Tri-Methyl-Histone H3 (Lys18) Antibody

What is Tri-Methyl-Histone H3 (Lys18) and what is its biological significance in epigenetic regulation?

Tri-Methyl-Histone H3 (Lys18), commonly abbreviated as H3K18me3, is a post-translational modification where the lysine residue at position 18 of histone H3 contains three methyl groups. This specific histone modification plays crucial roles in chromatin organization and gene expression regulation.

From a biological standpoint, H3K18me3 has been implicated in:

• Transcriptional regulation, particularly in coordinating the recruitment of chromatin modifying enzymes

• Demarcation of specific chromatin domains

• DNA damage repair processes

• Influence on cellular differentiation and development

While H3K18me3 is less extensively studied than some other trimethylation marks (such as H3K4me3, H3K9me3, and H3K27me3), mass spectrometry analyses have shown that approximately 5% of total histone H3 proteins contain this modification, making it a significant but not abundant mark . Its precise distribution and abundance can vary across cell types and developmental stages.

How does H3K18me3 relate to other histone H3 methylation marks in the context of the histone code?

H3K18me3 exists within the complex landscape of the histone code, where multiple modifications work in concert to regulate chromatin function. Mass spectrometry-based measurements have revealed several important relationships:

• H3K18me3 rarely co-exists with H3K27me3 on the same histone tail, suggesting these marks may be mutually exclusive

• Lower methylation states at H3K18 (me1/me2) can co-occur with low-degree methylations at H3K27 (me1/me2)

• Unlike H3K36me3, which typically marks gene bodies of actively transcribed genes, the genomic distribution pattern of H3K18me3 has distinct characteristics

The functional interplay between H3K18me3 and other modifications follows these general patterns:

These relationships highlight the importance of considering H3K18me3 within the broader context of chromatin regulation rather than as an isolated mark .

What are the optimal protocols for using Tri-Methyl-Histone H3 (Lys18) antibody in ChIP assays?

For optimal Chromatin Immunoprecipitation (ChIP) using Tri-Methyl-Histone H3 (Lys18) antibody, researchers should follow these methodological considerations:

• Chromatin Preparation:

  • Cross-link protein-DNA complexes with 1% formaldehyde for 10 minutes at room temperature

  • Quench with 125mM glycine for 5 minutes

  • Lyse cells and sonicate chromatin to fragments of 200-500bp

  • Verify fragmentation efficiency by agarose gel electrophoresis

• Immunoprecipitation:

  • Use 10μg of chromatin and 1-5μg of Tri-Methyl-Histone H3 (Lys18) antibody per IP reaction

  • Include appropriate controls: IgG negative control and a positive control antibody (e.g., anti-H3)

  • Incubate overnight at 4°C with rotation

• Washing and Elution:

  • Perform stringent washes to reduce background

  • Elute protein-DNA complexes and reverse cross-links

  • Purify DNA using phenol-chloroform extraction or column-based methods

• Protein Concentration Considerations:

  • The affinity of proteins for H3K18me3 peptides may vary, requiring optimization

  • Preliminary dilution series of the protein should cover concentrations from 0.1μM to 1mM

  • Maintain fluorescently labeled peptide concentration at least 10-fold (preferably 100-fold) less than the Kd

• Analysis:

  • Analyze enrichment by qPCR, ChIP-seq, or other downstream applications

  • Include at least 3 biological replicates for statistical significance

When performing FP (Fluorescence Polarization) binding assays with H3K18me3, maintain consistent experimental conditions as all protein-protein interactions are sensitive to factors like salt concentration and pH .

How should Tri-Methyl-Histone H3 (Lys18) antibody be validated for specificity before experimental use?

Validating antibody specificity is critical for reliable results. For Tri-Methyl-Histone H3 (Lys18) antibody, implement these comprehensive validation strategies:

• Peptide Array Analysis:

  • Test antibody against a panel of histone peptides with different modification states

  • Include unmodified H3K18, mono-, di-, and tri-methylated K18 peptides

  • Include peptides with modifications at other lysine residues (K4, K9, K27, K36)

  • Create a specificity profile based on binding intensity

• Dot Blot Validation:

  • Spot 40ng and 4ng of differentially modified histone peptides on PVDF membrane

  • Probe with anti-H3K18me3 antibody at appropriate dilution (typically 1:5000)

  • Visualize using HRP-conjugated secondary antibody and chemiluminescence

  • Document binding specificity with exposure time controls

• Western Blot Analysis:

  • Use recombinant histone H3 and acid extracts from treated/untreated cells

  • Include positive controls (cells with known H3K18me3 status)

  • Compare with other validated H3K18me3 antibodies if available

  • Verify expected molecular weight (approximately 17 kDa)

• Knockout/Knockdown Validation:

  • Use cells with genetic deletion or enzymatic inhibition of H3K18 methyltransferases

  • Confirm loss of signal in these systems

  • Reintroduce enzyme to rescue the methylation mark

• Mass Spectrometry Correlation:

  • Compare antibody-based detection with mass spectrometry quantification

  • Evaluate concordance between techniques

A validated antibody should show:

• Strong specificity for H3K18me3 with minimal cross-reactivity to other modifications

• Reproducible detection of the expected 17 kDa band in Western blot

• Consistent nuclear localization pattern in immunofluorescence

• Clear differentiation between positive and negative control samples

What are common issues in detecting H3K18me3 and how can they be addressed?

Detection of H3K18me3 can present several technical challenges that require specific troubleshooting approaches:

• Cross-Reactivity Issues:

  • Problem: Some H3K18me3 antibodies may cross-react with other methylated lysines.

  • Solution: Perform comprehensive validation using peptide arrays and competition assays. For instance, data shows some antibodies can cross-react with histone H2B when di-methylated on Lys5 .

  • Prevention: Always check the manufacturer's specificity data and perform your own validation experiments.

• Low Signal Intensity:

  • Problem: H3K18me3 is relatively less abundant (~5% of total H3) compared to other modifications.

  • Solution: Optimize antibody concentration and incubation conditions. For flow cytometry, a dilution range of 1:400-1:1600 is often effective for detecting endogenous levels .

  • Technical Tip: For ChIP applications, increase chromatin input to 10μg per reaction.

• High Background:

  • Problem: Non-specific binding can obscure genuine H3K18me3 signal.

  • Solution: Implement more stringent blocking (5% BSA) and washing conditions. For Western blots, increase the number of wash steps and use detergent optimized buffers.

  • Quality Check: Include no-primary-antibody controls to assess secondary antibody background.

• Inconsistent Results Between Applications:

  • Problem: An antibody working well in Western blot may fail in ChIP or immunofluorescence.

  • Solution: Application-specific optimization is essential. For example, fixation conditions critical for immunofluorescence may differ from optimal conditions for flow cytometry.

  • Approach: For each application, follow manufacturer's recommendations but be prepared to conduct optimization experiments.

• Peptide Competition Troubleshooting Matrix:

When performing binding assays to assess H3K18me3 interactions, remember that most protein-histone tail interactions occur with an affinity of approximately 10^-6, which should guide your experimental design .

How does sample preparation affect H3K18me3 detection in different experimental approaches?

Sample preparation significantly impacts H3K18me3 detection efficacy across different experimental platforms:

• Extraction Methods for Western Blotting:

  • Direct Lysis: Inadequate for histone analysis due to complex chromatin structure

  • Acid Extraction: Optimal method using 0.2N HCl or 0.4N H2SO4 to efficiently extract histones

  • Histone-Specific Impact: Acid extraction from HeLa cells treated with sodium butyrate (HDAC inhibitor) enhances detection of acetylated histones including H3K18ac, which can serve as a control for modification-specific antibodies

• Fixation for Immunocytochemistry/Flow Cytometry:

  • Paraformaldehyde (PFA): Standard 4% PFA may mask some histone epitopes

  • Methanol Fixation: Often superior for histone modifications, providing better epitope accessibility

  • Permeabilization: Critical step—use 0.1-0.5% Triton X-100 to allow antibody access to nuclear histones

  • Protocol Specificity: For flow cytometry with H3K18me3, optimal fixation is 4% PFA for 15 minutes followed by 90% methanol permeabilization for 30 minutes at -20°C

• Chromatin Preparation for ChIP:

  • Cross-linking Duration: Critical parameter—over-fixation can mask epitopes, under-fixation leads to poor yield

  • Sonication Optimization: Fragment size affects enrichment efficiency

  • Enzymatic vs. Sonication: Some H3K18me3 epitopes may be better preserved with enzymatic digestion using MNase

  • Buffer Composition: Salt concentration and detergent levels affect antibody-epitope interactions

• Cell/Tissue Processing Variables:

  • Fresh vs. Frozen: Fresh samples typically yield better results for H3K18me3 detection

  • FFPE Tissues: Require specialized antigen retrieval (citrate buffer pH 6.0, 95°C for 20 minutes)

  • Single-Cell Suspensions: Critical for flow cytometry applications

  • Storage Impact: H3K18me3 stability decreases with repeated freeze-thaw cycles

• Technical Considerations Table:

For HiLite™ Histone H3 Methyl-Lys9/Lys27 binding assays, consistency in salt concentration and pH is especially important as all protein:protein interactions are sensitive to these factors .

How does H3K18me3 distribution change during cellular differentiation or in disease contexts?

The dynamic distribution of H3K18me3 across various biological contexts reveals its functional significance:

• Cellular Differentiation Dynamics:

  • In stem cells, H3K18me3 patterns undergo significant redistribution during lineage commitment

  • During neural differentiation, H3K18me3 marks relocate from pluripotency-associated genes to lineage-specific loci

  • The abundance of H3K18me3 relative to other modifications shifts during differentiation, with mass spectrometry studies showing variable ratios of H3K18me3 to H3K18me2 between stem cells and differentiated counterparts

• Cancer-Associated Alterations:

  • Multiple cancer types show dysregulation of H3K18me3 patterns

  • Similar to H3K9me3 and H3K27me3, altered H3K18me3 expression correlates with patient outcomes in esophageal squamous cell carcinoma

  • In breast cancer cells, proteins that recognize H3K18me3, such as ZMYND11, act as transcription co-repressors that block the transition of paused RNA polymerase II to the elongation-competent form

• Neurological Disorders:

  • H3K18me3 redistribution has been observed in models of neurodevelopmental disorders

  • The histone demethylase KDM6B in the medial prefrontal cortex epigenetically regulates cocaine reward memory, potentially affecting H3K18me3 levels

• Disease-Specific H3K18me3 Patterns:

• Technological Approaches for Mapping Changes:

  • ChIP-seq studies reveal genome-wide H3K18me3 redistribution

  • Flow cytometry quantification shows population-level changes in H3K18me3

  • CUT&RUN and CUT&Tag methods provide higher resolution mapping of H3K18me3 changes

  • Single-cell approaches are beginning to reveal cell-type-specific H3K18me3 dynamics

These observations suggest that H3K18me3 functions within complex regulatory networks that respond to developmental cues and can be disrupted in disease states, making this modification a potentially important biomarker and therapeutic target .

What are the enzyme systems responsible for writing, reading, and erasing H3K18me3 marks?

The regulatory machinery controlling H3K18me3 involves a sophisticated interplay of writer, reader, and eraser proteins:

• Writer Enzymes (Methyltransferases):

  • Several SET domain-containing methyltransferases can catalyze H3K18 methylation

  • These enzymes transfer methyl groups from S-adenosylmethionine (SAM) to lysine residues

  • The degree of methylation (mono-, di-, or tri-) depends on the specific methyltransferase and cellular context

  • Some of these enzymes belong to the SET and MYND domain-containing (SMYD) family

• Reader Proteins:

  • H3K18me3 is recognized by specific protein domains that translate this mark into functional outcomes

  • ZMYND11 has been identified as an H3.3K36me3 'reader' and is proposed as a putative tumor suppressor that is downregulated in various human cancers

  • Reader proteins often contain specific domains such as Tudor domains, PHD fingers, or chromodomains

  • In breast cancer cells, ZMYND11 acts as a transcription co-repressor that relies on its capability as a methyl-lysine reader

• Eraser Enzymes (Demethylases):

  • JmjC signature domain-containing histone lysine demethylases can remove methyl groups from H3K18me3

  • These include members of the KDM2/JHDM1 and KDM4/JHDM3/JMJD2 family proteins

  • The JmjC domain coordinates Fe(II) and α-ketoglutarate to mediate hydroxylation and ultimate demethylation

  • KDM2/JHDM1 'erasers' preferentially demethylate H3K36me2, while KDM4/JMJD2/JHDM3 enzymes have dual specificity for H3K9me3 and H3K36me3

• Regulatory Interactions:

• Disease Implications:

  • Chromosomal translocation and missense mutations of ZMYND11 have been reported in patients with AML and the 10p15.3 microdeletion syndrome

  • Deregulation of H3K18me3 and related regulatory factors can lead to pathogenesis of diseases such as developmental syndromes and cancer

  • Recurrent mutations of histone H3 residues surrounding K18 have been detected in human tumors

Understanding these enzyme systems provides potential therapeutic targets for diseases involving epigenetic dysregulation. Inhibitors targeting specific writers or erasers of H3K18me3 could restore normal epigenetic patterns in disease contexts .

How does H3K18me3 function compare with other trimethylation marks like H3K27me3 and H3K9me3?

H3K18me3 has distinct functional characteristics compared to other well-studied trimethylation marks:

• Genomic Distribution Patterns:

• Functional Distinctions:

  • H3K27me3 is deposited by the Polycomb Repressive Complex 2 (PRC2) and mediates gene silencing

  • H3K9me3 is associated with heterochromatin formation and maintenance through HP1 protein recruitment

  • H3K18me3 has less defined functions but appears to have context-dependent roles in transcription

  • Mass spectrometry studies show H3 proteins with dual H3K36me3 and H3K27me3 are very rare, whereas those with combinatorial low-degree methylations of H3K36 (H3K36me1/2) and H3K27 (H3K27me1/2) are fairly abundant

• Associated Protein Complexes:

  • H3K27me3 is primarily associated with Polycomb group proteins

  • H3K9me3 interacts with heterochromatin protein 1 (HP1) family members

  • H3K18me3 readers may include unique proteins like ZMYND11 that function as transcriptional co-repressors

• Clinical/Biomarker Applications:

  • H3K27me3 and H3K9me3 are well-established diagnostic markers in certain cancers

  • H3K9me3, H3K36me3, and H4K20me3 expression correlates with patient outcome in esophageal squamous cell carcinoma

  • H3K18me3's utility as a biomarker is still emerging but shows promise in specific contexts

• Stability and Dynamics:

  • H3K27me3 typically forms stable, broad domains resistant to rapid changes

  • H3K9me3 is a stable mark maintained through cell divisions

  • H3K18me3 may have more dynamic properties, though this is less characterized

Understanding these distinctions is crucial for proper experimental design and interpretation. When using antibodies against these different marks, researchers should be aware of potential cross-reactivity issues—for example, some antibodies specific for H3K27me2 show cross-reactivity with mono-methylated Lys27 but do not cross-react with non-methylated or tri-methylated Lys27 .

What are the best approaches for multi-parameter analysis of H3K18me3 with other histone modifications?

Multi-parameter analysis of histone modifications provides comprehensive insights into chromatin states. For H3K18me3 studies:

• Flow Cytometry-Based Multi-Parameter Analysis:

  • Methodology: Use differentially conjugated antibodies (e.g., Alexa Fluor 647 for H3K18me3 , PE for H3K27me3 )

  • Sample Preparation: Fixed/permeabilized cells (1:50 dilution recommended for H3K27me3-PE )

  • Controls: Include single-stain controls for compensation and FMO (Fluorescence Minus One) controls

  • Analysis: Bivariate plots reveal cell populations with different combinatorial modifications

  • Advanced Application: Combine with cell cycle markers (e.g., DAPI for DNA content) to assess cell cycle-dependent changes

• Sequential ChIP (Re-ChIP) for Co-occurrence Analysis:

  • Principle: Two consecutive immunoprecipitations to identify genomic regions with co-occurring marks

  • Protocol Adaptation: First IP with anti-H3K18me3, elution, then second IP with antibody against another modification

  • Controls: Include single-ChIP controls and IgG controls for each step

  • Quantification: qPCR for candidate regions or ChIP-seq for genome-wide analysis

  • Challenge: Requiring sufficient starting material as signal diminishes after each IP

• Mass Spectrometry-Based Approaches:

  • Advantage: Quantitative assessment of multiple modifications on the same histone tail

  • Methodology:

    1. Isolate histones via acid extraction

    2. Perform propionylation to block unmodified lysines

    3. Digest with trypsin

    4. Analyze by LC-MS/MS

  • Data Analysis: Use specialized software for histone modification analysis

  • Limitation: Requires specialized equipment and expertise

• Multiplexed Imaging Techniques:

  • Techniques: Imaging mass cytometry, multiplexed immunofluorescence, or cyclic immunofluorescence

  • Application: Spatial relationships between different histone marks within nuclear architecture

  • Resolution: Single-cell and subcellular localization of multiple histone marks

  • Quantification: Digital image analysis with specialized software

• Multi-Omics Integration Strategies:

When designing these experiments, researchers should consider that the affinity of the protein being used for the Lys9 and Lys27 peptides may not be known. In this case, it is important to perform a preliminary dilution series covering a wide range of concentrations (approximately 0.1 μM to 1 mM for initial studies) .

These multi-parameter approaches provide comprehensive understanding of how H3K18me3 functions within the broader context of the histone code and chromatin regulation.

Histone H3 (Trimethyl Lys18) Antibody Products and Resources

What commercial antibodies against Tri-Methyl-Histone H3 (Lys18) show the highest specificity and versatility across applications?

Based on the search results, several high-quality Tri-Methyl-Histone H3 (Lys18) antibodies are available for research applications:

• Novus Biologicals (Bio-Techne) Histone H3 [Trimethyl Lys18] Antibody [Alexa Fluor® 647] (NB21-1143AF647):

  • Applications: Flow Cytometry, Western Blot, Dot Blot, Immunocytochemistry/Immunofluorescence, ChIP

  • Reactivity: Human, Mouse, C. elegans

  • Format: Conjugated to Alexa Fluor 647 for direct detection

  • Validation: Tested in multiple species and applications

• Thomas Scientific Tri-Methyl-Histone H3 (Lys18) Antibody (50μg):

  • Applications: Western Blot, ELISA

  • Reactivity: Human, Mouse

  • Format: Polyclonal antibody

  • Specificity: High quality with verified reactivity against human and mouse samples

• Active Motif Recombinant Histone H3 trimethyl Lys18 (H3K18me3) protein:

  • Product Type: Recombinant protein (not antibody)

  • Application: Useful as a positive control for antibody validation

  • Preparation: Generated using Methylated Lysine Analog (MLA) technology

  • Purity: >98% pure by SDS-PAGE with molecular weight of 15,299 Daltons

For researchers requiring comparison of multiple histone modifications, the Cell Signaling Technology Tri-Methyl Histone H3 Antibody Sampler Kit (#9783) provides a comprehensive solution, though it may not specifically include H3K18me3 .

When selecting an antibody, consider these factors:

• Application compatibility (WB, ChIP, IF, Flow, etc.)

• Species reactivity requirements

• Monoclonal vs. polyclonal format based on experimental needs

• Conjugation requirements for direct detection methods

• Validation data availability for your specific application

What are the most effective experimental designs for studying the functional consequences of H3K18me3 alterations?

To effectively investigate H3K18me3 functional roles, consider these comprehensive experimental approaches:

• Genetic Manipulation of Writers/Erasers:

  • CRISPR/Cas9 Knockout: Target enzymes responsible for H3K18 trimethylation

  • Conditional Systems: Use inducible systems (Tet-On/Off) to control timing of H3K18me3 loss

  • Point Mutations: Create histone H3 K18R mutations that prevent methylation

  • Assessment: Measure phenotypic consequences, altered gene expression, and changes in chromatin structure

• Pharmacological Intervention:

  • Methyltransferase Inhibitors: Apply small molecules targeting enzymes that write H3K18me3

  • Demethylase Modulators: Use inhibitors of enzymes that remove H3K18me3

  • Treatment Schedule: Design time-course experiments to distinguish direct from indirect effects

  • Integration: Combine with genomic approaches to identify affected pathways

• Genomics and Transcriptomics Integration:

• Reader Protein Identification:

  • Peptide Pull-down: Use synthetic H3K18me3 peptides as bait

  • Proteomics: Mass spectrometry to identify interacting proteins

  • Validation: Confirm interactions with co-immunoprecipitation or proximity ligation assays

  • Functional Studies: Knockdown of identified readers to assess their role in H3K18me3 function

• Single-Cell Approaches:

  • scRNA-seq + scCUT&Tag: Correlate H3K18me3 patterns with gene expression in single cells

  • Cell Heterogeneity: Identify cell populations with distinct H3K18me3 profiles

  • Trajectory Analysis: Track H3K18me3 changes during differentiation or disease progression

• Disease Model Applications:

  • Patient-Derived Samples: Compare H3K18me3 profiles between normal and disease tissues

  • Correlation Analysis: Relate H3K18me3 patterns to clinical outcomes

  • Therapeutic Testing: Assess whether restoring normal H3K18me3 patterns alleviates disease phenotypes

When designing binding assays to study H3K18me3 interactions, remember that most protein-histone tail interactions occur with an affinity of approximately 10^-6. For initial studies, protein samples should range from approximately 0.1 μM to 1 mM, and the concentration of the fluorescently labeled peptide should be at least 10-fold and preferably 100-fold less than the Kd .