{"gene":"RCBTB2","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1998,"finding":"CHC1L (RCBTB2) encodes a ubiquitously expressed protein with an N-terminal half showing strong homology to the seven tandem repeat structure of RCC1, a guanine nucleotide exchange factor (GEF) for the Ras-related GTPase Ran, classifying it as a new member of the RCC1-related GEF family. The gene spans 30 kb, comprises 14 exons, and maps to chromosome 13q14.3.","method":"cDNA cloning, genomic characterization, sequence homology analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — structural/sequence-based classification with genomic characterization; GEF activity inferred from homology, not directly demonstrated biochemically","pmids":["9806834"],"is_preprint":false},{"year":2002,"finding":"CHC1L (RCBTB2) is alternatively spliced at its 5' end to produce two protein isoforms of 551 and 526 amino acids. In prostate cancer, reduced expression is specifically attributable to decreased levels of the 551 aa isoform.","method":"Quantitative real-time RT-PCR, isoform expression analysis in primary prostate tumors vs. normal tissue","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct isoform-specific expression quantification in patient samples, single lab","pmids":["12115502"],"is_preprint":false},{"year":2012,"finding":"Mouse RC/BTB2 (RCBTB2 ortholog) contains three RCC1 domains in the N-terminus and a BTB domain in the C-terminus. In spermatids, RC/BTB2 co-localizes with acrosomal markers sp56 and peanut lectin, identifying it as an acrosomal protein. In transfected CHO cells, a GFP-tagged full-length RC/BTB2 and a GFP-tagged BTB domain localize to vesicles near the nuclear membrane, whereas the isolated RCC1 domain distributes throughout the cytoplasm, indicating the BTB domain mediates subcellular localization of the full-length protein.","method":"Immunofluorescence co-localization with acrosomal markers, GFP-tagged domain constructs in transfected CHO cells, Western blot during spermatogenesis time course","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization experiments with domain dissection in cell transfection, single lab, multiple methods","pmids":["22768142"],"is_preprint":false},{"year":2015,"finding":"RC/BTB2 (RCBTB2) localizes to Golgi bodies and centrosomes in NIH3T3 and IMCD3 cells. Stable shRNA-mediated knockdown of Rc/btb2 significantly reduces the percentage of cells forming primary cilia and shortens cilia length. Exogenous re-expression of RC/BTB2 in knockdown cells restores ciliogenesis, establishing RC/BTB2 as a necessary component of primary cilia formation, potentially through cargo transport from Golgi to centrosomes.","method":"Stable shRNA knockdown, immunofluorescence localization, cilia length measurement, rescue by exogenous expression in NIH3T3 and IMCD3 cell lines","journal":"Cytoskeleton (Hoboken, N.J.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with defined cellular phenotype, subcellular localization, and rescue experiment in two independent cell lines within a single study","pmids":["25762510"],"is_preprint":false},{"year":2015,"finding":"Chc1L knockout mice show an exaggerated proliferative response in bone marrow and spleen cells and develop histiocytic sarcoma or histiocyte-associated lymphoma by approximately two years of age, demonstrating that Chc1L functions as a tumor suppressor for histiocyte-rich neoplasms in vivo.","method":"Chc1L knockout mouse generation, histopathological analysis, ex vivo proliferation assay of bone marrow and spleen cells","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — defined loss-of-function (knockout mouse) with specific cellular and tumor phenotype readouts, replicated across heterozygous and homozygous animals","pmids":["26291700"],"is_preprint":false},{"year":2015,"finding":"RC/BTB2 (RCBTB2) is a binding partner of SPAG16S (sperm associated antigen 16S), a regulator of spermiogenesis, placing RC/BTB2 in the SPAG16S-dependent pathway of flagella and cilia formation.","method":"Protein-protein interaction (binding partner identification, cited as established prior to the 2015 ciliogenesis study)","journal":"Cytoskeleton (Hoboken, N.J.)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — interaction reported as established fact in abstract without detailing the specific binding assay used in this paper; single reference point","pmids":["25762510"],"is_preprint":false},{"year":2025,"finding":"RCBTB2 functions as a ubiquitin ligase that directly interacts with GPAA1 and promotes its ubiquitin-mediated proteasomal degradation (GPAA1 protein is downregulated without changes in mRNA levels upon RCBTB2 overexpression). RCBTB2 overexpression inhibits DU145 prostate cancer cell proliferation, migration, invasion, and epithelial-mesenchymal transition, and reduces xenograft tumor growth. GPAA1 knockdown recapitulates these phenotypes and reduces expression of aggrephagy-related factors such as p62.","method":"RCBTB2 overexpression cell line, co-immunoprecipitation, immunofluorescence co-localization, CCK-8 proliferation assay, scratch/Transwell migration-invasion assay, nude mouse xenograft model, GPAA1 knockdown, multi-omics analysis","journal":"American journal of cancer research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct interaction confirmed by Co-IP and co-localization, ubiquitin-mediated degradation established by protein-but-not-mRNA downregulation, multiple orthogonal functional assays and in vivo model in single study","pmids":["41244118"],"is_preprint":false},{"year":2023,"finding":"In normal oral mucosa, CHC1L (RCBTB2) protein displays predominantly nuclear localization. In oral squamous cell carcinoma, CHC1L protein undergoes subcellular mislocalization with significantly increased plasma membrane staining and reduced nuclear staining, suggesting dysregulation of its normal nuclear function in malignancy.","method":"Immunohistochemistry with quantitative subcellular localization scoring in OSCC vs. normal oral mucosa specimens","journal":"European journal of dentistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, descriptive IHC-based localization, no functional consequence directly demonstrated","pmids":["37311552"],"is_preprint":false}],"current_model":"RCBTB2 (CHC1L) is a multi-domain protein containing RCC1-like GEF domains and a C-terminal BTB domain; it functions as a ubiquitin ligase that targets GPAA1 for proteasomal degradation to suppress prostate cancer progression, localizes to Golgi bodies and centrosomes to mediate primary cilia formation (with its BTB domain directing subcellular localization), acts as a tumor suppressor in vivo (Chc1L knockout mice develop histiocytic sarcomas), and is a binding partner of SPAG16S during spermiogenesis."},"narrative":{"mechanistic_narrative":"RCBTB2 (CHC1L) is a multi-domain protein that combines an N-terminal RCC1-like seven-bladed repeat region with a C-terminal BTB domain, acting both as a regulator of microtubule-organizing-center function and as a tumor suppressor [PMID:9806834, PMID:26291700]. Through its BTB domain it is directed to vesicular and perinuclear compartments, and it localizes to Golgi bodies and centrosomes where it is required for primary cilium formation: loss of RCBTB2 reduces ciliogenesis and shortens cilia, a defect reversed by re-expression, consistent with a role in cargo transport from Golgi to centrosome [PMID:22768142, PMID:25762510]. RCBTB2 functions as a ubiquitin ligase, directly binding GPAA1 and driving its ubiquitin-mediated proteasomal degradation, and its overexpression suppresses prostate cancer cell proliferation, migration, invasion, epithelial-mesenchymal transition, and xenograft growth [PMID:41244118]. Consistent with a tumor-suppressive role, Chc1L-knockout mice develop histiocytic sarcoma, and reduced expression of its 551-amino-acid isoform is seen in prostate cancer [PMID:12115502, PMID:26291700]. The catalytic basis of its inferred RCC1-like GEF activity has not been directly demonstrated in the available corpus.","teleology":[{"year":1998,"claim":"Establishing the gene's domain architecture answered what protein family RCBTB2 belongs to, predicting a guanine-nucleotide-exchange-related function from its RCC1 homology.","evidence":"cDNA cloning, genomic characterization, and sequence homology analysis mapping the gene to 13q14.3","pmids":["9806834"],"confidence":"Medium","gaps":["GEF activity inferred from homology, never demonstrated biochemically","No substrate GTPase identified","Function of the C-terminal region not addressed"]},{"year":2002,"claim":"Isoform-resolved expression profiling addressed which RCBTB2 product is dysregulated in cancer, linking specific loss of the 551 aa isoform to prostate tumors.","evidence":"Quantitative RT-PCR isoform analysis in primary prostate tumors vs. normal tissue","pmids":["12115502"],"confidence":"Medium","gaps":["Correlation only; no causal mechanism for tumor suppression shown","Functional difference between the 551 and 526 aa isoforms unknown"]},{"year":2012,"claim":"Domain-dissection localization studies answered how RCBTB2 is targeted within the cell, showing the BTB domain rather than the RCC1 region directs subcellular localization, and placed the protein at the acrosome during spermatogenesis.","evidence":"Immunofluorescence co-localization with acrosomal markers and GFP-tagged domain constructs in transfected CHO cells","pmids":["22768142"],"confidence":"Medium","gaps":["Molecular basis of BTB-mediated targeting not defined","Acrosomal function not tested by loss-of-function","Done in mouse ortholog and CHO cells"]},{"year":2015,"claim":"Loss-of-function with rescue answered whether RCBTB2 has a cellular role at the centrosome, establishing it as a necessary component of primary cilium formation.","evidence":"Stable shRNA knockdown, Golgi/centrosome immunolocalization, cilia length measurement, and rescue by re-expression in NIH3T3 and IMCD3 cells","pmids":["25762510"],"confidence":"High","gaps":["Proposed Golgi-to-centrosome cargo transport mechanism not directly demonstrated","No identified ciliary cargo or transport machinery partner"]},{"year":2015,"claim":"A whole-animal knockout addressed whether RCBTB2 is a tumor suppressor in vivo, demonstrating that its loss drives histiocyte proliferation and neoplasia.","evidence":"Chc1L knockout mouse with histopathology and ex vivo proliferation assays of bone marrow and spleen cells","pmids":["26291700"],"confidence":"High","gaps":["Molecular pathway linking loss to histiocyte proliferation not defined","Tumor-suppressor mechanism not connected to ciliary or ubiquitin functions"]},{"year":2015,"claim":"A reported interaction placed RCBTB2 in a spermiogenesis signaling pathway, naming SPAG16S as a partner relevant to flagella and cilia formation.","evidence":"Binding-partner identification cited within the ciliogenesis study","pmids":["25762510"],"confidence":"Low","gaps":["Specific binding assay not detailed; single reference point","Functional consequence of the interaction not tested","No reciprocal validation"]},{"year":2023,"claim":"Tumor-versus-normal localization scoring addressed where RCBTB2 normally acts, indicating predominantly nuclear localization that is lost with plasma-membrane mislocalization in oral squamous cell carcinoma.","evidence":"Quantitative immunohistochemical subcellular localization scoring in OSCC vs. normal oral mucosa","pmids":["37311552"],"confidence":"Low","gaps":["Descriptive IHC only; no functional consequence demonstrated","Nuclear function of RCBTB2 not characterized","Inconsistent with Golgi/centrosome localization reported elsewhere; not reconciled"]},{"year":2025,"claim":"Identification of an enzymatic activity and substrate answered how RCBTB2 suppresses tumor progression at the molecular level, showing it is a ubiquitin ligase that degrades GPAA1.","evidence":"RCBTB2 overexpression, Co-IP, co-localization, protein-but-not-mRNA downregulation of GPAA1, proliferation/migration/invasion assays, GPAA1 knockdown, and a nude-mouse xenograft model","pmids":["41244118"],"confidence":"High","gaps":["E3 ligase catalytic machinery and ubiquitination site not defined","Relationship between ligase activity and the RCC1/BTB domains unresolved","Connection to ciliary and tumor-suppressor phenotypes not integrated"]},{"year":null,"claim":"How RCBTB2's distinct activities — RCC1-like domain, BTB-mediated localization, ciliogenesis, and GPAA1-directed ubiquitin ligase function — mechanistically integrate into a single tumor-suppressive program remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No direct demonstration of RCC1-like GEF activity or a target GTPase","Structural basis of substrate recognition by the ligase unknown","Conflicting subcellular localization reports (nuclear vs. Golgi/centrosome) not reconciled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[6]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[6]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[3]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[3]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[3]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[6]}],"complexes":[],"partners":["GPAA1","SPAG16"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O95199","full_name":"RCC1 and BTB domain-containing protein 2","aliases":["Chromosome condensation 1-like","CHC1-L","RCC1-like G exchanging factor","Regulator of chromosome condensation and BTB domain-containing protein 2"],"length_aa":551,"mass_kda":60.3,"function":"","subcellular_location":"Cytoplasmic vesicle, secretory vesicle, acrosome","url":"https://www.uniprot.org/uniprotkb/O95199/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RCBTB2","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ULK1","stoichiometry":10.0},{"gene":"ULK3","stoichiometry":10.0},{"gene":"VRK3","stoichiometry":10.0},{"gene":"ATXN2L","stoichiometry":0.2},{"gene":"CAPRIN1","stoichiometry":0.2},{"gene":"CLASP1","stoichiometry":0.2},{"gene":"CLASP2","stoichiometry":0.2},{"gene":"FXR1","stoichiometry":0.2},{"gene":"HDAC2","stoichiometry":0.2},{"gene":"HDAC3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/RCBTB2","total_profiled":1310},"omim":[{"mim_id":"607867","title":"RCC1 DOMAIN- AND BTB DOMAIN-CONTAINING PROTEIN 1; RCBTB1","url":"https://www.omim.org/entry/607867"},{"mim_id":"603524","title":"RCC1 DOMAIN- AND BTB DOMAIN-CONTAINING PROTEIN 2; RCBTB2","url":"https://www.omim.org/entry/603524"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Golgi apparatus","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RCBTB2"},"hgnc":{"alias_symbol":[],"prev_symbol":["CHC1L"]},"alphafold":{"accession":"O95199","domains":[{"cath_id":"2.130.10.30","chopping":"27-370","consensus_level":"medium","plddt":96.2969,"start":27,"end":370},{"cath_id":"3.30.710.10","chopping":"379-545","consensus_level":"medium","plddt":88.9509,"start":379,"end":545}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95199","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95199-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95199-F1-predicted_aligned_error_v6.png","plddt_mean":90.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RCBTB2","jax_strain_url":"https://www.jax.org/strain/search?query=RCBTB2"},"sequence":{"accession":"O95199","fasta_url":"https://rest.uniprot.org/uniprotkb/O95199.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95199/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95199"}},"corpus_meta":[{"pmid":"18353163","id":"PMC_18353163","title":"Low expression of ZHX2, but not RCBTB2 or RAN, is associated with poor outcome in multiple myeloma.","date":"2008","source":"British journal of haematology","url":"https://pubmed.ncbi.nlm.nih.gov/18353163","citation_count":30,"is_preprint":false},{"pmid":"12115502","id":"PMC_12115502","title":"CHC1-L, a candidate gene for prostate carcinogenesis at 13q14.2, is frequently affected by loss of heterozygosity and underexpressed in human prostate cancer.","date":"2002","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/12115502","citation_count":23,"is_preprint":false},{"pmid":"9806834","id":"PMC_9806834","title":"cDNA cloning, gene characterization and 13q14.3 chromosomal assignment of CHC1-L, a chromosome condensation regulator-like guanine nucleotide exchange factor.","date":"1998","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/9806834","citation_count":19,"is_preprint":false},{"pmid":"20568903","id":"PMC_20568903","title":"Expression of RAN, ZHX-2, and CHC1L genes in multiple myeloma patients and in myeloma cell lines treated with HDAC and Dnmts inhibitors.","date":"2010","source":"Neoplasma","url":"https://pubmed.ncbi.nlm.nih.gov/20568903","citation_count":13,"is_preprint":false},{"pmid":"14504426","id":"PMC_14504426","title":"A culture device demonstrates that hydrostatic pressure increases mRNA of RGS5 in neuroblastoma and CHC1-L in lymphocytic cells.","date":"2003","source":"Cells, tissues, organs","url":"https://pubmed.ncbi.nlm.nih.gov/14504426","citation_count":13,"is_preprint":false},{"pmid":"25762510","id":"PMC_25762510","title":"RC/BTB2 is essential for formation of primary cilia in mammalian cells.","date":"2015","source":"Cytoskeleton (Hoboken, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/25762510","citation_count":6,"is_preprint":false},{"pmid":"22768142","id":"PMC_22768142","title":"Mouse RC/BTB2, a member of the RCC1 superfamily, localizes to spermatid acrosomal vesicles.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22768142","citation_count":5,"is_preprint":false},{"pmid":"26291700","id":"PMC_26291700","title":"Chromosome Condensation 1-Like (Chc1L) Is a Novel Tumor Suppressor Involved in Development of Histiocyte-Rich Neoplasms.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26291700","citation_count":2,"is_preprint":false},{"pmid":"37311552","id":"PMC_37311552","title":"Preliminary Study on the Expression of CLLD7 and CHC1L Proteins in Oral Squamous Cell Carcinoma.","date":"2023","source":"European journal of dentistry","url":"https://pubmed.ncbi.nlm.nih.gov/37311552","citation_count":1,"is_preprint":false},{"pmid":"39091920","id":"PMC_39091920","title":"Familial 46, XY Disorder of Sexual Development identified in a Ph+BCR::ABL1 Acute Lymphoblastic Leukemia septuagenarian female with RCBTB2::LPAR6 fusion gene: a case report.","date":"2024","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/39091920","citation_count":1,"is_preprint":false},{"pmid":"38679985","id":"PMC_38679985","title":"Expression of CLLD7 and CHC1L Proteins in Oral Epithelial Dysplasia in a Group of Thai Patients.","date":"2024","source":"Asian Pacific journal of cancer prevention : APJCP","url":"https://pubmed.ncbi.nlm.nih.gov/38679985","citation_count":0,"is_preprint":false},{"pmid":"41244118","id":"PMC_41244118","title":"The ubiquitin ligase RCBTB2 regulates aggrephagy and inhibits prostate cancer progression by targeting GPAA1 for degradation.","date":"2025","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/41244118","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8269,"output_tokens":2200,"usd":0.028903,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9220,"output_tokens":2990,"usd":0.060425,"stage2_stop_reason":"end_turn"},"total_usd":0.089328,"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\": 1998,\n      \"finding\": \"CHC1L (RCBTB2) encodes a ubiquitously expressed protein with an N-terminal half showing strong homology to the seven tandem repeat structure of RCC1, a guanine nucleotide exchange factor (GEF) for the Ras-related GTPase Ran, classifying it as a new member of the RCC1-related GEF family. The gene spans 30 kb, comprises 14 exons, and maps to chromosome 13q14.3.\",\n      \"method\": \"cDNA cloning, genomic characterization, sequence homology analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — structural/sequence-based classification with genomic characterization; GEF activity inferred from homology, not directly demonstrated biochemically\",\n      \"pmids\": [\"9806834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CHC1L (RCBTB2) is alternatively spliced at its 5' end to produce two protein isoforms of 551 and 526 amino acids. In prostate cancer, reduced expression is specifically attributable to decreased levels of the 551 aa isoform.\",\n      \"method\": \"Quantitative real-time RT-PCR, isoform expression analysis in primary prostate tumors vs. normal tissue\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct isoform-specific expression quantification in patient samples, single lab\",\n      \"pmids\": [\"12115502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Mouse RC/BTB2 (RCBTB2 ortholog) contains three RCC1 domains in the N-terminus and a BTB domain in the C-terminus. In spermatids, RC/BTB2 co-localizes with acrosomal markers sp56 and peanut lectin, identifying it as an acrosomal protein. In transfected CHO cells, a GFP-tagged full-length RC/BTB2 and a GFP-tagged BTB domain localize to vesicles near the nuclear membrane, whereas the isolated RCC1 domain distributes throughout the cytoplasm, indicating the BTB domain mediates subcellular localization of the full-length protein.\",\n      \"method\": \"Immunofluorescence co-localization with acrosomal markers, GFP-tagged domain constructs in transfected CHO cells, Western blot during spermatogenesis time course\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization experiments with domain dissection in cell transfection, single lab, multiple methods\",\n      \"pmids\": [\"22768142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RC/BTB2 (RCBTB2) localizes to Golgi bodies and centrosomes in NIH3T3 and IMCD3 cells. Stable shRNA-mediated knockdown of Rc/btb2 significantly reduces the percentage of cells forming primary cilia and shortens cilia length. Exogenous re-expression of RC/BTB2 in knockdown cells restores ciliogenesis, establishing RC/BTB2 as a necessary component of primary cilia formation, potentially through cargo transport from Golgi to centrosomes.\",\n      \"method\": \"Stable shRNA knockdown, immunofluorescence localization, cilia length measurement, rescue by exogenous expression in NIH3T3 and IMCD3 cell lines\",\n      \"journal\": \"Cytoskeleton (Hoboken, N.J.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with defined cellular phenotype, subcellular localization, and rescue experiment in two independent cell lines within a single study\",\n      \"pmids\": [\"25762510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Chc1L knockout mice show an exaggerated proliferative response in bone marrow and spleen cells and develop histiocytic sarcoma or histiocyte-associated lymphoma by approximately two years of age, demonstrating that Chc1L functions as a tumor suppressor for histiocyte-rich neoplasms in vivo.\",\n      \"method\": \"Chc1L knockout mouse generation, histopathological analysis, ex vivo proliferation assay of bone marrow and spleen cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — defined loss-of-function (knockout mouse) with specific cellular and tumor phenotype readouts, replicated across heterozygous and homozygous animals\",\n      \"pmids\": [\"26291700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RC/BTB2 (RCBTB2) is a binding partner of SPAG16S (sperm associated antigen 16S), a regulator of spermiogenesis, placing RC/BTB2 in the SPAG16S-dependent pathway of flagella and cilia formation.\",\n      \"method\": \"Protein-protein interaction (binding partner identification, cited as established prior to the 2015 ciliogenesis study)\",\n      \"journal\": \"Cytoskeleton (Hoboken, N.J.)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — interaction reported as established fact in abstract without detailing the specific binding assay used in this paper; single reference point\",\n      \"pmids\": [\"25762510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RCBTB2 functions as a ubiquitin ligase that directly interacts with GPAA1 and promotes its ubiquitin-mediated proteasomal degradation (GPAA1 protein is downregulated without changes in mRNA levels upon RCBTB2 overexpression). RCBTB2 overexpression inhibits DU145 prostate cancer cell proliferation, migration, invasion, and epithelial-mesenchymal transition, and reduces xenograft tumor growth. GPAA1 knockdown recapitulates these phenotypes and reduces expression of aggrephagy-related factors such as p62.\",\n      \"method\": \"RCBTB2 overexpression cell line, co-immunoprecipitation, immunofluorescence co-localization, CCK-8 proliferation assay, scratch/Transwell migration-invasion assay, nude mouse xenograft model, GPAA1 knockdown, multi-omics analysis\",\n      \"journal\": \"American journal of cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction confirmed by Co-IP and co-localization, ubiquitin-mediated degradation established by protein-but-not-mRNA downregulation, multiple orthogonal functional assays and in vivo model in single study\",\n      \"pmids\": [\"41244118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In normal oral mucosa, CHC1L (RCBTB2) protein displays predominantly nuclear localization. In oral squamous cell carcinoma, CHC1L protein undergoes subcellular mislocalization with significantly increased plasma membrane staining and reduced nuclear staining, suggesting dysregulation of its normal nuclear function in malignancy.\",\n      \"method\": \"Immunohistochemistry with quantitative subcellular localization scoring in OSCC vs. normal oral mucosa specimens\",\n      \"journal\": \"European journal of dentistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, descriptive IHC-based localization, no functional consequence directly demonstrated\",\n      \"pmids\": [\"37311552\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RCBTB2 (CHC1L) is a multi-domain protein containing RCC1-like GEF domains and a C-terminal BTB domain; it functions as a ubiquitin ligase that targets GPAA1 for proteasomal degradation to suppress prostate cancer progression, localizes to Golgi bodies and centrosomes to mediate primary cilia formation (with its BTB domain directing subcellular localization), acts as a tumor suppressor in vivo (Chc1L knockout mice develop histiocytic sarcomas), and is a binding partner of SPAG16S during spermiogenesis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RCBTB2 (CHC1L) is a multi-domain protein that combines an N-terminal RCC1-like seven-bladed repeat region with a C-terminal BTB domain, acting both as a regulator of microtubule-organizing-center function and as a tumor suppressor [#0, #4]. Through its BTB domain it is directed to vesicular and perinuclear compartments, and it localizes to Golgi bodies and centrosomes where it is required for primary cilium formation: loss of RCBTB2 reduces ciliogenesis and shortens cilia, a defect reversed by re-expression, consistent with a role in cargo transport from Golgi to centrosome [#2, #3]. RCBTB2 functions as a ubiquitin ligase, directly binding GPAA1 and driving its ubiquitin-mediated proteasomal degradation, and its overexpression suppresses prostate cancer cell proliferation, migration, invasion, epithelial-mesenchymal transition, and xenograft growth [#6]. Consistent with a tumor-suppressive role, Chc1L-knockout mice develop histiocytic sarcoma, and reduced expression of its 551-amino-acid isoform is seen in prostate cancer [#1, #4]. The catalytic basis of its inferred RCC1-like GEF activity has not been directly demonstrated in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing the gene's domain architecture answered what protein family RCBTB2 belongs to, predicting a guanine-nucleotide-exchange-related function from its RCC1 homology.\",\n      \"evidence\": \"cDNA cloning, genomic characterization, and sequence homology analysis mapping the gene to 13q14.3\",\n      \"pmids\": [\"9806834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"GEF activity inferred from homology, never demonstrated biochemically\",\n        \"No substrate GTPase identified\",\n        \"Function of the C-terminal region not addressed\"\n      ]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Isoform-resolved expression profiling addressed which RCBTB2 product is dysregulated in cancer, linking specific loss of the 551 aa isoform to prostate tumors.\",\n      \"evidence\": \"Quantitative RT-PCR isoform analysis in primary prostate tumors vs. normal tissue\",\n      \"pmids\": [\"12115502\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Correlation only; no causal mechanism for tumor suppression shown\",\n        \"Functional difference between the 551 and 526 aa isoforms unknown\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Domain-dissection localization studies answered how RCBTB2 is targeted within the cell, showing the BTB domain rather than the RCC1 region directs subcellular localization, and placed the protein at the acrosome during spermatogenesis.\",\n      \"evidence\": \"Immunofluorescence co-localization with acrosomal markers and GFP-tagged domain constructs in transfected CHO cells\",\n      \"pmids\": [\"22768142\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular basis of BTB-mediated targeting not defined\",\n        \"Acrosomal function not tested by loss-of-function\",\n        \"Done in mouse ortholog and CHO cells\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Loss-of-function with rescue answered whether RCBTB2 has a cellular role at the centrosome, establishing it as a necessary component of primary cilium formation.\",\n      \"evidence\": \"Stable shRNA knockdown, Golgi/centrosome immunolocalization, cilia length measurement, and rescue by re-expression in NIH3T3 and IMCD3 cells\",\n      \"pmids\": [\"25762510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Proposed Golgi-to-centrosome cargo transport mechanism not directly demonstrated\",\n        \"No identified ciliary cargo or transport machinery partner\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"A whole-animal knockout addressed whether RCBTB2 is a tumor suppressor in vivo, demonstrating that its loss drives histiocyte proliferation and neoplasia.\",\n      \"evidence\": \"Chc1L knockout mouse with histopathology and ex vivo proliferation assays of bone marrow and spleen cells\",\n      \"pmids\": [\"26291700\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular pathway linking loss to histiocyte proliferation not defined\",\n        \"Tumor-suppressor mechanism not connected to ciliary or ubiquitin functions\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"A reported interaction placed RCBTB2 in a spermiogenesis signaling pathway, naming SPAG16S as a partner relevant to flagella and cilia formation.\",\n      \"evidence\": \"Binding-partner identification cited within the ciliogenesis study\",\n      \"pmids\": [\"25762510\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Specific binding assay not detailed; single reference point\",\n        \"Functional consequence of the interaction not tested\",\n        \"No reciprocal validation\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Tumor-versus-normal localization scoring addressed where RCBTB2 normally acts, indicating predominantly nuclear localization that is lost with plasma-membrane mislocalization in oral squamous cell carcinoma.\",\n      \"evidence\": \"Quantitative immunohistochemical subcellular localization scoring in OSCC vs. normal oral mucosa\",\n      \"pmids\": [\"37311552\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Descriptive IHC only; no functional consequence demonstrated\",\n        \"Nuclear function of RCBTB2 not characterized\",\n        \"Inconsistent with Golgi/centrosome localization reported elsewhere; not reconciled\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of an enzymatic activity and substrate answered how RCBTB2 suppresses tumor progression at the molecular level, showing it is a ubiquitin ligase that degrades GPAA1.\",\n      \"evidence\": \"RCBTB2 overexpression, Co-IP, co-localization, protein-but-not-mRNA downregulation of GPAA1, proliferation/migration/invasion assays, GPAA1 knockdown, and a nude-mouse xenograft model\",\n      \"pmids\": [\"41244118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"E3 ligase catalytic machinery and ubiquitination site not defined\",\n        \"Relationship between ligase activity and the RCC1/BTB domains unresolved\",\n        \"Connection to ciliary and tumor-suppressor phenotypes not integrated\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RCBTB2's distinct activities — RCC1-like domain, BTB-mediated localization, ciliogenesis, and GPAA1-directed ubiquitin ligase function — mechanistically integrate into a single tumor-suppressive program remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No direct demonstration of RCC1-like GEF activity or a target GTPase\",\n        \"Structural basis of substrate recognition by the ligase unknown\",\n        \"Conflicting subcellular localization reports (nuclear vs. Golgi/centrosome) not reconciled\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GPAA1\", \"SPAG16\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":4,"faith_total":4,"faith_pct":100.0}}