{"gene":"MKRN2","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2017,"finding":"MKRN2 is a RING finger domain-dependent E3 ubiquitin ligase that binds to the p65 subunit of NF-κB, promotes its K48-linked polyubiquitination and proteasome-dependent degradation, thereby suppressing NF-κB transactivation. MKRN2 was identified via yeast two-hybrid screening with PDLIM2, and MKRN2 and PDLIM2 synergistically promote p65 polyubiquitination and degradation. MKRN2 knockdown in dendritic cells increased nuclear p65 and augmented proinflammatory cytokine production.","method":"Yeast two-hybrid screening, Co-IP, in vitro ubiquitination assay, RING domain mutagenesis, shRNA knockdown, cytokine measurement","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including yeast two-hybrid, Co-IP, in vitro ubiquitination, domain mutagenesis, and functional knockdown","pmids":["28378844"],"is_preprint":false},{"year":2008,"finding":"Xenopus makorin-2 (mkrn2) functions as a neurogenesis inhibitor acting downstream of PI3K and Akt and upstream of GSK-3β; overexpression suppresses PI3K/Akt-induced neural marker (NCAM) expression and upregulates GSK-3β mRNA and protein, while morpholino knockdown induces double axis in tadpoles.","method":"Xenopus animal cap explant assay, morpholino antisense knockdown, overexpression of constitutively active PI3K/Akt and dominant negative GSK-3β, Western blot, RT-PCR","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — epistasis established by multiple genetic manipulations (constitutively active/dominant negative constructs) in Xenopus embryos, replicated with multiple markers","pmids":["18198183"],"is_preprint":false},{"year":2010,"finding":"The third C3H zinc finger, Cys-His motif, and C3HC4 RING zinc finger of mkrn2 are essential and sufficient for its anti-neurogenic activity; a C-terminal truncation mutant containing only these domains (mkrn2(s)-7) recapitulates the full-length phenotype of dorso-posterior deficiencies in tadpoles and inhibits NCAM expression and induces GSK-3β in animal cap assays.","method":"N- and C-terminal truncation mutagenesis, Xenopus overexpression, animal cap explant assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1–2 — domain mapping by systematic mutagenesis in Xenopus functional assay, single lab","pmids":["20167204"],"is_preprint":false},{"year":2016,"finding":"Mkrn2 knockout in mice causes male infertility characterized by low sperm number, poor motility, aberrant morphology, spermiation failure, and misarrangement of ectoplasmic specialization in testes; mechanistically, Odf2 (a vital spermatogenesis protein) expression is significantly decreased in knockout testes.","method":"Mkrn2 knockout mouse model, histology, sperm analysis, Western blot for Odf2","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with defined cellular phenotype and molecular mechanism (Odf2 loss); replicated in human infertility samples","pmids":["28008940"],"is_preprint":false},{"year":2020,"finding":"Mkrn2 deficiency in mice causes abnormally high testicular apoptosis through the p53/PERP signaling pathway; MKRN2 normally suppresses PERP expression, and PERP acts as a negative regulator of spermatogenesis whose ectopic expression induces male infertility.","method":"Mkrn2 knockout mouse model, digital gene expression profiling (DGE), GSEA, KEGG pathway analysis, protein expression analysis","journal":"Asian journal of andrology","confidence":"Medium","confidence_rationale":"Tier 2–3 — KO model with transcriptomic pathway mapping; mechanistic link to p53/PERP established by gene expression rather than direct biochemical interaction assay","pmids":["31489847"],"is_preprint":false},{"year":2020,"finding":"MKRN2 ubiquitinates IGF2BP3 (an RNA-binding protein) to promote its degradation, thereby regulating CD44 and PDPN expression; MKRN2 knockdown in neuroblastoma SHSY5Y cells promotes proliferation and migration in an IGF2BP3-dependent manner.","method":"shRNA knockdown, Co-IP, pulldown, in vitro ubiquitination assay, Western blot","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro ubiquitination assay plus functional knockdown, single lab","pmids":["32560817"],"is_preprint":false},{"year":2020,"finding":"MKRN2 interacts with and ubiquitinates p53 to promote its degradation, thereby regulating melanoma cell proliferation; MKRN2 downregulation inhibits melanoma cell growth in a p53-dependent manner (confirmed by p53 CRISPR knockout rescue).","method":"Co-IP, GST pulldown, in vitro ubiquitination assay, CRISPR-Cas9 p53 knockout, MTT and colony formation assays","journal":"Oncology letters","confidence":"High","confidence_rationale":"Tier 1 — in vitro ubiquitination assay, Co-IP, GST pulldown, and genetic rescue with p53 KO, multiple orthogonal methods","pmids":["32194692"],"is_preprint":false},{"year":2020,"finding":"MKRN2 physically interacts with GLE1 (a DEAD-box helicase activator involved in mRNA export termination) as identified by affinity-purification mass spectrometry; MKRN2 binds selectively to the 3' UTR of a diverse subset of mRNAs; morpholino knockdown or CRISPR/Cas9 knockout of MKRN2 partially rescues retinal developmental defects upon GLE1 depletion in zebrafish, establishing epistasis; knockdown of MKRN2 enhances nuclear export of MKRN2-associated mRNAs.","method":"Affinity purification–mass spectrometry, zebrafish morpholino knockdown, CRISPR/Cas9 knockout, genetic epistasis, ribonomic (RIP-seq) approaches","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — AP-MS protein interaction, genetic epistasis in zebrafish, ribonomics; multiple orthogonal methods","pmids":["32460013"],"is_preprint":false},{"year":2018,"finding":"MKRN2 inhibits migration and invasion of non-small-cell lung cancer cells through downregulation of the PI3K/Akt pathway, as demonstrated by MKRN2 silencing and overexpression experiments in NSCLC cell lines.","method":"MKRN2 siRNA knockdown and overexpression, migration and invasion assays, Western blot for PI3K/Akt pathway components","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional KD/OE with pathway placement, single lab, no direct biochemical substrate identification","pmids":["30103781"],"is_preprint":false},{"year":2022,"finding":"MKRN2 promotes ubiquitination-mediated degradation of PKM2 (pyruvate kinase M2) and attenuates PKM2's effect on ERK signaling, thereby inhibiting gastric cancer cell proliferation.","method":"Co-IP, ubiquitination assay, overexpression and knockdown, CCK-8, in vivo xenograft","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 2 — ubiquitination assay with pathway readout; single lab","pmids":["35196650"],"is_preprint":false},{"year":2023,"finding":"MKRN2 interacts with STAT1; Co-IP assays show a direct MKRN2–STAT1 interaction in testis and MEF cells, and STAT1 expression is significantly decreased in MKRN2 knockout testes. MKRN2 also regulates SIX4 and tenascin C (TNC) expression via EBF transcription factor 2 (EBF2).","method":"Mkrn2 knockout mouse model, Co-IP, Western blot, qRT-PCR","journal":"Frontiers in endocrinology","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP interaction validated in KO model; downstream pathway partially characterized","pmids":["36967804"],"is_preprint":false},{"year":2024,"finding":"MKRN2 associates with influenza A virus (IAV) mRNA and positively regulates IAV mRNA nuclear-cytoplasmic trafficking, potentially through an association with the RNA export mediator GLE1; in the absence of MKRN2, IAV mRNAs accumulate in the nucleus and may be degraded by the nuclear RNA exosome complex.","method":"RNA interactome capture (RIC), MKRN2 knockdown, fluorescence microscopy for mRNA localization, functional viral replication assays","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 — RIC interaction data plus functional KD with subcellular mRNA localization readout; single lab","pmids":["38753876"],"is_preprint":false},{"year":2025,"finding":"MKRN2 selectively inhibits IL-6 translation (not transcription) in LPS-activated macrophages by binding Il6 mRNA and attaching K29-linked polyubiquitin chains to Lys179 of PAIP1 (a translation initiation coactivator), blocking PAIP1–eIF4A interaction and reducing translational efficiency of Il6 mRNA; LysM-Cre+Mkrn2fl/fl mice showed increased serum IL-6 after LPS and increased severity of experimental colitis.","method":"Conditional macrophage-specific Mkrn2 knockout, RNA-binding assays, ubiquitination assay with K29-linkage specificity, Co-IP for PAIP1–eIF4A interaction, polysome profiling, experimental colitis model","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 1 — mechanistic dissection with specific ubiquitin chain type, substrate site mutagenesis (K179), protein interaction disruption, translation assays, and conditional KO in vivo","pmids":["40524017"],"is_preprint":false},{"year":2024,"finding":"MKRN2 is a substrate of lncCCKAR-5; lncCCKAR-5 acts as a scaffold facilitating interaction between MKRN2 and LMNA, promoting ubiquitin-mediated degradation of LMNA, with this effect augmented by N6-adenosine methylation of lncCCKAR-5.","method":"Co-IP, ubiquitination assay, lncRNA overexpression/knockdown, Western blot","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP and ubiquitination assay demonstrating MKRN2-mediated LMNA degradation scaffolded by lncCCKAR-5; single lab","pmids":["38242315"],"is_preprint":false},{"year":2025,"finding":"MKRN2 directly targets PPP2CA (Protein Phosphatase 2 Catalytic Subunit Alpha) for K48-linked ubiquitination at its K41 residue, leading to proteasomal degradation of PPP2CA; this results in increased β-catenin phosphorylation and decreased β-catenin protein levels, causing inactivation of Wnt signaling and apoptosis in clear cell renal cell carcinoma cells.","method":"Co-IP, immunofluorescence, K48-linkage-specific ubiquitination assay, site-directed mutagenesis (K41), in vivo xenograft","journal":"International journal of biological sciences","confidence":"High","confidence_rationale":"Tier 1 — ubiquitination site identified and validated by mutagenesis, Co-IP, linkage-specific assay, and in vivo validation","pmids":["40959281"],"is_preprint":false},{"year":2025,"finding":"MKRN2 mediates ubiquitination of CSDE1 at four specific lysine residues (K81, K91, K208, K727); MKRN2 and CSDE1 co-localize in liquid-liquid phase separation (LLPS) condensates, and disruption of either protein impairs condensate formation; Mkrn2 knockout mice exhibit sex-specific social abnormalities resembling ASD; MARK1 and HNRNPUL2 mRNAs are identified as ubiquitination-dependent targets of CSDE1.","method":"Mass spectrometry substrate identification, lysine mutagenesis, LLPS assays in HEK293 and SH-SY5Y cells, Mkrn2 knockout mice, behavioral assays","journal":"Frontiers in cellular neuroscience","confidence":"High","confidence_rationale":"Tier 1–2 — ubiquitination sites validated by mutagenesis, LLPS mechanistic assays, and in vivo KO behavioral phenotype","pmids":["41757349"],"is_preprint":false},{"year":2025,"finding":"MKRN2 is recruited to stress granules (SGs) in a manner dependent on active ubiquitination (UBA1 activity); MKRN2 promotes SG formation and disassembly following stress recovery by preventing accumulation of defective ribosomal products (DRiPs) within SGs.","method":"Proximity proteomics (BioID), UBA1 inhibition, MKRN2 localization imaging, stress granule formation and dissolution assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — proximity proteomics and functional imaging; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.10.15.682570"],"is_preprint":true},{"year":2026,"finding":"The covalent molecular glue DPB directly modifies Cys335 of MKRN2's E3 ligase domain and creates a neo-interface that recruits the ribosomal protein RPS7 to MKRN2, inducing ubiquitination and proteasomal degradation of RPS7, triggering nucleolar stress and apoptosis selectively in p53-deficient NSCLC cells; this synthetic lethal effect depends on a functional MKRN2–RPS7 axis.","method":"Quantitative thiol-reactivity proteomics (QTRP), biophysical assays, site-directed mutagenesis (Cys335), Co-IP-mass spectrometry, genetic KO/rescue, in vivo orthotopic mouse model","journal":"British journal of pharmacology","confidence":"High","confidence_rationale":"Tier 1 — covalent modification site identified by proteomics and validated by mutagenesis, mechanistic Co-IP-MS, and in vivo validation","pmids":["41991154"],"is_preprint":false},{"year":2025,"finding":"MKRN2 promotes ubiquitination-mediated degradation of p53 in lung epithelial cells; Co-IP confirms direct MKRN2–p53 interaction; MKRN2 overexpression reduces LPS-induced apoptosis and lung injury through p53 downregulation.","method":"Co-IP, ubiquitination assay, transcriptome sequencing, adenovirus-mediated overexpression, siRNA knockdown, in vivo LPS ARDS model","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and ubiquitination assay with in vivo validation; consistent with prior p53 ubiquitination findings in other cell types","pmids":["40885043"],"is_preprint":false},{"year":2025,"finding":"MKRN2 directly targets NF-κB p65 for proteasomal degradation via its E3 ubiquitin ligase activity, constraining NF-κB/COX2-mediated inflammatory signaling in the tumor microenvironment; MKRN2 deficiency promotes M1-to-M2 macrophage polarization switch and tumor growth acceleration in MKRN2 knockout mice.","method":"MKRN2 knockout mice, tumor implantation models, immune cell composition analysis (flow cytometry), Western blot for p65/COX2","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2–3 — consistent with prior p65 ubiquitination finding (PMID 28378844); KO mouse model with immune phenotype; mechanistic details largely inherited from earlier work","pmids":["40925500"],"is_preprint":false},{"year":2026,"finding":"MKRN2 promotes HCC cell proliferation through activation of the p38 MAPK signaling pathway; MKRN2 depletion arrests the cell cycle at G1/S and reduces c-Myc activation; RNA-seq analysis placed MKRN2 in cell cycle regulation and p38 MAPK signaling.","method":"MKRN2 knockdown, RNA-seq, flow cytometry, CCK-8/colony/EdU assays, in vivo xenograft","journal":"Human cell","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional KD with RNA-seq pathway placement and cell cycle readout; direct biochemical substrate in the p38 pathway not identified","pmids":["41741886"],"is_preprint":false}],"current_model":"MKRN2 is an RNA-binding RING-finger E3 ubiquitin ligase that suppresses NF-κB signaling by targeting p65 for proteasomal degradation, inhibits IL-6 translation by conjugating K29-linked ubiquitin chains to the translation coactivator PAIP1 to block its interaction with eIF4A, ubiquitinates multiple substrates including p53, IGF2BP3, PKM2, PPP2CA, CSDE1, and RPS7 to regulate cell proliferation and apoptosis, interacts with GLE1 to selectively restrain nuclear export of specific mRNAs, regulates neurogenesis downstream of PI3K/Akt and upstream of GSK-3β, and is required for spermiogenesis and male fertility in mice."},"narrative":{"teleology":[{"year":2008,"claim":"Establishing that MKRN2 functions in vertebrate neural development, acting as a neurogenesis inhibitor positioned downstream of PI3K/Akt and upstream of GSK-3β, provided the first signaling-pathway context for this gene.","evidence":"Xenopus animal cap explants with constitutively active/dominant-negative PI3K, Akt, and GSK-3β constructs; morpholino knockdown","pmids":["18198183"],"confidence":"High","gaps":["Direct biochemical substrate in the PI3K/Akt–GSK-3β axis not identified","Whether the RING E3 activity is required for the anti-neurogenic function was not tested"]},{"year":2010,"claim":"Domain-mapping revealed that the third C3H zinc finger, Cys-His motif, and RING domain are the minimal region sufficient for anti-neurogenic activity, focusing mechanistic attention on the RING-containing C-terminus.","evidence":"Systematic N- and C-terminal truncation mutagenesis in Xenopus overexpression assay","pmids":["20167204"],"confidence":"Medium","gaps":["Point mutations in the RING finger were not tested for catalytic dead activity","Binding partners for truncated constructs not identified"]},{"year":2016,"claim":"Genetic knockout in mice demonstrated that MKRN2 is essential for spermiogenesis and male fertility, with loss causing ectoplasmic specialization defects and reduced Odf2 expression, establishing an in vivo physiological requirement.","evidence":"Mkrn2 knockout mouse; histology, sperm analysis, Western blot for Odf2","pmids":["28008940"],"confidence":"High","gaps":["Whether Odf2 is a direct ubiquitination substrate of MKRN2 was not tested","Cell-autonomous versus paracrine contributions not dissected"]},{"year":2017,"claim":"Identification of p65 as a direct MKRN2 ubiquitination substrate established MKRN2 as a bona fide E3 ligase suppressing NF-κB-driven inflammation, defining its first characterized enzymatic activity and substrate.","evidence":"Yeast two-hybrid, Co-IP, in vitro ubiquitination, RING mutagenesis, shRNA knockdown in dendritic cells","pmids":["28378844"],"confidence":"High","gaps":["Specific lysine sites on p65 targeted by MKRN2 not mapped","Relative contribution of MKRN2 versus other p65 E3 ligases unclear"]},{"year":2020,"claim":"The substrate repertoire of MKRN2 was expanded to include p53 and IGF2BP3, showing that MKRN2 promotes their proteasomal degradation to regulate cancer cell proliferation, and the spermatogenesis phenotype was linked to the p53/PERP apoptotic axis.","evidence":"Co-IP, GST pulldown, in vitro ubiquitination, CRISPR p53 KO rescue in melanoma; shRNA in neuroblastoma; Mkrn2 KO mouse testis transcriptomics","pmids":["32194692","32560817","31489847"],"confidence":"High","gaps":["Ubiquitin chain type for p53 and IGF2BP3 not determined","Whether p53 degradation is direct versus via an intermediate in the PERP pathway not resolved"]},{"year":2020,"claim":"Discovery that MKRN2 physically interacts with GLE1 and binds mRNA 3′ UTRs established a non-degradative, RNA-regulatory role: MKRN2 selectively restrains nuclear export of associated mRNAs, with genetic epistasis in zebrafish retinal development confirming functional partnership with GLE1.","evidence":"AP-MS, RIP-seq, zebrafish morpholino and CRISPR KO epistasis","pmids":["32460013"],"confidence":"High","gaps":["Whether MKRN2 ubiquitinates GLE1 or another export factor was not tested","Determinants of mRNA selectivity not defined"]},{"year":2022,"claim":"PKM2 was identified as another ubiquitination substrate, linking MKRN2 to metabolic reprogramming via suppression of PKM2-ERK signaling in gastric cancer.","evidence":"Co-IP, ubiquitination assay, overexpression/knockdown, xenograft model","pmids":["35196650"],"confidence":"Medium","gaps":["Ubiquitin chain type and target lysines on PKM2 not mapped","Single-lab finding"]},{"year":2024,"claim":"The GLE1–MKRN2 mRNA export axis was shown to be co-opted by influenza A virus, with MKRN2 positively regulating viral mRNA nuclear-to-cytoplasmic trafficking; this extended the mRNA export function to a pathogen context.","evidence":"RNA interactome capture, MKRN2 knockdown, fluorescence microscopy for mRNA localization, viral replication assays","pmids":["38753876"],"confidence":"Medium","gaps":["Direct ubiquitination of a viral or host factor in mRNA export not demonstrated","Generality to other viruses unknown"]},{"year":2024,"claim":"MKRN2 was shown to ubiquitinate LMNA when scaffolded by the lncRNA lncCCKAR-5, introducing lncRNA-dependent substrate recruitment as a regulatory mechanism for MKRN2.","evidence":"Co-IP, ubiquitination assay, lncRNA overexpression/knockdown","pmids":["38242315"],"confidence":"Medium","gaps":["Ubiquitin chain type on LMNA not determined","Whether other lncRNAs similarly redirect MKRN2 substrate specificity is unknown","Single-lab finding"]},{"year":2025,"claim":"A major mechanistic advance resolved how MKRN2 controls inflammation at the translational level: MKRN2 conjugates K29-linked ubiquitin to PAIP1-K179, disrupting PAIP1–eIF4A interaction and selectively blocking IL-6 mRNA translation in macrophages, with conditional KO mice showing exacerbated colitis.","evidence":"Macrophage-specific conditional KO, K29-linkage-specific ubiquitination assay, PAIP1 K179 mutagenesis, polysome profiling, experimental colitis model","pmids":["40524017"],"confidence":"High","gaps":["Whether K29-linked ubiquitination is used for other MKRN2 substrates beyond PAIP1 is unknown","How MKRN2 achieves mRNA selectivity for IL-6 versus other transcripts is unresolved"]},{"year":2025,"claim":"PPP2CA was identified as a K48-ubiquitination substrate at K41, mechanistically connecting MKRN2 to Wnt/β-catenin pathway inactivation and apoptosis in renal cell carcinoma, and providing one of the most fully mapped substrate-site-chain type-pathway cascades for MKRN2.","evidence":"Co-IP, K48-linkage-specific ubiquitination, K41 site-directed mutagenesis, xenograft","pmids":["40959281"],"confidence":"High","gaps":["Whether MKRN2 regulation of PP2A extends to other PP2A substrates is untested","Structural basis for PPP2CA recognition unknown"]},{"year":2025,"claim":"MKRN2 was shown to ubiquitinate CSDE1 at four mapped lysines and to co-localize with CSDE1 in LLPS condensates; Mkrn2 KO mice displayed sex-specific social behavioral abnormalities resembling ASD, linking MKRN2's phase-separation and ubiquitin ligase activities to neuronal function.","evidence":"Mass spectrometry, lysine mutagenesis, LLPS assays, Mkrn2 KO mouse behavioral testing","pmids":["41757349"],"confidence":"High","gaps":["Causal chain from CSDE1 ubiquitination to behavioral phenotype not fully established","Whether LLPS condensate function requires catalytic activity is unclear"]},{"year":2026,"claim":"A covalent molecular glue (DPB) was shown to modify MKRN2-Cys335 and create a neo-interface recruiting the ribosomal protein RPS7 for MKRN2-mediated ubiquitination and degradation, triggering nucleolar stress and synthetic lethality in p53-null NSCLC — demonstrating that MKRN2 can be pharmacologically redirected to novel substrates.","evidence":"QTRP proteomics, Cys335 mutagenesis, Co-IP-MS, genetic KO/rescue, orthotopic xenograft","pmids":["41991154"],"confidence":"High","gaps":["Whether endogenous RPS7 is a physiological MKRN2 substrate is unknown","Long-term in vivo safety and selectivity of DPB not established"]},{"year":null,"claim":"Key open questions include the structural basis for MKRN2's broad substrate recognition, the rules governing its use of distinct ubiquitin chain types (K48 versus K29) on different substrates, and the relationship between its RNA-binding, phase-separation, and E3 ligase functions in an integrated cellular model.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal or cryo-EM structure of MKRN2 or any MKRN2–substrate complex","Chain-type selectivity mechanism unexplored biochemically","Relative physiological importance of translational control versus protein degradation roles unranked"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,6,9,12,14,15,17]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[7,11,12]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,6,12,14,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[12,19]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[7,11]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[12,15]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,12,19]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,8,14]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,6,9,12,14,15,17]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[4,14,17]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[7,11,12]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[7,11]}],"complexes":[],"partners":["RELA","PDLIM2","GLE1","PAIP1","TP53","PPP2CA","CSDE1","PKM2"],"other_free_text":[]},"mechanistic_narrative":"MKRN2 is an RNA-binding RING-finger E3 ubiquitin ligase that governs inflammatory signaling, translational control, mRNA export, and cell fate decisions by targeting a broad array of substrates for ubiquitin-dependent degradation or functional modification. MKRN2 suppresses NF-κB signaling by catalyzing K48-linked polyubiquitination and proteasomal degradation of p65, acting synergistically with PDLIM2, and constrains IL-6 translation in macrophages by conjugating K29-linked ubiquitin chains to PAIP1 at Lys179, disrupting the PAIP1–eIF4A interaction required for translational initiation [PMID:28378844, PMID:40524017]. Additional validated ubiquitination substrates include p53, PKM2, PPP2CA (K48-linked at K41, inactivating Wnt/β-catenin signaling), IGF2BP3, CSDE1 (four mapped sites; co-localizes with MKRN2 in liquid–liquid phase-separation condensates), LMNA, and the chemically induced neo-substrate RPS7, through which MKRN2 mediates nucleolar stress and synthetic lethality in p53-deficient cells [PMID:32194692, PMID:40959281, PMID:41757349, PMID:41991154]. MKRN2 also binds mRNA 3′ UTRs and interacts with the mRNA export factor GLE1 to selectively restrain nuclear export of associated transcripts, a function co-opted by influenza A virus for viral mRNA trafficking, and is required for spermiogenesis in mice through regulation of Odf2 and the p53/PERP axis [PMID:32460013, PMID:38753876, PMID:28008940]."},"prefetch_data":{"uniprot":{"accession":"Q9H000","full_name":"E3 ubiquitin-protein ligase makorin-2","aliases":["RING finger protein 62","RING-type E3 ubiquitin transferase makorin-2"],"length_aa":416,"mass_kda":46.9,"function":"E3 ubiquitin ligase catalyzing the covalent attachment of ubiquitin moieties onto substrate proteins (By similarity). Promotes the polyubiquitination and proteasome-dependent degradation of RELA/p65, thereby suppressing RELA-mediated NF-kappaB transactivation and negatively regulating inflammatory responses (By similarity). Plays a role in the regulation of spermiation and in male fertility (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9H000/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MKRN2","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"UBA1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/MKRN2","total_profiled":1310},"omim":[{"mim_id":"608426","title":"MAKORIN 2; MKRN2","url":"https://www.omim.org/entry/608426"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MKRN2"},"hgnc":{"alias_symbol":["RNF62","HSPC070"],"prev_symbol":[]},"alphafold":{"accession":"Q9H000","domains":[{"cath_id":"-","chopping":"7-51","consensus_level":"high","plddt":79.0229,"start":7,"end":51},{"cath_id":"-","chopping":"168-234","consensus_level":"medium","plddt":91.0913,"start":168,"end":234},{"cath_id":"-","chopping":"257-325","consensus_level":"high","plddt":91.3271,"start":257,"end":325},{"cath_id":"-","chopping":"326-388","consensus_level":"medium","plddt":71.4316,"start":326,"end":388}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H000","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H000-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H000-F1-predicted_aligned_error_v6.png","plddt_mean":71.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MKRN2","jax_strain_url":"https://www.jax.org/strain/search?query=MKRN2"},"sequence":{"accession":"Q9H000","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H000.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H000/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H000"}},"corpus_meta":[{"pmid":"11042152","id":"PMC_11042152","title":"Cloning and functional analysis of cDNAs with open reading frames for 300 previously undefined genes expressed in CD34+ hematopoietic stem/progenitor cells.","date":"2000","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/11042152","citation_count":161,"is_preprint":false},{"pmid":"25814643","id":"PMC_25814643","title":"Genetic Variations in MicroRNA-Binding Sites Affect MicroRNA-Mediated Regulation of Several Genes Associated With Cardio-metabolic Phenotypes.","date":"2015","source":"Circulation. Cardiovascular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25814643","citation_count":59,"is_preprint":false},{"pmid":"28378844","id":"PMC_28378844","title":"MKRN2 is a novel ubiquitin E3 ligase for the p65 subunit of NF-κB and negatively regulates inflammatory responses.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28378844","citation_count":58,"is_preprint":false},{"pmid":"30103781","id":"PMC_30103781","title":"MKRN2 inhibits migration and invasion of non-small-cell lung cancer by negatively regulating the PI3K/Akt pathway.","date":"2018","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/30103781","citation_count":46,"is_preprint":false},{"pmid":"21172006","id":"PMC_21172006","title":"The vertebrate makorin ubiquitin ligase gene family has been shaped by large-scale duplication and retroposition from an ancestral gonad-specific, maternal-effect gene.","date":"2010","source":"BMC 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MKRN2 was identified via yeast two-hybrid screening with PDLIM2, and MKRN2 and PDLIM2 synergistically promote p65 polyubiquitination and degradation. MKRN2 knockdown in dendritic cells increased nuclear p65 and augmented proinflammatory cytokine production.\",\n      \"method\": \"Yeast two-hybrid screening, Co-IP, in vitro ubiquitination assay, RING domain mutagenesis, shRNA knockdown, cytokine measurement\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including yeast two-hybrid, Co-IP, in vitro ubiquitination, domain mutagenesis, and functional knockdown\",\n      \"pmids\": [\"28378844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Xenopus makorin-2 (mkrn2) functions as a neurogenesis inhibitor acting downstream of PI3K and Akt and upstream of GSK-3β; overexpression suppresses PI3K/Akt-induced neural marker (NCAM) expression and upregulates GSK-3β mRNA and protein, while morpholino knockdown induces double axis in tadpoles.\",\n      \"method\": \"Xenopus animal cap explant assay, morpholino antisense knockdown, overexpression of constitutively active PI3K/Akt and dominant negative GSK-3β, Western blot, RT-PCR\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — epistasis established by multiple genetic manipulations (constitutively active/dominant negative constructs) in Xenopus embryos, replicated with multiple markers\",\n      \"pmids\": [\"18198183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The third C3H zinc finger, Cys-His motif, and C3HC4 RING zinc finger of mkrn2 are essential and sufficient for its anti-neurogenic activity; a C-terminal truncation mutant containing only these domains (mkrn2(s)-7) recapitulates the full-length phenotype of dorso-posterior deficiencies in tadpoles and inhibits NCAM expression and induces GSK-3β in animal cap assays.\",\n      \"method\": \"N- and C-terminal truncation mutagenesis, Xenopus overexpression, animal cap explant assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — domain mapping by systematic mutagenesis in Xenopus functional assay, single lab\",\n      \"pmids\": [\"20167204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Mkrn2 knockout in mice causes male infertility characterized by low sperm number, poor motility, aberrant morphology, spermiation failure, and misarrangement of ectoplasmic specialization in testes; mechanistically, Odf2 (a vital spermatogenesis protein) expression is significantly decreased in knockout testes.\",\n      \"method\": \"Mkrn2 knockout mouse model, histology, sperm analysis, Western blot for Odf2\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined cellular phenotype and molecular mechanism (Odf2 loss); replicated in human infertility samples\",\n      \"pmids\": [\"28008940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Mkrn2 deficiency in mice causes abnormally high testicular apoptosis through the p53/PERP signaling pathway; MKRN2 normally suppresses PERP expression, and PERP acts as a negative regulator of spermatogenesis whose ectopic expression induces male infertility.\",\n      \"method\": \"Mkrn2 knockout mouse model, digital gene expression profiling (DGE), GSEA, KEGG pathway analysis, protein expression analysis\",\n      \"journal\": \"Asian journal of andrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — KO model with transcriptomic pathway mapping; mechanistic link to p53/PERP established by gene expression rather than direct biochemical interaction assay\",\n      \"pmids\": [\"31489847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MKRN2 ubiquitinates IGF2BP3 (an RNA-binding protein) to promote its degradation, thereby regulating CD44 and PDPN expression; MKRN2 knockdown in neuroblastoma SHSY5Y cells promotes proliferation and migration in an IGF2BP3-dependent manner.\",\n      \"method\": \"shRNA knockdown, Co-IP, pulldown, in vitro ubiquitination assay, Western blot\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro ubiquitination assay plus functional knockdown, single lab\",\n      \"pmids\": [\"32560817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MKRN2 interacts with and ubiquitinates p53 to promote its degradation, thereby regulating melanoma cell proliferation; MKRN2 downregulation inhibits melanoma cell growth in a p53-dependent manner (confirmed by p53 CRISPR knockout rescue).\",\n      \"method\": \"Co-IP, GST pulldown, in vitro ubiquitination assay, CRISPR-Cas9 p53 knockout, MTT and colony formation assays\",\n      \"journal\": \"Oncology letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro ubiquitination assay, Co-IP, GST pulldown, and genetic rescue with p53 KO, multiple orthogonal methods\",\n      \"pmids\": [\"32194692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MKRN2 physically interacts with GLE1 (a DEAD-box helicase activator involved in mRNA export termination) as identified by affinity-purification mass spectrometry; MKRN2 binds selectively to the 3' UTR of a diverse subset of mRNAs; morpholino knockdown or CRISPR/Cas9 knockout of MKRN2 partially rescues retinal developmental defects upon GLE1 depletion in zebrafish, establishing epistasis; knockdown of MKRN2 enhances nuclear export of MKRN2-associated mRNAs.\",\n      \"method\": \"Affinity purification–mass spectrometry, zebrafish morpholino knockdown, CRISPR/Cas9 knockout, genetic epistasis, ribonomic (RIP-seq) approaches\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — AP-MS protein interaction, genetic epistasis in zebrafish, ribonomics; multiple orthogonal methods\",\n      \"pmids\": [\"32460013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MKRN2 inhibits migration and invasion of non-small-cell lung cancer cells through downregulation of the PI3K/Akt pathway, as demonstrated by MKRN2 silencing and overexpression experiments in NSCLC cell lines.\",\n      \"method\": \"MKRN2 siRNA knockdown and overexpression, migration and invasion assays, Western blot for PI3K/Akt pathway components\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional KD/OE with pathway placement, single lab, no direct biochemical substrate identification\",\n      \"pmids\": [\"30103781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MKRN2 promotes ubiquitination-mediated degradation of PKM2 (pyruvate kinase M2) and attenuates PKM2's effect on ERK signaling, thereby inhibiting gastric cancer cell proliferation.\",\n      \"method\": \"Co-IP, ubiquitination assay, overexpression and knockdown, CCK-8, in vivo xenograft\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ubiquitination assay with pathway readout; single lab\",\n      \"pmids\": [\"35196650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MKRN2 interacts with STAT1; Co-IP assays show a direct MKRN2–STAT1 interaction in testis and MEF cells, and STAT1 expression is significantly decreased in MKRN2 knockout testes. MKRN2 also regulates SIX4 and tenascin C (TNC) expression via EBF transcription factor 2 (EBF2).\",\n      \"method\": \"Mkrn2 knockout mouse model, Co-IP, Western blot, qRT-PCR\",\n      \"journal\": \"Frontiers in endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP interaction validated in KO model; downstream pathway partially characterized\",\n      \"pmids\": [\"36967804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MKRN2 associates with influenza A virus (IAV) mRNA and positively regulates IAV mRNA nuclear-cytoplasmic trafficking, potentially through an association with the RNA export mediator GLE1; in the absence of MKRN2, IAV mRNAs accumulate in the nucleus and may be degraded by the nuclear RNA exosome complex.\",\n      \"method\": \"RNA interactome capture (RIC), MKRN2 knockdown, fluorescence microscopy for mRNA localization, functional viral replication assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RIC interaction data plus functional KD with subcellular mRNA localization readout; single lab\",\n      \"pmids\": [\"38753876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MKRN2 selectively inhibits IL-6 translation (not transcription) in LPS-activated macrophages by binding Il6 mRNA and attaching K29-linked polyubiquitin chains to Lys179 of PAIP1 (a translation initiation coactivator), blocking PAIP1–eIF4A interaction and reducing translational efficiency of Il6 mRNA; LysM-Cre+Mkrn2fl/fl mice showed increased serum IL-6 after LPS and increased severity of experimental colitis.\",\n      \"method\": \"Conditional macrophage-specific Mkrn2 knockout, RNA-binding assays, ubiquitination assay with K29-linkage specificity, Co-IP for PAIP1–eIF4A interaction, polysome profiling, experimental colitis model\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic dissection with specific ubiquitin chain type, substrate site mutagenesis (K179), protein interaction disruption, translation assays, and conditional KO in vivo\",\n      \"pmids\": [\"40524017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MKRN2 is a substrate of lncCCKAR-5; lncCCKAR-5 acts as a scaffold facilitating interaction between MKRN2 and LMNA, promoting ubiquitin-mediated degradation of LMNA, with this effect augmented by N6-adenosine methylation of lncCCKAR-5.\",\n      \"method\": \"Co-IP, ubiquitination assay, lncRNA overexpression/knockdown, Western blot\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP and ubiquitination assay demonstrating MKRN2-mediated LMNA degradation scaffolded by lncCCKAR-5; single lab\",\n      \"pmids\": [\"38242315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MKRN2 directly targets PPP2CA (Protein Phosphatase 2 Catalytic Subunit Alpha) for K48-linked ubiquitination at its K41 residue, leading to proteasomal degradation of PPP2CA; this results in increased β-catenin phosphorylation and decreased β-catenin protein levels, causing inactivation of Wnt signaling and apoptosis in clear cell renal cell carcinoma cells.\",\n      \"method\": \"Co-IP, immunofluorescence, K48-linkage-specific ubiquitination assay, site-directed mutagenesis (K41), in vivo xenograft\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — ubiquitination site identified and validated by mutagenesis, Co-IP, linkage-specific assay, and in vivo validation\",\n      \"pmids\": [\"40959281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MKRN2 mediates ubiquitination of CSDE1 at four specific lysine residues (K81, K91, K208, K727); MKRN2 and CSDE1 co-localize in liquid-liquid phase separation (LLPS) condensates, and disruption of either protein impairs condensate formation; Mkrn2 knockout mice exhibit sex-specific social abnormalities resembling ASD; MARK1 and HNRNPUL2 mRNAs are identified as ubiquitination-dependent targets of CSDE1.\",\n      \"method\": \"Mass spectrometry substrate identification, lysine mutagenesis, LLPS assays in HEK293 and SH-SY5Y cells, Mkrn2 knockout mice, behavioral assays\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ubiquitination sites validated by mutagenesis, LLPS mechanistic assays, and in vivo KO behavioral phenotype\",\n      \"pmids\": [\"41757349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MKRN2 is recruited to stress granules (SGs) in a manner dependent on active ubiquitination (UBA1 activity); MKRN2 promotes SG formation and disassembly following stress recovery by preventing accumulation of defective ribosomal products (DRiPs) within SGs.\",\n      \"method\": \"Proximity proteomics (BioID), UBA1 inhibition, MKRN2 localization imaging, stress granule formation and dissolution assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proximity proteomics and functional imaging; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.10.15.682570\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The covalent molecular glue DPB directly modifies Cys335 of MKRN2's E3 ligase domain and creates a neo-interface that recruits the ribosomal protein RPS7 to MKRN2, inducing ubiquitination and proteasomal degradation of RPS7, triggering nucleolar stress and apoptosis selectively in p53-deficient NSCLC cells; this synthetic lethal effect depends on a functional MKRN2–RPS7 axis.\",\n      \"method\": \"Quantitative thiol-reactivity proteomics (QTRP), biophysical assays, site-directed mutagenesis (Cys335), Co-IP-mass spectrometry, genetic KO/rescue, in vivo orthotopic mouse model\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — covalent modification site identified by proteomics and validated by mutagenesis, mechanistic Co-IP-MS, and in vivo validation\",\n      \"pmids\": [\"41991154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MKRN2 promotes ubiquitination-mediated degradation of p53 in lung epithelial cells; Co-IP confirms direct MKRN2–p53 interaction; MKRN2 overexpression reduces LPS-induced apoptosis and lung injury through p53 downregulation.\",\n      \"method\": \"Co-IP, ubiquitination assay, transcriptome sequencing, adenovirus-mediated overexpression, siRNA knockdown, in vivo LPS ARDS model\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and ubiquitination assay with in vivo validation; consistent with prior p53 ubiquitination findings in other cell types\",\n      \"pmids\": [\"40885043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MKRN2 directly targets NF-κB p65 for proteasomal degradation via its E3 ubiquitin ligase activity, constraining NF-κB/COX2-mediated inflammatory signaling in the tumor microenvironment; MKRN2 deficiency promotes M1-to-M2 macrophage polarization switch and tumor growth acceleration in MKRN2 knockout mice.\",\n      \"method\": \"MKRN2 knockout mice, tumor implantation models, immune cell composition analysis (flow cytometry), Western blot for p65/COX2\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — consistent with prior p65 ubiquitination finding (PMID 28378844); KO mouse model with immune phenotype; mechanistic details largely inherited from earlier work\",\n      \"pmids\": [\"40925500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MKRN2 promotes HCC cell proliferation through activation of the p38 MAPK signaling pathway; MKRN2 depletion arrests the cell cycle at G1/S and reduces c-Myc activation; RNA-seq analysis placed MKRN2 in cell cycle regulation and p38 MAPK signaling.\",\n      \"method\": \"MKRN2 knockdown, RNA-seq, flow cytometry, CCK-8/colony/EdU assays, in vivo xenograft\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional KD with RNA-seq pathway placement and cell cycle readout; direct biochemical substrate in the p38 pathway not identified\",\n      \"pmids\": [\"41741886\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MKRN2 is an RNA-binding RING-finger E3 ubiquitin ligase that suppresses NF-κB signaling by targeting p65 for proteasomal degradation, inhibits IL-6 translation by conjugating K29-linked ubiquitin chains to the translation coactivator PAIP1 to block its interaction with eIF4A, ubiquitinates multiple substrates including p53, IGF2BP3, PKM2, PPP2CA, CSDE1, and RPS7 to regulate cell proliferation and apoptosis, interacts with GLE1 to selectively restrain nuclear export of specific mRNAs, regulates neurogenesis downstream of PI3K/Akt and upstream of GSK-3β, and is required for spermiogenesis and male fertility in mice.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MKRN2 is an RNA-binding RING-finger E3 ubiquitin ligase that governs inflammatory signaling, translational control, mRNA export, and cell fate decisions by targeting a broad array of substrates for ubiquitin-dependent degradation or functional modification. MKRN2 suppresses NF-κB signaling by catalyzing K48-linked polyubiquitination and proteasomal degradation of p65, acting synergistically with PDLIM2, and constrains IL-6 translation in macrophages by conjugating K29-linked ubiquitin chains to PAIP1 at Lys179, disrupting the PAIP1–eIF4A interaction required for translational initiation [PMID:28378844, PMID:40524017]. Additional validated ubiquitination substrates include p53, PKM2, PPP2CA (K48-linked at K41, inactivating Wnt/β-catenin signaling), IGF2BP3, CSDE1 (four mapped sites; co-localizes with MKRN2 in liquid–liquid phase-separation condensates), LMNA, and the chemically induced neo-substrate RPS7, through which MKRN2 mediates nucleolar stress and synthetic lethality in p53-deficient cells [PMID:32194692, PMID:40959281, PMID:41757349, PMID:41991154]. MKRN2 also binds mRNA 3′ UTRs and interacts with the mRNA export factor GLE1 to selectively restrain nuclear export of associated transcripts, a function co-opted by influenza A virus for viral mRNA trafficking, and is required for spermiogenesis in mice through regulation of Odf2 and the p53/PERP axis [PMID:32460013, PMID:38753876, PMID:28008940].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Establishing that MKRN2 functions in vertebrate neural development, acting as a neurogenesis inhibitor positioned downstream of PI3K/Akt and upstream of GSK-3β, provided the first signaling-pathway context for this gene.\",\n      \"evidence\": \"Xenopus animal cap explants with constitutively active/dominant-negative PI3K, Akt, and GSK-3β constructs; morpholino knockdown\",\n      \"pmids\": [\"18198183\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical substrate in the PI3K/Akt–GSK-3β axis not identified\", \"Whether the RING E3 activity is required for the anti-neurogenic function was not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Domain-mapping revealed that the third C3H zinc finger, Cys-His motif, and RING domain are the minimal region sufficient for anti-neurogenic activity, focusing mechanistic attention on the RING-containing C-terminus.\",\n      \"evidence\": \"Systematic N- and C-terminal truncation mutagenesis in Xenopus overexpression assay\",\n      \"pmids\": [\"20167204\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Point mutations in the RING finger were not tested for catalytic dead activity\", \"Binding partners for truncated constructs not identified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Genetic knockout in mice demonstrated that MKRN2 is essential for spermiogenesis and male fertility, with loss causing ectoplasmic specialization defects and reduced Odf2 expression, establishing an in vivo physiological requirement.\",\n      \"evidence\": \"Mkrn2 knockout mouse; histology, sperm analysis, Western blot for Odf2\",\n      \"pmids\": [\"28008940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Odf2 is a direct ubiquitination substrate of MKRN2 was not tested\", \"Cell-autonomous versus paracrine contributions not dissected\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of p65 as a direct MKRN2 ubiquitination substrate established MKRN2 as a bona fide E3 ligase suppressing NF-κB-driven inflammation, defining its first characterized enzymatic activity and substrate.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, in vitro ubiquitination, RING mutagenesis, shRNA knockdown in dendritic cells\",\n      \"pmids\": [\"28378844\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific lysine sites on p65 targeted by MKRN2 not mapped\", \"Relative contribution of MKRN2 versus other p65 E3 ligases unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The substrate repertoire of MKRN2 was expanded to include p53 and IGF2BP3, showing that MKRN2 promotes their proteasomal degradation to regulate cancer cell proliferation, and the spermatogenesis phenotype was linked to the p53/PERP apoptotic axis.\",\n      \"evidence\": \"Co-IP, GST pulldown, in vitro ubiquitination, CRISPR p53 KO rescue in melanoma; shRNA in neuroblastoma; Mkrn2 KO mouse testis transcriptomics\",\n      \"pmids\": [\"32194692\", \"32560817\", \"31489847\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ubiquitin chain type for p53 and IGF2BP3 not determined\", \"Whether p53 degradation is direct versus via an intermediate in the PERP pathway not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Discovery that MKRN2 physically interacts with GLE1 and binds mRNA 3′ UTRs established a non-degradative, RNA-regulatory role: MKRN2 selectively restrains nuclear export of associated mRNAs, with genetic epistasis in zebrafish retinal development confirming functional partnership with GLE1.\",\n      \"evidence\": \"AP-MS, RIP-seq, zebrafish morpholino and CRISPR KO epistasis\",\n      \"pmids\": [\"32460013\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MKRN2 ubiquitinates GLE1 or another export factor was not tested\", \"Determinants of mRNA selectivity not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"PKM2 was identified as another ubiquitination substrate, linking MKRN2 to metabolic reprogramming via suppression of PKM2-ERK signaling in gastric cancer.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, overexpression/knockdown, xenograft model\",\n      \"pmids\": [\"35196650\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin chain type and target lysines on PKM2 not mapped\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The GLE1–MKRN2 mRNA export axis was shown to be co-opted by influenza A virus, with MKRN2 positively regulating viral mRNA nuclear-to-cytoplasmic trafficking; this extended the mRNA export function to a pathogen context.\",\n      \"evidence\": \"RNA interactome capture, MKRN2 knockdown, fluorescence microscopy for mRNA localization, viral replication assays\",\n      \"pmids\": [\"38753876\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitination of a viral or host factor in mRNA export not demonstrated\", \"Generality to other viruses unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"MKRN2 was shown to ubiquitinate LMNA when scaffolded by the lncRNA lncCCKAR-5, introducing lncRNA-dependent substrate recruitment as a regulatory mechanism for MKRN2.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, lncRNA overexpression/knockdown\",\n      \"pmids\": [\"38242315\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin chain type on LMNA not determined\", \"Whether other lncRNAs similarly redirect MKRN2 substrate specificity is unknown\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A major mechanistic advance resolved how MKRN2 controls inflammation at the translational level: MKRN2 conjugates K29-linked ubiquitin to PAIP1-K179, disrupting PAIP1–eIF4A interaction and selectively blocking IL-6 mRNA translation in macrophages, with conditional KO mice showing exacerbated colitis.\",\n      \"evidence\": \"Macrophage-specific conditional KO, K29-linkage-specific ubiquitination assay, PAIP1 K179 mutagenesis, polysome profiling, experimental colitis model\",\n      \"pmids\": [\"40524017\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether K29-linked ubiquitination is used for other MKRN2 substrates beyond PAIP1 is unknown\", \"How MKRN2 achieves mRNA selectivity for IL-6 versus other transcripts is unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"PPP2CA was identified as a K48-ubiquitination substrate at K41, mechanistically connecting MKRN2 to Wnt/β-catenin pathway inactivation and apoptosis in renal cell carcinoma, and providing one of the most fully mapped substrate-site-chain type-pathway cascades for MKRN2.\",\n      \"evidence\": \"Co-IP, K48-linkage-specific ubiquitination, K41 site-directed mutagenesis, xenograft\",\n      \"pmids\": [\"40959281\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MKRN2 regulation of PP2A extends to other PP2A substrates is untested\", \"Structural basis for PPP2CA recognition unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"MKRN2 was shown to ubiquitinate CSDE1 at four mapped lysines and to co-localize with CSDE1 in LLPS condensates; Mkrn2 KO mice displayed sex-specific social behavioral abnormalities resembling ASD, linking MKRN2's phase-separation and ubiquitin ligase activities to neuronal function.\",\n      \"evidence\": \"Mass spectrometry, lysine mutagenesis, LLPS assays, Mkrn2 KO mouse behavioral testing\",\n      \"pmids\": [\"41757349\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal chain from CSDE1 ubiquitination to behavioral phenotype not fully established\", \"Whether LLPS condensate function requires catalytic activity is unclear\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"A covalent molecular glue (DPB) was shown to modify MKRN2-Cys335 and create a neo-interface recruiting the ribosomal protein RPS7 for MKRN2-mediated ubiquitination and degradation, triggering nucleolar stress and synthetic lethality in p53-null NSCLC — demonstrating that MKRN2 can be pharmacologically redirected to novel substrates.\",\n      \"evidence\": \"QTRP proteomics, Cys335 mutagenesis, Co-IP-MS, genetic KO/rescue, orthotopic xenograft\",\n      \"pmids\": [\"41991154\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous RPS7 is a physiological MKRN2 substrate is unknown\", \"Long-term in vivo safety and selectivity of DPB not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the structural basis for MKRN2's broad substrate recognition, the rules governing its use of distinct ubiquitin chain types (K48 versus K29) on different substrates, and the relationship between its RNA-binding, phase-separation, and E3 ligase functions in an integrated cellular model.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal or cryo-EM structure of MKRN2 or any MKRN2–substrate complex\", \"Chain-type selectivity mechanism unexplored biochemically\", \"Relative physiological importance of translational control versus protein degradation roles unranked\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 6, 9, 12, 14, 15, 17]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [7, 11, 12]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 6, 12, 14, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [12, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [7, 11]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [12, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0168256\", \"supporting_discovery_ids\": [0, 12, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 12, 19]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 8, 14]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 6, 9, 12, 14, 15, 17]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4, 14, 17]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [7, 11, 12]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [7, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"RELA\", \"PDLIM2\", \"GLE1\", \"PAIP1\", \"TP53\", \"PPP2CA\", \"CSDE1\", \"PKM2\"],\n    \"other_free_text\": []\n  }\n}\n```"}