Recombinant Human C-C chemokine receptor type 6 (CCR6)

What is the structure and function of human CCR6, and how does it differ from other chemokine receptors?

Human CCR6 is a 374 amino acid G protein-coupled receptor with a molecular weight of approximately 42.5 kDa . Unlike most chemokine receptors that exhibit promiscuous binding to multiple ligands, CCR6 is distinctive in that it binds specifically to only one chemokine ligand, CCL20 (also known as MIP-3 alpha) .

The gene for CCR6 is located on the long arm of Chromosome 6 (6q27) on the Watson (plus) strand, spanning 139,737 bases . The protein belongs to family A of the G protein-coupled receptor superfamily and has been designated CD196 (cluster of differentiation 196) .

CCR6 functions primarily in regulating the migration and recruitment of dendritic cells and T cells during inflammatory and immunological responses. It plays a key role in B-lineage maturation and antigen-driven B-cell differentiation . The receptor is expressed in lymphatic tissues (spleen, lymph nodes) and non-lymphatic tissues (pancreas, colon, appendix, small intestine) .

What expression systems are recommended for producing functional recombinant human CCR6, and what are their comparative advantages?

Several expression systems have been used to produce recombinant human CCR6, each with distinct advantages depending on research needs:

• Mammalian Cell Expression Systems:

  • Provide proper post-translational modifications and protein folding

  • Result in a full-length (374 aa) CCR6 protein with a molecular weight of 42.5 kDa

  • Often used with C-terminal tags (e.g., 10xHis-tag) for purification

  • Ideal for functional studies requiring properly folded and modified receptor

  • Allows for expression of CCR6 in virus-like particles (VLPs) that better mimic native membrane environment

• Escherichia coli Expression Systems:

  • More cost-effective and typically yield higher protein quantities

  • Often used for partial CCR6 expression (e.g., 1-47 aa fragment)

  • Can include both N-terminal (10xHis) and C-terminal (Myc) tags

  • Suitable for structural studies, antibody production, and protein-protein interaction studies

  • Generally achieves >85% purity by SDS-PAGE

  • Less suitable for functional assays requiring proper receptor folding and signaling

• HEK293-Based Stable Expression Systems:

  • The Flp-InTRex293 system enables targeted integration of a single copy expression vector

  • Creates isogenic cell lines expressing wild-type or mutant CCR6

  • Allows for direct comparison of expression levels and response to ligand stimulations

  • Particularly useful for studying CCR6 mutations and their functional consequences

For studying CCR6 internalization and trafficking, expression systems with C-terminal GFP tags have proven valuable when combined with time-lapse microscopy or flow cytometry .

What are the most effective methods for detecting and quantifying CCR6 expression in different experimental contexts?

Researchers have several validated methodologies for detecting and quantifying CCR6 expression:

• Flow Cytometry:

  • Most commonly used for cell surface CCR6 detection

  • Utilizes monoclonal antibodies (clone 53103 has been used by HLDA to establish CD designation)

  • Available with various conjugations (PE, APC) for multicolor analysis

  • Can detect native CCR6 on primary cells or recombinant expression in cell lines

  • Caution: Some commercially available antibodies show background non-specific staining due to homology between different chemokine receptors

• Affinity-Based Probe Labeling:

  • Novel approach using affinity-based probes (AfBPs) that target specific domains

  • Similar to techniques developed for other chemokine receptors like CCR2

  • Enables visualization via fluorescent tag incorporation through click chemistry

  • Allows for SDS-PAGE and mass spectrometry-based detection depending on the reporter tag

• Reporter Systems:

  • Transgenic multi-chemokine receptor reporter mice express spectrally distinct fluorescent reporters

  • Allows tracking of CCR expression dynamics in myeloid cells

  • Overcomes limitations of antibody-based detection

  • Compatible with additional reporters for complex tissue section analysis

• Quantitative PCR:

  • For measuring CCR6 mRNA expression levels

  • Particularly useful when protein detection is challenging

  • Can be analyzed using 2^-ΔCT values to quantify relative expression

• Western Blotting:

  • Most effective with tagged CCR6 constructs

  • Can help identify different glycosylation states and post-translational modifications

  • Note: Enzyme digestion of tissues may cleave external portions of chemokine receptors, preventing antibody detection

Each method has specific advantages depending on whether native or recombinant CCR6 is being studied, and whether protein localization, quantification, or functional assessment is the primary goal.

How can researchers effectively study CCR6 internalization and trafficking dynamics?

Studying CCR6 internalization and trafficking requires specialized techniques:

• Time-lapse Microscopy with Fluorescently Tagged CCR6:

  • C-terminal GFP-tagged CCR6 constructs enable real-time visualization

  • Treatment with CCL20 (50 nM) while recording allows tracking of receptor movement

  • Quantification can be performed using ImageJ software

  • Analysis reveals a weak, constitutive, ligand-independent internalization and recycling of CCR6, with slower kinetics than other chemokine receptors

• Colocalization Studies:

  • Determine intracellular trafficking pathways by examining colocalization with:

    • Early endosome antigen 1 (EEA1)-positive vesicles

    • Rab5-positive vesicles (early endosomes)

    • Rab11-positive vesicles (recycling compartments)

  • Helps determine the specific trafficking route taken by CCR6

• Flow Cytometry-Based Internalization Assays:

  • Allows quantitative measurement of receptor downregulation from cell surface

  • Can be performed on cell lines with stably expressed CCR6 variants

  • Permits comparison between wild-type and mutant receptors

• Truncation and Mutation Analysis:

  • Creating truncated forms of CCR6 (e.g., H8+ or H8-) to study domain-specific roles

  • C-terminus appears dispensable for receptor internalization based on experimental evidence

  • Fluorescent labeling of cell membrane receptors followed by flow cytometry analysis can quantify internalization rates

• Scavenging Ability Assessment:

  • Compare CCR6 with other atypical chemokine receptors (ACKRs)

  • Research indicates CCR6 binds chemerin but does not perform scavenging

  • Unlike ACKRs, CCR6 does not effectively internalize, recycle, and scavenge its ligand

What are the established protocols for studying CCR6-mediated cell migration and chemotaxis?

Researchers investigating CCR6-mediated migration and chemotaxis employ several standardized approaches:

• Transwell Migration Assays:

  • Quantifies migration toward CCL20 gradients

  • Allows comparison between CCR6-expressing and control cells

  • Used to evaluate how overexpression or inhibition affects migration rates

  • Effective for both cell lines and primary cells (e.g., Th17 cells)

• Cell Arrest Assays Under Flow Conditions:

  • Mimics physiological conditions in blood vessels

  • Measures arrest of CCR6+ cells (e.g., Th17 cells) on inflamed endothelium

  • Uses HUVEC monolayers with CCL20 or β-defensin-2 as stimuli

  • Demonstrates CD54-dependent arrest that is CCR6-specific

  • Allows discrimination between different T cell subsets (Th17 vs. Th1/Th2)

• Combined Migration and Cytotoxicity Assays:

  • Particularly useful for studies involving immune cell function

  • Example: Enhanced migration of CXCR6-transduced OT-1 T cells toward CXCL16-expressing tumor cells resulted in enhanced target cell lysis

  • Similar principles apply to CCR6-expressing cells and their cytotoxic function

• Real-time Migration Visualization:

  • Microscopy-based approaches to track cell movement

  • Can be combined with fluorescently labeled cells and time-lapse imaging

  • Quantifies velocity, directionality, and response time to CCL20 gradients

• In vivo Adoptive Transfer Models:

  • Transfer of CCR6-expressing cells into wild-type recipient animals

  • Tracking of migration to sites of inflammation (e.g., skin, joints)

  • Evaluation of progeny macrophage phenotypes shows upregulation of other chemokine receptors (CCR1, CCR5) as cells differentiate

Important methodological considerations:

• Use of appropriate blocking controls (CCR6 antagonists or blocking antibodies)

• Inclusion of CCR6-negative cells as controls

• Consideration of receptor internalization kinetics (transient loss of CCR6 expression following antigen-specific activation)

• Verification that enzyme treatments used in cell isolation do not cleave the extracellular portion of CCR6

What allosteric modulators and antagonists are available for CCR6, and how can they be effectively utilized in research?

Several classes of CCR6 modulators have been developed and characterized:

• Small Molecule Allosteric Antagonists:

  • Oxomorpholine analogues (OXM1 and OXM2) bind to an extracellular pocket and disrupt the receptor activation network

  • Discovered through ligand-based virtual screening using SQA1 as seed compound

  • Demonstrate robust inhibition of CCL20-mediated chemotaxis in primary human T cells

  • Significantly stabilize CCR6 in thermal shift assays, confirming direct target engagement

  • Additive stabilization observed when analogues from different series are combined

• Monoclonal Antibodies:

  • Anti-hCCR6 mAbs (e.g., 6H12 and 29A6) have been generated that specifically react with CCR6-transfected cells

  • Do not cross-react with other chemokine receptors (CCR5, CCR7, CCR8, CCR9)

  • Recognize different epitopes in the N-terminal region of CCR6:

    • Most mAbs target amino acids 1-28

    • Some (like 29A6) recognize peptide 18-46

  • Useful for both detection and functional blockade

• Peptide-Based Inhibitors:

  • CCL20 locked dimer has shown efficacy as a CCR6 antagonist

  • Successfully blocked both skin and joint inflammation in IL-23 mini-circle model

  • Effective in both prevention and therapeutic settings

• Engineered Variants of CCL20:

  • Modified versions of the natural ligand that bind but do not activate signaling

  • Useful for competitive inhibition studies

Research applications:

• Structure-Function Studies:

  • Allosteric modulators reveal conformational changes in CCR6

  • Thermal shift assays with different antagonist combinations help map binding sites

  • Point mutations (e.g., L134^3.41W) can enhance receptor expression for structural studies

• Therapeutic Development Models:

  • For testing CCR6-targeted therapies in autoimmune diseases

  • Used in animal models of psoriasis with promising results

  • Potential applications in rheumatoid arthritis and other inflammatory conditions

• Signaling Pathway Dissection:

  • Selective blockade of specific downstream pathways

  • Investigation of biased signaling through CCR6

For optimal experimental design, researchers should consider:

• Antagonist specificity (verify lack of activity on other chemokine receptors)

• Concentration ranges (based on documented thermal shift or functional assays)

• Appropriate positive controls (CCL20 stimulation) and negative controls

• Potential for combination with other receptor modulators to study signaling cross-talk

How does CCR6 function differ between cell types, and what methodological approaches best capture these differences?

CCR6 demonstrates significant functional heterogeneity across cell types, requiring specialized methodological approaches:

• T Cell Subsets:

  • CCR6 is expressed on various T cell populations including Th17, Th1, Th2, and Treg cells

  • Predominant expression on IL-17A/F and IL-22-producing CD4+ T cells

  • Functional differences can be studied using:

    • Flow cytometric sorting of CCR6+ T cell subsets followed by cytokine profiling

    • Single-cell RNA sequencing to correlate CCR6 expression with transcriptional profiles

    • Cell-specific knockout or reporter models

  • Methodological insight: Antigen-specific activation induces transient loss of CCR6 expression (both transcriptionally and at protein level) with slow kinetics

• Dendritic Cells:

  • CCR6 regulates immature dendritic cell (DC) migration

  • Expression is regulated by cytokines: IL-4 and IFNγ suppress expression in Langerhans cells while IL-10 induces expression

  • Study approaches:

    • DC differentiation cultures with cytokine modulation

    • Trafficking studies in CCR6-reporter or knockout models

    • In vitro to in vivo DC transfer experiments

• B Cells:

  • Important for B-lineage maturation and antigen-driven differentiation

  • Methodologies include:

    • B cell development assays in the presence of CCR6 antagonists

    • In vivo B cell trafficking studies using adoptive transfer

    • Germinal center response analysis in CCR6-deficient models

• Myeloid Cell Plasticity:

  • Monocyte-to-macrophage differentiation involves dynamic changes in chemokine receptor expression

  • Studies show Ly6C^hi monocytes initially express mainly CCR2, then induce CCR1 and CCR5 as they differentiate

  • By day 9, mature monocyte-derived DCs express mainly CCR1 and CCR5, independent of CCR2

  • Optimal approaches:

    • Time-course analyses using multi-chemokine receptor reporter mice

    • In vitro differentiation cultures followed by reporter expression analysis

    • Adoptive transfer experiments to trace receptor expression changes in vivo

• Cell Line Models:

  • Different CCR6-expressing cell lines show distinct patterns of receptor glycosylation and processing

  • The molecular weight of CCR6 varies by cell type (~52 kDa, ~49 kDa, ~36 kDa bands observed)

  • Methodological consideration: PNGase treatment, which cleaves N-glycans, results in a ~45 kDa band, indicating importance of post-translational modifications

What are the advantages and limitations of different tags for recombinant CCR6 purification and detection?

Various tagging strategies offer distinct advantages and limitations for CCR6 research:

• His-Tags:

  • Advantages:

    • Efficient purification using nickel or cobalt affinity chromatography

    • Available as N-terminal (10xHis) or C-terminal (10xHis) variants

    • Minimal interference with protein function in many cases

    • Compatible with denaturing conditions for purification

  • Limitations:

    • C-Terminal His-tags can only be tested under denaturing conditions

    • May affect receptor trafficking or ligand binding if located near functional domains

    • Detection antibodies may show variable sensitivity

• Acyl Carrier Protein (ACP) Tags:

  • Advantages:

    • Allows fluorescent labeling of cell membrane receptors

    • Useful for studying receptor internalization

    • Compatible with truncation studies (H8+ or H8-)

    • Enables quantitative analysis by flow cytometry

  • Limitations:

    • May affect natural receptor dynamics

    • Requires additional labeling steps

• GFP/Fluorescent Protein Tags:

  • Advantages:

    • Direct visualization without additional labeling steps

    • Valuable for time-lapse microscopy and tracking receptor movement

    • C-terminal GFP-tags particularly useful for internalization studies

    • Compatible with co-localization studies using fluorescently labeled vesicle markers

  • Limitations:

    • Relatively large tag may interfere with receptor function

    • Potential for altered trafficking due to tag size

    • Photobleaching during extended imaging sessions

• Dual-Tag Systems:

  • Advantages:

    • N-Terminal 10xHis-Tagged and C-Terminal Myc-Tagged combinations offer versatility

    • Enable sequential purification strategies for higher purity

    • Allow detection with different antibodies to confirm full-length expression

  • Limitations:

    • More complex construct design

    • Potential for additive interference with receptor function

• Click Chemistry-Compatible Tags:

  • Advantages:

    • Incorporation of click handles allows post-expression labeling

    • Versatile application in both SDS-PAGE and mass spectrometry-based proteomics

    • Can be used with different reporter tags (fluorescent or biotin) depending on application

    • Demonstrated high specificity in multiple assay setups

  • Limitations:

    • Requires additional chemical biology expertise

    • Multi-step protocols increase experimental complexity

Key considerations for tag selection:

• Research purpose (purification, localization, functional studies)

• Expression system compatibility

• Potential interference with ligand binding or signaling

• Detection method requirements

• Need for multiple detection strategies

What are the key technical challenges in studying CCR6-mediated signaling, and how can they be addressed?

Researchers face several technical challenges when investigating CCR6 signaling:

• Distinguishing G Protein-Dependent and Independent Signaling:

  • Challenge: CCR6 contains an altered amino acid sequence (QGYRVFS) in place of the conserved DRYLAIV motif required for G protein-mediated responses

  • Solutions:

    • Use of BRET/FRET-based G protein activation assays to directly measure coupling

    • Comparative analysis with signaling-deficient mutants

    • Selective G protein inhibitors (pertussis toxin for Gαi)

    • Phosphorylation-specific antibodies to track downstream events

• Conflicting Reports on Signaling Outcomes:

  • Challenge: Earlier studies reported CCR6-mediated MAPK activation and cell migration, but recent findings question this

  • Solutions:

    • Careful controls including receptor-negative cells

    • Dose-response studies across concentration ranges

    • Time-course experiments to capture transient signals

    • Validation in multiple cell types and with different stimulation protocols

• Ligand Specificity Questions:

  • Challenge: While CCL20 is established as the primary ligand, some studies suggest CCR6 may bind other chemokines (CCL2, CCL5, CCL7, CCL8, CCL19, CCL21) or β-defensins

  • Solutions:

    • Direct binding assays with purified components

    • Competition studies with validated ligands

    • Cell-based functional assays with specific readouts

    • Receptor mutants to map binding determinants

• Receptor Internalization and Signaling:

  • Challenge: Debate about whether CCR6 undergoes constitutive or ligand-induced internalization

  • Solutions:

    • Time-lapse microscopy with fluorescently tagged receptors

    • Flow cytometry-based internalization assays

    • Comparison with well-characterized chemokine receptors

    • Analysis of internalization-deficient mutants

• Distinguishing Direct vs. Indirect Effects:

  • Challenge: CCR6 may function as a ligand-presenting molecule rather than directly signaling

  • Solutions:

    • Co-culture systems with cells expressing different receptor components

    • Biochemical studies of receptor complexes

    • Mutational analysis of key signaling residues

    • Careful selection of readouts specific to direct CCR6 signaling

• Post-translational Modifications:

  • Challenge: CCR6 undergoes glycosylation and other modifications that affect function

  • Solutions:

    • Treatment with PNGase to remove N-glycans

    • Analysis of receptor size by Western blotting

    • Mass spectrometry to map modification sites

    • Mutational analysis of potential modification sites

Technical approaches to address these challenges:

What are the latest methodological advances for studying CCR6's role in autoimmune and inflammatory diseases?

Recent methodological innovations have enhanced our understanding of CCR6 in disease contexts:

• Multi-Chemokine Receptor Reporter Systems:

  • Transgenic reporter mice expressing spectrally distinct fluorescent proteins for CCR1, CCR2, CCR3, and CCR5

  • Allows simultaneous tracking of multiple chemokine receptors during inflammation

  • Reveals that chemokine receptor expression is more selective than previously anticipated

  • Enables precise definition of receptor expression patterns on myeloid cells in resting and inflamed conditions

  • Compatible with additional reporters used in CODEX technology for tissue section analysis

• Mouse Models of Inflammation:

  • IL-23 mini-circle model in B10.RIII mice shows both skin and joint involvement

  • Novel CCR6 antagonist (CCL20 locked dimer) effectively blocks inflammation in both prevention and therapeutic settings

  • Entheses of treated mice express high levels of CCL20, suggesting a role in enthesitis characteristic of psoriatic arthritis

  • Models support the role of CCR6 in psoriasis and potentially other autoimmune conditions

• In vitro Th17 Cell Systems:

  • In situ-differentiated, skin-derived Th17 clones activated via TCR-CD3 complexes

  • Production of CCL20 in addition to IL-17 and IL-22

  • IL-17 and IL-22 synergistically induce production of human β-defensin-2 by epidermal keratinocytes

  • Both CCL20 and β-defensin-2 induce arrest of Th17 cells on HUVEC in a CD54-dependent, CCR6-specific manner

• Single-Cell Technologies:

  • Single-cell RNA sequencing to identify CCR6+ cell populations

  • CITE-seq approaches combining transcriptome and surface protein analysis

  • Spatial transcriptomics to map CCR6+ cells within inflamed tissues

  • Correlation of CCR6 expression with cytokine production and disease progression

• Therapeutic Targeting Approaches:

  • CCR6 inhibition as an alternative to targeting downstream effectors (IL-17, IL-22)

  • Preclinical studies in animal models of psoriasis showing promising results

  • Potential applications in other autoimmune diseases including rheumatoid arthritis

  • Investigation of CCR6 as a biomarker for therapeutic responsiveness

• Cancer Research Applications:

  • CCR6 identified as a potential druggable target to mitigate EGFR inhibitor resistance

  • Pharmacological inhibition of CCR6 effectively reverses acquired resistance to EGFR inhibitors in cancer cells

  • Disrupts mitochondrial oxidative phosphorylation, a cellular process commonly associated with therapy resistance

  • RNA sequencing reveals that CCR6 inhibition plus erlotinib treatment reverses expression patterns of genes involved in oxidative phosphorylation

Methodological considerations for disease-focused CCR6 research:

• Use of patient-derived samples to validate findings from animal models

• Combination of genetic and pharmacological approaches to target CCR6

• Integration of multiple 'omics' technologies for comprehensive pathway analysis

• Careful selection of disease models that recapitulate key aspects of human pathology

• Validation of findings across different experimental systems and disease models