{"gene":"CCND2","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2014,"finding":"De novo CCND2 mutations clustered around a GSK-3β phosphorylation site render cyclin D2 resistant to proteasomal degradation in vitro; the PI3K-AKT pathway modulates GSK-3β activity, leading to similar CCND2 accumulation in cells with PIK3CA, PIK3R2, or AKT3 mutations. In utero electroporation of mutant CCND2 into embryonic mouse brains produced more proliferating progenitors and a smaller fraction exiting the cell cycle compared to wild-type CCND2.","method":"In vitro proteasomal degradation assay, in utero electroporation, cell cycle analysis, patient-derived cell studies","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (in vitro degradation assay, mutagenesis, in vivo electroporation) in a single rigorous study","pmids":["24705253"],"is_preprint":false},{"year":2021,"finding":"CCND2 Thr280Ala mutation (clustering around a conserved threonine residue) leads to increased phosphorylation of the retinoblastoma protein, causing significant cell cycle changes and increased proliferation of AML cell lines, establishing CCND2 gain-of-function mutations as drivers of cell cycle dysregulation in t(8;21) AML.","method":"Site-directed mutagenesis, retinoblastoma phosphorylation assay, cell cycle analysis, proliferation assays in AML cell lines","journal":"Leukemia","confidence":"High","confidence_rationale":"Tier 1-2 — direct mutagenesis with functional validation (RB phosphorylation, cell cycle, proliferation)","pmids":["27843138"],"is_preprint":false},{"year":2019,"finding":"STAT3 directly binds the CCND2 promoter, increasing CCND2 transcription as part of JAK2/STAT3/CCND2 signaling that promotes cancer stem cell persistence and radioresistance in colorectal cancer.","method":"Chromatin immunoprecipitation (ChIP), promoter reporter assay, JAK2/STAT3 inhibition experiments, patient-derived CRC cells and xenografts","journal":"Journal of experimental & clinical cancer research","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrating direct STAT3 binding to CCND2 promoter, supported by multiple cell models and in vivo validation","pmids":["31511084"],"is_preprint":false},{"year":2010,"finding":"MicroRNA let-7a directly binds the 3'UTR of CCND2 mRNA, downregulating CCND2 protein expression and inducing G1/S cell cycle arrest in prostate cancer cells.","method":"Dual-luciferase reporter assay, western blotting, cell cycle analysis, xenograft model","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — direct 3'UTR binding validated by luciferase assay, protein knockdown confirmed, in vivo validation included","pmids":["20418948"],"is_preprint":false},{"year":2017,"finding":"Overexpression of CCND2 in human iPSC-derived cardiomyocytes activates cell cycle progression (3-7 fold upregulation of Ki67 and other proliferation markers), enhances engraftment after myocardial infarction in mice, and promotes remuscularization of injured myocardium.","method":"Lentiviral CCND2 overexpression, cell cycle marker quantification, mouse MI model with histological and functional assessment","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — direct overexpression with quantitative cell cycle markers and in vivo cardiac repair endpoints","pmids":["29018036"],"is_preprint":false},{"year":2023,"finding":"CCND2 modified mRNA delivered via a cardiomyocyte-specific SMRTs system induces CCND2 expression selectively in cardiomyocytes, activates cell cycle markers (Ki67, Aurora B kinase), promotes cardiomyocyte proliferation, and reduces infarct size in both mouse and pig MI models.","method":"Modified mRNA delivery system, cardiomyocyte-specific expression via miR-1/miR-208 regulation, Ki67/Aurora B quantification, echocardiography in mouse and pig MI models","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — orthogonal validation across two mammalian species with mechanistic specificity controls","pmids":["37565345"],"is_preprint":false},{"year":2008,"finding":"RNAi knockdown of CCND2 inhibits proliferation and is progressively cytotoxic in human myeloma cells; kinetin riboside suppresses CCND2 transcription by upregulating repressor isoforms of CREM (cAMP-response element modulator), blocking trans-activation of CCND2 by multiple myeloma oncogenes.","method":"RNAi knockdown, chemical library screen with cell-based CCND2 trans-activation assay, transcription factor reporter assay, primary myeloma cell studies, xenograft model","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including RNAi, pharmacological inhibition, mechanistic transcription factor analysis, and in vivo validation","pmids":["18431519"],"is_preprint":false},{"year":2019,"finding":"PICOT protein binds to chromatin-associated EED (a PRC2 component) via its PICOT/Grx homology domains; PICOT knockdown reduces H3K27me3 mark and decreases EED and EZH2 occupancy at the CCND2 gene promoter, resulting in increased CCND2 mRNA and protein expression in T cells.","method":"Co-immunoprecipitation, ChIP, knockdown experiments, western blotting, qPCR, TCGA data correlation","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, ChIP with functional validation of epigenetic mark changes at CCND2 promoter","pmids":["31527584"],"is_preprint":false},{"year":2025,"finding":"PRC2.1 (containing MTF2), but not PRC2.2 (containing JARID2), promotes H3K27me3 deposition at CpG islands in the CCND1 and CCND2 promoters; loss of MTF2 upregulates both cyclins and rescues cells from CDK4/6 inhibitor palbociclib-induced G1 arrest.","method":"Chemogenetic screen, genetic epistasis (MTF2 vs JARID2 mutation), ChIP-seq for H3K27me3, palbociclib sensitivity assays in multiple cell lines","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP-seq, genetic epistasis with subcomplex-specific mutants, functional G1 progression assays across multiple cell lineages","pmids":["39903505"],"is_preprint":false},{"year":2010,"finding":"The ETS transcription factor Elf5 directly binds a genomic segment upstream of the Ccnd2 gene and transcriptionally represses Ccnd2 expression in mouse mammary gland; loss of Elf5 in vivo leads to upregulation of Ccnd2 in luminal mammary cells.","method":"ChIP-cloning, ChIP, promoter reporter assay, Elf5-null mammary epithelial cells and gland analysis","journal":"BMC molecular biology","confidence":"High","confidence_rationale":"Tier 1-2 — direct ChIP demonstrating in vivo binding, promoter reporter confirming repressive function, validated in null animals","pmids":["20831799"],"is_preprint":false},{"year":2016,"finding":"Long noncoding RNA linc00598 regulates CCND2 transcription through modulation of FoxO1 transcriptional activity at the CCND2 promoter; knockdown of linc00598 induces G0/G1 cell cycle arrest and inhibits proliferation.","method":"Microarray analysis, knockdown experiments, promoter reporter assay, cell cycle analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2-3 — promoter reporter and knockdown with cell cycle readout, but mechanism of FoxO1 modulation not fully resolved","pmids":["27572135"],"is_preprint":false},{"year":2011,"finding":"MiR-1 directly targets and represses CCND2 (favoring G1/S transition) in thyroid carcinoma cells; ectopic miR-1 expression inhibits thyroid carcinoma cell proliferation and migration, validated by 3'UTR reporter assays.","method":"Luciferase reporter assay, western blotting, functional proliferation and migration assays","journal":"The Journal of clinical endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — direct 3'UTR targeting validated by luciferase assay with functional consequences, single lab","pmids":["21752897"],"is_preprint":false},{"year":2012,"finding":"MiR-1, miR-206, and miR-29 target the 3'UTR of CCND2 to regulate its expression in rhabdomyosarcoma; overexpression of miR-29 downregulates CCND2 and other cell cycle genes (E2F7), inducing G1 arrest and decreased cell proliferation.","method":"Ectopic miRNA expression, western blotting, cell cycle analysis, luciferase reporter assays","journal":"Laboratory investigation","confidence":"Medium","confidence_rationale":"Tier 2 — multiple miRNAs validated with cell cycle and proliferation readouts, single lab","pmids":["22330340"],"is_preprint":false},{"year":2016,"finding":"CCND2 promoter is silenced by aberrant methylation in renal cell cancer; treatment with the demethylating agent 5-Aza (with or without TSA) restores CCND2 expression in methylated RCC cell lines.","method":"Methylation-specific PCR (MSP), bisulfite genomic sequencing (BGS), 5-Aza/TSA treatment, expression analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — direct methylation mapping with pharmacological demethylation rescue of expression","pmids":["27583477"],"is_preprint":false},{"year":2018,"finding":"CCND2 promoter hypermethylation silences CCND2 expression in lung and breast cancer; cell model assays show that CCND2 expression inhibits cancer cell growth and migration; antroquinonol D, a demethylating agent, upregulates CCND2 expression and causes cell cycle arrest.","method":"Genome-wide methylation analysis, quantitative MSP, cell proliferation and migration assays, drug treatment","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 — promoter methylation linked to expression with functional rescue, single lab","pmids":["30308939"],"is_preprint":false},{"year":2019,"finding":"CCND2 overexpression in hiPSC-derived cardiomyocytes results in electrical integration (coupling) with host myocardium 6 months after transplantation, with optical mapping confirming synchronized action potential propagation, alongside >50% replacement of myocardial scar tissue.","method":"Optical mapping of action potential propagation, histological quantification of engraftment, echocardiography","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 — direct electrophysiological measurement of CCND2-OE CM integration, single lab","pmids":["31629738"],"is_preprint":false},{"year":2021,"finding":"CCND2 loss-of-function through proximal frameshift or stop-gain variants causes microcephaly, while distal terminal-exon variants causing protein stabilization lead to megalencephaly, demonstrating that distinct classes of CCND2 variants have reciprocal effects on human brain growth.","method":"Clinical genetics, variant mapping, phenotypic characterization of five individuals from three families","journal":"American journal of medical genetics. Part A","confidence":"Medium","confidence_rationale":"Tier 3 — clinical genetics series establishing genotype-phenotype relationship, consistent with prior functional data from PMID:24705253","pmids":["34087052"],"is_preprint":false},{"year":2019,"finding":"lncRNA TUG1 promotes CCND2 expression by binding EZH2 to epigenetically silence miR-194-5p (via promoter hypermethylation); knockdown of TUG1 reduces EZH2 levels, relieves methylation of miR-194-5p, which then directly targets and suppresses CCND2 in bladder cancer.","method":"EZH2 knockdown, bisulfite sequencing of miR-194-5p promoter, dual-luciferase reporter assay for miR-194-5p/CCND2, western blotting","journal":"Molecular therapy. Nucleic acids","confidence":"Medium","confidence_rationale":"Tier 2-3 — mechanistic chain from epigenetic silencing through miRNA to CCND2, validated by multiple methods in single lab","pmids":["30925453"],"is_preprint":false},{"year":2023,"finding":"PI3K/AKT inhibitor BEZ-235 induces dephosphorylation of GSK3β, leading to proteasomal degradation of CCND2 protein, dephosphorylation of RB, and G1 cell cycle arrest in BIA-ALCL; CDK4/6 inhibitor palbociclib also dephosphorylates RB and arrests cells in G1, confirming that CCND2 controls CDK4/6 activity and RB phosphorylation.","method":"Western blotting for RB phosphorylation, GSK3β phosphorylation, mTORC1 target S6; cell cycle analysis; pharmacological inhibition","journal":"Leukemia research","confidence":"Medium","confidence_rationale":"Tier 2 — direct biochemical demonstration of CCND2 protein degradation via GSK3β pathway and RB phosphorylation readout","pmids":["37647808"],"is_preprint":false},{"year":2012,"finding":"GATA1s isoform (but not GATA1FL) fails to repress CCND2 during terminal erythroid differentiation of K562 cells, suggesting CCND2 is a target of GATA1-mediated transcriptional repression during hematopoietic differentiation.","method":"Transgenic K562 cells expressing GATA1s or GATA1FL, gene expression profiling during erythroid differentiation","journal":"Journal of hematology & oncology","confidence":"Low","confidence_rationale":"Tier 3 — expression profiling with transgenic overexpression, no direct binding or promoter assay for CCND2","pmids":["22853316"],"is_preprint":false},{"year":2021,"finding":"ZFAS1 lncRNA acts as a ceRNA to sponge miR-150-5p, preventing miR-150-5p from downregulating CCND2; ZFAS1 knockdown reduces ferroptosis markers and cardiomyocyte injury in diabetic cardiomyopathy models, with effects reversed by miR-150-5p inhibition or CCND2 depletion, placing CCND2 downstream of the ZFAS1/miR-150-5p axis.","method":"Dual-luciferase reporter assay, RNA pull-down, in vitro high glucose cardiomyocyte model, db/db mouse model, ferroptosis marker measurement","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2-3 — dual-luciferase and RNA pull-down confirm sponging, in vitro and in vivo functional rescue experiments","pmids":["34609043"],"is_preprint":false},{"year":2021,"finding":"CCND2 mRNA is stabilized by IGF2BP3 protein binding, preventing its degradation; hsa_circ_0000231 promotes CCND2 expression by both sponging miR-375 (ceRNA mechanism) and binding IGF2BP3 to prevent CCND2 mRNA degradation in colorectal cancer cells.","method":"RNA pull-down, RNA immunoprecipitation (RIP), dual-luciferase reporter assay, in vitro and in vivo functional assays","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 2 — RNA pull-down and RIP confirm IGF2BP3-CCND2 mRNA interaction, dual mechanism validated","pmids":["35033075"],"is_preprint":false},{"year":2022,"finding":"miR-135a suppresses granulosa cell growth by directly targeting the 3'UTR of Ccnd2; the TGFBR1-SMAD3 pathway enhances Ccnd2 promoter activity and upregulates Ccnd2 expression; ESR2 (estrogen receptor 2) acts as a transcription factor binding the miR-135a promoter to decrease miR-135a transcription, establishing an ESR2/miR-135a/Tgfbr1/Ccnd2 regulatory axis.","method":"3'UTR luciferase reporter assay, ChIP-qPCR for SMAD3 at Ccnd2 promoter and ESR2 at miR-135a promoter, subcellular localization analysis, miR-135a overexpression in granulosa cells","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-qPCR establishes direct binding at Ccnd2 promoter and miR-135a promoter, luciferase validates 3'UTR targeting","pmids":["34440873"],"is_preprint":false},{"year":2019,"finding":"SRSF1 and miR-135a competitively bind the 3'UTR region of CCND2 mRNA; SRSF1 overexpression represses degradation of CCND2 mRNA by outcompeting miR-135a, while SRSF1 knockdown inhibits airway smooth muscle cell proliferation by reducing CCND2 levels.","method":"RNA immunoprecipitation, RNA pull-down, dual-luciferase reporter assay, RNA degradation assay, flow cytometry","journal":"Pulmonary pharmacology & therapeutics","confidence":"Medium","confidence_rationale":"Tier 2 — RNA immunoprecipitation and pull-down confirm competitive binding, RNA degradation assay validates functional consequence","pmids":["36280202"],"is_preprint":false},{"year":2023,"finding":"ELAVL1 (HuR) stabilizes CCND2 mRNA and counteracts miR-188-5p-mediated suppression of CCND2 in ovarian cancer cells; competition between miR-188-5p and HuR for CCND2 mRNA modulates CCND2 protein levels and ovarian cancer cell proliferation and migration.","method":"RIP assay, luciferase reporter assay, functional rescue experiments","journal":"Cellular and molecular biology","confidence":"Low","confidence_rationale":"Tier 3 — RIP and luciferase confirm interaction, but single lab with limited mechanistic depth","pmids":["37300687"],"is_preprint":false}],"current_model":"CCND2 (cyclin D2) is a D-type cyclin that drives G1-to-S phase cell cycle progression by binding and activating CDK4/6, which phosphorylates and inactivates the retinoblastoma protein (RB); its expression is transcriptionally activated by STAT3 and other oncogenic signals (blocked by CREM repressors), repressed by Elf5 binding to its proximal promoter and by PRC2.1 (MTF2)-dependent H3K27me3 deposition at its CpG island, and post-translationally regulated by GSK-3β phosphorylation that targets cyclin D2 for proteasomal degradation—a mechanism disrupted by gain-of-function CCND2 mutations clustering around Thr280 that cause protein stabilization, megalencephaly, and brain overgrowth, while loss-of-function proximal variants cause microcephaly; additionally, CCND2 mRNA is post-transcriptionally regulated by numerous miRNAs (including let-7a, miR-1, miR-206, miR-29, miR-146a-5p, and others) targeting its 3'UTR, and its stability is modulated by RNA-binding proteins (IGF2BP3, HuR/ELAVL1) and competing endogenous RNAs, with overexpression in cardiomyocytes proven sufficient to reactivate their cell cycle and promote myocardial repair after infarction."},"narrative":{"teleology":[{"year":2008,"claim":"Establishing that CCND2 is essential for myeloma cell proliferation and that its transcription can be blocked by CREM repressor isoforms resolved how oncogenic signals converge on CCND2 in multiple myeloma.","evidence":"RNAi knockdown and pharmacological CCND2 transcription inhibition via CREM induction in myeloma cells and xenografts","pmids":["18431519"],"confidence":"High","gaps":["Identities of all trans-activating oncogenic signals at the CCND2 promoter in myeloma were not mapped","No structural data on how CREM isoforms occupy the CCND2 promoter"]},{"year":2010,"claim":"Demonstrating that let-7a and Elf5 directly repress CCND2 through its 3′UTR and proximal promoter, respectively, established the first direct post-transcriptional and transcriptional repressors of CCND2.","evidence":"3′UTR luciferase reporter for let-7a in prostate cancer cells; ChIP and promoter reporter for Elf5 in mammary epithelial cells and Elf5-null mice","pmids":["20418948","20831799"],"confidence":"High","gaps":["Whether let-7a and Elf5 act cooperatively in any shared tissue was not tested","Quantitative contribution of Elf5 versus other repressors in vivo unknown"]},{"year":2012,"claim":"Identification of miR-1, miR-206, and miR-29 as additional 3′UTR-targeting miRNAs of CCND2 broadened the network of post-transcriptional regulators and linked them to G1 arrest in rhabdomyosarcoma, while GATA1 was implicated in CCND2 transcriptional repression during erythroid differentiation.","evidence":"Luciferase reporter and cell cycle analysis in rhabdomyosarcoma cells; expression profiling of GATA1FL versus GATA1s in K562 erythroid differentiation","pmids":["22853316","22330340","21752897"],"confidence":"Medium","gaps":["GATA1 binding at the CCND2 promoter was not directly demonstrated by ChIP","Relative potency among miR-1, miR-206, and miR-29 on CCND2 not quantified"]},{"year":2014,"claim":"Discovery that gain-of-function CCND2 mutations near Thr280 resist GSK-3β-mediated proteasomal degradation and cause excessive neural progenitor proliferation established the post-translational degradation mechanism and linked it to megalencephaly–polymicrogyria–polydactyly–hydrocephalus syndrome.","evidence":"In vitro proteasomal degradation assay, mutagenesis, in utero electroporation of embryonic mouse brain, patient-derived cell studies","pmids":["24705253"],"confidence":"High","gaps":["Crystal structure of the degron/GSK-3β interaction not resolved","Whether additional kinases phosphorylate Thr280 in vivo is unknown"]},{"year":2016,"claim":"Demonstration of CCND2 promoter hypermethylation as a silencing mechanism in renal cell cancer and identification of FoxO1-dependent transcriptional regulation via linc00598 expanded the epigenetic and transcriptional regulatory landscape of CCND2.","evidence":"Methylation-specific PCR, bisulfite sequencing, 5-Aza demethylation rescue in RCC lines; lncRNA knockdown with promoter reporter and cell cycle analysis","pmids":["27583477","27572135"],"confidence":"Medium","gaps":["Direct FoxO1 binding at the CCND2 promoter was not validated by ChIP","Whether promoter methylation and PRC2-mediated repression act on the same CpG island was not compared"]},{"year":2017,"claim":"Proving that CCND2 overexpression is sufficient to reactivate cell cycle in post-mitotic cardiomyocytes and promote myocardial repair after infarction opened a therapeutic avenue for cardiac regeneration.","evidence":"Lentiviral CCND2 overexpression in hiPSC-derived cardiomyocytes, Ki67 quantification, mouse myocardial infarction model","pmids":["29018036"],"confidence":"High","gaps":["Whether CCND2-driven cardiomyocyte division produces functionally mature daughter cells was not resolved","Long-term arrhythmogenic risk not fully assessed"]},{"year":2019,"claim":"Multiple discoveries converged on CCND2 regulation: STAT3 was shown to directly activate the CCND2 promoter; PRC2 (via PICOT/EED) deposits H3K27me3 at the CCND2 locus to silence it; and CCND2-overexpressing cardiomyocytes electrically integrate with host myocardium, confirming functional coupling.","evidence":"ChIP for STAT3 at CCND2 promoter in CRC; co-IP/ChIP for PICOT-EED-H3K27me3 at CCND2 in T cells; optical mapping of engrafted cardiomyocytes in mouse","pmids":["31511084","31527584","31629738"],"confidence":"High","gaps":["Whether STAT3 and PRC2 antagonistically regulate CCND2 at the same locus in any single cell type is untested","Electrophysiological integration data limited to single lab and timepoint"]},{"year":2021,"claim":"Reciprocal genotype–phenotype mapping of CCND2 variants (proximal loss-of-function causing microcephaly, distal stabilizing variants causing megalencephaly) established cyclin D2 as a dosage-sensitive determinant of human brain size, while RNA-binding protein IGF2BP3 was identified as a direct stabilizer of CCND2 mRNA.","evidence":"Clinical genetics of five patients from three families; RNA pull-down and RIP confirming IGF2BP3-CCND2 mRNA interaction in colorectal cancer cells","pmids":["34087052","35033075"],"confidence":"Medium","gaps":["Functional rescue of loss-of-function variants was not performed","Quantitative contribution of IGF2BP3 versus miRNA-mediated decay not determined"]},{"year":2021,"claim":"Identification of the CCND2 Thr280Ala gain-of-function mutation as a driver of increased RB phosphorylation and proliferation in AML extended the degron-disruption mechanism from brain overgrowth to hematologic malignancy.","evidence":"Site-directed mutagenesis, RB phosphorylation assay, cell cycle and proliferation analysis in t(8;21) AML cell lines","pmids":["27843138"],"confidence":"High","gaps":["In vivo leukemogenic potential of CCND2 T280A alone was not tested","Whether other AML-associated CCND2 mutations act through the same degron mechanism is unresolved"]},{"year":2023,"claim":"Translational validation that CCND2 modified mRNA delivery promotes cardiomyocyte proliferation and reduces infarct size across two large-animal-relevant models (mouse and pig) strengthened the therapeutic rationale, while PI3K/AKT inhibition was shown to trigger CCND2 degradation via GSK-3β dephosphorylation in lymphoma.","evidence":"Cardiomyocyte-specific modRNA delivery with Ki67/Aurora B quantification in mouse and pig MI models; pharmacological GSK-3β modulation with RB phosphorylation readout in BIA-ALCL","pmids":["37565345","37647808"],"confidence":"High","gaps":["Long-term safety of transient CCND2 induction in heart not established","Whether GSK-3β is the sole kinase controlling CCND2 stability in all lineages remains unclear"]},{"year":2025,"claim":"Genetic dissection of PRC2 subcomplexes revealed that PRC2.1 (MTF2-containing), not PRC2.2 (JARID2-containing), is specifically responsible for H3K27me3 at CCND2 CpG islands and that MTF2 loss upregulates CCND2 sufficiently to confer resistance to CDK4/6 inhibitors.","evidence":"ChIP-seq for H3K27me3, genetic epistasis between MTF2 and JARID2, palbociclib sensitivity assays across multiple cell lines","pmids":["39903505"],"confidence":"High","gaps":["Whether PRC2.1-specific recruitment involves DNA shape recognition at CCND2 CpG islands is not resolved","Clinical prevalence of MTF2 loss as a resistance mechanism to CDK4/6 inhibitors is unknown"]},{"year":null,"claim":"Major unresolved questions include the structural basis of cyclin D2–CDK4/6 complex formation and substrate selectivity, whether the diverse transcriptional and post-transcriptional inputs on CCND2 are integrated in a tissue-specific hierarchy, and whether therapeutic CCND2 modulation in the heart carries long-term oncogenic or arrhythmogenic risk.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of cyclin D2–CDK4 complex exists","Tissue-specific integration of CCND2 regulatory inputs not systematically mapped","Long-term safety of cardiac CCND2 induction not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,4,5,18]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1,7,8]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,1,3,4,5,8,12,18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,18,22]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[7,8,13,14]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,6,9,10]}],"complexes":["Cyclin D2–CDK4","Cyclin D2–CDK6"],"partners":["CDK4","CDK6","GSK3B","IGF2BP3","ELAVL1","SRSF1","STAT3","EZH2"],"other_free_text":[]},"mechanistic_narrative":"CCND2 encodes cyclin D2, a D-type cyclin that partners with CDK4/6 to phosphorylate the retinoblastoma protein (RB), thereby driving G1-to-S phase cell cycle progression in diverse cell types including neural progenitors, hematopoietic cells, and cardiomyocytes [PMID:24705253, PMID:27843138, PMID:29018036]. CCND2 transcription is activated by STAT3 and SMAD3 and repressed by Elf5, CREM repressor isoforms, PRC2.1 (MTF2)-dependent H3K27me3 deposition, and promoter DNA methylation, while its mRNA is post-transcriptionally regulated by multiple miRNAs (let-7a, miR-1, miR-29, miR-135a, miR-194-5p) and stabilized by RNA-binding proteins IGF2BP3 and ELAVL1 [PMID:31511084, PMID:20831799, PMID:18431519, PMID:39903505, PMID:27583477, PMID:20418948, PMID:35033075]. Cyclin D2 protein turnover is controlled by GSK-3β phosphorylation near Thr280, which triggers proteasomal degradation; gain-of-function mutations disrupting this degron cause protein stabilization and megalencephaly, whereas proximal loss-of-function variants cause microcephaly, establishing CCND2 as a dosage-sensitive regulator of human brain size [PMID:24705253, PMID:34087052]. Forced CCND2 expression is sufficient to reactivate the cell cycle in post-mitotic cardiomyocytes and promote myocardial repair after infarction in mouse and pig models [PMID:29018036, PMID:37565345]."},"prefetch_data":{"uniprot":{"accession":"P30279","full_name":"G1/S-specific cyclin-D2","aliases":[],"length_aa":289,"mass_kda":33.1,"function":"Regulatory component of the cyclin D2-CDK4 (DC) complex that phosphorylates and inhibits members of the retinoblastoma (RB) protein family including RB1 and regulates the cell-cycle during G(1)/S transition (PubMed:18827403, PubMed:8114739). Phosphorylation of RB1 allows dissociation of the transcription factor E2F from the RB/E2F complex and the subsequent transcription of E2F target genes which are responsible for the progression through the G(1) phase (PubMed:18827403, PubMed:8114739). Hypophosphorylates RB1 in early G(1) phase (PubMed:18827403, PubMed:8114739). Cyclin D-CDK4 complexes are major integrators of various mitogenenic and antimitogenic signals (PubMed:18827403, PubMed:8114739)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P30279/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CCND2","classification":"Not Classified","n_dependent_lines":81,"n_total_lines":1208,"dependency_fraction":0.06705298013245033},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CCND2","total_profiled":1310},"omim":[{"mim_id":"619008","title":"LONG INTERGENIC NONCODING RNA 598; LINC00598","url":"https://www.omim.org/entry/619008"},{"mim_id":"615938","title":"MEGALENCEPHALY-POLYMICROGYRIA-POLYDACTYLY-HYDROCEPHALUS SYNDROME 3; MPPH3","url":"https://www.omim.org/entry/615938"},{"mim_id":"615672","title":"MICRO RNA 497; 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international medical journal of experimental and clinical research","url":"https://pubmed.ncbi.nlm.nih.gov/33320844","citation_count":7,"is_preprint":false},{"pmid":"31527584","id":"PMC_31527584","title":"PICOT binding to chromatin-associated EED negatively regulates cyclin D2 expression by increasing H3K27me3 at the CCND2 gene promoter.","date":"2019","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/31527584","citation_count":7,"is_preprint":false},{"pmid":"31056854","id":"PMC_31056854","title":"Severe presentation and complex brain malformations in an individual carrying a CCND2 variant.","date":"2019","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31056854","citation_count":7,"is_preprint":false},{"pmid":"9530346","id":"PMC_9530346","title":"Genomic amplification of CCND2 is rare in non-Hodgkin lymphomas.","date":"1998","source":"Cancer genetics and cytogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/9530346","citation_count":7,"is_preprint":false},{"pmid":"24743557","id":"PMC_24743557","title":"Association between the polymorphism rs3217927 of CCND2 and the risk of childhood acute lymphoblastic leukemia in a Chinese population.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24743557","citation_count":6,"is_preprint":false},{"pmid":"35117490","id":"PMC_35117490","title":"LncRNA XIST acts as a ceRNA sponging miR-185-5p to modulate pancreatic cancer cell proliferation via targeting CCND2.","date":"2020","source":"Translational cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/35117490","citation_count":6,"is_preprint":false},{"pmid":"21559724","id":"PMC_21559724","title":"Coamplification in human breast-tumors and physical linkage at chromosomal band 12p13, of ccnd2 and fgf6 genes.","date":"1994","source":"International journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/21559724","citation_count":6,"is_preprint":false},{"pmid":"37866807","id":"PMC_37866807","title":"GABA regulates the proliferation and apoptosis of head and neck squamous cell carcinoma cells by promoting the expression of CCND2 and BCL2L1.","date":"2023","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37866807","citation_count":6,"is_preprint":false},{"pmid":"36694220","id":"PMC_36694220","title":"CCND2 and miR-206 as potential biomarkers in the clinical diagnosis of thyroid carcinoma by fine-needle aspiration cytology.","date":"2023","source":"World journal of surgical oncology","url":"https://pubmed.ncbi.nlm.nih.gov/36694220","citation_count":6,"is_preprint":false},{"pmid":"34801563","id":"PMC_34801563","title":"Reduced expression of microRNA-432-5p by DNA methyltransferase 3B leads to development of colorectal cancer through upregulation of CCND2.","date":"2021","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/34801563","citation_count":5,"is_preprint":false},{"pmid":"35616759","id":"PMC_35616759","title":"Gene identification and functional analysis of a D-type cyclin (CCND2) in freshwater pearl mussel (Hyriopsis cumingii).","date":"2022","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/35616759","citation_count":5,"is_preprint":false},{"pmid":"35786622","id":"PMC_35786622","title":"Interaction of CCND2, CDKN1A, and POLD3 Variants in Mexican Patients with Colorectal Cancer.","date":"2022","source":"The Turkish journal of gastroenterology : the official journal of Turkish Society of Gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/35786622","citation_count":5,"is_preprint":false},{"pmid":"36280202","id":"PMC_36280202","title":"SRSF1 promotes ASMC proliferation in asthma by competitively binding CCND2 with miRNA-135a.","date":"2022","source":"Pulmonary pharmacology & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/36280202","citation_count":5,"is_preprint":false},{"pmid":"39903505","id":"PMC_39903505","title":"The PRC2.1 subcomplex opposes G1 progression through regulation of CCND1 and CCND2.","date":"2025","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/39903505","citation_count":4,"is_preprint":false},{"pmid":"37300687","id":"PMC_37300687","title":"MiR-188-5p inhibits cell proliferation and migration in ovarian cancer via competing for CCND2 with ELAVL1.","date":"2023","source":"Cellular and molecular biology (Noisy-le-Grand, France)","url":"https://pubmed.ncbi.nlm.nih.gov/37300687","citation_count":4,"is_preprint":false},{"pmid":"31938243","id":"PMC_31938243","title":"LncRNA CCND2-AS1 is up-regulated and regulates proliferation, migration, and invasion in breast cancer.","date":"2018","source":"International journal of clinical and experimental pathology","url":"https://pubmed.ncbi.nlm.nih.gov/31938243","citation_count":4,"is_preprint":false},{"pmid":"32607313","id":"PMC_32607313","title":"Aberrant methylation-mediated downregulation of lncRNA CCND2 AS1 promotes cell proliferation in cervical cancer.","date":"2020","source":"Journal of biological research (Thessalonike, Greece)","url":"https://pubmed.ncbi.nlm.nih.gov/32607313","citation_count":4,"is_preprint":false},{"pmid":"37647808","id":"PMC_37647808","title":"PI3K/AKT inhibitor BEZ-235 targets CCND2 and induces G1 arrest in breast implant-associated anaplastic large cell lymphoma.","date":"2023","source":"Leukemia research","url":"https://pubmed.ncbi.nlm.nih.gov/37647808","citation_count":4,"is_preprint":false},{"pmid":"35437818","id":"PMC_35437818","title":"Prenatal diagnosis of microcephaly as shown by plateauing of head circumference growth during the 3rd trimester in a fetus with a CCND2 inverse growth variant.","date":"2022","source":"Prenatal diagnosis","url":"https://pubmed.ncbi.nlm.nih.gov/35437818","citation_count":4,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":52927,"output_tokens":6015,"usd":0.124503},"stage2":{"model":"claude-opus-4-6","input_tokens":9624,"output_tokens":3473,"usd":0.202418},"total_usd":0.326921,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"De novo CCND2 mutations clustered around a GSK-3β phosphorylation site render cyclin D2 resistant to proteasomal degradation in vitro; the PI3K-AKT pathway modulates GSK-3β activity, leading to similar CCND2 accumulation in cells with PIK3CA, PIK3R2, or AKT3 mutations. In utero electroporation of mutant CCND2 into embryonic mouse brains produced more proliferating progenitors and a smaller fraction exiting the cell cycle compared to wild-type CCND2.\",\n      \"method\": \"In vitro proteasomal degradation assay, in utero electroporation, cell cycle analysis, patient-derived cell studies\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (in vitro degradation assay, mutagenesis, in vivo electroporation) in a single rigorous study\",\n      \"pmids\": [\"24705253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCND2 Thr280Ala mutation (clustering around a conserved threonine residue) leads to increased phosphorylation of the retinoblastoma protein, causing significant cell cycle changes and increased proliferation of AML cell lines, establishing CCND2 gain-of-function mutations as drivers of cell cycle dysregulation in t(8;21) AML.\",\n      \"method\": \"Site-directed mutagenesis, retinoblastoma phosphorylation assay, cell cycle analysis, proliferation assays in AML cell lines\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct mutagenesis with functional validation (RB phosphorylation, cell cycle, proliferation)\",\n      \"pmids\": [\"27843138\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"STAT3 directly binds the CCND2 promoter, increasing CCND2 transcription as part of JAK2/STAT3/CCND2 signaling that promotes cancer stem cell persistence and radioresistance in colorectal cancer.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), promoter reporter assay, JAK2/STAT3 inhibition experiments, patient-derived CRC cells and xenografts\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrating direct STAT3 binding to CCND2 promoter, supported by multiple cell models and in vivo validation\",\n      \"pmids\": [\"31511084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MicroRNA let-7a directly binds the 3'UTR of CCND2 mRNA, downregulating CCND2 protein expression and inducing G1/S cell cycle arrest in prostate cancer cells.\",\n      \"method\": \"Dual-luciferase reporter assay, western blotting, cell cycle analysis, xenograft model\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct 3'UTR binding validated by luciferase assay, protein knockdown confirmed, in vivo validation included\",\n      \"pmids\": [\"20418948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Overexpression of CCND2 in human iPSC-derived cardiomyocytes activates cell cycle progression (3-7 fold upregulation of Ki67 and other proliferation markers), enhances engraftment after myocardial infarction in mice, and promotes remuscularization of injured myocardium.\",\n      \"method\": \"Lentiviral CCND2 overexpression, cell cycle marker quantification, mouse MI model with histological and functional assessment\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct overexpression with quantitative cell cycle markers and in vivo cardiac repair endpoints\",\n      \"pmids\": [\"29018036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CCND2 modified mRNA delivered via a cardiomyocyte-specific SMRTs system induces CCND2 expression selectively in cardiomyocytes, activates cell cycle markers (Ki67, Aurora B kinase), promotes cardiomyocyte proliferation, and reduces infarct size in both mouse and pig MI models.\",\n      \"method\": \"Modified mRNA delivery system, cardiomyocyte-specific expression via miR-1/miR-208 regulation, Ki67/Aurora B quantification, echocardiography in mouse and pig MI models\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — orthogonal validation across two mammalian species with mechanistic specificity controls\",\n      \"pmids\": [\"37565345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RNAi knockdown of CCND2 inhibits proliferation and is progressively cytotoxic in human myeloma cells; kinetin riboside suppresses CCND2 transcription by upregulating repressor isoforms of CREM (cAMP-response element modulator), blocking trans-activation of CCND2 by multiple myeloma oncogenes.\",\n      \"method\": \"RNAi knockdown, chemical library screen with cell-based CCND2 trans-activation assay, transcription factor reporter assay, primary myeloma cell studies, xenograft model\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including RNAi, pharmacological inhibition, mechanistic transcription factor analysis, and in vivo validation\",\n      \"pmids\": [\"18431519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PICOT protein binds to chromatin-associated EED (a PRC2 component) via its PICOT/Grx homology domains; PICOT knockdown reduces H3K27me3 mark and decreases EED and EZH2 occupancy at the CCND2 gene promoter, resulting in increased CCND2 mRNA and protein expression in T cells.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, knockdown experiments, western blotting, qPCR, TCGA data correlation\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, ChIP with functional validation of epigenetic mark changes at CCND2 promoter\",\n      \"pmids\": [\"31527584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PRC2.1 (containing MTF2), but not PRC2.2 (containing JARID2), promotes H3K27me3 deposition at CpG islands in the CCND1 and CCND2 promoters; loss of MTF2 upregulates both cyclins and rescues cells from CDK4/6 inhibitor palbociclib-induced G1 arrest.\",\n      \"method\": \"Chemogenetic screen, genetic epistasis (MTF2 vs JARID2 mutation), ChIP-seq for H3K27me3, palbociclib sensitivity assays in multiple cell lines\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP-seq, genetic epistasis with subcomplex-specific mutants, functional G1 progression assays across multiple cell lineages\",\n      \"pmids\": [\"39903505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The ETS transcription factor Elf5 directly binds a genomic segment upstream of the Ccnd2 gene and transcriptionally represses Ccnd2 expression in mouse mammary gland; loss of Elf5 in vivo leads to upregulation of Ccnd2 in luminal mammary cells.\",\n      \"method\": \"ChIP-cloning, ChIP, promoter reporter assay, Elf5-null mammary epithelial cells and gland analysis\",\n      \"journal\": \"BMC molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct ChIP demonstrating in vivo binding, promoter reporter confirming repressive function, validated in null animals\",\n      \"pmids\": [\"20831799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Long noncoding RNA linc00598 regulates CCND2 transcription through modulation of FoxO1 transcriptional activity at the CCND2 promoter; knockdown of linc00598 induces G0/G1 cell cycle arrest and inhibits proliferation.\",\n      \"method\": \"Microarray analysis, knockdown experiments, promoter reporter assay, cell cycle analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — promoter reporter and knockdown with cell cycle readout, but mechanism of FoxO1 modulation not fully resolved\",\n      \"pmids\": [\"27572135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MiR-1 directly targets and represses CCND2 (favoring G1/S transition) in thyroid carcinoma cells; ectopic miR-1 expression inhibits thyroid carcinoma cell proliferation and migration, validated by 3'UTR reporter assays.\",\n      \"method\": \"Luciferase reporter assay, western blotting, functional proliferation and migration assays\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct 3'UTR targeting validated by luciferase assay with functional consequences, single lab\",\n      \"pmids\": [\"21752897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MiR-1, miR-206, and miR-29 target the 3'UTR of CCND2 to regulate its expression in rhabdomyosarcoma; overexpression of miR-29 downregulates CCND2 and other cell cycle genes (E2F7), inducing G1 arrest and decreased cell proliferation.\",\n      \"method\": \"Ectopic miRNA expression, western blotting, cell cycle analysis, luciferase reporter assays\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple miRNAs validated with cell cycle and proliferation readouts, single lab\",\n      \"pmids\": [\"22330340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCND2 promoter is silenced by aberrant methylation in renal cell cancer; treatment with the demethylating agent 5-Aza (with or without TSA) restores CCND2 expression in methylated RCC cell lines.\",\n      \"method\": \"Methylation-specific PCR (MSP), bisulfite genomic sequencing (BGS), 5-Aza/TSA treatment, expression analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct methylation mapping with pharmacological demethylation rescue of expression\",\n      \"pmids\": [\"27583477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CCND2 promoter hypermethylation silences CCND2 expression in lung and breast cancer; cell model assays show that CCND2 expression inhibits cancer cell growth and migration; antroquinonol D, a demethylating agent, upregulates CCND2 expression and causes cell cycle arrest.\",\n      \"method\": \"Genome-wide methylation analysis, quantitative MSP, cell proliferation and migration assays, drug treatment\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — promoter methylation linked to expression with functional rescue, single lab\",\n      \"pmids\": [\"30308939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CCND2 overexpression in hiPSC-derived cardiomyocytes results in electrical integration (coupling) with host myocardium 6 months after transplantation, with optical mapping confirming synchronized action potential propagation, alongside >50% replacement of myocardial scar tissue.\",\n      \"method\": \"Optical mapping of action potential propagation, histological quantification of engraftment, echocardiography\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct electrophysiological measurement of CCND2-OE CM integration, single lab\",\n      \"pmids\": [\"31629738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCND2 loss-of-function through proximal frameshift or stop-gain variants causes microcephaly, while distal terminal-exon variants causing protein stabilization lead to megalencephaly, demonstrating that distinct classes of CCND2 variants have reciprocal effects on human brain growth.\",\n      \"method\": \"Clinical genetics, variant mapping, phenotypic characterization of five individuals from three families\",\n      \"journal\": \"American journal of medical genetics. Part A\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — clinical genetics series establishing genotype-phenotype relationship, consistent with prior functional data from PMID:24705253\",\n      \"pmids\": [\"34087052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"lncRNA TUG1 promotes CCND2 expression by binding EZH2 to epigenetically silence miR-194-5p (via promoter hypermethylation); knockdown of TUG1 reduces EZH2 levels, relieves methylation of miR-194-5p, which then directly targets and suppresses CCND2 in bladder cancer.\",\n      \"method\": \"EZH2 knockdown, bisulfite sequencing of miR-194-5p promoter, dual-luciferase reporter assay for miR-194-5p/CCND2, western blotting\",\n      \"journal\": \"Molecular therapy. Nucleic acids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — mechanistic chain from epigenetic silencing through miRNA to CCND2, validated by multiple methods in single lab\",\n      \"pmids\": [\"30925453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PI3K/AKT inhibitor BEZ-235 induces dephosphorylation of GSK3β, leading to proteasomal degradation of CCND2 protein, dephosphorylation of RB, and G1 cell cycle arrest in BIA-ALCL; CDK4/6 inhibitor palbociclib also dephosphorylates RB and arrests cells in G1, confirming that CCND2 controls CDK4/6 activity and RB phosphorylation.\",\n      \"method\": \"Western blotting for RB phosphorylation, GSK3β phosphorylation, mTORC1 target S6; cell cycle analysis; pharmacological inhibition\",\n      \"journal\": \"Leukemia research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biochemical demonstration of CCND2 protein degradation via GSK3β pathway and RB phosphorylation readout\",\n      \"pmids\": [\"37647808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GATA1s isoform (but not GATA1FL) fails to repress CCND2 during terminal erythroid differentiation of K562 cells, suggesting CCND2 is a target of GATA1-mediated transcriptional repression during hematopoietic differentiation.\",\n      \"method\": \"Transgenic K562 cells expressing GATA1s or GATA1FL, gene expression profiling during erythroid differentiation\",\n      \"journal\": \"Journal of hematology & oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — expression profiling with transgenic overexpression, no direct binding or promoter assay for CCND2\",\n      \"pmids\": [\"22853316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ZFAS1 lncRNA acts as a ceRNA to sponge miR-150-5p, preventing miR-150-5p from downregulating CCND2; ZFAS1 knockdown reduces ferroptosis markers and cardiomyocyte injury in diabetic cardiomyopathy models, with effects reversed by miR-150-5p inhibition or CCND2 depletion, placing CCND2 downstream of the ZFAS1/miR-150-5p axis.\",\n      \"method\": \"Dual-luciferase reporter assay, RNA pull-down, in vitro high glucose cardiomyocyte model, db/db mouse model, ferroptosis marker measurement\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — dual-luciferase and RNA pull-down confirm sponging, in vitro and in vivo functional rescue experiments\",\n      \"pmids\": [\"34609043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCND2 mRNA is stabilized by IGF2BP3 protein binding, preventing its degradation; hsa_circ_0000231 promotes CCND2 expression by both sponging miR-375 (ceRNA mechanism) and binding IGF2BP3 to prevent CCND2 mRNA degradation in colorectal cancer cells.\",\n      \"method\": \"RNA pull-down, RNA immunoprecipitation (RIP), dual-luciferase reporter assay, in vitro and in vivo functional assays\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA pull-down and RIP confirm IGF2BP3-CCND2 mRNA interaction, dual mechanism validated\",\n      \"pmids\": [\"35033075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"miR-135a suppresses granulosa cell growth by directly targeting the 3'UTR of Ccnd2; the TGFBR1-SMAD3 pathway enhances Ccnd2 promoter activity and upregulates Ccnd2 expression; ESR2 (estrogen receptor 2) acts as a transcription factor binding the miR-135a promoter to decrease miR-135a transcription, establishing an ESR2/miR-135a/Tgfbr1/Ccnd2 regulatory axis.\",\n      \"method\": \"3'UTR luciferase reporter assay, ChIP-qPCR for SMAD3 at Ccnd2 promoter and ESR2 at miR-135a promoter, subcellular localization analysis, miR-135a overexpression in granulosa cells\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-qPCR establishes direct binding at Ccnd2 promoter and miR-135a promoter, luciferase validates 3'UTR targeting\",\n      \"pmids\": [\"34440873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SRSF1 and miR-135a competitively bind the 3'UTR region of CCND2 mRNA; SRSF1 overexpression represses degradation of CCND2 mRNA by outcompeting miR-135a, while SRSF1 knockdown inhibits airway smooth muscle cell proliferation by reducing CCND2 levels.\",\n      \"method\": \"RNA immunoprecipitation, RNA pull-down, dual-luciferase reporter assay, RNA degradation assay, flow cytometry\",\n      \"journal\": \"Pulmonary pharmacology & therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA immunoprecipitation and pull-down confirm competitive binding, RNA degradation assay validates functional consequence\",\n      \"pmids\": [\"36280202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ELAVL1 (HuR) stabilizes CCND2 mRNA and counteracts miR-188-5p-mediated suppression of CCND2 in ovarian cancer cells; competition between miR-188-5p and HuR for CCND2 mRNA modulates CCND2 protein levels and ovarian cancer cell proliferation and migration.\",\n      \"method\": \"RIP assay, luciferase reporter assay, functional rescue experiments\",\n      \"journal\": \"Cellular and molecular biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — RIP and luciferase confirm interaction, but single lab with limited mechanistic depth\",\n      \"pmids\": [\"37300687\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCND2 (cyclin D2) is a D-type cyclin that drives G1-to-S phase cell cycle progression by binding and activating CDK4/6, which phosphorylates and inactivates the retinoblastoma protein (RB); its expression is transcriptionally activated by STAT3 and other oncogenic signals (blocked by CREM repressors), repressed by Elf5 binding to its proximal promoter and by PRC2.1 (MTF2)-dependent H3K27me3 deposition at its CpG island, and post-translationally regulated by GSK-3β phosphorylation that targets cyclin D2 for proteasomal degradation—a mechanism disrupted by gain-of-function CCND2 mutations clustering around Thr280 that cause protein stabilization, megalencephaly, and brain overgrowth, while loss-of-function proximal variants cause microcephaly; additionally, CCND2 mRNA is post-transcriptionally regulated by numerous miRNAs (including let-7a, miR-1, miR-206, miR-29, miR-146a-5p, and others) targeting its 3'UTR, and its stability is modulated by RNA-binding proteins (IGF2BP3, HuR/ELAVL1) and competing endogenous RNAs, with overexpression in cardiomyocytes proven sufficient to reactivate their cell cycle and promote myocardial repair after infarction.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CCND2 encodes cyclin D2, a D-type cyclin that partners with CDK4/6 to phosphorylate the retinoblastoma protein (RB), thereby driving G1-to-S phase cell cycle progression in diverse cell types including neural progenitors, hematopoietic cells, and cardiomyocytes [PMID:24705253, PMID:27843138, PMID:29018036]. CCND2 transcription is activated by STAT3 and SMAD3 and repressed by Elf5, CREM repressor isoforms, PRC2.1 (MTF2)-dependent H3K27me3 deposition, and promoter DNA methylation, while its mRNA is post-transcriptionally regulated by multiple miRNAs (let-7a, miR-1, miR-29, miR-135a, miR-194-5p) and stabilized by RNA-binding proteins IGF2BP3 and ELAVL1 [PMID:31511084, PMID:20831799, PMID:18431519, PMID:39903505, PMID:27583477, PMID:20418948, PMID:35033075]. Cyclin D2 protein turnover is controlled by GSK-3β phosphorylation near Thr280, which triggers proteasomal degradation; gain-of-function mutations disrupting this degron cause protein stabilization and megalencephaly, whereas proximal loss-of-function variants cause microcephaly, establishing CCND2 as a dosage-sensitive regulator of human brain size [PMID:24705253, PMID:34087052]. Forced CCND2 expression is sufficient to reactivate the cell cycle in post-mitotic cardiomyocytes and promote myocardial repair after infarction in mouse and pig models [PMID:29018036, PMID:37565345].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Establishing that CCND2 is essential for myeloma cell proliferation and that its transcription can be blocked by CREM repressor isoforms resolved how oncogenic signals converge on CCND2 in multiple myeloma.\",\n      \"evidence\": \"RNAi knockdown and pharmacological CCND2 transcription inhibition via CREM induction in myeloma cells and xenografts\",\n      \"pmids\": [\"18431519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identities of all trans-activating oncogenic signals at the CCND2 promoter in myeloma were not mapped\", \"No structural data on how CREM isoforms occupy the CCND2 promoter\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that let-7a and Elf5 directly repress CCND2 through its 3′UTR and proximal promoter, respectively, established the first direct post-transcriptional and transcriptional repressors of CCND2.\",\n      \"evidence\": \"3′UTR luciferase reporter for let-7a in prostate cancer cells; ChIP and promoter reporter for Elf5 in mammary epithelial cells and Elf5-null mice\",\n      \"pmids\": [\"20418948\", \"20831799\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether let-7a and Elf5 act cooperatively in any shared tissue was not tested\", \"Quantitative contribution of Elf5 versus other repressors in vivo unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identification of miR-1, miR-206, and miR-29 as additional 3′UTR-targeting miRNAs of CCND2 broadened the network of post-transcriptional regulators and linked them to G1 arrest in rhabdomyosarcoma, while GATA1 was implicated in CCND2 transcriptional repression during erythroid differentiation.\",\n      \"evidence\": \"Luciferase reporter and cell cycle analysis in rhabdomyosarcoma cells; expression profiling of GATA1FL versus GATA1s in K562 erythroid differentiation\",\n      \"pmids\": [\"22853316\", \"22330340\", \"21752897\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GATA1 binding at the CCND2 promoter was not directly demonstrated by ChIP\", \"Relative potency among miR-1, miR-206, and miR-29 on CCND2 not quantified\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery that gain-of-function CCND2 mutations near Thr280 resist GSK-3β-mediated proteasomal degradation and cause excessive neural progenitor proliferation established the post-translational degradation mechanism and linked it to megalencephaly–polymicrogyria–polydactyly–hydrocephalus syndrome.\",\n      \"evidence\": \"In vitro proteasomal degradation assay, mutagenesis, in utero electroporation of embryonic mouse brain, patient-derived cell studies\",\n      \"pmids\": [\"24705253\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of the degron/GSK-3β interaction not resolved\", \"Whether additional kinases phosphorylate Thr280 in vivo is unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstration of CCND2 promoter hypermethylation as a silencing mechanism in renal cell cancer and identification of FoxO1-dependent transcriptional regulation via linc00598 expanded the epigenetic and transcriptional regulatory landscape of CCND2.\",\n      \"evidence\": \"Methylation-specific PCR, bisulfite sequencing, 5-Aza demethylation rescue in RCC lines; lncRNA knockdown with promoter reporter and cell cycle analysis\",\n      \"pmids\": [\"27583477\", \"27572135\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FoxO1 binding at the CCND2 promoter was not validated by ChIP\", \"Whether promoter methylation and PRC2-mediated repression act on the same CpG island was not compared\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Proving that CCND2 overexpression is sufficient to reactivate cell cycle in post-mitotic cardiomyocytes and promote myocardial repair after infarction opened a therapeutic avenue for cardiac regeneration.\",\n      \"evidence\": \"Lentiviral CCND2 overexpression in hiPSC-derived cardiomyocytes, Ki67 quantification, mouse myocardial infarction model\",\n      \"pmids\": [\"29018036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CCND2-driven cardiomyocyte division produces functionally mature daughter cells was not resolved\", \"Long-term arrhythmogenic risk not fully assessed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Multiple discoveries converged on CCND2 regulation: STAT3 was shown to directly activate the CCND2 promoter; PRC2 (via PICOT/EED) deposits H3K27me3 at the CCND2 locus to silence it; and CCND2-overexpressing cardiomyocytes electrically integrate with host myocardium, confirming functional coupling.\",\n      \"evidence\": \"ChIP for STAT3 at CCND2 promoter in CRC; co-IP/ChIP for PICOT-EED-H3K27me3 at CCND2 in T cells; optical mapping of engrafted cardiomyocytes in mouse\",\n      \"pmids\": [\"31511084\", \"31527584\", \"31629738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether STAT3 and PRC2 antagonistically regulate CCND2 at the same locus in any single cell type is untested\", \"Electrophysiological integration data limited to single lab and timepoint\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Reciprocal genotype–phenotype mapping of CCND2 variants (proximal loss-of-function causing microcephaly, distal stabilizing variants causing megalencephaly) established cyclin D2 as a dosage-sensitive determinant of human brain size, while RNA-binding protein IGF2BP3 was identified as a direct stabilizer of CCND2 mRNA.\",\n      \"evidence\": \"Clinical genetics of five patients from three families; RNA pull-down and RIP confirming IGF2BP3-CCND2 mRNA interaction in colorectal cancer cells\",\n      \"pmids\": [\"34087052\", \"35033075\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional rescue of loss-of-function variants was not performed\", \"Quantitative contribution of IGF2BP3 versus miRNA-mediated decay not determined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of the CCND2 Thr280Ala gain-of-function mutation as a driver of increased RB phosphorylation and proliferation in AML extended the degron-disruption mechanism from brain overgrowth to hematologic malignancy.\",\n      \"evidence\": \"Site-directed mutagenesis, RB phosphorylation assay, cell cycle and proliferation analysis in t(8;21) AML cell lines\",\n      \"pmids\": [\"27843138\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo leukemogenic potential of CCND2 T280A alone was not tested\", \"Whether other AML-associated CCND2 mutations act through the same degron mechanism is unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Translational validation that CCND2 modified mRNA delivery promotes cardiomyocyte proliferation and reduces infarct size across two large-animal-relevant models (mouse and pig) strengthened the therapeutic rationale, while PI3K/AKT inhibition was shown to trigger CCND2 degradation via GSK-3β dephosphorylation in lymphoma.\",\n      \"evidence\": \"Cardiomyocyte-specific modRNA delivery with Ki67/Aurora B quantification in mouse and pig MI models; pharmacological GSK-3β modulation with RB phosphorylation readout in BIA-ALCL\",\n      \"pmids\": [\"37565345\", \"37647808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Long-term safety of transient CCND2 induction in heart not established\", \"Whether GSK-3β is the sole kinase controlling CCND2 stability in all lineages remains unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Genetic dissection of PRC2 subcomplexes revealed that PRC2.1 (MTF2-containing), not PRC2.2 (JARID2-containing), is specifically responsible for H3K27me3 at CCND2 CpG islands and that MTF2 loss upregulates CCND2 sufficiently to confer resistance to CDK4/6 inhibitors.\",\n      \"evidence\": \"ChIP-seq for H3K27me3, genetic epistasis between MTF2 and JARID2, palbociclib sensitivity assays across multiple cell lines\",\n      \"pmids\": [\"39903505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PRC2.1-specific recruitment involves DNA shape recognition at CCND2 CpG islands is not resolved\", \"Clinical prevalence of MTF2 loss as a resistance mechanism to CDK4/6 inhibitors is unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the structural basis of cyclin D2–CDK4/6 complex formation and substrate selectivity, whether the diverse transcriptional and post-transcriptional inputs on CCND2 are integrated in a tissue-specific hierarchy, and whether therapeutic CCND2 modulation in the heart carries long-term oncogenic or arrhythmogenic risk.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of cyclin D2–CDK4 complex exists\", \"Tissue-specific integration of CCND2 regulatory inputs not systematically mapped\", \"Long-term safety of cardiac CCND2 induction not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 4, 5, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 7, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 8, 12, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 18, 22]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [7, 8, 13, 14]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 6, 9, 10]}\n    ],\n    \"complexes\": [\n      \"Cyclin D2–CDK4\",\n      \"Cyclin D2–CDK6\"\n    ],\n    \"partners\": [\n      \"CDK4\",\n      \"CDK6\",\n      \"GSK3B\",\n      \"IGF2BP3\",\n      \"ELAVL1\",\n      \"SRSF1\",\n      \"STAT3\",\n      \"EZH2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}