Phospho-JUN (T91) Antibody

What is c-Jun and why is its phosphorylation at T91 significant?

c-Jun is a transcription factor that functions as a component of the AP-1 complex, recognizing and binding to the AP-1 consensus motif 5'-TGA[GC]TCA-3' . It plays crucial roles in diverse cellular processes including cell cycle regulation, differentiation, organogenesis, apoptosis, and tumor transformation .

The phosphorylation of c-Jun at threonine 91 (T91) is particularly significant because:

• It occurs as part of a sequential phosphorylation pattern alongside other sites (S63, S73, and T93)

• T91 phosphorylation, together with T93, induces conformational changes in c-Jun that enhance the accessibility of carboxy-terminal sites to protein phosphatases

• The timing of T91 phosphorylation differs from other sites, occurring later than S63 and S73 phosphorylation, which has implications for temporal regulation of c-Jun activity

Understanding T91 phosphorylation provides insights into the complex regulation of c-Jun and its downstream transcriptional targets in both normal cellular functions and pathological conditions.

How does T91 phosphorylation differ from other c-Jun phosphorylation sites?

T91 phosphorylation exhibits distinct characteristics compared to other phosphorylation sites on c-Jun:

• Phosphorylation kinetics: Time-resolved NMR studies have revealed that JNK-mediated phosphorylation of c-Jun occurs with differing rates in the order: S63 > S73 > T91 ≈ T93 . This creates an intrinsic temporal order of phosphorylation events.

• Structural location: T91 and T93 are located farther from the D-motif (MAPK binding motif, residues 32-50) compared to S63 and S73, which partially explains their slower phosphorylation rates .

• Amino acid preference: JNK kinases demonstrate preferential phosphorylation of serine over threonine residues, contributing to the slower modification of T91 compared to S63 and S73 .

• Functional outcomes: While S63 and S73 phosphorylation are often associated with enhanced transcriptional activity, T91 and T93 phosphorylation affect protein conformation and can modulate the accessibility of other regions to phosphatases .

These differences highlight the complex regulation of c-Jun through site-specific phosphorylation patterns that enable fine-tuned control of its various functions.

What are the available research tools for studying c-Jun T91 phosphorylation?

Several specialized antibodies and research tools are available for investigating c-Jun T91 phosphorylation:

• Antibodies specific to phospho-T91:

  • Rabbit polyclonal antibodies against phospho-c-Jun-T91

  • Rabbit monoclonal antibodies against phospho-c-Jun (Thr91)

• Dual-specificity antibodies:

  • Mouse monoclonal antibodies recognizing both phospho-T91 and phospho-T93

• Genetically engineered c-Jun variants:

  • TTSS variant (S63T/S73T/T91S/T93S) for studying the importance of amino acid identity in phosphorylation patterns

  • 2SA mutant (S63A/S73A) to isolate and study T91/T93 phosphorylation

  • mDock and cDock constructs with transposed D-motif positions to study spatial effects on phosphorylation efficiency

• Analytical techniques:

  • Time-resolved NMR spectroscopy for monitoring phosphorylation kinetics in real-time

  • Immunoblotting with phospho-specific antibodies

  • Immunocytochemistry for cellular localization studies

These tools enable researchers to investigate the spatial, temporal, and functional aspects of T91 phosphorylation in various experimental settings.

How can I optimize western blotting protocols for detecting phospho-c-Jun (T91)?

Optimizing western blotting for phospho-c-Jun (T91) detection requires attention to several critical factors:

• Sample preparation:

  • Use phosphatase inhibitors (e.g., sodium orthovanadate, sodium fluoride) in lysis buffers

  • Process samples quickly and maintain cold temperatures to prevent dephosphorylation

  • Consider using stimuli like anisomycin to activate JNK pathways and enhance detectable phosphorylation

• Antibody selection and dilution:

  • For phospho-c-Jun (T91) detection, use recommended antibody dilutions (typically 1:500-1:1000)

  • Validate antibody specificity using phosphorylation site mutants (T91A) as negative controls

  • Consider using antibodies that detect both T91 and T93 phosphorylation for stronger signals

• Troubleshooting weak signals:

  • Ensure adequate protein loading (30-50 μg of total protein)

  • Optimize transfer conditions for proteins in the 36-48 kDa range where c-Jun is detected

  • Implement signal enhancement systems (e.g., enhanced chemiluminescence)

  • Extend primary antibody incubation time to overnight at 4°C

• Positive controls:

  • Use UV irradiation or anisomycin-treated cell lysates as positive controls

  • Include recombinant phosphorylated c-Jun protein standards when available

• Expected molecular weight:

  • Look for bands at approximately 36-48 kDa, as reported in antibody specification sheets

Attention to these methodological details will enhance the reliability and sensitivity of phospho-c-Jun (T91) detection by western blotting.

What are the optimal conditions for immunohistochemical detection of phospho-c-Jun (T91)?

For successful immunohistochemical (IHC) detection of phospho-c-Jun (T91), consider the following methodological guidance:

• Tissue fixation and preparation:

  • Use 4% paraformaldehyde fixation for optimal epitope preservation

  • Consider antigen retrieval methods (citrate buffer pH 6.0 or EDTA buffer pH 9.0)

  • For formalin-fixed paraffin-embedded tissues, perform heat-induced epitope retrieval

• Antibody parameters:

  • Use recommended dilutions for IHC-P applications (1:50-1:200)

  • Optimize incubation time and temperature (typically overnight at 4°C)

  • Consider using signal amplification systems for low-abundance phospho-epitopes

• Controls and validation:

  • Include positive control tissues with known c-Jun activation (e.g., tissues with activated stress pathways)

  • Use negative controls by omitting primary antibody

  • Validate specificity using blocking peptides or tissues from c-Jun knockout models

• Signal localization interpretation:

  • Nuclear localization is expected for transcriptionally active phospho-c-Jun

  • Be aware that some antibodies against phospho-c-Jun may show unexpected cytoplasmic staining patterns, as observed with the Y172 clone

  • Confirm nuclear localization with counterstains like DAPI

• Troubleshooting:

  • For weak signals, extend antibody incubation time or increase concentration

  • For high background, optimize blocking conditions and increase washing steps

  • Consider tyramide signal amplification for low-abundance phospho-epitopes

Following these guidelines will improve the specificity and sensitivity of phospho-c-Jun (T91) detection in tissue sections for immunohistochemical applications.

How can I distinguish between T91 and other phosphorylation sites in c-Jun experimentally?

Distinguishing between phosphorylation at T91 and other sites requires specialized techniques and careful experimental design:

• Site-specific phospho-antibodies:

  • Use antibodies that specifically recognize phospho-T91 without cross-reactivity to other phosphorylation sites

  • Validate antibody specificity using phosphomimetic mutants (T91D/E) and phospho-deficient mutants (T91A)

  • Consider simultaneous probing with different phospho-specific antibodies to compare phosphorylation patterns

• Phosphorylation kinetics analysis:

  • Perform time-course experiments as T91 phosphorylation occurs later than S63/S73 phosphorylation

  • Use time-resolved NMR spectroscopy to monitor phosphorylation events in real-time

  • Compare phosphorylation rates using quantitative western blotting with site-specific antibodies

• Mutational analysis:

  • Generate single-site mutants (T91A) to eliminate specific phosphorylation events

  • Create compound mutants (e.g., S63A/S73A) to isolate T91/T93 phosphorylation

  • Use the TTSS variant (S63T/S73T/T91S/T93S) to evaluate the impact of amino acid identity on phosphorylation patterns

• Mass spectrometry approaches:

  • Use phosphopeptide mapping with liquid chromatography-tandem mass spectrometry (LC-MS/MS)

  • Apply multiple reaction monitoring (MRM) for quantitative analysis of site-specific phosphorylation

  • Consider phospho-enrichment techniques prior to mass spectrometry analysis

These methodological approaches provide complementary information for distinguishing T91 phosphorylation from modifications at other sites on the c-Jun protein.

How does the temporal order of c-Jun phosphorylation affect its transcriptional activity?

The temporal sequence of c-Jun phosphorylation creates a dynamic regulation system that modulates its transcriptional activity in multiple ways:

• Sequential activation model:

  • The established order of phosphorylation (S63 > S73 > T91 ≈ T93) creates a temporal gradient of c-Jun activation

  • This may enable differential activation of early and late response genes based on phosphorylation status

  • The rapid phosphorylation at S63 likely initiates transcriptional activation, while later T91/T93 phosphorylation may modulate or terminate certain responses

• Conformational effects on DNA binding:

  • T91/T93 phosphorylation induces conformational changes that affect c-Jun's interaction with DNA and transcriptional co-factors

  • These conformational changes potentially create different "versions" of activated c-Jun with distinct target gene preferences

  • The timing of these conformational changes provides a mechanism for shifting transcriptional programs during extended signaling events

• Impact on protein-protein interactions:

  • Different phosphorylation states may preferentially interact with specific FOS family members or other AP-1 complex components

  • The temporal sequence can regulate the composition of AP-1 complexes formed at different time points after stimulus

  • This enables fine-tuning of transcriptional responses through differential partner recruitment

• Regulation of protein stability and turnover:

  • The phosphorylation sequence affects protein half-life through modulating ubiquitination and degradation

  • Later phosphorylation events (T91/T93) may trigger feedback mechanisms that attenuate c-Jun activity

This complex temporal regulation allows cells to translate the duration and intensity of upstream signals into appropriate transcriptional responses, providing a mechanism for contextual gene expression control.

What is the relationship between T91 phosphorylation and JNK binding efficiency?

The relationship between T91 phosphorylation and JNK binding involves spatial and mechanistic factors that influence phosphorylation efficiency:

• D-motif proximity effects:

  • Research has demonstrated that the relative position of the D-motif (MAPK binding motif, residues 32-50) significantly affects phosphorylation efficiency at different sites

  • T91 is located farther from the D-motif than S63/S73, contributing to its slower phosphorylation rate

  • Experimental transposition of the D-motif (mDock and cDock constructs) altered phosphorylation kinetics, confirming the importance of spatial relationships

• Binding dynamics model:

  • JNK initially binds to the D-motif of c-Jun

  • After binding, phosphorylation occurs in a distance-dependent manner, with sites closer to the D-motif (S63/S73) being phosphorylated more efficiently than distant sites (T91/T93)

  • This "tethered" mechanism creates the observed gradient of phosphorylation rates

• Processivity considerations:

  • JNK shows limited processivity in c-Jun phosphorylation, requiring multiple binding events to complete phosphorylation at all sites

  • The need for dissociation and rebinding contributes to the temporal sequence of phosphorylation

  • This mechanism allows for regulation at each step through competing phosphatases or other binding partners

• Structural consequences of partial phosphorylation:

  • Initial phosphorylation events may induce subtle conformational changes that affect subsequent JNK binding efficiency

  • These structural alterations could either enhance or inhibit access to remaining phosphorylation sites

Understanding this relationship provides insights into the molecular mechanisms underlying the ordered phosphorylation of c-Jun and has implications for developing interventions that could modulate specific phosphorylation events.

How do mutations in c-Jun phosphorylation sites affect cellular signaling outcomes?

Mutations in c-Jun phosphorylation sites create diverse cellular signaling alterations with significant biological consequences:

These mutations reveal several key insights about c-Jun signaling:

• Site-specific functions: Different phosphorylation sites control distinct aspects of c-Jun activity, from transcriptional activation (S63/S73) to conformational regulation (T91/T93) .

• Temporal importance: The sequence and timing of phosphorylation events are functionally significant, as demonstrated by the altered signaling patterns in the TTSS variant .

• Pathway integration: Mutations in c-Jun phosphorylation sites affect its role in integrating multiple signaling pathways, including stress responses, apoptosis regulation, and cellular differentiation .

• Context-dependent outcomes: The consequences of phosphorylation site mutations vary depending on cell type and stimulus, highlighting the context-specific nature of c-Jun function.

These findings demonstrate that c-Jun phosphorylation represents a sophisticated regulatory system where specific patterns of modification enable precise control of diverse cellular responses.

How do different JNK isoforms affect the pattern of c-Jun T91 phosphorylation?

Different JNK isoforms (JNK1, JNK2, JNK3) exhibit distinct patterns of interaction with c-Jun that influence T91 phosphorylation:

• Isoform-specific phosphorylation kinetics:

  • Both JNK1 and JNK2 have been shown to phosphorylate c-Jun at T91, but with some differences in efficiency

  • Time-resolved NMR experiments demonstrated that JNK1 and JNK2 both phosphorylate c-Jun sites in the order S63 > S73 > T91 ≈ T93, but the absolute rates may differ between isoforms

  • JNK3, predominantly expressed in neurons and cardiac tissue, may have unique phosphorylation patterns relevant to these specialized cell types

• Binding affinity differences:

  • JNK isoforms show different affinities for the D-motif of c-Jun

  • These binding differences affect the efficiency of phosphorylation at distal sites like T91

  • The degree of processivity (ability to perform multiple phosphorylation events before dissociating) varies between JNK isoforms

• Tissue-specific considerations:

  • The predominant JNK isoform varies by tissue type, creating tissue-specific patterns of c-Jun phosphorylation

  • In neurons, where JNK3 is abundant, T91 phosphorylation may occur with different kinetics than in tissues where JNK1/2 predominate

  • These differences contribute to tissue-specific responses to stimuli that activate the JNK-c-Jun pathway

• Therapeutic implications:

  • Isoform-specific inhibitors may selectively block certain patterns of c-Jun phosphorylation

  • Understanding the isoform-specific patterns aids in developing targeted interventions for conditions involving aberrant c-Jun activation

These isoform-specific differences highlight the complexity of c-Jun regulation and suggest that the pattern of T91 phosphorylation may vary depending on the cellular context and the specific JNK isoforms expressed.

What techniques can resolve contradictory data about T91 phosphorylation in different experimental systems?

When facing contradictory results regarding T91 phosphorylation across different experimental systems, several advanced techniques and methodological approaches can help resolve discrepancies:

• Standardized phosphorylation analysis:

  • Apply multiple detection methods in parallel (western blotting, mass spectrometry, NMR)

  • Use the same antibody clones across experiments with validated specificity controls

  • Implement absolute quantification methods with phosphopeptide standards

• Cell type and context normalization:

  • Compare phosphorylation in identical cell types under standardized culture conditions

  • Account for variations in basal JNK activity across cell types

  • Normalize for differences in c-Jun expression levels between systems

• Stimulus calibration:

  • Establish dose-response curves for various stimuli (anisomycin, UV, growth factors)

  • Measure upstream JNK activation to ensure comparable pathway activation

  • Create time-course profiles with multiple sampling points to capture transient phosphorylation events

• Advanced analytical approaches:

  • Apply phosphoproteomics with multiple enrichment strategies

  • Use parallel reaction monitoring (PRM) mass spectrometry for site-specific quantification

  • Implement single-cell phosphorylation analysis to account for cellular heterogeneity

• Mathematical modeling:

  • Develop kinetic models incorporating known parameters of JNK-c-Jun interactions

  • Apply sensitivity analysis to identify parameters that might explain system-specific variations

  • Use computational approaches to integrate data from multiple experimental systems

A systematic application of these approaches can help identify whether contradictory data stem from methodological differences, biological variations, or context-dependent regulation of T91 phosphorylation across experimental systems.

How does the intrinsically disordered nature of c-Jun TAD influence T91 phosphorylation dynamics?

The intrinsically disordered nature of the c-Jun transactivation domain (TAD) creates unique regulatory features that influence T91 phosphorylation dynamics:

• Structural flexibility implications:

  • NMR studies confirm that c-Jun TAD (residues 1-151) containing all four phosphorylation sites exhibits characteristics of an intrinsically disordered protein

  • The narrow chemical shift dispersion in 2D 1H, 15N correlation spectra and secondary chemical shift analysis reveal no significant populations of secondary structure

  • This disorder allows c-Jun to adopt multiple conformations, influencing the accessibility of T91 to kinases and phosphatases

• Coupled folding and binding mechanisms:

  • The disordered nature of c-Jun TAD likely enables coupled folding and binding when interacting with JNK

  • This mechanism allows for high-specificity but low-affinity interactions that facilitate the transient nature of signaling events

  • The disorder-to-order transition upon JNK binding may create a sequential exposure of phosphorylation sites, contributing to the observed phosphorylation order

• Phosphorylation-induced conformational changes:

  • Initial phosphorylation events can induce local structural changes that affect the accessibility of subsequent sites like T91

  • The addition of phosphate groups to disordered regions can promote local structure formation through charge interactions

  • These phosphorylation-dependent conformational changes contribute to the sequential and regulated nature of c-Jun activation

• Impact on interaction networks:

  • The disordered TAD enables c-Jun to interact with multiple partners through different binding modes

  • T91 phosphorylation within this disordered context may serve as a molecular switch that reconfigures the interaction landscape

  • The flexible nature allows for integration of multiple signals through combinatorial post-translational modifications

Understanding the relationship between intrinsic disorder and phosphorylation dynamics provides insights into how c-Jun achieves both specificity and adaptability in its regulatory functions through controlled T91 phosphorylation.

How can phospho-c-Jun (T91) be used as a biomarker in disease research?

Phospho-c-Jun (T91) has emerging potential as a biomarker in various disease contexts due to its specific regulation and functional implications:

• Cancer research applications:

  • c-Jun is involved in colorectal cancer through KRAS-mediated transcriptional activation of USP28

  • The specific pattern of T91 phosphorylation relative to other sites may serve as an indicator of aberrant JNK pathway activation in tumors

  • Monitoring the ratio of different phosphorylated forms (pT91 vs. pS63/pS73) could provide insights into tumor progression mechanisms

• Neurodegenerative disease research:

  • c-Jun phosphorylation patterns are altered in models of neurodegeneration

  • The Y172 antibody's specific staining pattern in motoneurons may be relevant to understanding synapse-specific processes in motor neuron diseases

  • T91 phosphorylation status could serve as an indicator of stress response activation in neuronal populations

• Inflammatory condition assessment:

  • c-Jun regulates inflammatory gene expression through AP-1 complexes

  • T91 phosphorylation dynamics may reflect the activation state of specific inflammatory pathways

  • Temporal analysis of T91 phosphorylation could help distinguish acute from chronic inflammatory states

• Methodological considerations for biomarker development:

  • Standardize detection methods for consistent quantification across samples

  • Establish normal ranges of T91 phosphorylation in relevant tissues

  • Develop multiplex assays that simultaneously measure multiple phosphorylation sites to create "phosphorylation signatures"

• Validation requirements:

  • Correlate T91 phosphorylation with clinical outcomes in patient cohorts

  • Compare with established biomarkers to determine added diagnostic or prognostic value

  • Verify stability of the phospho-epitope under various sample processing conditions

These applications highlight the potential utility of phospho-c-Jun (T91) as a specific biomarker that reflects not just pathway activation but also the temporal and qualitative nature of cellular stress responses in disease contexts.

What role does T91 phosphorylation play in the transition between neuronal survival and death decisions?

T91 phosphorylation of c-Jun contributes to the complex regulatory network governing neuronal fate decisions:

• Dual function in neuronal contexts:

  • c-Jun has been reported to function as a regulator of both neuronal death and survival/protection/regeneration pathways

  • The phosphorylation status at T91, in combination with other sites, may act as a molecular switch between these opposing functions

  • The timing of T91 phosphorylation relative to other sites potentially determines whether pro-survival or pro-death pathways are activated

• Integration with survival pathways:

  • In some neuronal contexts, c-Jun activation contributes to regenerative responses after injury

  • The specific combination of phosphorylation at T91 and other sites may determine whether c-Jun associates with neuroprotective gene promoters

  • The slower kinetics of T91 phosphorylation might create a temporal window during which protective programs can be initiated before potential transition to apoptotic pathways

• Cross-talk with apoptotic machinery:

  • c-Jun can regulate FASLG/CD95L transcription in T cells, contributing to activation-induced cell death

  • Similar mechanisms may operate in neurons, with T91 phosphorylation potentially modulating the strength of this pro-apoptotic signal

  • The conformational changes induced by T91 phosphorylation could alter c-Jun's interaction with apoptotic gene promoters

• Spatial considerations in neurons:

  • The Y172 antibody (which recognizes phospho-c-Jun at Ser63) showed distinct cytoplasmic staining patterns in motoneurons, suggesting compartmentalized signaling

  • T91 phosphorylation might similarly exhibit spatial regulation within neuronal compartments (soma vs. dendrites vs. axons)

  • This spatial distribution could contribute to localized responses that determine survival or death outcomes

Understanding the specific role of T91 phosphorylation in neuronal fate decisions could provide new targets for interventions in neurodegenerative diseases and traumatic injuries by selectively modulating the protective versus destructive functions of c-Jun.

How might targeted modulation of T91 phosphorylation be achieved for therapeutic purposes?

Targeted modulation of c-Jun T91 phosphorylation represents a promising therapeutic strategy that could enable precise intervention in JNK-c-Jun signaling pathways:

• Structural-based inhibitor design:

  • Develop peptide inhibitors that mimic the region around T91 to competitively inhibit JNK-mediated phosphorylation

  • Design small molecules that bind to JNK and selectively interfere with T91 phosphorylation while preserving other functions

  • Utilize knowledge of the conformational changes induced by initial phosphorylation events to target T91 specifically

• Phosphorylation site-specific approaches:

  • Create bivalent inhibitors that target both the JNK D-motif binding region and regions specific to T91 recognition

  • Develop antibody-drug conjugates that recognize specific conformations of partially phosphorylated c-Jun

  • Apply engineered phosphatases with enhanced specificity for the T91 phosphorylation site

• Temporal modulation strategies:

  • Design time-released inhibitors that specifically target late-phase JNK activity when T91 phosphorylation normally occurs

  • Develop compounds that alter the kinetics of JNK-c-Jun interactions to specifically modulate T91 phosphorylation rates

  • Create oscillating inhibition systems that allow specific patterns of phosphorylation to occur while blocking others

• Cell type-specific delivery mechanisms:

  • Utilize tissue-specific delivery systems to target T91 modulation in specific cell populations

  • Develop cell-penetrating peptides conjugated to T91-modifying enzymes

  • Design conditional expression systems that respond to disease-specific signals to modulate T91 phosphorylation

• Potential therapeutic applications:

  • Cancer therapy: Targeting aberrant c-Jun signaling in tumors where it drives proliferation

  • Neurodegenerative diseases: Modulating the balance between protective and destructive c-Jun functions

  • Inflammatory conditions: Attenuating specific aspects of the inflammatory response by fine-tuning c-Jun activity

These approaches would enable more precise intervention in c-Jun signaling compared to general JNK inhibitors, potentially reducing side effects while preserving beneficial aspects of JNK-c-Jun signaling.