Phospho-KAT5 (Ser90) Antibody

What is the biological significance of KAT5 Ser90 phosphorylation?

Ser90 phosphorylation on KAT5/TIP60 serves as a critical priming event that enables subsequent phosphorylation at Ser86 by GSK3 . This phosphorylation cascade appears to be constitutive under normal cellular conditions, though the exact regulatory mechanisms of Ser90 phosphorylation remain to be fully characterized . The priming phosphorylation at Ser90 is essential for the proper control of KAT5 activity, which ultimately affects diverse downstream cellular processes including autophagy induction . Research indicates that while cyclin-dependent kinases can catalyze this priming phosphorylation, the complete regulatory pathway remains under investigation .

How does Phospho-KAT5 (Ser90) relate to the better-characterized Ser86 phosphorylation?

Phosphorylation at Ser90 serves as a prerequisite priming site for GSK3-mediated phosphorylation at Ser86 . This represents a classic example of a phosphorylation-dependent cascade, where one phosphorylation event enables a subsequent modification. Research has identified the peptide covering amino acid residues 81 to 96 as containing both Ser86 and Ser90, with Ser90 functioning as the priming site for Ser86 phosphorylation . The relationship between these two phosphorylation events is hierarchical - without Ser90 phosphorylation, GSK3 cannot effectively phosphorylate Ser86, which has significant implications for KAT5's role in autophagy regulation and other cellular processes .

What cellular pathways are regulated by KAT5 Ser90 phosphorylation?

KAT5 Ser90 phosphorylation, through its role in enabling Ser86 phosphorylation, influences several key cellular pathways:

• Autophagy regulation: Phosphorylation at Ser86 (which requires Ser90 priming) directly affects serum deprivation-induced autophagy. Knock-in of Kat5 S86A in MEF cells impairs autophagy induction, demonstrating the importance of this phosphorylation cascade .

• ULK1 interaction and acetylation: Phosphorylated KAT5 shows enhanced interaction with ULK1, a key regulator of autophagy. This interaction is particularly pronounced under serum deprivation conditions, coinciding with increased Ser86 phosphorylation .

• Innate immune response: While not directly linked to Ser90 phosphorylation in the search results, KAT5 plays a broader role in innate immune responses to DNA viruses by acetylating cGAS, enhancing its DNA-binding ability .

What experimental methods are recommended for detecting Phospho-KAT5 (Ser90) in cellular samples?

For effective detection of Phospho-KAT5 (Ser90) in cellular samples, consider the following methodological approach:

• Western blot analysis: Using a specific monoclonal antibody against phospho-Ser90-KAT5. While the search results mention a specific antibody against phospho-Ser86-KAT5 , similar approaches can be applied for Ser90.

• Cell treatment conditions: To study dynamics of Ser90 phosphorylation, researchers should consider:

  • Serum deprivation experiments (0.1% FBS for 12-24 hours)

  • Treatment with GSK3 inhibitors to observe effects on the phosphorylation cascade

  • siRNA-mediated knockdown of relevant kinases

• Immunoprecipitation followed by mass spectrometry: This approach can confirm phosphorylation status and identify other potential post-translational modifications that might interact with Ser90 phosphorylation .

• Phosphatase inhibitor treatments: Using inhibitors like okadaic acid can help preserve phosphorylation states during experimental procedures, as phosphorylation events often have high turnover rates .

How can researchers effectively distinguish between phosphorylation at Ser90 versus other phosphorylation sites on KAT5?

Distinguishing between different phosphorylation sites on KAT5 requires careful experimental design:

• Site-specific antibodies: Use highly specific monoclonal antibodies that recognize only phospho-Ser90 and not other phosphorylated residues. Antibody validation should include peptide competition assays and testing on phospho-null mutants .

• Phospho-null mutants: Generate S90A mutants (where serine is replaced with alanine) as negative controls for antibody specificity testing .

• Mass spectrometry analysis: Perform targeted mass spectrometry on the peptide covering amino acid residues 81 to 96, which contains both Ser86 and Ser90 . This allows precise identification of phosphorylation patterns.

• Functional assays with point mutants: Compare the functional consequences of S90A, S86A, and double mutants to distinguish the specific effects of each phosphorylation site .

• Phosphatase treatment controls: Include samples treated with lambda phosphatase to confirm that observed signals are indeed due to phosphorylation .

What are the typical challenges in working with Phospho-KAT5 (Ser90) Antibody and how can researchers overcome them?

Common challenges and solutions when working with phospho-specific antibodies like Phospho-KAT5 (Ser90) include:

• Cross-reactivity issues:

  • Challenge: Antibodies may recognize similar phosphorylation motifs on other proteins.

  • Solution: Always validate with KAT5 knockdown/knockout controls and include peptide competition assays .

• Phosphorylation dynamics and stability:

  • Challenge: Phosphorylation events often have high turnover rates due to active phosphatases.

  • Solution: Include phosphatase inhibitors (e.g., okadaic acid) in lysis buffers; perform cell fractionation to identify compartment-specific phosphorylation patterns .

• Signal-to-noise ratio:

  • Challenge: Low abundance of phosphorylated protein can result in weak signals.

  • Solution: Enrich phosphorylated proteins using immunoprecipitation; use treatments that enhance phosphorylation (serum deprivation for KAT5) .

• Epitope masking:

  • Challenge: Protein interactions or conformational changes may mask the phosphorylated epitope.

  • Solution: Test multiple lysis conditions with different detergents; consider native versus denaturing conditions based on experimental goals .

How does the interplay between Ser90 phosphorylation and other post-translational modifications of KAT5 affect its function?

KAT5 undergoes multiple post-translational modifications that work in concert to regulate its diverse functions:

• Phosphorylation-acetylation cascade: Research indicates a complex interplay between phosphorylation and acetylation events. While the search results don't explicitly describe interactions between Ser90 phosphorylation and acetylation, KAT5 itself functions as an acetyltransferase for multiple targets including ULK1 and cGAS .

• Tyrosine phosphorylation: KAT5 undergoes tyrosine phosphorylation, particularly at Tyr-44, in response to DNA damage. This modification enhances KAT5 binding to H3K9me3 and its acetyltransferase activity toward ATM . The potential crosstalk between serine phosphorylation (at Ser90/Ser86) and tyrosine phosphorylation warrants investigation.

• Chromatin binding-dependent phosphorylation: Tyrosine phosphorylation of KAT5 accumulates when the protein is bound to chromatin, potentially protecting it from phosphatases . This suggests that cellular localization may affect phosphorylation patterns, including at Ser90.

• Functional consequences: Different modification patterns likely direct KAT5 toward specific functions:

  • Ser86/Ser90 phosphorylation → autophagy regulation via ULK1 interaction

  • Tyrosine phosphorylation → DNA damage response via ATM activation

  • Acetylation activity → innate immune response via cGAS modification

Researchers investigating these interactions should design experiments that simultaneously track multiple modifications under various cellular conditions.

What methodological approaches can resolve contradictory findings regarding KAT5 Ser90 phosphorylation in different experimental systems?

When facing contradictory findings across experimental systems, consider these methodological approaches:

• Cell type-specific differences:

  • Systematically compare phosphorylation patterns across multiple cell types (e.g., HCT116, MEF, THP-1, HeLa, RPE1) that have been used in KAT5 studies .

  • Establish baseline expression levels of relevant kinases (CDKs, GSK3) and phosphatases across cell lines.

• Temporal dynamics analysis:

  • Implement time-course experiments with high temporal resolution.

  • Based on IR-induced tyrosine phosphorylation kinetics, which occurs rapidly (within minutes) , Ser90 phosphorylation might also show rapid dynamics.

• Subcellular localization:

  • Perform cell fractionation studies to determine whether phosphorylated KAT5 localizes differently between nucleoplasmic and chromatin fractions .

  • Consider that phosphorylation patterns may vary between cellular compartments.

• Pathway perturbation approaches:

  • Use multiple methods to perturb regulatory pathways:

    • Pharmacological inhibitors (GSK3 inhibitors)

    • Genetic approaches (siRNA, CRISPR-Cas9)

    • Physiological stimuli (serum deprivation, DNA damage)

  • Compare results across these different perturbation methods to identify consistent patterns .

• Validation across model systems:

  • When possible, validate key findings in primary cells and in vivo models to ensure physiological relevance .

How can Phospho-KAT5 (Ser90) Antibody be effectively employed in multiplex assays to study KAT5's role in coordinating autophagy and immune responses?

For multiplex assays investigating KAT5's coordinating role between autophagy and immunity:

• Sequential immunoprecipitation strategy:

  • First IP: Use Phospho-KAT5 (Ser90) Antibody to pull down phosphorylated KAT5

  • Second IP: Probe for interacting partners specific to either autophagy (ULK1) or immune response (cGAS)

  • This approach can reveal whether distinct pools of phosphorylated KAT5 associate with different pathways

• Proximity ligation assays (PLA):

  • Design PLA experiments to simultaneously detect:

    • KAT5-Ser90 phosphorylation and ULK1 interaction (autophagy pathway)

    • KAT5 and cGAS interaction (immune pathway)

  • This approach provides spatial information about these interactions in situ

• Imaging-based multiplexing:

  • Implement multiplexed immunofluorescence using spectrally distinct fluorophores

  • Co-staining for phospho-KAT5 (Ser90), autophagy markers (LC3, ULK1), and immune response markers (cGAS, STING)

  • Include subcellular markers to determine compartmentalization of interactions

• Multi-omics approach:

  • Combine phosphoproteomics, acetylomics, and interactomics from the same samples

  • This comprehensive approach can reveal how KAT5's phosphorylation status correlates with its acetyltransferase activity toward different substrates

What experimental design would best elucidate the kinases responsible for Ser90 phosphorylation under different cellular conditions?

To identify and characterize the kinases responsible for Ser90 phosphorylation:

• Kinase inhibitor screen:

  • Systematically test inhibitors against candidate kinases, including:

    • Cyclin-dependent kinases (mentioned as possible priming kinases)

    • GSK3 (known to phosphorylate Ser86 following Ser90 phosphorylation)

    • Other stress-responsive kinases

  • Monitor Ser90 phosphorylation by western blot after inhibitor treatment

• In vitro kinase assays:

  • Generate recombinant KAT5 protein or peptides containing the Ser90 site

  • Test purified kinases for their ability to phosphorylate Ser90 in vitro

  • Validate with mass spectrometry to confirm the exact phosphorylation site

• Genetic screening approach:

  • Implement CRISPR-Cas9 screens targeting kinases

  • Use Ser90 phosphorylation as the readout

  • Secondary validation using individual gene knockouts or kinase-dead mutants

• Condition-specific analysis:

  • Compare kinase requirements across multiple cellular conditions:

    • Normal growth vs. serum deprivation (autophagy induction)

    • DNA damage (IR exposure)

    • Viral infection (HSV-1)

  • This approach can identify condition-specific regulatory mechanisms

• Phosphorylation site mutants as tools:

  • Create a series of mutants around the Ser90 site to determine sequence requirements

  • Include mutations that mimic or prevent phosphorylation (S90E or S90A)

  • These tools can help validate both the antibody specificity and functional importance

How can Phospho-KAT5 (Ser90) Antibody be used to investigate the relationship between KAT5 phosphorylation and its acetyltransferase activity?

To investigate this relationship, researchers should consider:

• Correlation analysis:

  • Perform parallel assays measuring Ser90 phosphorylation levels and KAT5 acetyltransferase activity

  • Design experiments that track both modifications under various conditions:

    • Serum deprivation (induces KAT5 Ser86 phosphorylation)

    • DNA damage (induces tyrosine phosphorylation)

    • Viral infection (influences KAT5-mediated acetylation of cGAS)

• Activity assays with phosphorylation-site mutants:

  • Compare acetyltransferase activity of:

    • Wild-type KAT5

    • S90A mutant (prevents phosphorylation)

    • S90E mutant (phosphomimetic)

  • Test activity against known substrates including histones, ULK1, and cGAS

• Structural biology approaches:

  • Investigate whether Ser90 phosphorylation induces conformational changes in KAT5

  • Consider techniques such as hydrogen-deuterium exchange mass spectrometry or limited proteolysis to detect structural changes

• Temporal dynamics:

  • Implement time-course experiments that track the sequence of:

    • Ser90 phosphorylation

    • Ser86 phosphorylation

    • Substrate acetylation

  • This approach can establish the causal relationship between these events

What are the comparative advantages of using Phospho-KAT5 (Ser90) Antibody versus genetic approaches (S90A mutants) in studying KAT5 function?

Both antibody-based and genetic approaches offer distinct advantages in studying KAT5 function:

For comprehensive studies, researchers should consider combining both approaches:

• Use antibodies to establish physiological relevance and dynamics

• Use genetic mutants to establish causal relationships and mechanisms

• Cross-validate key findings using both approaches

How might Phospho-KAT5 (Ser90) detection be integrated into studies of neurodegenerative diseases, given KAT5's role in autophagy regulation?

Integrating Phospho-KAT5 (Ser90) detection into neurodegenerative disease research:

• Disease-relevant models for analysis:

  • Analyze phosphorylation patterns in:

    • Patient-derived neurons or brain tissue

    • Animal models of Alzheimer's, Parkinson's, or Huntington's disease

    • Cell models expressing disease-associated proteins (Aβ, tau, α-synuclein, huntingtin)

  • Compare with age-matched controls to identify disease-specific alterations

• Mechanistic connections to explore:

  • KAT5's role in autophagy regulation through ULK1 acetylation is particularly relevant as autophagy dysfunction is implicated in most neurodegenerative diseases

  • Investigate whether disease-associated proteins affect KAT5 Ser90 phosphorylation

  • Determine if restoring normal phosphorylation patterns can rescue autophagy defects

• Methodological considerations:

  • Implement immunohistochemistry with Phospho-KAT5 (Ser90) Antibody in brain sections

  • Combine with markers of autophagy, protein aggregation, and neuronal health

  • Consider microdissection of specific brain regions followed by biochemical analysis

• Therapeutic implications:

  • Screen compounds that modulate KAT5 phosphorylation

  • Test whether manipulating KAT5 Ser90 phosphorylation affects clearance of disease-associated protein aggregates

  • Explore GSK3 inhibitors (which would affect the Ser90-Ser86 phosphorylation cascade) for their effects on autophagy in neurodegeneration models

What are the critical validation steps needed when implementing Phospho-KAT5 (Ser90) Antibody in a new experimental system?

When implementing Phospho-KAT5 (Ser90) Antibody in a new experimental system, researchers should complete these critical validation steps:

• Antibody specificity validation:

  • Peptide competition assays with phosphorylated and non-phosphorylated peptides

  • Testing on lysates from cells expressing wild-type KAT5 versus S90A mutant

  • Phosphatase treatment of samples to confirm signal loss

  • Western blot analysis to confirm single band of appropriate molecular weight

• Physiological regulation demonstration:

  • Confirm that the antibody detects changes in phosphorylation under conditions known to affect KAT5:

    • Serum deprivation (should increase GSK3-mediated phosphorylation)

    • Treatment with GSK3 inhibitors (should reduce signal)

    • Potentially other stress conditions

• Cell type-specific optimization:

  • Optimize extraction conditions for different cell types

  • Determine baseline expression levels of KAT5 and relevant kinases

  • Establish appropriate positive controls for each cell type

• Technical parameter optimization:

  • Antibody dilution titration

  • Blocking conditions optimization

  • Signal detection method selection based on expected abundance

  • Fixation method testing for immunofluorescence applications

• Functional correlation:

  • Validate that detected phosphorylation correlates with expected downstream effects:

    • ULK1 interaction

    • Autophagy induction

    • Potential effects on other KAT5 functions

What technical considerations should be made when using Phospho-KAT5 (Ser90) Antibody in complex tissue samples versus cell cultures?

Working with Phospho-KAT5 (Ser90) Antibody in tissue samples versus cell cultures requires different technical approaches:

Additional considerations for tissue analysis:

• Phosphorylation states may rapidly change post-mortem, requiring careful sample handling

• Region-specific variations in phosphorylation may exist, particularly in tissues like brain

• Consider laser capture microdissection for region-specific analysis in heterogeneous tissues