PAXIP1 Antibody

What is PAXIP1 and why is it significant in cellular research?

PAXIP1 (PAX Interacting With Transcription-Activation Domain Protein 1) is a multifunctional protein containing six BRCT domains organized into three tandem pairs. The C-terminal tandem mediates recruitment to DNA lesions . PAXIP1 is essential for cells to progress through mitosis and plays critical roles in:

• DNA damage response (DDR) signaling networks

• Epigenetic regulation as part of the MLL3/MLL4-COMPASS-like complex

• Cell cycle regulation, particularly through interaction with WEE1 kinase

• Transcriptional activation of specific genes during development

PAXIP1 has emerged as a significant protein in cancer research due to its involvement in sensitizing lung cancer cells to WEE1 inhibitor AZD1775 in combination with platinum-based treatment . Recent studies also highlight its prognostic relevance in hepatocellular carcinoma and its function in modulating immune cell recruitment .

How should I select the appropriate PAXIP1 antibody for my specific research application?

Selection should be guided by the following methodological considerations:

For cross-species applications, consider antibodies with confirmed reactivity across multiple species. For example, some commercially available antibodies show reactivity with human, mouse, rat, cow, dog, zebrafish, guinea pig, horse, rabbit, Xenopus laevis, chicken, and monkey samples .

What controls should I implement when validating a PAXIP1 antibody?

Proper validation requires multiple controls:

• Positive tissue controls:

  • Tonsil tissue serves as an effective positive control for PAXIP1 antibodies in IHC applications

  • Nuclear staining should be predominantly observed, with some cases showing cytoplasmic staining

• Negative controls:

  • Omit primary antibody while maintaining secondary antibody

  • Use normal liver tissue, which shows minimal PAXIP1 expression compared to HCC

• Specificity validation:

  • Perform antibody testing with recombinant PAXIP1 protein fragments

  • Use PAXIP1 knockout or knockdown cells/tissues (noting that complete knockout is embryonically lethal)

  • Test with synthetic peptide blocking experiment using the immunizing peptide

• Band validation in Western blotting:

  • Expected molecular weight for full-length PAXIP1 is approximately 121.3 kilodaltons

  • Verify using PAXIP1 overexpression constructs in cells with low endogenous levels

How can I optimize chromatin immunoprecipitation (ChIP) protocols for PAXIP1?

Optimizing PAXIP1 ChIP requires specific methodological adjustments:

• Crosslinking optimization:

  • Use 1% formaldehyde for 10 minutes at room temperature

  • Consider dual crosslinking with 2 mM disuccinimidyl glutarate (DSG) for 30 minutes followed by 1% formaldehyde for 10 minutes for enhanced protein-protein crosslinking

• Sonication conditions:

  • Use Bioruptor® Pico (Diagenode) or equivalent sonication system

  • Aim for chromatin fragments between 200-500 bp

  • Verify fragmentation by agarose gel electrophoresis

• Antibody selection and preparation:

  • Use 5 μg of PAXIP1 antibody per ChIP reaction (e.g., PAXIP1 ab70434, abcam)

  • Pre-conjugate with 50 μl of magnetic Protein A beads before adding to chromatin

• Library preparation and sequencing:

  • For modern NGS approaches, use paired-end sequencing (51 bp reads)

  • Perform adapter trimming before alignment using seqpurge

  • Align to appropriate reference genome (e.g., GRCh38.102) using Burrows-Wheeler Aligner (v0.7.17) with mem algorithm

  • Filter based on MAPQ quality ≥20 and remove duplicate reads

• Data analysis considerations:

  • Use MACS2 (v2.1.2) for peak calling over input

  • Generate consensus peaks between biological replicates using mspc tool

  • For visualization, merge mapped reads of replicate samples using SAMtools

What are the methodological considerations for PAXIP1 co-immunoprecipitation studies?

Successful co-IP experiments for PAXIP1 require specific buffer compositions and conditions:

• Lysis buffer composition:

  • Use CHAPS lysis buffer [0.5% CHAPS, 150 mM NaCl, 10 mM Hepes, pH 7.4] to maintain protein-protein interactions

  • Alternative: NETN buffer for specific interaction studies

• Antibody quantities and incubation:

  • Use 5 μg of α-PAXIP1 antibody per 500 μg of whole cell lysate

  • Allow immune complexes to form for 1 hour at 4°C

  • Add 20 μl of protein A/G Sepharose beads and incubate overnight with rotation at 4°C

• Washing conditions:

  • Wash beads three times with the lysis buffer

  • Maintain cold temperature (4°C) throughout the procedure

• Elution and analysis:

  • Boil in Laemmli buffer for 5 minutes

  • Analyze by western blotting using antibodies against suspected interaction partners

• Interaction verification strategy:

  • Perform reciprocal IP with antibodies against suspected interaction partners

  • Include controls for non-specific binding (IgG control)

  • Consider using transfected tagged versions of PAXIP1 (such as TAP-tagged constructs) for cleaner results

For investigating the PAXIP1-WEE1 interaction specifically, researchers have successfully used pull-down assays with PAXIP1 tBRCT C2 constructs expressed in 293T cells, followed by western blot analysis with WEE1 antibodies .

How can I investigate PAXIP1's involvement in the DNA damage response pathway?

To study PAXIP1 in DNA damage response contexts:

• Induction of DNA damage:

  • Use cisplatin (DNA crosslinking agent) which has shown interactions with PAXIP1 activity

  • Alternatively, use ionizing radiation, UV, or hydroxyurea as DNA damaging agents

• Monitoring PAXIP1 recruitment:

  • Use immunofluorescence to visualize PAXIP1 localization to damage sites

  • Co-stain with γ-H2AX, a marker of DNA double-strand breaks

  • Perform time-course analyses to monitor recruitment kinetics

• Functional assays:

  • Assess cell cycle checkpoint activation in PAXIP1-depleted cells

  • Monitor CDK1 phosphorylation status at Y15 as PAXIP1 regulates WEE1 kinase activity which phosphorylates CDK1

  • Track caspase 3-mediated apoptosis in PAXIP1-expressing cells treated with WEE1 inhibitor AZD1775 and cisplatin

• Interaction studies:

  • Investigate PAXIP1 interaction with 53BP1 during DNA damage response

  • Examine PAXIP1 recruitment to DNA lesions mediated by its C-terminal tandem BRCT domains

• Chromatin studies:

  • Assess histone modifications (particularly H3K4me3) at sites of DNA damage

  • PAXIP1 as part of the MLL3/MLL4-COMPASS-like complex influences histone methylation patterns

How can PAXIP1 antibodies be used to evaluate potential biomarkers in cancer research?

PAXIP1 has emerging value as a cancer biomarker that can be evaluated through these methodological approaches:

• Tissue microarray (TMA) analysis:

  • Optimize staining protocols using α-PAXIP1 rabbit primary antibody (HPA006694, Sigma) at 1:20 concentration

  • Use appropriate visualization system (e.g., Ventana OmniMap α-rabbit IgG as secondary antibody)

  • Counterstain with Hematoxylin for nuclear visualization

  • Score based on staining intensity (0-4 scale, with 0 as 'no stain' to 4 being 'highest staining intensity')

• Prognostic significance assessment:

  • Analyze survival curves based on PAXIP1 expression levels

  • In HCC, high PAXIP1 expression correlates with low survival rates (AUC value range: 0.66-0.59 for 1-, 3- and 5-year prognoses)

  • Conduct both univariate and multivariate Cox regression analyses to determine if PAXIP1 is an independent prognostic factor

• Co-expression with other markers:

  • Evaluate PAXIP1 and WEE1 co-expression in tumors

  • Approximately one-third of lung tumors are positive for both PAXIP1 and WEE1

  • In HCC, assess correlation between PAXIP1 and immune checkpoint molecules (PDCD1, CD274, CTLA4)

• Relationship to treatment response:

  • PAXIP1 and WEE1 levels may serve as mechanism-based biomarkers of response when WEE1 inhibitor AZD1775 is combined with DNA damaging agents

  • Higher PAXIP1 expression may increase sensitivity to chemotherapy drugs including axitinib, lenalidomide, pazopanib, sorafenib, and XL-184 in HCC treatment

What is the significance of PAXIP1 subcellular localization in disease states?

The subcellular localization of PAXIP1 provides important insights:

• Nuclear vs. cytoplasmic distribution:

  • PAXIP1 shows predominantly nuclear staining in normal tissues

  • In certain cancer samples, marked cytoplasmic staining has been observed

  • Use confocal microscopy with co-staining for nuclear markers to precisely quantify distribution

• Tumor-specific patterns:

  • Nuclear staining in tumor areas typically exhibits a homogeneous pattern

  • Characterize as "strong" or "weak" in comparison with positive control samples

  • Document heterogeneity across different regions of tumor samples

• Correlation with disease progression:

  • Compare PAXIP1 localization patterns between early-stage and advanced tumors

  • Assess relationship between localization and clinical outcomes

• Relationship to functional states:

  • Nuclear PAXIP1 associates with its roles in transcriptional regulation and DNA repair

  • Cytoplasmic PAXIP1 may indicate altered function or sequestration

  • Consider co-immunoprecipitation studies in different cellular fractions to identify compartment-specific interaction partners

How can PAXIP1 be targeted in immunotherapy research?

PAXIP1's relationship with immune function offers novel research directions:

• Immune cell infiltration analysis:

  • PAXIP1 expression positively correlates with the infiltration of CD4+ T cells, neutrophils, macrophages, B cells, and myeloid dendritic cells in HCC

  • Use multiplex immunofluorescence to examine co-localization of PAXIP1 with immune cell markers

• Checkpoint inhibitor relationships:

  • PAXIP1 expression shows significant positive correlation with immune checkpoint molecules:

    • PDCD1 (PD1)

    • CD274 (PD-L1)

    • CTLA4

  • Investigate whether PAXIP1 expression levels predict response to checkpoint inhibitor therapies

• T cell development implications:

  • PAXIP1 regulates thymocyte development

  • Paxip1 knockout mice show a marked increase in CD4+ and CD8+ single-positive T cell populations

  • Investigate PAXIP1's role in mature T cell function and activation

• Therapeutic targeting strategies:

  • Consider whether PAXIP1 inhibition might enhance immunotherapy responses

  • Examine combination approaches targeting both PAXIP1 and immune checkpoint pathways

Why might I observe multiple bands when using PAXIP1 antibodies in Western blot?

Multiple bands in PAXIP1 Western blots can result from several biological and technical factors:

• Isoform detection:

  • PAXIP1 has multiple splice variants

  • Antibodies recognizing different epitopes may detect distinct isoform patterns

  • Compare results using antibodies targeting different regions (e.g., N-terminal vs. C-terminal)

• Post-translational modifications:

  • PAXIP1 undergoes phosphorylation that can alter migration patterns

  • Consider phosphatase treatment of lysates to confirm if bands represent phosphorylated forms

• Proteolytic degradation:

  • Include protease inhibitor cocktails in lysis buffers

  • Avoid repeated freeze-thaw cycles of samples

  • Process samples quickly and maintain cold temperatures

• Cross-reactivity:

  • Verify specificity using PAXIP1 knockdown samples

  • Test antibody on recombinant PAXIP1 protein to confirm expected molecular weight

  • Optimize blocking conditions to reduce non-specific binding

• Protein complexes:

  • Ensure complete sample denaturation before SDS-PAGE

  • Consider increasing SDS concentration or boiling time for resistant complexes

How can I optimize PAXIP1 detection in immunohistochemistry applications?

For optimal IHC detection of PAXIP1:

• Antigen retrieval optimization:

  • Test both heat-induced epitope retrieval (HIER) and enzymatic retrieval methods

  • For HIER, compare citrate buffer (pH 6.0) vs. EDTA buffer (pH 9.0)

  • Optimize retrieval time (10-30 minutes) based on tissue type

• Antibody dilution titration:

  • Begin with manufacturer's recommended dilution (e.g., 1:20 for HPA006694, Sigma)

  • Prepare a dilution series to determine optimal concentration

  • Include positive control tissue (tonsil tissue recommended for PAXIP1)

• Detection system selection:

  • For chromogenic detection, use Ventana OmniMap α-rabbit IgG or equivalent detection system

  • Consider automated staining systems (e.g., Ventana Discovery XT) for reproducibility

  • For fluorescent detection, select fluorophores that don't overlap with nuclear stains

• Counterstaining considerations:

  • Use Hematoxylin for nuclear visualization

  • Adjust counterstaining time to ensure it doesn't obscure PAXIP1 nuclear staining

• Scoring system standardization:

  • Implement a consistent scoring scale (e.g., 0-4) where 0 represents 'no stain' and 4 indicates 'highest staining intensity'

  • Consider all cores with scores 1-4 as 'positive'

  • Document both intensity and percentage of positive cells

What are the key methodological considerations for studying PAXIP1 interactions with chromatin structure?

PAXIP1's role in chromatin organization requires specific experimental approaches:

• ChIP-seq experimental design:

  • Perform parallel ChIP-seq for PAXIP1 and histone modifications (especially H3K4me1)

  • Include input controls and appropriate normalization

  • Consider dual crosslinking to capture both protein-DNA and protein-protein interactions

• 3D genome architecture analysis:

  • PAXIP1 and STAG2 converge to maintain 3D genome architecture

  • Consider Hi-C or ChIA-PET experiments to map long-range chromatin interactions

  • Analyze promoter/enhancer contacts influenced by PAXIP1

• Data integration approaches:

  • Integrate PAXIP1 binding data with:

    • Transcriptome analysis (RNA-seq)

    • Histone modification patterns

    • Transcription factor binding (particularly those interacting with PAXIP1)

  • Use computational tools to identify enriched motifs in PAXIP1-bound regions

• Functional validation:

  • Perform PAXIP1 knockdown followed by ChIP-seq of key histone marks

  • Analyze effects on enhancer activity using reporter assays

  • Examine chromatin accessibility changes using ATAC-seq

• Context-specific considerations:

  • PAXIP1 functions may vary between cell types and conditions

  • Compare PAXIP1 chromatin interactions in normal vs. disease states

  • Assess PAXIP1 binding changes in response to stress or DNA damage

How can PAXIP1 antibodies be used to study its role in V(D)J recombination and immune system development?

PAXIP1 plays critical roles in immune system development that can be studied through:

• Histone modification analysis at immune loci:

  • PAXIP1 loss in developing thymocytes diminishes Jα H3K4me3 and germline transcription

  • Study histone modifications at antigen receptor loci using ChIP-seq with PAXIP1 and H3K4me3 antibodies

  • Compare modifications in wildtype vs. PAXIP1-deficient models

• DNA break formation and repair assessment:

  • PAXIP1 regulates RAG-mediated cleavage and repair during V(D)J recombination

  • Monitor double-strand break formation using γ-H2AX staining

  • Assess unresolved TCR breaks in PAXIP1-deficient models

• Natural killer T cell development analysis:

  • PAXIP1 is essential for NKT cell development

  • Use flow cytometry with lineage-specific markers to quantify NKT cell populations

  • Compare TCRα chain recombination patterns between control and PAXIP1-depleted cells

• S1pr1 expression regulation:

  • PAXIP1 controls the transcriptional activation of sphingosine-1-phosphate receptor S1pr1

  • Analyze S1pr1 expression levels using qRT-PCR and Western blot

  • Examine PAXIP1 binding to the S1pr1 promoter/enhancer regions using ChIP

• Thymocyte trafficking studies:

  • PAXIP1 is required for T cell migration from the thymus to the periphery

  • Track labeled T cells to assess migration patterns in vivo

  • Compare cell numbers in thymus vs. peripheral lymphoid organs in control and PAXIP1-deficient models

What novel approaches can be used to study PAXIP1's role in cancer therapeutic resistance?

Emerging methodologies to investigate PAXIP1 in therapeutic resistance include:

• Combination therapy screening:

  • PAXIP1 potentiates the combination of WEE1 inhibitor AZD1775 and platinum-based therapy

  • Screen various drug combinations in cell lines with different PAXIP1 expression levels

  • Use patient-derived xenograft models expressing both PAXIP1 and WEE1 to test synergistic effects

• Mechanistic pathway analysis:

  • PAXIP1 BRCT domains regulate WEE1-mediated phosphorylation of CDK1

  • Monitor CDK1 phosphorylation status at Y15 in response to therapy

  • Track caspase-3-mediated apoptosis in cells with varying PAXIP1 levels

• Predictive biomarker development:

  • WEE1 and PAXIP1 levels may serve as mechanism-based biomarkers of response

  • Develop immunohistochemistry-based scoring systems for clinical samples

  • Correlate expression patterns with treatment outcomes in patient cohorts

• Resistance mechanism identification:

  • Generate resistant cell lines through prolonged drug exposure

  • Compare PAXIP1 expression, localization, and interaction partners between sensitive and resistant lines

  • Perform CRISPR screens to identify genes that modify PAXIP1-dependent drug responses

• Targeted degradation approaches:

  • Explore the potential of PAXIP1-targeted PROTACs or molecular glues

  • Test whether PAXIP1 degradation enhances sensitivity to existing therapies

  • Identify synthetic lethal interactions with PAXIP1 depletion : https://pmc.ncbi.nlm.nih.gov/articles/PMC4936941/ : https://www.antibodies-online.com/antibody/6738771/anti-PAX+Interacting+With+Transcription-Activation+Domain+Protein+1+PAXIP1+AA+248-297+antibody/ : https://aacrjournals.org/mct/article/15/7/1669/148189/PAXIP1-Potentiates-the-Combination-of-WEE1 : https://pmc.ncbi.nlm.nih.gov/articles/PMC5536937/ : https://www.antibodies-online.com/antibody/928548/anti-PAX+Interacting+With+Transcription-Activation+Domain+Protein+1+PAXIP1+N-Term+antibody/ : https://pmc.ncbi.nlm.nih.gov/articles/PMC11704871/ : https://pmc.ncbi.nlm.nih.gov/articles/PMC3525809/ : https://www.atlasantibodies.com/products/primary-antibodies/triple-a-polyclonals/anti-paxip1-antibody-hpa006694-100ul/?language=en : https://academic.oup.com/nar/article/51/18/9576/7127223 : https://www.biocompare.com/pfu/110447/soids/324393/Antibodies/PAXIP1