Recombinant Mouse C-C chemokine receptor type 4 (Ccr4)

What is C-C chemokine receptor type 4 (CCR4) and what are its primary functions in mouse models?

CCR4 is a seven-transmembrane G protein-coupled receptor that serves as a key regulator of T cell trafficking and immune responses. In mice, CCR4 functions primarily as a receptor for the chemokines CCL17 (TARC) and CCL22 (MDC), mediating the migration of various T cell subsets to sites of inflammation.

CCR4 has been identified as a marker for several T cell populations, including T helper type 2 (Th2) cells and T helper type 17 (Th17) cells . It plays a critical role in regulating the balance between proinflammatory T cells and anti-inflammatory regulatory T cells (Tregs) . Recent studies have demonstrated that CCR4 deficiency in mouse models leads to exacerbated inflammation in various disease models, highlighting its importance in immune homeostasis.

Methodological approach: To study CCR4 function in mice, researchers typically employ flow cytometry with fluorescently-labeled antibodies to detect receptor expression, chemotaxis assays to evaluate migratory responses, and genetic approaches (knockout or conditional knockout models) to assess the impact of CCR4 deficiency on immune responses in various disease contexts.

Which cell types express CCR4 in mice and how does this expression pattern influence research applications?

In mice, CCR4 exhibits a distinct expression pattern predominantly on lymphoid cells:

• T helper type 2 (Th2) cells

• T helper type 17 (Th17) cells

• Regulatory T cells (Tregs)

• Memory CD4+ T lymphocytes, particularly skin-homing populations

• Subset of thymocytes

• Some dendritic cell populations

While human CCR4 has been extensively characterized, mouse CCR4 shows a similar pattern with "high expression in most single-positive CD4+ thymocytes and on a major fraction of blood memory CD4 lymphocytes, including skin-homing memory cells" .

Methodological approach: Researchers can isolate specific cell populations from mouse lymphoid tissues for functional studies using magnetic bead selection or flow cytometry sorting based on CCR4 expression. Single-cell RNA sequencing provides comprehensive analysis of CCR4 expression across immune cell subsets in different physiological and pathological conditions.

What are the optimal expression systems for producing functional recombinant mouse CCR4?

Producing functional recombinant mouse CCR4 presents significant challenges due to its complex structure as a multi-pass membrane protein. The table below compares different expression systems:

Methodological approach: Mammalian expression systems (particularly HEK293 cells) are generally preferred for producing functional mouse CCR4, as they provide the appropriate cellular machinery for proper folding and post-translational modifications. For optimal results, researchers should incorporate purification tags (His, FLAG, or Strep) and consider using tetracycline-inducible expression systems to control expression levels.

How can the purity and functionality of recombinant mouse CCR4 be assessed?

A comprehensive quality assessment protocol for recombinant mouse CCR4 should include both purity and functional analyses:

Purity Assessment:

• SDS-PAGE with Coomassie or silver staining

• Western blotting using specific anti-CCR4 antibodies

• Size exclusion chromatography to evaluate homogeneity

• Mass spectrometry for precise molecular characterization

Functional Assessment:

• Ligand binding assays using radiolabeled or fluorescently-labeled CCL17/CCL22

• Surface plasmon resonance (SPR) to measure binding kinetics and affinity

• GTPγS binding assays to evaluate G-protein coupling

• Calcium flux assays in cells expressing recombinant CCR4

• Chemotaxis assays using transwell systems

Methodological approach: Researchers should establish clear acceptance criteria for both purity (typically >90% by SDS-PAGE) and functionality (ligand binding with Kd values in the nanomolar range). Comparing the properties of recombinant mouse CCR4 with the native receptor expressed in primary mouse T cells provides validation of physiological relevance.

How does CCR4 deficiency impact immune responses in mouse disease models?

CCR4 knockout or deficiency in mice reveals complex and sometimes paradoxical roles in disease pathogenesis:

In atherosclerosis models: "Genetic deletion of CCR4 in hypercholesterolemic mice accelerates the development of early atherosclerotic lesions characterized by an inflammatory plaque phenotype. This was associated with proinflammatory T helper type 1 (Th1) cell-skewed responses in peripheral lymphoid tissues, para-aortic lymph nodes, and atherosclerotic aorta" .

The mechanistic basis for this effect was identified: "CCR4 deficiency in Tregs impaired their suppressive function and migration to the atherosclerotic aorta and augmented Th1 cell-mediated immune responses through defective regulation of dendritic cell function, which accelerated aortic inflammation and atherosclerotic lesion development" .

Additional disease models affected by CCR4 deficiency include:

• Allergic airway inflammation: Reduced Th2 cell recruitment

• Atopic dermatitis: Decreased skin inflammation

• Autoimmune disorders: Variable effects depending on the relative importance of effector vs. regulatory T cells

• Tumor immunity: Enhanced anti-tumor responses in some models

Methodological approach: When studying CCR4-deficient mice, researchers should comprehensively analyze immune cell populations using flow cytometry, measure tissue-specific cytokine profiles, and evaluate cell migration patterns using adoptive transfer of labeled cells or intravital microscopy.

What molecular techniques can be used to study CCR4 signaling pathways in mouse cells?

CCR4 signaling can be investigated using various complementary techniques:

Calcium Mobilization Assays:

• Fura-2 or Fluo-4 loading for ratiometric or single-wavelength detection

• Real-time kinetic measurements in primary mouse T cells or cell lines

• Comparison of CCR4 wild-type vs. mutant receptor signaling

Phosphorylation Analysis:

• Western blotting for downstream signaling molecules (ERK1/2, AKT, p38)

• Phospho-flow cytometry for single-cell resolution

• Phosphoproteomic analysis for comprehensive pathway mapping

Protein-Protein Interaction Studies:

• Co-immunoprecipitation of CCR4 with G proteins or β-arrestins

• BRET/FRET assays for real-time interaction monitoring

• Proximity ligation assays in fixed cells or tissues

Gene Expression Analysis:

• RNA-seq following CCR4 activation in different T cell subsets

• ChIP-seq to identify transcription factors activated downstream of CCR4

• Single-cell transcriptomics to capture heterogeneity in responses

Methodological approach: For robust signaling studies, researchers should use multiple complementary techniques and include appropriate controls (receptor antagonists, pertussis toxin for Gαi inhibition). Time-course experiments are essential to capture both rapid (seconds to minutes) and delayed (hours) signaling events.

How can CRISPR-Cas9 technology be utilized to study CCR4 function in mouse models?

CRISPR-Cas9 technology offers versatile approaches to interrogate CCR4 biology:

Genome Editing Applications:

• Generation of complete CCR4 knockout mice

• Introduction of point mutations to study structure-function relationships

• Creation of reporter knock-ins (GFP, luciferase) under endogenous control

• Conditional alleles for tissue-specific or inducible deletion

• Humanization of mouse CCR4 for translational studies

Similar genome editing approaches have been successfully applied to chemokine receptors: "This study provides an effective approach to create a CXCR4 mutation...without leaving any genetic footprint inside cells" . These techniques can be adapted for CCR4 research.

Methodological approach: For successful CRISPR-Cas9 editing of CCR4, researchers should:

• Design multiple guide RNAs targeting the desired region

• Test editing efficiency in mouse cell lines before moving to primary cells or zygotes

• Include appropriate repair templates for precise mutations or insertions

• Screen founders using sequencing and functional assays

• Validate phenotypes across multiple independent lines

What are the challenges in translating findings from recombinant mouse CCR4 studies to in vivo contexts?

Translating findings from recombinant protein studies to physiological contexts presents several challenges:

Technical Challenges:

• Maintaining native conformation of CCR4 after purification

• Ensuring appropriate post-translational modifications

• Recreating the proper membrane environment

• Accounting for protein-protein interactions absent in purified systems

Biological Considerations:

• Differences in expression levels between recombinant and endogenous systems

• Cell type-specific signaling contexts

• Impact of the inflammatory microenvironment on receptor function

• Compensatory mechanisms in knockout models

• Potential differences between acute (antagonist) vs. chronic (genetic) inhibition

Methodological approach: To bridge this translational gap, researchers should:

• Validate recombinant protein findings in primary mouse cells

• Compare pharmacological inhibition with genetic approaches

• Use conditional and inducible knockout models to minimize developmental effects

• Perform detailed dose-response studies with inhibitors

• Consider the impact of the microenvironment on receptor function

How does CCR4 participate in T cell differentiation and function in mouse models?

CCR4 plays multifaceted roles in T cell biology beyond simple chemotaxis:

T Cell Differentiation:

• CCR4 expression is induced during Th2 and Th17 differentiation

• CCR4 signaling may reinforce lineage commitment

• CCR4 deficiency can skew responses toward Th1 phenotypes

Regulatory T Cell Function:

• CCR4 is required for optimal Treg migration to tissues

• CCR4-deficient Tregs show impaired suppressive function

• CCR4 contributes to Treg homeostasis in certain tissues

T Cell Activation:

• CCR4-deficient T cells show altered activation profiles

• "The expression of activation marker CTLA-4 in peripheral LN CD4+Foxp3− non-Tregs was higher in Ccr4−/−Apoe−/− mice than in Apoe−/− mice"

• "We found a marked increase in the mRNA expression of activation-associated molecules (Ctla4, Cd44, and Cd103) in splenic non-Tregs from Ccr4−/−Apoe−/− mice"

Cytokine Production:

• CCR4 deficiency affects cytokine profiles: "Compared with those from Apoe−/− mice, splenic CD4+ T cells from Ccr4−/−Apoe−/− mice secreted more Th1-related cytokine IFN-γ, Th2-related cytokine IL-13, Th17-related cytokine IL-17, and various inflammation-related cytokines and chemokines"

Methodological approach: When studying CCR4's role in T cell function, researchers should isolate defined T cell subsets (naïve, memory, Th1, Th2, Th17, Treg) from wild-type and CCR4-deficient mice and comprehensively analyze their phenotype, migration, proliferation, survival, and effector functions under various stimulation conditions.

What strategies can optimize the solubility and stability of recombinant mouse CCR4?

As a seven-transmembrane protein, CCR4 presents significant challenges for maintaining stability in solution:

Solubilization Strategies:

• Detergent screening (DDM, LMNG, GDN, and CHAPS often perform well)

• Lipid nanodiscs for membrane protein stabilization

• Styrene maleic acid lipid particles (SMALPs) for native-like environment

• Saposin-lipoprotein nanoparticles as alternative scaffold

Stabilization Approaches:

• Addition of cholesterol or specific lipids

• Inclusion of ligands during purification

• Introduction of thermostabilizing mutations

• Fusion with soluble partners (T4 lysozyme, BRIL)

Buffer Optimization:

• pH screening (typically 7.0-8.0)

• Salt concentration and type

• Glycerol or sucrose as stabilizing agents

• Antioxidants to prevent oxidation of cysteine residues

Methodological approach: Researchers should perform systematic stability screening using techniques like differential scanning fluorimetry, size exclusion chromatography, and functional binding assays to identify optimal conditions. Long-term stability should be assessed at different temperatures (4°C, -20°C, -80°C) with regular functional testing.

How can post-translational modifications of mouse CCR4 be characterized and their functional impact assessed?

Post-translational modifications (PTMs) critically impact CCR4 function:

Key CCR4 Post-translational Modifications:

• N-linked glycosylation: Affects folding and trafficking

• Tyrosine sulfation: Modulates ligand binding

• Palmitoylation: Influences receptor stability and localization

• Phosphorylation: Regulates desensitization and signaling

Analytical Techniques:

• Mass spectrometry for comprehensive PTM mapping

• Site-directed mutagenesis to create PTM-deficient variants

• Glycosidase treatments to assess glycosylation impact

• Metabolic labeling to study dynamic modifications

Functional Impact Assessment:

• Ligand binding assays comparing wild-type and PTM-deficient variants

• Trafficking studies using fluorescence microscopy

• Signaling assays (calcium flux, ERK phosphorylation)

• Receptor internalization and recycling kinetics

Methodological approach: Researchers should initially characterize the PTM profile of native mouse CCR4 in primary T cells as a reference, then compare this to recombinant CCR4 produced in different expression systems. Systematic mutation of PTM sites followed by functional testing will reveal their relative importance.

How can recombinant mouse CCR4 facilitate drug discovery targeting chemokine receptors?

Recombinant mouse CCR4 serves as a valuable tool in therapeutic development:

Drug Discovery Applications:

• High-throughput screening platforms

• Structure-based drug design

• Antibody development and characterization

• Bispecific agent engineering

• Species cross-reactivity testing

Screening Methodologies:

• Competitive binding assays

• Functional antagonism assays (calcium flux, β-arrestin recruitment)

• Receptor internalization assays

• Allosteric modulator identification

Translation to Human Applications:

• Parallel testing on mouse and human CCR4

• Identification of species-conserved binding pockets

• Understanding of species-specific signaling differences

• Development of mouse models for in vivo testing

Methodological approach: Researchers should establish robust cell-based assays with recombinant mouse CCR4, optimize them for high-throughput screening, and include appropriate controls and counter-screens to identify selective compounds. Testing active compounds in both mouse and human systems early in development facilitates later translational studies.

What are emerging technologies that could enhance the study of recombinant mouse CCR4?

Several cutting-edge technologies are transforming CCR4 research:

Structural Biology Approaches:

• Cryo-electron microscopy for receptor-ligand complexes

• Hydrogen-deuterium exchange mass spectrometry for conformational dynamics

• Single-particle tracking for receptor diffusion and clustering

• Alphascreen/HTRF for protein-protein interaction screening

Genetic Engineering Tools:

• Base editing for precise single nucleotide modifications

• Prime editing for targeted insertions and deletions

• CRISPR activation/interference for endogenous gene regulation

• Genetic code expansion for site-specific incorporation of modified amino acids

Advanced Imaging Techniques:

• Super-resolution microscopy for nanoscale receptor organization

• FRET-based biosensors for signaling visualization

• Live cell imaging with labeled chemokines

• Intravital multiphoton microscopy for in vivo migration studies

Methodological approach: When implementing these technologies, researchers should begin with proof-of-concept studies in well-characterized systems before applying them to more complex biological questions. Combining multiple complementary approaches provides the most robust insights into CCR4 biology.

How do mouse CCR4 ligand interactions compare with the human receptor, and what are the implications for translational research?

Understanding species differences is crucial for translational studies:

Ligand Binding Comparisons:

• Mouse and human CCR4 both bind CCL17 and CCL22

• Binding affinities may differ between species

• Subtle differences in binding pocket structure can affect antagonist binding

• Species-specific post-translational modifications may influence ligand recognition

Signaling Differences:

• G-protein coupling efficiency may vary between species

• Biased signaling profiles might differ for the same ligand

• Receptor internalization and recycling kinetics can vary

• Differential interactions with regulatory proteins

Translational Implications:

• Drug candidates should be tested against both mouse and human CCR4

• Species differences may affect in vivo efficacy predictions

• Humanized mouse models may be needed for certain studies

• Careful interpretation of mouse data when extrapolating to humans

Methodological approach: Side-by-side comparative studies using identical experimental conditions for mouse and human CCR4 are essential. This should include detailed pharmacological characterization (binding affinity, potency, efficacy) for both natural ligands and synthetic compounds to identify any species differences that might impact translational research.

What are the most significant unresolved questions in mouse CCR4 research?

Despite significant advances, several key questions remain in CCR4 biology:

Structural Biology:

• How does CCR4 conformation change upon ligand binding?

• What is the structural basis for ligand selectivity?

• How do different intracellular signaling proteins recognize activated CCR4?

Signaling Biology:

• What determines biased signaling through CCR4?

• How does the signaling profile differ across T cell subsets?

• What is the cross-talk between CCR4 and other chemokine receptors?

Therapeutic Applications:

• Can selective modulation of CCR4 function be achieved without impairing beneficial immune responses?

• How can CCR4 targeting be applied to inflammatory diseases beyond its current applications?

• What biomarkers can predict response to CCR4-targeted therapies?

Methodological approach: Addressing these questions requires interdisciplinary approaches combining structural biology, advanced imaging, genetic engineering, and systems biology. Long-term, carefully designed studies in relevant disease models will be particularly important for translating mechanistic insights into therapeutic applications.

How can optimized recombinant mouse CCR4 systems advance understanding of chemokine biology?

Well-characterized recombinant mouse CCR4 systems can drive significant advances:

Benefits for Basic Research:

• Detailed structure-function studies

• Precise mapping of ligand binding sites

• Identification of allosteric modulatory sites

• Understanding of receptor dynamics and trafficking

Contributions to Systems Biology:

• Quantitative measurement of binding and signaling parameters

• Mathematical modeling of chemokine network function

• Predictive models of cell migration in complex environments

• Integration of receptor function with broader immune signaling networks

Technology Development:

• Novel biosensors for CCR4 activation

• High-throughput screening platforms

• Development of engineered cells for immunotherapy

• Creation of modified receptors with novel functions

Methodological approach: To maximize the impact of recombinant CCR4 systems, researchers should focus on creating well-validated, reproducible tools that are accessible to the broader scientific community. This includes detailed protocols for expression and purification, comprehensive characterization data, and availability of key reagents through repositories or commercial sources.