Recombinant Rabbit Gastrin/cholecystokinin type B receptor (CCKBR)

Basic Structure and Function of Rabbit CCKBR

Q: What is the molecular structure of rabbit CCKBR and how does it compare to other species?

A: Rabbit CCKBR is encoded by a gene containing a 1356-bp open reading frame consisting of five exons interrupted by four introns. The gene encodes a protein of 452 amino acids that functions as a G-protein coupled receptor. Comparative analysis reveals 93-97% amino acid sequence similarity with corresponding cDNAs previously identified in human, canine, and rodent brain or gastric tissues . The protein has an observed molecular weight of approximately 50kDa and is primarily localized to the cell membrane . This high degree of evolutionary conservation suggests critical functional importance across mammalian species and makes rabbit CCKBR a valuable model for translational research.

Expression Patterns of CCKBR in Normal vs. Pathological States

Q: How does CCKBR expression differ between normal and disease states, particularly in pancreatic tissue?

Signaling Pathways Mediated by CCKBR Activation

Q: What are the primary signaling pathways activated by CCKBR and their downstream effects?

A: CCKBR activation initiates several key signaling cascades with distinct cellular outcomes. Upon gastrin binding, CCKBR undergoes a conformational change that exchanges GDP for GTP on the Gα subunits . This activation leads to:

• PI3K/Akt/eIF4B pathway: Critical for regulation of intestinal glucose absorption, particularly in the context of type 2 diabetes

• Calcium signaling pathway: Originally identified as the primary mechanism for gastric acid secretion regulation

• Rho GTPase signaling: Including RhoA, Rac1, Cdc42, and Rab43, affecting cytoskeletal reorganization, intracellular trafficking, and Golgi orientation

• Paxillin phosphorylation: Essential for focal adhesion formation, cellular adhesion, motility, and invasion, particularly relevant in cancer progression

These pathways collectively contribute to CCKBR's diverse biological functions ranging from metabolic regulation to cell migration and cancer progression.

CCKBR in Central Nervous System Function

Q: What roles does CCKBR play in the central nervous system and how can recombinant models help study these functions?

A: CCKBR is widely distributed throughout the central nervous system where it serves as a critical modulator of several neurological functions including anxiety, analgesia, arousal, and neuroleptic activity . Recombinant rabbit CCKBR models provide valuable tools for studying these functions by allowing controlled expression in experimental systems. When investigating CCKBR-mediated neurological effects, researchers should consider:

• Region-specific expression patterns in the brain

• Neurotransmitter interactions, particularly with dopaminergic and GABAergic systems

• Receptor trafficking and internalization dynamics

• Differential responses to various ligands including gastrin and cholecystokinin peptides

Research models using recombinant rabbit CCKBR can help elucidate the mechanistic basis for CCKBR's role in neuropsychiatric conditions and potential therapeutic applications.

Genetic Variations in CCKBR and Their Significance

Q: What genetic polymorphisms have been identified in CCKBR and how do they impact receptor function?

A: Several genetic variations in CCKBR have been identified with functional consequences. A notable single nucleotide polymorphism (SNP) in the CCKBR gene has been discovered that predicts survival and risk of pancreatic cancer . In functional studies, particular attention should be given to:

• The specific variant cholecystokinin C receptor (CCKCR), which when overexpressed in AsPC-1 pancreatic cancer cells significantly increases cell growth by up to 60% compared to wild-type and vector-transfected cells

• Enhanced proliferation confirmed by increased BrdU uptake in cells overexpressing this receptor variant

• The contrasting lack of significant growth changes observed when the standard CCKBR was overexpressed in the same cancer cell line

These findings highlight how genetic variations in CCKBR can substantially alter receptor functionality and downstream cellular responses, with particular relevance for cancer research.

Advanced Methodologies for CCKBR Expression and Purification

Q: What are the optimal techniques for expressing and purifying recombinant rabbit CCKBR for structural and functional studies?

A: Successful expression and purification of functional recombinant rabbit CCKBR requires specialized approaches due to its nature as a membrane-bound G-protein coupled receptor. Based on current research methodologies:

• Expression systems:

  • Mammalian expression systems (HEK293, CHO cells) are preferred for proper folding and post-translational modifications

  • Baculovirus-insect cell systems provide higher yields while maintaining most mammalian-like processing

• Construct design considerations:

  • Include the complete 452-amino acid sequence to preserve the receptor's native structure

  • Consider fusion tags (His6, FLAG) positioned to minimize interference with ligand binding domains

  • For crystallography studies, inclusion of thermostabilizing mutations or fusion with stabilizing proteins

• Purification strategy:

  • Detergent solubilization (typically with DDM, LMNG, or other mild detergents)

  • Affinity chromatography followed by size exclusion chromatography

  • Reconstitution into nanodiscs or lipidic cubic phase for structural studies

Verification of functionality after purification should include ligand binding assays using labeled gastrin or cholecystokinin peptides.

CCKBR in Metabolic Regulation and Diabetes Research

Q: How does the intestinal Gastrin/CCKBR axis influence glucose homeostasis and what experimental models best demonstrate this relationship?

A: Recent research has revealed that the intestinal Gastrin/CCKBR axis plays a significant protective role against type 2 diabetes (T2D) through regulation of intestinal glucose absorption. Key findings and experimental approaches include:

• Genetic models: Intestinal epithelial cell-specific Cckbr knockout mice demonstrate pre-diabetes mellitus (Pre-DM) that rapidly progresses to T2D when fed high-fat diet (HFD, 60% fat) . This model provides direct evidence for CCKBR's protective role.

• Mechanism of action: The Gastrin/CCKBR axis reduces intestinal glucose absorption primarily through:

  • Down-regulation of intestinal sodium-glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2) expressions

  • Stimulation of incretin secretion

  • Activation of the PI3K/Akt/eIF4B signaling pathway

• Translational applications: Gastrin-SiO2 microspheres (20 mg kg−1 d−1) designed for specific intestinal CCKBR stimulation (without systemic absorption) markedly reduce glucose absorption in duodenum samples obtained from T2D patients .

These findings establish intestinal CCKBR as a potential therapeutic target for T2D management, with particular relevance for developing targeted delivery systems that modify intestinal glucose absorption without systemic effects.

CCKBR-Targeted Imaging and Therapeutic Strategies

Q: What approaches are most effective for developing CCKBR-targeted imaging agents and therapeutics for pancreatic cancer?

A: CCKBR represents a promising target for both imaging and therapy in pancreatic cancer due to its overexpression pattern. Effective development strategies should consider:

• Targeting rationale: CCKBR is rare in normal pancreas but becomes significantly overexpressed in PanIN lesions and pancreatic cancer . This differential expression provides excellent tumor specificity.

• Imaging applications:

  • CCKBR-targeted nanoparticles can be functionalized with imaging agents (fluorescent dyes, radioisotopes)

  • These allow for early detection of precancerous lesions and tumors with high specificity

• Therapeutic approaches:

  • RNA interference (RNAi) techniques to silence gastrin mRNA expression have demonstrated inhibition of growth and metastasis of human pancreatic cancer

  • CCKBR-targeted drug delivery systems can enhance the specificity of chemotherapeutic agents

  • Consideration of the signaling pathway for targeted inhibition (particularly focusing on paxillin activation)

• Dual-function systems:

  • Development of theranostic agents that combine imaging capabilities with therapeutic payloads

  • Utilization of gastrin analogues modified to carry imaging or therapeutic components

When developing these agents, researchers should verify target specificity using both CCKBR-positive and CCKBR-negative cell lines to confirm mechanism of action.

Role of CCKBR in Cancer Cell Migration and Metastasis

Q: What molecular mechanisms explain how CCKBR activation promotes directional migration in cancer cells, and how can these be experimentally assessed?

A: CCKBR activation by gastrin promotes directional migration of cancer cells through several intricate molecular mechanisms that can be experimentally evaluated:

• Golgi reorientation and directional polarization:

  • Gastrin promotes Golgi reorientation through activation of paxillin via the CCKBR-Gα12/13-RhoA signaling pathway

  • This spatial reorganization is essential for directional migration

• Paxillin activation cascade:

  • Upon gastrin binding, activated CCKBR undergoes conformational change that exchanges GDP for GTP on Gα subunits

  • GTP-bound Gα interacts with downstream effectors, activating various second messengers

  • Phosphorylated paxillin is essential for focal adhesion formation, cellular adhesion, motility, and invasion

• Experimental assessment methods:

  • Wound healing assays with live cell imaging to track directional movement

  • Transwell migration assays with gradient-distributed chemoattractants

  • Immunofluorescence visualization of Golgi orientation relative to the leading edge

  • Western blot analysis of phosphorylated paxillin levels following CCKBR activation

  • Small GTPase activity assays (RhoA, Rac1, Cdc42) to assess pathway activation

• In vivo validation:

  • Orthotopic pancreatic cancer models with CCKBR manipulation to assess metastatic potential

  • Tracking of labeled cancer cells to monitor migration patterns and metastatic spread

These mechanistic insights provide potential targets for therapeutic intervention to reduce metastasis in CCKBR-expressing cancers.

Comparative Analysis of CCKBR vs. CCKA Receptor Functions

Q: How do the functions and signaling mechanisms of CCKBR differ from CCKA receptors, and what experimental approaches best distinguish between them?

A: While both CCKBR and CCKA (also known as CCK1R) bind cholecystokinin, they exhibit distinct functional profiles, tissue distributions, and signaling mechanisms that require specific experimental approaches to differentiate:

• Binding preferences:

  • CCKBR: Binds both gastrin and cholecystokinin with similar affinity

  • CCKA: Has approximately 500-1000 fold higher affinity for sulfated CCK than for gastrin

• Tissue distribution differences:

  • CCKBR: Predominantly expressed in the central nervous system and gastric mucosa, with pathological expression in pancreatic cancer

  • CCKA: Primarily expressed in pancreatic acinar cells, gallbladder, and specific brain regions

• Experimental differentiation approaches:

  • Selective antagonists: Use of L-365,260 (selective for CCKBR) versus devazepide (selective for CCKA)

  • Expression analysis: Receptor-specific antibodies for immunohistochemistry or Western blotting

  • Functional assays: Measurement of gastric acid secretion (CCKBR) versus pancreatic enzyme secretion (CCKA)

  • Calcium mobilization patterns: Different temporal signatures of calcium release

• Signaling pathway distinctions:

  • CCKBR preferentially couples to Gαq/11 and Gα12/13 proteins

  • CCKA predominantly signals through Gαq/11 and Gαi proteins

Understanding these differences is crucial when designing targeted therapeutics or conducting mechanistic studies to ensure pathway specificity.

Methods for Assessing CCKBR-Ligand Interactions

Q: What techniques provide the most comprehensive analysis of binding kinetics and structural interactions between CCKBR and its ligands?

A: Comprehensive analysis of CCKBR-ligand interactions requires a multi-technique approach:

• Binding assays:

  • Radioligand binding assays using [125I]-gastrin or [125I]-CCK

  • Surface plasmon resonance (SPR) for real-time binding kinetics

  • Isothermal titration calorimetry (ITC) for thermodynamic parameters

  • Fluorescence-based assays with labeled ligands for high-throughput screening

• Structural analysis methods:

  • X-ray crystallography of CCKBR with bound ligands (challenging for GPCRs)

  • Cryo-electron microscopy for visualization of receptor-ligand complexes

  • NMR spectroscopy for dynamic interaction studies

  • Computational modeling including molecular docking and molecular dynamics simulations

• Functional readouts:

  • BRET/FRET assays to monitor conformational changes upon ligand binding

  • G-protein activation assays (GTPγS binding)

  • β-arrestin recruitment assays

  • Calcium mobilization assays using fluorescent indicators

• Mutagenesis approaches:

  • Alanine scanning mutagenesis to identify critical binding residues

  • Site-directed mutagenesis based on computational predictions

  • Generation of chimeric receptors to identify domain-specific interactions

When implementing these techniques, researchers should consider using the rabbit CCKBR model due to its high structural similarity to human CCKBR (93-97% amino acid similarity) , making findings potentially translatable to human applications.

CCKBR in Gastric Function and Pathology

Q: How does CCKBR contribute to normal gastric physiology and pathological conditions, and what models best represent these roles?

A: CCKBR plays crucial roles in gastric physiology and pathology through several mechanisms:

• Physiological functions:

  • Regulation of gastric acid secretion through activation of parietal cells

  • Modulation of gastric motility and emptying

  • Influence on gastric mucosal growth and differentiation

  • Integration of neuroendocrine signals affecting hunger and satiety

• Pathological implications:

  • Involvement in gastric inflammatory conditions

  • Association with gastric cancer development

  • Potential role in functional dyspepsia and other motility disorders

  • Contribution to stress-induced gastric damage

• Experimental models:

  • Isolated gastric glands for secretion studies

  • Organoid cultures to study epithelial cell responses

  • Recombinant expression in cell lines (e.g., AGS cells)

  • Transgenic mouse models with CCKBR modifications

  • Specific models using rabbit CCKBR due to its sequential similarity to human CCKBR

• Assessment methods:

  • Acid secretion measurement using aminopyrine accumulation

  • Intracellular calcium imaging for signaling studies

  • Histological analysis of mucosal changes

  • Gene expression profiling to identify downstream targets

Research focused on gastric CCKBR function particularly benefits from the rabbit model due to its physiological similarities to humans in gastric function.

CCKBR Polymorphisms and Disease Susceptibility

Q: What methodologies are most effective for investigating the relationship between CCKBR genetic variations and disease risk?

A: Investigating the relationship between CCKBR genetic variations and disease risk requires a multi-faceted methodological approach:

• Genetic screening methods:

  • Next-generation sequencing for comprehensive variant detection

  • Targeted genotyping assays for known SNPs of interest

  • Digital PCR for detecting low-frequency variants

  • Methylation analysis to assess epigenetic modifications

• Case-control studies:

  • Comparison of variant frequencies between affected and non-affected individuals

  • Sample size calculations to ensure adequate statistical power

  • Stratification by clinical and demographic factors to identify subgroup effects

  • Longitudinal designs to assess variant impact on disease progression

• Functional validation:

  • Development of cellular models expressing specific CCKBR variants (as demonstrated with the CCKCR variant)

  • Proliferation assays (MTS, BrdU incorporation) to assess growth effects

  • Signaling pathway analysis to determine mechanistic differences

  • Receptor binding and internalization studies to evaluate pharmacodynamic changes

• Translational approaches:

  • Generation of knock-in animal models for specific variants

  • Patient-derived organoids or xenografts to assess variant effects in more complex systems

  • Pharmacogenomic analysis to determine variant impact on treatment response

An exemplary application of these approaches revealed that a specific CCKBR variant (CCKCR) increases cell growth by up to 60% in pancreatic cancer cells , demonstrating how genetic variation can substantially impact disease biology.

Therapeutic Targeting of the Gastrin/CCKBR Axis in Metabolic Disease

Q: What experimental approaches are most suitable for developing CCKBR-targeted interventions for type 2 diabetes?

A: Development of CCKBR-targeted interventions for type 2 diabetes requires specialized experimental approaches based on recent findings about the protective role of the intestinal Gastrin/CCKBR axis:

• Targeted delivery systems:

  • Gastrin-SiO2 microspheres (20 mg kg−1 d−1) have demonstrated efficacy by specifically stimulating intestinal CCKBR without systemic absorption

  • Evaluation of alternative formulations that maintain intestinal specificity

  • Assessment of optimal dosing regimens for sustained effects

• Mechanism validation studies:

  • Measurement of intestinal glucose absorption using ex vivo intestinal preparations

  • Analysis of SGLT1 and GLUT2 expression in response to treatment

  • Quantification of incretin hormone secretion to confirm pathway activation

  • Monitoring of PI3K/Akt/eIF4B pathway components

• Preclinical models:

  • Intestinal epithelial cell-specific Cckbr knockout mice on high-fat diet as a disease model

  • Diet-induced diabetic models treated with CCKBR agonists

  • Comparative studies in different animal models to assess translational potential

  • Long-term safety and efficacy evaluations

• Clinical translation approaches:

  • Ex vivo studies using human duodenal samples from T2D patients

  • Biomarker development to identify likely responders

  • Combination approaches with existing anti-diabetic therapies

These methodologies build upon the discovery that Gastrin-SiO2 microspheres markedly reduce glucose absorption in duodenum samples from T2D patients , suggesting significant therapeutic potential.

Crosstalk Between CCKBR and Other Signaling Pathways

Q: How can researchers effectively investigate the interactions between CCKBR signaling and other major cellular pathways in cancer and metabolic diseases?

A: Investigating CCKBR signaling crosstalk with other pathways requires sophisticated experimental designs:

• Omics-based approaches:

  • Phosphoproteomics to identify changes in protein phosphorylation patterns following CCKBR activation

  • Transcriptomics to determine gene expression changes and pathway enrichment

  • Metabolomics to assess metabolic alterations resulting from pathway interactions

  • Interactomics using proximity labeling or co-immunoprecipitation to identify direct protein interactions

• Pathway inhibition studies:

  • Selective inhibition of candidate interacting pathways (e.g., MAPK, JAK/STAT, Wnt)

  • siRNA/shRNA knockdown of key pathway components

  • CRISPR/Cas9-mediated gene editing to remove specific nodes in interacting pathways

  • Small molecule inhibitor combinations with dose-response matrices

• Real-time signaling analysis:

  • FRET/BRET biosensors to monitor pathway activation dynamics

  • Live-cell imaging with pathway-specific reporters

  • Single-cell analysis to assess heterogeneity in pathway crosstalk

  • Kinetic analysis of signaling events to establish causality

• Pathway integration models:

  • Mathematical modeling of pathway interactions

  • Network analysis to identify key nodes and feedback loops

  • Systems biology approaches to predict emergent properties

  • Verification of model predictions with targeted experiments

An example of this approach is seen in research connecting CCKBR activation to Rho GTPase signaling and paxillin in cancer cell migration , and in studies linking CCKBR to PI3K/Akt/eIF4B signaling in glucose absorption regulation .