XRCC4 Antibody

What is XRCC4 and why is it important in research?

XRCC4 is a core protein in the NHEJ pathway, which repairs double-strand breaks in DNA. It forms part of a complex that includes the Ku heterodimer (Ku70/Ku80), DNA-PKcs, DNA ligase IV, XLF, and PAXX. XRCC4 specifically interacts with XLF and promotes the ligation of DNA strands by DNA ligase IV . Its importance in research stems from its critical role in maintaining genomic integrity and its associations with human diseases. Mutations and polymorphisms in XRCC4 have been linked to microcephaly, dwarfism, and cancer susceptibility . Research into XRCC4 provides insights into DNA repair mechanisms and potential therapeutic targets for cancer treatment.

What applications are XRCC4 antibodies commonly used for?

XRCC4 antibodies are used in multiple applications across molecular and cellular biology research:

These applications enable researchers to study XRCC4 expression, localization, and interactions with other proteins in the DNA repair pathway.

Why does XRCC4 show different molecular weights in Western blots?

While the calculated molecular weight of XRCC4 is approximately 35-38 kDa based on its amino acid sequence (310 amino acids), it typically appears at 50-55 kDa in Western blots . This discrepancy occurs due to post-translational modifications, particularly phosphorylation events that occur during DNA damage responses. XRCC4 is phosphorylated by DNA-PKcs and other kinases during DNA repair, which increases its apparent molecular weight on SDS-PAGE gels. Additionally, the elongated structure of XRCC4 with its coiled-coil domain contributes to anomalous migration during electrophoresis . Researchers should be aware of this discrepancy when identifying XRCC4 bands in their experiments.

What species reactivity can be expected with XRCC4 antibodies?

The species reactivity of XRCC4 antibodies varies by manufacturer and clone. From the available search results:

When planning experiments with animal models, researchers should verify the cross-reactivity of their chosen antibody with the target species to ensure reliable results.

How can researchers validate the specificity of XRCC4 antibodies?

Validating antibody specificity is crucial for reliable research results. For XRCC4 antibodies, consider these approaches:

• Positive controls: Use cell lines known to express XRCC4, such as HEK293T cells transfected with XRCC4 expression vectors .

• Negative controls: Compare with XRCC4 knockdown or knockout samples. The search results mention that knockdown of XRCC4 expression in hepatocellular carcinoma and triple-negative breast cancer cells has been studied .

• Peptide competition assays: Pre-incubate the antibody with the immunizing peptide to block specific binding.

• Multiple antibody validation: Use different antibodies targeting different epitopes of XRCC4 to confirm results.

• Western blot analysis: Confirm a single band at the expected molecular weight (approximately 50 kDa for XRCC4) .

• Immunoprecipitation followed by mass spectrometry: This can verify the identity of the precipitated protein.

What methodological considerations are important when using XRCC4 antibodies for co-immunoprecipitation studies?

When conducting co-immunoprecipitation (co-IP) experiments with XRCC4 antibodies to study protein interactions:

• Buffer optimization: Use buffers that preserve protein-protein interactions while minimizing background. The search results mention co-IP experiments with XRCC4 and DNA ligase IV that successfully demonstrate their interaction .

• Antibody selection: Choose antibodies specifically validated for IP applications. For example, Cell Signaling #23908 is recommended at a 1:50 dilution for IP .

• Controls: Include IgG controls to identify non-specific binding and input controls to verify protein expression before IP.

• Cross-linking considerations: In some cases, mild cross-linking may help preserve transient or weak interactions in the NHEJ complex.

• Detection strategy: After IP, proteins can be detected by Western blotting with antibodies against XRCC4, DNA ligase IV, or other interacting partners .

• Native conditions: Consider native conditions to preserve the structural integrity of the XRCC4-DNA ligase IV complex, especially given the importance of the helix-loop-helix structure in the inter-BRCT linker region and the second BRCT domain interactions .

How can XRCC4 antibodies be used to study the structural changes in the XRCC4-DNA ligase IV complex?

The XRCC4-DNA ligase IV interaction involves significant structural changes, including a kink in the tail region of XRCC4 induced by the second BRCT domain of DNA ligase IV . To study these structural changes:

• Epitope-specific antibodies: Use antibodies targeting different regions of XRCC4, particularly those that might be affected by conformational changes upon binding to DNA ligase IV.

• Proximity ligation assays: These can detect protein-protein interactions in situ and provide spatial information about the complex.

• FRET-based approaches: When combined with fluorescently tagged proteins, these can reveal conformational changes in live cells.

• IP followed by structural analysis: Immunoprecipitate the complex using XRCC4 antibodies and analyze its structure through techniques like hydrogen-deuterium exchange mass spectrometry.

• Mutational analysis: Create mutations at key interaction sites (e.g., residues 170-172 of XRCC4 where the kink occurs) and use antibodies to study how these affect complex formation .

What approaches can be used to study XRCC4 in the context of cancer treatment sensitivity?

Research indicates that knockdown of XRCC4 expression increases sensitivity to treatments in certain cancers . To investigate this:

• Expression correlation studies: Use XRCC4 antibodies in Western blots or IHC to correlate XRCC4 expression levels with treatment response in patient samples or cell lines.

• Functional knockdown studies: After XRCC4 knockdown, use antibodies to confirm reduced protein levels before assessing treatment sensitivity.

• Phosphorylation status: Use phospho-specific antibodies to determine if XRCC4 phosphorylation status correlates with treatment sensitivity.

• Combination with DNA damage markers: Co-stain with markers of DNA damage (γ-H2AX) to assess if XRCC4 levels correlate with unrepaired damage after treatment.

• In vivo models: Use XRCC4 antibodies for IHC in xenograft models to assess protein expression before and after treatment.

This approach is particularly relevant for hepatocellular carcinoma cells treated with doxorubicin and triple-negative breast cancer cells exposed to ionizing radiation, where XRCC4 expression has been linked to treatment sensitivity .

What are the optimal storage and handling conditions for XRCC4 antibodies?

Proper storage and handling are essential for maintaining antibody performance:

• Storage temperature: Store at -20°C to -80°C for long-term storage, as recommended for products like NBP2-74896 .

• Aliquoting: While some manufacturers advise against aliquoting (e.g., "Do not aliquot the antibody" ), dividing into single-use aliquots can generally reduce freeze-thaw cycles.

• Reconstitution: For lyophilized antibodies, follow manufacturer's recommendations. For NBP2-74896, adding 100µL distilled water to achieve approximately 1 mg/mL concentration is recommended .

• Buffer considerations: Some antibodies are provided in PBS only (e.g., 66621-1-PBS) , while others may contain preservatives or stabilizers.

• Freeze-thaw cycles: Minimize these as recommended by manufacturers to maintain antibody activity .

How should researchers optimize XRCC4 antibody dilutions for different applications?

Optimization strategies vary by application:

• Western blotting: Start with the manufacturer's recommended dilution (e.g., 1:1000 for Cell Signaling #23908 or 1:2000 for Novus Biologicals NBP2-74896 ). Perform a dilution series if needed.

• Immunohistochemistry: Begin with the suggested dilution (e.g., 1:50 for NBP2-74896 ), considering tissue type and fixation method. Paraffin-embedded lung tissue and adenocarcinoma of endometrium have been successfully stained with XRCC4 antibodies .

• Immunoprecipitation: Use more concentrated antibody solutions (e.g., 1:50 as suggested for Cell Signaling #23908 ).

• Signal enhancement: Consider using signal amplification systems for low abundance targets, particularly in tissues with minimal XRCC4 expression.

• Background reduction: Include appropriate blocking reagents to minimize non-specific binding.

• Incubation conditions: Optimize temperature and duration based on application requirements.

What are common issues when using XRCC4 antibodies and how can they be resolved?

Researchers may encounter several challenges:

• Multiple bands in Western blot: Could indicate degradation products, splice variants, or post-translational modifications. Verify with positive and negative controls.

• Weak or no signal: May require optimizing antibody concentration, incubation conditions, or detection methods. Consider the sensitivity of the antibody (e.g., Cell Signaling #23908 is rated for "Endogenous" sensitivity ).

• High background: Improve blocking conditions, increase washing steps, or dilute the antibody further.

• Inconsistent results: Standardize sample preparation, particularly for phosphorylated forms of XRCC4 that may be affected by phosphatase activity.

• Species cross-reactivity issues: Verify antibody reactivity with your experimental model. Cell Signaling #23908 shows reactivity with human, mouse, and rat samples .

How can XRCC4 antibodies be used to study NHEJ complex formation in response to DNA damage?

To investigate dynamic NHEJ complex assembly:

• Time-course experiments: Use XRCC4 antibodies in combination with other NHEJ component antibodies to track complex formation at different times after DNA damage induction.

• Chromatin immunoprecipitation (ChIP): Apply XRCC4 antibodies to study recruitment to DNA damage sites.

• Immunofluorescence co-localization: Combine XRCC4 antibodies with antibodies against other NHEJ factors to visualize complex formation at DNA break sites.

• Proximity ligation assay: Detect in situ protein-protein interactions between XRCC4 and other NHEJ components following DNA damage.

• Sequential ChIP: Use to determine if multiple NHEJ factors (including XRCC4) occupy the same DNA regions during repair.

• Biochemical fractionation: Combined with Western blotting using XRCC4 antibodies to track protein redistribution between cellular compartments after damage.

These approaches can provide insights into how the NHEJ complex, including XRCC4, DNA ligase IV, XLF, and PAXX, assembles and functions in response to DNA damage .

How can XRCC4 antibodies contribute to research on XRCC4-related human diseases?

XRCC4 mutations and polymorphisms have been linked to microcephaly, dwarfism, and cancer susceptibility . Researchers can use XRCC4 antibodies to:

• Clinical correlation studies: Compare XRCC4 expression levels in patient samples with clinical outcomes.

• Mutation impact analysis: Use antibodies that recognize wild-type but not mutant forms to screen patient samples.

• Functional studies: Investigate how disease-associated mutations affect XRCC4's interactions with other proteins using co-IP with XRCC4 antibodies.

• Tissue-specific expression: Use IHC with XRCC4 antibodies to study expression patterns in tissues affected by XRCC4-related diseases.

• Biomarker development: Evaluate XRCC4 as a potential biomarker for cancer susceptibility or treatment response.

This research direction is particularly relevant given the established links between XRCC4 and various human diseases .

What role can XRCC4 antibodies play in developing DNA repair-targeted cancer therapies?

The finding that XRCC4 knockdown increases sensitivity to treatments in certain cancers suggests potential therapeutic applications :

• Target validation: Use XRCC4 antibodies to confirm target engagement of drugs designed to inhibit or modulate XRCC4 function.

• Resistance mechanisms: Investigate changes in XRCC4 expression or post-translational modifications in treatment-resistant cancers.

• Combination therapy studies: Use XRCC4 antibodies to assess expression levels before and after treatment to guide combination therapy approaches.

• Patient stratification: Develop IHC-based assays using XRCC4 antibodies to identify patients likely to respond to DNA repair-targeted therapies.

• Functional assays: Utilize XRCC4 antibodies in high-throughput screens to identify compounds that disrupt XRCC4-DNA ligase IV interactions.

This approach is supported by evidence that XRCC4 knockdown enhances sensitivity to doxorubicin in hepatocellular carcinoma cells and to ionizing radiation in triple-negative breast cancer cells .