance to apoptosis.

#### 3.2.3 PLCγ-Ca²⁺ Pathway
Phospholipase Cγ (PLCγ) binds to phosphorylated Tyr-1021 in the C-terminal tail. PLCγ hydrolyzes PIP2 to generate IP3 and DAG. IP3 triggers Ca²⁺ release from the endoplasmic reticulum, while DAG activates protein kinase C (PKC). This pathway regulates cell migration and cytoskeletal reorganization.

#### 3.2.4 JAK-STAT Pathway
PDGFRβ can activate JAK kinases (JAK1, JAK2, TYK2) either directly or through associated adaptors. Activated JAKs phosphorylate STAT transcription factors (STAT1, STAT3, STAT5), which dimerize and translocate to the nucleus to regulate gene expression. The STAT5 pathway is particularly important in PDGFRβ fusion-driven leukemias, where constitutive STAT5 activation drives proliferation and blocks differentiation.

#### 3.2.5 SRC Family Kinases
SRC family kinases (SFKs) bind to PDGFRβ through their SH2 domains and are activated upon receptor stimulation. SFKs phosphorylate additional substrates including FAK and paxillin, contributing to cell migration and adhesion dynamics.

### 3.3 Negative Regulation and Receptor Downregulation

PDGFRβ signaling is tightly regulated at multiple levels:

- **Receptor internalization**: Upon ligand binding, PDGFRβ is internalized via clathrin-mediated endocytosis. The internalized receptor is either recycled to the plasma membrane or sorted to lysosomes for degradation. The E3 ubiquitin ligase CBL binds to phosphorylated Tyr-1009 and ubiquitinates the receptor, tagging it for lysosomal degradation.
- **Protein tyrosine phosphatases**: PTPN1 (PTP1B), PTPN2 (TC-PTP), and PTPRJ (DEP-1) dephosphorylate PDGFRβ, terminating signaling. PTPN1 is localized to the ER membrane and dephosphorylates the receptor during endocytic trafficking.
- **Suppressor of cytokine signaling (SOCS) proteins**: SOCS1 and SOCS3 bind to phosphorylated PDGFRβ and inhibit JAK-STAT signaling.
- **Sprouty proteins**: SPRY2 and SPRY4 are induced by PDGFRβ signaling and feedback-inhibit the RAS-MAPK pathway.

### 3.4 Protein-Protein Interaction Networks

The PDGFRβ interactome is extensive, with over 100 confirmed interaction partners cataloged in BioGRID and STRING databases. Key interaction hubs include:

- **GRB2**: Adaptor protein linking receptor to RAS-MAPK pathway
- **PIK3R1 (p85)**: Regulatory subunit of PI3K
- **PLCG1**: Phospholipase Cγ1
- **PTPN11 (SHP2)**: Protein tyrosine phosphatase with adaptor functions
- **SRC**: Non-receptor tyrosine kinase
- **CBL**: E3 ubiquitin ligase
- **NCK1/NCK2**: Adaptor proteins regulating actin cytoskeleton
- **SHC1**: Adaptor protein linking receptor to RAS pathway
- **STAT1/STAT3/STAT5A/STAT5B**: Signal transducers and activators of transcription
- **JAK1/JAK2/TYK2**: Janus kinases

### 3.5 Physiological Functions

PDGFRβ signaling is essential for:

- **Pericyte recruitment and vascular maturation**: PDGFRβ is the primary receptor on pericytes, and PDGF-BB secreted by endothelial cells acts as a chemoattractant for pericyte precursor cells. PDGFRβ-null mice die embryonically due to microaneurysm formation and vascular leakage, demonstrating the critical role of PDGFRβ in vascular development.
- **Wound healing and tissue repair**: PDGFRβ signaling in fibroblasts and myofibroblasts promotes proliferation, migration, and extracellular matrix production during wound healing.
- **Mesangial cell development**: In the kidney, PDGFRβ is required for the development of mesangial cells, which provide structural support to glomerular capillaries.
- **CNS development**: PDGFRβ is expressed in oligodendrocyte precursor cells (OPCs) and is required for their proliferation and differentiation. PDGFRβ signaling also regulates blood-brain barrier integrity through pericyte-endothelial interactions.
- **Bone development**: PDGFRβ signaling in osteoblast precursors regulates bone formation and remodeling. Gain-of-function mutations cause craniosynostosis and overgrowth syndromes.

### 3.6 Signaling in Disease Contexts

In cancer, PDGFRβ signaling can be dysregulated through multiple mechanisms:

- **Autocrine/paracrine loops**: Many solid tumors (e.g., mesothelioma, gastric cancer, bladder cancer) overexpress both PDGF-BB and PDGFRβ, creating autocrine stimulatory loops.
- **Activating mutations**: Somatic gain-of-function mutations in the kinase domain or JM domain lead to constitutive activation.
- **Gene amplification**: PDGFRB copy number gain has been reported in sarcomatoid NSCLC, mesothelioma, and other tumors.
- **Gene fusions**: Chromosomal rearrangements fusing PDGFRB to various partner genes result in constitutive kinase activation (see Section 4).

```mermaid
sequenceDiagram
    participant L as "PDGF-BB/DD"
    participant R as "PDGFRβ (monomer)"
    participant R2 as "PDGFRβ (dimer)"
    participant K as "Kinase Domain"
    participant P as "PI3K/AKT"
    participant M as "RAS/MAPK"
    participant S as "STAT5"
    participant N as "Nucleus"
    L->>R: Ligand binding
    R->>R2: Receptor dimerization
    R2->>K: Trans-autophosphorylation
    K->>K: JM domain displacement, A-loop activation
    K->>P: Phosphorylate Tyr740/751 → PI3K recruitment
    K->>M: Phosphorylate Tyr716 → GRB2/SOS → RAS
    K->>S: Phosphorylate Tyr → JAK/STAT activation
    P->>N: AKT → FOXO/GSK3β → gene expression
    M->>N: ERK → ELK1/MYC → proliferation
    S->>N: STAT5 dimer → target gene transcription
```

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Germline Mutations and Developmental Syndromes

#### 4.1.1 Infantile Myofibromatosis (IM)
Infantile myofibromatosis is a mesenchymal disorder characterized by the development of benign tumors (myofibromas) in skin, bone, muscle, and viscera. Both germline and somatic mutations in PDGFRB have been implicated:

- **p.Arg561Cys**: The most common recurrent mutation, located in the juxtamembrane domain. This mutation disrupts autoinhibition, leading to constitutive kinase activation. It is found in both sporadic and familial cases of IM.
- **p.Tyr562Asp**: Another JM domain mutation that activates the receptor.
- **p.Pro584Leu**: Located in the kinase domain N-lobe, this mutation enhances kinase activity.
- **p.Asp850Val**: An activation loop mutation that stabilizes the active conformation.

The clinical spectrum of IM ranges from solitary lesions to multicentric disease with visceral involvement. Patients with germline PDGFRB mutations typically present with more severe, early-onset disease. Importantly, IM tumors show remarkable responsiveness to imatinib, with rapid and durable responses reported even in refractory cases.

#### 4.1.2 Kosaki Overgrowth Syndrome (KOGS)
Kosaki overgrowth syndrome (OMIM #616592) is a rare disorder characterized by postnatal overgrowth, distinctive facial features, cardiac defects, and connective tissue abnormalities. It is caused by the specific gain-of-function mutation p.Trp566Arg in the juxtamembrane domain. This mutation is unique in that it causes constitutive receptor activation but with altered signaling preferences compared to other activating mutations. The p.Trp566Arg mutation has been shown to promote osteoblast differentiation and bone overgrowth, explaining the skeletal phenotype.

#### 4.1.3 Penttinen Premature Aging Syndrome
This progeroid syndrome is caused by the p.Pro584Leu mutation in PDGFRB. The phenotype includes lipoatrophy, skin atrophy, and distinctive facial features, reflecting the role of PDGFRβ in connective tissue homeostasis.

#### 4.1.4 Primary Familial Brain Calcification (PFBC)
PFBC (also known as Fahr's disease) is a neurodegenerative disorder characterized by bilateral calcification of the basal ganglia and other brain regions. Loss-of-function mutations in PDGFRB cause autosomal dominant PFBC. The pathogenic mechanism involves impaired pericyte function and blood-brain barrier disruption, leading to calcium deposition. Most PFBC-associated mutations are missense variants that reduce receptor expression or kinase activity, contrasting with the gain-of-function mutations seen in IM and KOGS.

#### 4.1.5 Craniosynostosis
A specific gain-of-function mutation (p.Trp566Arg) in PDGFRB causes syndromic craniosynostosis with overgrowth. Mouse models with this mutation exhibit premature fusion of cranial sutures, and haploinsufficiency of RUNX2 rescues the phenotype, indicating a genetic interaction between PDGFRB and RUNX2 pathways.

### 4.2 Somatic Mutations in Solid Tumors

#### 4.2.1 Intracranial Aneurysms
Somatic activating mutations in PDGFRB have been identified in a significant proportion of intracranial aneurysms, particularly fusiform aneurysms. The most common mutation is p.Tyr562Cys, which is mosaic (present in a subset of cells). These mutations promote smooth muscle cell phenotype modulation, leading to vessel wall weakening and aneurysm formation. The high prevalence of PDGFRB mutations in intracranial aneurysms (up to 13% in some series) suggests a potential role for TKI therapy in preventing aneurysm progression.

#### 4.2.2 Sarcomas with Myogenic Differentiation
Recurrent hotspot PDGFRB mutations have been identified in high-grade sarcomas with myogenic differentiation. These include p.Asp850Val and p.Asp850His in the activation loop, which confer constitutive kinase activity. These sarcomas may be amenable to TKI therapy, although clinical data are limited.

#### 4.2.3 Cardiac Intimal Sarcoma
A case of undifferentiated cardiac intimal sarcoma was found to harbor an activating PDGFRB mutation, suggesting a potential therapeutic target in this rare and aggressive tumor.

### 4.3 Gene Fusions and Hematological Malignancies

#### 4.3.1 Myeloid/Lymphoid Neoplasms with Eosinophilia and PDGFRB Rearrangement
This is a distinct entity in the WHO classification of hematological malignancies, characterized by constitutive activation of PDGFRB through gene fusion. Over 70 different fusion partners have been identified. The most common is ETV6::PDGFRB, resulting from t(5;12)(q32;p13). Other recurrent partners include:

| Fusion Partner | Translocation | Disease Association | Reference |
|---|---|---|---|
| ETV6 | t(5;12)(q32;p13) | CMML with eosinophilia | |
| CCDC6 | t(5;10)(q33;q21) | CMML, MLN-eo | |
| CCDC88C | t(5;14)(q32;q32) | MLN-eo | |
| CSNK2A1 | t(5;20)(q32;p13) | MLN-eo | |
| DIAPH1 | t(5;5)(q32;q35) | MLN-eo | |
| GCC2 | t(2;5)(q37;q31) | CEL | |
| HIP1 | t(5;7)(q33;q11.2) | CMML | |
| MPRIP | t(5;17)(q32;p11.2) | MLN-eo | |
| MYO18A | t(5;17)(q33;q11.2) | MPN with eosinophilia | |
| NDE1/NDEL1 | t(5;16)(q33;p13) | JMML, MLN-eo | |
| PCM1 | t(5;8)(q32;p22) | MPN, MDS/MPN | |
| PRKG2 | t(4;5)(q21;q33) | aCML | |
| RABEP1 | t(5;17)(q33;p13) | CMML | |
| SART3 | t(5;12)(q32;q24) | MLN-eo | |
| SPECC1 | t(5;17)(q33;q11) | MLN-eo | |
| SPTBN1 | t(5;5)(q32;q33) | aCML | |
| STRN3 | t(5;14)(q32;q24) | AML | |
| TERF2 | t(5;16)(q32;q22) | Ph-like ALL | |
| TNIP1 | t(5;5)(q32;q33) | MDS, MLN-eo | |
| TPR | t(5;1)(q32;q25) | Ph-like ALL | |
| TRIP11 | t(5;14)(q32;q31) | MLN-eo | |
| WNK1 | t(5;12)(q32;p13) | MLN-eo | |
| Daple (CCDC88C) | t(5;14)(q32;q32) | Leukemia | |
| MRC1 | t(5;10)(q32;q22) | JXG | |
| EBF1 | t(5;5)(q32;q33) | Ph-like ALL | |
| ANKRD26 | - | NLCH | |

The fusion proteins typically retain the dimerization domain of the partner protein, which drives constitutive dimerization and activation of the PDGFRβ kinase domain. The resulting chimeric proteins are potent oncogenes that activate the same downstream pathways as the wild-type receptor (RAS-MAPK, PI3K-AKT, JAK-STAT), but in a ligand-independent, constitutive manner.

#### 4.3.2 Philadelphia-like Acute Lymphoblastic Leukemia (Ph-like ALL)
PDGFRB fusions are found in approximately 5-10% of Ph-like ALL cases, a high-risk subtype of B-ALL characterized by a gene expression profile similar to Philadelphia chromosome-positive ALL but lacking BCR::ABL1. Common fusion partners in Ph-like ALL include EBF1, TERF2, TPR, and various others. These fusions are often cytogenetically cryptic and require RNA sequencing for detection. Patients with PDGFRB-rearranged Ph-like ALL may benefit from TKI therapy, although resistance mutations can emerge.

#### 4.3.3 Other Hematological Malignancies
PDGFRB rearrangements have been reported in:
- Chronic myelomonocytic leukemia (CMML) with eosinophilia
- Atypical chronic myeloid leukemia (aCML)
- Juvenile myelomonocytic leukemia (JMML)
- Acute myeloid leukemia (AML)
- Myelodysplastic syndromes (MDS)
- Myeloproliferative neoplasms (MPN)
- T-cell lymphoblastic lymphoma

### 4.4 Copy Number Alterations

PDGFRB gene copy number gain (CNG) has been reported in several solid tumors:

- **Malignant pleural mesothelioma**: PDGFRB CNG is observed in a subset of cases and is paradoxically associated with improved survival. This may reflect a less aggressive tumor biology or increased sensitivity to PDGFR-targeted therapies.
- **Sarcomatoid non-small cell lung cancer**: PDGFRB CNG is associated with PDGFRβ protein overexpression and may represent a therapeutic target.
- **Storiform collagenoma**: Concurrent PTEN and PDGFRB alterations characterize this rare mesenchymal skin tumor.

### 4.5 Polymorphic Variants and Pharmacogenomics

Single nucleotide polymorphisms (SNPs) in PDGFRB have been associated with variable responses to therapy:

- **rs246395** and **rs3828610**: These SNPs in the PDGFRB gene influence the efficacy of platelet-rich plasma (PRP) therapy in treating tennis elbow (lateral epicondylitis). Patients with certain genotypes show better responses to PRP, suggesting that PDGFRB variants may predict treatment outcomes.
- **rs3828610**: Associated with differential PDGFRB expression levels, potentially affecting tissue repair capacity.

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## 5. Host-Pathogen & Viral Interactions

### 5.1 Viral Exploitation of PDGFRB

Several viruses have evolved mechanisms to exploit PDGFRB signaling for their own benefit:

#### 5.1.1 Human Cytomegalovirus (HCMV)
HCMV encodes

## Related Clinical & Scientific Guides

* [PIK3CA (PI3K Alpha): Helical and Kinase Domain Hotspot Mutations and Isoform-Specific Inhibition](/knowledge/bioinformatics/genes/cancer-genomics/pik3ca-gene-structure-function-pathway)
* [ENTPD5 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/entpd5-gene-structure-function-pathway)
* [PDGFB Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/cancer-genomics/pdgfb-gene-structure-function-pathway)