RAD21 Antibody

What is RAD21 and why is it important in research?

RAD21 (also known as HR21, SCC1, NXP1) is a component of the cohesin complex essential for chromosome segregation and error-free DNA repair. As a member of the cohesin complex, RAD21 is involved in sister chromatid cohesion from DNA replication in S phase to segregation in mitosis. This function is critical for proper chromosome segregation, post-replicative DNA repair, and prevention of inappropriate recombination between repetitive regions .

In interphase, cohesins including RAD21 may function in controlling gene expression by binding to numerous sites within the genome. RAD21 has been shown to bind to and repress the APOB gene promoter and may control RUNX1 gene expression . The importance of RAD21 in research extends to cancer studies, as enhanced RAD21 expression has been associated with poor prognosis in certain cancers .

When working with RAD21 antibodies in Western blot applications, researchers should be aware of two distinct bands:

• Full-length RAD21 is typically observed around 120-130 kDa

• Cleaved RAD21 is detected around 70-72 kDa

The observed molecular weight of 120 kDa is higher than the calculated molecular weight of 72 kDa (for a 631 amino acid protein) . This discrepancy is likely due to post-translational modifications. When interpreting Western blot results, researchers should note that RAD21 cleavage occurs during apoptosis, resulting in the appearance of the lower molecular weight band .

Proper validation of RAD21 antibodies is essential for reliable experimental results. A recommended validation protocol includes:

• Specificity testing: Use siRNA knockdown of RAD21 to confirm antibody specificity. For example, using siRNA knockdown of human RAD21 gene in MCF10A cells and preparing cell blocks for immunohistochemistry validation .

• Western blot validation: Compare bands from control and RAD21-depleted samples. The full-length RAD21 band (120-130 kDa) and cleaved RAD21 (70-72 kDa) should be significantly reduced in knockdown samples .

• Positive controls: Include cell lines known to express RAD21, such as A549, HeLa, or MDCK cells .

• Quantification: For Western blots, normalize RAD21 signal to a loading control such as pan-actin. Measure relative protein expression from a minimum of three independent experiments .

• Cross-reactivity testing: Verify species reactivity if working with non-human samples, as reactivity may vary between antibodies .

How does RAD21 expression correlate with cancer prognosis?

Research has shown that enhanced RAD21 expression is associated with poor prognosis in certain cancers. In breast cancer, RAD21 has been evaluated as both a prognostic and predictive marker:

• Prognostic value: Studies have assessed RAD21 expression in both in situ and invasive breast carcinomas using immunohistochemistry. Enhanced RAD21 expression has been correlated with poorer patient outcomes .

• Molecular mechanisms: RAD21's role in chromosome segregation and DNA repair may contribute to genomic instability when dysregulated, potentially promoting cancer progression. Additionally, RAD21 is involved in regulating genes that control epithelial-mesenchymal transition (EMT), a process important in cancer metastasis .

• Methodological approach: To study RAD21's prognostic significance, researchers typically perform:

  • Immunohistochemistry on tissue microarrays with anti-RAD21 antibodies

  • Correlation of expression levels with clinicopathological parameters and survival data

  • Integration of genomic and transcriptomic analyses to understand the molecular mechanisms

What are the optimal methods for studying RAD21-dependent chromatin architecture?

RAD21, as part of the cohesin complex, plays a crucial role in mediating chromatin architecture. To study RAD21-dependent chromatin interactions, researchers can employ the following methods:

• Chromosome Conformation Capture (3C) assay: This technique allows detection of gene-specific intrachromosomal architecture regulated by cohesin:

  • Protocol outline: Formaldehyde cross-linking, restriction enzyme digestion (e.g., BamHI or XbaI), ligation, and PCR quantification

  • Anchor selection: Based on chromatin immunoprecipitation (ChIP) data showing high enrichment of RAD21, select appropriate anchor regions (e.g., TGFB1_6 and ITGA5_6 amplicons)

  • Controls: Normalize cross-linking frequency and ligation efficiencies relative to the ligation frequency of adjacent restriction fragments in a ubiquitously expressed gene like ERCC3

  • Comparative analysis: Compare 3C profiles between control and RAD21-depleted cells to identify RAD21-dependent chromatin interactions

• Chromatin Immunoprecipitation (ChIP): To identify RAD21 binding sites and correlate them with gene expression:

  • Use epithelial (e.g., MCF7) and mesenchymal (e.g., HCC1143) cell lines to compare RAD21 enrichment patterns

  • Correlate RAD21 binding with gene expression levels in different cell types

  • Identify regions where RAD21 enrichment is negatively correlated with gene transcription levels

• Integration with gene expression analysis: Combine ChIP and 3C data with transcriptomic analysis to understand how RAD21-mediated chromatin architecture regulates gene expression .

How can I optimize RAD21 antibody usage for chromatin immunoprecipitation (ChIP) assays?

Chromatin immunoprecipitation using RAD21 antibodies requires careful optimization. Based on published protocols, the following approach is recommended:

What are the best methods to detect both full-length and cleaved RAD21 in apoptotic studies?

RAD21 cleavage is an important event during apoptosis. To effectively study both full-length and cleaved forms:

• Western blot optimization:

  • Use gradient gels (4-12% or 4-20%) to achieve good separation between the 120-130 kDa full-length and 70-72 kDa cleaved forms

  • The Bio-Techne monoclonal antibody (NB100-386) is specifically validated to detect both forms

  • Run appropriate molecular weight markers to accurately identify both bands

  • Include positive controls for apoptosis (e.g., cells treated with apoptosis inducers)

• Quantification approach:

  • Normalize band intensity to loading controls such as pan-actin

  • Calculate the ratio of cleaved to full-length RAD21 as a measure of apoptotic activity

  • Perform a minimum of three independent experiments for statistical validity

• Immunofluorescence detection:

  • RAD21 exhibits both nuclear and cytoplasmic localization

  • Full-length RAD21 is predominantly nuclear, while cleaved RAD21 may redistribute to the cytoplasm

  • Counterstain with DAPI to visualize nuclei and assess subcellular localization

• Flow cytometry:

  • Can be used to correlate RAD21 cleavage with other apoptotic markers

  • Allows for quantitative analysis at the single-cell level

How can I assess RAD21 function in epithelial-mesenchymal transition (EMT)?

RAD21 has been implicated in controlling EMT plasticity in cancer cells. To study RAD21's role in EMT:

• RAD21 knockdown approach:

  • Use siRNA for transient depletion or shRNA for stable knockdown of RAD21

  • For transient studies, a time-course experiment (12h, 24h, 48h post-transfection) allows detection of early and late EMT gene expression changes

  • Western blot confirmation of knockdown efficiency is essential

• Target gene assessment:

  • Monitor expression changes in EMT markers (E-cadherin, vimentin, etc.)

  • Key RAD21-regulated genes involved in EMT include TGFB1 and ITGA5

  • ITGA5 responds more rapidly to RAD21 depletion (within 12h) than TGFB1 (48h)

• Functional assays:

  • Migration and invasion assays to assess mesenchymal characteristics

  • Cell morphology analysis

  • Cell-cell adhesion assays

• Chromatin architecture analysis:

  • 3C assay to examine changes in chromatin looping at EMT-related genes

  • ChIP to analyze RAD21 binding patterns at these genes

  • Correlation between RAD21 binding strength and gene expression levels

• Comparative cell line approach:

  • Compare epithelial cell lines (e.g., MCF7) with mesenchymal cell lines (e.g., HCC1143)

  • Analyze differences in RAD21 binding patterns and chromatin architecture

  • Correlate with EMT gene expression profiles

What is the recommended protocol for RAD21 antibody validation in Western blot?

A robust validation protocol for RAD21 antibodies in Western blot includes:

• Sample preparation:

  • Prepare total protein extracts from appropriate cell lines (e.g., A549, HeLa, MCF7)

  • Include RAD21-depleted samples (siRNA or shRNA knockdown) as specificity controls

  • Load 20-50 μg of total protein per lane

• Western blot procedure:

  • Use 6-8% gels or gradient gels for optimal separation of the high molecular weight RAD21

  • Transfer to PVDF or nitrocellulose membrane

  • Block with 5% non-fat milk or BSA in TBST

• Antibody incubation:

  • Primary antibody: Dilute according to manufacturer's recommendation (typically 1:500 to 1:4000)

  • For Abcam ab992 (rabbit polyclonal): 1:500

  • For Bio-Techne NB100-386 (mouse monoclonal): 1:500 for ECL detection

  • For Proteintech 27071-1-AP (rabbit polyclonal): 1:1000-1:4000

  • Secondary antibody: HRP-conjugated or fluorescent (e.g., Alexa 680 anti-rabbit, IRDye800-conjugated anti-mouse)

• Detection and quantification:

  • For colorimetric detection: Use DAB substrate

  • For fluorescent detection: Use Li-Cor Odyssey system

  • Normalize RAD21 signal to loading control (e.g., pan-actin)

  • Perform at least three independent experiments for quantification

• Expected results:

  • Full-length RAD21: 120-130 kDa band

  • Cleaved RAD21: ~70-72 kDa band

  • Both bands should be reduced in RAD21 knockdown samples

How should I optimize immunohistochemistry protocols for RAD21 detection?

Optimizing immunohistochemistry for RAD21 detection requires attention to several key parameters:

• Fixation and tissue processing:

  • Standard formalin fixation and paraffin embedding is suitable

  • Ensure consistent fixation times to prevent variability

• Antigen retrieval:

  • Recommended: TE buffer pH 9.0

  • Alternative: Citrate buffer pH 6.0

  • Heat-induced epitope retrieval (pressure cooker or microwave) is typically more effective than enzymatic retrieval

• Blocking and antibody incubation:

  • Block endogenous peroxidase activity with H₂O₂ (e.g., 3% H₂O₂ for five minutes)

  • Block non-specific binding with serum or BSA

  • Primary antibody:

    • For Proteintech 27071-1-AP: 1:50-1:500 dilution

    • Incubate for 1-2 hours at room temperature or overnight at 4°C

  • Secondary antibody: HRP-conjugated appropriate to primary antibody species

• Detection system:

  • DAB (3,3'-diaminobenzidine) substrate for visualization

  • Counterstain with hematoxylin to visualize nuclei

• Controls:

  • Negative control: Replace primary antibody with anti-rabbit IgG

  • Positive control: Use tissues known to express RAD21 (e.g., human breast cancer tissue)

  • Validation control: Use RAD21 siRNA knockdown cell blocks

• Evaluation:

  • Assess nuclear and cytoplasmic staining patterns

  • Score intensity and percentage of positive cells for quantitative analysis

  • For cancer studies, correlate with clinicopathological parameters

What controls should be used when studying RAD21 depletion effects?

When studying the effects of RAD21 depletion, proper controls are essential to ensure experimental validity:

• Knockdown controls:

  • Non-targeting siRNA/shRNA control: Essential to control for non-specific effects of the knockdown procedure

  • Rescue experiment: Re-expression of RAD21 to confirm that observed phenotypes are specifically due to RAD21 depletion

  • Time-course analysis: To distinguish between early direct effects and later secondary effects

• Expression controls:

  • Western blot verification of knockdown efficiency at the protein level

  • qRT-PCR confirmation of knockdown at the mRNA level

  • Normalize to appropriate housekeeping genes (e.g., 18S rRNA)

• Functional controls:

  • For EMT studies: Include both epithelial (MCF7, SNU16) and mesenchymal (HCC1143) cell lines as reference points

  • For gene expression studies: Verify expression changes using both microarray and qRT-PCR approaches

  • For chromatin architecture studies: Include a control gene (e.g., ERCC3) that forms gene-specific 3D chromatin structure but is not affected by RAD21 depletion

• Technical controls for 3C assays:

  • Cross-linking efficiency control

  • Digestion efficiency control

  • Ligation efficiency control

  • Primer efficiency control

  • Normalization to control regions

• Biological replicates:

  • Perform at least three independent experiments to ensure reproducibility

  • Use different cell passages to account for potential variability

How stable are RAD21 antibodies and what are the optimal storage conditions?

Proper storage and handling of RAD21 antibodies is crucial for maintaining their activity and specificity:

• Storage conditions:

  • Store at -20°C as recommended by manufacturers

  • Aliquoting is generally unnecessary for -20°C storage of small volumes

  • Proteintech 27071-1-AP: Store in PBS with 0.02% sodium azide and 50% glycerol pH 7.3

  • Stability: Typically stable for one year after shipment when stored properly

• Working solution preparation:

  • Thaw antibodies on ice

  • Avoid repeated freeze-thaw cycles

  • Dilute in appropriate buffer according to application

  • For some applications, addition of BSA (0.1%) may help stability

• Handling precautions:

  • Centrifuge briefly before opening vial to collect solution at the bottom

  • Use sterile technique when handling antibodies

  • Return to -20°C storage promptly after use

• Quality control indicators:

  • Visible precipitates may indicate antibody degradation

  • Significant loss of activity may occur with improper storage

  • Always include positive controls to verify antibody performance

How can I troubleshoot weak or non-specific RAD21 antibody signals?

When encountering problems with RAD21 antibody performance, consider these troubleshooting approaches:

• Weak or no signal:

  • Increase antibody concentration (decrease dilution)

  • Extend incubation time (e.g., overnight at 4°C)

  • Optimize antigen retrieval for IHC/ICC (test both TE buffer pH 9.0 and citrate buffer pH 6.0)

  • Increase protein loading for Western blot

  • Ensure protein transfer efficiency by using stain-free gels or Ponceau staining

  • Check if RAD21 is expressed in your sample type

• Non-specific bands or background:

  • Increase antibody dilution

  • Optimize blocking conditions (test different blocking agents: BSA, non-fat milk, normal serum)

  • Include additional washing steps

  • Pre-adsorb antibody with non-specific proteins

  • For Western blot: Run gradient gels for better separation of the high molecular weight RAD21 protein

  • For IHC: Optimize counterstaining protocol

• Variability between experiments:

  • Standardize protein extraction method

  • Use consistent cell culture conditions

  • Normalize to reliable loading controls

  • Use the same antibody lot when possible

  • Include positive controls in each experiment

• Antibody specificity confirmation:

  • Use RAD21 knockdown or knockout samples as negative controls

  • Test multiple RAD21 antibodies targeting different epitopes

  • For phospho-specific antibodies, include phosphatase-treated samples as controls