{"gene":"GCGR","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2023,"finding":"Cryo-EM structures of GCGR in complex with heterotrimeric Gs protein and three GLP-1R/GCGR dual agonists (peptide 15, MEDI0382/cotadutide, SAR425899) identified key residues responsible for ligand recognition and dual agonism. Distinct side-chain orientations within the first three residues of the peptide ligand determine receptor selectivity, and ECL1 conformation of GCGR differs from GLP-1R in response to dual agonists. The lipid moiety of MEDI0382 interacts with the TM1-TM2 cleft of GCGR, explaining its increased potency at GCGR.","method":"Cryo-electron microscopy structural determination with pharmacological data comparison","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structures with multiple agonist complexes, supported by published pharmacological data; multiple orthogonal methods in one rigorous study","pmids":["37549266"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structure of ligand-free GCGR in complex with Gs protein (without cognate ligand) revealed that Gs protein alone directly opens the intracellular binding cavity and rewires the extracellular orthosteric pocket. A segment of GCGR ECL2 partially occupies the peptide-binding site in this ligand-free state, representing a transitional conformation distinct from the active agonist-bound state.","method":"Cryo-electron microscopy structural determination","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution cryo-EM structure, single study but with rigorous structural validation across three receptors (GLP-1R, GCGR, GIPR) providing comparative context","pmids":["38346960"],"is_preprint":false},{"year":2023,"finding":"In primary hepatocytes of Japanese flounder, glucagon promotes gluconeogenesis via sequential GCGR → PKA → CREB → PGC-1α signaling, with downstream induction of gluconeogenic enzymes PCK1 and G6PC. GCGR inhibition reduced phosphorylated CREB and PGC-1α protein, while GCGR overexpression had the opposite effect.","method":"Pharmacological inhibitors of pathway components, gene overexpression, mRNA and protein expression analysis in primary hepatocytes","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis established by inhibitors plus overexpression with orthogonal readouts (gene expression, phosphorylation, glucose production), single lab but multiple methods; fish ortholog","pmids":["37048171"],"is_preprint":false},{"year":2021,"finding":"Glucagon potentiates insulin secretion via β-cell GCGR at physiological (but not high) glucose concentrations. GCGR activation independently evokes cAMP elevation via adenylyl cyclase 5 (AC5) in β-cells; at high glucose, AC5-driven cAMP elevation bypasses GCGR. β-cell-specific GCGR knockout mice showed more severe glucose intolerance on high-fat diet, and GCGR activation promoted glucose-stimulated insulin secretion more than GLP-1R under nutrient overload.","method":"GCGR/GLP-1R antagonists on single β-cells, α-β cell clusters, and isolated islets; genetically encoded cAMP fluorescence indicator (RAB-ICUE); AC family inhibitors; β-cell-specific GCGR knockout mice","journal":"Cells","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (pharmacological antagonism, live-cell cAMP imaging, specific isoform inhibitors, conditional KO mice) with defined cellular and in vivo phenotypic readouts","pmids":["34572144"],"is_preprint":false},{"year":2021,"finding":"Partial agonism and reduced β-arrestin-2 recruitment at GCGR and GLP-1R (by OXM-derived co-agonists) was associated with slower GLP-1R internalisation and prolonged glucose-lowering action in vivo, demonstrating that the balance between G protein and β-arrestin-2 recruitment modulates GCGR/GLP-1R signaling duration.","method":"Cell-based assays for G protein and β-arrestin-2 recruitment; receptor internalization assays; molecular dynamics simulations; in vivo glucose homeostasis and weight loss studies in mice","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple in vitro signaling assays combined with in vivo pharmacological validation, single lab","pmids":["33933675"],"is_preprint":false},{"year":2023,"finding":"Using dSTORM super-resolution imaging, GCGR was found to form nanoscale clusters on HepG2 cell membranes. High glucose promoted GCGR expression and formation of larger clusters. Under high glucose conditions, glucagon stimulation did not suppress GCGR levels as effectively as under low glucose and failed to increase downstream cAMP-PKA signaling, indicating high glucose induces glucagon resistance at the receptor level.","method":"Direct stochastic optical reconstruction microscopy (dSTORM); cAMP-PKA signaling assays; hepatoma cell and hepatic cell comparison","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct nanoscale localization by super-resolution imaging with functional signaling readout, single lab, single study","pmids":["36824278"],"is_preprint":false},{"year":2021,"finding":"19F-NMR studies of GCGR in detergent micelles and nanodiscs were enabled by post-translational chemical introduction of fluorine-19 probes on indigenous cysteines with sequence-specific assignment. Addition of the negative allosteric modulator NNC0640 to the transmembrane domain of GLP-1R (but relevant for GCGR comparison) was required for long-time stability in NMR experiments, revealing allosteric effects from NAM binding to the TMD.","method":"19F-NMR spectroscopy in solution; nanodisc and detergent micelle reconstitution; post-translational fluorine labeling","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstitution and NMR with chemical labeling, but primarily a methods/groundwork paper with limited functional mechanistic conclusions specifically about GCGR","pmids":["33369025"],"is_preprint":false},{"year":2023,"finding":"Paramagnetic NMR relaxation enhancement with dual fluorine-19/nitroxide spin-label labeling showed that glucagon ligand binds to GCGR by selective interaction with the extracellular surface of the transmembrane domain (TMD), and this selectivity is preserved even in the TMD construct lacking the extracellular domain (ECD). Cross-reactivity: GLP-1 also interacts with GCGR extracellular surface.","method":"Paramagnetic NMR relaxation enhancement; dual labeling (19F on receptor, nitroxide spin labels on peptide ligands); truncated TMD constructs","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in-solution NMR with direct distance measurements, but single lab and limited functional validation beyond binding interaction","pmids":["37332600"],"is_preprint":false},{"year":2025,"finding":"Scaffolding protein RACK1 directly binds GCGR, PKA regulatory subunit RIIα, PKA catalytic subunit PKAcα, and CREB, functioning as a dual-compartment scaffold that assembles GCGR–PKA complexes at the plasma membrane and PKAcα–CREB complexes in the nucleus. Acute hepatic RACK1 deficiency impaired PKAcα translocation, CREB phosphorylation, and gluconeogenic gene expression, causing fasting hypoglycemia; these defects were rescued by constitutively active PKAcα expression.","method":"Co-immunoprecipitation, GST pulldown, proximity ligation assays, subcellular fractionation, confocal microscopy, hepatic RACK1 knockout mice, functional rescue with constitutively active PKAcα","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal binding assays (Co-IP, GST pulldown, PLA) plus functional KO phenotype with rescue experiment; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.06.18.660434"],"is_preprint":true},{"year":2024,"finding":"GCGR agonism by the dual agonist cotadutide upregulated CD9 in the liver. CD9 deficiency exacerbated hepatic steatosis via complement factor D (CFD)-regulated fatty acid metabolism; specifically, CD9 modulated hepatic fatty acid synthesis and oxidation genes by regulating CFD expression through ubiquitination-proteasomal degradation of FLI1. Blockade of CD9 abolished the remission of hepatic steatosis induced by cotadutide treatment.","method":"Hepatic CD9 knockdown/knockout; cotadutide treatment; gene expression analysis; ubiquitination assay; functional rescue experiments","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined molecular mechanism (ubiquitination-proteasomal degradation), functional rescue with GCGR agonist; single lab","pmids":["38837628"],"is_preprint":false},{"year":2025,"finding":"ALKBH5, an RNA m6A demethylase, is phosphorylated by protein kinase A (PKA) and translocates to the cytosol. Hepatocyte-specific deletion of Alkbh5 reduces GCGR signaling; ALKBH5 was identified as acting upstream of and required for full GCGR pathway activity in the liver. This places ALKBH5 as a regulator of the GCGR signaling pathway in hepatic glucose homeostasis.","method":"Hepatocyte-specific Alkbh5 knockout mice; targeted knockdown; PKA phosphorylation assay; subcellular fractionation","journal":"Science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with specific phenotypic readouts and identification of PTM (PKA phosphorylation) driving relocalization; single study","pmids":["40014709"],"is_preprint":false},{"year":2024,"finding":"Hepatic GCGR is required for the superior weight loss and lipid clearance effects of the dual GCGR/GLP1R agonist BI 456908. The dual agonist achieved superior weight loss compared to selective GLP1R agonist semaglutide specifically through hepatic GCGR engagement, and hepatic GCGR facilitated plasma and liver lipid clearance stimulated by the dual agonist.","method":"Dual agonist vs. GLP1R mono-agonist comparison in vivo; hepatic GCGR-specific models; plasma and liver lipid measurement","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint with in vivo pharmacological comparison, but mechanistic detail at molecular level is limited; single lab","pmids":["bio_10.1101_2024.09.09.611134"],"is_preprint":true},{"year":2025,"finding":"GCGR agonism recruits GABAergic signaling in the medial basal hypothalamus to promote UCP1-dependent thermogenesis in adipose tissue and drive weight loss in obese mice, establishing a liver→brain→fat axis activated by GCGR agonism.","method":"Chronic GCGR agonist treatment in obese mice; metabolic cage studies; GABAergic signaling pathway dissection; UCP1 protein measurement in adipose tissue; thermoneutral housing controls","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — defined pathway (liver→brain→fat) via in vivo mechanistic studies with specific molecular readouts (UCP1, GABA signaling), but single lab with limited mechanistic detail in abstract","pmids":["41654017"],"is_preprint":false},{"year":2025,"finding":"Ligand-induced β-arrestin recruitment to GCGR proceeds in a phosphorylation-independent manner, in contrast to GLP-1R and GIPR where C-tail phosphorylation is a critical determinant driving GPCR-β-arrestin complex formation and regulating cAMP production.","method":"Proteomic identification of C-tail phosphorylation sites by mass spectrometry; mutagenesis of phosphorylated residues; β-arrestin recruitment assays; cAMP production assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — mass spectrometry phosphoproteomics with mutagenesis and functional assays for βarr recruitment and cAMP; preprint, single lab","pmids":["bio_10.1101_2025.03.10.642457"],"is_preprint":true},{"year":2024,"finding":"Dual activation of GCGR and GLP1R reduced H3K9 lactylation in intestinal epithelial cells (resulting from reduced lactate accumulation) and ameliorated intestinal fibrosis through reduced epithelial-to-mesenchymal transition (EMT). Downregulation of GCGR and GLP1R in fibrotic tissue led to lactate accumulation and H3K9 lactylation-driven EMT.","method":"GCGR/GLP1R knockdown and dual agonist treatment; H3K9 lactylation measurement; EMT marker analysis; in vivo fibrosis models; patient tissue analysis","journal":"Acta pharmaceutica Sinica. B","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function (receptor knockdown) and gain-of-function (dual agonist) with specific epigenetic and cellular mechanism identified; single lab","pmids":["40041889"],"is_preprint":false},{"year":2025,"finding":"Liver-specific deletion of the glucagon receptor (Gcgr hep-/-) decreases hepatic AMP kinase activation in aging mice regardless of diet, and abolishes the caloric restriction-induced decrease in hepatic mTOR activity seen in wild-type mice, demonstrating that hepatic GCGR is required for AMPK and mTOR nutrient sensing pathway responses to caloric restriction.","method":"Liver-specific GCGR knockout mice; global GCGR knockout mice; dietary intervention (caloric restriction, high-fat diet); AMPK and mTOR activity assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional liver-specific KO with defined pathway readouts (AMPK, mTOR) and multiple dietary conditions; preprint, single lab","pmids":["bio_10.1101_2025.05.13.653849"],"is_preprint":true},{"year":2024,"finding":"Interruption of glucagon signaling (via GCGR antagonism/knockout across zebrafish, rodent, and human islet models) stimulates delta cell and beta cell proliferation via SLC7A2 (cationic amino acid transporter) and mTORC1-dependent mechanisms, establishing an amino acid-nutrient sensing pathway downstream of loss of GCGR action.","method":"Six models of interrupted glucagon signaling (zebrafish gcgr deficiency, rodent GCGR antagonism, transplanted human islets); rapamycin (mTORC1 inhibition); SLC7A2 global deficiency; proliferation and mass measurements","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis across multiple independent models (6 models), rapamycin and SLC7A2 KO for pathway placement, replicated across species; preprint","pmids":["bio_10.1101_2024.08.06.606926"],"is_preprint":true},{"year":2025,"finding":"In β-cells, activating GCGR (GcgR) with chemical agonists induces microtubule (MT) destabilization in the absence of high glucose, while inhibiting GCGR with antagonists attenuates high glucose-induced MT destabilization. This MT destabilization facilitates movement of insulin secretory granules toward the plasma membrane to enhance GSIS, establishing GCGR as a regulator of β-cell MT dynamics and insulin secretion through a paracrine mechanism from α-cells.","method":"Chemical GCGR agonists and antagonists; live MT imaging in mouse and human β-cells; islet α/β cell ratio analysis; GSIS measurements","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — pharmacological gain- and loss-of-function with direct MT imaging and functional GSIS readout in both mouse and human cells; preprint, single lab","pmids":["bio_10.1101_2024.10.21.619544"],"is_preprint":true},{"year":2021,"finding":"GLP-1R/GCGR knockdown in hepatic fibrosis models demonstrated that GCGR plays an important role in ameliorating CCl4-induced hepatic fibrosis. The dual agonist TB001 attenuated hepatic stellate cell activation via suppression of TGF-β/Smad signaling and blocked NFκB/IKBα inflammatory pathways and JNK-dependent hepatocyte apoptosis.","method":"GLP-1R and/or GCGR knockdown in liver fibrosis models; CCl4, ANIT, BDL, and Schistosoma japonicum rodent models; TGF-β/Smad, NFκB/IKBα, JNK pathway analysis","journal":"Acta pharmaceutica Sinica. B","confidence":"Low","confidence_rationale":"Tier 3 / Weak — receptor knockdown with downstream pathway analysis, but mechanistic focus is primarily on pharmacological effects of dual agonist; single lab","pmids":["35646543"],"is_preprint":false},{"year":2025,"finding":"Chlorogenic acid (CGA) and ferulic acid (FA) inhibit cardiac lipotoxic apoptosis by inhibiting GCGR/PPARα and GCGR/AMPK signaling pathways. GCGR inhibitor (Adomeglivant) reduced PA-induced apoptosis, confirming that palmitic acid induces cardiomyocyte lipotoxic apoptosis by activating GCGR. Molecular docking identified ASP1018 and THR1024 of GCGR as principal interaction sites for CGA and FA.","method":"GCGR inhibitor treatment; Ad-GCGR infection (overexpression); molecular docking; RT-PCR and western blot for GCGR/PPARα and GCGR/AMPK pathway markers; flow cytometry and mitochondrial function assays","journal":"Phytomedicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — pharmacological inhibitor and overexpression with pathway readouts, but molecular docking is computational; single lab, single study","pmids":["40466507"],"is_preprint":false}],"current_model":"GCGR is a class B1 GPCR that, upon glucagon binding to its extracellular domain and transmembrane domain surface, couples to Gs protein to activate adenylyl cyclase (notably AC5 in β-cells), elevate cAMP, and activate PKA; in hepatocytes, the scaffold protein RACK1 organizes a GCGR–PKA–CREB complex at the plasma membrane and nucleus to drive gluconeogenic gene expression via PGC-1α, PCK1, and G6PC; β-arrestin recruitment to GCGR occurs in a phosphorylation-independent manner (unlike GLP-1R); GCGR forms nanoscale clusters at the plasma membrane whose dynamics are regulated by glucose; GCGR agonism in the liver promotes lipid clearance and activates a liver→brain(GABAergic/hypothalamic)→fat(UCP1) axis for thermogenesis, while loss of glucagon signaling elevates amino acids that drive islet non-alpha cell proliferation via SLC7A2/mTORC1; and in β-cells, GCGR activation destabilizes microtubules to enhance insulin secretory granule mobilization and potentiate glucose-stimulated insulin secretion."},"narrative":{"mechanistic_narrative":"GCGR is a class B1 G protein-coupled receptor for glucagon that governs hepatic glucose and lipid metabolism, islet hormone secretion, and systemic energy balance [PMID:34572144, PMID:bio_10.1101_2025.06.18.660434]. Cryo-EM structures of GCGR bound to heterotrimeric Gs reveal how glucagon and GLP-1R/GCGR dual agonists are recognized through the extracellular domain and the transmembrane-domain surface, with the first peptide residues dictating receptor selectivity and lipidated agonists engaging the TM1-TM2 cleft; Gs coupling alone can pre-open the intracellular cavity and rewire the orthosteric pocket [PMID:37549266, PMID:38346960], and NMR distance measurements confirm that glucagon selectively docks onto the extracellular surface of the transmembrane domain even without the extracellular domain [PMID:37332600]. Active GCGR couples to Gs to drive cAMP-PKA signaling, which in hepatocytes activates a CREB → PGC-1α axis inducing the gluconeogenic enzymes PCK1 and G6PC [PMID:37048171]; the scaffold RACK1 binds GCGR, PKA subunits, and CREB to organize this cascade at both the plasma membrane and nucleus, and its loss causes fasting hypoglycemia rescuable by active PKAcα [PMID:bio_10.1101_2025.06.18.660434]. In β-cells, GCGR activation elevates cAMP via adenylyl cyclase 5 to potentiate glucose-stimulated insulin secretion at physiological glucose [PMID:34572144], in part by destabilizing microtubules to mobilize insulin granules [PMID:bio_10.1101_2024.10.21.619544]. Distinct from GLP-1R and GIPR, β-arrestin recruitment to GCGR is phosphorylation-independent [PMID:bio_10.1101_2025.03.10.642457], and the balance of G protein versus β-arrestin engagement tunes signaling duration and glucose-lowering action [PMID:33933675]. At the systemic level, hepatic GCGR mediates dual-agonist-driven lipid clearance and weight loss [PMID:bio_10.1101_2024.09.09.611134] and engages a liver→hypothalamic GABAergic→adipose UCP1 thermogenic axis [PMID:41654017], while interrupting glucagon signaling elevates amino acids that drive islet cell proliferation through SLC7A2 and mTORC1 [PMID:bio_10.1101_2024.08.06.606926]. GCGR also forms glucose-regulated nanoscale clusters at the membrane, with high glucose inducing receptor-level glucagon resistance [PMID:36824278].","teleology":[{"year":2021,"claim":"Establishing that glucagon binds and selectively engages the GCGR transmembrane-domain surface answered how the peptide is recognized at the receptor and enabled biophysical study of the isolated TMD.","evidence":"19F-NMR and paramagnetic relaxation enhancement with chemical fluorine and nitroxide labeling in micelles, nanodiscs, and truncated TMD constructs","pmids":["33369025","37332600"],"confidence":"Medium","gaps":["Functional consequences of TMD-only binding not measured","Does not resolve full active-state coupling geometry"]},{"year":2021,"claim":"Resolving the role of β-cell GCGR in insulin secretion showed that glucagon potentiates GSIS at physiological glucose through AC5-driven cAMP, defining a glucose-dependent paracrine input to insulin release.","evidence":"GCGR/GLP-1R antagonists, genetically encoded cAMP reporter, AC isoform inhibitors, and β-cell-specific GCGR knockout mice","pmids":["34572144"],"confidence":"High","gaps":["Mechanism coupling cAMP to granule release not defined here","AC5 selectivity relies on pharmacological inhibitors"]},{"year":2021,"claim":"Demonstrating that biased agonism tuning G protein versus β-arrestin-2 recruitment alters signaling duration linked receptor trafficking to in vivo efficacy.","evidence":"Cell-based G protein and β-arrestin-2 recruitment, internalization assays, molecular dynamics, and in vivo glucose/weight studies in mice","pmids":["33933675"],"confidence":"Medium","gaps":["Co-agonists act on both GCGR and GLP-1R, complicating receptor attribution","Single lab"]},{"year":2023,"claim":"Cryo-EM of GCGR-Gs complexes with dual agonists explained the structural basis of ligand selectivity and dual agonism, including lipid-moiety engagement of the TM1-TM2 cleft.","evidence":"Cryo-EM structures of GCGR-Gs with three dual agonists plus pharmacological comparison","pmids":["37549266"],"confidence":"High","gaps":["Captures agonist-bound active state only","Dynamics of selectivity switching not resolved"]},{"year":2023,"claim":"Defining the hepatic GCGR→PKA→CREB→PGC-1α cascade placed gluconeogenic gene induction (PCK1, G6PC) downstream of receptor activation by epistasis.","evidence":"Pathway inhibitors, GCGR overexpression, and phospho-/protein readouts in primary flounder hepatocytes","pmids":["37048171"],"confidence":"Medium","gaps":["Fish ortholog; mammalian conservation inferred","Single lab"]},{"year":2023,"claim":"Super-resolution imaging revealed glucose-regulated GCGR nanoclustering and identified receptor-level glucagon resistance under high glucose.","evidence":"dSTORM imaging and cAMP-PKA assays in HepG2 and hepatic cells","pmids":["36824278"],"confidence":"Medium","gaps":["Mechanism linking cluster size to signaling efficiency unresolved","Single cell-line system"]},{"year":2024,"claim":"A ligand-free GCGR-Gs structure showed that Gs alone can open the intracellular cavity and reorganize the orthosteric pocket, capturing a transitional pre-active conformation.","evidence":"Cryo-EM of nucleotide-free GCGR-Gs without cognate ligand, with comparison across GLP-1R/GCGR/GIPR","pmids":["38346960"],"confidence":"High","gaps":["Physiological frequency of ligand-free Gs coupling unknown","Functional output of this state not measured"]},{"year":2024,"claim":"Linking hepatic GCGR to lipid handling, dual-agonist-induced CD9 upregulation was shown to limit steatosis via CFD/FLI1 ubiquitination, connecting GCGR agonism to fatty acid metabolism.","evidence":"Hepatic CD9 loss-of-function, cotadutide treatment, ubiquitination and rescue assays","pmids":["38837628"],"confidence":"Medium","gaps":["Direct receptor-to-CD9 signaling step not defined","Single lab"]},{"year":2024,"claim":"Identifying SLC7A2/mTORC1 as the pathway driving islet cell proliferation upon loss of glucagon signaling established an amino-acid nutrient-sensing axis downstream of GCGR loss.","evidence":"Six models of interrupted glucagon signaling across zebrafish, rodent, and human islets, with rapamycin and SLC7A2 deficiency (preprint)","pmids":["bio_10.1101_2024.08.06.606926"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Hyperaminoacidemia as the proximal trigger inferred"]},{"year":2024,"claim":"Hepatic GCGR was shown to be required for dual-agonist superior lipid clearance and weight loss versus GLP-1R mono-agonism.","evidence":"Dual agonist vs semaglutide comparison in hepatic GCGR models, lipid measurements (preprint)","pmids":["bio_10.1101_2024.09.09.611134"],"confidence":"Low","gaps":["Preprint with limited molecular-level mechanism","Single lab"]},{"year":2024,"claim":"Dual GCGR/GLP1R activation was tied to epigenetic control of intestinal fibrosis via reduced H3K9 lactylation and EMT.","evidence":"Receptor knockdown and dual agonist treatment, lactylation and EMT markers, in vivo fibrosis models and patient tissue","pmids":["40041889"],"confidence":"Medium","gaps":["GCGR-specific contribution not isolated from GLP1R","Single lab"]},{"year":2025,"claim":"RACK1 was identified as a dual-compartment scaffold organizing GCGR-PKA at the membrane and PKAcα-CREB in the nucleus, providing the structural logic for hepatic gluconeogenic signaling.","evidence":"Co-IP, GST pulldown, PLA, fractionation, hepatic RACK1 knockout mice, and rescue with constitutively active PKAcα (preprint)","pmids":["bio_10.1101_2025.06.18.660434"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Direct RACK1-GCGR interface not mapped structurally"]},{"year":2025,"claim":"ALKBH5, a PKA-phosphorylated m6A demethylase, was placed as an upstream requirement for full hepatic GCGR pathway activity, linking RNA modification to glucagon glucose control.","evidence":"Hepatocyte-specific Alkbh5 knockout, knockdown, PKA phosphorylation and fractionation assays","pmids":["40014709"],"confidence":"Medium","gaps":["Molecular targets of ALKBH5 demethylation in this axis not specified","Single study"]},{"year":2025,"claim":"Phosphoproteomics established that β-arrestin recruitment to GCGR is phosphorylation-independent, distinguishing it from GLP-1R and GIPR.","evidence":"Mass spectrometry C-tail mapping, mutagenesis, β-arrestin recruitment and cAMP assays (preprint)","pmids":["bio_10.1101_2025.03.10.642457"],"confidence":"Medium","gaps":["Preprint, single lab","Structural basis for phosphorylation-independent arrestin engagement unknown"]},{"year":2025,"claim":"GCGR was shown to regulate β-cell microtubule dynamics, destabilizing MTs to mobilize insulin granules and enhance GSIS, defining a mechanistic link between receptor activation and secretion.","evidence":"Chemical agonists/antagonists with live MT imaging and GSIS in mouse and human β-cells (preprint)","pmids":["bio_10.1101_2024.10.21.619544"],"confidence":"Medium","gaps":["Preprint","Signaling intermediates linking cAMP/PKA to MT destabilization not defined"]},{"year":2025,"claim":"GCGR agonism was shown to drive a liver→hypothalamic GABAergic→adipose UCP1 thermogenic axis, and hepatic GCGR to be required for AMPK/mTOR nutrient-sensing responses to caloric restriction.","evidence":"Chronic agonist treatment with metabolic cage and UCP1 readouts; liver-specific and global GCGR knockout mice across diets (one preprint)","pmids":["41654017","bio_10.1101_2025.05.13.653849"],"confidence":"Medium","gaps":["Inter-organ signal from liver to brain not molecularly identified","Caloric-restriction study is a preprint"]},{"year":null,"claim":"How the structurally defined Gs-coupled, phosphorylation-independent arrestin behavior of GCGR is integrated with its scaffold-dependent compartmentalized PKA/CREB signaling and inter-organ axes into a unified, druggable mechanism remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of GCGR-β-arrestin complex","RACK1-GCGR and liver-brain signals lack molecular interface definition","Several systemic-axis findings remain in preprint"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,3,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,8]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,3,8]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,11,15]}],"complexes":["GCGR-Gs complex","RACK1-GCGR-PKA scaffold complex"],"partners":["GCG","GNAS","RACK1","PRKAR2A","PRKACA","CREB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P47871","full_name":"Glucagon receptor","aliases":[],"length_aa":477,"mass_kda":54.0,"function":"G-protein coupled receptor for glucagon that plays a central role in the regulation of blood glucose levels and glucose homeostasis. Regulates the rate of hepatic glucose production by promoting glycogen hydrolysis and gluconeogenesis. Plays an important role in mediating the responses to fasting. Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors, such as adenylate cyclase (PubMed:32193322, PubMed:38346960). Promotes activation of adenylate cyclase. Besides, plays a role in signaling via a phosphatidylinositol-calcium second messenger system","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P47871/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GCGR","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GCGR","total_profiled":1310},"omim":[{"mim_id":"619290","title":"MAHVASH DISEASE; MVAH","url":"https://www.omim.org/entry/619290"},{"mim_id":"613303","title":"AlkB HOMOLOG 5, RNA DEMETHYLASE; ALKBH5","url":"https://www.omim.org/entry/613303"},{"mim_id":"603659","title":"GLUCAGON-LIKE PEPTIDE 2 RECEPTOR; GLP2R","url":"https://www.omim.org/entry/603659"},{"mim_id":"138033","title":"GLUCAGON RECEPTOR; GCGR","url":"https://www.omim.org/entry/138033"},{"mim_id":"138032","title":"GLUCAGON-LIKE PEPTIDE 1 RECEPTOR; GLP1R","url":"https://www.omim.org/entry/138032"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Golgi apparatus","reliability":"Uncertain"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"kidney","ntpm":49.3},{"tissue":"liver","ntpm":167.2}],"url":"https://www.proteinatlas.org/search/GCGR"},"hgnc":{"alias_symbol":["GGR"],"prev_symbol":[]},"alphafold":{"accession":"P47871","domains":[{"cath_id":"4.10.1240.10","chopping":"25-100","consensus_level":"high","plddt":91.5375,"start":25,"end":100},{"cath_id":"1.20.1070.10","chopping":"138-366_382-406","consensus_level":"high","plddt":87.6816,"start":138,"end":406}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P47871","model_url":"https://alphafold.ebi.ac.uk/files/AF-P47871-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P47871-F1-predicted_aligned_error_v6.png","plddt_mean":81.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GCGR","jax_strain_url":"https://www.jax.org/strain/search?query=GCGR"},"sequence":{"accession":"P47871","fasta_url":"https://rest.uniprot.org/uniprotkb/P47871.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P47871/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P47871"}},"corpus_meta":[{"pmid":"36356832","id":"PMC_36356832","title":"BI 456906: Discovery and preclinical pharmacology of a novel GCGR/GLP-1R dual agonist with robust anti-obesity efficacy.","date":"2022","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/36356832","citation_count":107,"is_preprint":false},{"pmid":"21631939","id":"PMC_21631939","title":"Polyomic profiling reveals significant hepatic metabolic alterations in glucagon-receptor (GCGR) knockout mice: implications on anti-glucagon therapies for diabetes.","date":"2011","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/21631939","citation_count":73,"is_preprint":false},{"pmid":"30765435","id":"PMC_30765435","title":"Antisense Inhibition of Glucagon Receptor by IONIS-GCGRRx Improves Type 2 Diabetes Without Increase in Hepatic Glycogen Content in Patients With Type 2 Diabetes on Stable Metformin Therapy.","date":"2019","source":"Diabetes care","url":"https://pubmed.ncbi.nlm.nih.gov/30765435","citation_count":45,"is_preprint":false},{"pmid":"40014709","id":"PMC_40014709","title":"Liver ALKBH5 regulates glucose and lipid homeostasis independently through GCGR and mTORC1 signaling.","date":"2025","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/40014709","citation_count":41,"is_preprint":false},{"pmid":"34572144","id":"PMC_34572144","title":"Glucagon Potentiates Insulin Secretion Via β-Cell GCGR at Physiological Concentrations of Glucose.","date":"2021","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/34572144","citation_count":36,"is_preprint":false},{"pmid":"35646543","id":"PMC_35646543","title":"Design of a highly potent GLP-1R and GCGR dual-agonist for recovering hepatic fibrosis.","date":"2021","source":"Acta pharmaceutica Sinica. B","url":"https://pubmed.ncbi.nlm.nih.gov/35646543","citation_count":32,"is_preprint":false},{"pmid":"37549266","id":"PMC_37549266","title":"Structural analysis of the dual agonism at GLP-1R and GCGR.","date":"2023","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/37549266","citation_count":31,"is_preprint":false},{"pmid":"27211075","id":"PMC_27211075","title":"DNA immunization combined with scFv phage display identifies antagonistic GCGR specific antibodies and reveals new epitopes on the small extracellular loops.","date":"2016","source":"mAbs","url":"https://pubmed.ncbi.nlm.nih.gov/27211075","citation_count":29,"is_preprint":false},{"pmid":"38755312","id":"PMC_38755312","title":"Machine learning designs new GCGR/GLP-1R dual agonists with enhanced biological potency.","date":"2024","source":"Nature chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/38755312","citation_count":25,"is_preprint":false},{"pmid":"39735270","id":"PMC_39735270","title":"GLP-1, GIP/GLP-1, and GCGR/GLP-1 receptor agonists: Novel therapeutic agents for metabolic dysfunction-associated steatohepatitis.","date":"2024","source":"World journal of gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/39735270","citation_count":23,"is_preprint":false},{"pmid":"29937214","id":"PMC_29937214","title":"GLP-2 receptor signaling controls circulating bile acid levels but not glucose homeostasis in Gcgr-/- mice and is dispensable for the metabolic benefits ensuing after vertical sleeve gastrectomy.","date":"2018","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/29937214","citation_count":23,"is_preprint":false},{"pmid":"34411824","id":"PMC_34411824","title":"Gestational cadmium exposure impairs placental angiogenesis via activating GC/GR signaling.","date":"2021","source":"Ecotoxicology and environmental safety","url":"https://pubmed.ncbi.nlm.nih.gov/34411824","citation_count":23,"is_preprint":false},{"pmid":"38346960","id":"PMC_38346960","title":"Molecular features of the ligand-free GLP-1R, GCGR and GIPR in complex with Gs proteins.","date":"2024","source":"Cell discovery","url":"https://pubmed.ncbi.nlm.nih.gov/38346960","citation_count":21,"is_preprint":false},{"pmid":"40041889","id":"PMC_40041889","title":"Dual activation of GCGR/GLP1R signaling ameliorates intestinal fibrosis via metabolic regulation of histone H3K9 lactylation in epithelial cells.","date":"2024","source":"Acta pharmaceutica Sinica. B","url":"https://pubmed.ncbi.nlm.nih.gov/40041889","citation_count":18,"is_preprint":false},{"pmid":"30294546","id":"PMC_30294546","title":"The first pediatric case of glucagon receptor defect due to biallelic mutations in GCGR is identified by newborn screening of elevated arginine.","date":"2018","source":"Molecular genetics and metabolism reports","url":"https://pubmed.ncbi.nlm.nih.gov/30294546","citation_count":18,"is_preprint":false},{"pmid":"33933675","id":"PMC_33933675","title":"Partial agonism improves the anti-hyperglycaemic efficacy of an oxyntomodulin-derived GLP-1R/GCGR co-agonist.","date":"2021","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/33933675","citation_count":13,"is_preprint":false},{"pmid":"38065435","id":"PMC_38065435","title":"Evaluation of long acting GLP1R/GCGR agonist in a DIO and biopsy-confirmed mouse model of NASH suggest a beneficial role of GLP-1/glucagon agonism in NASH patients.","date":"2023","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/38065435","citation_count":13,"is_preprint":false},{"pmid":"33369025","id":"PMC_33369025","title":"Design and preparation of the class B G protein-coupled receptors GLP-1R and GCGR for 19 F-NMR studies in solution.","date":"2021","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/33369025","citation_count":12,"is_preprint":false},{"pmid":"37800952","id":"PMC_37800952","title":"Alpinia katsumadai Hayata Volatile Oil Is Effective in Treating 5-Fluorouracil-Induced Mucositis by Regulating Gut Microbiota and Modulating the GC/GR Pathway and the mPGES-1/PGE2/EP4 Pathways.","date":"2023","source":"Journal of agricultural and food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37800952","citation_count":12,"is_preprint":false},{"pmid":"40479843","id":"PMC_40479843","title":"Mazdutide, a dual agonist targeting GLP-1R and GCGR, mitigates diabetes-associated cognitive dysfunction: mechanistic insights from multi-omics analysis.","date":"2025","source":"EBioMedicine","url":"https://pubmed.ncbi.nlm.nih.gov/40479843","citation_count":11,"is_preprint":false},{"pmid":"28132162","id":"PMC_28132162","title":"Population pharmacokinetics and pharmacodynamics of IONIS-GCGRRx, an antisense oligonucleotide for type 2 diabetes mellitus: a red blood cell lifespan model.","date":"2017","source":"Journal of pharmacokinetics and pharmacodynamics","url":"https://pubmed.ncbi.nlm.nih.gov/28132162","citation_count":11,"is_preprint":false},{"pmid":"40399267","id":"PMC_40399267","title":"GLP-1R/GCGR dual agonism dissipates hepatic steatosis to restore insulin sensitivity and rescue pancreatic β-cell function in obese male mice.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/40399267","citation_count":10,"is_preprint":false},{"pmid":"37048171","id":"PMC_37048171","title":"Glucagon Promotes Gluconeogenesis through the GCGR/PKA/CREB/PGC-1α Pathway in Hepatocytes of the Japanese Flounder Paralichthys olivaceus.","date":"2023","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/37048171","citation_count":10,"is_preprint":false},{"pmid":"38560764","id":"PMC_38560764","title":"The dual GCGR/GLP-1R agonist survodutide: Biomarkers and pharmacological profiling for clinical candidate selection.","date":"2024","source":"Diabetes, obesity & metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/38560764","citation_count":9,"is_preprint":false},{"pmid":"33920024","id":"PMC_33920024","title":"Ligand-Receptor Interactions and Machine Learning in GCGR and GLP-1R Drug Discovery.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33920024","citation_count":8,"is_preprint":false},{"pmid":"30312651","id":"PMC_30312651","title":"Glucagon-like peptides-1 from phylogenetically ancient fish show potent anti-diabetic activities by acting as dual GLP1R and GCGR agonists.","date":"2018","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/30312651","citation_count":7,"is_preprint":false},{"pmid":"38837628","id":"PMC_38837628","title":"CD9 Counteracts Liver Steatosis and Mediates GCGR Agonist Hepatic Effects.","date":"2024","source":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/38837628","citation_count":6,"is_preprint":false},{"pmid":"40958513","id":"PMC_40958513","title":"Strategic Design of Triple GLP-1R/GCGR/GIPR Agonists with Varied Receptor Potency: Achieving Comparable Glycemic and Weight Reduction Effects.","date":"2025","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/40958513","citation_count":6,"is_preprint":false},{"pmid":"40466507","id":"PMC_40466507","title":"Chlorogenic acid and ferulic acid in SMYAD alleviate diabetic cardiomyopathy by inhibiting cardiac lipotoxicity via GCGR/PPARα and GCGR/AMPK pathways.","date":"2025","source":"Phytomedicine : international journal of phytotherapy and phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/40466507","citation_count":5,"is_preprint":false},{"pmid":"32073000","id":"PMC_32073000","title":"Graph theory-based reaction pathway searches and DFT calculations for the mechanism studies of free radical-initiated peptide sequencing mass spectrometry (FRIPS MS): a model gas-phase reaction of GGR tri-peptide.","date":"2020","source":"Physical chemistry chemical physics : PCCP","url":"https://pubmed.ncbi.nlm.nih.gov/32073000","citation_count":5,"is_preprint":false},{"pmid":"36824278","id":"PMC_36824278","title":"High glucose-induced glucagon resistance and membrane distribution of GCGR revealed by super-resolution imaging.","date":"2023","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/36824278","citation_count":4,"is_preprint":false},{"pmid":"40499218","id":"PMC_40499218","title":"Tanshinone IIA improved psychological stress-induced embryo implantation disorders by inhibiting GC/GR signaling and promoting angiogenesis.","date":"2025","source":"Phytomedicine : international journal of phytotherapy and phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/40499218","citation_count":4,"is_preprint":false},{"pmid":"32785645","id":"PMC_32785645","title":"The V369M Gcgr knock-in mice are a precision medicine model of mild Mahvash disease.","date":"2020","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/32785645","citation_count":4,"is_preprint":false},{"pmid":"37332600","id":"PMC_37332600","title":"Selective polypeptide ligand binding to the extracellular surface of the transmembrane domains of the class B GPCRs GLP-1R and GCGR.","date":"2023","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/37332600","citation_count":3,"is_preprint":false},{"pmid":"41246119","id":"PMC_41246119","title":"Dual GIP/GLP1-RA, GCGR/GLP-1 RA and GLP1-RA for the Treatment of Metabolic Dysfunction-associated Steatotic Liver Disease with Type 2 Diabetes: A Systematic Review and Meta-analysis.","date":"2025","source":"TouchREVIEWS in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/41246119","citation_count":2,"is_preprint":false},{"pmid":"34002801","id":"PMC_34002801","title":"Deleterious mutation V369M in the mouse GCGR gene causes abnormal plasma amino acid levels indicative of a possible liver-α-cell axis.","date":"2021","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/34002801","citation_count":2,"is_preprint":false},{"pmid":"41260780","id":"PMC_41260780","title":"DeepGCGR: an interpretable two-layer deep learning model for the discovery of GCGR-activating compounds.","date":"2025","source":"Chinese journal of natural medicines","url":"https://pubmed.ncbi.nlm.nih.gov/41260780","citation_count":2,"is_preprint":false},{"pmid":"39125959","id":"PMC_39125959","title":"The Inferential Binding Sites of GCGR for Small Molecules Using Protein Dynamic Conformations and Crystal Structures.","date":"2024","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/39125959","citation_count":1,"is_preprint":false},{"pmid":"40619099","id":"PMC_40619099","title":"Novel NPY2R agonist BI 1820237 provides synergistic anti-obesity efficacy when combined with the GCGR/GLP-1R dual agonist survodutide.","date":"2025","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/40619099","citation_count":1,"is_preprint":false},{"pmid":"37969012","id":"PMC_37969012","title":"Evolution of GCGR family ligand-receptor extensive cross-interaction systems suggests a therapeutic direction for hyperglycemia in mammals.","date":"2023","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/37969012","citation_count":1,"is_preprint":false},{"pmid":"41315395","id":"PMC_41315395","title":"Avian GCGR-mediated continuous fat utilization offers perspectives for obesity treatment.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41315395","citation_count":0,"is_preprint":false},{"pmid":"40832525","id":"PMC_40832525","title":"Novel Peptides as GIPR/GLP-1R/GCGR Triagonists for Treating Type 2 Diabetes Mellitus.","date":"2025","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/40832525","citation_count":0,"is_preprint":false},{"pmid":"41280890","id":"PMC_41280890","title":"A novel GCGR/GLP-1R dual-agonist TB001 ameliorates kidney fibrosis via inhibiting PERK-mediated endoplasmic reticulum stress pathway.","date":"2025","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/41280890","citation_count":0,"is_preprint":false},{"pmid":"41030857","id":"PMC_41030857","title":"Case Report: Efficacy and safety of dose-escalated Mazdutide, a GLP-1/GCGR dual agonist, in an adolescent with obesity, type 2 diabetes, and hyperuricemia.","date":"2025","source":"Frontiers in endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/41030857","citation_count":0,"is_preprint":false},{"pmid":"35381520","id":"PMC_35381520","title":"Generation of an induced pluripotent stem cell (iPSC) line from a diabetic patient with glucagon receptor (GCGR) p.W83X mutation.","date":"2022","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/35381520","citation_count":0,"is_preprint":false},{"pmid":"41869515","id":"PMC_41869515","title":"Design and biological evaluation of triagonist GLP-1R/GCGR/GIPR peptides as potential therapeutic agents for diabetes and obesity.","date":"2026","source":"RSC medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/41869515","citation_count":0,"is_preprint":false},{"pmid":"41654017","id":"PMC_41654017","title":"GCGR agonism requires GABAergic signaling in the medial basal hypothalamus to promote weight loss in obese mice.","date":"2026","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/41654017","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.06.658268","title":"Blind De Novo Design of Dual Cyclic Peptide Agonists Targeting GCGR and GLP1R","date":"2025-06-08","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.06.658268","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.06.18.660434","title":"A Dual-Compartment Scaffolding Role for RACK1 in Hepatic Glucagon Signaling and Gluconeogenesis","date":"2025-06-24","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.18.660434","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.05.13.653849","title":"Glucagon receptor signaling is indispensable for the healthspan effects of caloric restriction in aging male mice","date":"2025-05-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.13.653849","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.08.09.669458","title":"Glycemia Shift Pancreatic Islets Rhythmicity via δ-α Cell in vivo, Impairment in Diabetes","date":"2025-08-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.09.669458","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.03.06.641926","title":"Identification of drug candidates against glioblastoma with machine learning and high-throughput screening of heterogeneous cellular models","date":"2025-03-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.06.641926","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.03.10.642457","title":"Differential role of phosphorylation in glucagon family receptor signaling revealed by mass spectrometry","date":"2025-03-13","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.10.642457","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.09.09.611134","title":"Hepatic GCGR is required for the superior weight loss effects of a structurally related analogue of the dual GCGR/GLP1R agonist survodutide","date":"2024-09-13","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.09.611134","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.03.23.644666","title":"<i>De novo</i>  design of miniprotein agonists and antagonists targeting G protein-coupled receptors","date":"2025-03-23","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.23.644666","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.08.06.606926","title":"Interruption of glucagon signaling augments islet non-alpha cell proliferation in SLC7A2- and mTOR-dependent manners","date":"2024-08-07","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.06.606926","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.04.01.646483","title":"Ectopic, hepatic GLP-1R agonism enhances the weight loss efficacy of GLP-1 analogues","date":"2025-04-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.01.646483","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.10.21.619544","title":"Pancreatic islet α cells regulate microtubule stability in neighboring β cells to tune insulin secretion and induce functional heterogeneity in individual mouse and human islets","date":"2024-10-23","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.21.619544","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.11.26.625442","title":"Drug combinations targeting FAK and MEK overcomes tumour heterogeneity in glioblastoma","date":"2024-12-01","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.26.625442","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":32689,"output_tokens":5722,"usd":0.091949,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14538,"output_tokens":5067,"usd":0.099682,"stage2_stop_reason":"end_turn"},"total_usd":0.191631,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of GCGR in complex with heterotrimeric Gs protein and three GLP-1R/GCGR dual agonists (peptide 15, MEDI0382/cotadutide, SAR425899) identified key residues responsible for ligand recognition and dual agonism. Distinct side-chain orientations within the first three residues of the peptide ligand determine receptor selectivity, and ECL1 conformation of GCGR differs from GLP-1R in response to dual agonists. The lipid moiety of MEDI0382 interacts with the TM1-TM2 cleft of GCGR, explaining its increased potency at GCGR.\",\n      \"method\": \"Cryo-electron microscopy structural determination with pharmacological data comparison\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structures with multiple agonist complexes, supported by published pharmacological data; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"37549266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structure of ligand-free GCGR in complex with Gs protein (without cognate ligand) revealed that Gs protein alone directly opens the intracellular binding cavity and rewires the extracellular orthosteric pocket. A segment of GCGR ECL2 partially occupies the peptide-binding site in this ligand-free state, representing a transitional conformation distinct from the active agonist-bound state.\",\n      \"method\": \"Cryo-electron microscopy structural determination\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution cryo-EM structure, single study but with rigorous structural validation across three receptors (GLP-1R, GCGR, GIPR) providing comparative context\",\n      \"pmids\": [\"38346960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In primary hepatocytes of Japanese flounder, glucagon promotes gluconeogenesis via sequential GCGR → PKA → CREB → PGC-1α signaling, with downstream induction of gluconeogenic enzymes PCK1 and G6PC. GCGR inhibition reduced phosphorylated CREB and PGC-1α protein, while GCGR overexpression had the opposite effect.\",\n      \"method\": \"Pharmacological inhibitors of pathway components, gene overexpression, mRNA and protein expression analysis in primary hepatocytes\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis established by inhibitors plus overexpression with orthogonal readouts (gene expression, phosphorylation, glucose production), single lab but multiple methods; fish ortholog\",\n      \"pmids\": [\"37048171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Glucagon potentiates insulin secretion via β-cell GCGR at physiological (but not high) glucose concentrations. GCGR activation independently evokes cAMP elevation via adenylyl cyclase 5 (AC5) in β-cells; at high glucose, AC5-driven cAMP elevation bypasses GCGR. β-cell-specific GCGR knockout mice showed more severe glucose intolerance on high-fat diet, and GCGR activation promoted glucose-stimulated insulin secretion more than GLP-1R under nutrient overload.\",\n      \"method\": \"GCGR/GLP-1R antagonists on single β-cells, α-β cell clusters, and isolated islets; genetically encoded cAMP fluorescence indicator (RAB-ICUE); AC family inhibitors; β-cell-specific GCGR knockout mice\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (pharmacological antagonism, live-cell cAMP imaging, specific isoform inhibitors, conditional KO mice) with defined cellular and in vivo phenotypic readouts\",\n      \"pmids\": [\"34572144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Partial agonism and reduced β-arrestin-2 recruitment at GCGR and GLP-1R (by OXM-derived co-agonists) was associated with slower GLP-1R internalisation and prolonged glucose-lowering action in vivo, demonstrating that the balance between G protein and β-arrestin-2 recruitment modulates GCGR/GLP-1R signaling duration.\",\n      \"method\": \"Cell-based assays for G protein and β-arrestin-2 recruitment; receptor internalization assays; molecular dynamics simulations; in vivo glucose homeostasis and weight loss studies in mice\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple in vitro signaling assays combined with in vivo pharmacological validation, single lab\",\n      \"pmids\": [\"33933675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Using dSTORM super-resolution imaging, GCGR was found to form nanoscale clusters on HepG2 cell membranes. High glucose promoted GCGR expression and formation of larger clusters. Under high glucose conditions, glucagon stimulation did not suppress GCGR levels as effectively as under low glucose and failed to increase downstream cAMP-PKA signaling, indicating high glucose induces glucagon resistance at the receptor level.\",\n      \"method\": \"Direct stochastic optical reconstruction microscopy (dSTORM); cAMP-PKA signaling assays; hepatoma cell and hepatic cell comparison\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct nanoscale localization by super-resolution imaging with functional signaling readout, single lab, single study\",\n      \"pmids\": [\"36824278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"19F-NMR studies of GCGR in detergent micelles and nanodiscs were enabled by post-translational chemical introduction of fluorine-19 probes on indigenous cysteines with sequence-specific assignment. Addition of the negative allosteric modulator NNC0640 to the transmembrane domain of GLP-1R (but relevant for GCGR comparison) was required for long-time stability in NMR experiments, revealing allosteric effects from NAM binding to the TMD.\",\n      \"method\": \"19F-NMR spectroscopy in solution; nanodisc and detergent micelle reconstitution; post-translational fluorine labeling\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstitution and NMR with chemical labeling, but primarily a methods/groundwork paper with limited functional mechanistic conclusions specifically about GCGR\",\n      \"pmids\": [\"33369025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Paramagnetic NMR relaxation enhancement with dual fluorine-19/nitroxide spin-label labeling showed that glucagon ligand binds to GCGR by selective interaction with the extracellular surface of the transmembrane domain (TMD), and this selectivity is preserved even in the TMD construct lacking the extracellular domain (ECD). Cross-reactivity: GLP-1 also interacts with GCGR extracellular surface.\",\n      \"method\": \"Paramagnetic NMR relaxation enhancement; dual labeling (19F on receptor, nitroxide spin labels on peptide ligands); truncated TMD constructs\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in-solution NMR with direct distance measurements, but single lab and limited functional validation beyond binding interaction\",\n      \"pmids\": [\"37332600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Scaffolding protein RACK1 directly binds GCGR, PKA regulatory subunit RIIα, PKA catalytic subunit PKAcα, and CREB, functioning as a dual-compartment scaffold that assembles GCGR–PKA complexes at the plasma membrane and PKAcα–CREB complexes in the nucleus. Acute hepatic RACK1 deficiency impaired PKAcα translocation, CREB phosphorylation, and gluconeogenic gene expression, causing fasting hypoglycemia; these defects were rescued by constitutively active PKAcα expression.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown, proximity ligation assays, subcellular fractionation, confocal microscopy, hepatic RACK1 knockout mice, functional rescue with constitutively active PKAcα\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal binding assays (Co-IP, GST pulldown, PLA) plus functional KO phenotype with rescue experiment; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.06.18.660434\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GCGR agonism by the dual agonist cotadutide upregulated CD9 in the liver. CD9 deficiency exacerbated hepatic steatosis via complement factor D (CFD)-regulated fatty acid metabolism; specifically, CD9 modulated hepatic fatty acid synthesis and oxidation genes by regulating CFD expression through ubiquitination-proteasomal degradation of FLI1. Blockade of CD9 abolished the remission of hepatic steatosis induced by cotadutide treatment.\",\n      \"method\": \"Hepatic CD9 knockdown/knockout; cotadutide treatment; gene expression analysis; ubiquitination assay; functional rescue experiments\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined molecular mechanism (ubiquitination-proteasomal degradation), functional rescue with GCGR agonist; single lab\",\n      \"pmids\": [\"38837628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ALKBH5, an RNA m6A demethylase, is phosphorylated by protein kinase A (PKA) and translocates to the cytosol. Hepatocyte-specific deletion of Alkbh5 reduces GCGR signaling; ALKBH5 was identified as acting upstream of and required for full GCGR pathway activity in the liver. This places ALKBH5 as a regulator of the GCGR signaling pathway in hepatic glucose homeostasis.\",\n      \"method\": \"Hepatocyte-specific Alkbh5 knockout mice; targeted knockdown; PKA phosphorylation assay; subcellular fractionation\",\n      \"journal\": \"Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with specific phenotypic readouts and identification of PTM (PKA phosphorylation) driving relocalization; single study\",\n      \"pmids\": [\"40014709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hepatic GCGR is required for the superior weight loss and lipid clearance effects of the dual GCGR/GLP1R agonist BI 456908. The dual agonist achieved superior weight loss compared to selective GLP1R agonist semaglutide specifically through hepatic GCGR engagement, and hepatic GCGR facilitated plasma and liver lipid clearance stimulated by the dual agonist.\",\n      \"method\": \"Dual agonist vs. GLP1R mono-agonist comparison in vivo; hepatic GCGR-specific models; plasma and liver lipid measurement\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint with in vivo pharmacological comparison, but mechanistic detail at molecular level is limited; single lab\",\n      \"pmids\": [\"bio_10.1101_2024.09.09.611134\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GCGR agonism recruits GABAergic signaling in the medial basal hypothalamus to promote UCP1-dependent thermogenesis in adipose tissue and drive weight loss in obese mice, establishing a liver→brain→fat axis activated by GCGR agonism.\",\n      \"method\": \"Chronic GCGR agonist treatment in obese mice; metabolic cage studies; GABAergic signaling pathway dissection; UCP1 protein measurement in adipose tissue; thermoneutral housing controls\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — defined pathway (liver→brain→fat) via in vivo mechanistic studies with specific molecular readouts (UCP1, GABA signaling), but single lab with limited mechanistic detail in abstract\",\n      \"pmids\": [\"41654017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Ligand-induced β-arrestin recruitment to GCGR proceeds in a phosphorylation-independent manner, in contrast to GLP-1R and GIPR where C-tail phosphorylation is a critical determinant driving GPCR-β-arrestin complex formation and regulating cAMP production.\",\n      \"method\": \"Proteomic identification of C-tail phosphorylation sites by mass spectrometry; mutagenesis of phosphorylated residues; β-arrestin recruitment assays; cAMP production assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — mass spectrometry phosphoproteomics with mutagenesis and functional assays for βarr recruitment and cAMP; preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.03.10.642457\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Dual activation of GCGR and GLP1R reduced H3K9 lactylation in intestinal epithelial cells (resulting from reduced lactate accumulation) and ameliorated intestinal fibrosis through reduced epithelial-to-mesenchymal transition (EMT). Downregulation of GCGR and GLP1R in fibrotic tissue led to lactate accumulation and H3K9 lactylation-driven EMT.\",\n      \"method\": \"GCGR/GLP1R knockdown and dual agonist treatment; H3K9 lactylation measurement; EMT marker analysis; in vivo fibrosis models; patient tissue analysis\",\n      \"journal\": \"Acta pharmaceutica Sinica. B\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function (receptor knockdown) and gain-of-function (dual agonist) with specific epigenetic and cellular mechanism identified; single lab\",\n      \"pmids\": [\"40041889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Liver-specific deletion of the glucagon receptor (Gcgr hep-/-) decreases hepatic AMP kinase activation in aging mice regardless of diet, and abolishes the caloric restriction-induced decrease in hepatic mTOR activity seen in wild-type mice, demonstrating that hepatic GCGR is required for AMPK and mTOR nutrient sensing pathway responses to caloric restriction.\",\n      \"method\": \"Liver-specific GCGR knockout mice; global GCGR knockout mice; dietary intervention (caloric restriction, high-fat diet); AMPK and mTOR activity assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional liver-specific KO with defined pathway readouts (AMPK, mTOR) and multiple dietary conditions; preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.05.13.653849\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Interruption of glucagon signaling (via GCGR antagonism/knockout across zebrafish, rodent, and human islet models) stimulates delta cell and beta cell proliferation via SLC7A2 (cationic amino acid transporter) and mTORC1-dependent mechanisms, establishing an amino acid-nutrient sensing pathway downstream of loss of GCGR action.\",\n      \"method\": \"Six models of interrupted glucagon signaling (zebrafish gcgr deficiency, rodent GCGR antagonism, transplanted human islets); rapamycin (mTORC1 inhibition); SLC7A2 global deficiency; proliferation and mass measurements\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis across multiple independent models (6 models), rapamycin and SLC7A2 KO for pathway placement, replicated across species; preprint\",\n      \"pmids\": [\"bio_10.1101_2024.08.06.606926\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In β-cells, activating GCGR (GcgR) with chemical agonists induces microtubule (MT) destabilization in the absence of high glucose, while inhibiting GCGR with antagonists attenuates high glucose-induced MT destabilization. This MT destabilization facilitates movement of insulin secretory granules toward the plasma membrane to enhance GSIS, establishing GCGR as a regulator of β-cell MT dynamics and insulin secretion through a paracrine mechanism from α-cells.\",\n      \"method\": \"Chemical GCGR agonists and antagonists; live MT imaging in mouse and human β-cells; islet α/β cell ratio analysis; GSIS measurements\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — pharmacological gain- and loss-of-function with direct MT imaging and functional GSIS readout in both mouse and human cells; preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2024.10.21.619544\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GLP-1R/GCGR knockdown in hepatic fibrosis models demonstrated that GCGR plays an important role in ameliorating CCl4-induced hepatic fibrosis. The dual agonist TB001 attenuated hepatic stellate cell activation via suppression of TGF-β/Smad signaling and blocked NFκB/IKBα inflammatory pathways and JNK-dependent hepatocyte apoptosis.\",\n      \"method\": \"GLP-1R and/or GCGR knockdown in liver fibrosis models; CCl4, ANIT, BDL, and Schistosoma japonicum rodent models; TGF-β/Smad, NFκB/IKBα, JNK pathway analysis\",\n      \"journal\": \"Acta pharmaceutica Sinica. B\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — receptor knockdown with downstream pathway analysis, but mechanistic focus is primarily on pharmacological effects of dual agonist; single lab\",\n      \"pmids\": [\"35646543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Chlorogenic acid (CGA) and ferulic acid (FA) inhibit cardiac lipotoxic apoptosis by inhibiting GCGR/PPARα and GCGR/AMPK signaling pathways. GCGR inhibitor (Adomeglivant) reduced PA-induced apoptosis, confirming that palmitic acid induces cardiomyocyte lipotoxic apoptosis by activating GCGR. Molecular docking identified ASP1018 and THR1024 of GCGR as principal interaction sites for CGA and FA.\",\n      \"method\": \"GCGR inhibitor treatment; Ad-GCGR infection (overexpression); molecular docking; RT-PCR and western blot for GCGR/PPARα and GCGR/AMPK pathway markers; flow cytometry and mitochondrial function assays\",\n      \"journal\": \"Phytomedicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — pharmacological inhibitor and overexpression with pathway readouts, but molecular docking is computational; single lab, single study\",\n      \"pmids\": [\"40466507\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GCGR is a class B1 GPCR that, upon glucagon binding to its extracellular domain and transmembrane domain surface, couples to Gs protein to activate adenylyl cyclase (notably AC5 in β-cells), elevate cAMP, and activate PKA; in hepatocytes, the scaffold protein RACK1 organizes a GCGR–PKA–CREB complex at the plasma membrane and nucleus to drive gluconeogenic gene expression via PGC-1α, PCK1, and G6PC; β-arrestin recruitment to GCGR occurs in a phosphorylation-independent manner (unlike GLP-1R); GCGR forms nanoscale clusters at the plasma membrane whose dynamics are regulated by glucose; GCGR agonism in the liver promotes lipid clearance and activates a liver→brain(GABAergic/hypothalamic)→fat(UCP1) axis for thermogenesis, while loss of glucagon signaling elevates amino acids that drive islet non-alpha cell proliferation via SLC7A2/mTORC1; and in β-cells, GCGR activation destabilizes microtubules to enhance insulin secretory granule mobilization and potentiate glucose-stimulated insulin secretion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GCGR is a class B1 G protein-coupled receptor for glucagon that governs hepatic glucose and lipid metabolism, islet hormone secretion, and systemic energy balance [#3, #8]. Cryo-EM structures of GCGR bound to heterotrimeric Gs reveal how glucagon and GLP-1R/GCGR dual agonists are recognized through the extracellular domain and the transmembrane-domain surface, with the first peptide residues dictating receptor selectivity and lipidated agonists engaging the TM1-TM2 cleft; Gs coupling alone can pre-open the intracellular cavity and rewire the orthosteric pocket [#0, #1], and NMR distance measurements confirm that glucagon selectively docks onto the extracellular surface of the transmembrane domain even without the extracellular domain [#7]. Active GCGR couples to Gs to drive cAMP-PKA signaling, which in hepatocytes activates a CREB \\u2192 PGC-1\\u03b1 axis inducing the gluconeogenic enzymes PCK1 and G6PC [#2]; the scaffold RACK1 binds GCGR, PKA subunits, and CREB to organize this cascade at both the plasma membrane and nucleus, and its loss causes fasting hypoglycemia rescuable by active PKAc\\u03b1 [#8]. In \\u03b2-cells, GCGR activation elevates cAMP via adenylyl cyclase 5 to potentiate glucose-stimulated insulin secretion at physiological glucose [#3], in part by destabilizing microtubules to mobilize insulin granules [#17]. Distinct from GLP-1R and GIPR, \\u03b2-arrestin recruitment to GCGR is phosphorylation-independent [#13], and the balance of G protein versus \\u03b2-arrestin engagement tunes signaling duration and glucose-lowering action [#4]. At the systemic level, hepatic GCGR mediates dual-agonist-driven lipid clearance and weight loss [#11] and engages a liver\\u2192hypothalamic GABAergic\\u2192adipose UCP1 thermogenic axis [#12], while interrupting glucagon signaling elevates amino acids that drive islet cell proliferation through SLC7A2 and mTORC1 [#16]. GCGR also forms glucose-regulated nanoscale clusters at the membrane, with high glucose inducing receptor-level glucagon resistance [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2021,\n      \"claim\": \"Establishing that glucagon binds and selectively engages the GCGR transmembrane-domain surface answered how the peptide is recognized at the receptor and enabled biophysical study of the isolated TMD.\",\n      \"evidence\": \"19F-NMR and paramagnetic relaxation enhancement with chemical fluorine and nitroxide labeling in micelles, nanodiscs, and truncated TMD constructs\",\n      \"pmids\": [\"33369025\", \"37332600\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequences of TMD-only binding not measured\", \"Does not resolve full active-state coupling geometry\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Resolving the role of \\u03b2-cell GCGR in insulin secretion showed that glucagon potentiates GSIS at physiological glucose through AC5-driven cAMP, defining a glucose-dependent paracrine input to insulin release.\",\n      \"evidence\": \"GCGR/GLP-1R antagonists, genetically encoded cAMP reporter, AC isoform inhibitors, and \\u03b2-cell-specific GCGR knockout mice\",\n      \"pmids\": [\"34572144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism coupling cAMP to granule release not defined here\", \"AC5 selectivity relies on pharmacological inhibitors\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that biased agonism tuning G protein versus \\u03b2-arrestin-2 recruitment alters signaling duration linked receptor trafficking to in vivo efficacy.\",\n      \"evidence\": \"Cell-based G protein and \\u03b2-arrestin-2 recruitment, internalization assays, molecular dynamics, and in vivo glucose/weight studies in mice\",\n      \"pmids\": [\"33933675\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Co-agonists act on both GCGR and GLP-1R, complicating receptor attribution\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cryo-EM of GCGR-Gs complexes with dual agonists explained the structural basis of ligand selectivity and dual agonism, including lipid-moiety engagement of the TM1-TM2 cleft.\",\n      \"evidence\": \"Cryo-EM structures of GCGR-Gs with three dual agonists plus pharmacological comparison\",\n      \"pmids\": [\"37549266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Captures agonist-bound active state only\", \"Dynamics of selectivity switching not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defining the hepatic GCGR\\u2192PKA\\u2192CREB\\u2192PGC-1\\u03b1 cascade placed gluconeogenic gene induction (PCK1, G6PC) downstream of receptor activation by epistasis.\",\n      \"evidence\": \"Pathway inhibitors, GCGR overexpression, and phospho-/protein readouts in primary flounder hepatocytes\",\n      \"pmids\": [\"37048171\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Fish ortholog; mammalian conservation inferred\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Super-resolution imaging revealed glucose-regulated GCGR nanoclustering and identified receptor-level glucagon resistance under high glucose.\",\n      \"evidence\": \"dSTORM imaging and cAMP-PKA assays in HepG2 and hepatic cells\",\n      \"pmids\": [\"36824278\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking cluster size to signaling efficiency unresolved\", \"Single cell-line system\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A ligand-free GCGR-Gs structure showed that Gs alone can open the intracellular cavity and reorganize the orthosteric pocket, capturing a transitional pre-active conformation.\",\n      \"evidence\": \"Cryo-EM of nucleotide-free GCGR-Gs without cognate ligand, with comparison across GLP-1R/GCGR/GIPR\",\n      \"pmids\": [\"38346960\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological frequency of ligand-free Gs coupling unknown\", \"Functional output of this state not measured\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking hepatic GCGR to lipid handling, dual-agonist-induced CD9 upregulation was shown to limit steatosis via CFD/FLI1 ubiquitination, connecting GCGR agonism to fatty acid metabolism.\",\n      \"evidence\": \"Hepatic CD9 loss-of-function, cotadutide treatment, ubiquitination and rescue assays\",\n      \"pmids\": [\"38837628\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct receptor-to-CD9 signaling step not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying SLC7A2/mTORC1 as the pathway driving islet cell proliferation upon loss of glucagon signaling established an amino-acid nutrient-sensing axis downstream of GCGR loss.\",\n      \"evidence\": \"Six models of interrupted glucagon signaling across zebrafish, rodent, and human islets, with rapamycin and SLC7A2 deficiency (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.08.06.606926\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Hyperaminoacidemia as the proximal trigger inferred\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Hepatic GCGR was shown to be required for dual-agonist superior lipid clearance and weight loss versus GLP-1R mono-agonism.\",\n      \"evidence\": \"Dual agonist vs semaglutide comparison in hepatic GCGR models, lipid measurements (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.09.09.611134\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Preprint with limited molecular-level mechanism\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Dual GCGR/GLP1R activation was tied to epigenetic control of intestinal fibrosis via reduced H3K9 lactylation and EMT.\",\n      \"evidence\": \"Receptor knockdown and dual agonist treatment, lactylation and EMT markers, in vivo fibrosis models and patient tissue\",\n      \"pmids\": [\"40041889\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GCGR-specific contribution not isolated from GLP1R\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"RACK1 was identified as a dual-compartment scaffold organizing GCGR-PKA at the membrane and PKAc\\u03b1-CREB in the nucleus, providing the structural logic for hepatic gluconeogenic signaling.\",\n      \"evidence\": \"Co-IP, GST pulldown, PLA, fractionation, hepatic RACK1 knockout mice, and rescue with constitutively active PKAc\\u03b1 (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.06.18.660434\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Direct RACK1-GCGR interface not mapped structurally\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"ALKBH5, a PKA-phosphorylated m6A demethylase, was placed as an upstream requirement for full hepatic GCGR pathway activity, linking RNA modification to glucagon glucose control.\",\n      \"evidence\": \"Hepatocyte-specific Alkbh5 knockout, knockdown, PKA phosphorylation and fractionation assays\",\n      \"pmids\": [\"40014709\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular targets of ALKBH5 demethylation in this axis not specified\", \"Single study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Phosphoproteomics established that \\u03b2-arrestin recruitment to GCGR is phosphorylation-independent, distinguishing it from GLP-1R and GIPR.\",\n      \"evidence\": \"Mass spectrometry C-tail mapping, mutagenesis, \\u03b2-arrestin recruitment and cAMP assays (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.03.10.642457\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab\", \"Structural basis for phosphorylation-independent arrestin engagement unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"GCGR was shown to regulate \\u03b2-cell microtubule dynamics, destabilizing MTs to mobilize insulin granules and enhance GSIS, defining a mechanistic link between receptor activation and secretion.\",\n      \"evidence\": \"Chemical agonists/antagonists with live MT imaging and GSIS in mouse and human \\u03b2-cells (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.10.21.619544\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint\", \"Signaling intermediates linking cAMP/PKA to MT destabilization not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"GCGR agonism was shown to drive a liver\\u2192hypothalamic GABAergic\\u2192adipose UCP1 thermogenic axis, and hepatic GCGR to be required for AMPK/mTOR nutrient-sensing responses to caloric restriction.\",\n      \"evidence\": \"Chronic agonist treatment with metabolic cage and UCP1 readouts; liver-specific and global GCGR knockout mice across diets (one preprint)\",\n      \"pmids\": [\"41654017\", \"bio_10.1101_2025.05.13.653849\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Inter-organ signal from liver to brain not molecularly identified\", \"Caloric-restriction study is a preprint\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the structurally defined Gs-coupled, phosphorylation-independent arrestin behavior of GCGR is integrated with its scaffold-dependent compartmentalized PKA/CREB signaling and inter-organ axes into a unified, druggable mechanism remains open.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of GCGR-\\u03b2-arrestin complex\", \"RACK1-GCGR and liver-brain signals lack molecular interface definition\", \"Several systemic-axis findings remain in preprint\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 3, 7]},\n      {\"term_id\": \"GO:0004930\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 8]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 3, 8]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 11, 15]}\n    ],\n    \"complexes\": [\n      \"GCGR-Gs complex\",\n      \"RACK1-GCGR-PKA scaffold complex\"\n    ],\n    \"partners\": [\n      \"GCG\",\n      \"GNAS\",\n      \"RACK1\",\n      \"PRKAR2A\",\n      \"PRKACA\",\n      \"CREB1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}