Phospho-AHR/AHRR (S36) Antibody

What is the Phospho-AHR/AHRR (S36) Antibody and what does it detect?

The Phospho-AHR/AHRR (S36) Antibody is a polyclonal antibody raised in rabbits that specifically recognizes the aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor repressor (AHRR) when phosphorylated at serine 36. This antibody is designed to detect post-translational modifications that play critical roles in regulating the activity of these proteins . The antibody binds to a synthetic peptide derived from human Ah Receptor around the phosphorylation site of S36, allowing researchers to specifically monitor this modification state in experimental contexts .

The detection of phosphorylation at S36 is particularly important because this post-translational modification influences the functional activity of AHR/AHRR, which are crucial transcription factors involved in sensing environmental toxins and regulating cellular responses to xenobiotics and endogenous ligands .

What cellular processes are regulated by the AHR pathway?

The AHR functions as a ligand-activated transcription factor that enables cells to adapt to changing environmental conditions by sensing compounds from various sources including the environment, diet, microbiome, and cellular metabolism . Upon ligand binding, AHR undergoes a conformational change, translocates to the nucleus, heterodimerizes with the aryl hydrocarbon receptor nuclear translocator (ARNT), and binds to xenobiotic response elements (XREs) to induce transcription of target genes .

AHR regulates numerous biological processes including:

• Xenobiotic metabolism - activation of phase I and II metabolizing enzymes (e.g., CYP1A1)

• Immune modulation - influencing T cell differentiation and immune responses

• Cell cycle regulation and cellular differentiation

• Angiogenesis and hematopoiesis

• Drug and lipid metabolism

• Cell motility and migration

Additionally, AHR has been implicated in circadian rhythm regulation through inhibition of core circadian component PER1 expression .

What are the validated applications for this antibody?

The Phospho-AHR/AHRR (S36) Antibody has been validated for multiple research applications, primarily Western blotting (WB) and immunohistochemistry (IHC) . The recommended dilution ranges are 1:500-1:2000 for Western blot and 1:100-1:300 for immunohistochemistry applications . The antibody demonstrates reactivity across human, mouse, and rat samples, making it suitable for comparative studies across these species .

What are the optimal protocols for Western blotting with Phospho-AHR/AHRR (S36) Antibody?

When performing Western blot analysis with the Phospho-AHR/AHRR (S36) Antibody, researchers should consider the following methodological approach:

Sample Preparation:

• Extract total protein from cells or tissues using a phosphatase inhibitor-containing lysis buffer to preserve phosphorylation status

• Quantify protein concentration using Bradford or BCA assay

• Denature samples in Laemmli buffer (containing SDS and β-mercaptoethanol) at 95°C for 5 minutes

Gel Electrophoresis and Transfer:

• Load 20-50 μg of protein per lane on an 8-10% SDS-PAGE gel

• Separate proteins at 120V until adequate resolution

• Transfer to PVDF or nitrocellulose membrane at 100V for 60-90 minutes using cold transfer buffer

Antibody Incubation:

• Block membrane with 5% BSA (preferred over milk for phospho-antibodies) in TBST for 1 hour at room temperature

• Incubate with Phospho-AHR/AHRR (S36) Antibody at 1:1000 dilution in 5% BSA/TBST overnight at 4°C

• Wash 3 times with TBST, 5 minutes each

• Incubate with HRP-conjugated anti-rabbit secondary antibody at 1:5000 in 5% BSA/TBST for 1 hour at room temperature

• Wash 3 times with TBST, 5 minutes each

Detection:

• Apply ECL substrate and detect signal using chemiluminescence imaging system

• Expected molecular weight of AHR is approximately 95-110 kDa

For optimal results, always include a positive control (cells treated with known AHR ligands like TCDD or FICZ) and a negative control (untreated cells or phosphatase-treated lysate) .

What controls should be included when working with phospho-specific antibodies?

When designing experiments using the Phospho-AHR/AHRR (S36) Antibody, several critical controls should be incorporated to ensure result validity and interpretability:

Essential Controls:

• Total AHR/AHRR Antibody Control: Parallel blots or reprobes with an antibody recognizing total AHR/AHRR (regardless of phosphorylation status) to normalize phospho-specific signals to total protein levels.

• Phosphatase Treatment Control: Treatment of duplicate samples with lambda phosphatase to remove phosphate groups, which should eliminate signal from phospho-specific antibody.

• Ligand-Induced Phosphorylation:

  • Positive control: Cells treated with known AHR activators (TCDD, FICZ) to induce phosphorylation

  • Negative control: Untreated cells or cells pre-treated with AHR antagonist (CH223191) before ligand exposure

• Kinase Inhibitor Control: Treatment with CK2 inhibitors (like CX-4945) to reduce phosphorylation and confirm phospho-specificity

• Loading Control: Probing for housekeeping proteins (β-actin, GAPDH) to ensure equal loading across samples

These controls help distinguish specific phosphorylation events from artifacts and provide necessary context for interpreting experimental results with phospho-specific antibodies .

How can AHR phosphorylation be induced in experimental settings?

Inducing AHR phosphorylation experimentally is essential for studying the functional consequences of this modification. Several approaches have been validated:

Ligand-Based Induction Methods:

• Exogenous Ligand Treatment:

  • TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) at 10 nM concentration for 1-2 hours

  • FICZ (6-formylindolo[3,2-b]carbazole) at 100-300 nM for rapid induction

  • Other AHR ligands such as kynurenine or indole derivatives

• Timing Considerations: AHR phosphorylation occurs rapidly after ligand exposure, with peak phosphorylation typically observed between 30 minutes and 2 hours post-treatment, followed by a gradual decline .

• Cell-Type Specific Protocols:

  • For T cells (such as Karpas 299 or Jurkat cells): Culture in RPMI 1640 Medium before ligand exposure

  • For hepatocyte models (Hepa-1c1c7): Culture in MEM Alpha medium for optimal response

• Combined Approaches: Pre-treatment with CK2 inhibitor (CX-4945, 5 μM for 1 hour) prior to ligand exposure to study the role of specific kinases in AHR phosphorylation

Research has shown that different AHR ligands induce various degrees of phosphorylation, which may contribute to ligand-specific downstream effects and transcriptional responses .

What is the relationship between AHR phosphorylation and AHR-ARNT heterodimer formation?

The phosphorylation of AHR appears to be mechanistically linked to its interaction with ARNT and subsequent transcriptional activity. Research indicates that:

AHR activation by ligand binding initiates a cascade that leads to nuclear translocation and dimerization with ARNT. This process appears to be connected to the phosphorylation state of both proteins . Studies have shown that ARNT isoform 1 undergoes phosphorylation at serine 77 (S77) in an AhR-dependent manner, which is critical for optimal transcriptional activation of AhR target genes .

The molecular mechanism involves several key steps:

• Ligand binding to AHR causes conformational changes and nuclear translocation

• Nuclear AHR forms a heterodimer with ARNT

• This dimerization likely facilitates the recruitment of kinases such as CK2

• CK2 phosphorylates ARNT isoform 1 at S77, creating a "phosphorylation cascade"

• This phosphorylation serves as a "rheostat" for AhR target gene expression

The interaction between AHR and ARNT appears to be influenced by phosphorylation states, as mutation of the S77 phosphorylation site on ARNT isoform 1 (S77A) significantly reduced the expression of TCDD-responsive genes in multiple cell types . This suggests that phosphorylation events, including potentially S36 phosphorylation on AHR itself, may regulate the formation, stability, or transcriptional activity of the AHR-ARNT complex.

How does AHR phosphorylation influence immune cell differentiation and function?

AHR phosphorylation plays a significant role in immune cell differentiation and function, particularly in T cell subsets:

T Cell Differentiation Regulation:

The phosphorylation status of AHR appears to influence T cell polarization, with differential effects depending on the specific ligands and cellular context. Research indicates that:

• AHR activation by TCDD promotes regulatory T cell (Treg) differentiation, contributing to immunosuppression

• Conversely, FICZ (an endogenous AHR ligand) can promote pro-inflammatory TH17 differentiation in certain contexts

• The relative expression levels of ARNT isoforms and their phosphorylation status may serve as a molecular switch that controls T cell fate decisions

Molecular Mechanisms:

The phosphorylation-dependent activities appear to be mediated through several mechanisms:

• Differential recruitment of transcriptional coregulators based on phosphorylation status

• Altered chromatin remodeling activities

• Distinct gene expression programs activated by different phosphorylation patterns

Importantly, CK2-mediated phosphorylation has been shown to regulate the TH17/Treg balance, with CK2 inhibition promoting Treg generation while inhibiting TH17 differentiation . This suggests that targeting phosphorylation pathways could provide therapeutic approaches for modulating immune responses in autoimmune disorders.

What are the implications of AHR phosphorylation in cancer research?

AHR phosphorylation has significant implications for cancer research, as it may influence tumor development, progression, and therapeutic responses:

Cancer-Related Functions:

• Tumor Microenvironment Regulation: Phosphorylated AHR may alter the tumor microenvironment through effects on immune cell infiltration and function

• Immunosuppressive Mechanisms: AHR activation by tryptophan catabolites can promote tumor immune evasion, with phosphorylation potentially regulating this process

• Cell Motility and Metastasis: AHR plays a role in regulating cancer cell motility, with phosphorylation potentially serving as a molecular switch for this function

• Therapeutic Targeting: Understanding phosphorylation-dependent AHR activities could lead to novel therapeutic approaches:

  • Disrupting specific phosphorylation events rather than total AHR inhibition

  • Modulating AHR phosphorylation to enhance anti-tumor immunity

  • Combining AHR-targeted therapies with existing immunotherapies

• Hematological Malignancies: There is evidence that manipulating the ARNT isoform ratio or targeting AHR/ARNT phosphorylation may offer therapeutic options for treating hematological malignancies

The Phospho-AHR/AHRR (S36) Antibody provides researchers with a valuable tool to investigate these phosphorylation-dependent mechanisms in various cancer models and patient samples .

What are common challenges when working with Phospho-AHR/AHRR (S36) Antibody?

When working with Phospho-AHR/AHRR (S36) Antibody, researchers may encounter several technical challenges that require specific troubleshooting approaches:

Common Issues and Solutions:

• Low Signal Intensity:

  • Problem: Insufficient phosphorylated protein in samples

  • Solution: Treat cells with strong AHR activators (TCDD, FICZ) to increase phosphorylation levels

  • Problem: Phosphorylation lost during sample preparation

  • Solution: Use fresh phosphatase inhibitor cocktails in all buffers; keep samples cold throughout processing

• High Background Signal:

  • Problem: Non-specific binding of antibody

  • Solution: Increase blocking time/concentration (5% BSA recommended over milk); optimize antibody dilution (start with 1:1000 for WB); increase wash steps

  • Problem: Cross-reactivity with other phosphoproteins

  • Solution: Use peptide competition assays to confirm specificity; compare with non-phospho antibody results

• Inconsistent Results:

  • Problem: Variability in phosphorylation status between experiments

  • Solution: Standardize cell culture conditions; control timing between stimulation and lysis; use internal controls in each experiment

  • Problem: Degradation of phosphorylated proteins

  • Solution: Process samples quickly; avoid freeze-thaw cycles; use protease inhibitors along with phosphatase inhibitors

• Multiple Bands in Western Blot:

  • Problem: Detection of multiple isoforms or degradation products

  • Solution: Validate bands using siRNA knockdown; compare with expected molecular weight (AHR: ~95-110 kDa)

How can phosphorylation dynamics be accurately quantified?

Accurately quantifying AHR phosphorylation dynamics requires robust methodological approaches to capture both temporal changes and relative phosphorylation levels:

Quantification Methods:

• Western Blot Densitometry:

  • Normalize phospho-AHR signal to total AHR protein levels

  • Use time-course experiments with multiple time points (0, 15, 30, 60, 120 min after ligand exposure)

  • Compare ratio of phospho:total protein across experimental conditions

  • Employ image analysis software with linear dynamic range

• Phospho-specific ELISA:

  • Provides more quantitative results than Western blotting

  • Allows high-throughput analysis of multiple samples

  • Can detect small changes in phosphorylation levels

  • Requires careful validation with appropriate controls

• Phosphoproteomics Approaches:

  • Mass spectrometry-based quantification of phosphopeptides

  • Can identify multiple phosphorylation sites simultaneously

  • Requires specialized equipment but provides comprehensive analysis

  • Use SILAC or TMT labeling for comparative quantification

• Kinetics Analysis:

  • Plot phosphorylation levels against time after stimulation

  • Calculate rate constants for phosphorylation and dephosphorylation

  • Compare kinetics between different ligands or experimental conditions

  • Identify factors that influence phosphorylation/dephosphorylation rates

For robust analysis, researchers should include multiple technical and biological replicates and apply appropriate statistical tests to determine significance of observed changes .

How can researchers address contradictory results in AHR phosphorylation studies?

Addressing contradictory results in AHR phosphorylation studies requires systematic analysis of experimental variables and methodological differences:

Resolution Strategies:

• Cell Type Considerations:

  • Different cell types may exhibit distinct AHR phosphorylation patterns

  • Compare results across multiple relevant cell lines (e.g., Karpas 299, Jurkat, and Peer T cells for immune studies; Hepa-1c1c7 for hepatocyte models)

  • Consider tissue-specific expression of kinases, phosphatases, and ARNT isoforms

• Ligand-Specific Effects:

  • Different AHR ligands (TCDD, FICZ, kynurenine) may induce distinct phosphorylation patterns

  • Compare multiple ligands at equimolar concentrations

  • Consider ligand-specific AHR conformational changes that might affect phosphorylation site accessibility

• Temporal Dynamics Analysis:

  • Contradictory results may stem from different time points examined

  • Conduct comprehensive time-course experiments (15 min to 24 hours)

  • Consider rapid, transient phosphorylation events that might be missed in end-point assays

• Technical Approach Comparison:

  • Different antibodies may recognize distinct epitopes around the phosphorylation site

  • Validate findings using multiple detection methods (Western blot, mass spectrometry, ELISA)

  • Consider phospho-mimetic and phospho-dead mutants to confirm functional roles

• ARNT Isoform Considerations:

  • The ratio of ARNT isoforms (particularly isoforms 1 and 3) significantly affects AHR signaling

  • Characterize ARNT isoform expression in study systems

  • Consider how ARNT isoform phosphorylation (particularly at S77) interacts with AHR phosphorylation at S36

When publishing results, researchers should clearly document all experimental conditions that might influence phosphorylation status, including cell density, passage number, serum conditions, and exact timing of treatments .