FAM35A Antibody

What is FAM35A and why is it significant in DNA repair research?

FAM35A is a previously uncharacterized protein that has been identified as a novel interactor of the REV7/RIF1/53BP1 complex, which plays a crucial role in DNA double-strand break repair. The significance of FAM35A lies in its structural composition and functional role in DNA damage response. Structurally, FAM35A contains an unstructured N-terminal region and a C-terminal region harboring three OB-fold domains similar to those in the single-stranded DNA-binding protein RPA .

Functionally, FAM35A modulates DNA damage sensitivity and influences repair pathway choice between homologous recombination and non-homologous end-joining. Research has shown that FAM35A re-localizes in damaged cell nuclei following exposure to DNA-damaging agents, suggesting direct involvement in DNA repair processes . The gene is altered at high frequency in prostate cancers (up to 13%) and is significantly less expressed in metastatic cases, highlighting its potential as a therapeutically relevant cancer marker .

Which applications are most suitable for FAM35A antibody detection?

FAM35A antibodies can be utilized in multiple immunoassay techniques for effective detection and characterization. According to available research data, the following applications have been validated for FAM35A antibody detection:

• Western Blot (WB): Effective for detecting FAM35A protein expression levels and validating knockdown experiments

• Enzyme-linked Immunosorbent Assay (ELISA): Suitable for quantitative measurement of FAM35A in solution

• Immunofluorescence (IF): Appropriate for studying FAM35A subcellular localization, particularly its re-localization into nuclear foci following DNA damage

• Immunoprecipitation (IP): Useful for studying protein-protein interactions, as demonstrated in co-immunoprecipitation studies with REV7, 53BP1, and RIF1

• Immunohistochemistry (IHC): Can be used for detecting FAM35A in tissue samples, which may be particularly relevant for cancer studies

When selecting an antibody application, researchers should consider their specific experimental objectives and the cellular context in which FAM35A is being studied.

How can researchers visualize FAM35A localization in response to DNA damage?

To visualize FAM35A localization in response to DNA damage, researchers can employ immunofluorescence techniques using anti-FAM35A antibodies. Based on published methodologies, the following protocol has proven effective:

• Generate a cell line stably expressing GFP-FAM35A or utilize anti-FAM35A antibodies for endogenous protein detection

• Induce DNA damage by exposing cells to appropriate agents (e.g., mitomycin C at 100 ng/ml for 24 hours, as reported in studies)

• Fix cells and perform immunostaining with anti-GFP antibodies (for GFP-FAM35A) or direct anti-FAM35A antibodies

• Counterstain nuclei with DAPI to provide context for nuclear localization

• Visualize using fluorescence microscopy

Research has demonstrated that FAM35A concentrates into distinct nuclear foci following exposure to DNA-damaging agents, indicating its direct involvement in DNA repair processes . When analyzing results, it's important to compare the localization pattern between untreated and treated conditions to accurately assess damage-induced changes.

What are the recommended protocols for FAM35A antibody validation?

Thorough validation of FAM35A antibodies is essential for ensuring reliable experimental results. Based on established research methodologies, a comprehensive validation approach should include:

• Western blot analysis: Verify antibody specificity by detecting a band of the expected molecular weight (~92 kDa for FAM35A isoform 1)

• siRNA-mediated knockdown controls: Compare antibody signal in control versus FAM35A-depleted cells to confirm specificity

• Immunoprecipitation tests: Assess antibody capability to pull down FAM35A and its known interacting partners like REV7, 53BP1, and RIF1

• Peptide competition assays: Confirm binding specificity by pre-incubating the antibody with purified FAM35A protein or peptide

• Cross-reactivity assessment: Particularly important given the existence of three FAM35A pseudogenes with high sequence identity (>98%) to evaluate antibody specificity

When selecting commercial antibodies, researchers should review validation data provided by manufacturers and consider performing additional validation specific to their experimental system.

How can FAM35A antibodies be used to investigate its interaction with the DNA damage response machinery?

FAM35A antibodies can be strategically employed to elucidate its interactions with the DNA damage response machinery through several sophisticated approaches:

• Co-immunoprecipitation (Co-IP) assays: FAM35A antibodies can be used to pull down protein complexes, followed by immunoblotting for known or suspected interaction partners. Research has successfully demonstrated interactions between FAM35A and key DNA repair proteins including REV7, RIF1, 53BP1, BLM, and TOP3A using this approach .

• Proximity ligation assays (PLA): While not explicitly mentioned in the search results, this technique could provide in situ visualization of FAM35A interactions with partner proteins, offering spatial context within the cell.

• ChIP-like approaches: FAM35A antibodies could be used to investigate chromatin association at sites of DNA damage.

• DNA damage-dependent analyses: The search results indicate that RIF1 and 53BP1 associations with FAM35A increase following mitomycin C exposure, suggesting damage-induced complex formation . Researchers can design time-course experiments using FAM35A antibodies to track the temporal dynamics of these interactions following DNA damage.

• Reciprocal validation: As demonstrated in the search results, both approaches—immunoprecipitating FAM35A to detect binding partners and immunoprecipitating suspected partners to detect FAM35A—should be employed for robust validation of interactions .

What are the specific considerations when using FAM35A antibodies in cancer research models?

When employing FAM35A antibodies in cancer research models, several critical considerations must be addressed:

• Expression variability across cancer types: FAM35A alterations occur at varying frequencies across cancer types, with prostate cancers showing the highest rate (up to 13%) . Researchers should verify FAM35A expression in their specific cancer model before designing antibody-based experiments.

• BRCA1-deficient contexts: FAM35A is notably absent in at least one widely used BRCA1-mutant cancer cell line (HCC1937) with anomalous resistance to PARP inhibitors . When working with BRCA1-deficient models, researchers should first confirm FAM35A status rather than assuming its presence.

• Metastatic versus primary tumors: FAM35A is significantly less expressed in metastatic prostate cancers compared to primary tumors . This differential expression pattern necessitates careful interpretation of antibody-based detection in metastatic models.

• Correlation with treatment response: Given that FAM35A depletion affects sensitivity to DNA-damaging agents differently in normal versus BRCA1-deficient backgrounds , researchers should consider these context-dependent effects when interpreting antibody-based measurements in treatment response studies.

• Pseudogene consideration: The presence of three FAM35A pseudogenes with high sequence identity (>98%) may complicate genetic analysis . Antibody-based protein detection can provide valuable complementary data to genetic approaches in such cases.

How can researchers study the impact of FAM35A on DNA repair pathway choice using antibody-based approaches?

Researchers can employ several antibody-based strategies to investigate FAM35A's role in DNA repair pathway choice:

• Immunofluorescence co-localization studies: Using FAM35A antibodies alongside markers for homologous recombination (HR) or non-homologous end joining (NHEJ) pathways can reveal spatial relationships at DNA damage sites. The search results indicate that FAM35A depletion affects end joining in a plasmid integration assay, suggesting its involvement in pathway choice .

• Foci formation analysis: Quantifying nuclear foci of key repair factors (γH2AX, FANCD2, RAD51) in FAM35A-depleted versus control cells can provide insights into pathway utilization. Research has shown that FAM35A depletion leads to increased RAD51 foci formation even in undamaged cells, suggesting elevated HR activity .

• Chromatin fraction analysis: Using FAM35A antibodies to assess its recruitment to chromatin following DNA damage, particularly in the context of manipulated repair pathway components.

• Proximity ligation assays: To detect in situ interactions between FAM35A and proteins specific to different repair pathways.

• Sequential ChIP (re-ChIP): To determine if FAM35A co-occupies damaged chromatin with factors specific to particular repair pathways.

The experimental design should include appropriate controls and consider the timing of assessments, as pathway choice can be cell cycle-dependent and temporally regulated after damage induction.

What methodological approaches can address the challenge of FAM35A pseudogenes when using antibody detection?

The presence of three FAM35A pseudogenes with high sequence identity (>98%) presents significant challenges for genetic and protein analyses. Researchers can implement the following methodological approaches when using antibody detection:

• Combined protein and transcript analysis: Use FAM35A antibodies for protein detection alongside carefully designed RT-qPCR assays that can distinguish between transcripts from the functional gene versus pseudogenes.

• Western blot correlation with functional assays: Since pseudogenes may not produce functional proteins, correlate antibody detection with functional readouts like those described in the search results (e.g., DNA damage sensitivity, repair pathway choice) .

• Knockdown/knockout validation approaches: When performing FAM35A depletion studies, validate using both antibody detection and functional assays that correspond to known FAM35A activities .

• Recombinant protein expression: Validate antibody specificity using cells expressing tagged recombinant FAM35A, as demonstrated in the search results with FLAG-HA-tagged FAM35A .

• Mass spectrometry validation: Confirm antibody specificity by immunoprecipitating the detected protein and identifying it through mass spectrometry, as described in the research where FAM35A was identified as a REV7-interacting protein .

How should researchers interpret FAM35A antibody data in the context of BRCA1 deficiency?

When interpreting FAM35A antibody data in BRCA1-deficient contexts, researchers should consider several important factors:

• Opposing sensitivity patterns: While FAM35A depletion sensitizes normal cells to DNA-damaging agents like mitomycin C and etoposide, it counterintuitively increases resistance to camptothecin in BRCA1-mutant cells . This suggests context-dependent functions that must be carefully interpreted.

• Expression variability: The search results indicate that FAM35A is absent in at least one widely used BRCA1-mutant cancer cell line (HCC1937) with anomalous resistance to PARP inhibitors . Researchers should always verify FAM35A expression status in their BRCA1-deficient model.

• Repair pathway dynamics: In FAM35A-depleted cells, RAD51 foci (a marker of homologous recombination) show increased formation even without exogenous damage . This suggests that loss of FAM35A may partially restore HR capacity in BRCA1-deficient cells, which could explain treatment resistance phenomena.

• Therapeutic implications: The differential response to DNA-damaging agents based on BRCA1 and FAM35A status has significant implications for cancer therapy. Antibody-based detection of FAM35A could potentially serve as a biomarker for treatment response prediction.

• Mechanistic investigations: When designing experiments to explore the relationship between FAM35A and BRCA1, researchers should include appropriate controls and consider parallel assessment of multiple DNA repair markers to fully contextualize their findings.

What are the optimal conditions for using FAM35A antibodies in different experimental systems?

Based on the research methodologies described in the search results, the following conditions are recommended for FAM35A antibody applications:

• Western Blot analysis:

  • Antibody dilution: 1:200 for polyclonal anti-FAM35A (HPA036582, Sigma-Aldrich)

  • Secondary antibody: HRP-conjugated anti-rabbit IgG at 1:10,000 dilution

  • Detection: Enhanced chemiluminescence (ECL) reagents

• Immunofluorescence:

  • Cell fixation: Standard paraformaldehyde fixation following exposure to DNA-damaging agents (e.g., mitomycin C at 100 ng/ml for 24 hours)

  • For tagged FAM35A: Anti-GFP antibody at 1:200 dilution (Clontech, 632592)

  • Nuclear counterstain: DAPI

• Immunoprecipitation:

  • Cell lysis buffer: 0.5B buffer (500 mM KCl, 20 mM Tris-HCl [pH 8.0], 5 mM MgCl₂, 10% glycerol, 1 mM PMSF, 0.1% Tween 20, 10 mM β-mercaptoethanol)

  • Dilution buffer: 2B buffer (40 mM Tris-HCl [pH 8.0], 20% glycerol, 0.4 mM EDTA, 0.2% Tween 20)

  • Wash buffer: 0.1B buffer (100 mM KCl, 20 mM Tris-HCl [pH 8.0], 5 mM MgCl₂, 10% glycerol, 1 mM PMSF, 0.1% Tween 20, 10 mM β-mercaptoethanol)

  • Immunoprecipitation duration: 4 hours at 4°C

Optimization may be required for specific cell types or experimental conditions not covered in the available research.

How can researchers troubleshoot common issues with FAM35A antibody applications?

When working with FAM35A antibodies, researchers may encounter several challenges. Here are methodological approaches to troubleshoot common issues:

• High background in immunofluorescence:

  • Increase blocking duration and concentration

  • Optimize antibody concentration through titration experiments

  • Include additional washing steps with detergent-containing buffer

  • Use monoclonal antibodies if specificity is a concern due to FAM35A pseudogenes

• Weak or absent signal in Western blots:

  • Verify protein expression levels, considering that FAM35A expression varies across cell types and is absent in some cancer cell lines like HCC1937

  • Optimize protein extraction methods, considering that FAM35A contains both structured and unstructured regions

  • Adjust transfer conditions for high molecular weight proteins (~92 kDa for FAM35A isoform 1)

  • Consider sample preparation modifications to prevent protein degradation

• Failed immunoprecipitation:

  • Verify antibody binding capacity using the established protocols described in the research

  • Optimize lysis conditions to preserve protein-protein interactions

  • Consider crosslinking approaches for transient interactions

  • For co-immunoprecipitation experiments, verify that interacting partners (e.g., REV7, 53BP1, RIF1) are expressed in your cellular system

• Inconsistent results following DNA damage induction:

  • Standardize damage induction protocols (e.g., 100 ng/ml MMC for 24 hours as used in the research)

  • Include positive controls for DNA damage (e.g., γH2AX staining)

  • Consider the timing of analysis, as FAM35A responses may be dynamic

What controls are essential when using FAM35A antibodies in functional studies?

When conducting functional studies using FAM35A antibodies, the following controls are essential for result validation and interpretation:

• Expression controls:

  • Positive control: Cell line with confirmed FAM35A expression (e.g., HEK293 or U2OS as used in the research)

  • Negative control: FAM35A-depleted cells using validated siRNA or the HCC1937 cell line that naturally lacks FAM35A expression

• Specificity controls:

  • Peptide competition assay: Pre-incubation of antibody with purified FAM35A protein or peptide

  • Multiple antibody validation: Using different antibodies targeting distinct epitopes of FAM35A

  • Recombinant expression: GFP-tagged or FLAG-HA-tagged FAM35A as positive controls

• Functional validation controls:

  • DNA damage markers: γH2AX foci as indicators of DNA damage response activation

  • Pathway-specific markers: FANCD2 foci for Fanconi anemia pathway, RAD51 foci for homologous recombination

  • Complementation experiments: Rescue of phenotypes by expressing siRNA-resistant FAM35A constructs

• Interaction controls:

  • Input samples: To verify expression of potential interacting proteins

  • IgG control: Non-specific antibody of the same isotype for immunoprecipitation experiments

  • Reciprocal co-immunoprecipitation: Pull down with antibodies against interaction partners to confirm FAM35A association

Including these controls will significantly enhance the reliability and interpretability of results obtained using FAM35A antibodies.

How does FAM35A antibody detection correlate with cancer progression markers?

FAM35A detection using antibody-based methods has shown significant correlations with cancer progression markers, particularly in prostate cancer. Research findings indicate:

• Expression level correlation: FAM35A is significantly less expressed in metastatic prostate cancers compared to primary tumors, suggesting its potential utility as a progression marker . Antibody-based detection methods such as immunohistochemistry and Western blotting can quantify this differential expression.

• Genetic alteration frequency: The FAM35A gene is altered at high frequency in prostate cancers (up to 13%) . Correlating antibody-detected protein levels with genetic status can provide insights into the functional consequences of these alterations.

• BRCA1-deficiency context: FAM35A is absent in at least one widely used BRCA1-mutant cancer cell line (HCC1937) with anomalous resistance to PARP inhibitors . This suggests that loss of FAM35A may contribute to treatment resistance mechanisms in BRCA1-deficient cancers.

• DNA repair pathway markers: Research shows that FAM35A depletion affects the formation of RAD51 foci, a marker of homologous recombination . Combined antibody detection of FAM35A and repair pathway markers could provide a more comprehensive assessment of tumor DNA repair capacity.

• Treatment response prediction: The differential effect of FAM35A depletion on sensitivity to DNA-damaging agents in normal versus BRCA1-deficient backgrounds suggests its potential as a biomarker for treatment response prediction .

What methodological approaches can researchers use to study FAM35A in patient-derived samples?

For studying FAM35A in patient-derived samples, researchers can employ several methodological approaches using antibodies:

• Immunohistochemistry (IHC) on tissue microarrays:

  • This approach allows assessment of FAM35A expression across multiple patient samples simultaneously

  • Quantification using digital pathology tools can provide objective measurement of expression levels

  • Correlation with clinical parameters and outcomes can establish prognostic value

• Multiplex immunofluorescence:

  • Enables co-detection of FAM35A with other markers of DNA repair pathways

  • Provides spatial information about protein localization within the tumor microenvironment

  • Can reveal heterogeneity of expression across different regions of the tumor

• Patient-derived organoids or xenografts:

  • FAM35A antibodies can be used to monitor expression in these models that better recapitulate tumor complexity

  • Western blot and immunoprecipitation can assess protein levels and interactions

  • Treatment response studies can correlate FAM35A status with drug sensitivity

• Circulating tumor cells (CTCs) analysis:

  • Antibody-based detection of FAM35A in CTCs could potentially serve as a liquid biopsy approach

  • May provide insights into expression in metastatic disease

• Correlation with genomic data:

  • Integrated analysis combining antibody-detected protein levels with genomic alterations

  • Particularly relevant given the high frequency of FAM35A alterations in prostate cancer (up to 13%)

When working with patient samples, researchers should validate antibody specificity in relevant tissue types and consider fixation and processing effects on epitope preservation.

How can FAM35A antibodies be used to evaluate potential synthetic lethality in cancer therapy?

FAM35A antibodies can be instrumental in evaluating synthetic lethal interactions in cancer therapy through several methodological approaches:

• Expression screening in treatment response studies:

  • Use FAM35A antibodies to screen cancer cell lines or patient-derived samples for expression levels

  • Correlate expression with response to DNA-damaging agents or PARP inhibitors

  • The research indicates that in BRCA1-mutant contexts, FAM35A status affects drug sensitivity

• Combinatorial treatment assessment:

  • Monitor FAM35A expression and localization when combining different therapeutic agents

  • Assess changes in interaction partners (REV7, 53BP1, RIF1) using co-immunoprecipitation and FAM35A antibodies

  • Evaluate DNA repair pathway activation markers in relation to FAM35A status

• Genetic-pharmacologic interaction studies:

  • Use FAM35A antibodies to confirm protein depletion in genetic knockdown experiments

  • Combine with drug treatments to identify synergistic effects

  • The research shows FAM35A depletion sensitizes normal cells to mitomycin C and etoposide but increases resistance to camptothecin in BRCA1-mutant cells

• Post-treatment mechanism analysis:

  • Apply FAM35A antibodies in immunofluorescence studies to track nuclear foci formation after treatment

  • Assess interaction with DNA damage response proteins following therapy

  • Evaluate changes in repair pathway choice (NHEJ vs. HR) in relation to FAM35A status

• Validation in resistant models:

  • Compare FAM35A expression between sensitive and resistant cell lines

  • The finding that FAM35A is absent in the PARP inhibitor-resistant HCC1937 cell line suggests its relevance to resistance mechanisms

These approaches can help identify context-dependent vulnerabilities based on FAM35A status, potentially informing more precise therapeutic strategies.

What are the most promising research applications for new generation FAM35A antibodies?

As antibody technology advances, several promising research applications for next-generation FAM35A antibodies emerge:

• Super-resolution microscopy applications:

  • High-specificity antibodies compatible with techniques like STORM or PALM could reveal detailed spatial organization of FAM35A at DNA damage sites

  • This could provide insights into the relationship between FAM35A's OB-fold domains, which are structurally homologous to RPA , and its function in DNA repair

• Intrabody applications:

  • Cell-permeable antibodies or nanobodies against FAM35A could enable real-time tracking of protein dynamics in living cells

  • This would be particularly valuable for understanding FAM35A's temporal recruitment to DNA damage sites

• Domain-specific antibodies:

  • Antibodies targeting specific domains (N-terminal unstructured region versus C-terminal OB-fold domains) could help dissect domain-specific functions

  • The search results indicate FAM35A contains distinct functional regions with different properties

• Post-translational modification detection:

  • Antibodies specifically recognizing modified forms of FAM35A could reveal regulation mechanisms

  • The research identifies DNA damage-dependent post-translational modifications, including ubiquitination and phosphorylation at S339

• Therapeutic development:

  • Given the differential effects of FAM35A depletion in normal versus BRCA1-deficient contexts , antibody-drug conjugates targeting FAM35A could potentially exploit cancer-specific vulnerabilities

These applications would significantly advance our understanding of FAM35A's role in DNA repair and potentially lead to new diagnostic or therapeutic approaches.

How might researchers design experiments to resolve contradictory findings related to FAM35A function?

The search results reveal potentially contradictory findings regarding FAM35A function, particularly its opposing effects on DNA damage sensitivity in normal versus BRCA1-deficient contexts. Researchers can design experiments to resolve these contradictions using the following methodological approaches:

• Context-dependent mechanistic studies:

  • Use FAM35A antibodies to track protein localization and interactions in parallel in both normal and BRCA1-deficient isogenic cell lines

  • Perform time-course analyses following DNA damage to identify temporal differences in response

• Domain-specific functional analysis:

  • Generate domain-specific antibodies targeting the N-terminal unstructured region versus the C-terminal OB-fold domains

  • Create domain deletion constructs and use antibodies to verify expression and localization

  • Assess each domain's contribution to the contradictory phenotypes observed

• Interaction network mapping:

  • Use FAM35A antibodies in comprehensive immunoprecipitation studies across different cellular contexts

  • Apply quantitative proteomics to identify context-specific interaction partners

  • The research shows FAM35A interacts with REV7, RIF1, 53BP1, BLM, and TOP3A , but these interactions may vary by context

• Pathway-specific reporters:

  • Combine FAM35A antibody detection with fluorescent reporters for HR and NHEJ pathways

  • Assess pathway utilization in real-time following DNA damage in different genetic backgrounds

• Genome-wide synthetic interaction screens:

  • Use FAM35A antibodies to validate knockdown/knockout efficiency in screens for genetic interactions

  • Identify context-dependent genetic dependencies that explain contradictory phenotypes

These approaches would help reconcile the observation that FAM35A depletion sensitizes normal cells to DNA-damaging agents while increasing resistance in BRCA1-mutant contexts , potentially revealing nuanced mechanisms of DNA repair regulation.