C-JUN Human (241 a.a.)
Description
Molecular Composition
Key Interactions
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Forms heterodimers with FOS family proteins (e.g., c-Fos) to create the AP-1 transcription factor complex .
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Binds AP-1 consensus sequences (5'-TGA[GC]TCA-3') to regulate target genes .
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Interacts with PU.1 and C/EBPβ in macrophages to coactivate inflammatory genes like IL-1β without direct DNA binding .
Transcriptional Regulation
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AP-1 Activation: Drives expression of genes involved in cell cycle progression (e.g., cyclin D1), apoptosis (e.g., FASLG), and inflammation (e.g., COX2) .
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Dual Phosphorylation: Phosphorylation at Ser63/73 and Thr91/93 by JNK enhances transcriptional activity .
Disease Associations
Experimental Models
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In Vitro Studies:
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In Vivo Models:
Therapeutic Targeting
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Inhibitors: Tylophorine (plant alkaloid) induces G1 arrest by downregulating c-Jun targets like cyclin A2 .
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Gene Therapy: Antisense c-jun (AS-c-jun) reduces apoptosis in β-cells .
Controversies and Emerging Insights
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Context-Dependent Roles:
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Phosphorylation Dynamics:
Key Research Findings
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Macrophage Polarization: c-Jun deletion shifts macrophages toward anti-inflammatory states (↑Arg1, ↓Cox2), mitigating arthritis .
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Neurodegeneration: c-Jun upregulation in Alzheimer’s models correlates with transposable element mobilization and neuroinflammation .
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T-Cell Development: c-Jun regulates αβ/γδ T-cell lineage choice by suppressing IL-7Rα expression .
Future Directions
Product Specs
Q&A
What is the functional significance of C-JUN in human cell development?
C-JUN acts on chromatin loci to influence cell fate specification, particularly as cells exit pluripotency. Although widely expressed across various cell types in early embryogenesis, C-JUN is not essential for maintaining pluripotency. Instead, it functions as a repressor to constrain mesoderm development while having minimal impact on ectoderm differentiation .
This context-dependent activity is critical for proper embryonic development, as C-JUN interacts with specific protein complexes to regulate chromatin accessibility at developmental genes. The protein's role varies significantly between differentiation pathways, making it an important factor in understanding lineage commitment mechanisms.
How does C-JUN function in transcriptional regulation?
C-JUN can operate through two distinct mechanisms:
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As a DNA-binding activator: C-JUN binds directly to AP-1 sequences to drive gene expression
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As a coactivator: C-JUN functions as a cofactor for other transcription factors (like PU.1 in macrophages) without direct DNA binding
The mechanism whereby C-JUN switches between these modes involves its basic domain, which can either interact with DNA or participate in protein-protein interactions. Notably, C-JUN homodimers bind AP-1 sequences with lower affinity than heterodimers formed with other AP-1 family members . When functioning as a coactivator, C-JUN enhances transcription by facilitating the assembly of the RNA polymerase II preinitiation complex with minimal effect on local chromatin status .
What structural features enable C-JUN's dual functionality?
Human C-JUN consists of 241 amino acids in its native form and contains several key functional domains:
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Basic DNA-binding domain: Contains four critical residues (positions R270, N271, C278, R279) that can either contact DNA or participate in protein-protein interactions
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Leucine zipper dimerization domain: Enables formation of homo- and heterodimers
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Transactivation domain: Contains phosphorylation sites regulated by the JNK pathway
The recombinant form often used in research includes a 20-amino acid His tag at the N-terminus, resulting in a 261-amino acid protein with a molecular mass of 27.3kDa . The fact that the same basic domain residues mediate both DNA binding and protein interactions creates a mutually exclusive switch between C-JUN's functions as a direct transcription factor and as a coactivator .
How does C-JUN regulate mesoderm differentiation in human pluripotent stem cells?
C-JUN acts as a chromatin repressor that specifically limits mesoderm differentiation during human pluripotent stem cell differentiation through several mechanisms:
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C-JUN interacts with the MBD3-NuRD complex to maintain chromatin in a low accessibility state at mesoderm-related genes
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This interaction specifically inhibits the activation of key mesoderm factors such as EOMES and GATA4
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Knocking out C-JUN or inhibiting it with a JNK inhibitor alleviates this suppression, promoting mesoderm cell differentiation
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Conversely, overexpressing C-JUN redirects differentiation toward a fibroblast-like lineage
Experimental evidence shows that in a 3-day mesoderm induction system using CHIR99021 (WNT pathway activator), C-JUN knockout cells show increased proportions of PDGFRA+ mesoderm cells compared to wild-type cells. This phenotype can be replicated using the JNK inhibitor SP600125 .
What is the relationship between C-JUN and the MBD3-NuRD complex?
C-JUN and the MBD3-NuRD complex have a complex, context-dependent relationship:
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C-JUN can directly interact with MBD3, a component of the NuRD complex
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This interaction recruits the NuRD complex (a co-repressor that mediates gene silencing through histone deacetylation and chromatin remodeling) to target genes
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The interaction is disrupted by C-JUN N-terminal phosphorylation, which is induced by JNK signaling
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Knockdown of MBD3 enhances mesoderm generation, whereas MBD3 overexpression impedes it
The dynamic nature of this interaction provides a mechanism for fine-tuning gene expression during development. When C-JUN is phosphorylated, its interaction with MBD3 is disrupted, potentially alleviating repression of mesoderm genes .
How does C-JUN antagonize WNT signaling during mesoderm formation?
WNT signaling plays a pivotal role in mesoderm specification and cardiac development. C-JUN functions as an antagonist to WNT signaling during the transition from pluripotent stem cells to mesoderm through the following mechanisms:
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C-JUN is rapidly degraded following CHIR99021 treatment (WNT activator), with a concomitant decrease in mRNA levels
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Deletion of C-JUN leads to upregulation of β-CATENIN expression, enhancing WNT signaling and expediting mesoderm formation
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Elevated C-JUN expression suppresses β-CATENIN and redirects cell fate toward a fibroblast-like state
This antagonistic relationship explains previous observations that C-JUN knockout enhances cardiac generation (mesoderm-derived), while C-JUN overexpression inhibits this process .
What techniques are most effective for studying C-JUN's dual functionality?
To investigate C-JUN's role as both a DNA-binding transcription factor and a coactivator, researchers should consider:
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Mutational analysis: Create point mutations in C-JUN's basic domain:
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Protein-protein interaction assays:
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DNA binding assays:
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Electrophoretic mobility shift assays (EMSA) to assess direct DNA binding
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Chromatin immunoprecipitation (ChIP) to identify genomic binding sites
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Functional validation:
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Reporter gene assays using AP-1 responsive elements
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Analysis of target gene expression in the presence of wildtype vs. mutant C-JUN
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These approaches allow for distinguishing between C-JUN's direct transcriptional effects and its coactivator functions in different cellular contexts.
What are optimal methods for C-JUN knockout and inhibition studies?
Based on the research methodologies described in the search results, effective approaches include:
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Genetic manipulation:
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Pharmacological inhibition:
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Validation approaches:
Combining genetic and pharmacological approaches provides complementary evidence and controls for potential off-target effects of either method.
How can researchers effectively produce and purify recombinant C-JUN protein?
To obtain high-quality recombinant human C-JUN protein for in vitro studies:
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Expression system:
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Purification approach:
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Quality control:
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SDS-PAGE to confirm purity and correct molecular weight
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Western blotting with anti-C-JUN antibodies
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Functional assays to confirm DNA binding activity
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Mass spectrometry to verify protein identity
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For functional studies, researchers should consider whether post-translational modifications absent in E. coli-expressed protein might affect activity in specific experimental contexts.
How should researchers interpret contradictory findings about C-JUN function across different model systems?
When faced with seemingly contradictory results regarding C-JUN function:
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Consider species-specific differences:
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Evaluate cellular context:
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C-JUN has opposing effects in different cell types (inhibits mesoderm but minimal effect on ectoderm)
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Temporal dynamics of C-JUN expression affect its function (initial downregulation followed by reactivation during mesoderm differentiation)
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Interactions with different protein partners may alter C-JUN function
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Examine methodology differences:
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Complete knockout versus partial knockdown
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Constitutive versus inducible/temporal manipulation
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Different differentiation protocols or culture conditions
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Analyze signaling pathway crosstalk:
A comprehensive evaluation considering these factors helps reconcile apparent contradictions and build a more nuanced understanding of C-JUN biology.
What bioinformatic approaches are most valuable for analyzing C-JUN genomic targets?
For comprehensive analysis of C-JUN genomic targets:
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Integrated genomic approaches:
Technique Application Data Output ChIP-seq Identify C-JUN binding sites Genome-wide binding profile ATAC-seq Assess chromatin accessibility Open chromatin regions RNA-seq Measure gene expression changes Differential expression CUT&RUN Higher resolution binding Precise binding locations HiC/3C Chromatin interactions Long-range regulatory contacts -
Motif analysis:
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Identify enriched AP-1 motifs in C-JUN binding sites
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Discover co-occurring motifs for potential interaction partners
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Compare motif enrichment between different cell types/conditions
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Integration with protein interaction data:
These approaches provide a comprehensive view of how C-JUN regulates gene expression across the genome in different cellular contexts.
How might modulation of C-JUN activity be leveraged for directed differentiation in regenerative medicine?
Based on C-JUN's role in mesoderm differentiation, strategic manipulation could enhance regenerative medicine applications:
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Cardiac regeneration:
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Temporary inhibition of C-JUN (using JNK inhibitors or genetic approaches) could enhance mesoderm differentiation and subsequent cardiomyocyte generation
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Temporal modulation might be required to match developmental sequences
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This approach could improve efficiency of cardiac differentiation protocols for cell therapy or tissue engineering
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Prevention of fibrosis:
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Since C-JUN overexpression redirects differentiation toward fibroblast-like lineages, inhibiting C-JUN during tissue regeneration might reduce fibrotic scarring
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This could be particularly relevant for cardiac repair after myocardial infarction
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Balancing differentiation pathways:
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C-JUN inhibition could be combined with pathway activators (e.g., WNT modulators) for synergistic effects on mesoderm differentiation
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Sequential modulation of C-JUN at different stages might optimize differentiation outcomes
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Small molecule approaches:
Understanding the precise temporal requirements for C-JUN inhibition during differentiation is essential for translating these findings to clinical applications.
What are the potential implications of C-JUN research for understanding developmental disorders?
C-JUN's role in early embryonic development suggests several implications for developmental disorders:
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Congenital heart defects:
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Developmental signaling disorders:
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Human-specific developmental processes:
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Disease modeling approaches:
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Patient-derived iPSCs with genetic variants affecting C-JUN or its pathway components
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CRISPR-engineered mutations in C-JUN interaction domains
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Small molecule modulators of C-JUN activity to assess developmental phenotypes
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These research directions could provide insights into pathogenic mechanisms and potential therapeutic approaches for developmental disorders.
Product Science Overview
The Jun Proto-Oncogene, also known as c-Jun, is a crucial component of the Activator Protein 1 (AP-1) transcription factor complex. This protein plays a significant role in regulating gene expression in response to a variety of stimuli, including stress, cytokines, growth factors, and infections.
c-Jun is highly similar to the viral protein and interacts directly with specific target DNA sequences to regulate gene expression . It is activated by the c-Jun N-terminal kinase (JNK) pathway and forms a part of the AP-1 early response transcription factor in combination with c-Fos . The c-Jun gene is intronless and is mapped to the chromosomal region 1p32-p31, which is involved in both translocations and deletions in human malignancies .
The c-Jun recombinant protein is typically stored at 4°C if it will be used within 2-4 weeks. For longer storage periods, it is recommended to keep it frozen at -20°C with the addition of a carrier protein such as 0.1% HSA or BSA to prevent degradation . It is important to avoid multiple freeze-thaw cycles to maintain the protein’s integrity.
