Phospho-TP53 (T387) Antibody

What is the Phospho-TP53 (T387) antibody and what epitope does it recognize?

The Phospho-TP53 (T387) antibody specifically recognizes the human p53 protein when phosphorylated at threonine 387. This antibody is typically a polyclonal IgG raised in rabbit hosts against a synthesized peptide derived from the human p53 region surrounding the T387 phosphorylation site. The immunogen generally encompasses amino acids 344-393 of the human p53 protein . The antibody is designed to detect only the phosphorylated form of p53 at this specific residue, making it valuable for studying post-translational modifications of p53 during various cellular processes.

What applications can the Phospho-TP53 (T387) antibody be used for?

Phospho-TP53 (T387) antibodies have been validated for multiple research applications including ELISA and immunohistochemistry (IHC) . While not explicitly mentioned in the provided search results, phospho-specific antibodies like this are also commonly used in Western blotting, immunoprecipitation, and immunofluorescence assays. The specific applications will depend on the individual antibody's validation data, and researchers should consult the manufacturer's recommendations for optimal dilutions in each application (e.g., 1:100-1:300 for IHC, 1:5000 for ELISA based on product specifications) .

How does the T387 phosphorylation site compare to other p53 phosphorylation sites?

The T387 phosphorylation site is one of multiple regulatory phosphorylation sites on p53. While sites like Ser15 and Ser20 are well-documented for their roles in reducing MDM2 interaction and enhancing p53 stability following DNA damage , T387 phosphorylation appears particularly important for 14-3-3 protein interactions . Other significant phosphorylation sites include Thr81 and Ser392 , each with distinct functional consequences. Ser392 phosphorylation influences growth suppressor function, DNA binding, and transcriptional activation of p53, and is notably increased in human tumors . The T387 site specifically enables a unique binding mode with 14-3-3 proteins, particularly 14-3-3σ, which has been studied in detail using structural biology approaches .

What are the optimal storage and handling conditions for Phospho-TP53 (T387) antibodies?

For long-term storage, Phospho-TP53 (T387) antibodies should be stored at -20°C for up to one year. For short-term storage and frequent use, 4°C for up to one month is recommended . It's crucial to avoid repeated freeze-thaw cycles as this can degrade antibody quality and reduce specificity. The antibody is typically supplied in a buffer containing PBS with 50% glycerol, 0.5% BSA, and 0.02% sodium azide to maintain stability . Researchers should aliquot the antibody upon receipt to minimize freeze-thaw cycles and follow manufacturer-specific recommendations, as formulations may vary between suppliers.

How should I optimize immunohistochemistry protocols for Phospho-TP53 (T387) antibody?

For immunohistochemistry applications, begin with the manufacturer's recommended dilution range (typically 1:100-1:300 for Phospho-TP53 (T387) antibodies) . Optimization should include:

• Antigen retrieval method testing (citrate buffer vs. EDTA buffer)

• Antibody concentration titration

• Incubation time and temperature adjustments

• Selection of appropriate detection systems

Include proper controls in each experiment: positive controls (samples known to express phosphorylated p53 at T387), negative controls (samples without primary antibody), and ideally, phosphatase-treated samples to confirm phospho-specificity. Because phospho-epitopes can be sensitive to tissue fixation conditions, minimizing the time between tissue collection and fixation is crucial for preserving phosphorylation status. Validate findings with alternative methods such as Western blotting when possible.

What methodological approaches can be used to confirm the specificity of Phospho-TP53 (T387) antibody detection?

Several methodological approaches can validate antibody specificity:

• Phosphatase treatment: Treating one sample set with lambda phosphatase before antibody incubation should eliminate signal if the antibody is truly phospho-specific.

• Peptide competition assays: Pre-incubating the antibody with the phosphorylated peptide immunogen should block specific binding, while incubation with the non-phosphorylated version should not affect binding.

• Knockout/knockdown controls: Using p53-null cells (like H1299) as negative controls or p53-knockdown samples can verify specificity.

• Induction experiments: Treating cells with DNA-damaging agents known to induce p53 phosphorylation at T387 (such as adriamycin, camptothecin, or irradiation) and observing increased signal .

• Multiple detection methods: Confirming results across different techniques (Western blotting, IHC, immunoprecipitation) increases confidence in specificity.

Researchers should also compare reactivity patterns with available literature data on p53 T387 phosphorylation under various treatment conditions .

How do I interpret conflicting signals between total p53 and Phospho-TP53 (T387) antibody detection?

Discrepancies between total p53 and phospho-T387 p53 detection can occur for several reasons:

• Temporal dynamics: Phosphorylation at T387 may occur transiently or at specific cell cycle phases, while total p53 levels change more gradually.

• Subpopulation specificity: Only a subset of p53 molecules may be phosphorylated at T387 under given conditions.

• Epitope masking: Protein-protein interactions, particularly with 14-3-3 proteins, may mask the T387 epitope and prevent antibody binding despite phosphorylation being present .

• Antibody sensitivity differences: The phospho-specific antibody may have different detection thresholds compared to total p53 antibodies.

To resolve these conflicts, researchers should:

• Perform time-course experiments to identify optimal detection windows

• Use immunoprecipitation followed by Western blotting to enrich for phosphorylated forms

• Consider cell fractionation to determine if phospho-T387 p53 localizes to specific subcellular compartments

• Compare results with other phospho-p53 antibodies (like Ser15, Ser20) to establish relative phosphorylation patterns

What are common technical challenges with Phospho-TP53 (T387) antibody experiments and how can they be addressed?

Common challenges include:

• High background: May result from insufficient blocking or non-specific binding. Address by:

  • Increasing blocking time/concentration

  • Using alternative blocking reagents (milk vs. BSA)

  • Including 0.1-0.3% Tween-20 in wash buffers

  • Titrating primary antibody concentration

• Loss of phospho-epitope detection:

  • Minimize time between sample collection and fixation/lysis

  • Include phosphatase inhibitors in all buffers

  • Avoid excessive sample heating

  • Consider using phosphatase inhibitors like okadaic acid in cell culture prior to lysis

• Inconsistent results between experiments:

  • Standardize treatment conditions precisely

  • Maintain consistent sample processing times

  • Use the same lot of antibody when possible

  • Include internal controls in each experiment

  • Normalize phospho-signal to total p53 levels

• Cross-reactivity with other phospho-proteins:

  • Validate with peptide competition assays

  • Compare patterns with knockout controls

  • Consider using alternative detection methods for confirmation

How should I quantify and normalize Phospho-TP53 (T387) signals in Western blot experiments?

For accurate quantification:

How can Phospho-TP53 (T387) antibodies be leveraged for studying p53-14-3-3 protein interactions?

The interaction between phosphorylated p53 at T387 and 14-3-3 proteins, particularly 14-3-3σ, represents an important regulatory mechanism for p53 function. Researchers can leverage Phospho-TP53 (T387) antibodies for these advanced studies through:

• Co-immunoprecipitation assays: Using anti-phospho-T387 antibodies to immunoprecipitate p53 and probing for associated 14-3-3 proteins, or vice versa. This approach has successfully demonstrated interactions between p53 phosphorylated at T387 and 14-3-3 isoforms including γ, ε, ζ, and σ .

• Proximity ligation assays (PLA): For visualizing the interaction in situ within cells following DNA damage induction.

• Competition studies: Using phospho-T387 peptides to disrupt p53-14-3-3 interactions in cellular models and observing phenotypic consequences.

• Structure-function analyses: Based on crystallography data showing that the p53 peptide interacts with the 14-3-3 binding groove via a unique turn conformation induced by G389 and P390, researchers can design mutants to probe this interaction .

• Combination with other phospho-specific antibodies: Since diphosphorylated p53 peptides (containing modifications at combinations of S366, S378, and T387) show much higher binding affinities to 14-3-3 proteins , researchers can investigate these multi-phosphorylation patterns.

These approaches can help elucidate how 14-3-3 binding to phosphorylated p53 regulates its stability, subcellular localization, and transcriptional activity.

What methodologies can determine the kinetics and dynamics of p53 T387 phosphorylation in response to cellular stress?

Advanced methodologies to study T387 phosphorylation dynamics include:

• Live-cell imaging: Using phospho-specific antibody fragments conjugated to cell-permeable peptides or fluorescent proteins with phospho-binding domains.

• Pulsed stable isotope labeling with amino acids in cell culture (pSILAC) combined with mass spectrometry: To measure the rates of phosphorylation and dephosphorylation at T387 relative to other p53 modifications.

• Temporal phosphoproteomics: Collecting samples across multiple timepoints after stress induction (radiation, chemotherapeutic agents like adriamycin or camptothecin) to map the sequence of phosphorylation events.

• Kinase activity assays: To identify and characterize the specific kinases responsible for T387 phosphorylation under different stress conditions.

• Phosphatase inhibitor studies: Using specific inhibitors to determine which phosphatases regulate T387 dephosphorylation.

• Single-cell analyses: Techniques like mass cytometry (CyTOF) with phospho-specific antibodies can reveal cell-to-cell variability in phosphorylation responses.

• Computational modeling: Integrating experimental data to create predictive models of p53 modification patterns.

These approaches can help establish the temporal relationship between T387 phosphorylation and other p53 modifications, providing insights into the sequential regulation of p53 activity.

How can Phospho-TP53 (T387) antibodies be integrated with other methodologies to study conformational changes in p53?

The phosphorylation of p53 at T387 likely influences its conformation, particularly in the context of 14-3-3 protein binding. Researchers can combine phospho-specific antibodies with other techniques to study these conformational dynamics:

These integrated approaches can provide unprecedented insights into how T387 phosphorylation regulates p53 conformation and function.

What is the functional significance of p53 T387 phosphorylation in the context of DNA damage response?

The phosphorylation of p53 at T387 appears to be part of the cellular response to DNA damage, though its precise functional significance remains under investigation. From available research:

• DNA damage induction: T387 phosphorylation has been observed following treatment with DNA-damaging agents including adriamycin, camptothecin, and irradiation , suggesting it forms part of the DNA damage response pathway.

• 14-3-3 protein binding: The phosphorylation at T387 creates a binding site for 14-3-3 proteins, particularly 14-3-3σ, with the interaction being structurally characterized through crystallography . This binding has a measured dissociation constant (Kd) of approximately 16.3 ± 0.7 μM as determined by isothermal titration calorimetry .

• Potential functions: While the physiological significance of T387 phosphorylation requires further elucidation , it likely contributes to:

  • Modulating p53 protein stability

  • Regulating subcellular localization

  • Influencing transcriptional activity or target gene specificity

  • Affecting interactions with other regulatory proteins

• Cooperative modifications: T387 phosphorylation appears to work cooperatively with other p53 phosphorylation sites (S366, S378), as diphosphorylated peptides show much higher affinities for 14-3-3 proteins than monophosphorylated peptides , suggesting a complex regulatory code.

• Stress-specificity: Different cellular stresses may induce distinct patterns of p53 phosphorylation, with T387 potentially responding to specific types or intensities of DNA damage.

Further research is needed to fully characterize how T387 phosphorylation integrates with other p53 modifications to determine cellular outcomes following DNA damage.

How does the interaction between 14-3-3 proteins and phosphorylated p53 at T387 affect p53 function?

The interaction between 14-3-3 proteins and p53 phosphorylated at T387 represents a sophisticated regulatory mechanism:

• Structural basis: Crystallography studies reveal that the p53 T387 phosphopeptide interacts with the 14-3-3σ binding groove through a unique turn conformation induced by G389 and P390, allowing the C-terminus to form a salt bridge interaction with R60 of 14-3-3σ . This structural insight provides the foundation for understanding the functional consequences.

• Binding characteristics: The interaction has moderate affinity (Kd = 16.3 ± 0.7 μM by ITC, 23 ± 3 μM by FP) , which is typical for regulatory protein-protein interactions that need to be reversible.

• Secondary binding site: Interestingly, there is evidence for a phosphorylation-independent secondary interaction between 14-3-3σ and p53, mediated by the C-terminal domain (CTD) of 14-3-3σ (amino acids 153-248) . This suggests a complex binding mode that may affect multiple aspects of p53 function.

• Potential functional outcomes:

  • Stabilization of p53 by preventing MDM2-mediated degradation

  • Modulation of p53 tetramerization and DNA-binding properties

  • Alteration of p53's transcriptional activity toward specific gene targets

  • Regulation of p53 subcellular localization

• Cooperative regulation: The enhanced binding of diphosphorylated p53 peptides suggests that 14-3-3 proteins may preferentially interact with p53 molecules that have undergone multiple phosphorylation events , potentially serving as "readers" of a complex p53 modification code.

• Isoform specificity: Different 14-3-3 isoforms (γ, ε, ζ, σ, τ) can interact with phosphorylated p53 , potentially leading to isoform-specific outcomes that may vary by cell type or stress condition.

Understanding this interaction mechanism provides opportunities for targeted therapeutic interventions that could modulate p53 function in cancer and other diseases.

What is known about the kinases and phosphatases that regulate p53 T387 phosphorylation status?

While the search results don't specifically identify the kinases and phosphatases regulating T387 phosphorylation, we can draw some inferences from the broader p53 literature:

• Potential kinases: Based on the context of DNA damage-induced phosphorylation, candidates may include:

  • Checkpoint kinases (Chk1, Chk2) - known to phosphorylate other p53 sites like Ser20

  • DNA damage response kinases (ATM, ATR, DNA-PK) - established regulators of p53 through sites like Ser15 and Ser37

  • Cyclin-dependent kinases (CDKs) - potential regulators during cell cycle progression

  • Casein kinase 2 (CK2) - known to phosphorylate sites in p53's C-terminal domain

• Phosphatases: Potential regulators include:

  • PP2A (Protein Phosphatase 2A) - a major serine/threonine phosphatase

  • Wip1 (Wild-type p53-induced phosphatase) - known to dephosphorylate multiple p53 sites

  • PP1 (Protein Phosphatase 1) - regulates numerous cellular processes including stress responses

• Context-dependent regulation: The phosphorylation status likely depends on:

  • Cell type and tissue context

  • Nature and severity of cellular stress

  • Cell cycle phase

  • Presence of specific signaling pathways

• Dysregulation in disease: Alterations in kinase/phosphatase activity in cancer could affect T387 phosphorylation patterns.

• Experimental approaches to identify regulators:

  • Kinase/phosphatase inhibitor screening

  • Genetic knockdown/knockout studies

  • In vitro kinase/phosphatase assays with purified enzymes

  • Phosphoproteomics following perturbation of candidate enzymes