RAD51C Antibody

What is RAD51C and what is its biological significance?

RAD51C is a pivotal component of the homologous recombination (HR) pathway responsible for repairing DNA double-strand breaks within the nucleus. RAD51C, also called R51H3 and Rad51l2a, is essential for maintaining genomic stability, preventing mutations, and thwarting neoplastic transformations .

RAD51C is a paralog of RAD51 that participates in multiple distinct protein complexes:

• The BCDX2 complex (RAD51B-RAD51C-RAD51D-XRCC2)

• The CX3 complex (RAD51C-XRCC3)

• The PALB2-scaffolded HR complex containing BRCA2

These complexes function at different stages of the BRCA1-BRCA2-dependent HR pathway. RAD51C is crucial for:

• Facilitating checkpoint signaling by promoting CHK2 activation

• RAD51 foci formation in response to DNA damage

• Branch migration and Holliday junction resolution

• Protecting RAD51 from ubiquitin-mediated degradation following DNA damage

• Maintaining centrosome number in mitosis

What types of RAD51C antibodies are available and how do they differ?

Several types of RAD51C antibodies are available for research applications:

Monoclonal antibodies:

• Mouse monoclonal IgG1 (such as 2H11) developed against human RAD51C protein

• Available in various conjugated forms including:

  • Non-conjugated

  • Agarose-conjugated (for immunoprecipitation)

  • HRP-conjugated (for enhanced western blotting)

  • Fluorophore-conjugated: FITC, PE, and Alexa Fluor variants (for immunofluorescence)

Polyclonal antibodies:

• Rabbit polyclonal antibodies (such as ab95069) raised against synthetic peptides from human RAD51C

What are the validated applications for RAD51C antibodies?

RAD51C antibodies have been validated for several experimental applications:

Western Blotting (WB):

• Reliably detects RAD51C proteins (~42 kDa) from mouse, rat, and human origins

• Recommended dilutions range from 1:1000 for standard WB to 1:50-1:250 for Simple Western™ applications

Immunoprecipitation (IP):

• Effective for pulling down RAD51C complexes to study protein-protein interactions

• Particularly useful for investigating RAD51C interactions with other DNA repair proteins

Immunofluorescence (IF):

• Visualization of RAD51C foci formation after DNA damage

• Recommended dilutions of 1:200-1:800

• Can detect RAD51C localization at sites of DNA damage in human cell lines

Co-immunoprecipitation studies:

• Investigating RAD51C's interactions with other proteins like RAD51D and XRCC2

What are the optimal conditions for detecting RAD51C foci formation?

For successful visualization of RAD51C foci after DNA damage:

• DNA damage induction: RAD51C foci can be detected after irradiation with doses as low as 1 Gy, with significant formation observed at 10 Gy

• Timing: Examine cells within several hours post-irradiation; RAD51C foci persist longer than RAD51 foci

• Cell types: RAD51C foci have been successfully visualized in several human cell lines including HeLa, U2OS, WI38, and HCT116

• Antibody considerations:

  • Some antibodies may not efficiently visualize RAD51C foci in mouse fibroblasts

  • Fluorophore-conjugated antibodies (FITC, PE, Alexa Fluor) can enhance detection sensitivity

• Controls: Include non-irradiated control cells and RAD51C-depleted cells (via siRNA) to validate antibody specificity

What methodological controls should be included when using RAD51C antibodies?

To ensure reliable results with RAD51C antibodies, implement these controls:

Positive controls:

• Cell lines known to express RAD51C (HeLa, U2OS)

• Cell extracts from cells expressing tagged RAD51C (such as GFP-RAD51C or HA-RAD51C)

Negative controls:

• RAD51C-depleted cells using siRNA or shRNA

• Isotype control antibodies to rule out non-specific binding

Validation approaches:

• Establish single-cell clones expressing siRNA-resistant RAD51C (RAD51C*) to confirm antibody specificity

• Use GFP-tagged RAD51C expressed at levels comparable to endogenous protein to confirm localization patterns

• For co-localization studies, include alternative DNA damage markers (such as γH2AX)

How can RAD51C antibodies be used to investigate DNA repair mechanisms?

RAD51C antibodies enable detailed investigation of DNA repair mechanisms through several approaches:

Temporal dynamics of repair complex assembly:

• RAD51C persists at DNA break sites longer than RAD51, suggesting distinct early and late roles in HR repair

• Follow time-course experiments after DNA damage to track when RAD51C assembles and disassembles from damage sites

Differential complex formation analysis:

• RAD51C operates in at least two distinct multiprotein complexes (BCDX2 and CX3)

• Sequential immunoprecipitation using antibodies against different complex components can distinguish which complex is active during specific repair phases

Holliday junction resolution studies:

• RAD51C is implicated in branch migration and Holliday junction resolution in late stages of HR

• Chromatin immunoprecipitation (ChIP) using RAD51C antibodies can detect association with Holliday junctions

Checkpoint activation mechanisms:

• RAD51C facilitates CHK2 activation to promote cell cycle arrest after DNA damage

• Combine RAD51C immunoprecipitation with phospho-CHK2 detection to examine this signaling pathway

What approaches can determine if RAD51C deficiency affects sensitivity to PARP inhibitors?

RAD51C deficiency correlates with increased sensitivity to PARP inhibitors, which can be investigated through:

Cell viability assays:

• Compare olaparib sensitivity between RAD51C-proficient and RAD51C-deficient cancer cells

• Measure IC50 values to quantify differences in sensitivity

Mechanistic studies:

• Analyze cell cycle distribution changes (G2-M arrest) following PARP inhibitor treatment in RAD51C-deficient cells

• Assess apoptosis markers to determine if cell death is enhanced in RAD51C-deficient cells

Genetic complementation:

• Restore RAD51C expression in deficient cell lines to confirm attenuation of PARP inhibitor sensitivity

• Silence RAD51C in resistant cell lines to enhance sensitivity to olaparib

RAD51 foci quantification:

• Measure RAD51 foci formation in RAD51C-deficient cells treated with PARP inhibitors

• Reduced RAD51 foci formation indicates compromised HR repair capacity

In vivo validation:

• Xenograft models using RAD51C-deficient tumors show significant growth suppression with olaparib treatment

How can RAD51C antibodies help distinguish between early and late functions in homologous recombination?

Evidence supports both early and late roles for RAD51C in HR, which can be investigated using:

Early function analysis:

• Co-immunostaining of RAD51C with RAD51 after DNA damage to assess filament formation

• In BRCA2-deficient cells, RAD51C foci form while RAD51 fails to associate with damage sites, suggesting RAD51C acts as a platform for RAD51 assembly

Late function analysis:

• RAD51C persists at break sites after RAD51 dissociates, indicating involvement in post-invasion HR activities

• Time-course studies using RAD51C antibodies can track its association with late-stage repair intermediates

Complex-specific functions:

• The RAD51B-RAD51C complex functions as a mediator of RAD51 nucleoprotein complex assembly (early role)

• The RAD51C-XRCC3 complex binds to Holliday junctions (late role)

• Co-immunoprecipitation with complex-specific partners can distinguish these distinct functions

Meiotic studies:

• RAD51C foci maintenance on mouse meiotic chromosomes at late prophase I stages coincides with Holliday junction resolution

• Immunofluorescence with RAD51C antibodies can track these meiotic functions

What approaches can investigate RAD51C variants associated with cancer risk?

RAD51C variants have been linked to increased breast and ovarian cancer risk, which can be studied through:

Variant identification and classification:

• Over 3,000 harmful genetic changes that could disrupt normal RAD51C function have been identified

• These changes increase ovarian cancer risk six-fold and aggressive breast cancer subtypes four-fold

Functional assays:

• Use RAD51C antibodies to assess protein expression and localization of variant forms

• Compare DNA damage-induced foci formation between wild-type and variant RAD51C

Protein interaction studies:

• Immunoprecipitation with RAD51C antibodies to determine if variants affect interactions with partner proteins like RAD51D and XRCC2

• Assess complex formation efficiency using co-immunoprecipitation approaches

DNA repair capacity:

• Measure homologous recombination efficiency in cells expressing RAD51C variants

• Analyze sensitivity to DNA-damaging agents and PARP inhibitors in cells with RAD51C variants

Hypomorphic allele identification:

• Recently discovered hypomorphic alleles lessen RAD51C function without completely disabling it

• Western blotting with RAD51C antibodies can help quantify reduced protein levels associated with these alleles

What methods can overcome cross-reactivity challenges when using RAD51C antibodies?

While some RAD51C antibodies (like 2H11) show no cross-reactivity with other RAD51 family members, others may require additional validation:

Antibody validation strategies:

• Use RAD51C knockout or knockdown cells as negative controls to confirm specificity

• Test antibodies on cell lines overexpressing different RAD51 paralogs to assess cross-reactivity

Signal verification approaches:

• Confirm results with multiple RAD51C antibodies targeting different epitopes

• For critical experiments, validate observations using complementary techniques (e.g., mass spectrometry)

Immunodepletion controls:

• Pre-absorb antibodies with recombinant RAD51C protein before immunostaining to confirm signal specificity

• Sequential immunodepletion can help distinguish between RAD51 family members

Advanced imaging techniques:

• Super-resolution microscopy can help distinguish between closely associated RAD51 family proteins

• Proximity ligation assays (PLA) can verify specific interactions between RAD51C and partner proteins

How can RAD51C antibodies be used to study checkpoint signaling?

RAD51C plays critical roles in checkpoint activation following DNA damage:

Cell cycle analysis:

• RAD51C is required for S-phase accumulation after irradiation with 1 Gy

• RAD51C-depleted cells fail to properly arrest at G2/M transition in response to DNA damage

Methodological approach:

• Transfect cells with control siRNA or RAD51C-specific siRNA

• Irradiate cells (1-10 Gy) 48 hours after transfection

• Analyze cell cycle distribution by FACS 2 hours after irradiation

• Detect phosphorylated histone H3 to identify mitotic cells

• Compare cell cycle profiles between RAD51C-proficient and RAD51C-depleted cells

CHK2 activation studies:

• RAD51C facilitates checkpoint signaling by promoting CHK2 phosphorylation

• Immunoprecipitate CHK2 from control and RAD51C-depleted cells after DNA damage

• Analyze phosphorylation status using phospho-specific antibodies

Mitotic entry checkpoint:

• Primary MEFs with RAD51C knockdown enter mitosis despite unrepaired chromatid and chromosome breaks

• Combine immunofluorescence for RAD51C with metaphase spread analysis to correlate RAD51C levels with chromosomal breaks

What considerations are important when using RAD51C antibodies for visualizing nuclear foci?

Successful visualization of RAD51C nuclear foci requires attention to several factors:

Fixation and permeabilization:

• Optimal fixation methods (e.g., 4% paraformaldehyde followed by permeabilization with 0.5% Triton X-100) are crucial for maintaining nuclear structure while allowing antibody access

DNA damage induction methods:

• Various DNA damaging agents can be used:

  • Ionizing radiation (1-10 Gy) produces robust foci formation

  • Partial irradiation of nuclei with ultrasoft x-rays (∼2 Gy) can create defined damage areas for co-localization studies

  • Chemical agents (e.g., etoposide) can also induce RAD51C foci

Co-localization studies:

• RAD51C foci overlap with RAD51 foci at DNA damage sites

• Use appropriate fluorophore combinations to avoid spectral overlap

• Consider sequential staining if antibody species compatibility is an issue

Antibody selection:

• Different antibodies may perform differently in immunofluorescence applications

• Fluorophore-conjugated primary antibodies may enhance detection of low-abundance proteins

• Consider signal amplification methods for detecting subtle changes in localization

Quantification approaches:

• High-content imaging systems can automate foci counting

• Establish clear criteria for what constitutes a focus (size, intensity threshold)

• Compare foci numbers, size, and intensity between experimental conditions

How can RAD51C antibodies be used in studying epigenetic regulation?

RAD51C expression is subject to epigenetic regulation, which can be studied using:

Epigenetic alterations:

• RAD51C expression is downregulated in some cancer cells due to epigenetic changes

• Low RAD51C expression is observed in certain gastric cancer tissues

Methodological approaches:

• Treat cells with epigenetic modifiers (DNA methyltransferase inhibitors, histone deacetylase inhibitors)

• Use western blotting with RAD51C antibodies to assess changes in protein expression

• Correlate protein expression with mRNA levels and DNA methylation status

• Perform chromatin immunoprecipitation (ChIP) to study histone modifications at the RAD51C promoter

Clinical correlations:

• Compare RAD51C protein levels (by immunohistochemistry) in cancer tissues versus normal tissues

• Correlate RAD51C expression with methylation markers and patient outcomes

What are the best approaches for detecting RAD51C-dependent protein complexes?

RAD51C participates in multiple protein complexes with distinct functions, which can be studied through:

Complex identification:

• The BCDX2 complex (RAD51B-RAD51C-RAD51D-XRCC2) acts at early stages of HR

• The CX3 complex (RAD51C-XRCC3) functions at later stages

Co-immunoprecipitation strategies:

• Use antibodies against RAD51C to pull down associated proteins

• Immunoblot for complex-specific components (e.g., RAD51D, XRCC2, XRCC3)

• Reverse co-IP with antibodies against complex partners to confirm interactions

Sequential immunoprecipitation:

• First IP with anti-RAD51C, then re-IP with antibodies against specific complex components

• This approach can distinguish distinct complexes containing RAD51C

Bridging interactions:

• RAD51C directly interacts with RAD51D but not XRCC2

• RAD51D bridges the interaction between RAD51C and XRCC2

• Determine direct versus indirect interactions through yeast two-hybrid validation

Experimental verification examples:

• Immunoprecipitation using α-XRCC2 or α-RAD51D can pull down RAD51C (detected at ~42 kDa)

• HA-tagged RAD51D can co-precipitate both XRCC2 and RAD51C, confirming complex formation

How can RAD51C antibodies be used to analyze cancer therapeutic responses?

RAD51C status affects response to certain cancer therapies, particularly PARP inhibitors:

Biomarker development:

• RAD51C deficiency may serve as a biomarker for predicting antitumor effects of PARP inhibitors like olaparib

• Immunohistochemistry with RAD51C antibodies can assess expression levels in tumor samples

Response prediction:

• RAD51C-deficient cancer cells show:

  • Higher sensitivity to olaparib

  • Enhanced G2-M cell-cycle arrest

  • Increased apoptosis after PARP inhibitor treatment

Resistance mechanisms:

• Monitor RAD51C expression in tumors that develop resistance to PARP inhibitors

• Test if restoration of RAD51C function correlates with acquired resistance

Combination therapy strategies:

• Assess how targeting RAD51C might sensitize resistant tumors to other therapies

• Quantify RAD51C expression and localization before and after treatment

Xenograft models:

• RAD51C antibodies can be used to confirm protein status in tumor tissues

• Correlate RAD51C expression levels with olaparib response in patient-derived xenografts