CTNNB1 (Ab-41/45) Antibody

What is CTNNB1 (Ab-41/45) Antibody and what epitope does it recognize?

CTNNB1 (Ab-41/45) Antibody is a rabbit polyclonal antibody that specifically recognizes β-catenin when phosphorylated at Threonine 41 and Serine 45 positions. The antibody was raised against a synthetic peptide sequence around amino acids 39-43/43-47 (A-T-T-T-A-P-S-L-S) derived from human β-catenin . It detects endogenous levels of total β-catenin protein when these specific residues are phosphorylated .

This phospho-specific antibody is critical for investigating the regulation of β-catenin stability and function, as phosphorylation at these sites serves as a key regulatory mechanism in the Wnt signaling pathway. The antibody has been purified by affinity chromatography using epitope-specific phosphopeptide, with antibodies against non-phosphopeptide removed by chromatography .

What are the recommended applications and experimental conditions for CTNNB1 (Ab-41/45) Antibody?

The CTNNB1 (Ab-41/45) Antibody has been validated for the following applications:

• Western Blot (WB): Recommended dilution range of 1:500-1:1000

• ELISA: Recommended dilution of 1:20000 for high-sensitivity detection

• Confocal Fluorescence Microscopy: Can be used for immunofluorescence analysis with appropriate secondary antibodies

For optimal Western blot results, researchers should use cell lysates from validated positive controls such as HeLa and HT29 cells, which have been demonstrated to express detectable levels of phosphorylated β-catenin . The antibody has been confirmed to react with human, mouse, and rat samples .

For immunofluorescence applications, a protocol using successive focal planes with confocal microscopy has been described, which can be performed with AlexaFluor-conjugated secondary antibodies (488, 546, 633, or 405) .

How should CTNNB1 (Ab-41/45) Antibody be stored and handled for optimal results?

For maximum stability and activity retention, follow these storage and handling guidelines:

• Long-term storage: Maintain at -20°C or -80°C to prevent antibody degradation

• Working aliquots: Upon receipt, divide into small aliquots to avoid repeated freeze-thaw cycles

• Formulation: The antibody is supplied at 1.0 mg/mL in phosphate buffered saline (without Mg²⁺ and Ca²⁺), pH 7.4, 150mM NaCl, 0.02% sodium azide, and 50% glycerol

• Shelf life: Typically stable for 12 months from date of receipt when stored properly

• Handling tip: If small volumes become entrapped in the vial cap during shipping, briefly centrifuge the vial to collect the liquid at the bottom

For short-term storage (up to 2 weeks), the antibody can be maintained refrigerated at 2-8°C , but this should be avoided for longer periods to prevent loss of activity.

How does phosphorylation at Thr41/Ser45 affect β-catenin function in the Wnt signaling pathway?

Phosphorylation at Thr41 and Ser45 plays a critical regulatory role in β-catenin function and Wnt signaling:

• Destruction complex regulation: In the absence of Wnt ligands, β-catenin forms a complex with AXIN1, AXIN2, APC, CSNK1A1 (CK1α), and GSK3B that promotes its phosphorylation at N-terminal Ser and Thr residues, leading to ubiquitination and subsequent proteasomal degradation .

• Sequential phosphorylation: Ser45 phosphorylation by CK1 acts as a priming event for subsequent phosphorylation at Ser33/Ser37/Thr41 by GSK3β . This sequential phosphorylation is essential for targeting β-catenin for degradation.

• Mutation consequences: Mutations at codons 41 (T41A, T41I) or 45 (S45F, S45P) inhibit phosphorylation, protecting β-catenin from degradation and resulting in its nuclear accumulation . These mutations have been identified in various cancers and are associated with constitutive activation of Wnt target genes.

• Cell adhesion impacts: Phosphorylation status at these sites may also affect β-catenin's role in cell adhesion, potentially influencing its association with E-cadherin at adherens junctions . Wnt5a has been proposed to promote β-catenin/E-cadherin association via CK1α-mediated phosphorylation of β-catenin at Ser45 .

• Differential biological effects: Research suggests that the oncogenic potential of different β-catenin mutations varies, with codon 41 mutations potentially having higher oncogenic activity than mutations in other regions .

What are the recommended controls when using CTNNB1 (Ab-41/45) Antibody in Western blot experiments?

Implementing proper controls is crucial for reliable interpretation of results with CTNNB1 (Ab-41/45) Antibody:

Positive Controls:

• Cell lines: HeLa and HT29 cells have been validated as positive controls

• SW626 cells: Also demonstrated to express detectable levels of phosphorylated β-catenin

Negative Controls:

• Phosphatase treatment: Samples treated with lambda phosphatase to remove phosphorylation can serve as negative controls

• CK1 inhibition: Inhibition of CK1 can reduce phosphorylation at Ser45, which is required for priming β-catenin

• Normal tissue: Normal colon mucosa samples have been used as controls in mutation studies

Specificity Controls:

• Peptide competition: Pre-incubation of the antibody with the phospho-peptide immunogen can confirm specificity

• Comparison with non-phospho antibody: Using both phospho-specific and total β-catenin antibodies in parallel can validate phosphorylation-specific signals

• Mutant samples: Cell lines or tissues with known CTNNB1 mutations at codons 41/45 can serve as biological controls for altered phosphorylation

Loading Controls:

• Standard loading controls such as actin, β-tubulin, or total β-catenin should be included to normalize protein loading

How can different phosphorylated forms of β-catenin be distinguished experimentally?

Distinguishing between various phosphorylated forms of β-catenin requires strategic experimental approaches:

• Phospho-specific antibodies: Using antibodies targeting different phosphorylation sites allows discrimination between specific forms:

  • P41/45-β-catenin antibody for Thr41/Ser45 phosphorylation

  • P33/37/41-β-catenin antibody for Ser33/Ser37/Thr41 phosphorylation

  • Non-phospho β-catenin antibody for the active, unphosphorylated form

• Sequential immunoblotting: Stripping and reprobing membranes with different phospho-specific antibodies allows comparison of multiple phosphorylation states in the same samples .

• Kinase/phosphatase treatments:

  • CK1 inhibition specifically affects Ser45 phosphorylation

  • GSK3β inhibition affects Ser33/Ser37/Thr41 phosphorylation

  • Lambda phosphatase treatment removes all phosphorylation

• Subcellular fractionation: Different phosphorylated forms may have distinct subcellular localizations:

  • P33/37/41-β-catenin has been observed at cell contacts in a Ca²⁺-dependent manner

  • Non-phosphorylated β-catenin accumulates in the nucleus

• Immunoprecipitation analysis: IP with phospho-specific antibodies followed by Western blotting can isolate specific phosphorylated pools of β-catenin .

• Confocal microscopy: Co-staining with different phospho-specific antibodies and cellular markers can visualize the spatial distribution of distinct phosphorylated forms .

How do mutations at codons 41 and 45 of CTNNB1 affect antibody recognition and what are the implications for cancer research?

Mutations at codons 41 and 45 have significant implications for antibody recognition and cancer biology:

Mutation Types and Frequencies:

• T41A (threonine to alanine): Most common mutation (43% in one study)

• T41I (threonine to isoleucine): Less common (3%)

• S45F (serine to phenylalanine): 8% frequency in the same cohort

• S45P (serine to proline): 3% frequency

Effects on Antibody Recognition:

• These mutations prevent phosphorylation at the affected residues, resulting in reduced or absent binding of phospho-specific antibodies

• Conversely, non-phospho β-catenin antibodies show increased binding to mutant forms

• Studies have shown significant correlation between non-phospho β-catenin nuclear expression and positive CTNNB1 mutation status (p = 0.025)

Research Implications:

• Diagnostic applications: Nuclear expression of non-phospho β-catenin has been correlated with poor outcome in COX-2 inhibitor therapy (p = 0.022), while conventional β-catenin antibodies did not show this correlation .

• Mutation detection: Immunohistochemical staining with non-phospho β-catenin antibodies can serve as a surrogate marker for CTNNB1 mutations, potentially reducing the need for sequencing in some contexts .

• Differential oncogenic potential: Evidence suggests mutations at codon 41 may have higher oncogenic potential than other mutations, which has implications for prognosis and treatment strategies .

• Treatment resistance: All four cases with mutations in codon 45 in one study showed progressive disease with COX-2 inhibitor therapy, suggesting potential therapeutic implications .

What experimental approaches are recommended to study the relationship between β-catenin phosphorylation status and subcellular localization?

Investigating the connection between β-catenin phosphorylation and localization requires sophisticated methodological approaches:

• Confocal immunofluorescence microscopy:

  • Use of successive focal planes to precisely localize different phosphorylated forms

  • Co-staining with markers for specific subcellular compartments (E-cadherin for cell membrane, nucleoporin for nuclear envelope)

  • Double- and triple-labeling techniques with standard filter sets and laser lines

  • High-resolution imaging with appropriate objectives (60× NA1.35 or 100× NA1.45)

• Subcellular fractionation and Western blotting:

  • Separation of cytoplasmic, membrane, and nuclear fractions

  • Western blot analysis with phospho-specific antibodies to quantify distribution

  • Validation with compartment-specific markers (E-cadherin, nucleoporin, tubulin)

• Live cell imaging with fluorescently tagged constructs:

  • Wild-type and phosphorylation-site mutant β-catenin constructs (T41A, S45F)

  • Time-lapse microscopy to track dynamic changes in localization

  • Response to Wnt pathway activation or inhibition

• Calcium manipulation experiments:

  • Ca²⁺ chelation to disrupt calcium-dependent cell adhesion

  • Monitoring of P33/37/41-β-catenin localization, which exhibits Ca²⁺-dependent cell contact localization

• Kinase/phosphatase manipulations:

  • CK1 inhibition to prevent Ser45 phosphorylation

  • GSK3β inhibition or Wnt stimulation to prevent Ser33/Ser37/Thr41 phosphorylation

  • Correlation of phosphorylation changes with localization shifts

How can CTNNB1 (Ab-41/45) Antibody be utilized to investigate β-catenin's dual role in Wnt signaling and cell adhesion?

β-catenin uniquely functions in both signaling and adhesion, and CTNNB1 (Ab-41/45) Antibody can help dissect these roles:

• Differential complex analysis:

  • Immunoprecipitation with CTNNB1 (Ab-41/45) Antibody followed by detection of associated proteins

  • Co-immunoprecipitation with E-cadherin antibodies to determine if phosphorylated forms associate with adhesion complexes

  • Studies indicate P33/37/41-β-catenin may not associate with E-cadherin despite localization at cell contacts

• Junction dynamics studies:

  • Time-course experiments during junction formation or disassembly

  • Analysis of phosphorylated β-catenin during these processes

  • Research suggests N-terminally phosphorylated β-catenin may be involved in junction formation or recycling

• Wnt pathway manipulation:

  • Wnt5a has been proposed to promote β-catenin/E-cadherin association via CK1α-mediated phosphorylation at Ser45

  • Comparing canonical versus non-canonical Wnt effects on phosphorylation status

  • Analyzing membrane versus nuclear pools after pathway activation

• Tyrosine phosphorylation interactions:

  • Investigating cross-talk between Ser/Thr phosphorylation at sites 41/45 and tyrosine phosphorylation

  • Tyrosine phosphorylation reportedly reduces E-cadherin-β-catenin association at the membrane

  • Combined immunostaining for both modifications

• Mutation effects on adhesion:

  • Comparing adhesion strength and dynamics in cells with wild-type versus mutant (T41A, S45F) β-catenin

  • Analyzing whether phosphorylation-preventing mutations affect both signaling and adhesion functions

What methodological considerations are important when using CTNNB1 (Ab-41/45) Antibody for analyzing tumor samples?

Analysis of tumor samples presents unique challenges requiring specific methodological approaches:

• Sample preparation optimization:

  • Immediate fixation is critical to preserve phosphorylation status

  • Formalin-fixed, paraffin-embedded (FFPE) tissues require standardized fixation times

  • Fresh frozen samples may better preserve phosphorylation epitopes

  • Antigen retrieval methods must be carefully optimized for phospho-epitopes

• Complementary mutation analysis:

  • Parallel DNA extraction for CTNNB1 exon 3 sequencing

  • PCR amplification targeting codons 33-45 with appropriate primers

  • Direct sequencing to identify mutations at codons 41 and 45

  • Correlation of mutation status with antibody staining patterns

• Comparative antibody panels:

  • Use of multiple antibodies (phospho-β-catenin, non-phospho β-catenin, total β-catenin)

  • Studies indicate non-phospho β-catenin antibodies may better correlate with mutation status than conventional β-catenin antibodies (p = 0.025 vs. p = 0.43)

• Subcellular localization assessment:

  • Careful evaluation of membrane, cytoplasmic, and nuclear staining

  • Nuclear expression of non-phospho β-catenin has been correlated with CTNNB1 mutations and poor outcomes in some cancers

  • Quantitative scoring systems for different subcellular compartments

• Controls and validation:

  • Inclusion of known mutation-positive and wild-type samples as controls

  • Peptide competition controls to confirm antibody specificity

  • Pathologist-blinded scoring to minimize interpretation bias

  • Correlation with clinical outcomes for prognostic validation

What is the relationship between CTNNB1 mutations at codons 41/45 and clinical outcomes in cancer?

Research has revealed significant correlations between CTNNB1 mutations and clinical outcomes:

Mutation Distribution and Frequencies:

Clinical Correlations:

• All four cases with mutations at codon 45 showed progressive disease with COX-2 inhibitor therapy

• Nuclear expression of non-phospho β-catenin significantly correlated with poor outcome in COX-2 inhibitor therapy (p = 0.022)

• Conventional β-catenin antibody staining did not show significant correlation with treatment outcomes (p = 0.38)

Oncogenic Potential:

• Evidence suggests mutations at codon 41 may have higher oncogenic potential than other mutations

• In DMH-induced colon tumors, >90% of mutations represented C→T transitions at codon 41 resulting in T41I

• Proposed model suggests codon 41 mutations bear higher oncogenic potential but occur less frequently than mutations in the codon 33 cluster region

How do different experimental models help elucidate the role of phosphorylated β-catenin in normal and pathological contexts?

Various experimental models have contributed to our understanding of phosphorylated β-catenin:

• Cell line models:

  • HeLa and HT29 cells: Validated for expression of phosphorylated β-catenin

  • SW626 cells: Used for studying phosphorylated forms of β-catenin

  • These models allow investigation of regulatory mechanisms and protein interactions

• Animal models:

  • DMH-induced rat colon tumors: 36% displayed mutations in Ctnnb1, with 11/12 showing identical transitions at codon 41

  • These models helped establish the differential oncogenic potential of various mutations

  • Low-dose post-initiation treatment with chlorophyllin shifted the Ctnnb1 mutational spectrum from codons 32/34 to codons 41/45

• Patient-derived samples:

  • Studies of desmoid-type fibromatosis samples revealed correlations between non-phospho β-catenin staining and CTNNB1 mutation status

  • Analysis of 40 patients receiving COX-2 inhibitor treatment showed differential treatment responses based on mutation status

• In vitro phosphorylation systems:

  • Sequential phosphorylation by CK1 and GSK3β

  • Investigation of how phosphorylation affects protein stability and interactions

  • Studies of how Tau acetylates and stabilizes β-catenin, promoting cell survival

What is the detailed molecular mechanism of β-catenin phosphorylation and how does it integrate with other post-translational modifications?

The phosphorylation of β-catenin involves a complex regulatory cascade:

• Sequential phosphorylation process:

  • CK1α first phosphorylates β-catenin at Ser45, which serves as a priming event

  • This priming enables GSK3β to subsequently phosphorylate β-catenin at Ser33, Ser37, and Thr41

  • The fully phosphorylated form is recognized by the F-box protein β-TrCP, leading to ubiquitination and degradation

• Destruction complex coordination:

  • Axin and APC serve as scaffolds for the destruction complex

  • APC tumor suppressor functions in regulating β-catenin in both Wnt signaling and cell adhesion/migration

  • PP2A may counteract kinase activity within the complex

• Cross-talk with other modifications:

  • Tau can acetylate β-catenin at K49, promoting its stabilization and anti-apoptotic function

  • Mutation of Tau's acetyltransferase domain or co-expressing non-acetylatable β-catenin-K49R prevents increased β-catenin signaling

  • Tyrosine phosphorylation of β-catenin reduces E-cadherin-β-catenin association at the membrane

• Wnt pathway integration:

  • Wnt signaling inhibits the destruction complex, preventing β-catenin phosphorylation

  • Non-phosphorylated β-catenin accumulates and translocates to the nucleus

  • Nuclear β-catenin acts as a coactivator for TCF/LEF transcription factors, activating Wnt-responsive genes

  • Wnt5a may promote β-catenin/E-cadherin association via CK1α-mediated phosphorylation at Ser45 without affecting Ser33

The intricate regulation of β-catenin phosphorylation highlights the importance of specific phospho-antibodies like CTNNB1 (Ab-41/45) for dissecting these molecular mechanisms in both normal cellular processes and disease pathology.