Phospho-MYC (S373) Antibody

What is Phospho-MYC (S373) Antibody and what specifically does it detect?

Phospho-MYC (S373) Antibody is a rabbit polyclonal antibody specifically designed to detect the MYC protein only when phosphorylated at serine 373. This antibody recognizes the post-translational modification state of MYC without cross-reactivity to unphosphorylated MYC at this site. The antibody is developed using a phospho-specific peptide corresponding to residues surrounding S373 of human c-Myc as the immunogen .

The antibody has high specificity for the phosphorylated form of MYC, allowing researchers to precisely analyze this particular phosphorylation state in various experimental contexts. Most commercially available versions are affinity-purified from rabbit antiserum using epitope-specific immunogens to ensure specificity .

What are the common applications for Phospho-MYC (S373) Antibody?

Phospho-MYC (S373) Antibody has been validated for several key research applications:

Each application requires specific optimization depending on sample type and experimental conditions .

What is the biological significance of MYC phosphorylation at serine 373?

MYC is a proto-oncogene and nuclear phosphoprotein that plays critical roles in cell cycle progression, apoptosis, and cellular transformation . Phosphorylation at serine 373 is a key regulatory mechanism that impacts:

• Regulation of MYC protein activity and stability

• DNA binding capability and transcriptional activity

• Protein-protein interactions, particularly with MAX, its heterodimeric partner

Research has demonstrated that the phosphorylation state at S373 affects the α-helical propensity of MYC protein structure. According to biophysical studies, the S373D phosphomimetic mutation results in a dissociation constant (Kᴅ) of 23.0 ± 9.0 nM for MAX binding, which is comparable but not identical to actual phosphorylation (approximately 4-fold difference) . This suggests phosphorylation at this site regulates MYC-MAX complex formation, which is essential for MYC's function as a transcription factor.

How should Phospho-MYC (S373) Antibody be stored and handled?

For optimal performance, follow these storage and handling recommendations:

• Store at -20°C upon receipt

• For long-term storage, keep at -20°C or -80°C in small aliquots to prevent freeze-thaw cycles

• For short-term storage (up to 6 months), maintain refrigerated at 2-8°C

• The antibody is typically supplied in PBS containing 50% glycerol, 0.5% BSA, and 0.02% sodium azide as stabilizers

• When handling, avoid repeated freeze-thaw cycles as this can reduce antibody activity and yield inconsistent results

Proper storage conditions are critical for maintaining antibody specificity and reactivity over time.

How does phosphorylation at S373 compare with other phosphorylation sites in MYC regulation?

MYC activity is regulated through multiple phosphorylation sites, with S373 functioning differently from other well-studied sites like T58 and S62:

Research indicates that while T58/S62 phosphorylation primarily regulates MYC protein stability through the ubiquitin-proteasome pathway via Fbw7 interaction, S373 phosphorylation appears more directly involved in modulating MYC's interaction with MAX and its transcriptional activity .

The combined effect of phosphorylation at both S373 and T400 would theoretically increase the Kᴅ for MAX binding to approximately 6 μM if the effects at both sites were independent, which is consistent with the lack of detectable binding in ITC experiments with the S373D/T400D double mutant .

What experimental controls should be included when using Phospho-MYC (S373) Antibody?

For rigorous research with phospho-specific antibodies, include these essential controls:

• Phosphatase treatment control: Treat a portion of your sample with lambda phosphatase to demonstrate that antibody reactivity is lost when phosphorylation is removed.

• Phospho-mimetic controls: When performing functional studies, compare results using:

  • Wild-type MYC

  • MYC with S373D mutation (phosphomimetic)

  • MYC with S373A mutation (phospho-deficient)

  The S373D mutation has been shown to mimic phosphorylation with a Kᴅ for MAX binding (23.0 ± 9.0 nM) that approximates but doesn't perfectly match true phosphorylation effects .

• Stimulus-specific controls: Include samples treated with phosphorylation-inducing stimuli. For example, UV treatment has been shown to induce S373 phosphorylation in multiple cell lines (HEK293T, Raw264.7, PC12) .

• Positive sample control: The antibody has been validated in A-431 cells, making this a suitable positive control for initial testing .

• Cross-reactivity assessment: Test reactivity against phospho-mutants (S373A) to confirm specificity for the phosphorylated form .

These controls will help validate specificity and ensure reliable interpretation of experimental results.

How do the S373D and S373E phosphomimetic mutations compare to actual phosphorylation?

Phosphomimetic mutations are commonly used to study phosphorylation effects, but their accuracy in mimicking true phosphorylation varies:

• Chemical shift analysis: NMR studies show that the S373D mutation mimics the chemical shift changes observed upon phosphorylation to a large extent, while the S373E variant behaves more similarly to unphosphorylated MYC WT .

• Binding kinetics: ITC measurements at 298K show that MYC S373D binding to MAX yields a dissociation constant (Kᴅ) of 23 nM, which is comparable but not identical to phosphorylated MYC WT-2P (97 nM). This approximately 4-fold difference indicates that Asp provides a close but slightly imperfect mimicking of a phosphate group .

• Stoichiometry effects: Unlike the T400D mutation which alters binding stoichiometry to 2:1 (MYC:MAX), the S373D mutation maintains the expected 1:1 stoichiometry similar to phosphorylated wild-type protein .

• Structural effects: The decrease in α-helical propensity caused by the S373D mutation is independent of the T400D mutation, suggesting little long-range interaction between these sites .

For the most accurate experimental design, researchers should consider these differences when interpreting results based on phosphomimetic mutations rather than actual phosphorylation.

What are the specific technical considerations for Western blot applications using Phospho-MYC (S373) Antibody?

When performing Western blot with Phospho-MYC (S373) Antibody, consider these technical aspects:

• Expected molecular weight: While the calculated MW of MYC is approximately 51kDa, the observed band typically appears at ~60kDa due to post-translational modifications . Some samples may show both the 50kDa and 60kDa bands.

• Sample preparation:

  • Include phosphatase inhibitors in lysis buffers to prevent dephosphorylation during extraction

  • Avoid excessive freeze-thaw cycles of samples which can affect phosphorylation status

  • Consider stimulating cells with UV treatment to increase phosphorylation levels at S373 for positive controls

• Blocking optimization:

  • For phospho-specific antibodies, BSA-based blocking solutions (3-5%) often perform better than milk-based blockers, as milk contains phosphoproteins that may interfere with detection

• Dilution optimization:

  • Start with the recommended 1:500-1:1000 dilution range

  • Optimize based on signal-to-noise ratio for your specific sample type

• Positive controls:

  • A-431 cell lysate is recommended as a positive control

  • HEK293T, Raw264.7, and PC12 cell lysates treated with UV have also been validated

• Signal detection:

  • Enhanced chemiluminescence (ECL) systems are recommended for sensitive detection

  • Consider longer exposure times than standard antibodies, as phospho-specific signals may be weaker

How can Phospho-MYC (S373) Antibody be used to study MYC's role in cancer development?

MYC is frequently dysregulated in cancer, making phospho-specific antibodies valuable tools in oncology research:

• Tumor profiling: Phospho-MYC (S373) Antibody can be used in IHC to analyze phosphorylation patterns across tumor samples. This has been validated in human breast carcinoma tissue at 1:100 dilution .

• Pathway analysis: Since MYC phosphorylation is regulated by upstream kinase signaling, this antibody can help map altered signaling pathways in cancer cells:

  • Determine which oncogenic signaling pathways affect S373 phosphorylation status

  • Compare with T58/S62 phosphorylation patterns to build a comprehensive view of MYC regulation

• Therapeutic response monitoring: The antibody can be used to measure changes in MYC phosphorylation status following treatment with:

  • Kinase inhibitors

  • Cell cycle modulators

  • Transcriptional regulators

• Correlation with functional outcomes: Researchers can correlate S373 phosphorylation levels with:

  • Cell proliferation rates

  • Apoptotic response

  • Gene expression changes in MYC target genes

  • Resistance to specific therapies

• Comparison with other MYC regulatory mechanisms: Integrate phosphorylation data with other MYC regulatory mechanisms:

  • Unlike T58/S62 phosphorylation which primarily affects MYC stability through Fbw7-mediated degradation , S373 phosphorylation appears to more directly affect MYC's binding to MAX and subsequently its transcriptional activity

  • This differential regulation suggests multiple approaches for therapeutic targeting

What methodological approaches can distinguish between different phosphorylated forms of MYC?

Distinguishing between different phosphorylated forms of MYC requires specific methodological approaches:

• Sequential immunoprecipitation:

  • First IP with one phospho-specific antibody (e.g., pS373)

  • Then analyze the immunoprecipitated material with a different phospho-specific antibody (e.g., pT58/pS62)

  • This approach determines if both phosphorylations occur on the same molecule

• Phosphatase treatment combined with Western blotting:

  • Treat samples with different phosphatases with varying specificities

  • Analyze the resulting patterns with multiple phospho-specific antibodies

  • This reveals the interdependence of different phosphorylation events

• 2D gel electrophoresis:

  • Separate proteins first by isoelectric point, then by molecular weight

  • Blot with total MYC antibody to visualize all phospho-forms

  • Compare to parallel blots with phospho-specific antibodies

• Mass spectrometry:

  • Immunoprecipitate MYC using either total or phospho-specific antibodies

  • Perform MS analysis to identify and quantify all phosphorylation sites simultaneously

  • Compare phosphorylation patterns across different experimental conditions

• Bioluminescence resonance energy transfer (BRET) assays:

  • Create BRET sensors with phospho-specific binding domains

  • Monitor specific phosphorylation events in real-time in living cells

  • This allows temporal analysis of different phosphorylation events

These approaches can help researchers understand the complex interplay between different phosphorylation sites and their combined effects on MYC function.

What are the limitations of Phospho-MYC (S373) Antibody that researchers should consider?

Despite its utility, researchers should be aware of several limitations when working with Phospho-MYC (S373) Antibody:

• Antibody specificity variations:

  • Lot-to-lot variation may occur, requiring validation with each new lot

  • Cross-reactivity with structurally similar phosphorylation motifs should be assessed

• Technical limitations:

  • Background signal in certain tissues, especially those with high endogenous phosphatase activity

  • Potential loss of phosphorylation during sample preparation if phosphatase inhibitors are inadequate

  • The need to optimize fixation conditions for IHC applications to preserve phospho-epitopes

• Biological context limitations:

  • Phosphorylation status may change rapidly during cell lysis, potentially leading to artifacts

  • Phosphorylation at S373 may be transient or context-dependent, making detection challenging in some systems

  • Interactions between multiple phosphorylation sites can complicate interpretation of single-site analysis

• Interpretation challenges:

  • The presence of phosphorylation doesn't necessarily indicate functional activity

  • The relationship between S373 phosphorylation and other post-translational modifications requires careful experimental design to elucidate

To address these limitations, researchers should implement rigorous controls, validate results with complementary approaches, and consider the biological context when interpreting data.

How can Phospho-MYC (S373) Antibody be integrated with other research tools to gain comprehensive insights into MYC biology?

For comprehensive understanding of MYC biology, integrate Phospho-MYC (S373) Antibody with these complementary approaches:

• Multi-parametric analysis combinations:

  • Combine with other phospho-specific antibodies (T58/S62) to create a phosphorylation profile

  • Integrate with ubiquitination analysis to connect phosphorylation to protein stability regulation

  • Pair with chromatin immunoprecipitation (ChIP) to correlate phosphorylation with genomic binding

• Advanced imaging applications:

  • Use in super-resolution microscopy to visualize subcellular localization of phosphorylated MYC

  • Apply in multiplexed immunofluorescence to simultaneously detect multiple MYC modifications

  • Implement in live-cell imaging with genetically encoded biosensors to track phosphorylation dynamics

• Functional genomics integration:

  • Correlate phosphorylation data with RNA-seq to link phosphorylation status to transcriptional outputs

  • Combine with CRISPR/Cas9 gene editing of kinases/phosphatases to identify regulatory enzymes

  • Integrate with interactome studies to define phosphorylation-dependent protein interactions

• Systems biology approaches:

  • Develop computational models incorporating phosphorylation data to predict MYC activity

  • Use phospho-proteomic data to position S373 phosphorylation within broader signaling networks

  • Apply machine learning to identify patterns associating S373 phosphorylation with cellular phenotypes

This integrated approach allows researchers to move beyond simply detecting phosphorylation to understanding its functional significance within the complex regulatory network controlling MYC activity in normal and disease states.