GRB2 Human
Description
Introduction to GRB2 Human
GRB2 (Growth Factor Receptor-Bound Protein 2) is a 25 kDa adaptor protein critical for interlinking extracellular signals from receptor tyrosine kinases (RTKs) to intracellular signaling cascades, such as the Ras/MAPK/ERK pathway . Encoded by the GRB2 gene on human chromosome 17 (17q24-q25), it serves as a non-enzymatic scaffold that coordinates interactions between phosphorylated receptors and downstream effectors . GRB2’s structure and conformational dynamics enable its role in diverse cellular processes, including proliferation, survival, and differentiation, while its dysregulation is implicated in cancers and viral pathogenesis .
Functional Roles in Cellular Signaling
GRB2 acts as a critical mediator in RTK signaling:
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RTK Activation: Upon ligand binding (e.g., EGF, FGF), RTK dimerization triggers tyrosine phosphorylation, recruiting GRB2 via its SH2 domain .
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Ras Activation: GRB2’s N-terminal SH3 domain binds SOS1, which catalyzes Ras-GDP to Ras-GTP transition, initiating MAPK/ERK signaling .
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LAT Clustering: In T cells, GRB2 binds phosphorylated LAT (Linker for Activation of T cells), stabilizing microclusters and recruiting signaling hubs .
Key Pathways Modulated by GRB2:
Dimerization and Conformational Dynamics
GRB2 exists in equilibrium between monomeric and dimeric states, with dimerization mediated by SH2 domain-swapping . This conformational change is essential for:
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LAT Oligomerization: GRB2 dimers bridge LAT molecules, forming multivalent complexes critical for T cell cytokine production .
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SOS1 Recruitment: Dimeric GRB2 binds SOS1 via both SH3 domains, enhancing Ras activation .
Mutagenesis Studies:
| Mutation | Effect | Functional Impact |
|---|---|---|
| N188/N214 | Stabilizes monomer | Impaired LAT clustering, reduced IL-2 release |
| V122/V123 Hinge | Promotes dimerization | Enhanced membrane localization |
Subcellular Localization and Compartmentalization
GRB2 primarily resides in the cytoplasm, but translocates to the plasma membrane upon RTK activation . Membrane recruitment enables interactions with:
Recent studies suggest nuclear localization under stress conditions, where GRB2 may modulate DNA repair via interactions with PTEN .
Disease Associations and Pathological Roles
GRB2 dysregulation is implicated in:
Research Advances and Therapeutic Implications
Therapeutic Targets:
Product Specs
Q&A
GRB2 (Growth Factor Receptor-Bound Protein 2) is a critical adaptor protein in cellular signaling and DNA repair. Below are research-focused FAQs addressing experimental design, methodological challenges, and advanced mechanistic studies.
What experimental approaches are used to study GRB2-protein interactions in signal transduction?
GRB2’s SH2 and SH3 domains mediate interactions with phosphorylated tyrosine residues and proline-rich motifs, respectively. Key methods include:
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Co-immunoprecipitation (Co-IP) with EGFR or other receptor tyrosine kinases (RTKs) to identify binding partners .
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SH2 domain mutagenesis (e.g., R86K mutation) to disrupt phosphotyrosine binding, followed by Western blotting to assess Ras/ERK pathway activation .
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CRISPR/Cas9 knockout (KO) models to study GRB2-dependent signaling cascades in cell differentiation and survival .
Example Data Table: Common GRB2 Binding Partners
| Partner Protein | Interaction Domain | Functional Outcome | Citation |
|---|---|---|---|
| EGFR | SH2 | Ras/ERK activation | |
| SOS1 | SH3 | GTPase signaling | |
| MRE11 | SH3 | DNA repair initiation |
How do researchers validate GRB2’s role in B-cell development and immune responses?
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Conditional KO mice (e.g., B-cell-specific Grb2 deletion) show impaired follicular B-cell maturation and reduced IgG memory responses .
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Calcium flux assays reveal enhanced BCR-induced Ca²⁺ signaling in GRB2-deficient B cells, linked to dysregulated PI3K-Akt pathways .
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IL-2 release assays in T-cell lymphoma models demonstrate defective LAT clustering upon TCR stimulation in GRB2 dimerization mutants .
How does GRB2 regulate homology-directed repair (HDR) in DNA damage response (DDR)?
GRB2 recruits MRE11 to γH2AX-marked double-strand breaks (DSBs) and facilitates error-free HDR:
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Ubiquitination assays show RBBP6-mediated ubiquitination of GRB2 at lysine-109 (K109) releases MRE11 for resection .
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HDR efficiency assays using DR-GFP or RAD51 foci quantification reveal ~60% reduction in GRB2-KO cells .
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Synthetic lethality with PARP inhibitors occurs in GRB2-deficient cells, mimicking BRCA mutant phenotypes .
Key Finding: High nuclear GRB2 (nGRB2) correlates with advanced breast cancer stages, suggesting prognostic value in HDR-proficient tumors .
What experimental strategies resolve contradictions in GRB2’s cytoplasmic vs. nuclear roles?
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Subcellular fractionation with anti-GRB2 antibodies confirms nuclear localization in ~30% of HeLa cells .
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FRET/FLIM microscopy tracks GRB2-MRE11 complexes at DSBs, distinguishing them from cytoplasmic RTK complexes .
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Domain-swapping mutants (e.g., SH2 dimerization-disrupting mutants) impair LAT clustering in T cells, clarifying structure-function relationships .
How do GRB2 isoforms influence experimental outcomes in cancer models?
The alternatively spliced isoform (lacking SH2 domain) induces apoptosis via unresolved ER stress:
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Isoform-specific siRNA knockdown in 293T cells shows 40% increased caspase-3 activation compared to wild-type .
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Xenograft models expressing the truncated isoform exhibit reduced tumor growth, linked to impaired Ras/ERK signaling .
Methodological Considerations
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Contradiction Management: Discrepancies in GRB2’s role in EGFR endocytosis (e.g., vs. ) may stem from cell-type-specific dimerization requirements.
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Technical Pitfalls: Overexpression of SH3 domain mutants can artifactually sequester proline-rich partners like SOS1, necessitating titration controls .
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Biomarker Development: IHC for nGRB2 and MRE11 co-staining in TCGA datasets identifies HDR-proficient breast cancers eligible for PARPi trials .
Product Science Overview
Growth Factor Receptor-Bound Protein 2 (GRB2) is a crucial adaptor protein involved in signal transduction and cell communication. In humans, the GRB2 protein is encoded by the GRB2 gene. This protein plays a pivotal role in various cellular processes, including cell growth, differentiation, and survival.
GRB2 is composed of one SH2 (Src Homology 2) domain flanked by two SH3 (Src Homology 3) domains . The SH2 domain binds to phosphorylated tyrosine residues on receptor tyrosine kinases (RTKs) or other scaffold proteins, while the SH3 domains interact with proline-rich regions of other proteins .
- SH2 Domain: This domain has a high affinity for phosphorylated tyrosine-containing peptides, typically recognizing sequences with the motif pY-X-N-X, where X is generally a hydrophobic residue .
- SH3 Domains: The N-terminal SH3 domain binds to proline-rich peptides and can interact with the Ras-guanine exchange factor SOS. The C-terminal SH3 domain binds to peptides conforming to a P-X-I/L/V-D/N-R-X-X-K-P motif, allowing it to specifically bind to proteins such as Gab-1 .
GRB2 is essential for linking RTKs to the Ras signaling pathway. Upon ligand binding and activation of RTKs, GRB2 is recruited to the phosphorylated tyrosine residues on the receptor through its SH2 domain. GRB2 then binds to the SOS protein via its SH3 domains, facilitating the activation of Ras, a small GTPase . This activation triggers a cascade of downstream signaling events, ultimately leading to cell proliferation, survival, and differentiation .
GRB2 is widely expressed and is vital for multiple cellular functions. Inhibition of GRB2 function impairs developmental processes in various organisms and blocks the transformation and proliferation of various cell types . Targeted gene disruption of GRB2 in mice is lethal at an early embryonic stage, highlighting its critical role in development .
GRB2’s involvement in key signaling pathways makes it a potential target for therapeutic interventions. Abnormalities in GRB2 function or expression are associated with various diseases, including cancers and immune disorders . Understanding the structure and function of GRB2 can provide novel insights and strategies for developing therapeutic approaches aimed at modulating its activity .
