Recombinant Rat Probable G-protein coupled receptor 135 (Gpr135)

What is G-protein coupled receptor 135 (Gpr135) and how is it classified?

G-protein coupled receptor 135 (Gpr135) is a protein-coding gene that belongs to the G protein-coupled receptor (GPCR) family. It is classified as an orphan receptor, meaning its endogenous ligand has not yet been definitively identified. The receptor is located on chromosome 14 in humans and exhibits spontaneous activity for β-arrestin recruitment, suggesting a signaling pathway that functions independently of known ligands . Phylogenetic studies have classified G-protein coupled receptor 135 (Gpr135) among the melatonin receptor subfamily, along with two other orphan receptors, GPR61 and GPR62 . This classification provides a foundation for understanding potential functional relationships, though experimental evidence indicates G-protein coupled receptor 135 does not directly bind melatonin .

What expression systems are recommended for studying recombinant rat G-protein coupled receptor 135 (Gpr135)?

For recombinant expression of rat G-protein coupled receptor 135 (Gpr135), HEK293T cells have been successfully employed as demonstrated in multiple studies . When establishing expression systems, researchers should consider several methodological approaches:

• Epitope tagging: Addition of an HA-tag or similar at the amino-terminal extremity allows for detection and verification of expression .

• Expression verification: Successful expression should be confirmed using multiple techniques:

  • Confocal immunofluorescence microscopy to verify cell surface expression in intact cells

  • Western blotting of membrane preparations (with careful attention to denaturation conditions)

  • Functional assays to confirm receptor activity

It's important to note that standard denaturation conditions (95°C for 10 minutes) may lead to receptor aggregation for some GPCRs. For optimal detection of monomeric G-protein coupled receptor 135 (Gpr135), modified denaturation conditions such as 55°C for 15 minutes or room temperature for 16 hours may be preferable .

How does rat G-protein coupled receptor 135 (Gpr135) compare to the human ortholog?

Rat and human G-protein coupled receptor 135 (Gpr135) display notable differences in their pharmacological profiles, particularly in their responses to ligands. Research has shown species-selective activity among potential GPCR agonists . While human and rat orthologs may both exhibit constitutive activity in β-arrestin recruitment assays, they can respond differently to chemical compounds . These species differences should be carefully considered when designing experiments and interpreting results, especially when attempting to translate findings between rat models and human applications. When developing or testing compounds, it is recommended to screen against both orthologs simultaneously to identify species-selective effects early in the research process .

What signaling pathways are activated by rat G-protein coupled receptor 135 (Gpr135)?

G-protein coupled receptor 135 (Gpr135) demonstrates a distinctive signaling profile characterized primarily by constitutive β-arrestin recruitment rather than classical G-protein dependent pathways. Experimental evidence suggests:

• β-arrestin pathway: G-protein coupled receptor 135 (Gpr135) shows spontaneous recruitment of β-arrestin1 and β-arrestin2 in a ligand-independent manner . This can be detected using the PathHunter™ enzyme complementation assay.

• cAMP pathway: Unlike some orphan GPCRs (such as GPR61 and GPR62), G-protein coupled receptor 135 (Gpr135) appears to be "silent" on the cAMP pathway, showing no significant effect on basal or forskolin-stimulated cAMP levels .

• Inositol phosphate (IP1) production: G-protein coupled receptor 135 (Gpr135) does not demonstrate constitutive activity in the Gq/IP1 pathway, distinguishing it from GPR62 which does show such activity .

These findings suggest G-protein coupled receptor 135 (Gpr135) may be considered a β-arrestin-biased receptor at physiologically relevant expression levels, such as those observed in pancreatic beta cells .

What methods are recommended for investigating G-protein coupled receptor 135 (Gpr135) heteromer formation?

G-protein coupled receptor 135 (Gpr135) has been shown to form heteromeric complexes with melatonin receptors, particularly MT2. To investigate such heteromer formation, researchers can employ multiple complementary techniques:

• Bioluminescence Resonance Energy Transfer (BRET) assays in living cells:

  • Perform donor saturation experiments with increasing acceptor-to-donor ratios

  • Include appropriate negative controls (e.g., CCR5 receptor) to distinguish specific from non-specific interactions

  • A hyperbolic BRET signal increase indicates specific heteromer formation, while linear increases suggest non-specific interactions

• Co-immunoprecipitation experiments:

  • Co-express G-protein coupled receptor 135 (Gpr135) with potential heteromer partners

  • Immunoprecipitate one receptor and detect the presence of the partner receptor

  • Include appropriate controls to confirm specificity

• Functional studies to assess heteromer-specific signaling:

  • Evaluate how co-expression affects signaling properties (e.g., β-arrestin recruitment)

  • Employ competition assays with untagged receptors to confirm specificity

These techniques should be used in combination, as each provides different and complementary evidence for heteromer formation .

How can constitutive activity of rat G-protein coupled receptor 135 (Gpr135) be reliably measured?

Measuring the constitutive activity of G-protein coupled receptor 135 (Gpr135) requires careful experimental design and appropriate controls. Based on its signaling profile, β-arrestin recruitment assays provide the most reliable readout:

• Dose-dependent expression experiments:

  • Transfect increasing amounts of receptor expression vector

  • Confirm proportional receptor expression levels (via western blot or flow cytometry)

  • Measure corresponding increases in β-arrestin recruitment

  • Establish minimal expression levels that produce detectable activity

• Competition assays to confirm specificity:

  • Co-transfect with untagged β-arrestin2 (or β-arrestin2-YFP)

  • Observe reduction in complementation signal (typically 40-50%)

  • Verify expression levels remain unchanged

• Correlation with physiological expression:

  • Quantify mRNA levels by Q-PCR and compare with levels in native tissues

  • Ensure experimental expression levels approximate physiological conditions

For rat G-protein coupled receptor 135 (Gpr135), studies have determined that as little as 1 ng of expression vector can promote significant β-arrestin2 recruitment, with mRNA levels closely matching those observed in pancreatic EndoC-βH1 cell lines .

What approaches have proven successful for identifying ligands for orphan G-protein coupled receptors like G-protein coupled receptor 135 (Gpr135)?

Identifying ligands for orphan G-protein coupled receptors remains challenging but several approaches have shown promise for receptors like G-protein coupled receptor 135 (Gpr135):

• Receptor-β-arrestin-2 interaction assays:

  • This approach has successfully identified compounds with agonist activity at both human and rat orthologs of related orphan receptors

  • The assay can detect both constitutive activity and ligand-induced changes

• Yeast-based functional assays:

  • Saccharomyces cerevisiae-based assays employing chimeric G-proteins (e.g., Gpa1-Gα13)

  • Can confirm G-protein coupling and activation by potential ligands

• [35S]GTP[S] binding assays:

  • Using epitope-tagged G-proteins to monitor receptor-mediated G-protein activation

  • Provides direct evidence of G-protein coupling in response to ligands

• Comparative pharmacology across species:

  • Testing compounds against both human and rat orthologs simultaneously

  • Helps identify species-selective ligands and conserved mechanisms

When designing screens for G-protein coupled receptor 135 (Gpr135) ligands, researchers should be aware of its bias toward β-arrestin recruitment over G-protein signaling pathways.

How should species differences be addressed when studying rat G-protein coupled receptor 135 (Gpr135)?

Species differences present a significant consideration in G-protein coupled receptor 135 (Gpr135) research, as compounds can show marked species selectivity:

• Dual-ortholog screening approach:

  • Always test compounds against both rat and human G-protein coupled receptor 135 (Gpr135)

  • Categorize compounds based on their species selectivity profile

• Classification of compound selectivity patterns:

  • Non-selective compounds: similar potency at both orthologs (e.g., cromolyn disodium, dicumarol)

  • Human-selective compounds: activity only at human G-protein coupled receptor 135 (e.g., pamoate, niflumic acid)

  • Rat-selective compounds: markedly selective for rat ortholog (e.g., zaprinast, luteolin)

• Validation across multiple assay systems:

  • Confirm activity in both arrestin-recruitment and G-protein activation assays

  • Use functional assays in physiologically relevant cell types when possible

Understanding these species differences is essential for correctly attributing function and extrapolating findings from rat models to human applications. Researchers should explicitly state which species ortholog is being studied in publications and consider possible translational limitations .

What roles has G-protein coupled receptor 135 (Gpr135) been implicated in based on current research?

G-protein coupled receptor 135 (Gpr135) has been implicated in several physiological and pathological processes, though many of these associations require further validation:

• Melatonin signaling modulation:

  • G-protein coupled receptor 135 (Gpr135) forms heteromers with melatonin receptor MT2

  • This interaction inhibits melatonin-induced β-arrestin recruitment to MT2

  • Suggests a role in regulating melatonin signaling pathways

• Energy metabolism:

  • Cold exposure increases G-protein coupled receptor 135 (Gpr135) expression in mouse liver

  • Methylation studies suggest potential links to type 2 diabetes

  • May play a role in metabolic regulation

• Developmental processes:

  • Identified as one of the methylated placental genes associated with maternal cigarette smoking during pregnancy

  • Potentially connected to pregnancy complications and developmental outcomes

• Disease associations:

  • Substance abuse

  • Schizophrenia

  • Various genetic syndromes including Phelan-McDermid syndrome, Potocki-Lupski syndrome, and Smith-Magenis syndrome

  • Intellectual developmental disorders

  • Cancer

These associations provide direction for further research but require mechanistic validation through targeted studies.

How does G-protein coupled receptor 135 (Gpr135) expression respond to chemical exposures?

G-protein coupled receptor 135 (Gpr135) expression demonstrates dynamic responses to various chemical exposures, suggesting potential roles in xenobiotic response pathways:

These varied responses suggest G-protein coupled receptor 135 (Gpr135) may be involved in cellular responses to environmental toxicants and hormones. Researchers interested in environmental toxicology or endocrine disruption should consider G-protein coupled receptor 135 (Gpr135) as a potential molecular target or biomarker .

What are the key technical challenges in studying recombinant rat G-protein coupled receptor 135 (Gpr135)?

Research with recombinant rat G-protein coupled receptor 135 (Gpr135) presents several technical challenges that researchers should anticipate:

• Protein denaturation and detection issues:

  • Standard denaturation conditions (95°C) may cause receptor aggregation

  • Modified conditions (55°C for 15 min or room temperature for 16 hours) may be required for detection of monomeric protein

  • Western blot optimization may be necessary for reliable detection

• Constitutive activity quantification:

  • Distinguishing constitutive activity from overexpression artifacts

  • Establishing physiologically relevant expression levels

  • Normalizing β-arrestin recruitment data appropriately

• Heteromer characterization challenges:

  • Separating effects of direct interaction from downstream signaling crosstalk

  • Confirming specificity with appropriate controls

  • Translating in vitro findings to physiological contexts

• Ligand identification difficulties:

  • No validated endogenous ligand has been identified

  • Potential species differences in ligand responsiveness

  • Selection of appropriate functional readouts for screening

• Antibody limitations:

  • Lack of validated antibodies for native G-protein coupled receptor 135 (Gpr135)

  • Reliance on epitope tagging for detection

  • Difficulties in studying endogenous receptor expression

Researchers should incorporate appropriate controls and validation steps to address these challenges in their experimental designs.

What emerging methodologies might advance our understanding of G-protein coupled receptor 135 (Gpr135)?

Several cutting-edge approaches could significantly advance G-protein coupled receptor 135 (Gpr135) research:

• CRISPR/Cas9 genome editing:

  • Generation of knock-out and knock-in models to study physiological roles

  • Introduction of tags at endogenous loci to study native expression levels

  • Creation of reporter lines for live-cell imaging of receptor trafficking

• Cryo-electron microscopy:

  • Determination of G-protein coupled receptor 135 (Gpr135) structure alone and in complex with interacting proteins

  • Insights into binding pockets for rational drug design

  • Structural basis for heteromerization with melatonin receptors

• Single-cell transcriptomics:

  • Precise mapping of G-protein coupled receptor 135 (Gpr135) expression across tissues

  • Correlation with other signaling components

  • Identification of cell populations where G-protein coupled receptor 135 (Gpr135) may play critical roles

• Advanced biosensor technologies:

  • FRET/BRET-based sensors for real-time monitoring of receptor conformational changes

  • Multiplexed detection of different signaling pathways

  • Spatial and temporal resolution of signaling events in living cells

• Artificial intelligence approaches:

  • In silico screening for potential ligands

  • Prediction of functional interactions based on structural and genomic data

  • Integration of multi-omics data to position G-protein coupled receptor 135 (Gpr135) in broader signaling networks

These methodologies, especially when combined, could provide unprecedented insights into G-protein coupled receptor 135 (Gpr135) biology and pharmacology.

How might understanding G-protein coupled receptor 135 (Gpr135) contribute to therapeutic development?

The exploration of G-protein coupled receptor 135 (Gpr135) biology has several potential implications for therapeutic development:

• Melatonin signaling modulation:

  • G-protein coupled receptor 135 (Gpr135) heteromerization with MT2 affects melatonin signaling

  • Could provide novel approaches to disorders involving melatonin dysregulation

  • Potential applications in sleep disorders, circadian rhythm disorders, and related conditions

• Metabolic disorder treatments:

  • Based on associations with energy metabolism and diabetes

  • Could represent an exploratory target for metabolic syndrome or obesity

  • Cold-induced expression in liver suggests potential role in thermogenesis

• Neuropsychiatric applications:

  • Associations with substance abuse and schizophrenia suggest potential relevance

  • Could provide novel approaches to these difficult-to-treat conditions

• Biased signaling therapeutics:

  • G-protein coupled receptor 135 (Gpr135) displays β-arrestin-biased signaling

  • Understanding this bias could inform development of functionally selective drugs

  • May allow targeting of specific signaling pathways while avoiding others

Realizing these therapeutic possibilities will require further characterization of G-protein coupled receptor 135 (Gpr135)'s physiological roles and the development of selective pharmacological tools to modulate its activity.