Phospho-Histone H4 (Thr80) Antibody

Basic Research Questions

• What is Phospho-Histone H4 (Thr80) Antibody and what does it detect?

  Phospho-Histone H4 (Thr80) Antibody is a polyclonal antibody that specifically recognizes histone H4 when phosphorylated at threonine 80. This post-translational modification occurs on the core histone H4, which is one of the fundamental components of the nucleosome structure in eukaryotic chromatin. The antibody is typically derived from rabbit hosts and detects endogenous Histone H4 (Phospho Thr80) protein in various species including human, mouse, and rat samples . The specificity is achieved through affinity purification from rabbit antiserum using specific immunogens designed around the phosphorylated Thr80 residue .

• What applications is Phospho-Histone H4 (Thr80) Antibody suitable for?

  Phospho-Histone H4 (Thr80) Antibody has been validated primarily for Western Blot (WB) applications, with recommended dilutions typically between 1:1000-2000 . Some commercially available antibodies have also been validated for immunohistochemistry (IHC) with recommended dilutions of 1:100-200 . While not explicitly validated for all applications, researchers have successfully used similar histone modification antibodies in chromatin immunoprecipitation (ChIP) experiments to study the genomic distribution of specific histone modifications . When adapting this antibody for applications beyond those explicitly validated, thorough controls are essential to confirm specificity.

• What are the optimal storage conditions and stability parameters for Phospho-Histone H4 (Thr80) Antibody?

  For maximum stability and performance, Phospho-Histone H4 (Thr80) Antibody should be stored at -20°C . Most commercial preparations are formulated in PBS (pH 7.4) containing preservatives such as 0.02% sodium azide and stabilizers like 50% glycerol . The antibody typically maintains reactivity for up to one year from the date of receipt when stored properly . To maintain antibody integrity, repeated freeze-thaw cycles should be avoided . For working solutions, aliquoting the antibody and storing unused portions at -20°C can help preserve functionality over time.

• How is specificity ensured for Phospho-Histone H4 (Thr80) Antibody?

  Specificity of Phospho-Histone H4 (Thr80) Antibody is typically validated through multiple complementary approaches:

  • Peptide dot-blot analysis comparing reactivity with various phospho-peptides (H4T80ph, H4T30ph, H4T96ph, etc.)

  • Comparison of reactivity between wild-type histone H4 and H4T80A mutants

  • Phosphatase treatment tests that demonstrate loss of signal upon removal of phosphate groups

  • Immunoblot analysis using recombinant proteins versus cellular extracts

  In one study validating an H4T80ph antibody, researchers showed that the antibody specifically recognized H4T80ph peptides but not other H4 phospho-peptides or histone H3T80ph peptides. The signal was also significantly reduced upon phosphatase treatment, confirming phosphorylation-specific recognition .

Intermediate Research Questions

• What is the biological significance of H4T80 phosphorylation in cellular processes?

  H4T80 phosphorylation plays a crucial role in the DNA damage response pathway. Research has demonstrated that this modification is involved in DNA damage checkpoint (DDC) activation and subsequent recovery mechanisms . The phosphorylation of H4T80 appears to be regulated in response to genotoxic stress, helping to coordinate temporary cell cycle arrest and activation of DNA repair mechanisms.

  In yeast models, cells with H4T80A mutations (preventing phosphorylation at this site) display hypersensitivity to DNA damaging agents, indicating the phosphorylation's importance in DNA damage response . This suggests that H4T80 phosphorylation serves as a molecular switch in chromatin to facilitate repair processes following DNA damage.

• Which kinases are responsible for H4T80 phosphorylation in different organisms?

  In yeast, the Cla4 kinase (a PAK family kinase) has been identified as the primary enzyme responsible for H4T80 phosphorylation. Research has shown that:

  • Deletion of CLA4 (but not related kinases SKM1 or STE20) results in DNA damage hypersensitivity

  • cla4Δ mutant cells exhibit significantly reduced H4T80ph levels compared to wild-type cells

  • Recombinant Cla4 can directly phosphorylate H4 in vitro, specifically at the T80 residue

  • A kinase-dead version of Cla4 (Cla4K594A) fails to phosphorylate H4T80

  In mammalian systems, while not explicitly described for H4T80, related research on H4S47 phosphorylation has identified PAK2 kinase as responsible . This suggests that PAK family kinases may generally be involved in histone H4 phosphorylation events.

• How can researchers detect changes in H4T80 phosphorylation levels in response to experimental conditions?

  Changes in H4T80 phosphorylation levels can be monitored using several complementary approaches:

  1. Western Blot Analysis: Using Phospho-Histone H4 (Thr80) Antibody to compare protein extracts from treated versus untreated samples. For example, one study demonstrated increased H4T80ph following treatment with Nocodazole (1μg/ml, 24hr) .

  2. Immunohistochemistry: To visualize spatial distribution of H4T80ph in tissue sections, using appropriate dilutions (1:100-200) of the antibody .

  3. Chromatin Immunoprecipitation (ChIP): To examine genomic distribution of H4T80ph, following protocols similar to those used for other histone modifications .

  4. Quantitative Mass Spectrometry: For absolute quantification of phosphorylation stoichiometry, though this requires specialized equipment and expertise.

  For all methods, appropriate controls should include phosphatase treatment (negative control) and known inducers of the modification (positive control).

Advanced Research Questions

• What experimental controls are essential when working with Phospho-Histone H4 (Thr80) Antibody?

  Rigorous experimental design with Phospho-Histone H4 (Thr80) Antibody should include:

  1. Specificity Controls:

     • Peptide competition assay using phosphorylated vs non-phosphorylated peptides

     • Comparison with H4T80A mutant samples (should show no signal)

     • Phosphatase treatment of samples (should abolish signal)

  2. Technical Controls:

     • Total H4 antibody in parallel experiments to normalize for histone levels

     • Loading controls appropriate for the cellular fraction being analyzed

     • Positive controls from cells treated with agents known to induce H4T80 phosphorylation

  3. Biological Controls:

     • Wild-type vs kinase-deficient cells (e.g., CLA4 knockout in yeast)

     • Time-course experiments to capture dynamics of phosphorylation

     • Cell-cycle synchronized populations to control for cell-cycle variation

  These controls help distinguish specific signals from potential artifacts and enable accurate interpretation of results in the biological context.

• How does H4T80 phosphorylation interact with other histone modifications in the DNA damage response pathway?

  The interaction between H4T80 phosphorylation and other histone modifications represents a complex aspect of the histone code during DNA damage response. While the search results do not provide direct information on the cross-talk between H4T80ph and other modifications, we can draw insights from related research:

  1. Modification Proximity Analysis: The threonine 80 residue of histone H4 is positioned near other modifiable residues, creating potential for collaborative or antagonistic relationships.

  2. Sequential Modification Patterns: Research methodologies to investigate this include:

     • Sequential ChIP (re-ChIP) experiments to identify co-occurrence of modifications

     • Mass spectrometry analysis of enriched modified histones

     • Genetic studies using histone mutants that prevent specific modifications

  3. Enzyme Recruitment: H4T80 phosphorylation may serve as a recognition site for readers of histone modifications that subsequently recruit additional enzymes that place or remove other histone marks.

  Future research should focus on comprehensive analysis of modification patterns appearing in concert with H4T80ph during different stages of the DNA damage response.

• What methodological approaches can be used to study the genomic distribution of H4T80 phosphorylation?

  To map the genomic locations enriched for H4T80 phosphorylation, researchers can employ:

  1. ChIP-seq Protocol Adaptation:

     • Crosslink cells with 1% formaldehyde for 10 minutes at room temperature

     • Quench with 0.125M glycine

     • Lyse cells in appropriate buffer (50mM HEPES pH 7.5, 1% Triton X-100, 140mM NaCl, 1mM EDTA, 0.1% sodium deoxycholate, protease inhibitors)

     • Sonicate to achieve mean DNA fragment size of 0.5-1kb

     • Immunoprecipitate using Phospho-Histone H4 (Thr80) Antibody

     • Process DNA for next-generation sequencing

  2. CUT&RUN or CUT&Tag Adaptations:

     • These newer techniques offer higher signal-to-noise ratio and require fewer cells

     • Protocol modification would include using the Phospho-Histone H4 (Thr80) Antibody with appropriate validation

  3. High-Resolution Analysis:

     • For precise localization, ChIP-exo or ChIP-nexus methods provide near base-pair resolution

     • These approaches help determine if H4T80ph is precisely positioned relative to genomic features

  Bioinformatic analysis should include comparison with known genomic features (promoters, enhancers, DNA damage-prone regions) and integration with transcriptional data to elucidate functional consequences.

• How can researchers differentiate between cell cycle-dependent and DNA damage-induced H4T80 phosphorylation?

  Distinguishing between these contexts requires carefully designed experiments:

  1. Cell Synchronization Approach:

     • Synchronize cells at different cell cycle phases using established methods (thymidine block, nocodazole treatment, etc.)

     • Perform western blot analysis of H4T80ph levels across synchronized populations

     • Compare with asynchronous populations with and without DNA damage induction

     • Control experiments should include cell cycle markers (Cyclin B, phospho-Histone H3 Ser10)

  2. Kinase Inhibition Strategy:

     • Employ specific inhibitors of DNA damage response kinases (ATM/ATR inhibitors)

     • Monitor effects on H4T80ph levels following DNA damage

     • Compare with effects of inhibiting cell-cycle regulated kinases

  3. Genomic Distribution Comparison:

     • Perform ChIP-seq for H4T80ph in synchronized cells vs. DNA-damaged cells

     • Analyze differential enrichment patterns

     • Correlate with known cell-cycle regulated genes and DNA damage response elements

  These approaches, individually or in combination, can help dissect the distinct roles of H4T80 phosphorylation in normal cell cycle progression versus DNA damage response.

Research Applications and Techniques

• What are the optimal extraction methods for preserving H4T80 phosphorylation for antibody detection?

  Preserving phosphorylation marks during histone extraction requires careful attention to extraction conditions:

  1. Phosphatase Inhibitor Cocktails:

     • Always include phosphatase inhibitors (sodium fluoride, sodium orthovanadate, β-glycerophosphate, pyrophosphate)

     • Use freshly prepared inhibitors at appropriate concentrations

     • Add inhibitors to all buffers used in the extraction procedure

  2. Extraction Protocols:

     • For total histones: Acid extraction using 0.2N HCl or 0.4N H₂SO₄

     • For nuclear extracts: Low-salt extraction followed by nuclear lysis

     • For chromatin fractions: Triton X-100 extraction of cytoplasmic proteins followed by nuclease digestion

  3. Temperature Considerations:

     • Perform all extraction steps at 4°C

     • Process samples quickly to minimize phosphatase activity

     • Avoid repeated freeze-thaw cycles of extracted samples

  These precautions help maintain the native phosphorylation state, ensuring accurate analysis of H4T80 phosphorylation levels.

• How can researchers quantitatively assess changes in H4T80 phosphorylation levels?

  Quantitative assessment of H4T80 phosphorylation requires:

  1. Western Blot Quantification:

     • Use total H4 antibody on parallel blots to normalize for histone loading

     • Employ standardized loading curves with known quantities of recombinant proteins

     • Use digital image analysis software for densitometry measurements

     • Calculate the ratio of phosphorylated to total H4

  2. Mass Spectrometry Approaches:

     • Employ stable isotope labeling with amino acids in cell culture (SILAC)

     • Use multiple reaction monitoring (MRM) for targeted quantification

     • Apply label-free quantification with appropriate internal standards

  3. ELISA-Based Methods:

     • Develop sandwich ELISA using capture antibody against H4 and detection with Phospho-Histone H4 (Thr80) Antibody

     • Create standard curves using synthetic phosphopeptides

  Each method has distinct advantages and limitations, and combining multiple approaches provides more robust quantification.