FGFR1 Human, (22-285)

What is the basic structure and function of FGFR1?

FGFR1 is a transmembrane receptor tyrosine kinase that spans the cell membrane, with its extracellular domain interacting with fibroblast growth factors (FGFs) and its intracellular domain initiating signaling cascades. The protein is involved in cellular processes including cell division, regulation of growth and maturation, angiogenesis, wound healing, and embryonic development. The FGFR1 protein's strategic positioning allows it to interact with FGFs outside the cell and transduce signals that help the cell respond to its microenvironment. When an FGF binds to FGFR1, it initiates a series of intracellular chemical reactions that direct cellular changes or functional adaptations .

What distinguishes the 22-285 amino acid region of FGFR1?

The 22-285 region of human FGFR1, which is part of the extracellular domain, encompasses the first two immunoglobulin-like domains (D1 and D2) and part of the acid box region. This segment is particularly important because it contains the primary FGF binding site in D2, which is critical for ligand specificity and receptor activation. This region does not include the transmembrane or tyrosine kinase domains, making it valuable for research focused specifically on ligand binding properties without introducing downstream signaling effects.

How does FGFR1 signaling regulate cellular processes?

FGFR1 signaling regulates multiple cellular processes through distinct pathways:

• Cell Cycle Progression: FGFR1 promotes cell cycle progression by suppressing CDK inhibitors p21 and p27 through c-Myc activation .

• Protein Kinase Activation: FGFR1 increases AKT activity and Skp2 levels, resulting in nuclear exclusion and reduction of cell cycle inhibitors .

• Inflammatory Signaling: In certain cancer contexts, FGFR1 augments NF-κB signaling through tyrosine phosphorylation of TAK1, sustaining inflammatory pathways that promote disease progression .

The coordination of these pathways enables FGFR1 to serve as a critical regulator of developmental processes and adult tissue homeostasis.

What experimental approaches are most effective for studying FGFR1 function?

Several complementary approaches have proven effective for investigating FGFR1 function:

• Loss-of-function studies: Using siRNA depletion (70-80% knockdown efficiency), antibody neutralization, or small molecule inhibition (e.g., SU5402) .

• Gain-of-function studies: Overexpression of wild-type FGFR1 or constitutively active variants (e.g., Fc-R1TK fusion constructs) .

• Protein-protein interaction analysis: Co-immunoprecipitation to identify binding partners such as TAK1 .

• Phosphorylation assessment: Western blotting with phospho-specific antibodies to detect activation of FGFR1 and downstream signaling components .

• In vivo developmental models: Xenopus embryo manipulation through microinjection of FGFR1-blocking antibodies to assess developmental functions .

For the specific 22-285 region, structural studies using X-ray crystallography or cryo-EM in combination with ligand binding assays are particularly informative.

How can researchers effectively modulate FGFR1 activity in experimental systems?

Researchers can modulate FGFR1 activity through multiple approaches:

Appropriate controls should include vehicle (DMSO 1:1000) for chemical treatments or control siRNA (e.g., luciferase siRNA) for genetic approaches .

What cell models are most appropriate for studying FGFR1 (22-285) functions?

The selection of cellular models should be aligned with specific research questions:

• For normal physiological functions: Telomerase-immortalized human urothelial cells or human mesenchymal stem cells (hMSCs) provide models for studying physiological FGFR1 signaling .

• For cancer-related research: Prostate cancer lines such as DU145 (high FGFR1 expression) and LNCaP (low FGFR1, high FGFR2 expression) offer contrasting models to study receptor isoform-specific effects .

• For developmental studies: Xenopus embryo systems allow for in vivo assessment of FGFR1 function through targeted microinjection techniques .

• For recombinant protein studies: HEK293 cells provide an effective system for expressing and studying protein-protein interactions involving the FGFR1 (22-285) fragment .

When studying the 22-285 region specifically, expression systems optimized for secreted protein production may be preferred as this domain lacks the transmembrane region.

How does the FGFR1 (22-285) region contribute to ligand specificity?

The 22-285 region, particularly the D2 domain within this segment, contains structural elements critical for FGF binding specificity. This region participates in:

• Direct ligand interaction through a hydrophobic groove in D2 that forms the primary binding site for FGF ligands

• Cooperative binding with heparan sulfate proteoglycans, which form ternary complexes essential for receptor activation

• Determining binding preferences among the 22 different FGF ligands, contributing to tissue-specific responses

Research approaches to study these interactions include surface plasmon resonance, isothermal titration calorimetry, and crystallographic studies of receptor-ligand complexes.

What interacting partners have been identified for FGFR1, and how do they influence signaling outcomes?

FGFR1 interacts with multiple proteins that influence its signaling:

• FGF ligands: Direct activators that bind the extracellular domain .

• TAK1 complex: FGFR1 forms a complex with TAK1 and TAB1, but not with other components of the TNFα receptor complex. This interaction occurs via TAK1's kinase domain and is enhanced by FGFR1 kinase activity .

• FRS2α: Acts as an adaptor protein that becomes phosphorylated upon FGFR1 activation, creating binding sites for downstream effectors .

• c-Myc: Functions downstream of FGFR1 to suppress transcription of CDK inhibitors p21 and p27, promoting cell cycle progression .

• PI3K/AKT pathway components: Activated by FGFR1 to increase Skp2 levels, leading to degradation of cell cycle inhibitors .

These interactions collectively determine the specificity and amplitude of cellular responses to FGFR1 activation.

How does FGFR1 tyrosine kinase activity regulate TAK1 function and inflammatory signaling?

FGFR1 regulates TAK1 function through direct tyrosine phosphorylation:

• FGFR1 forms a physical complex with TAK1 via TAK1's kinase domain, with this interaction being enhanced by FGFR1 kinase activity .

• FGFR1 phosphorylates TAK1 on multiple tyrosine residues within its kinase domain, particularly at four key sites identified through in silico screening .

• This phosphorylation stabilizes TAK1 and sustains NF-κB signaling, promoting inflammatory responses .

• The FGFR1-TAK1 interaction appears to be receptor isoform-specific, as FGFR2-expressing cells (e.g., LNCaP) do not show enhanced NF-κB signaling in response to FGF1 .

This cross-talk mechanism explains how ectopic FGFR1 expression in cancer cells can promote inflammation in the tumor microenvironment, potentially contributing to disease progression.

How does FGFR1 dysregulation contribute to cancer development and progression?

FGFR1 dysregulation contributes to cancer through multiple mechanisms:

• Overexpression: FGFR1 is overexpressed in >80% of prostate cancers and many urothelial carcinomas , suggesting a driver role in these malignancies.

• Inflammatory promotion: FGFR1 augments NF-κB signaling in prostate cancer cells, promoting inflammation that supports tumor progression .

• Cell cycle acceleration: By suppressing CDK inhibitors through multiple mechanisms, FGFR1 promotes unrestricted proliferation .

• Chromosomal translocation: In 8p11 myeloproliferative syndrome, chromosomal translocations involving FGFR1 create fusion proteins with constitutive kinase activity .

These mechanisms position FGFR1 as both a therapeutic target and a biomarker for certain cancer types.

What is the role of FGFR1 in stem cell regulation and developmental processes?

FGFR1 serves critical functions in stem cell biology and development:

• Mesenchymal stem cell proliferation: FGFR1 activity is rate-limiting for self-renewal of human MSCs through antagonism of CDK inhibitors .

• Neural development: FGFR1 is essential for the formation, survival, and migration of neurons, particularly those producing gonadotropin-releasing hormone (GnRH) .

• Olfactory processing: FGFR1 plays a role in the development and function of specialized olfactory neurons .

• Embryonic morphogenesis: FGFR1 signaling is critical for ventral mesoderm formation during development, as demonstrated by defects observed upon inhibition of its signaling in Xenopus embryos .

• Craniofacial and skeletal development: FGFR1 signaling contributes to the development of craniofacial bones, hand/foot bones, and long bones in the limbs .

These developmental roles provide context for understanding how FGFR1 mutations lead to congenital disorders.

What therapeutic approaches target FGFR1 in disease contexts?

Therapeutic strategies targeting FGFR1 include:

• Small molecule inhibitors: Compounds like SU5402 (25 μM) that block FGFR1 kinase activity .

• Neutralizing antibodies: Anti-FGFR1 antibodies that block ligand binding and receptor activation .

• RNA interference: siRNA approaches targeting FGFR1 expression (e.g., Hs_FGFR1_6) .

• Pathway inhibitors: Compounds targeting downstream effectors, including:

  • MEK inhibitors (U0126, 10 μM)

  • PI3K inhibitors (LY294002, 10 μM)

  • Protein kinase C inhibitors (Calphostin C, 10 μM)

  • p38 MAPK inhibitors (SB202190, 10 μM)

  • PLC inhibitors (U-73122, 100 μM)

  • Raf1 inhibitors (30 μM)

Clinical development of FGFR inhibitors is progressing, with increasing emphasis on selective inhibitors that minimize off-target effects on other FGFR family members.

How do FGFR1 isoforms and splice variants affect experimental outcomes and interpretation?

FGFR1 exists in multiple isoforms that can significantly impact research findings:

• IIIb vs. IIIc splice variants: These differ in the third immunoglobulin-like domain and have distinct ligand binding preferences. The IIIc variant (mentioned in search result ) is predominantly expressed in mesenchymal tissues, while IIIb is found in epithelial tissues.

• Expression level variation: FGFR1 expression differences between cell types (e.g., high in DU145, low in LNCaP) can lead to dramatically different responses to the same FGF stimulus .

• Truncated forms: Naturally occurring or experimentally created truncations (such as the 22-285 region) lack certain functional domains and may exhibit dominant-negative effects.

Researchers should carefully document which FGFR1 variant they are studying and consider how splice variants might influence experimental outcomes, especially in heterogeneous tissue samples.

What are the key considerations for designing and interpreting experiments with recombinant FGFR1 (22-285)?

When working with the FGFR1 (22-285) fragment, researchers should consider:

• Protein folding and stability: The isolated extracellular fragment may have different stability characteristics than the full-length receptor.

• Glycosylation status: Expression system choice affects glycosylation patterns, which can influence ligand binding properties.

• Heparan sulfate dependence: FGF-FGFR1 interactions typically require heparan sulfate; experimental designs should account for this co-factor.

• Multimeric states: The receptor fragment may form dimers or higher-order structures that affect binding kinetics.

• Buffer conditions: Ionic strength and pH significantly impact protein-protein interactions involving this domain.

Control experiments should include full-length extracellular domain constructs to validate that findings with the 22-285 fragment are physiologically relevant.

How can researchers address contradictory findings in FGFR1 signaling studies?

Contradictory findings in FGFR1 research may stem from several sources that researchers should systematically address:

• Cell type-specific effects: Compare results across multiple cell lines with documented FGFR expression profiles. For instance, FGFR1-high DU145 and FGFR1-low LNCaP cells show dramatically different responses to FGF1 .

• Experimental timing: FGFR1 signaling shows temporal dynamics, with early and late effects sometimes appearing contradictory. Time-course experiments are essential (e.g., the time-dependent phosphorylation of IKKα and IKKβ observed in DU145 cells) .

• Ligand specificity: Different FGF ligands can activate distinct downstream pathways through the same receptor. Specify which FGF was used (e.g., FGF1 at 2.5 ng/ml) .

• Pathway crosstalk: FGFR1 interacts with multiple signaling networks; combined pathway inhibition studies can resolve apparently contradictory single-pathway observations.

• Technical approach differences: Direct comparison of genetic (siRNA), pharmacological (SU5402), and immunological (neutralizing antibody) inhibition approaches can identify method-specific artifacts .

Systematic documentation of these variables in publications will help the field reconcile seemingly contradictory findings.

What emerging technologies are advancing our understanding of FGFR1 structure and function?

Cutting-edge technologies transforming FGFR1 research include:

• Cryo-electron microscopy: Enabling visualization of FGFR1 in complex with ligands and co-receptors at near-atomic resolution

• CRISPR-Cas9 genome editing: Allowing precise modification of FGFR1 in endogenous contexts to study variant functions

• Single-cell RNA sequencing: Revealing cell-type specific expression patterns and responses to FGFR1 signaling

• Protein engineering approaches: Creating biosensors to monitor FGFR1 activation in real-time within living cells

• Computational molecular dynamics: Simulating ligand binding and conformational changes in the receptor

These approaches are particularly valuable for understanding the 22-285 region's contribution to receptor dynamics and specificity.

What are the most significant unresolved questions regarding FGFR1 (22-285) in research applications?

Critical unresolved questions include:

• How do specific structural features within the 22-285 region determine binding preferences for different FGF ligands?

• What is the mechanistic relationship between the 22-285 region and receptor dimerization processes?

• How do post-translational modifications of the 22-285 region affect ligand binding and receptor activation?

• Can the 22-285 region be engineered to create receptor antagonists with therapeutic potential?

• What role does this region play in interactions with non-canonical FGFR1 binding partners?

Addressing these questions will advance both basic understanding and therapeutic applications related to FGFR1.

How might insights into FGFR1 (22-285) inform the development of next-generation therapeutics?

Research on the FGFR1 (22-285) region has several implications for therapeutic development:

• Selective inhibitors: Structural insights from this region can guide the design of isoform-selective FGFR inhibitors that minimize off-target effects.

• Decoy receptors: Engineered variants of the 22-285 region could function as ligand traps to sequester excess FGFs in pathological conditions.

• Targeting receptor-receptor interactions: Understanding how this region contributes to receptor dimerization could lead to novel allosteric modulators.

• Diagnostic applications: Knowledge of ligand-binding determinants within this region could improve imaging approaches for FGFR1-expressing tumors.

• Combination therapies: Understanding the intersection of FGFR1 with other pathways (e.g., NF-κB) suggests rational combination therapies targeting multiple nodes.

These approaches may address limitations of current FGFR inhibitors, which often lack selectivity among family members.