EIF4H Human
Description
Overview of EIF4H
EIF4H is encoded by the EIF4H gene located on chromosome 7q11.23. It functions as a cofactor for the RNA helicase EIF4A, enhancing mRNA unwinding during ribosome recruitment . Deletions in this genomic region are linked to Williams syndrome, a multisystem developmental disorder . Two splice variants produce isoforms of 25 kDa and 27 kDa, which share homology with EIF4B and exhibit distinct roles in translation regulation .
Key Features:
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Domains: Contains an RNA recognition motif (RRM) critical for RNA binding and helicase activation .
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Isoforms: Alternative splicing generates two isoforms with differential impacts on cell proliferation and apoptosis .
Interaction Network:
EIF4H forms a dynamic complex with EIF4A, EIF4G, and other initiation factors to regulate translation efficiency .
| Interaction Partner | Function | Score |
|---|---|---|
| EIF4A1 | ATP-dependent RNA helicase; unwinds mRNA secondary structures | 0.999 |
| EIF4G1 | Scaffold protein bridging mRNA cap recognition and ribosome recruitment | 0.993 |
| EIF4E | Binds mRNA 5' cap; facilitates ribosome binding | 0.987 |
| EIF4B | Enhances EIF4A helicase activity; promotes translation initiation | 0.984 |
Data derived from STRING interaction studies and structural analyses .
A. Translation Initiation
EIF4H increases EIF4A’s affinity for RNA by 2-fold and stimulates its helicase activity by ≥4-fold, enabling efficient scanning of structured 5' untranslated regions (UTRs) . This activity is critical for translating mRNAs encoding pro-growth and anti-apoptotic factors (e.g., c-Myc, BCL-xL) .
B. Oncogenic Role
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Overexpressed in lung carcinomas and correlates with chemotherapy resistance .
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Silencing EIF4H reduces tumor growth by 60% in vivo and downregulates oncogenic mRNAs (e.g., FGF-2, cyclin D1) .
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Isoform-specific effects: The long isoform (27 kDa) drives NIH3T3 cell transformation and invasion .
C. Neurodevelopmental Disorders
EIF4H deletions or mutations are implicated in:
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Williams syndrome (cardiovascular and cognitive abnormalities)
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Autism spectrum disorder and schizophrenia (via dysregulated synaptic protein synthesis)
A. Post-Translational Modifications
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Phosphorylation at Ser422 by S6 kinase enhances EIF4H’s role in cap-dependent translation .
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NF-κB transcriptionally upregulates EIF4H under stress, coupling translation to inflammatory signaling .
B. Complex Dynamics
The EIF4A/4G/4H complex adopts a flexible topology, with EIF4H stabilizing EIF4A’s closed conformation during ATP hydrolysis . This interaction is modulated by eIF4G’s HEAT domains, which recruit additional translation machinery .
Therapeutic Potential
EIF4H is a promising target in oncology due to its role in tumor progression and chemoresistance. Key findings include:
Product Specs
GFRDDFLGGR GGSRPGDRRT GPPMGSRFRD GPPLRGSNMD FREPTEEERA QRPRLQLKPR TVATPLNQVA NPNSAIFGGA RPREEVVQKE QE.
Q&A
What is the biochemical structure of human EIF4H and how does it contribute to translation initiation?
Human EIF4H is primarily composed of beta-sheet structures, similar to other RNA recognition motif-containing proteins . The protein is encoded by a gene located on chromosome 7q11.23 . EIF4H functions as an accessory factor that enhances translation initiation by stimulating protein synthesis and the ATP hydrolysis and helicase activities of eIF4A . Secondary structure analysis of human EIF4H by circular dichroism confirms its predominantly beta-sheet composition, which is critical for its RNA-binding capabilities .
Functionally, EIF4H participates in translation initiation through specific protein-protein interactions that stabilize conformational changes occurring in eIF4A during RNA binding, ATP hydrolysis, and RNA duplex unwinding . This stabilization is a key mechanism by which EIF4H enhances translation efficiency.
How is EIF4H expressed in normal human tissues compared to eIF4B?
EIF4H is expressed ubiquitously in human tissues, though its levels vary relative to another related factor, eIF4B . Northern blot analysis reveals tissue-specific expression patterns, with certain tissues showing higher EIF4H expression compared to others . Unlike some translation factors that show restricted expression, EIF4H's ubiquitous presence suggests a fundamental role in cellular protein synthesis across diverse tissue types.
Research methodology for tissue expression analysis typically involves Northern blotting or RNA-seq to quantify mRNA levels, and immunohistochemistry or Western blotting for protein detection. These approaches allow researchers to establish tissue-specific expression profiles that can be correlated with physiological functions.
What specific molecular mechanisms explain EIF4H's enhancement of eIF4A helicase activity?
EIF4H increases the affinity of eIF4A for RNA by approximately 2-fold without affecting ATP binding to eIF4A . More significantly, EIF4H stimulates the helicase activity of eIF4A at least 4-fold, predominantly by increasing the processivity of eIF4A . This enhancement is crucial for efficient unwinding of structured 5' UTRs in mRNAs.
The mechanistic model suggests that EIF4H functions through protein-protein interactions that stabilize conformational changes in eIF4A during its functional cycle . A detailed kinetic analysis shows that:
| Parameter | eIF4A alone | eIF4A + eIF4H | Fold change |
|---|---|---|---|
| RNA binding affinity | Lower | 2× higher | 2-fold increase |
| Helicase activity | Baseline | 4× higher | 4-fold increase |
| ATP binding | Baseline | No change | No effect |
For researchers studying these interactions, recommended methodologies include RNA-binding assays, ATP hydrolysis assays, and helicase activity assays using labeled RNA substrates with varying degrees of secondary structure.
How do the interactions between EIF4H and the eIF4F complex influence translation of specific mRNAs?
EIF4H is part of the translation initiation machinery that includes the eIF4F complex (composed of eIF4E, eIF4G, and eIF4A) . While approximately 90% of eIF4A exists as a free form (eIF4Af), a small proportion (about 10%) is present within the eIF4F complex (eIF4Ac) .
EIF4H's role becomes particularly important for mRNAs with complex 5' UTR structures. Research shows that elevated levels of EIF4H enhance the translation of specific mRNAs encoding:
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Cell-proliferation factors (c-Myc, cyclin D1)
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Angiogenic factors (FGF-2)
The mechanisms involved appear to be related to EIF4H's ability to enhance eIF4A's helicase activity, allowing more efficient unwinding of structured regions in these mRNAs' 5' UTRs. This selective enhancement explains how EIF4H overexpression in cancer cells can drive tumor progression by preferentially upregulating oncogenic proteins.
What experimental evidence supports EIF4H's oncogenic role in human cancers?
Multiple lines of evidence establish EIF4H as an oncogene:
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EIF4H is overexpressed in lung carcinomas and its expression levels are predictive of response to chemotherapy .
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Depletion of EIF4H in lung cancer cells enhances sensitization to chemotherapeutic drugs, decreases cell migration, and inhibits tumor growth in vivo .
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Each isoform of EIF4H acts as an oncogene when introduced into NIH3T3 cells, demonstrating its transforming potential .
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EIF4H overexpression reduces translation of mRNAs encoding cell-proliferation factors, angiogenic factors, and anti-apoptotic factors .
The experimental approach to establish oncogenic function typically involves:
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Expression analysis in tumor vs. normal tissues
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Cell-based assays following EIF4H knockdown/overexpression
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In vivo tumor growth models
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Translational profiling to identify affected mRNAs
How does EIF4H contribute to chemotherapy resistance in cancer cells?
Data indicate that EIF4H expression not only enhances the resistance of tumoral cells to chemotherapeutic drugs but also promotes tumor progression . The mechanism appears to involve the selective translation of mRNAs encoding anti-apoptotic proteins such as CIAP-1 and BCL-xL .
When EIF4H is depleted in lung cancer cells, they become more sensitive to chemotherapy, suggesting that EIF4H-mediated translational control provides a survival advantage to cancer cells under therapeutic stress . This resistance mechanism operates at the translational level, allowing rapid adaptation to stress conditions without requiring transcriptional changes.
For researchers studying chemoresistance mechanisms, methodological approaches should include:
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Combination studies of EIF4H inhibition with chemotherapeutic agents
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Translational profiling under treatment conditions
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Apoptotic pathway analysis in EIF4H-depleted versus control cells
What are the optimal experimental systems for studying EIF4H function in cancer biology?
Based on current research, the following experimental systems are recommended:
| Approach | Application | Advantages | Considerations |
|---|---|---|---|
| siRNA/shRNA knockdown | Loss-of-function studies | Specific targeting, titratable | Transient effect with siRNA |
| CRISPR-Cas9 knockout | Complete loss-of-function | Permanent modification | May be lethal in some cell types |
| Overexpression models | Gain-of-function studies | Mimics cancer state | Non-physiological levels |
| Patient-derived xenografts | In vivo drug testing | Maintains tumor heterogeneity | Resource intensive |
For cellular studies, lung cancer cell lines have been validated as appropriate models since EIF4H overexpression has been well-documented in lung carcinomas . When designing experiments, researchers should consider that EIF4H effects may be context-dependent and vary between cancer types.
What techniques are most effective for assessing EIF4H-dependent translational control?
For researchers investigating EIF4H's impact on translation:
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Polysome profiling: Fractionation of ribosomes to analyze actively translated mRNAs
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Ribosome profiling: Deep sequencing of ribosome-protected mRNA fragments to map translation with nucleotide resolution
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Bicistronic reporter assays: To distinguish cap-dependent from cap-independent translation
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m7GTP cap-binding assays: To analyze assembly of the translation initiation complex
When studying EIF4H's effects on specific mRNAs, researchers should focus on transcripts encoding proliferation factors (c-Myc, cyclin D1), angiogenic factors (FGF-2), and anti-apoptotic proteins (CIAP-1, BCL-xL), as these have been identified as EIF4H-responsive .
How does EIF4H function differ from other translation initiation factors in the eIF4F complex?
Unlike eIF4E (the cap-binding protein) which is rate-limiting for translation, eIF4A is present at ~3-6 molecules per ribosome and is solely cytoplasmic . In mammals, there exist two highly related eIF4A homologs: eIF4AI (DDX2A) and eIF4AII (DDX2B), which are 90% identical .
EIF4H functions as an accessory factor that stimulates eIF4A activity, rather than directly binding to mRNA caps or ribosomes. This stimulatory role places EIF4H in a unique position in the translation initiation cascade:
| Factor | Primary Function | Abundance | Role in Cancer |
|---|---|---|---|
| eIF4E | mRNA cap binding | Rate-limiting | Well-established oncogene |
| eIF4A | RNA helicase | 3-6 copies/ribosome | Target of anti-cancer drugs |
| eIF4G | Scaffold protein | Variable | Promotes translation of specific mRNAs |
| eIF4H | eIF4A stimulator | Variable by tissue | Emerging oncogenic role |
Understanding these distinctions is essential for researchers designing targeted approaches to modulate specific steps in translation initiation for therapeutic purposes.
How do MYC and EIF4H interact in a feed-forward regulatory loop in cancer cells?
MYC and the eIF4F complex (which is enhanced by EIF4H) operate in a feed-forward loop, each enhancing the expression of the other . Elevated MYC increases transcription of core eIF4F components including eIF4E, eIF4AI, and eIF4GI (but not eIF4AII or eIF4GII) .
In turn, MYC is one of the best-characterized translationally-controlled mRNAs, dependent on eIF4F activity . This creates a positive feedback loop where:
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MYC enhances eIF4F components' transcription
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Enhanced eIF4F (stimulated by EIF4H) increases MYC translation
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More MYC protein leads to further enhancement of eIF4F components
This relationship has important implications for cancer treatment. Specifically, elevated eIF4E resulting from MYC activity appears necessary to suppress apoptosis stemming from aberrant MYC activity . This intimate relationship provides an opportunity to interdict part of MYC's oncogenic function by inhibiting eIF4F activity .
For researchers studying this relationship, simultaneous monitoring of MYC levels and translation factors is recommended, along with intervention studies targeting specific components of this feed-forward loop.
Product Science Overview
EIF4H is involved in the process of translation initiation, which is the first step in the synthesis of proteins from mRNA. It functions by stimulating the RNA helicase activity of another protein called EIF4A . EIF4A is an ATP-dependent RNA helicase that unwinds secondary structures in the 5’ untranslated region (UTR) of mRNAs, facilitating the binding of the ribosome . EIF4H enhances this activity, thereby promoting the efficient recruitment of ribosomes to the mRNA .
The recombinant form of EIF4H is typically produced in E. coli and is available as a non-glycosylated polypeptide chain containing 272 amino acids . This recombinant protein includes a 24 amino acid His-tag at the N-terminus, which aids in its purification using chromatographic techniques . The protein is usually stored in a buffer containing Tris-HCl, NaCl, glycerol, and DTT to maintain its stability .
For research purposes, recombinant EIF4H should be stored at 2-4°C if it will be used within a few weeks. For longer-term storage, it is recommended to keep the protein frozen at -20°C, with the addition of a carrier protein to prevent degradation . Repeated freeze-thaw cycles should be avoided to maintain the protein’s integrity .
