Phospho-RUNX1 (Ser435) Antibody

What is the molecular basis of RUNX1 Ser435 phosphorylation and its biological significance?

RUNX1 (Runt-related transcription factor 1) is a key transcription factor that forms the heterodimeric complex core-binding factor (CBF) with CBFB. The phosphorylation at Serine 435 represents an important post-translational modification that modulates RUNX1 activity and function. This phosphorylation site is located within the 401-450 amino acid region of human RUNX1 .

RUNX1 and its binding partner CBFB recognize the core consensus binding sequence 5'-TGTGGT-3' (or rarely 5'-TGCGGT-3') within regulatory regions of target genes via the runt domain. The CBF complex binds to core sites of numerous enhancers and promoters, including those for murine leukemia virus, polyomavirus enhancer, T-cell receptor enhancers, and IL-3 and GM-CSF promoters . Phosphorylation at Ser435 likely affects these DNA-binding properties and subsequent transcriptional regulation, similar to how other phosphorylation events modulate RUNX1 function.

What are the key specifications of commercially available Phospho-RUNX1 (Ser435) antibodies?

How is specificity ensured for Phospho-RUNX1 (Ser435) antibodies?

Phospho-RUNX1 (Ser435) antibodies are designed to detect endogenous RUNX1 protein only when phosphorylated at Ser435, not in its unphosphorylated state . The specificity is achieved through:

• Targeted immunogen design: The antibodies are raised against synthetic peptides derived specifically from the human AML1 (RUNX1) around the phosphorylation site of Ser435 .

• Precise epitope mapping: The immunogen typically contains the peptide sequence S-N-S(p)-P-T, where S(p) represents the phosphorylated serine at position 435 .

• Affinity purification: The antibodies undergo affinity purification using epitope-specific immunogens to enrich for antibodies that specifically recognize the phosphorylated form .

• Validation testing: Manufacturers verify specificity through comparative analysis between phosphorylated and non-phosphorylated protein samples.

What are the recommended protocols for using Phospho-RUNX1 (Ser435) antibody in Western blot analysis?

When using Phospho-RUNX1 (Ser435) antibody for Western blot analysis, researchers should follow these methodological steps:

• Sample preparation:

  • Lyse cells in buffer containing phosphatase inhibitors to preserve phosphorylation status

  • Include positive controls (cells known to express phosphorylated RUNX1) and negative controls (phosphatase-treated samples)

• Gel electrophoresis and transfer:

  • Separate proteins using SDS-PAGE (typically 8-10% gels)

  • Transfer to PVDF or nitrocellulose membrane

• Blocking and antibody incubation:

  • Block membrane with 5% BSA in TBST (not milk, which contains phosphatases)

  • Dilute primary antibody 1:500-1:2000 in blocking buffer

  • Incubate overnight at 4°C

  • Wash with TBST

  • Incubate with appropriate HRP-conjugated secondary antibody

• Detection:

  • Use enhanced chemiluminescence (ECL) for detection

  • Expected molecular weight: ~49-55 kDa (calculated)

  • Some variants may appear at approximately 70 kDa

• Controls and validation:

  • Include total RUNX1 antibody on parallel blots to normalize phosphorylation levels

  • Consider lambda phosphatase treatment of duplicate samples to confirm phospho-specificity

How can researchers optimize ELISA protocols using Phospho-RUNX1 (Ser435) antibody?

For ELISA applications using Phospho-RUNX1 (Ser435) antibody, the following optimization steps are recommended:

• Coating concentration:

  • Determine optimal coating concentration of capture antibody (if using as capture)

  • When using as detection antibody, ensure appropriate antigen immobilization

• Antibody dilution:

  • Start with the recommended dilution of 1:10000 for ELISA applications

  • Perform titration experiments (1:5000 to 1:20000) to determine optimal concentration

• Buffer optimization:

  • Use phosphate-buffered saline with 0.05% Tween-20 (PBST) for washes

  • Consider 1% BSA or 3-5% non-fat dry milk in PBST for blocking

  • Include phosphatase inhibitors in sample buffers

• Signal development and quantification:

  • Use appropriate substrate (TMB for HRP-conjugated secondary antibodies)

  • Establish standard curves with recombinant phosphorylated RUNX1 protein

  • Determine linear range of detection

• Validation controls:

  • Include phosphorylated and non-phosphorylated RUNX1 controls

  • Consider phosphatase-treated samples as negative controls

How does phosphorylation at Ser435 compare with other RUNX1 phosphorylation sites in terms of functional impact?

RUNX1 undergoes multiple phosphorylation events that differentially regulate its function. Comparing Ser435 phosphorylation with other sites:

While Ser435 phosphorylation's specific functions are still being elucidated, research on other RUNX1 phosphorylation events suggests that it likely affects:

• Protein stability and degradation pathways

• Interaction with transcriptional co-regulators

• DNA binding capacity

• Transcriptional activation of target genes

Research on tyrosine phosphorylation by Src demonstrates that phosphorylation can increase RUNX1 transactivation through multiple mechanisms: increased stability, reduced histone deacetylase (HDAC) interaction, and increased DNA binding . Similar mechanisms may apply to Ser435 phosphorylation, though through different signaling pathways.

What experimental approaches can distinguish the specific effects of Ser435 phosphorylation from other RUNX1 modifications?

To isolate and study the specific effects of Ser435 phosphorylation on RUNX1 function, researchers can employ these advanced experimental approaches:

• Site-directed mutagenesis:

  • Generate Ser435 to alanine (S435A) mutants to prevent phosphorylation

  • Generate Ser435 to aspartate or glutamate (S435D/E) mutants to mimic constitutive phosphorylation

  • Compare these with wild-type RUNX1 in functional assays

• Phosphorylation-specific proteomic analysis:

  • Use mass spectrometry to quantify Ser435 phosphorylation levels in different cellular contexts

  • Perform phospho-enrichment using titanium dioxide or IMAC prior to MS analysis

  • Map the complete phosphorylation profile of RUNX1 to understand interplay between sites

• Kinase inhibitor studies:

  • Identify the kinase(s) responsible for Ser435 phosphorylation

  • Use specific kinase inhibitors to modulate Ser435 phosphorylation selectively

  • Monitor downstream effects on RUNX1 function

• Phosphorylation-specific interaction studies:

  • Perform co-immunoprecipitation experiments using wild-type and phospho-mutant RUNX1

  • Identify differential binding partners using mass spectrometry

  • Validate with direct binding assays

• Chromatin immunoprecipitation (ChIP) analysis:

  • Compare genomic binding profiles of wild-type, S435A, and S435D/E RUNX1 variants

  • Correlate binding changes with transcriptional outputs

  • Perform sequential ChIP to identify co-factor recruitment dependent on Ser435 phosphorylation

These approaches can be adapted from methodologies used to study tyrosine phosphorylation of RUNX1, which demonstrated that phosphorylation affects DNA binding to regulatory elements of target genes like Cebpa and Pu.1 .

What are the recommended approaches for studying RUNX1 Ser435 phosphorylation in hematopoietic development models?

To investigate RUNX1 Ser435 phosphorylation in hematopoietic development, researchers should consider these specialized approaches:

• In vitro hematopoietic differentiation systems:

  • Embryonic stem cell (ESC) or induced pluripotent stem cell (iPSC) differentiation

  • Conditional expression systems for wild-type vs. phospho-mutant RUNX1

  • Monitor lineage commitment using flow cytometry and single-cell transcriptomics

• Ex vivo primary cell culture:

  • Isolate hematopoietic stem and progenitor cells (HSPCs)

  • Transduce with lentiviral vectors expressing RUNX1 variants

  • Perform colony-forming assays to assess lineage potential

• In vivo models:

  • Generate knock-in mouse models with S435A or S435D mutations

  • Use conditional expression systems with hematopoietic-specific promoters

  • Analyze development of specific lineages at different stages

• Quantitative phosphorylation analysis:

  • Develop standardized protocols for sample collection and processing

  • Use phospho-flow cytometry to analyze Ser435 phosphorylation at single-cell level

  • Correlate phosphorylation status with differentiation markers

• Target gene analysis:

  • Perform RNA-seq after modulating Ser435 phosphorylation

  • Focus on known RUNX1 target genes like Cebpa and Pu.1

  • Validate with qRT-PCR and reporter assays

The importance of RUNX1 in hematopoiesis is well-established, with highest expression levels in thymus, bone marrow, and peripheral blood . Like other phosphorylation events, Ser435 phosphorylation likely plays a role in regulating RUNX1's ability to control hematopoietic development and differentiation.

How can researchers troubleshoot non-specific binding or weak signals when using Phospho-RUNX1 (Ser435) antibody?

When encountering issues with Phospho-RUNX1 (Ser435) antibody performance, consider these troubleshooting approaches:

Additional technical considerations:

• Perform phosphatase treatment controls to confirm signal specificity

• Include positive control samples from cells known to have high RUNX1 Ser435 phosphorylation

• Consider using enhanced detection systems for low abundance phospho-proteins

What considerations should be made when designing experiments to investigate the relationship between Ser435 phosphorylation and RUNX1's interaction with transcriptional machinery?

When studying how Ser435 phosphorylation affects RUNX1's interactions with transcriptional complexes, researchers should consider:

• Experimental system selection:

  • Choose cell lines with high endogenous RUNX1 expression (e.g., hematopoietic lines)

  • Consider systems where RUNX1 is known to be functionally important

  • Use models where phosphorylation can be modulated

• Protein-protein interaction studies:

  • Co-immunoprecipitation using Phospho-RUNX1 (Ser435) antibody

  • Compare immunoprecipitated complexes from phosphorylated vs. dephosphorylated samples

  • Consider proximity ligation assays for in situ detection of interactions

• Transcriptional complex analysis:

  • Investigate interactions with known RUNX1 partners (CBFB, HDACs)

  • Similar to tyrosine phosphorylation effects, Ser435 phosphorylation may affect HDAC interaction

  • Use chromatin immunoprecipitation followed by mass spectrometry (ChIP-MS) to identify differential recruitment of factors

• Functional readouts:

  • Luciferase reporter assays with RUNX1-responsive promoters

  • Gene expression analysis of known RUNX1 target genes

  • Analysis of histone modifications at RUNX1 target loci

• Structural considerations:

  • Predict structural changes induced by Ser435 phosphorylation

  • Consider how phosphorylation might affect protein conformation and interaction surfaces

  • Design truncation mutants to map interaction domains dependent on phosphorylation

Research on tyrosine phosphorylation shows that modification can reduce HDAC1 and HDAC3 interaction, increase protein stability, and enhance DNA binding . Experiments investigating Ser435 phosphorylation should be designed to test whether similar mechanisms apply.

What are the critical parameters for validating antibody specificity for Phospho-RUNX1 (Ser435) in different experimental contexts?

Rigorous validation of phospho-specific antibodies is crucial for experimental reliability. For Phospho-RUNX1 (Ser435) antibody, consider these validation approaches:

• Peptide competition assays:

  • Pre-incubate antibody with phosphorylated peptide (containing pSer435)

  • Pre-incubate with non-phosphorylated peptide as control

  • Compare signal reduction between conditions

• Phosphatase treatment controls:

  • Treat half of each sample with lambda phosphatase

  • Compare signal between treated and untreated samples

  • Signal should be eliminated in phosphatase-treated samples

• Genetic validation:

  • Use RUNX1 knockout or knockdown cells as negative controls

  • Express wild-type vs. S435A mutant RUNX1 in knockout background

  • Confirm absence of signal with S435A mutant

• Cross-reactivity assessment:

  • Test antibody against related phospho-proteins (other RUNX family members)

  • Evaluate performance in species mentioned in reactivity profile (human, mouse, rat)

  • Perform immunoblots with recombinant proteins

• Application-specific validation:

  • For Western blot: Verify single band at expected molecular weight (~49-55 kDa)

  • For ELISA: Establish standard curves with purified phospho-proteins

  • For immunoprecipitation: Confirm enrichment of phosphorylated protein

• Technical replication:

  • Compare results using different antibody lots

  • Test alternative phospho-specific antibodies targeting the same site

  • Validate key findings with orthogonal techniques (e.g., mass spectrometry)

Proper validation ensures that experimental observations truly reflect the biology of RUNX1 Ser435 phosphorylation rather than technical artifacts.

What emerging technologies could enhance the study of RUNX1 Ser435 phosphorylation dynamics in live cells?

Several cutting-edge approaches show promise for advancing our understanding of RUNX1 Ser435 phosphorylation:

• Phospho-specific biosensors:

  • Development of FRET-based biosensors specific for Ser435 phosphorylation

  • Real-time visualization of phosphorylation dynamics in living cells

  • Correlation with cellular processes and signaling events

• Proximity proteomics:

  • BioID or APEX2 fusion proteins with phospho-mutant RUNX1 variants

  • Mapping phosphorylation-dependent protein interaction networks

  • Identifying regulators and effectors of Ser435 phosphorylation

• Single-molecule imaging:

  • Super-resolution microscopy of phosphorylated RUNX1

  • Analysis of chromatin binding dynamics and residence time

  • Correlation with transcriptional bursting at target genes

• Phosphoproteomics with advanced multiplexing:

  • TMT or isobaric labeling for quantitative analysis across multiple conditions

  • Integration with other post-translational modifications

  • Systems-level analysis of phosphorylation networks

• CRISPR-based technologies:

  • Base editing to introduce S435A or S435D mutations in endogenous loci

  • CUT&RUN or CUT&Tag for high-resolution chromatin binding profiles

  • CRISPR activation/inhibition screens to identify regulators of Ser435 phosphorylation

These approaches could provide unprecedented insights into how Ser435 phosphorylation regulates RUNX1 function in normal development and disease contexts.

How might Phospho-RUNX1 (Ser435) antibodies be applied in clinical research contexts?

Phospho-RUNX1 (Ser435) antibodies could have valuable applications in clinical research:

• Biomarker development:

  • Assessment of RUNX1 Ser435 phosphorylation status in patient samples

  • Correlation with disease progression or treatment response

  • Potential prognostic indicator in hematological malignancies

• Therapeutic target validation:

  • Monitoring phosphorylation changes in response to kinase inhibitors

  • Identification of drugs that modulate RUNX1 phosphorylation

  • Correlation of phosphorylation status with functional outcomes

• Patient stratification:

  • Classification of patient samples based on RUNX1 phosphorylation patterns

  • Integration with other molecular markers

  • Development of personalized treatment approaches

• Therapy monitoring:

  • Serial assessment of RUNX1 phosphorylation during treatment

  • Correlation with minimal residual disease

  • Early identification of relapse or resistance mechanisms

• Drug discovery applications:

  • High-throughput screening assays for compounds affecting Ser435 phosphorylation

  • Target engagement studies for kinase inhibitors

  • Pharmacodynamic biomarker development