{"gene":"RABGGTA","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2000,"finding":"A G→A substitution mutation in a splice acceptor site within Rabggta (encoding the alpha-subunit of Rab geranylgeranyl transferase, RabGGTase/GGTase II) in the gunmetal mouse causes skipping of exon 1 and loss of start codon, reducing Rabggta protein and RabGGTase activity ~4-fold in platelets; this leads to significantly decreased geranylgeranylation and membrane association of Rab27, resulting in thrombocytopenia, prolonged bleeding, and reduced platelet granule contents.","method":"Positional cloning, splice-site mutation characterization, biochemical measurement of GGTase activity in platelets, and geranylgeranylation/membrane-association assay of Rab27 in mutant vs. wild-type platelets","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — positional cloning plus biochemical enzymatic activity assay plus substrate (Rab27) geranylgeranylation and membrane-association assay, multiple orthogonal methods in a single rigorous study","pmids":["10737774"],"is_preprint":false},{"year":1997,"finding":"The human RABGGTA gene (encoding the alpha-subunit of Rab geranylgeranyl transferase) is positioned in a tandem head-to-tail arrangement with the TGM1 gene, with the RABGGTA polyadenylation signal located only 2.3 kbp upstream of the TGM1 cap site; however, RT-PCR analysis under multiple differentiation conditions showed that RABGGTA expression in epidermal keratinocytes is unaffected by calcium concentration, retinoic acid, vitamin D3, or TPA, while TGM1 expression is strongly affected by these same stimuli—demonstrating the two genes are not functionally co-regulated despite close physical linkage.","method":"RT-PCR of RABGGTA and TGM1 expression in normal human epidermal keratinocytes under various differentiation conditions; genomic structure characterization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — RT-PCR expression analysis under multiple conditions, single lab, establishes negative functional co-regulation result","pmids":["9196026"],"is_preprint":false},{"year":2000,"finding":"The 5'-UTR structure of the human RABGGTA gene shares organizational features with the mouse Rabggta gene (exon alpha upstream of intron alpha), and features of the 5'-UTR are consistent with a housekeeping gene; sequencing of the entire coding region in patients with platelet storage pool deficiencies (alpha-SPD, delta-SPD, gray platelet syndrome) identified several polymorphisms but no obvious disease-causing mutations, indicating these patients do not have RABGGTA coding mutations.","method":"Sequencing of complete coding region and 5'-UTR of RABGGTA in patients with platelet storage pool deficiencies and normal individuals; comparative genomic analysis","journal":"Molecular genetics and metabolism","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — sequencing/structural characterization, single lab; establishes negative finding that SPD patients lack RABGGTA coding mutations","pmids":["11136552"],"is_preprint":false},{"year":2016,"finding":"Knockdown of RABGGTA (encoding a subunit of RabGGTase/GGTase II) in human cancer cell lines induces an anti-proliferative effect similar to zoledronic acid, and this effect is rescued by geranylgeranyl diphosphate (GGPP) supplementation, demonstrating that RABGGTA-mediated geranylgeranylation of Rab proteins mediates the anti-cancer mechanism of zoledronic acid.","method":"siRNA knockdown of RABGGTA in cancer cell lines (GBM, breast cancer); cell proliferation assay; GGPP rescue experiment","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD with defined proliferative phenotype plus GGPP rescue, single lab, two orthogonal approaches","pmids":["27462771"],"is_preprint":false},{"year":2022,"finding":"AAV8-mediated knockdown of liver RABGGTA (the alpha-subunit of GGTase II) in vivo causes systemic glucose metabolism disorders; pharmacological and genetic inhibition of GGTase II disrupts hepatic insulin signaling by blocking geranylgeranylation of RAB14, which inhibits AKT (Ser473) phosphorylation and impairs mTORC2 complex assembly; GGPP supplementation rescues the defect.","method":"AAV8-mediated in vivo liver-specific Rabggta knockdown; siRNA screening to identify RAB14; geranylgeranylation assay; AKT phosphorylation assay; mTORC2 assembly assay; GGPP rescue in vitro and in vivo","journal":"Metabolism: clinical and experimental","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo AAV knockdown with glucose metabolism phenotype, siRNA identification of RAB14 substrate, AKT phosphorylation assay, mTORC2 assembly assay, and GGPP rescue; multiple orthogonal methods in single lab","pmids":["34995578"],"is_preprint":false},{"year":2022,"finding":"AAV9-mediated knockdown of RABGGTA in skeletal muscle impairs glucose disposal in vivo without disrupting insulin signaling (AKT phosphorylation unaffected); geranylgeranylation deficiency of RAB8A (a GGTase II substrate) specifically inhibits insulin-stimulated GLUT4 translocation and glucose uptake in skeletal muscle cells, identifying RAB8A as the relevant Rab substrate downstream of RABGGTA in this tissue.","method":"AAV9-mediated in vivo skeletal muscle RABGGTA knockdown; glucose uptake assay; RAB8A geranylgeranylation-site mutation; GLUT4 translocation assay; AKT phosphorylation assay","journal":"Journal of cachexia, sarcopenia and muscle","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo AAV knockdown with defined metabolic phenotype plus geranylgeranylation site mutagenesis of substrate RAB8A plus GLUT4 translocation assay; multiple orthogonal methods, single lab","pmids":["35961942"],"is_preprint":false},{"year":2025,"finding":"In vivo CRISPR screening using CrAAVe-seq in mouse neurons validated Rabggta as an essential gene for neuronal survival; sgRNA-mediated depletion of Rabggta led to loss of neurons, establishing a required role for Rab geranylgeranylation in neuronal viability.","method":"In vivo pooled CRISPR screening (CrAAVe-seq) with AAV-delivered sgRNA libraries in mouse brains; validated by neuronal survival assay","journal":"Nature neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo pooled CRISPR screen with validation; single study, single lab","pmids":["40847019"],"is_preprint":false}],"current_model":"RABGGTA encodes the alpha-subunit of Rab geranylgeranyl transferase (RabGGTase/GGTase II), the enzyme that catalyzes geranylgeranylation of Rab GTPases; loss-of-function (gunmetal mouse mutation, siRNA/AAV knockdown) reduces Rab prenylation and membrane association, impairing platelet biogenesis (via Rab27), hepatic insulin signaling (via RAB14→mTORC2→AKT), skeletal muscle GLUT4 translocation (via RAB8A), neuronal survival, and cancer cell proliferation—effects rescued by geranylgeranyl pyrophosphate supplementation."},"narrative":{"mechanistic_narrative":"RABGGTA encodes the alpha-subunit of Rab geranylgeranyl transferase (RabGGTase/GGTase II), the enzyme that catalyzes geranylgeranylation of Rab GTPases, a lipid modification required for their membrane association and function [PMID:10737774]. Loss-of-function established by the gunmetal mouse splice-acceptor mutation reduces RabGGTase activity and decreases geranylgeranylation and membrane association of Rab27, producing thrombocytopenia, prolonged bleeding, and reduced platelet granule contents [PMID:10737774]. Through prenylation of distinct Rab substrates, RABGGTA supports tissue-specific signaling: in liver it geranylgeranylates RAB14 to permit mTORC2 assembly and AKT(Ser473) phosphorylation in hepatic insulin signaling [PMID:34995578], while in skeletal muscle it acts via RAB8A to enable insulin-stimulated GLUT4 translocation and glucose uptake without affecting AKT phosphorylation [PMID:35961942]. RABGGTA is also required for cancer cell proliferation, mediating the anti-proliferative action of zoledronic acid [PMID:27462771], and is essential for neuronal survival in vivo [PMID:40847019]; across these settings the prenylation-dependent phenotypes are rescued by geranylgeranyl pyrophosphate supplementation [PMID:27462771, PMID:34995578].","teleology":[{"year":1997,"claim":"Resolved whether RABGGTA, despite tight physical linkage to TGM1, shares its differentiation-dependent regulation, establishing RABGGTA as an independently regulated, housekeeping-like gene.","evidence":"RT-PCR of RABGGTA and TGM1 in keratinocytes under multiple differentiation stimuli plus genomic structure characterization","pmids":["9196026"],"confidence":"Medium","gaps":["Does not define RABGGTA protein function","Promoter/regulatory elements driving RABGGTA expression not mapped"]},{"year":2000,"claim":"Established that RABGGTA encodes the alpha-subunit of RabGGTase and that its loss reduces Rab27 geranylgeranylation and membrane association, linking the enzyme directly to platelet biogenesis.","evidence":"Positional cloning of the gunmetal mouse splice mutation, platelet GGTase activity assay, and Rab27 geranylgeranylation/membrane-association assay","pmids":["10737774"],"confidence":"High","gaps":["Other Rab substrates not enumerated","Structural basis of substrate selection not addressed","Residual ~4-fold-reduced activity may mask null phenotype"]},{"year":2000,"claim":"Tested whether human platelet storage pool deficiencies arise from RABGGTA coding mutations, finding only polymorphisms and excluding RABGGTA coding lesions as the cause in these patients.","evidence":"Sequencing of the complete RABGGTA coding region and 5'-UTR in SPD patients and controls","pmids":["11136552"],"confidence":"Medium","gaps":["Regulatory/non-coding variants not excluded","Negative result does not establish a positive disease mechanism"]},{"year":2016,"claim":"Connected RABGGTA-mediated Rab geranylgeranylation to cancer cell proliferation and identified it as the effector of zoledronic acid's anti-cancer action.","evidence":"siRNA knockdown of RABGGTA in GBM and breast cancer lines, proliferation assay, and GGPP rescue","pmids":["27462771"],"confidence":"Medium","gaps":["Specific Rab substrate(s) mediating proliferation not identified","Single lab, two cell-line types"]},{"year":2022,"claim":"Defined a tissue-specific substrate axis in liver, showing RABGGTA geranylgeranylates RAB14 to enable mTORC2 assembly and AKT phosphorylation in hepatic insulin signaling.","evidence":"AAV8 liver-specific Rabggta knockdown in vivo, siRNA screen identifying RAB14, geranylgeranylation/AKT/mTORC2 assays, and GGPP rescue","pmids":["34995578"],"confidence":"High","gaps":["Direct enzyme–RAB14 binding not structurally resolved","How RAB14 prenylation regulates mTORC2 assembly mechanistically unclear"]},{"year":2022,"claim":"Showed the relevant Rab substrate differs by tissue, with RABGGTA acting through RAB8A in skeletal muscle to control GLUT4 translocation independent of AKT.","evidence":"AAV9 muscle-specific RABGGTA knockdown in vivo, RAB8A geranylgeranylation-site mutagenesis, GLUT4 translocation and glucose uptake assays","pmids":["35961942"],"confidence":"High","gaps":["Mechanism coupling RAB8A prenylation to GLUT4 vesicle trafficking not detailed","Why AKT signaling is spared in muscle but not liver unexplained"]},{"year":2025,"claim":"Established RABGGTA as essential for neuronal survival in vivo, extending Rab geranylgeranylation requirement to neuronal viability.","evidence":"In vivo pooled CRISPR screen (CrAAVe-seq) in mouse brain with neuronal survival validation","pmids":["40847019"],"confidence":"Medium","gaps":["Rab substrate(s) underlying neuronal survival not identified","Cell-death pathway engaged upon depletion uncharacterized"]},{"year":null,"claim":"It remains unresolved how RABGGTA selects among different Rab substrates to produce tissue-specific signaling outcomes and what its physiological role is in human disease.","evidence":"No discovery in the corpus addresses substrate-selection determinants or a human Mendelian disease linkage","pmids":[],"confidence":"Low","gaps":["No structural model of substrate recognition in the corpus","No causative human disease mutation identified","Determinants of tissue-specific Rab substrate usage unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,4,5]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,4,5]}],"localization":[],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,5]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0]}],"complexes":["Rab geranylgeranyl transferase (GGTase II)"],"partners":["RAB27","RAB14","RAB8A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q92696","full_name":"Geranylgeranyl transferase type-2 subunit alpha","aliases":["Geranylgeranyl transferase type II subunit alpha","Rab geranyl-geranyltransferase subunit alpha","Rab GG transferase alpha","Rab GGTase alpha","Rab geranylgeranyltransferase subunit alpha"],"length_aa":567,"mass_kda":65.1,"function":"Catalyzes the transfer of a geranylgeranyl moiety from geranylgeranyl diphosphate to both cysteines of Rab proteins with the C-terminal sequence -XXCC, -XCXC and -CCXX, such as RAB1A, RAB3A, RAB5A and RAB7A","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q92696/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/RABGGTA","classification":"Common Essential","n_dependent_lines":1201,"n_total_lines":1208,"dependency_fraction":0.9942052980132451},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000100949","cell_line_id":"CID000449","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"big_aggregates","grade":2}],"interactors":[{"gene":"RABGGTB","stoichiometry":10.0},{"gene":"CHM","stoichiometry":4.0},{"gene":"EEF1E1;EEF1E1-BLOC1S5","stoichiometry":0.2},{"gene":"CHML","stoichiometry":0.2},{"gene":"SEC13","stoichiometry":0.2},{"gene":"SEC31A","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000449","total_profiled":1310},"omim":[{"mim_id":"605837","title":"HECT DOMAIN AND RCC1-LIKE DOMAIN 2; HERC2","url":"https://www.omim.org/entry/605837"},{"mim_id":"601905","title":"RAB GERANYLGERANYL TRANSFERASE, ALPHA SUBUNIT; RABGGTA","url":"https://www.omim.org/entry/601905"},{"mim_id":"190195","title":"TRANSGLUTAMINASE 1; TGM1","url":"https://www.omim.org/entry/190195"},{"mim_id":"179080","title":"RAB GERANYLGERANYL TRANSFERASE, BETA SUBUNIT; RABGGTB","url":"https://www.omim.org/entry/179080"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"esophagus","ntpm":63.4}],"url":"https://www.proteinatlas.org/search/RABGGTA"},"hgnc":{"alias_symbol":["PTAR3"],"prev_symbol":[]},"alphafold":{"accession":"Q92696","domains":[{"cath_id":"1.25.40.120","chopping":"17-158","consensus_level":"medium","plddt":95.6167,"start":17,"end":158},{"cath_id":"2.60.40.1130","chopping":"246-344","consensus_level":"high","plddt":93.5343,"start":246,"end":344},{"cath_id":"-","chopping":"359-415","consensus_level":"high","plddt":97.0361,"start":359,"end":415},{"cath_id":"3.80.10.10","chopping":"427-566","consensus_level":"high","plddt":96.1166,"start":427,"end":566}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92696","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q92696-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q92696-F1-predicted_aligned_error_v6.png","plddt_mean":93.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RABGGTA","jax_strain_url":"https://www.jax.org/strain/search?query=RABGGTA"},"sequence":{"accession":"Q92696","fasta_url":"https://rest.uniprot.org/uniprotkb/Q92696.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q92696/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92696"}},"corpus_meta":[{"pmid":"18172690","id":"PMC_18172690","title":"Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression.","date":"2008","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18172690","citation_count":227,"is_preprint":false},{"pmid":"10737774","id":"PMC_10737774","title":"Rab geranylgeranyl transferase alpha mutation in the gunmetal mouse reduces Rab prenylation and platelet synthesis.","date":"2000","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/10737774","citation_count":131,"is_preprint":false},{"pmid":"27534615","id":"PMC_27534615","title":"Gene signatures associated with adaptive humoral immunity following seasonal influenza A/H1N1 vaccination.","date":"2016","source":"Genes and 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(NCX1).","date":"2017","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/28755400","citation_count":15,"is_preprint":false},{"pmid":"35905627","id":"PMC_35905627","title":"Triphenyltin exposure induced abnormal morphological colouration in adult male guppies (Poecilia reticulata).","date":"2022","source":"Ecotoxicology and environmental safety","url":"https://pubmed.ncbi.nlm.nih.gov/35905627","citation_count":13,"is_preprint":false},{"pmid":"29574663","id":"PMC_29574663","title":"Assessment of Protein Prenylation Pathway in Multiple Sclerosis Patients.","date":"2018","source":"Journal of molecular neuroscience : MN","url":"https://pubmed.ncbi.nlm.nih.gov/29574663","citation_count":10,"is_preprint":false},{"pmid":"39096797","id":"PMC_39096797","title":"Sequential window acquisition of all theoretical mass spectra (SWATH-MS) as an emerging proteomics approach for the discovery of dark-cutting beef biomarkers.","date":"2024","source":"Meat 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keratinocytes.","date":"1997","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/9196026","citation_count":6,"is_preprint":false},{"pmid":"11136552","id":"PMC_11136552","title":"5'-UTR structural organization, transcript expression, and mutational analysis of the human Rab geranylgeranyl transferase alpha-subunit (RABGGTA) gene.","date":"2000","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/11136552","citation_count":5,"is_preprint":false},{"pmid":"35961942","id":"PMC_35961942","title":"Geranylgeranyl pyrophosphate depletion by statins compromises skeletal muscle insulin sensitivity.","date":"2022","source":"Journal of cachexia, sarcopenia and muscle","url":"https://pubmed.ncbi.nlm.nih.gov/35961942","citation_count":5,"is_preprint":false},{"pmid":"23639161","id":"PMC_23639161","title":"Genetic characterization and in vivo image analysis of novel zebrafish Danio rerio pigment 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disorders","url":"https://pubmed.ncbi.nlm.nih.gov/40712510","citation_count":1,"is_preprint":false},{"pmid":"41892366","id":"PMC_41892366","title":"CpG Methylation of Protein Prenyltransferase Genes FNTA, FNTB, PGGT1B and RABGGTA in Cancer Cell Lines.","date":"2026","source":"Epigenomes","url":"https://pubmed.ncbi.nlm.nih.gov/41892366","citation_count":0,"is_preprint":false},{"pmid":"41938339","id":"PMC_41938339","title":"Machine learning identifies molecular targets of Di (2-ethylhexyl) phthalate in pulmonary arterial hypertension.","date":"2026","source":"Frontiers in bioinformatics","url":"https://pubmed.ncbi.nlm.nih.gov/41938339","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12457,"output_tokens":2212,"usd":0.035276,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9294,"output_tokens":2570,"usd":0.05536,"stage2_stop_reason":"end_turn"},"total_usd":0.090636,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"A G→A substitution mutation in a splice acceptor site within Rabggta (encoding the alpha-subunit of Rab geranylgeranyl transferase, RabGGTase/GGTase II) in the gunmetal mouse causes skipping of exon 1 and loss of start codon, reducing Rabggta protein and RabGGTase activity ~4-fold in platelets; this leads to significantly decreased geranylgeranylation and membrane association of Rab27, resulting in thrombocytopenia, prolonged bleeding, and reduced platelet granule contents.\",\n      \"method\": \"Positional cloning, splice-site mutation characterization, biochemical measurement of GGTase activity in platelets, and geranylgeranylation/membrane-association assay of Rab27 in mutant vs. wild-type platelets\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — positional cloning plus biochemical enzymatic activity assay plus substrate (Rab27) geranylgeranylation and membrane-association assay, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"10737774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The human RABGGTA gene (encoding the alpha-subunit of Rab geranylgeranyl transferase) is positioned in a tandem head-to-tail arrangement with the TGM1 gene, with the RABGGTA polyadenylation signal located only 2.3 kbp upstream of the TGM1 cap site; however, RT-PCR analysis under multiple differentiation conditions showed that RABGGTA expression in epidermal keratinocytes is unaffected by calcium concentration, retinoic acid, vitamin D3, or TPA, while TGM1 expression is strongly affected by these same stimuli—demonstrating the two genes are not functionally co-regulated despite close physical linkage.\",\n      \"method\": \"RT-PCR of RABGGTA and TGM1 expression in normal human epidermal keratinocytes under various differentiation conditions; genomic structure characterization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — RT-PCR expression analysis under multiple conditions, single lab, establishes negative functional co-regulation result\",\n      \"pmids\": [\"9196026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The 5'-UTR structure of the human RABGGTA gene shares organizational features with the mouse Rabggta gene (exon alpha upstream of intron alpha), and features of the 5'-UTR are consistent with a housekeeping gene; sequencing of the entire coding region in patients with platelet storage pool deficiencies (alpha-SPD, delta-SPD, gray platelet syndrome) identified several polymorphisms but no obvious disease-causing mutations, indicating these patients do not have RABGGTA coding mutations.\",\n      \"method\": \"Sequencing of complete coding region and 5'-UTR of RABGGTA in patients with platelet storage pool deficiencies and normal individuals; comparative genomic analysis\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — sequencing/structural characterization, single lab; establishes negative finding that SPD patients lack RABGGTA coding mutations\",\n      \"pmids\": [\"11136552\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Knockdown of RABGGTA (encoding a subunit of RabGGTase/GGTase II) in human cancer cell lines induces an anti-proliferative effect similar to zoledronic acid, and this effect is rescued by geranylgeranyl diphosphate (GGPP) supplementation, demonstrating that RABGGTA-mediated geranylgeranylation of Rab proteins mediates the anti-cancer mechanism of zoledronic acid.\",\n      \"method\": \"siRNA knockdown of RABGGTA in cancer cell lines (GBM, breast cancer); cell proliferation assay; GGPP rescue experiment\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD with defined proliferative phenotype plus GGPP rescue, single lab, two orthogonal approaches\",\n      \"pmids\": [\"27462771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AAV8-mediated knockdown of liver RABGGTA (the alpha-subunit of GGTase II) in vivo causes systemic glucose metabolism disorders; pharmacological and genetic inhibition of GGTase II disrupts hepatic insulin signaling by blocking geranylgeranylation of RAB14, which inhibits AKT (Ser473) phosphorylation and impairs mTORC2 complex assembly; GGPP supplementation rescues the defect.\",\n      \"method\": \"AAV8-mediated in vivo liver-specific Rabggta knockdown; siRNA screening to identify RAB14; geranylgeranylation assay; AKT phosphorylation assay; mTORC2 assembly assay; GGPP rescue in vitro and in vivo\",\n      \"journal\": \"Metabolism: clinical and experimental\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo AAV knockdown with glucose metabolism phenotype, siRNA identification of RAB14 substrate, AKT phosphorylation assay, mTORC2 assembly assay, and GGPP rescue; multiple orthogonal methods in single lab\",\n      \"pmids\": [\"34995578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AAV9-mediated knockdown of RABGGTA in skeletal muscle impairs glucose disposal in vivo without disrupting insulin signaling (AKT phosphorylation unaffected); geranylgeranylation deficiency of RAB8A (a GGTase II substrate) specifically inhibits insulin-stimulated GLUT4 translocation and glucose uptake in skeletal muscle cells, identifying RAB8A as the relevant Rab substrate downstream of RABGGTA in this tissue.\",\n      \"method\": \"AAV9-mediated in vivo skeletal muscle RABGGTA knockdown; glucose uptake assay; RAB8A geranylgeranylation-site mutation; GLUT4 translocation assay; AKT phosphorylation assay\",\n      \"journal\": \"Journal of cachexia, sarcopenia and muscle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo AAV knockdown with defined metabolic phenotype plus geranylgeranylation site mutagenesis of substrate RAB8A plus GLUT4 translocation assay; multiple orthogonal methods, single lab\",\n      \"pmids\": [\"35961942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In vivo CRISPR screening using CrAAVe-seq in mouse neurons validated Rabggta as an essential gene for neuronal survival; sgRNA-mediated depletion of Rabggta led to loss of neurons, establishing a required role for Rab geranylgeranylation in neuronal viability.\",\n      \"method\": \"In vivo pooled CRISPR screening (CrAAVe-seq) with AAV-delivered sgRNA libraries in mouse brains; validated by neuronal survival assay\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo pooled CRISPR screen with validation; single study, single lab\",\n      \"pmids\": [\"40847019\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RABGGTA encodes the alpha-subunit of Rab geranylgeranyl transferase (RabGGTase/GGTase II), the enzyme that catalyzes geranylgeranylation of Rab GTPases; loss-of-function (gunmetal mouse mutation, siRNA/AAV knockdown) reduces Rab prenylation and membrane association, impairing platelet biogenesis (via Rab27), hepatic insulin signaling (via RAB14→mTORC2→AKT), skeletal muscle GLUT4 translocation (via RAB8A), neuronal survival, and cancer cell proliferation—effects rescued by geranylgeranyl pyrophosphate supplementation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RABGGTA encodes the alpha-subunit of Rab geranylgeranyl transferase (RabGGTase/GGTase II), the enzyme that catalyzes geranylgeranylation of Rab GTPases, a lipid modification required for their membrane association and function [#0]. Loss-of-function established by the gunmetal mouse splice-acceptor mutation reduces RabGGTase activity and decreases geranylgeranylation and membrane association of Rab27, producing thrombocytopenia, prolonged bleeding, and reduced platelet granule contents [#0]. Through prenylation of distinct Rab substrates, RABGGTA supports tissue-specific signaling: in liver it geranylgeranylates RAB14 to permit mTORC2 assembly and AKT(Ser473) phosphorylation in hepatic insulin signaling [#4], while in skeletal muscle it acts via RAB8A to enable insulin-stimulated GLUT4 translocation and glucose uptake without affecting AKT phosphorylation [#5]. RABGGTA is also required for cancer cell proliferation, mediating the anti-proliferative action of zoledronic acid [#3], and is essential for neuronal survival in vivo [#6]; across these settings the prenylation-dependent phenotypes are rescued by geranylgeranyl pyrophosphate supplementation [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Resolved whether RABGGTA, despite tight physical linkage to TGM1, shares its differentiation-dependent regulation, establishing RABGGTA as an independently regulated, housekeeping-like gene.\",\n      \"evidence\": \"RT-PCR of RABGGTA and TGM1 in keratinocytes under multiple differentiation stimuli plus genomic structure characterization\",\n      \"pmids\": [\"9196026\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not define RABGGTA protein function\", \"Promoter/regulatory elements driving RABGGTA expression not mapped\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that RABGGTA encodes the alpha-subunit of RabGGTase and that its loss reduces Rab27 geranylgeranylation and membrane association, linking the enzyme directly to platelet biogenesis.\",\n      \"evidence\": \"Positional cloning of the gunmetal mouse splice mutation, platelet GGTase activity assay, and Rab27 geranylgeranylation/membrane-association assay\",\n      \"pmids\": [\"10737774\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Other Rab substrates not enumerated\", \"Structural basis of substrate selection not addressed\", \"Residual ~4-fold-reduced activity may mask null phenotype\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Tested whether human platelet storage pool deficiencies arise from RABGGTA coding mutations, finding only polymorphisms and excluding RABGGTA coding lesions as the cause in these patients.\",\n      \"evidence\": \"Sequencing of the complete RABGGTA coding region and 5'-UTR in SPD patients and controls\",\n      \"pmids\": [\"11136552\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Regulatory/non-coding variants not excluded\", \"Negative result does not establish a positive disease mechanism\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Connected RABGGTA-mediated Rab geranylgeranylation to cancer cell proliferation and identified it as the effector of zoledronic acid's anti-cancer action.\",\n      \"evidence\": \"siRNA knockdown of RABGGTA in GBM and breast cancer lines, proliferation assay, and GGPP rescue\",\n      \"pmids\": [\"27462771\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific Rab substrate(s) mediating proliferation not identified\", \"Single lab, two cell-line types\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a tissue-specific substrate axis in liver, showing RABGGTA geranylgeranylates RAB14 to enable mTORC2 assembly and AKT phosphorylation in hepatic insulin signaling.\",\n      \"evidence\": \"AAV8 liver-specific Rabggta knockdown in vivo, siRNA screen identifying RAB14, geranylgeranylation/AKT/mTORC2 assays, and GGPP rescue\",\n      \"pmids\": [\"34995578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct enzyme–RAB14 binding not structurally resolved\", \"How RAB14 prenylation regulates mTORC2 assembly mechanistically unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed the relevant Rab substrate differs by tissue, with RABGGTA acting through RAB8A in skeletal muscle to control GLUT4 translocation independent of AKT.\",\n      \"evidence\": \"AAV9 muscle-specific RABGGTA knockdown in vivo, RAB8A geranylgeranylation-site mutagenesis, GLUT4 translocation and glucose uptake assays\",\n      \"pmids\": [\"35961942\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism coupling RAB8A prenylation to GLUT4 vesicle trafficking not detailed\", \"Why AKT signaling is spared in muscle but not liver unexplained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established RABGGTA as essential for neuronal survival in vivo, extending Rab geranylgeranylation requirement to neuronal viability.\",\n      \"evidence\": \"In vivo pooled CRISPR screen (CrAAVe-seq) in mouse brain with neuronal survival validation\",\n      \"pmids\": [\"40847019\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Rab substrate(s) underlying neuronal survival not identified\", \"Cell-death pathway engaged upon depletion uncharacterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how RABGGTA selects among different Rab substrates to produce tissue-specific signaling outcomes and what its physiological role is in human disease.\",\n      \"evidence\": \"No discovery in the corpus addresses substrate-selection determinants or a human Mendelian disease linkage\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of substrate recognition in the corpus\", \"No causative human disease mutation identified\", \"Determinants of tissue-specific Rab substrate usage unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 4, 5]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 5]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\"Rab geranylgeranyl transferase (GGTase II)\"],\n    \"partners\": [\"RAB27\", \"RAB14\", \"RAB8A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}