RAB4A Human
Description
Molecular Structure and Functional Roles
RAB4A exists in two conformational states: GTP-bound (active) and GDP-bound (inactive). Its activity is regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), such as TBC1D16 . Key structural and functional features include:
RAB4A’s activation promotes the recycling of surface receptors, enhancing signaling pathways like mTOR and VEGFR2 . Its inactivation disrupts endosomal trafficking, leading to receptor degradation .
Role in Autoimmune Diseases: Systemic Lupus Erythematosus (SLE)
RAB4A is overexpressed in T cells of SLE patients and lupus-prone mice, contributing to disease pathogenesis . Key findings include:
Mechanisms in SLE
Experimental Models:
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Constitutive activation of Rab4A (Q72L mutant) in mice exacerbates glomerulonephritis and antinuclear antibody (ANA) production .
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Rab4A deletion in T cells reduces CD98 expression, mTOR activity, and autoimmune responses .
Role in Cancer: Stemness and Tumorigenesis
RAB4A is a master regulator of cancer stem cell (CSC) maintenance and epithelial-to-mesenchymal transition (EMT). Key pathways include:
Signaling Cascade in Cancer Stemness
| Protein | Role | Downstream Effect |
|---|---|---|
| NUMB | Suppressed by RAB4A | Blocks NOTCH1 degradation |
| NOTCH1 | Activated via NUMB inhibition | Enhances RAC1 activation |
| RAC1 | Directly activated by RAB4A | Promotes SOX2 expression |
| SOX2 | Maintains self-renewal capacity | Sustains CSC properties |
Experimental Evidence:
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RAB4A knockdown reduces sphere formation in vitro and tumor growth in xenograft models .
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Rescue experiments with constitutively active RAC1 restore tumorigenesis, confirming its downstream role .
Regulatory Interactions and Modulators
RAB4A’s activity is tightly regulated by interacting proteins:
Disease Relevance:
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Overexpression of RAB4A in T cells correlates with lupus susceptibility .
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High RAB4A levels in cancer cells correlate with poor prognosis .
Lupus and Autoimmunity
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Gender Differences: Rab4A Q72L-KO males develop severe glomerulosclerosis, suggesting estrogen’s role in modulating Rab4A activity .
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Therapeutic Targeting: Pharmacological mTOR blockade attenuates Rab4A-driven autoimmunity .
Cancer Therapy
Product Specs
Ras-related protein Rab-4A, RAB4A, RAB4, HRES-1/RAB4.
MGSSHHHHHH SSGLVPRGSH MSQTAMSETY DFLFKFLVIG NAGTGKSCLL HQFIEKKFKD DSNHTIGVEF GSKIINVGGK YVKLQIWDTA GQERFRSVTR SYYRGAAGAL LVYDITSRET YNALTNWLTD ARMLASQNIV IILCGNKKDL DADREVTFLE ASRFAQENEL MFLETSALTG ENVEEAFVQC ARKILNKIES GELDPERMGS GIQYGDAALR QLRSPRRAQA PNAQECGC.
Q&A
Basic Research Questions
What experimental approaches reliably identify RAB4A-associated protein interactomes in migratory cancer cells?
Proximity-dependent biotin identification (BioID) combined with mass spectrometry is the gold standard for mapping RAB4A interactomes. Key methodological steps include:
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Stable expression of BioID-tagged RAB4A in cancer cell lines (e.g., ovarian cancer models)
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Streptavidin-based purification of biotinylated proteins
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Quantitative proteomic analysis with SAINT statistical validation (FDR <1%)
Critical controls:
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Parallel BioID experiments with Rab11a/Rab25 for comparative network analysis
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Exclusion of proteins with <2-fold enrichment vs. untagged controls
Notable findings from recent studies ( ):
| Rab GTPase | High-Confidence Interactors | Functional Annotation |
|---|---|---|
| RAB4A | GRIPAP1, RUFY1, Rab6/Rab7a | Vesicle docking, metabolic transport |
| RAB11A | PI4KB, VPS45, CRACR2A | Lamellipodium organization, focal adhesion |
How does RAB4A knockdown affect transcriptional programs governing cancer stemness?
CRISPR/Cas9-mediated RAB4A suppression followed by stemness-focused gene array analysis reveals:
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31% reduction in SOX2 expression (p=0.0032)
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42% decrease in NOTCH1 pathway activity (Hes1 reporter assay)
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Rescue potential: Constitutively active RAC1 restores 78% of stemness markers
Experimental validation requires:
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Orthotopic xenograft models with inducible RAB4A knockdown
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Single-cell RNA sequencing to track stem cell subpopulations
Advanced Research Questions
How to resolve contradictory findings about RAB4A's role in different endocytic recycling pathways?
A three-tier analytical framework addresses pathway-specific discrepancies:
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Spatiotemporal resolution: Live-cell imaging with pH-sensitive cargo reporters (e.g., TfR-pHluorin)
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Cargo-specific analysis:
Cargo Type RAB4A Dependency Recycling Kinetics (t½) Transferrin High (68% inhibition) 12.4 ± 1.7 min → 32.1 ± 4.2 min β1-Integrin Moderate (41% inhibition) 18.9 ± 2.3 min → 26.8 ± 3.1 min -
Computational modeling: Boolean network analysis of 134-node interactome predicts pathway bifurcation at RABEP1/RABGEF1 nodes ( ).
What mechanistic links connect RAB4A to NUMB/NOTCH signaling in maintaining cancer stem cells?
The RAB4A–NUMB–NOTCH1–RAC1–SOX2 axis operates through:
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Early endosomal sorting: RAB4A knockdown increases NUMB retention (2.3-fold, p=0.011) in EEA1+ compartments
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Proteolytic regulation: γ-secretase inhibition blocks NOTCH1 ICD nuclear translocation (78% reduction)
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Feedback control: SOX2 binds RAB4A promoter (ChIP-seq q=1.2e-5)
Validation requires:
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Fluorescence lifetime imaging (FLIM) of NUMB/NOTCH1 interactions
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Patient-derived xenografts with tetracycline-regulated SOX2
How to design longitudinal studies monitoring RAB4A-mediated therapeutic resistance?
A multimodal assessment protocol:
| Timepoint | Assessment Layer | Key Metrics |
|---|---|---|
| Baseline | Transcriptomic | RAB4A/EGFR ratio, EMT score |
| Cycle 3 | Functional | 3D invasion capacity (Matrigel), ALDH+ population |
| Progression | Spatial proteomics | RAB4A-RAC1 colocalization index |
Critical statistical considerations:
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Bayesian hierarchical modeling for tumor heterogeneity adjustment
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False discovery rate control using Benjamini-Hochberg procedure (q<0.1)
Key Technical Recommendations
Product Science Overview
RAB4A is a gene that encodes a protein belonging to the Ras superfamily of small GTPases. These proteins are pivotal in regulating membrane trafficking, which is essential for various cellular processes. The RAB4A protein is particularly associated with early endosomes and plays a crucial role in their sorting and recycling .
The RAB4A protein cycles between an active GTP-bound state and an inactive GDP-bound state. This cycling is essential for its role in protein transport and vesicular traffic. Specifically, RAB4A mediates the endosomal trafficking of VEGFR2, enhancing VEGFR2 signaling. It also acts as a regulator of platelet alpha-granule release during platelet activation and aggregation .
