{"gene":"NIFK","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2001,"finding":"NIFK (hNIFK) was identified as a binding partner of the FHA domain of Ki-67 (pKi-67). The interaction is mitosis-specific and phosphorylation-dependent, requiring two threonine residues within residues 226–269 of hNIFK (Thr-234 and Thr-238). A moiety of hNIFK co-localizes with pKi-67 at the peripheral region of mitotic chromosomes.","method":"In vitro binding assay with mitotically arrested cells, yeast two-hybrid domain mapping, Xenopus egg extract binding assay, immunofluorescence co-localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (in vitro binding, yeast two-hybrid, Xenopus egg extracts, immunofluorescence), single lab","pmids":["11342549"],"is_preprint":false},{"year":2004,"finding":"NMR solution structure of the Ki-67 FHA domain was determined and its binding to an ~44-residue fragment of hNIFK was characterized. The pThr site recognized by Ki-67 FHA is pThr234-Pro235 of hNIFK. Three factors control the interaction: the phosphothreonine residue, +1 to +3 residues, and an extended binding surface beyond the canonical pTXX(D/I/L) motif.","method":"NMR solution structure determination, HSQC NMR binding surface mapping, structural analysis of FHA domain–hNIFK fragment complex","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure with functional binding mapping using biologically relevant protein fragment, single lab with multiple orthogonal NMR methods","pmids":["14659764"],"is_preprint":false},{"year":2015,"finding":"NIFK is required for rRNA maturation via its RNA recognition motif (RRM). Silencing NIFK impairs cleavage of internal transcribed spacer (ITS) 1, leading to defective 28S and 5.8S rRNA maturation. The RRM of NIFK preferentially binds the 5'-region of ITS2 rRNA in a sequence- and secondary structure-dependent manner. NIFK knockdown causes reversible p53-dependent G1 arrest, possibly through RPL5/RPL11-mediated nucleolar stress. RNA-binding-deficient RRM mutants fail to rescue pre-rRNA processing or G1 progression.","method":"siRNA knockdown, RRM mutant complementation, rRNA processing assay, RNA-binding assay, cell cycle analysis, p53 pathway analysis","journal":"RNA biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods including loss-of-function, mutant rescue, RNA-binding assay, and cell cycle readout in single lab","pmids":["25826659"],"is_preprint":false},{"year":2016,"finding":"NIFK promotes lung cancer cell proliferation in a Ki-67-dependent manner and promotes metastasis by downregulating casein kinase 1α (CK1α), a suppressor of pro-metastatic TCF4/β-catenin signaling. NIFK knockdown upregulates CK1α; silencing CK1α in NIFK-knockdown cells restores TCF4/β-catenin transcriptional activity, cell migration, and metastasis. RUNX1 was identified as a transcription factor of CSNK1A1 (CK1α) that is negatively regulated by NIFK.","method":"siRNA knockdown, rescue experiments (CK1α silencing in NIFK-knockdown cells), in vitro migration/invasion assays, in vivo metastasis assay, transcriptional reporter assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Moderate — epistasis via double-knockdown rescue, in vitro and in vivo functional assays, pathway placement, single lab with multiple orthogonal methods","pmids":["26984280"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of yeast Nop15 (ortholog of human NIFK) at 2.0 Å reveals a C-terminal α-helical region that occludes the canonical RNA-binding surface of the RRM. SAXS and NMR show the C-terminal residues are highly flexible but essential for tight RNA binding. In the pre-ribosome (cryo-EM structure), dramatic rearrangement of the C-terminal region exposes the RNA-binding surface to contact the base of a stem-loop RNA target and forms a newly extended α-helix that makes additional protein interactions.","method":"X-ray crystallography (2.0 Å), SAXS, NMR, RNA-binding assays, cryo-EM comparison","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with SAXS, NMR, and RNA-binding analysis with functional validation, single lab with multiple orthogonal structural methods","pmids":["27789691"],"is_preprint":false},{"year":2003,"finding":"The nifk gene is widely expressed in adult mouse tissues beyond proliferating cells, and its mRNA is up-regulated in denervated hind limb skeletal muscle, suggesting functions beyond Ki-67 interaction.","method":"Differential display cloning, RT-PCR expression analysis in multiple tissues and denervated vs. innervated muscle","journal":"Cell biology international","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, expression analysis only, no direct mechanistic experiment beyond expression detection","pmids":["12798774"],"is_preprint":false},{"year":2023,"finding":"NIFK silencing in colorectal cancer cells inhibits cell growth, reduces metastasis, promotes apoptosis, and decreases lipid accumulation and fatty acid synthesis via downregulation of lipogenic enzymes. These effects are mediated through the MYC pathway, as c-MYC overexpression rescues the phenotypes caused by NIFK silencing.","method":"siRNA knockdown, c-MYC overexpression rescue, gene set enrichment analysis, western blot","journal":"Bioscience, biotechnology, and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic epistasis via rescue experiment (c-MYC OE rescuing NIFK-KD), single lab, limited mechanistic detail on direct connection","pmids":["37950567"],"is_preprint":false}],"current_model":"NIFK is a nucleolar RRM-containing protein that binds the FHA domain of Ki-67 in a mitosis-specific, phosphorylation-dependent manner (via pThr234-Pro235), participates in ribosome biogenesis by binding ITS2 rRNA through its RRM to facilitate ITS1 cleavage and 28S/5.8S rRNA maturation, and promotes cell proliferation and metastasis in cancer by supporting Ki-67-dependent proliferation and suppressing CK1α expression—thereby activating TCF4/β-catenin signaling—with structural studies of its yeast ortholog Nop15 revealing that conformational rearrangement of a flexible C-terminal region exposes the RNA-binding surface within the pre-ribosome."},"narrative":{"mechanistic_narrative":"NIFK is a nucleolar RRM-containing protein that bridges ribosome biogenesis and cell proliferation, originally defined by its mitosis-specific, phosphorylation-dependent association with the FHA domain of the proliferation marker Ki-67 [PMID:11342549]. This interaction is recognized through a phosphothreonine determinant in NIFK (pThr234-Pro235), with binding controlled by the phosphothreonine, its +1 to +3 residues, and an extended surface beyond the canonical FHA recognition motif [PMID:14659764]; a fraction of NIFK co-localizes with phosphorylated Ki-67 at the periphery of mitotic chromosomes [PMID:11342549]. In interphase, NIFK functions in rRNA maturation: its RRM binds the 5' region of ITS2 rRNA in a sequence- and structure-dependent manner to drive ITS1 cleavage and 28S/5.8S rRNA maturation, and loss of this activity triggers reversible p53-dependent G1 arrest via RPL5/RPL11-mediated nucleolar stress [PMID:25826659]. Structural work on the yeast ortholog Nop15 shows that a flexible C-terminal α-helical region occludes the RRM RNA-binding surface in the free protein and, upon incorporation into the pre-ribosome, rearranges to expose that surface for stem-loop RNA contact while extending into new protein interactions [PMID:27789691]. In cancer, NIFK supports Ki-67-dependent proliferation and promotes metastasis by downregulating CK1α through the transcription factor RUNX1, thereby activating pro-metastatic TCF4/β-catenin signaling [PMID:26984280], and supports colorectal cancer growth, lipogenesis, and survival through the c-MYC pathway [PMID:37950567].","teleology":[{"year":2001,"claim":"Established NIFK as a physiological partner of the proliferation marker Ki-67, answering whether Ki-67's FHA domain has a defined cell-cycle-regulated ligand.","evidence":"In vitro binding from mitotic cells, yeast two-hybrid domain mapping, Xenopus egg extract binding, and immunofluorescence co-localization","pmids":["11342549"],"confidence":"High","gaps":["Functional consequence of the Ki-67 interaction was not defined","Did not resolve the exact phospho-residue or kinase responsible"]},{"year":2004,"claim":"Defined the structural and chemical basis of Ki-67 FHA recognition of NIFK, refining the determinants beyond a simple phosphothreonine motif.","evidence":"NMR solution structure of the Ki-67 FHA domain and HSQC mapping of binding to an ~44-residue NIFK fragment","pmids":["14659764"],"confidence":"High","gaps":["Used a short peptide fragment rather than full-length proteins","Kinase generating pThr234 not identified"]},{"year":2015,"claim":"Assigned NIFK a direct molecular role in ribosome biogenesis, showing its RRM is required for ITS2-dependent pre-rRNA processing and that its loss imposes a p53-dependent cell-cycle checkpoint.","evidence":"siRNA knockdown, RRM mutant complementation, rRNA processing and RNA-binding assays, cell cycle and p53 pathway analysis","pmids":["25826659"],"confidence":"High","gaps":["Did not resolve how RRM engagement is coordinated within the assembling pre-ribosome","Relationship between rRNA function and the Ki-67 interaction unclear"]},{"year":2016,"claim":"Placed NIFK in a pro-tumorigenic signaling axis, showing it drives proliferation and metastasis by repressing CK1α via RUNX1 to release TCF4/β-catenin signaling.","evidence":"siRNA knockdown with CK1α double-knockdown epistasis rescue, migration/invasion assays, in vivo metastasis assay, transcriptional reporters","pmids":["26984280"],"confidence":"High","gaps":["Mechanism connecting nucleolar/RRM function to CK1α regulation not established","Direct vs indirect control of RUNX1/CSNK1A1 not resolved"]},{"year":2017,"claim":"Revealed the conformational mechanism by which the ortholog Nop15 RRM is autoinhibited and activated within the pre-ribosome, explaining how RNA-binding is gated.","evidence":"X-ray crystallography (2.0 Å), SAXS, NMR, RNA-binding assays, and cryo-EM comparison of yeast Nop15","pmids":["27789691"],"confidence":"High","gaps":["Conformational model derived from yeast ortholog, not human NIFK","Does not address regulation by the Ki-67 interaction"]},{"year":2023,"claim":"Extended NIFK's oncogenic role to colorectal cancer, linking its proliferative and lipogenic functions to the c-MYC pathway.","evidence":"siRNA knockdown with c-MYC overexpression rescue, gene set enrichment analysis, western blot","pmids":["37950567"],"confidence":"Medium","gaps":["Direct molecular link between NIFK and c-MYC not defined","Whether lipogenic effects depend on rRNA function untested"]},{"year":null,"claim":"How NIFK's nucleolar rRNA-processing activity is mechanistically coupled to its mitotic Ki-67 interaction and to its downstream control of CK1α/β-catenin and c-MYC signaling remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No mechanism unifying ribosome biogenesis with cancer signaling outputs","Kinase generating pThr234 unidentified","No structure of human NIFK within the human pre-ribosome"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[2,4]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[2]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[2,4]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,2]}],"complexes":["pre-ribosome"],"partners":["MKI67"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BYG3","full_name":"MKI67 FHA domain-interacting nucleolar phosphoprotein","aliases":["Nucleolar phosphoprotein Nopp34","Nucleolar protein interacting with the FHA domain of pKI-67","hNIFK"],"length_aa":293,"mass_kda":34.2,"function":"","subcellular_location":"Nucleus, nucleolus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q9BYG3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/NIFK","classification":"Common Essential","n_dependent_lines":1205,"n_total_lines":1208,"dependency_fraction":0.9975165562913907},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000155438","cell_line_id":"CID000721","localizations":[{"compartment":"nucleolus_gc","grade":3}],"interactors":[{"gene":"NPM1","stoichiometry":0.2},{"gene":"NPM3","stoichiometry":0.2},{"gene":"PSPC1","stoichiometry":0.2},{"gene":"RPS16","stoichiometry":0.2},{"gene":"RRP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000721","total_profiled":1310},"omim":[{"mim_id":"611970","title":"NUCLEOLAR PROTEIN INTERACTING WITH THE FHA DOMAIN OF MKI67; NIFK","url":"https://www.omim.org/entry/611970"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoli","reliability":"Enhanced"},{"location":"Nucleoli rim","reliability":"Enhanced"},{"location":"Mitotic chromosome","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NIFK"},"hgnc":{"alias_symbol":["Nop15","Nopp34","hNIFK"],"prev_symbol":["MKI67IP"]},"alphafold":{"accession":"Q9BYG3","domains":[{"cath_id":"3.30.70.330","chopping":"46-142","consensus_level":"high","plddt":93.516,"start":46,"end":142},{"cath_id":"1.20.5","chopping":"153-190","consensus_level":"medium","plddt":88.575,"start":153,"end":190}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BYG3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BYG3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BYG3-F1-predicted_aligned_error_v6.png","plddt_mean":72.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NIFK","jax_strain_url":"https://www.jax.org/strain/search?query=NIFK"},"sequence":{"accession":"Q9BYG3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BYG3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BYG3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BYG3"}},"corpus_meta":[{"pmid":"3470285","id":"PMC_3470285","title":"Products of the iron-molybdenum cofactor-specific biosynthetic genes, nifE and nifN, are structurally homologous to the products of the nitrogenase molybdenum-iron protein genes, nifD and nifK.","date":"1987","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/3470285","citation_count":126,"is_preprint":false},{"pmid":"30176290","id":"PMC_30176290","title":"Long non-coding RNA NIFK-AS1 inhibits M2 polarization of macrophages in endometrial cancer through targeting miR-146a.","date":"2018","source":"The international journal of biochemistry & cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/30176290","citation_count":99,"is_preprint":false},{"pmid":"10903367","id":"PMC_10903367","title":"Molecular evolution of nitrogen fixation: the evolutionary history of the nifD, nifK, nifE, and nifN genes.","date":"2000","source":"Journal of molecular evolution","url":"https://pubmed.ncbi.nlm.nih.gov/10903367","citation_count":96,"is_preprint":false},{"pmid":"11342549","id":"PMC_11342549","title":"A novel nucleolar protein, NIFK, interacts with the forkhead associated domain of Ki-67 antigen in mitosis.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11342549","citation_count":63,"is_preprint":false},{"pmid":"34374933","id":"PMC_34374933","title":"Upregulation of lncRNA NIFK-AS1 in hepatocellular carcinoma by m6A methylation promotes disease progression and sorafenib resistance.","date":"2021","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/34374933","citation_count":62,"is_preprint":false},{"pmid":"27407147","id":"PMC_27407147","title":"The novel regulatory ncRNA, NfiS, optimizes nitrogen fixation via base pairing with the nitrogenase gene nifK mRNA in Pseudomonas stutzeri A1501.","date":"2016","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/27407147","citation_count":48,"is_preprint":false},{"pmid":"14659764","id":"PMC_14659764","title":"Structure of human Ki67 FHA domain and its binding to a phosphoprotein fragment from hNIFK reveal unique recognition sites and new views to the structural basis of FHA domain functions.","date":"2004","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/14659764","citation_count":45,"is_preprint":false},{"pmid":"26984280","id":"PMC_26984280","title":"The nucleolar protein NIFK promotes cancer progression via CK1α/β-catenin in metastasis and Ki-67-dependent cell proliferation.","date":"2016","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/26984280","citation_count":39,"is_preprint":false},{"pmid":"7877490","id":"PMC_7877490","title":"Assessing horizontal transfer of nifHDK genes in eubacteria: nucleotide sequence of nifK from Frankia strain HFPCcI3.","date":"1995","source":"Molecular biology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/7877490","citation_count":33,"is_preprint":false},{"pmid":"3316182","id":"PMC_3316182","title":"Rhizobium meliloti nifN (fixF) gene is part of an operon regulated by a nifA-dependent promoter and codes for a polypeptide homologous to the nifK gene product.","date":"1987","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/3316182","citation_count":31,"is_preprint":false},{"pmid":"1429737","id":"PMC_1429737","title":"Electrophoretic studies on the assembly of the nitrogenase molybdenum-iron protein from the Klebsiella pneumoniae nifD and nifK gene products.","date":"1992","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/1429737","citation_count":29,"is_preprint":false},{"pmid":"20640414","id":"PMC_20640414","title":"Inferring the evolutionary history of Mo-dependent nitrogen fixation from phylogenetic studies of nifK and nifDK.","date":"2010","source":"Journal of molecular evolution","url":"https://pubmed.ncbi.nlm.nih.gov/20640414","citation_count":23,"is_preprint":false},{"pmid":"25826659","id":"PMC_25826659","title":"The RNA recognition motif of NIFK is required for rRNA maturation during cell cycle progression.","date":"2015","source":"RNA biology","url":"https://pubmed.ncbi.nlm.nih.gov/25826659","citation_count":21,"is_preprint":false},{"pmid":"3322261","id":"PMC_3322261","title":"A quantitative approach to sequence comparisons of nitrogenase MoFe protein alpha- and beta-subunits including the newly sequenced nifK gene from Klebsiella pneumoniae.","date":"1987","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/3322261","citation_count":18,"is_preprint":false},{"pmid":"9884228","id":"PMC_9884228","title":"Cloning and transcriptional analysis of the nifUHDK genes of Trichodesmium sp. IMS101 reveals stable nifD, nifDK and nifK transcripts.","date":"1998","source":"Microbiology (Reading, England)","url":"https://pubmed.ncbi.nlm.nih.gov/9884228","citation_count":11,"is_preprint":false},{"pmid":"27789691","id":"PMC_27789691","title":"Structural analysis reveals the flexible C-terminus of Nop15 undergoes rearrangement to recognize a pre-ribosomal RNA folding intermediate.","date":"2017","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/27789691","citation_count":9,"is_preprint":false},{"pmid":"22608550","id":"PMC_22608550","title":"Increased transcription of NOP15, involved in ribosome biogenesis in Saccharomyces cerevisiae, enhances the production yield of RNA as a source of nucleotide seasoning.","date":"2012","source":"Journal of bioscience and bioengineering","url":"https://pubmed.ncbi.nlm.nih.gov/22608550","citation_count":9,"is_preprint":false},{"pmid":"2120192","id":"PMC_2120192","title":"Analysis of Azotobacter vinelandii strains containing defined deletions in the nifD and nifK genes.","date":"1990","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/2120192","citation_count":5,"is_preprint":false},{"pmid":"36092356","id":"PMC_36092356","title":"A novel biomarker NIFK-AS1 promotes hepatocellular carcinoma cell cycle progression through interaction with SRSF10.","date":"2022","source":"Journal of gastrointestinal oncology","url":"https://pubmed.ncbi.nlm.nih.gov/36092356","citation_count":4,"is_preprint":false},{"pmid":"12798774","id":"PMC_12798774","title":"The nifk gene is widely expressed in mouse tissues and is up-regulated in denervated hind limb muscle.","date":"2003","source":"Cell biology international","url":"https://pubmed.ncbi.nlm.nih.gov/12798774","citation_count":3,"is_preprint":false},{"pmid":"37950567","id":"PMC_37950567","title":"The nucleolar protein NIFK accelerates the progression of colorectal cancer via activating MYC pathway.","date":"2023","source":"Bioscience, biotechnology, and biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37950567","citation_count":2,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.04.02.646848","title":"Transcriptional dynamics of nitrogen fixation and senescence in soybean nodules: A dual perspective on host and  <i>Bradyrhizobium</i>  regulation","date":"2025-04-06","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.02.646848","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12652,"output_tokens":2046,"usd":0.034323,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9091,"output_tokens":2477,"usd":0.05369,"stage2_stop_reason":"end_turn"},"total_usd":0.088013,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"NIFK (hNIFK) was identified as a binding partner of the FHA domain of Ki-67 (pKi-67). The interaction is mitosis-specific and phosphorylation-dependent, requiring two threonine residues within residues 226–269 of hNIFK (Thr-234 and Thr-238). A moiety of hNIFK co-localizes with pKi-67 at the peripheral region of mitotic chromosomes.\",\n      \"method\": \"In vitro binding assay with mitotically arrested cells, yeast two-hybrid domain mapping, Xenopus egg extract binding assay, immunofluorescence co-localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (in vitro binding, yeast two-hybrid, Xenopus egg extracts, immunofluorescence), single lab\",\n      \"pmids\": [\"11342549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"NMR solution structure of the Ki-67 FHA domain was determined and its binding to an ~44-residue fragment of hNIFK was characterized. The pThr site recognized by Ki-67 FHA is pThr234-Pro235 of hNIFK. Three factors control the interaction: the phosphothreonine residue, +1 to +3 residues, and an extended binding surface beyond the canonical pTXX(D/I/L) motif.\",\n      \"method\": \"NMR solution structure determination, HSQC NMR binding surface mapping, structural analysis of FHA domain–hNIFK fragment complex\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure with functional binding mapping using biologically relevant protein fragment, single lab with multiple orthogonal NMR methods\",\n      \"pmids\": [\"14659764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NIFK is required for rRNA maturation via its RNA recognition motif (RRM). Silencing NIFK impairs cleavage of internal transcribed spacer (ITS) 1, leading to defective 28S and 5.8S rRNA maturation. The RRM of NIFK preferentially binds the 5'-region of ITS2 rRNA in a sequence- and secondary structure-dependent manner. NIFK knockdown causes reversible p53-dependent G1 arrest, possibly through RPL5/RPL11-mediated nucleolar stress. RNA-binding-deficient RRM mutants fail to rescue pre-rRNA processing or G1 progression.\",\n      \"method\": \"siRNA knockdown, RRM mutant complementation, rRNA processing assay, RNA-binding assay, cell cycle analysis, p53 pathway analysis\",\n      \"journal\": \"RNA biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods including loss-of-function, mutant rescue, RNA-binding assay, and cell cycle readout in single lab\",\n      \"pmids\": [\"25826659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"NIFK promotes lung cancer cell proliferation in a Ki-67-dependent manner and promotes metastasis by downregulating casein kinase 1α (CK1α), a suppressor of pro-metastatic TCF4/β-catenin signaling. NIFK knockdown upregulates CK1α; silencing CK1α in NIFK-knockdown cells restores TCF4/β-catenin transcriptional activity, cell migration, and metastasis. RUNX1 was identified as a transcription factor of CSNK1A1 (CK1α) that is negatively regulated by NIFK.\",\n      \"method\": \"siRNA knockdown, rescue experiments (CK1α silencing in NIFK-knockdown cells), in vitro migration/invasion assays, in vivo metastasis assay, transcriptional reporter assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via double-knockdown rescue, in vitro and in vivo functional assays, pathway placement, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"26984280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of yeast Nop15 (ortholog of human NIFK) at 2.0 Å reveals a C-terminal α-helical region that occludes the canonical RNA-binding surface of the RRM. SAXS and NMR show the C-terminal residues are highly flexible but essential for tight RNA binding. In the pre-ribosome (cryo-EM structure), dramatic rearrangement of the C-terminal region exposes the RNA-binding surface to contact the base of a stem-loop RNA target and forms a newly extended α-helix that makes additional protein interactions.\",\n      \"method\": \"X-ray crystallography (2.0 Å), SAXS, NMR, RNA-binding assays, cryo-EM comparison\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with SAXS, NMR, and RNA-binding analysis with functional validation, single lab with multiple orthogonal structural methods\",\n      \"pmids\": [\"27789691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The nifk gene is widely expressed in adult mouse tissues beyond proliferating cells, and its mRNA is up-regulated in denervated hind limb skeletal muscle, suggesting functions beyond Ki-67 interaction.\",\n      \"method\": \"Differential display cloning, RT-PCR expression analysis in multiple tissues and denervated vs. innervated muscle\",\n      \"journal\": \"Cell biology international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, expression analysis only, no direct mechanistic experiment beyond expression detection\",\n      \"pmids\": [\"12798774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NIFK silencing in colorectal cancer cells inhibits cell growth, reduces metastasis, promotes apoptosis, and decreases lipid accumulation and fatty acid synthesis via downregulation of lipogenic enzymes. These effects are mediated through the MYC pathway, as c-MYC overexpression rescues the phenotypes caused by NIFK silencing.\",\n      \"method\": \"siRNA knockdown, c-MYC overexpression rescue, gene set enrichment analysis, western blot\",\n      \"journal\": \"Bioscience, biotechnology, and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic epistasis via rescue experiment (c-MYC OE rescuing NIFK-KD), single lab, limited mechanistic detail on direct connection\",\n      \"pmids\": [\"37950567\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NIFK is a nucleolar RRM-containing protein that binds the FHA domain of Ki-67 in a mitosis-specific, phosphorylation-dependent manner (via pThr234-Pro235), participates in ribosome biogenesis by binding ITS2 rRNA through its RRM to facilitate ITS1 cleavage and 28S/5.8S rRNA maturation, and promotes cell proliferation and metastasis in cancer by supporting Ki-67-dependent proliferation and suppressing CK1α expression—thereby activating TCF4/β-catenin signaling—with structural studies of its yeast ortholog Nop15 revealing that conformational rearrangement of a flexible C-terminal region exposes the RNA-binding surface within the pre-ribosome.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NIFK is a nucleolar RRM-containing protein that bridges ribosome biogenesis and cell proliferation, originally defined by its mitosis-specific, phosphorylation-dependent association with the FHA domain of the proliferation marker Ki-67 [#0]. This interaction is recognized through a phosphothreonine determinant in NIFK (pThr234-Pro235), with binding controlled by the phosphothreonine, its +1 to +3 residues, and an extended surface beyond the canonical FHA recognition motif [#1]; a fraction of NIFK co-localizes with phosphorylated Ki-67 at the periphery of mitotic chromosomes [#0]. In interphase, NIFK functions in rRNA maturation: its RRM binds the 5' region of ITS2 rRNA in a sequence- and structure-dependent manner to drive ITS1 cleavage and 28S/5.8S rRNA maturation, and loss of this activity triggers reversible p53-dependent G1 arrest via RPL5/RPL11-mediated nucleolar stress [#2]. Structural work on the yeast ortholog Nop15 shows that a flexible C-terminal α-helical region occludes the RRM RNA-binding surface in the free protein and, upon incorporation into the pre-ribosome, rearranges to expose that surface for stem-loop RNA contact while extending into new protein interactions [#4]. In cancer, NIFK supports Ki-67-dependent proliferation and promotes metastasis by downregulating CK1α through the transcription factor RUNX1, thereby activating pro-metastatic TCF4/β-catenin signaling [#3], and supports colorectal cancer growth, lipogenesis, and survival through the c-MYC pathway [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established NIFK as a physiological partner of the proliferation marker Ki-67, answering whether Ki-67's FHA domain has a defined cell-cycle-regulated ligand.\",\n      \"evidence\": \"In vitro binding from mitotic cells, yeast two-hybrid domain mapping, Xenopus egg extract binding, and immunofluorescence co-localization\",\n      \"pmids\": [\"11342549\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the Ki-67 interaction was not defined\", \"Did not resolve the exact phospho-residue or kinase responsible\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the structural and chemical basis of Ki-67 FHA recognition of NIFK, refining the determinants beyond a simple phosphothreonine motif.\",\n      \"evidence\": \"NMR solution structure of the Ki-67 FHA domain and HSQC mapping of binding to an ~44-residue NIFK fragment\",\n      \"pmids\": [\"14659764\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Used a short peptide fragment rather than full-length proteins\", \"Kinase generating pThr234 not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Assigned NIFK a direct molecular role in ribosome biogenesis, showing its RRM is required for ITS2-dependent pre-rRNA processing and that its loss imposes a p53-dependent cell-cycle checkpoint.\",\n      \"evidence\": \"siRNA knockdown, RRM mutant complementation, rRNA processing and RNA-binding assays, cell cycle and p53 pathway analysis\",\n      \"pmids\": [\"25826659\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how RRM engagement is coordinated within the assembling pre-ribosome\", \"Relationship between rRNA function and the Ki-67 interaction unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Placed NIFK in a pro-tumorigenic signaling axis, showing it drives proliferation and metastasis by repressing CK1α via RUNX1 to release TCF4/β-catenin signaling.\",\n      \"evidence\": \"siRNA knockdown with CK1α double-knockdown epistasis rescue, migration/invasion assays, in vivo metastasis assay, transcriptional reporters\",\n      \"pmids\": [\"26984280\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism connecting nucleolar/RRM function to CK1α regulation not established\", \"Direct vs indirect control of RUNX1/CSNK1A1 not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed the conformational mechanism by which the ortholog Nop15 RRM is autoinhibited and activated within the pre-ribosome, explaining how RNA-binding is gated.\",\n      \"evidence\": \"X-ray crystallography (2.0 Å), SAXS, NMR, RNA-binding assays, and cryo-EM comparison of yeast Nop15\",\n      \"pmids\": [\"27789691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational model derived from yeast ortholog, not human NIFK\", \"Does not address regulation by the Ki-67 interaction\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended NIFK's oncogenic role to colorectal cancer, linking its proliferative and lipogenic functions to the c-MYC pathway.\",\n      \"evidence\": \"siRNA knockdown with c-MYC overexpression rescue, gene set enrichment analysis, western blot\",\n      \"pmids\": [\"37950567\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link between NIFK and c-MYC not defined\", \"Whether lipogenic effects depend on rRNA function untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How NIFK's nucleolar rRNA-processing activity is mechanistically coupled to its mitotic Ki-67 interaction and to its downstream control of CK1α/β-catenin and c-MYC signaling remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mechanism unifying ribosome biogenesis with cancer signaling outputs\", \"Kinase generating pThr234 unidentified\", \"No structure of human NIFK within the human pre-ribosome\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [\"pre-ribosome\"],\n    \"partners\": [\"MKI67\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":5,"faith_total":5,"faith_pct":100.0}}