{"gene":"MXD1","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":1993,"finding":"MAD1 (Mad) protein forms heterodimers with Max in vivo during monocyte/macrophage differentiation. In undifferentiated U937 cells, Max is complexed with Myc; upon TPA-induced differentiation, Mad:Max complexes replace Myc:Max complexes, demonstrating a switch in Max heterocomplex composition accompanying differentiation.","method":"Co-immunoprecipitation from differentiating U937 cells; gel shift/DNA-binding assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, replicated across multiple labs in subsequent work","pmids":["8224841"],"is_preprint":false},{"year":1996,"finding":"MAD1 (Mad1) inhibits cell cycle progression from G1 to S phase when ectopically expressed in 3T3 cells, and this antiproliferative activity is tightly coupled to its function as a transcriptional repressor (repressor-dead mutants lose cell cycle inhibitory activity).","method":"Ectopic expression in 3T3 cells, cell cycle analysis by FACS, transcriptional repression assays with mutants","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — functional KO/overexpression with mechanistic follow-up via mutagenesis, strong evidence","pmids":["8649388"],"is_preprint":false},{"year":1995,"finding":"MAD1 blocks oncogenic transformation (Myc-Ras cotransformation) through multiple protein-protein interactions requiring: (1) an intact DNA-binding basic region, (2) the leucine zipper (for Max dimerization), and (3) an N-terminal domain for interaction with mSin3 corepressor.","method":"Focus formation transformation assays with Mad1 deletion mutants in rat embryo fibroblasts","journal":"Cell growth & differentiation","confidence":"High","confidence_rationale":"Tier 1–2 — structure-function mutagenesis with defined transformation readout, replicated","pmids":["7669717"],"is_preprint":false},{"year":1996,"finding":"MAD1 represses transcription through direct interaction of its N-terminal SIN3-interaction domain (SID) with the PAH2 domain of Sin3 (yeast ySin3/mammalian mSin3), recruiting Sin3 to promoters via DNA-bound Mad1:Max heterodimers.","method":"Yeast two-hybrid, in vitro binding, transcriptional repression reporter assays in sin3 mutant yeast","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including genetic and biochemical, replicated","pmids":["8754821"],"is_preprint":false},{"year":1999,"finding":"Ski protein is a component of the N-CoR/SMRT/mSin3/HDAC complex and is required for transcriptional repression mediated by Mad (MAD1). The oncogenic v-Ski, lacking the mSin3A-binding domain, acts in a dominant-negative fashion abrogating Mad-mediated repression. In ski-deficient mouse embryos, the Mad-Max target gene ornithine decarboxylase is ectopically expressed.","method":"Co-immunoprecipitation, transcriptional reporter assays, ski-knockout mouse embryo analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods + in vivo genetic validation","pmids":["10049357"],"is_preprint":false},{"year":2001,"finding":"PML interacts with multiple corepressors (c-Ski, N-CoR, mSin3A) and HDAC1, and this interaction is required for transcriptional repression mediated by MAD1. PML-RARalpha disrupts corepressor complex function and inhibits Mad-mediated repression.","method":"Co-immunoprecipitation, transcriptional repression reporter assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with functional reporter assays, multiple binding partners tested","pmids":["11430826"],"is_preprint":false},{"year":2003,"finding":"Crystal structures of Mad-Max bHLHZ domain heterodimer bound to E-box DNA (5'-CACGTG-3') at 2.0 Å resolution reveal that Mad-Max resembles the symmetric Max homodimer with structural differences in the coiled-coil leucine zipper region explaining preferential heterodimerization. Unlike Myc-Max, Mad-Max does not dimerize to form a bivalent heterotetramer.","method":"X-ray crystallography at 2.0 Å resolution","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with functional implications validated","pmids":["12553908"],"is_preprint":false},{"year":2000,"finding":"MAD1 (Mad) was identified as a direct transcriptional repressor of the hTERT (telomerase catalytic subunit) gene promoter. Mutation of Mad E-box DNA binding sites in the hTERT promoter caused de-repression, and this Mad-mediated repression was counteracted by ectopic Myc expression.","method":"Expression cloning screen, reporter gene assays with promoter mutants, endogenous hTERT promoter analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — genetic screen + reporter mutagenesis + endogenous promoter validation","pmids":["10723141"],"is_preprint":false},{"year":2004,"finding":"MAD1 represses rDNA transcription by interacting directly with the promoter of upstream binding factor (UBF), an rDNA regulatory factor, in granulocytic cells. Granulocytic cells deficient in MAD1 display increased cell volume, rDNA transcription and protein synthesis, demonstrating MAD1 regulates ribosome biogenesis and cell growth.","method":"Nuclear run-on assays, chromatin immunoprecipitation (ChIP), siRNA knockdown of UBF, MAD1-deficient cells","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — ChIP + nuclear run-on + genetic loss-of-function with defined cellular phenotype","pmids":["15282543"],"is_preprint":false},{"year":2008,"finding":"MAD1 protein is phosphorylated on serine 145 by p90 RSK and p70 S6 kinase downstream of PI3K/Akt and MAPK pathways upon serum or insulin stimulation. This phosphorylation accelerates ubiquitination and proteasomal degradation of MAD1, thereby promoting Myc transcriptional activity.","method":"In vitro kinase assays, site-directed mutagenesis (S145A), ubiquitination assays, proteasome inhibitor experiments","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay + mutagenesis + ubiquitination biochemistry","pmids":["18451027"],"is_preprint":false},{"year":2000,"finding":"MAD1 inhibits both cell proliferation and apoptosis. When induced in U2OS cells, MAD1 localizes to the nucleus, binds DNA as a Max heterodimer, reduces cellular growth, and interferes with Fas-, TRAIL-, and UV-induced apoptosis by reducing caspase-8 activation during Fas-mediated apoptosis.","method":"Tetracycline-regulated expression system in U2OS cells, apoptosis assays, caspase-8 activation measurement, microinjection experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — inducible expression system with multiple orthogonal functional readouts","pmids":["10744730"],"is_preprint":false},{"year":2002,"finding":"MAD1 and Myc bHLHZ domains have identical intrinsic DNA-binding specificities in vitro (both select CACGTG E-boxes), yet a chimeric Myc protein with the Mad1 bHLHZ domain can recapitulate Myc growth-promoting activity but not apoptotic function, indicating non-identical target gene sets in vivo.","method":"SELEX (selection and amplification of randomized oligonucleotides), chimeric protein functional assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — SELEX + in vivo functional chimera analysis with defined phenotypic readouts","pmids":["12149476"],"is_preprint":false},{"year":2010,"finding":"Kinetic analysis reveals that Mad:Max heterodimer formation has a rate constant approximately 2-fold lower than Myc:Max dimerization, and both dimerization and DNA-binding rates are concentration-independent (suggesting rate-limiting conformational changes). The monomer pathway (sequential binding to DNA) is kinetically favored over the pre-formed dimer pathway.","method":"Stopped-flow fluorescence polarization, Arrhenius activation energy analysis","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 — rigorous in vitro kinetic analysis, single study","pmids":["20170194"],"is_preprint":false},{"year":2012,"finding":"Vitamin D receptor (VDR) and 1,25-dihydroxyvitamin D (1,25D) regulate MXD1 expression and stability: 1,25D enhances MXD1 expression and protein stability, while inhibiting c-MYC expression and accelerating its turnover. F-box protein FBW7 (E3-ubiquitin ligase) controls stability of both c-MYC and MXD1; FBW7 ablation attenuates 1,25D regulation of both proteins.","method":"Cell-based and animal studies, protein stability assays, FBW7 knockdown, mathematical modeling, mouse VDR-knockout analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including genetic ablation + in vivo mouse model","pmids":["23112173"],"is_preprint":false},{"year":2011,"finding":"Solution NMR structure of the mSin3A PAH2 domain bound to the SID1 motif of Pf1 reveals structural features reminiscent of the Mad1/Mxd1:Sin3 interaction. The MRG15 subunit competes with Sin3 for binding to the same Pf1 segment containing SID1, showing competitive regulation within the repressor complex.","method":"NMR structure determination, binding assays, mutagenesis","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional binding validation","pmids":["21440557"],"is_preprint":false},{"year":2003,"finding":"p53 represses MAD1 (mitotic checkpoint MAD1) transcription through a 38-bp p53-responsive element in the MAD1 promoter. Repression involves recruitment of HDAC1 and co-repressor mSin3a to the MAD1 promoter (shown by ChIP), and is relieved by the HDAC inhibitor trichostatin A.","method":"Promoter truncation/reporter assays, chromatin immunoprecipitation (ChIP), trichostatin A treatment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP + reporter mutagenesis, single study","pmids":["12876282"],"is_preprint":false},{"year":2015,"finding":"MXD1 binds to the Sin3A repressor protein complex through increased association with HDAC-2, and directly binds E-box sites within the hTERT promoter to repress telomerase activity. This was demonstrated after miR-202 downregulation increases Mxd1 expression.","method":"ChIP at hTERT promoter, co-immunoprecipitation with Sin3A/HDAC-2, HDAC activity assay, telomerase activity assay","journal":"Cancer biology & therapy","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP + Co-IP + functional enzymatic assay, single study","pmids":["25611699"],"is_preprint":false},{"year":2017,"finding":"MXD1 directly binds E-box sites within the PTEN promoter to repress PTEN expression under hypoxia (confirmed by luciferase reporter and ChIP assays), leading to activation of PI3K/AKT signaling and cisplatin resistance in osteosarcoma cells.","method":"Luciferase reporter assay, chromatin immunoprecipitation (ChIP), siRNA knockdown, PI3K/AKT signaling analysis","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP + reporter assay + rescue experiment with PTEN siRNA, single study","pmids":["28543796"],"is_preprint":false},{"year":2020,"finding":"The SIN3-interaction domain (SID) derived from MXD1 protein functions as a highly effective transcriptional repressor domain when fused to dCas9 (CRISPRi), superior to the KRAB repressor domain in lymphoid cell lines, demonstrating the potency of the MXD1 SID in mediating transcriptional repression.","method":"CRISPRi library screening, competition assays, RT-qPCR, ChIP for MYC at target promoters","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — functional CRISPRi with genome-wide screening and validation","pmids":["32156728"],"is_preprint":false},{"year":2020,"finding":"MYCL and MXD1 regulate a shared but reciprocal transcriptional program during cDC1 (classical dendritic cell) maturation. MXD1 is induced in mature cDC1s (concomitant with repression of Mycl), and Mxd1-/- mature cDC1s exhibit impaired ability to inhibit the biosynthetic transcriptional signature supported by MYCL.","method":"Mxd1 and Mycl knockout mouse models, gene expression profiling","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined transcriptional phenotype, single study","pmids":["32071205"],"is_preprint":false},{"year":2000,"finding":"During adipocytic differentiation of 3T3-L1 cells, ectopic expression of Mad1 inhibits S phase entry and the proliferative burst, consequently inhibiting adipocytic differentiation. Mad4 and Mad1 are induced during late differentiation, while Mad3 is associated with S phase progression.","method":"Ectopic expression, BrdU incorporation, FACS cell cycle analysis, adipogenic differentiation assay","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — overexpression with defined proliferation and differentiation readouts","pmids":["10797315"],"is_preprint":false},{"year":2016,"finding":"MXD1 knockdown in CD34+ hematopoietic stem/progenitor cells mimics the effect of miR-382-5p overexpression, favoring granulocyte expansion and impairing megakaryocyte commitment, establishing MXD1 as a functional mediator of lineage choice in myelopoiesis. MXD1 was validated as a direct target of miR-382-5p by luciferase reporter assay.","method":"siRNA knockdown of MXD1, luciferase reporter assay, lineage differentiation assays from CD34+ cells","journal":"Stem cells and development","confidence":"Medium","confidence_rationale":"Tier 2 — validated target + loss-of-function with defined differentiation phenotype","pmids":["27520398"],"is_preprint":false}],"current_model":"MXD1 (MAD1) is a bHLH-leucine zipper transcriptional repressor that heterodimerizes with MAX to bind E-box sequences (CACGTG) and recruits the Sin3/HDAC corepressor complex via its N-terminal SIN3-interaction domain (SID), thereby antagonizing MYC:MAX-driven transcriptional activation; its expression is induced during differentiation and repressed by growth signals, and its protein stability is regulated by RSK/S6K-mediated phosphorylation of Ser145 leading to proteasomal degradation and by FBW7-dependent ubiquitination, while its transcriptional targets include hTERT, PTEN, UBF, and rDNA, positioning MXD1 as a molecular switch that couples extracellular growth signals to cell cycle exit and differentiation."},"narrative":{"teleology":[{"year":1993,"claim":"The identity of the MYC-antagonizing partner for MAX during differentiation was unknown; co-IP from differentiating U937 monocytes revealed that MAD1:MAX heterodimers replace MYC:MAX complexes upon TPA-induced differentiation, establishing the Myc/Max/Mad switching paradigm.","evidence":"Co-immunoprecipitation and gel-shift assays from differentiating U937 cells","pmids":["8224841"],"confidence":"High","gaps":["Mechanism by which differentiation signals induce MAD1 expression was not defined","Identity of MAD1 target genes was unknown","Whether MAD1 is required for differentiation (vs. sufficient) was not tested"]},{"year":1995,"claim":"The domains required for MAD1's tumor-suppressive function were undefined; deletion mutagenesis in transformation assays showed that MAD1 blocks MYC-RAS cotransformation through three separable requirements: DNA-binding basic region, leucine zipper for MAX dimerization, and an N-terminal domain for mSin3 corepressor interaction.","evidence":"Focus formation assays with MAD1 deletion mutants in rat embryo fibroblasts","pmids":["7669717"],"confidence":"High","gaps":["Direct biochemical characterization of the Sin3 interaction was not yet performed","Whether transformation suppression reflects transcriptional repression or other functions was not resolved"]},{"year":1996,"claim":"How MAD1 executes transcriptional repression was unclear; two studies established that MAD1's SID directly binds the PAH2 domain of Sin3, recruiting the Sin3/HDAC corepressor complex to E-box promoters, and that this repressive activity is essential for MAD1's ability to inhibit G1-to-S cell cycle progression.","evidence":"Yeast two-hybrid and in vitro binding for Sin3 interaction; FACS cell cycle analysis with repressor-dead mutants in 3T3 cells","pmids":["8754821","8649388"],"confidence":"High","gaps":["The full composition of the MAD1-recruited corepressor complex was not defined","Specific transcriptional targets mediating cell cycle arrest were unknown"]},{"year":1999,"claim":"The role of additional corepressor subunits in MAD1-mediated repression was unresolved; identification of Ski as a required component of the Sin3/HDAC complex, validated by ectopic ornithine decarboxylase expression in ski-null embryos, expanded the corepressor machinery necessary for MAD1 function.","evidence":"Co-IP, transcriptional reporters, ski-knockout mouse embryo analysis","pmids":["10049357"],"confidence":"High","gaps":["Whether Ski is required at all MAD1 target genes or a subset was not determined","Structural basis of Ski–Sin3 interaction in the context of MAD1 was unknown"]},{"year":2000,"claim":"Direct transcriptional targets of MAD1 were largely unknown; three studies identified hTERT as a direct MAD1 target via E-box-dependent repression, showed that MAD1 inhibits both proliferation and Fas/TRAIL-induced apoptosis, and demonstrated that MAD1 blocks the proliferative burst required for adipocyte differentiation.","evidence":"hTERT promoter reporter mutagenesis; inducible MAD1 expression in U2OS cells with apoptosis assays; BrdU/FACS in 3T3-L1 adipogenic differentiation","pmids":["10723141","10744730","10797315"],"confidence":"High","gaps":["Mechanism of apoptosis inhibition (whether transcription-dependent) was not fully clarified","Genome-wide target identification was not performed"]},{"year":2001,"claim":"Whether PML bodies contribute to MAD1-mediated repression was untested; PML was shown to interact with Sin3A, Ski, N-CoR, and HDAC1 and to be required for MAD1-mediated transcriptional repression, while PML-RARα disrupted this complex.","evidence":"Co-immunoprecipitation and transcriptional reporter assays","pmids":["11430826"],"confidence":"High","gaps":["Whether PML acts at all MAD1 targets or specifically at certain promoters was not resolved","In vivo relevance in leukemia beyond reporter assays was not tested"]},{"year":2002,"claim":"Whether MAD1 and MYC differ in intrinsic DNA-binding specificity was unclear; SELEX demonstrated identical E-box preferences in vitro, but chimeric MYC-MAD1 bHLHZ proteins could promote growth but not apoptosis, indicating in vivo functional divergence beyond DNA binding.","evidence":"SELEX and chimeric protein functional assays","pmids":["12149476"],"confidence":"High","gaps":["What determines differential in vivo target selection was not identified","Role of cofactor recruitment in target discrimination was not addressed"]},{"year":2003,"claim":"The atomic basis of MAD1:MAX heterodimerization and E-box recognition was unknown; the 2.0 Å crystal structure revealed structural differences in the leucine zipper explaining preferential heterodimerization and showed that, unlike MYC:MAX, MAD1:MAX does not form bivalent heterotetramers.","evidence":"X-ray crystallography at 2.0 Å resolution","pmids":["12553908"],"confidence":"High","gaps":["Structure of full-length MAD1 including the SID in complex with Sin3 was not obtained","How structural differences translate to chromatin-level function was not addressed"]},{"year":2004,"claim":"Whether MAD1 regulates ribosome biogenesis was untested; ChIP and nuclear run-on in granulocytic cells showed MAD1 represses rDNA transcription by targeting the UBF promoter, and MAD1-deficient cells exhibited increased cell volume and protein synthesis, establishing a role in cell growth control.","evidence":"ChIP, nuclear run-on, siRNA knockdown, MAD1-deficient granulocytic cells","pmids":["15282543"],"confidence":"High","gaps":["Whether MAD1 directly binds rDNA promoters in addition to UBF was not distinguished","Contribution to ribosome biogenesis in non-myeloid lineages was not assessed"]},{"year":2008,"claim":"How growth factor signaling eliminates MAD1 protein was unknown; RSK and S6K were identified as kinases that phosphorylate MAD1 at Ser145 downstream of PI3K and MAPK, triggering its ubiquitination and proteasomal degradation and thereby relieving repression of MYC target genes.","evidence":"In vitro kinase assays, S145A mutagenesis, ubiquitination and proteasome inhibitor experiments","pmids":["18451027"],"confidence":"High","gaps":["The E3 ubiquitin ligase responsible for Ser145-dependent degradation was not identified in this study","Whether other phosphorylation sites contribute to stability regulation was not tested"]},{"year":2012,"claim":"The E3 ligase controlling MAD1 turnover and the role of vitamin D signaling were unresolved; FBW7 was identified as the ubiquitin ligase regulating both MXD1 and c-MYC stability, and vitamin D/VDR signaling was shown to stabilize MXD1 while destabilizing c-MYC, with FBW7 ablation attenuating this regulation.","evidence":"FBW7 knockdown, protein stability assays, VDR-knockout mouse model, mathematical modeling","pmids":["23112173"],"confidence":"High","gaps":["Whether FBW7 recognizes a phosphodegron created by Ser145 phosphorylation specifically was not tested","Tissue-specific regulation of this axis in vivo was not fully characterized"]},{"year":2016,"claim":"Whether MXD1 influences hematopoietic lineage decisions beyond monocyte differentiation was untested; knockdown in CD34+ progenitors favored granulocyte expansion at the expense of megakaryocyte commitment, establishing MXD1 as a lineage-choice regulator in myelopoiesis.","evidence":"siRNA knockdown in CD34+ cells, lineage differentiation assays, luciferase reporter validation as miR-382-5p target","pmids":["27520398"],"confidence":"Medium","gaps":["Target genes mediating megakaryocyte vs. granulocyte fate decision were not identified","Whether this reflects MYC antagonism specifically was not demonstrated"]},{"year":2017,"claim":"MXD1's role under hypoxia was unexplored; ChIP and reporter assays showed MXD1 directly represses PTEN via E-box binding under hypoxic conditions, activating PI3K/AKT signaling and conferring cisplatin resistance in osteosarcoma.","evidence":"ChIP, luciferase reporter, siRNA knockdown in osteosarcoma cells under hypoxia","pmids":["28543796"],"confidence":"Medium","gaps":["Whether hypoxic PTEN repression is a general MXD1 function or cell-type specific was not assessed","MXD1 acting as a repressor of a tumor suppressor complicates the simple tumor-suppressive model and was not reconciled"]},{"year":2020,"claim":"The in vivo role of MXD1 in immune cell maturation was uncharacterized; Mxd1 knockout mice showed that MXD1 is required in mature cDC1 dendritic cells to repress the MYCL-driven biosynthetic program, and separately, the MXD1 SID was shown to be a potent transcriptional repressor domain when used in CRISPRi.","evidence":"Mxd1 and Mycl knockout mice with gene expression profiling; CRISPRi library screening in lymphoid cells","pmids":["32071205","32156728"],"confidence":"Medium","gaps":["Specific MXD1 target genes in cDC1 maturation were not defined","Whether the SID CRISPRi phenotype reflects endogenous MXD1 repression mechanisms fully was not established"]},{"year":null,"claim":"A comprehensive genome-wide map of direct MXD1 target genes across differentiation states, the structural basis for the full SID:Sin3:HDAC corepressor assembly, and the in vivo consequences of MXD1 loss in solid tissues remain to be established.","evidence":"","pmids":[],"confidence":"Low","gaps":["No genome-wide ChIP-seq or CUT&RUN map of MXD1 binding across multiple cell types has been reported in the timeline","Full-length MXD1:MAX:Sin3:HDAC complex structure is lacking","Conditional tissue-specific knockout phenotypes have not been described beyond immune lineages"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,6,7,11,16,17]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[1,3,7,8,16,17,18]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[10]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,3,7,8,16,17,18]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[3,4,5,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,13]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,20]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,19,20,21]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[9,13]}],"complexes":["MAD1:MAX heterodimer","Sin3/HDAC corepressor complex","Sin3A/N-CoR/Ski/HDAC complex"],"partners":["MAX","SIN3A","HDAC1","HDAC2","SKI","PML","FBW7"],"other_free_text":[]},"mechanistic_narrative":"MXD1 (MAD1) is a bHLH-leucine zipper transcriptional repressor that functions as a central antagonist of MYC-driven transcription, coupling growth factor signaling to cell cycle exit, differentiation, and control of ribosome biogenesis. MXD1 heterodimerizes with MAX to bind E-box (CACGTG) sequences, displacing MYC:MAX activating complexes at target promoters including hTERT, PTEN, UBF, and rDNA loci, and recruits the Sin3/HDAC corepressor complex via its N-terminal SIN3-interaction domain (SID), with additional requirement for Ski and PML as corepressor components [PMID:8224841, PMID:8754821, PMID:10049357, PMID:10723141, PMID:15282543, PMID:28543796]. MXD1 expression is induced upon myeloid, adipocytic, and dendritic cell differentiation, where it replaces MYC:MAX complexes and suppresses proliferative and biosynthetic gene programs; its loss impairs lineage-specific differentiation including megakaryocyte commitment and cDC1 maturation [PMID:8224841, PMID:10797315, PMID:32071205, PMID:27520398]. MXD1 protein stability is negatively regulated by RSK/S6K-mediated phosphorylation at Ser145, which triggers ubiquitination and proteasomal degradation, and by FBW7 E3-ubiquitin ligase activity, while vitamin D signaling stabilizes MXD1 protein [PMID:18451027, PMID:23112173]."},"prefetch_data":{"uniprot":{"accession":"Q05195","full_name":"Max dimerization protein 1","aliases":["Protein MAD"],"length_aa":221,"mass_kda":25.3,"function":"Component of a transcriptional repressor complex together with MAX (PubMed:8425218). In complex with MAX binds to the core DNA sequence 5'-CAC[GA]TG-3' (PubMed:8425218). Antagonizes MYC transcriptional activity by competing with MYC for MAX binding (PubMed:8425218). 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and MXD1 transcription factors regulate the fitness of murine dendritic cells.","date":"2020","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/32071205","citation_count":23,"is_preprint":false},{"pmid":"28543796","id":"PMC_28543796","title":"Mxd1 mediates hypoxia-induced cisplatin resistance in osteosarcoma cells by repression of the PTEN tumor suppressor gene.","date":"2017","source":"Molecular carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/28543796","citation_count":23,"is_preprint":false},{"pmid":"36289199","id":"PMC_36289199","title":"Juxtaposition of Bub1 and Cdc20 on phosphorylated Mad1 during catalytic mitotic checkpoint complex assembly.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/36289199","citation_count":23,"is_preprint":false},{"pmid":"10738221","id":"PMC_10738221","title":"Clinical implication of altered expression of Mad1 protein in human breast carcinoma.","date":"2000","source":"Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/10738221","citation_count":23,"is_preprint":false},{"pmid":"12639907","id":"PMC_12639907","title":"Dynamics of Myc/Max/Mad expression during luteinization of primate granulosa cells in vitro: association with periovulatory proliferation.","date":"2003","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/12639907","citation_count":23,"is_preprint":false},{"pmid":"27520398","id":"PMC_27520398","title":"miR-382-5p Controls Hematopoietic Stem Cell Differentiation Through the Downregulation of MXD1.","date":"2016","source":"Stem cells and development","url":"https://pubmed.ncbi.nlm.nih.gov/27520398","citation_count":22,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":41896,"output_tokens":4913,"usd":0.099692},"stage2":{"model":"claude-opus-4-6","input_tokens":8452,"output_tokens":3919,"usd":0.210352},"total_usd":0.310044,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"MAD1 (Mad) protein forms heterodimers with Max in vivo during monocyte/macrophage differentiation. In undifferentiated U937 cells, Max is complexed with Myc; upon TPA-induced differentiation, Mad:Max complexes replace Myc:Max complexes, demonstrating a switch in Max heterocomplex composition accompanying differentiation.\",\n      \"method\": \"Co-immunoprecipitation from differentiating U937 cells; gel shift/DNA-binding assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, replicated across multiple labs in subsequent work\",\n      \"pmids\": [\"8224841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"MAD1 (Mad1) inhibits cell cycle progression from G1 to S phase when ectopically expressed in 3T3 cells, and this antiproliferative activity is tightly coupled to its function as a transcriptional repressor (repressor-dead mutants lose cell cycle inhibitory activity).\",\n      \"method\": \"Ectopic expression in 3T3 cells, cell cycle analysis by FACS, transcriptional repression assays with mutants\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional KO/overexpression with mechanistic follow-up via mutagenesis, strong evidence\",\n      \"pmids\": [\"8649388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"MAD1 blocks oncogenic transformation (Myc-Ras cotransformation) through multiple protein-protein interactions requiring: (1) an intact DNA-binding basic region, (2) the leucine zipper (for Max dimerization), and (3) an N-terminal domain for interaction with mSin3 corepressor.\",\n      \"method\": \"Focus formation transformation assays with Mad1 deletion mutants in rat embryo fibroblasts\",\n      \"journal\": \"Cell growth & differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structure-function mutagenesis with defined transformation readout, replicated\",\n      \"pmids\": [\"7669717\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"MAD1 represses transcription through direct interaction of its N-terminal SIN3-interaction domain (SID) with the PAH2 domain of Sin3 (yeast ySin3/mammalian mSin3), recruiting Sin3 to promoters via DNA-bound Mad1:Max heterodimers.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding, transcriptional repression reporter assays in sin3 mutant yeast\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including genetic and biochemical, replicated\",\n      \"pmids\": [\"8754821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Ski protein is a component of the N-CoR/SMRT/mSin3/HDAC complex and is required for transcriptional repression mediated by Mad (MAD1). The oncogenic v-Ski, lacking the mSin3A-binding domain, acts in a dominant-negative fashion abrogating Mad-mediated repression. In ski-deficient mouse embryos, the Mad-Max target gene ornithine decarboxylase is ectopically expressed.\",\n      \"method\": \"Co-immunoprecipitation, transcriptional reporter assays, ski-knockout mouse embryo analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods + in vivo genetic validation\",\n      \"pmids\": [\"10049357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PML interacts with multiple corepressors (c-Ski, N-CoR, mSin3A) and HDAC1, and this interaction is required for transcriptional repression mediated by MAD1. PML-RARalpha disrupts corepressor complex function and inhibits Mad-mediated repression.\",\n      \"method\": \"Co-immunoprecipitation, transcriptional repression reporter assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with functional reporter assays, multiple binding partners tested\",\n      \"pmids\": [\"11430826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Crystal structures of Mad-Max bHLHZ domain heterodimer bound to E-box DNA (5'-CACGTG-3') at 2.0 Å resolution reveal that Mad-Max resembles the symmetric Max homodimer with structural differences in the coiled-coil leucine zipper region explaining preferential heterodimerization. Unlike Myc-Max, Mad-Max does not dimerize to form a bivalent heterotetramer.\",\n      \"method\": \"X-ray crystallography at 2.0 Å resolution\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional implications validated\",\n      \"pmids\": [\"12553908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MAD1 (Mad) was identified as a direct transcriptional repressor of the hTERT (telomerase catalytic subunit) gene promoter. Mutation of Mad E-box DNA binding sites in the hTERT promoter caused de-repression, and this Mad-mediated repression was counteracted by ectopic Myc expression.\",\n      \"method\": \"Expression cloning screen, reporter gene assays with promoter mutants, endogenous hTERT promoter analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic screen + reporter mutagenesis + endogenous promoter validation\",\n      \"pmids\": [\"10723141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"MAD1 represses rDNA transcription by interacting directly with the promoter of upstream binding factor (UBF), an rDNA regulatory factor, in granulocytic cells. Granulocytic cells deficient in MAD1 display increased cell volume, rDNA transcription and protein synthesis, demonstrating MAD1 regulates ribosome biogenesis and cell growth.\",\n      \"method\": \"Nuclear run-on assays, chromatin immunoprecipitation (ChIP), siRNA knockdown of UBF, MAD1-deficient cells\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP + nuclear run-on + genetic loss-of-function with defined cellular phenotype\",\n      \"pmids\": [\"15282543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MAD1 protein is phosphorylated on serine 145 by p90 RSK and p70 S6 kinase downstream of PI3K/Akt and MAPK pathways upon serum or insulin stimulation. This phosphorylation accelerates ubiquitination and proteasomal degradation of MAD1, thereby promoting Myc transcriptional activity.\",\n      \"method\": \"In vitro kinase assays, site-directed mutagenesis (S145A), ubiquitination assays, proteasome inhibitor experiments\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay + mutagenesis + ubiquitination biochemistry\",\n      \"pmids\": [\"18451027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MAD1 inhibits both cell proliferation and apoptosis. When induced in U2OS cells, MAD1 localizes to the nucleus, binds DNA as a Max heterodimer, reduces cellular growth, and interferes with Fas-, TRAIL-, and UV-induced apoptosis by reducing caspase-8 activation during Fas-mediated apoptosis.\",\n      \"method\": \"Tetracycline-regulated expression system in U2OS cells, apoptosis assays, caspase-8 activation measurement, microinjection experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — inducible expression system with multiple orthogonal functional readouts\",\n      \"pmids\": [\"10744730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MAD1 and Myc bHLHZ domains have identical intrinsic DNA-binding specificities in vitro (both select CACGTG E-boxes), yet a chimeric Myc protein with the Mad1 bHLHZ domain can recapitulate Myc growth-promoting activity but not apoptotic function, indicating non-identical target gene sets in vivo.\",\n      \"method\": \"SELEX (selection and amplification of randomized oligonucleotides), chimeric protein functional assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — SELEX + in vivo functional chimera analysis with defined phenotypic readouts\",\n      \"pmids\": [\"12149476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Kinetic analysis reveals that Mad:Max heterodimer formation has a rate constant approximately 2-fold lower than Myc:Max dimerization, and both dimerization and DNA-binding rates are concentration-independent (suggesting rate-limiting conformational changes). The monomer pathway (sequential binding to DNA) is kinetically favored over the pre-formed dimer pathway.\",\n      \"method\": \"Stopped-flow fluorescence polarization, Arrhenius activation energy analysis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — rigorous in vitro kinetic analysis, single study\",\n      \"pmids\": [\"20170194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Vitamin D receptor (VDR) and 1,25-dihydroxyvitamin D (1,25D) regulate MXD1 expression and stability: 1,25D enhances MXD1 expression and protein stability, while inhibiting c-MYC expression and accelerating its turnover. F-box protein FBW7 (E3-ubiquitin ligase) controls stability of both c-MYC and MXD1; FBW7 ablation attenuates 1,25D regulation of both proteins.\",\n      \"method\": \"Cell-based and animal studies, protein stability assays, FBW7 knockdown, mathematical modeling, mouse VDR-knockout analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including genetic ablation + in vivo mouse model\",\n      \"pmids\": [\"23112173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Solution NMR structure of the mSin3A PAH2 domain bound to the SID1 motif of Pf1 reveals structural features reminiscent of the Mad1/Mxd1:Sin3 interaction. The MRG15 subunit competes with Sin3 for binding to the same Pf1 segment containing SID1, showing competitive regulation within the repressor complex.\",\n      \"method\": \"NMR structure determination, binding assays, mutagenesis\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional binding validation\",\n      \"pmids\": [\"21440557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"p53 represses MAD1 (mitotic checkpoint MAD1) transcription through a 38-bp p53-responsive element in the MAD1 promoter. Repression involves recruitment of HDAC1 and co-repressor mSin3a to the MAD1 promoter (shown by ChIP), and is relieved by the HDAC inhibitor trichostatin A.\",\n      \"method\": \"Promoter truncation/reporter assays, chromatin immunoprecipitation (ChIP), trichostatin A treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP + reporter mutagenesis, single study\",\n      \"pmids\": [\"12876282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MXD1 binds to the Sin3A repressor protein complex through increased association with HDAC-2, and directly binds E-box sites within the hTERT promoter to repress telomerase activity. This was demonstrated after miR-202 downregulation increases Mxd1 expression.\",\n      \"method\": \"ChIP at hTERT promoter, co-immunoprecipitation with Sin3A/HDAC-2, HDAC activity assay, telomerase activity assay\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP + Co-IP + functional enzymatic assay, single study\",\n      \"pmids\": [\"25611699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MXD1 directly binds E-box sites within the PTEN promoter to repress PTEN expression under hypoxia (confirmed by luciferase reporter and ChIP assays), leading to activation of PI3K/AKT signaling and cisplatin resistance in osteosarcoma cells.\",\n      \"method\": \"Luciferase reporter assay, chromatin immunoprecipitation (ChIP), siRNA knockdown, PI3K/AKT signaling analysis\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP + reporter assay + rescue experiment with PTEN siRNA, single study\",\n      \"pmids\": [\"28543796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The SIN3-interaction domain (SID) derived from MXD1 protein functions as a highly effective transcriptional repressor domain when fused to dCas9 (CRISPRi), superior to the KRAB repressor domain in lymphoid cell lines, demonstrating the potency of the MXD1 SID in mediating transcriptional repression.\",\n      \"method\": \"CRISPRi library screening, competition assays, RT-qPCR, ChIP for MYC at target promoters\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional CRISPRi with genome-wide screening and validation\",\n      \"pmids\": [\"32156728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MYCL and MXD1 regulate a shared but reciprocal transcriptional program during cDC1 (classical dendritic cell) maturation. MXD1 is induced in mature cDC1s (concomitant with repression of Mycl), and Mxd1-/- mature cDC1s exhibit impaired ability to inhibit the biosynthetic transcriptional signature supported by MYCL.\",\n      \"method\": \"Mxd1 and Mycl knockout mouse models, gene expression profiling\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined transcriptional phenotype, single study\",\n      \"pmids\": [\"32071205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"During adipocytic differentiation of 3T3-L1 cells, ectopic expression of Mad1 inhibits S phase entry and the proliferative burst, consequently inhibiting adipocytic differentiation. Mad4 and Mad1 are induced during late differentiation, while Mad3 is associated with S phase progression.\",\n      \"method\": \"Ectopic expression, BrdU incorporation, FACS cell cycle analysis, adipogenic differentiation assay\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — overexpression with defined proliferation and differentiation readouts\",\n      \"pmids\": [\"10797315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"MXD1 knockdown in CD34+ hematopoietic stem/progenitor cells mimics the effect of miR-382-5p overexpression, favoring granulocyte expansion and impairing megakaryocyte commitment, establishing MXD1 as a functional mediator of lineage choice in myelopoiesis. MXD1 was validated as a direct target of miR-382-5p by luciferase reporter assay.\",\n      \"method\": \"siRNA knockdown of MXD1, luciferase reporter assay, lineage differentiation assays from CD34+ cells\",\n      \"journal\": \"Stem cells and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — validated target + loss-of-function with defined differentiation phenotype\",\n      \"pmids\": [\"27520398\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MXD1 (MAD1) is a bHLH-leucine zipper transcriptional repressor that heterodimerizes with MAX to bind E-box sequences (CACGTG) and recruits the Sin3/HDAC corepressor complex via its N-terminal SIN3-interaction domain (SID), thereby antagonizing MYC:MAX-driven transcriptional activation; its expression is induced during differentiation and repressed by growth signals, and its protein stability is regulated by RSK/S6K-mediated phosphorylation of Ser145 leading to proteasomal degradation and by FBW7-dependent ubiquitination, while its transcriptional targets include hTERT, PTEN, UBF, and rDNA, positioning MXD1 as a molecular switch that couples extracellular growth signals to cell cycle exit and differentiation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MXD1 (MAD1) is a bHLH-leucine zipper transcriptional repressor that functions as a central antagonist of MYC-driven transcription, coupling growth factor signaling to cell cycle exit, differentiation, and control of ribosome biogenesis. MXD1 heterodimerizes with MAX to bind E-box (CACGTG) sequences, displacing MYC:MAX activating complexes at target promoters including hTERT, PTEN, UBF, and rDNA loci, and recruits the Sin3/HDAC corepressor complex via its N-terminal SIN3-interaction domain (SID), with additional requirement for Ski and PML as corepressor components [PMID:8224841, PMID:8754821, PMID:10049357, PMID:10723141, PMID:15282543, PMID:28543796]. MXD1 expression is induced upon myeloid, adipocytic, and dendritic cell differentiation, where it replaces MYC:MAX complexes and suppresses proliferative and biosynthetic gene programs; its loss impairs lineage-specific differentiation including megakaryocyte commitment and cDC1 maturation [PMID:8224841, PMID:10797315, PMID:32071205, PMID:27520398]. MXD1 protein stability is negatively regulated by RSK/S6K-mediated phosphorylation at Ser145, which triggers ubiquitination and proteasomal degradation, and by FBW7 E3-ubiquitin ligase activity, while vitamin D signaling stabilizes MXD1 protein [PMID:18451027, PMID:23112173].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"The identity of the MYC-antagonizing partner for MAX during differentiation was unknown; co-IP from differentiating U937 monocytes revealed that MAD1:MAX heterodimers replace MYC:MAX complexes upon TPA-induced differentiation, establishing the Myc/Max/Mad switching paradigm.\",\n      \"evidence\": \"Co-immunoprecipitation and gel-shift assays from differentiating U937 cells\",\n      \"pmids\": [\"8224841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which differentiation signals induce MAD1 expression was not defined\", \"Identity of MAD1 target genes was unknown\", \"Whether MAD1 is required for differentiation (vs. sufficient) was not tested\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"The domains required for MAD1's tumor-suppressive function were undefined; deletion mutagenesis in transformation assays showed that MAD1 blocks MYC-RAS cotransformation through three separable requirements: DNA-binding basic region, leucine zipper for MAX dimerization, and an N-terminal domain for mSin3 corepressor interaction.\",\n      \"evidence\": \"Focus formation assays with MAD1 deletion mutants in rat embryo fibroblasts\",\n      \"pmids\": [\"7669717\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical characterization of the Sin3 interaction was not yet performed\", \"Whether transformation suppression reflects transcriptional repression or other functions was not resolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"How MAD1 executes transcriptional repression was unclear; two studies established that MAD1's SID directly binds the PAH2 domain of Sin3, recruiting the Sin3/HDAC corepressor complex to E-box promoters, and that this repressive activity is essential for MAD1's ability to inhibit G1-to-S cell cycle progression.\",\n      \"evidence\": \"Yeast two-hybrid and in vitro binding for Sin3 interaction; FACS cell cycle analysis with repressor-dead mutants in 3T3 cells\",\n      \"pmids\": [\"8754821\", \"8649388\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The full composition of the MAD1-recruited corepressor complex was not defined\", \"Specific transcriptional targets mediating cell cycle arrest were unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"The role of additional corepressor subunits in MAD1-mediated repression was unresolved; identification of Ski as a required component of the Sin3/HDAC complex, validated by ectopic ornithine decarboxylase expression in ski-null embryos, expanded the corepressor machinery necessary for MAD1 function.\",\n      \"evidence\": \"Co-IP, transcriptional reporters, ski-knockout mouse embryo analysis\",\n      \"pmids\": [\"10049357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Ski is required at all MAD1 target genes or a subset was not determined\", \"Structural basis of Ski–Sin3 interaction in the context of MAD1 was unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Direct transcriptional targets of MAD1 were largely unknown; three studies identified hTERT as a direct MAD1 target via E-box-dependent repression, showed that MAD1 inhibits both proliferation and Fas/TRAIL-induced apoptosis, and demonstrated that MAD1 blocks the proliferative burst required for adipocyte differentiation.\",\n      \"evidence\": \"hTERT promoter reporter mutagenesis; inducible MAD1 expression in U2OS cells with apoptosis assays; BrdU/FACS in 3T3-L1 adipogenic differentiation\",\n      \"pmids\": [\"10723141\", \"10744730\", \"10797315\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of apoptosis inhibition (whether transcription-dependent) was not fully clarified\", \"Genome-wide target identification was not performed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Whether PML bodies contribute to MAD1-mediated repression was untested; PML was shown to interact with Sin3A, Ski, N-CoR, and HDAC1 and to be required for MAD1-mediated transcriptional repression, while PML-RARα disrupted this complex.\",\n      \"evidence\": \"Co-immunoprecipitation and transcriptional reporter assays\",\n      \"pmids\": [\"11430826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PML acts at all MAD1 targets or specifically at certain promoters was not resolved\", \"In vivo relevance in leukemia beyond reporter assays was not tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Whether MAD1 and MYC differ in intrinsic DNA-binding specificity was unclear; SELEX demonstrated identical E-box preferences in vitro, but chimeric MYC-MAD1 bHLHZ proteins could promote growth but not apoptosis, indicating in vivo functional divergence beyond DNA binding.\",\n      \"evidence\": \"SELEX and chimeric protein functional assays\",\n      \"pmids\": [\"12149476\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"What determines differential in vivo target selection was not identified\", \"Role of cofactor recruitment in target discrimination was not addressed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The atomic basis of MAD1:MAX heterodimerization and E-box recognition was unknown; the 2.0 Å crystal structure revealed structural differences in the leucine zipper explaining preferential heterodimerization and showed that, unlike MYC:MAX, MAD1:MAX does not form bivalent heterotetramers.\",\n      \"evidence\": \"X-ray crystallography at 2.0 Å resolution\",\n      \"pmids\": [\"12553908\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length MAD1 including the SID in complex with Sin3 was not obtained\", \"How structural differences translate to chromatin-level function was not addressed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Whether MAD1 regulates ribosome biogenesis was untested; ChIP and nuclear run-on in granulocytic cells showed MAD1 represses rDNA transcription by targeting the UBF promoter, and MAD1-deficient cells exhibited increased cell volume and protein synthesis, establishing a role in cell growth control.\",\n      \"evidence\": \"ChIP, nuclear run-on, siRNA knockdown, MAD1-deficient granulocytic cells\",\n      \"pmids\": [\"15282543\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MAD1 directly binds rDNA promoters in addition to UBF was not distinguished\", \"Contribution to ribosome biogenesis in non-myeloid lineages was not assessed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"How growth factor signaling eliminates MAD1 protein was unknown; RSK and S6K were identified as kinases that phosphorylate MAD1 at Ser145 downstream of PI3K and MAPK, triggering its ubiquitination and proteasomal degradation and thereby relieving repression of MYC target genes.\",\n      \"evidence\": \"In vitro kinase assays, S145A mutagenesis, ubiquitination and proteasome inhibitor experiments\",\n      \"pmids\": [\"18451027\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The E3 ubiquitin ligase responsible for Ser145-dependent degradation was not identified in this study\", \"Whether other phosphorylation sites contribute to stability regulation was not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The E3 ligase controlling MAD1 turnover and the role of vitamin D signaling were unresolved; FBW7 was identified as the ubiquitin ligase regulating both MXD1 and c-MYC stability, and vitamin D/VDR signaling was shown to stabilize MXD1 while destabilizing c-MYC, with FBW7 ablation attenuating this regulation.\",\n      \"evidence\": \"FBW7 knockdown, protein stability assays, VDR-knockout mouse model, mathematical modeling\",\n      \"pmids\": [\"23112173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FBW7 recognizes a phosphodegron created by Ser145 phosphorylation specifically was not tested\", \"Tissue-specific regulation of this axis in vivo was not fully characterized\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Whether MXD1 influences hematopoietic lineage decisions beyond monocyte differentiation was untested; knockdown in CD34+ progenitors favored granulocyte expansion at the expense of megakaryocyte commitment, establishing MXD1 as a lineage-choice regulator in myelopoiesis.\",\n      \"evidence\": \"siRNA knockdown in CD34+ cells, lineage differentiation assays, luciferase reporter validation as miR-382-5p target\",\n      \"pmids\": [\"27520398\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Target genes mediating megakaryocyte vs. granulocyte fate decision were not identified\", \"Whether this reflects MYC antagonism specifically was not demonstrated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"MXD1's role under hypoxia was unexplored; ChIP and reporter assays showed MXD1 directly represses PTEN via E-box binding under hypoxic conditions, activating PI3K/AKT signaling and conferring cisplatin resistance in osteosarcoma.\",\n      \"evidence\": \"ChIP, luciferase reporter, siRNA knockdown in osteosarcoma cells under hypoxia\",\n      \"pmids\": [\"28543796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether hypoxic PTEN repression is a general MXD1 function or cell-type specific was not assessed\", \"MXD1 acting as a repressor of a tumor suppressor complicates the simple tumor-suppressive model and was not reconciled\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The in vivo role of MXD1 in immune cell maturation was uncharacterized; Mxd1 knockout mice showed that MXD1 is required in mature cDC1 dendritic cells to repress the MYCL-driven biosynthetic program, and separately, the MXD1 SID was shown to be a potent transcriptional repressor domain when used in CRISPRi.\",\n      \"evidence\": \"Mxd1 and Mycl knockout mice with gene expression profiling; CRISPRi library screening in lymphoid cells\",\n      \"pmids\": [\"32071205\", \"32156728\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific MXD1 target genes in cDC1 maturation were not defined\", \"Whether the SID CRISPRi phenotype reflects endogenous MXD1 repression mechanisms fully was not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive genome-wide map of direct MXD1 target genes across differentiation states, the structural basis for the full SID:Sin3:HDAC corepressor assembly, and the in vivo consequences of MXD1 loss in solid tissues remain to be established.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No genome-wide ChIP-seq or CUT&RUN map of MXD1 binding across multiple cell types has been reported in the timeline\", \"Full-length MXD1:MAX:Sin3:HDAC complex structure is lacking\", \"Conditional tissue-specific knockout phenotypes have not been described beyond immune lineages\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 6, 7, 11, 16, 17]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1, 3, 7, 8, 16, 17, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 3, 7, 8, 16, 17, 18]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [3, 4, 5, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 13]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 20]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 19, 20, 21]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [9, 13]}\n    ],\n    \"complexes\": [\n      \"MAD1:MAX heterodimer\",\n      \"Sin3/HDAC corepressor complex\",\n      \"Sin3A/N-CoR/Ski/HDAC complex\"\n    ],\n    \"partners\": [\n      \"MAX\",\n      \"SIN3A\",\n      \"HDAC1\",\n      \"HDAC2\",\n      \"SKI\",\n      \"PML\",\n      \"FBW7\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}