gpr161 Antibody

Basic Research Applications

• What is GPR161 and why is it important in research?

  GPR161 is an orphan G protein-coupled receptor (GPCR) that functions as a critical regulator of Hedgehog signaling pathway through multiple mechanisms. In the absence of Hedgehog signals, GPR161 localizes to primary cilia and maintains GLI transcription factors in their repressor forms . Upon Hedgehog pathway activation, GPR161 exits cilia by internalizing to recycling endosomal compartments . GPR161 is constitutively active and drives elevated cAMP via activation of Gs proteins .

  Research significance:

  • Developmental biology: GPR161 mutations lead to developmental defects due to its role in morphogenesis

  • Cancer research: GPR161 is overexpressed in triple-negative breast cancer and correlates with poor prognosis

  • Cell signaling: Provides a unique model for studying compartmentalized signaling in primary cilia

  GPR161 Properties	Details
  Molecular Weight	Calculated: 59 kDa; Observed: 59-70 kDa
  Cellular Location	Primary cilia, recycling endosomes
  Key Functions	Hedgehog pathway repression, cAMP signaling, PKA regulation

• What antibody applications are validated for GPR161 detection?

  GPR161 antibodies have been validated for multiple applications with specific dilution recommendations:

  Application	Recommended Dilution	Validated Cell/Tissue Types
  Western Blot (WB)	1:500-1:8000	Mouse brain tissue, rat brain tissue
  Immunofluorescence (IF)/ICC	1:200-1:800	ARPE-19 cells, hTERT-RPE1 cells, MDCK cells, C2C12 cells
  Immunoprecipitation (IP)	Application-specific	Validated in multiple publications
  Co-immunoprecipitation (CoIP)	Application-specific	Validated in multiple publications

  For optimal results, antibody dilutions should be empirically determined for each experimental system, as detection sensitivity may vary between tissue types and experimental conditions .

• How can I validate GPR161 antibody specificity in my experiments?

  Comprehensive validation requires multiple complementary approaches:

  • Genetic controls: The most definitive validation uses GPR161 knockout or knockdown models. Several studies have utilized GPR161 knockout MEFs or CRISPR-based knockouts to confirm antibody specificity .

  • Recombinant expression systems: Studies have employed stably expressed tagged GPR161 variants (LAP-tagged, Venus-YFP-tagged) that can be detected by both anti-GFP and anti-GPR161 antibodies to confirm specificity .

  • Expected localization patterns: Proper GPR161 antibodies should show expected subcellular localization patterns (ciliary and/or vesicular distribution) that change upon Hedgehog pathway stimulation (e.g., with Smoothened agonist SAG) .

  • Molecular weight verification: Proper antibody detection should recognize the expected molecular weight (calculated ~59 kDa, observed 59-70 kDa) with the larger band representing potential post-translational modifications .

Intermediate Research Applications

• What's the best methodology for detecting ciliary versus extraciliary GPR161 pools?

  Differentiating between ciliary and extraciliary GPR161 pools requires specialized techniques:

  • High-resolution immunofluorescence microscopy: Confocal or super-resolution microscopy with ciliary markers (acetylated tubulin or Arl13b) and GPR161 antibodies (1:200-1:800 dilution) allows visualization of ciliary localization .

  • Compartment-specific manipulation:

    • INPP5E knockdown increases ciliary GPR161 levels through defects in TULP3 cargo release

    • β-arrestin 1/2 knockout prevents GPR161 removal from cilia

    • BBS4 knockdown prevents GPR161 exit from cilia

  • Expressing GPR161 mutants: The GPR161 mut1 variant (ciliary localization defective but cAMP signaling competent) allows direct comparison of ciliary versus extraciliary signaling functions .

  • Endosomal co-localization: Recycling endosomal pools can be identified by co-labeling with endocytosed fluorescent transferrin to identify GPR161-containing vesicles in the recycling endocytic compartment .

• How do I design experiments to study GPR161's interaction with PKA signaling?

  Several methodological approaches have been established:

  • TR-FRET cAMP assays: Time-resolved FRET-based assays using long-lived fluorophores (lathanides) provide sensitive detection of cAMP levels with minimal background interference .

  • cAMP-agarose protein precipitation:

    • Use PKA-selective Rp-8-AHA-cAMP agarose resin to precipitate endogenous PKA regulatory subunit-associated protein complexes

    • Include negative controls with excess cAMP (1 mM) to mask cAMP binding sites

    • Analyze precipitated complexes by immunoblotting or mass spectrometry

  • PKA anchoring protein (AKAP) domain analysis:

    • In vitro binding assays using GST-fusion proteins of GPR161 C-terminal tail variants

    • Immunoprecipitation of Venus-YFP-tagged GPR161 variants followed by detection of associated PKA subunits

    • Renilla Luciferase protein-fragment complementation assay (PCA) to monitor direct interaction between GPR161 and PKA regulatory subunits

  • Peptide array analysis: Overlapping 25-mer peptides derived from GPR161 can be used to map the specific residues responsible for PKA regulatory subunit binding .

• What experimental approaches are recommended for studying GPR161 trafficking?

  Trafficking studies require multiple complementary techniques:

  • Ciliary entry manipulation:

    • INPP5E knockdown to increase TULP3, IFT-A and GPR161 levels in cilia

    • Expression of TULP3 variants to modulate ciliary entry

  • Ciliary exit manipulation:

    • β-arrestin 1/2 knockout to prevent GPR161 removal from cilia

    • BBS4 knockdown to prevent GPR161 exit from cilia via the BBSome

    • Smoothened agonist (SAG) treatment to stimulate Hedgehog pathway activation and GPR161 removal

  • Live imaging techniques:

    • LAP-tagged or Venus-YFP-tagged GPR161 for real-time visualization

    • Photobleaching techniques (FRAP) to measure protein mobility

  • Endosomal trafficking analysis:

    • Co-labeling with endocytosed fluorescent transferrin to identify recycling endosomes

    • Vesicular co-localization studies with markers for different endosomal compartments

Advanced Research Applications

• How can I investigate the specific mechanisms of GPR161's constitutive activity?

  Studying GPR161's constitutive activity requires sophisticated biophysical and cellular approaches:

  • Structural biology approaches:

    • Cryo-electron microscopy (cryo-EM) of purified GPR161 complexed with G proteins (e.g., miniGs) to determine active conformations at high resolution (2.7 Å)

    • Structural analysis of the extracellular loop 2 (ECL2) that occupies the canonical GPCR orthosteric ligand pocket

  • G-protein coupling assays:

    • MiniGs protein fragment complementation assay to measure basal G-protein recruitment

    • cAMP assays using optimized NanoLuciferase fragment complementation (NanoBiT) to quantify signaling activity

    • Comparison with other constitutively active receptors (e.g., GPR52) or ligand-dependent receptors (e.g., β2AR)

  • Domain mutational analysis:

    • Site-directed mutagenesis of key residues identified in structural studies

    • Generation of phosphorylation-deficient mutants (S428A/S429A) or phosphomimetic mutants (S428D/S429D)

    • Leucine mutants (L458A, L465P, L477A) to disrupt protein-protein interactions

  • Sterol binding analysis:

    • Photoaffinity labeling with sterol analogs containing UV-activated diazirine groups (LKM38, KK231)

    • Identification of sterol-binding residues by LC-MS/MS sequencing of labeled peptides

    • Molecular dynamics simulations to study sterol binding site dynamics

• What approaches can elucidate GPR161's role in cancer progression?

  Complex experimental designs are required to study GPR161 in cancer:

  • Patient-derived xenograft models:

    • Transplantation of patient-derived breast cancer samples with varying GPR161 expression levels

    • Analysis of tumor growth, invasion, and metastasis

  • 3D culture systems:

    • MCF-10A acini formation in 3D culture shows that GPR161 overexpression leads to:

      • Increased cell proliferation (57.5% vs 6.3% of acini showing Ki67+ cells in lumens)

      • Multiacinar structures with disrupted morphogenesis

      • Invasive behavior when cultured in Matrigel/collagen mixtures

      • Disrupted Laminin-V staining, indicating invasive potential

  • Signaling pathway analysis:

    • GPR161 forms a signaling complex with β-arrestin 2 and IQ motif containing GTPase Activating Protein 1

    • GPR161 amplified breast tumors activate mTOR signaling and decrease IQGAP1 phosphorylation

    • Cells overexpressing GPR161 show increased E-cadherin intracellular accumulation

  • Migration and invasion assays:

    • Transwell migration assays show a twofold increase in migratory ability in cells overexpressing GPR161

    • Collagen invasion assays demonstrate increased invasive potential

• How do I design experiments to differentiate between GPR161's G-protein dependent and PKA-dependent functions?

  Distinguishing these functions requires sophisticated genetic and pharmacological approaches:

  • Genetic uncoupling strategies:

    • Use GPR161 mut1 variant (ciliary localization defective but cAMP signaling competent)

    • Compare phenotypes between Gpr161 knockout and Gpr161 mut1/ko or Gpr161 mut1/mut1 animals

    • Analyze tissue-specific differences in Gli repressor formation and Hedgehog target gene expression

  • Structure-guided mutational analysis:

    • Generate mutations that specifically disrupt G-protein coupling based on cryo-EM structural data

    • Create mutations that specifically disrupt PKA binding without affecting G-protein coupling

    • Analyze downstream effects on Gli repressor formation and Hedgehog target gene expression

  • Pathway-specific readouts:

    • Monitor Gli2/3 processing to determine Gli activator vs. repressor formation

    • Analyze ciliary accumulation of Gli2

    • Measure expression of Hedgehog target genes through qPCR or RNA in situ hybridization (e.g., Ptch1, Gli1, Hoxd13)

  • Tissue-specific analyses:

    • Compare neural tube patterning (which requires Gli activator function)

    • Analyze limb development and polydactyly (which depends on Gli repressor function)

    • Examine midface development (which requires Gli repressor function)

• How can I implement advanced techniques to study GPR161's sterol-binding properties?

  Studying sterol binding requires specialized biophysical and biochemical approaches:

  • Photoaffinity labeling with sterol probes:

    • Use sterol analogs with photo-activatable diazirine groups (LKM38, KK231)

    • Position diazirine groups on different parts of the sterol (B-ring vs. aliphatic tail)

    • Perform LC-MS/MS after photoaffinity labeling to identify exact binding residues

  • Structure-guided mutagenesis:

    • Target residues in the extrahelical site adjacent to transmembrane helices 6 and 7

    • Generate mutations that prevent sterol binding

    • Assess effects on G-protein coupling and downstream signaling

  • Functional assays after sterol manipulation:

    • Deplete cellular sterols using inhibitors of sterol synthesis

    • Supplement with specific sterols to rescue function

    • Monitor effects on GPR161 conformation and G-protein coupling

  • Molecular dynamics simulations:

    • Model sterol binding to GPR161 based on cryo-EM structures

    • Simulate effects of mutations on sterol binding dynamics

    • Predict conformational changes associated with sterol binding and G-protein coupling

Technical Troubleshooting

• What are the common technical challenges in GPR161 western blotting and how can they be resolved?

  Western blotting for GPR161 presents several technical challenges:

  • Multiple bands/variable molecular weight: GPR161 has a calculated molecular weight of 59 kDa but may appear as a 70 kDa band due to post-translational modifications .

    • Solution: Include positive controls with recombinant or overexpressed GPR161

    • Verify specificity using GPR161 knockdown/knockout samples

  • Low endogenous expression levels: GPR161 may be expressed at low levels in some tissues.

    • Solution: Increase protein loading (50-100 μg of total protein)

    • Use enhanced chemiluminescence detection systems

    • Consider antibody concentrations at the higher end of recommended range (1:500 for WB)

  • Membrane protein extraction issues: As a transmembrane protein, GPR161 may be difficult to extract.

    • Solution: Use specialized lysis buffers containing appropriate detergents (0.5% Triton X-100)

    • Consider membrane protein extraction kits

    • Avoid excessive heating which may cause aggregation

  • Verification strategy: To confirm specificity, use different antibodies targeting distinct epitopes or tagged versions of GPR161 that can be detected with anti-tag antibodies .

• What controls are essential when investigating GPR161's role in Hedgehog signaling?

  Rigorous controls are necessary for Hedgehog signaling studies:

  • Positive pathway controls:

    • Smoothened agonist (SAG) treatment to activate the pathway

    • Monitor expected changes in GPR161 localization (exit from cilia)

    • Verify pathway activation by Gli2 accumulation in cilia

  • Negative pathway controls:

    • Smoothened antagonist (e.g., cyclopamine) to inhibit the pathway

    • Verify pathway inhibition by Gli3 repressor formation

  • Genetic controls:

    • GPR161 knockout or knockdown cells/tissues

    • Compare with GPR161 mut1 (ciliary localization defective but signaling competent)

    • Include Gli2 or Gli3 knockouts to distinguish activator vs. repressor phenotypes

  • Readout verification:

    • Multiple Hedgehog target genes (Ptch1, Gli1)

    • Protein-level verification of Gli processing

    • Phenotypic analysis in relevant developmental contexts

  • Cell type considerations: Different cell types show varying dependence on Gli activator vs. repressor activity, making tissue/cell selection crucial for experimental design .