Phospho-RELA (Ser281) Antibody

What is the role of Ser281 phosphorylation in NF-κB p65 (RELA) signaling?

Serine 281 phosphorylation of NF-κB p65 is one of several key phosphorylation sites that regulate transcriptional activity during inflammatory responses. Research has shown that during inflammation, phosphorylation at Ser-281 (along with other sites including Ser-276, Ser-311, Ser-468, Ser-529, Ser-536, and Thr-435) stimulates transcriptional activity of the NF-κB complex . This post-translational modification is part of the complex regulatory network that controls NF-κB-mediated gene expression in response to various stimuli, particularly those related to inflammatory conditions.

NF-κB serves as a pleiotropic transcription factor present in almost all cell types and functions as the endpoint of numerous signal transduction events. These events are initiated by a wide range of stimuli related to biological processes including inflammation, immunity, differentiation, cell growth, tumorigenesis, and apoptosis . Understanding the specific role of Ser281 phosphorylation helps researchers elucidate the fine-tuning mechanisms of this crucial signaling pathway.

How does Phospho-RELA (Ser281) differ from other phosphorylation sites on the p65 subunit?

While multiple phosphorylation sites exist on the p65 subunit, each site has distinct functional implications for NF-κB signaling. Ser281 phosphorylation occurs within the amino acid range 247-296 of the human NF-κB p65 protein . This region is distinct from other well-studied phosphorylation sites such as Ser536 (commonly associated with canonical NF-κB activation).

Different phosphorylation sites can influence various aspects of NF-κB function:

• Ser276 and Ser311: Often associated with DNA binding capacity

• Ser468 and Ser536: Typically linked to transcriptional activation

• Thr254: Involved in stabilization and nuclear translocation

• Ser281: Stimulates transcriptional activity during inflammatory responses

These site-specific modifications allow for nuanced regulation of NF-κB activity in different cellular contexts and in response to different stimuli, creating a complex regulatory network that fine-tunes inflammatory and immune responses.

What is the molecular weight and structure of the NF-κB p65 protein recognized by this antibody?

The NF-κB p65 protein (RELA) has a calculated molecular weight of approximately 60-65 kDa. According to the product information, the calculated molecular weight is 60219 Da or approximately 65 kDa as noted in other sources . The protein contains a Rel-like domain that facilitates DNA binding and dimerization with other NF-κB family members.

The NF-κB complex typically exists as a homo- or heterodimeric structure formed by Rel-like domain-containing proteins including RELA/p65, RELB, NFKB1/p105, NFKB1/p50, REL, and NFKB2/p52. The heterodimeric RELA-NFKB1 complex appears to be the most abundant form . These dimers bind to κB sites in the DNA of their target genes, with different dimer combinations exhibiting distinct preferences for specific κB sites, binding with variable affinity and specificity.

What are the recommended applications for Phospho-RELA (Ser281) antibodies in research?

Based on the search results, Phospho-RELA (Ser281) antibodies are validated for several research applications:

When designing experiments, researchers should optimize antibody concentrations for their specific experimental conditions. The dilution ranges provided serve as starting points, and the actual working concentration may vary depending on the specific tissue, cell type, and detection method employed .

How should samples be prepared for optimal detection of phospho-Ser281 in Western blot analysis?

For optimal detection of phosphorylated NF-κB p65 at Ser281 in Western blot analysis, researchers should follow these methodological guidelines:

• Sample preparation: Cells or tissues should be lysed in a buffer containing phosphatase inhibitors (e.g., sodium fluoride, sodium orthovanadate, β-glycerophosphate) to preserve phosphorylation status. Protease inhibitors should also be included to prevent protein degradation.

• Protein denaturation: Samples should be denatured in SDS-containing buffer with reducing agents (e.g., β-mercaptoethanol or DTT) and heated at 95°C for 5 minutes.

• Gel electrophoresis conditions: Use 8-10% SDS-PAGE gels for optimal separation of proteins around 65 kDa.

• Transfer and blocking: After transferring proteins to a PVDF or nitrocellulose membrane, block with 5% (w/v) BSA in TBST for optimal results when working with phospho-specific antibodies .

• Primary antibody incubation: Incubate membranes overnight at 4°C with the Phospho-NF-κB p65 (Ser281) antibody at the recommended dilution in blocking buffer .

• Controls: Include both phosphorylated and non-phosphorylated controls to verify antibody specificity.

Note that specific band detection at approximately 60-65 kDa confirms the presence of phosphorylated p65 at Ser281 .

What experimental models are suitable for studying Ser281 phosphorylation in the context of inflammation?

Several experimental models have been employed to study Ser281 phosphorylation in inflammatory contexts:

• Cell culture models:

  • Retinal endothelial cells (RECs) and Müller cells exposed to high glucose conditions to mimic diabetic retinopathy

  • Immune cells (macrophages, dendritic cells) stimulated with inflammatory agents like LPS, TNF-α, or IL-1β

  • Epithelial or endothelial cells in inflammatory disease models

• Animal models:

  • The antibody reacts with human, mouse, and rat samples , making these species suitable for in vivo studies

  • Models of chronic inflammation, including diabetic retinopathy, arthritis, or inflammatory bowel disease

• Human tissue samples:

  • Paraffin-embedded or frozen tissue sections from patients with inflammatory conditions

  • Biopsy samples from affected tissues in various inflammatory diseases

When designing experiments, researchers should consider the timeframe of NF-κB activation and phosphorylation events, which often occur rapidly (within minutes to hours) following stimulation. Sequential sampling is recommended to capture the dynamic nature of these phosphorylation events.

How should Phospho-RELA (Ser281) antibodies be stored and handled to maintain activity?

Proper storage and handling of Phospho-RELA (Ser281) antibodies are crucial for maintaining their activity and specificity:

• Long-term storage: Store antibodies at -20°C for up to one year from the date of receipt . The antibodies are typically formulated in PBS containing 50% glycerol, 0.5% BSA, and 0.02% sodium azide , which helps maintain stability during freezing.

• Short-term storage: For frequent use over the course of a month, antibodies can be stored at 4°C .

• Avoid freeze-thaw cycles: Repeated freeze-thaw cycles should be avoided as they can denature antibodies and reduce their activity . Aliquoting antibodies upon receipt is recommended if they will be used for multiple experiments over time.

• Working dilutions: Prepare working dilutions fresh on the day of the experiment and store any remaining diluted antibody at 4°C for short periods only.

• Handling precautions: When handling the antibody, maintain sterile conditions and avoid contamination. Note that these products contain sodium azide (0.02%), which is toxic and should be handled with appropriate safety measures .

What controls should be included when using Phospho-RELA (Ser281) antibodies?

For rigorous experimental design, several controls should be included when using Phospho-RELA (Ser281) antibodies:

• Positive controls:

  • Cells or tissues treated with known NF-κB activators (e.g., TNF-α, IL-1β, LPS)

  • Recombinant phosphorylated p65 protein (if available)

• Negative controls:

  • Unstimulated cells or tissues (basal conditions)

  • Samples treated with phosphatase to remove phosphorylation

  • Samples from p65 knockout models (if available)

• Antibody controls:

  • Primary antibody omission control

  • Isotype control (rabbit IgG at equivalent concentration)

  • Blocking peptide competition assay using the synthesized peptide derived from human NF-κB p65 around the phosphorylation site of Ser281 (amino acid range: 247-296)

• Specificity controls:

  • Parallel detection with total p65 antibody to normalize phospho-specific signals

  • Comparison with other phospho-specific antibodies targeting different p65 sites

These controls help validate the specificity of the observed signals and ensure that the detected phosphorylation is authentic and biologically relevant.

What are the differences between polyclonal and monoclonal Phospho-RELA (Ser281) antibodies?

The Phospho-RELA (Ser281) antibodies described in the search results are polyclonal antibodies produced in rabbits . Understanding the differences between polyclonal and monoclonal antibodies is important for experimental design:

Polyclonal Phospho-RELA (Ser281) antibodies:

• Derived from multiple B-cell lineages in immunized rabbits

• Recognize multiple epitopes on the phosphorylated region (amino acids 247-296)

• Offer potentially higher sensitivity due to binding of multiple epitopes

• May have batch-to-batch variation requiring validation for each lot

• Typically affinity-purified from rabbit antiserum using epitope-specific immunogen

Monoclonal Phospho-RELA (Ser281) antibodies:

• Would be derived from a single B-cell clone (not mentioned in the search results)

• Would recognize a single epitope on the phosphorylated Ser281 region

• Would offer higher specificity but potentially lower sensitivity

• Would have higher consistency between batches

The choice between polyclonal and monoclonal antibodies depends on the specific research question and application. Polyclonal antibodies may be preferred for applications where signal amplification is important (e.g., IHC of weakly expressed proteins), while monoclonal antibodies would be advantageous for applications requiring high specificity and consistency.

How does Ser281 phosphorylation coordinate with other post-translational modifications of NF-κB p65?

NF-κB p65 undergoes multiple post-translational modifications (PTMs) that collectively regulate its activity. Ser281 phosphorylation operates within this complex network:

• Coordination with other phosphorylation events:
  Research has shown that during inflammation, phosphorylation occurs at multiple sites including Ser-276, Ser-281, Ser-311, Ser-468, Ser-529, Ser-536, and Thr-435, which collectively stimulate transcriptional activity . These different phosphorylation events may occur sequentially or simultaneously depending on the stimulus and cellular context.

• Cross-talk with other PTMs:
  Beyond phosphorylation, NF-κB p65 is regulated by acetylation, methylation, ubiquitination, and SUMOylation. The phosphorylation status of Ser281 may influence or be influenced by these other modifications. For example:

  • Phosphorylation may create binding sites for acetyltransferases

  • Phosphorylation may prevent ubiquitin-mediated degradation

  • Certain phosphorylation patterns may prime the protein for subsequent modifications

• Temporal dynamics:
  The timing of Ser281 phosphorylation relative to other modifications is an important consideration in understanding NF-κB regulation. Some phosphorylation events occur early in the activation process, while others may be delayed and associated with the resolution phase of inflammation.

Advanced research approaches to study this coordination include mass spectrometry-based proteomics, proximity ligation assays, and the use of phospho-mimetic or phospho-deficient mutants in functional studies.

What kinases are responsible for phosphorylating RELA at Ser281, and how are they regulated?

• Potential kinases:

  • Protein Kinase A (PKA)

  • Protein Kinase C (PKC) isoforms

  • Mitogen-Activated Protein Kinases (MAPKs)

  • IκB Kinases (IKKs)

  • Glycogen Synthase Kinase 3 (GSK3)

• Regulatory mechanisms:
  These kinases are typically regulated by:

  • Upstream signaling cascades initiated by cytokines (TNF-α, IL-1β)

  • Pattern recognition receptors (TLRs, NLRs)

  • Growth factor receptors

  • Stress-activated pathways

  • Cross-talk with other signaling pathways

• Research approaches to identify responsible kinases:

  • In vitro kinase assays with recombinant proteins

  • Kinase inhibitor studies in cellular models

  • Phosphorylation site prediction algorithms followed by experimental validation

  • Genetic approaches (kinase knockdown/knockout) combined with phospho-specific antibody detection

  • Proximity ligation assays to detect kinase-substrate interactions

Identifying the specific kinases responsible for Ser281 phosphorylation would provide valuable insights into the regulation of NF-κB activity and potentially offer new therapeutic targets for modulating inflammatory responses.

How does Ser281 phosphorylation influence NF-κB p65 binding to specific genomic regions?

The influence of Ser281 phosphorylation on NF-κB p65 binding to specific genomic regions is a sophisticated aspect of transcriptional regulation:

• DNA binding selectivity:
  Phosphorylation of p65 can alter its affinity for different κB sites in the genome. The search results indicate that different NF-κB dimer combinations have distinct preferences for different κB sites, binding with distinguishable affinity and specificity . Ser281 phosphorylation may contribute to this selectivity by:

  • Inducing conformational changes that affect DNA-binding domain structure

  • Altering the electrostatic properties of the protein-DNA interface

  • Modifying interactions with other transcription factors or cofactors

• Chromatin association:
  The search results mention that p65 associates with chromatin at the NF-κB promoter region via association with DDX1 . Ser281 phosphorylation might affect these interactions by:

  • Regulating recruitment of chromatin-modifying enzymes

  • Influencing interactions with nucleosomes or chromatin remodeling complexes

  • Affecting the stability of p65 binding to enhancer or promoter regions

• Gene-specific effects:
  Ser281 phosphorylation may have gene-specific effects on NF-κB target genes, contributing to the selective regulation of inflammatory gene expression. This could be studied using:

  • ChIP-seq experiments comparing wild-type and phospho-mutant p65

  • Genome-wide approaches like CUT&RUN or CUT&Tag with phospho-specific antibodies

  • Reporter gene assays with different κB site variants

Understanding how Ser281 phosphorylation influences genomic binding patterns would provide insights into the mechanisms of selective gene regulation by NF-κB during different inflammatory conditions.

What are common issues when using Phospho-RELA (Ser281) antibodies in immunohistochemistry, and how can they be addressed?

Several technical challenges may arise when using Phospho-RELA (Ser281) antibodies for immunohistochemistry (IHC):

• High background staining:

  • Cause: Insufficient blocking, excessive antibody concentration, or non-specific binding

  • Solution: Increase blocking time (60-90 minutes), use 5% normal serum from the same species as the secondary antibody, optimize primary antibody dilution (start with 1:100-1:300 as recommended ), and include 0.1-0.3% Triton X-100 in the blocking buffer for better penetration

• Weak or absent signal:

  • Cause: Inadequate antigen retrieval, low phosphorylation levels, or epitope masking

  • Solution: Optimize antigen retrieval methods (try both heat-induced epitope retrieval with citrate buffer pH 6.0 and protease-based methods), ensure tissues are fixed appropriately (10% neutral buffered formalin for 24-48 hours), and verify that samples were collected and processed quickly to preserve phosphorylation status

• Non-specific staining:

  • Cause: Cross-reactivity with other phospho-epitopes or endogenous peroxidase activity

  • Solution: Pre-absorb the antibody with non-phosphorylated peptide, block endogenous peroxidase activity with 0.3% H₂O₂ in methanol, and include additional washing steps with high-salt PBS

• Inconsistent results between experiments:

  • Cause: Variations in tissue processing, antibody lots, or incubation conditions

  • Solution: Standardize tissue processing protocols, validate each new antibody lot, and maintain consistent incubation times and temperatures

When optimizing IHC protocols, it's advisable to include known positive controls (e.g., tissues from animals treated with inflammatory stimuli) and appropriate negative controls to validate staining specificity.

How can researchers validate the specificity of Phospho-RELA (Ser281) antibody signals in their experimental system?

Validating antibody specificity is crucial for ensuring the reliability of experimental results. For Phospho-RELA (Ser281) antibodies, consider these validation approaches:

• Phosphatase treatment control:

  • Treat duplicate samples with lambda phosphatase before immunoblotting or immunostaining

  • Loss of signal after phosphatase treatment confirms phospho-specificity

• Stimulation-dependent phosphorylation:

  • Compare samples from unstimulated cells/tissues with those stimulated with known NF-κB activators (TNF-α, IL-1β, LPS)

  • Increased phospho-Ser281 signal after stimulation supports antibody specificity

• Genetic approaches:

  • Use RELA knockout/knockdown models as negative controls

  • Generate phospho-deficient mutants (S281A) and compare to wild-type

  • Utilize phospho-mimetic mutants (S281D or S281E) as positive controls

• Peptide competition assay:

  • Pre-incubate the antibody with the immunizing phosphopeptide (amino acids 247-296 containing phosphorylated Ser281)

  • Specific signals should be abolished or significantly reduced

• Multi-method confirmation:

  • Verify phosphorylation using alternative methods like mass spectrometry

  • Compare results across different applications (WB, IHC, IF) to ensure consistency

  • Use multiple antibodies targeting the same phospho-site if available

• Kinase inhibition:

  • Treat samples with inhibitors of kinases predicted to target Ser281

  • Reduction in signal supports specificity for the phosphorylated form

These validation approaches should be adapted to the specific experimental system and research question to ensure robust and reliable results.

What methodological considerations are important when studying the dynamics of Ser281 phosphorylation in response to inflammatory stimuli?

Studying the dynamics of Ser281 phosphorylation requires careful methodological considerations:

• Temporal resolution:

  • NF-κB activation and phosphorylation occur rapidly (minutes to hours)

  • Design time-course experiments with appropriate sampling intervals (e.g., 0, 5, 15, 30, 60, 120 minutes, 4, 8, 24 hours)

  • Consider both early (activation) and late (resolution) phases of the inflammatory response

• Stimulus considerations:

  • Different inflammatory stimuli may induce distinct phosphorylation patterns

  • Titrate stimulus concentration to avoid oversaturation of signaling pathways

  • Consider using physiologically relevant stimuli for the cell type or tissue under investigation

• Sample preservation:

  • Rapid sample processing is critical to preserve phosphorylation status

  • Use phosphatase inhibitors (sodium fluoride, sodium orthovanadate, β-glycerophosphate) in all buffers

  • For tissue samples, consider snap-freezing or using specialized phospho-preserving fixatives

• Quantification methods:

  • Use appropriate quantification methods for different techniques:

    • Western blot: Densitometry normalized to total p65 levels

    • IHC/IF: Digital image analysis with appropriate controls for background subtraction

    • Flow cytometry: Median fluorescence intensity relative to unstained controls

• Single-cell versus population analyses:

  • Consider that NF-κB signaling can be heterogeneous within cell populations

  • Where possible, complement population-based approaches (Western blot) with single-cell techniques (IF, flow cytometry)

• Pathway cross-talk:

  • Account for cross-talk with other signaling pathways that may influence Ser281 phosphorylation

  • Consider using specific pathway inhibitors to dissect regulatory mechanisms

By addressing these methodological considerations, researchers can obtain more reliable and physiologically relevant data on the dynamics of Ser281 phosphorylation in inflammatory contexts.