{"gene":"MPHOSPH8","run_date":"2026-06-10T02:59:51","timeline":{"discoveries":[{"year":2010,"finding":"MPP8 chromodomain directly binds methylated H3K9 (H3K9me2/me3) in vivo and in vitro, and MPP8 targets the E-cadherin gene promoter to repress it; knockdown reduces DNMT3A localization at the E-cadherin CpG island, decreasing DNA methylation there. MPP8 also physically interacts with H3K9 methyltransferases GLP and ESET, as well as DNMT3A.","method":"Chromodomain binding assays (in vitro and in vivo), ChIP, Co-immunoprecipitation, knockdown with reporter/methylation readout","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, ChIP, in vitro binding, and functional knockdown with defined molecular phenotype; independently replicated in subsequent papers","pmids":["20871592"],"is_preprint":false},{"year":2011,"finding":"G9a and GLP dimethylate Dnmt3a at K44 (mouse; equivalent to K47 human DNMT3A); the MPP8 chromodomain specifically recognizes this dimethylated Dnmt3a-K44me2. MPP8 also interacts with self-methylated GLP in a methylation-dependent manner. The MPP8 chromodomain forms a homodimer in solution and in crystals, suggesting a dimeric MPP8 bridges methylated Dnmt3a and GLP to form a Dnmt3a–MPP8–GLP/G9a silencing complex.","method":"In vitro methylation assay, crystal structure of MPP8 chromodomain dimer, Co-IP, peptide binding assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay, crystal structure, and Co-IP with multiple orthogonal methods in one study","pmids":["22086334"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of human MPP8 chromodomain in complex with H3K9me3 peptide (residues 1–15) reveals a conserved aromatic cage (Phe59, Trp80, Tyr83) plus Asp87 that encloses the trimethyl-lysine, enabling discrimination of H3K9 from H3K27. The chromodomain forms a homodimer via domain-swapping of two β-strands. Modeled phosphorylation of cage residue Tyr83 is predicted to modulate methyl-lysine binding.","method":"X-ray crystallography, solution studies (dimerization), peptide binding affinity measurement","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Strong — two independent crystal structures of MPP8 chromodomain–H3K9me3 complex reported (PMID 22022377 and 21419134), consistent findings","pmids":["22022377"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of MPP8 chromodomain–H3K9me3 peptide complex defines contacts with at least six H3 residues (Q5–S10); three aromatic residues (Phe59, Trp80, Tyr83) form a partial hydrophobic cage. MPP8 harbors an N-terminal chromodomain and C-terminal ankyrin repeat domain. Binding affinities for H3K9me3 and H3K9me2 are sub-micromolar.","method":"X-ray crystallography, fluorescence polarization binding assay","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus quantitative binding assay; consistent with independent structure from PMID 22022377","pmids":["21419134"],"is_preprint":false},{"year":2013,"finding":"MPP8 is phosphorylated by cyclin B1–Cdk1 in vitro and in cells during mitosis; this phosphorylation causes MPP8 to dissociate from chromatin during metaphase-to-anaphase. An MPP8 STA mutant (all Cdk consensus sites substituted to Ala) fails to dissociate from chromatin during early mitosis, demonstrating that Cdk-dependent phosphorylation regulates MPP8 chromatin association.","method":"In vitro kinase assay (cyclin B1-Cdk1 + MPP8), site-directed mutagenesis (STA mutant), mitotic kinase inhibitor experiments, chromatin fractionation","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis plus cellular fractionation in a single study","pmids":["23416073"],"is_preprint":false},{"year":2013,"finding":"The mitochondrial peptide Humanin (HN) physically interacts with MPP8; co-immunoprecipitation confirmed the interaction. The MPP8-binding site on HN maps to residues 5–12, and the HN-binding domain on MPP8 maps to residues 431–560.","method":"Co-immunoprecipitation, peptide mapping, deletion analysis","journal":"Journal of peptide science","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, Co-IP and deletion mapping, no functional consequence established","pmids":["23532874"],"is_preprint":false},{"year":2015,"finding":"MPP8 physically interacts with SIRT1 deacetylase. SIRT1 antagonizes PCAF-catalyzed acetylation of MPP8 at K439, protecting MPP8 from ubiquitin-proteasome degradation. Conversely, MPP8 recruits SIRT1 to target promoters for H4K16 deacetylation after MPP8 binds methyl-H3K9. Disrupting either MPP8 methyl-H3K9 binding or the SIRT1 interaction de-represses E-cadherin and reduces EMT phenotypes.","method":"Co-IP, site-directed mutagenesis (K439 acetylation site), ubiquitin-proteasome assay, ChIP, knockdown with EMT phenotype readout","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP, mutagenesis, ChIP, and functional knockdown with mechanistic pathway defined in a single study","pmids":["25870236"],"is_preprint":false},{"year":2015,"finding":"MPP8 physically interacts with PRC1 complex components in co-immunoprecipitation experiments. MPP8 knockdown in HeLa cells de-represses testis-specific genes, and depletion in murine ES cells induces mesoderm differentiation genes (Cdx2, Brachyury).","method":"Co-immunoprecipitation, shRNA knockdown with gene expression readout","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, Co-IP and knockdown phenotype, limited mechanistic resolution","pmids":["25660450"],"is_preprint":false},{"year":2018,"finding":"G9a/GLP tri-methylates ATF7IP at an H3K9-like mimic motif in mouse embryonic stem cells; MPP8 recognizes this methylated ATF7IP via its chromodomain. SETDB1/MPP8-mediated reporter-provirus silencing is delayed in mESCs expressing an unmethylatable ATF7IP mutant, implicating ATF7IP methylation in SETDB1/MPP8-mediated transgene silencing.","method":"Comprehensive substrate screen (MS-based), in vitro methylation assay, chromodomain binding assay, unmethylatable mutant cell line, reporter-provirus silencing assay","journal":"Epigenetics & chromatin","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay, direct binding assay, and functional cell-based silencing assay with mutagenesis in one study","pmids":["30286792"],"is_preprint":false},{"year":2019,"finding":"MPP8 physically interacts with SETDB1 in embryonic stem cells and co-regulates a significant number of common genomic targets, especially satellite DNA repeats, as shown by combined biochemical, transcriptomic, and genomic (ChIP/CUT&RUN) analyses.","method":"Co-immunoprecipitation, RNA-seq, ChIP-seq/genomic profiling","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus genome-wide co-occupancy and transcriptomic rescue, single lab","pmids":["31557926"],"is_preprint":false},{"year":2021,"finding":"MPP8 is essential for ground-state pluripotency in mESCs; its depletion causes cell cycle arrest and spontaneous differentiation. SETDB1 recruits MPP8 to its genomic target loci. Unexpectedly, MPP8 lacking the chromodomain still efficiently represses LINE-1 elements, while the unannotated C-terminus is essential for function. MPP8 represses LINE1 elements through its association with the HUSH core complex, independently of detectable chromatin binding and maintenance of H3K9me3 levels.","method":"Auxin-inducible degron depletion, domain deletion mutants, ChIP-seq, RNA-seq, rescue experiments","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — inducible depletion, domain-deletion rescue, and genome-wide profiling with orthogonal methods; replicated across multiple approaches","pmids":["34031396"],"is_preprint":false},{"year":2021,"finding":"A peptidomimetic ligand (UNC5246) targeting the MPP8 chromodomain was developed; biotinylated UNC5246 in chemoproteomics studies revealed HRP2 (hepatoma-derived growth factor-related protein 2) as a novel MPP8-associated protein. HRP2 was shown to colocalize with MPP8 at the E-cadherin gene locus.","method":"One-bead one-compound (OBOC) combinatorial screening, chemoproteomics pulldown, ChIP colocalization","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, chemical pulldown and ChIP colocalization; novel interaction identified but mechanistic consequence not deeply characterized","pmids":["34415726"],"is_preprint":false},{"year":2023,"finding":"MPP8 regulates the LIF/STAT3 signaling pathway activity and Nanog expression in mESCs. Induced degradation of MPP8 protein impairs mESC proliferation, colony formation, LIF/STAT3 pathway activity, and differentiation capacity.","method":"miniIAA7-tagged degron cell lines, auxin-induced degradation, reporter assays for STAT3 activity, colony formation assay","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — inducible degradation with defined signaling pathway readout, single lab, mechanistic link between MPP8 and STAT3 not fully resolved","pmids":["37626833"],"is_preprint":false},{"year":2024,"finding":"Crystal structure of the MPP8 C-terminal domain (CTD) reveals five ankyrin repeats followed by a PINIT-domain-like fold. AlphaFold3 modeling predicts the MPP8 CTD interacts with SPOC and novel-fold domains in TASOR; point mutations at these predicted interfaces abolish HUSH-dependent transcriptional repression in a cell-based reporter assay. The MPP8 chromodomain binds sequences in SETDB1, ATF7IP, G9a, and GLP with similar or higher affinity than H3K9me3, suggesting MPP8 recruits H3K9 methyltransferases via its chromodomain.","method":"X-ray crystallography (MPP8 CTD), AlphaFold3 structural modeling, site-directed mutagenesis at predicted interfaces, cell-based HUSH reporter assay, binding affinity measurements","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus mutagenesis validated by functional reporter assay and quantitative binding measurements in a single study","pmids":["39638237"],"is_preprint":false},{"year":2026,"finding":"Covalent fragment screening identified two acrylamide-containing fragments that covalently label MPP8 at cysteine 99 (C99), which is adjacent to the methyl-lysine binding pocket of the chromodomain, providing a site for potential covalent antagonist development.","method":"MALDI-TOF mass spectrometry covalent fragment screening, glutathione reactivity assay for selectivity","journal":"SLAS discovery","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct MS identification of labeled residue, single lab, functional consequence on chromodomain binding not fully characterized in abstract","pmids":["41621721"],"is_preprint":false},{"year":2024,"finding":"PRC1.6 complex colocalizes with the HUSH complex at active promoters genome-wide; PRC1.6 binding at a subset of HUSH-silenced genes is dependent on the core HUSH component MPP8, as shown by genome-wide chromatin profiling and loss-of-function experiments.","method":"Proximity labeling (C-BERST), forward genetic screen, ChIP-seq/genome-wide profiling, MPP8 loss-of-function","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — proximity proteomics plus genetic screen plus ChIP-seq, but preprint and single lab","pmids":[],"is_preprint":true},{"year":2025,"finding":"In human iPSCs, MPP8 depletion (as a core HUSH component) induces expression of young LINE-1 elements and interferon-stimulated genes (ISGs) directly, without IFN signaling, suggesting MPP8 directly represses ISGs as transcriptional targets at the chromatin level. CUT&Tag confirmed MPP8 enrichment at HUSH-regulated ISGs.","method":"MPP8 depletion in iPSCs, RNA-seq, CUT&Tag chromatin profiling","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — CUT&Tag plus RNA-seq with depletion, preprint and single lab","pmids":[],"is_preprint":true},{"year":2025,"finding":"MPP8 is targeted for proteasomal degradation by the adenoviral E3 ubiquitin ligase complex (E1B-55K and E4orf6) during HAdV infection, identifying MPP8 as a host restriction factor for adenovirus that the virus actively counteracts.","method":"Protein degradation assays, co-immunoprecipitation with viral proteins, proteasome inhibitor rescue","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, single lab, proteasomal degradation shown but mechanistic detail of ubiquitylation not fully characterized in abstract","pmids":[],"is_preprint":true}],"current_model":"MPP8 is a chromodomain-containing epigenetic reader protein that binds H3K9me2/3 marks (and methylated non-histone substrates including Dnmt3a-K44me2 and ATF7IP) via a structurally defined aromatic cage, and serves as a scaffold within the HUSH complex (with TASOR and Periphilin) to coordinate transcriptional silencing of retroelements, proviruses, and target genes by recruiting H3K9 methyltransferases (SETDB1, G9a/GLP, ESET) and DNMT3A through its chromodomain, while its C-terminal ankyrin-PINIT domain mediates TASOR interaction; MPP8 chromatin association is negatively regulated by Cdk1-cyclin B1-dependent phosphorylation during mitosis, and SIRT1 stabilizes MPP8 by removing PCAF-catalyzed K439 acetylation while MPP8 reciprocally recruits SIRT1 for H4K16 deacetylation at target loci."},"narrative":{"mechanistic_narrative":"MPHOSPH8 (MPP8) is a chromodomain-containing epigenetic reader that couples recognition of methylated histone and non-histone marks to transcriptional silencing of target genes and repeated genomic elements [PMID:20871592, PMID:34031396]. Its N-terminal chromodomain encloses trimethyl-lysine within a conserved aromatic cage (Phe59, Trp80, Tyr83 plus Asp87) that discriminates H3K9me3 from H3K27 and binds H3K9me2/me3 with sub-micromolar affinity, and the domain forms a domain-swapped homodimer [PMID:22022377, PMID:21419134]. Beyond histones, the chromodomain reads methylated marks on silencing-machinery components—Dnmt3a-K44me2, self-methylated GLP, and G9a/GLP-trimethylated ATF7IP—and binds methyltransferase sequences (SETDB1, ATF7IP, G9a, GLP) with affinity comparable to or exceeding H3K9me3, allowing MPP8 to bridge DNMT3A with G9a/GLP and to recruit H3K9 methyltransferases [PMID:22086334, PMID:30286792, PMID:39638237]. MPP8 represses the E-cadherin promoter, where it directs DNMT3A-dependent CpG methylation and recruits SIRT1 for H4K16 deacetylation, thereby promoting EMT; SIRT1 reciprocally stabilizes MPP8 by reversing PCAF-catalyzed K439 acetylation that otherwise targets MPP8 for proteasomal degradation [PMID:20871592, PMID:25870236]. As a core subunit of the HUSH complex, MPP8 silences LINE-1 elements and proviruses through its unannotated C-terminus—a five-ankyrin-repeat plus PINIT-like fold that engages TASOR—independently of its chromodomain and of detectable chromatin binding [PMID:34031396, PMID:39638237]. MPP8 is essential for ground-state pluripotency in mouse ES cells, where its loss causes cell cycle arrest, spontaneous differentiation, and impaired LIF/STAT3 signaling [PMID:34031396, PMID:37626833]. Its chromatin association is cell-cycle-regulated: cyclin B1–Cdk1 phosphorylates MPP8 during mitosis to drive its dissociation from chromatin at the metaphase-to-anaphase transition [PMID:23416073].","teleology":[{"year":2010,"claim":"Established MPP8 as an H3K9 methyl-mark reader that physically links a chromatin signal to DNA methylation, defining its core role as a silencing scaffold.","evidence":"Chromodomain binding assays, ChIP, Co-IP, and knockdown with methylation readout at the E-cadherin promoter","pmids":["20871592"],"confidence":"High","gaps":["Did not resolve the structural basis of methyl-lysine recognition","Did not establish whether MPP8 acts within a defined multiprotein complex"]},{"year":2011,"claim":"Defined the atomic basis of methyl-lysine discrimination and showed the chromodomain reads methylated non-histone substrates, extending MPP8 reading beyond H3K9.","evidence":"Crystal structures of MPP8 chromodomain with H3K9me3, fluorescence polarization binding, in vitro methylation, and Co-IP for Dnmt3a-K44me2 and self-methylated GLP","pmids":["22086334","22022377","21419134"],"confidence":"High","gaps":["Functional importance of chromodomain homodimerization in cells not established","Predicted Tyr83 phosphorylation modulating binding not experimentally verified"]},{"year":2013,"claim":"Showed MPP8 chromatin association is cell-cycle-controlled by mitotic phosphorylation, revealing dynamic regulation of the silencing reader.","evidence":"In vitro cyclin B1–Cdk1 kinase assay, STA phospho-site mutant, and chromatin fractionation through mitosis","pmids":["23416073"],"confidence":"High","gaps":["The phosphatase reversing this modification is unidentified","Functional consequence for silencing of specific target loci not measured"]},{"year":2013,"claim":"Identified a physical interaction between MPP8 and the mitochondrial peptide Humanin, mapping the reciprocal binding regions.","evidence":"Co-IP, peptide mapping, and deletion analysis localizing the HN-binding site to MPP8 residues 431–560","pmids":["23532874"],"confidence":"Medium","gaps":["No functional consequence of the interaction established","Single lab, no reciprocal or structural validation"]},{"year":2015,"claim":"Connected MPP8 to an acetylation-controlled stability switch and to histone deacetylation at target loci, integrating it into EMT regulation.","evidence":"Co-IP, K439 acetylation mutant, ubiquitin-proteasome assay, ChIP, and knockdown with EMT readout for SIRT1/PCAF; Co-IP and knockdown for PRC1 components","pmids":["25870236","25660450"],"confidence":"High","gaps":["Mechanism by which acetylation triggers degradation not resolved","PRC1 interaction lacks structural or reciprocal validation"]},{"year":2018,"claim":"Demonstrated that methylation of ATF7IP, not only histones, is read by MPP8 and is required for SETDB1/MPP8 provirus silencing, broadening the methyl-mark reading model.","evidence":"MS substrate screen, in vitro methylation, chromodomain binding, and unmethylatable ATF7IP mutant in a reporter-provirus silencing assay","pmids":["30286792"],"confidence":"High","gaps":["Did not quantify contribution of ATF7IP methylation versus H3K9me at endogenous loci"]},{"year":2019,"claim":"Showed genome-wide co-occupancy and functional co-regulation of MPP8 with SETDB1, especially at satellite repeats, establishing repeat-element silencing as a shared genomic program.","evidence":"Co-IP, RNA-seq, and ChIP-seq/CUT&RUN co-occupancy analysis in ES cells","pmids":["31557926"],"confidence":"Medium","gaps":["Directionality of recruitment between MPP8 and SETDB1 not resolved here","Single lab"]},{"year":2021,"claim":"Revealed that MPP8 represses LINE-1 via the HUSH complex through its C-terminus independently of the chromodomain and detectable chromatin binding, and that MPP8 is essential for pluripotency.","evidence":"Auxin-inducible degron depletion, domain-deletion rescue, ChIP-seq, and RNA-seq in mESCs; chemoproteomics with the chromodomain ligand UNC5246 identifying HRP2","pmids":["34031396","34415726"],"confidence":"High","gaps":["Structural basis of the C-terminal HUSH interaction not defined here","Functional role of HRP2 interaction not characterized"]},{"year":2023,"claim":"Linked MPP8 to LIF/STAT3 signaling and Nanog expression, connecting its silencing activity to pluripotency-maintaining signaling.","evidence":"miniIAA7 degron depletion with STAT3 reporter, colony formation, and differentiation assays in mESCs","pmids":["37626833"],"confidence":"Medium","gaps":["Mechanistic link between MPP8 chromatin function and STAT3 activity unresolved","Direct versus indirect effect on Nanog not distinguished"]},{"year":2024,"claim":"Provided the structural basis for MPP8's chromodomain-independent function, defining the C-terminal ankyrin-PINIT fold that engages TASOR and showing the chromodomain directly binds methyltransferase sequences.","evidence":"Crystal structure of MPP8 CTD, AlphaFold3 modeling of the TASOR interface, interface mutagenesis validated in a HUSH reporter assay, and binding affinity measurements","pmids":["39638237"],"confidence":"High","gaps":["Direct experimental structure of the MPP8 CTD–TASOR complex not solved","Stoichiometry of MPP8 within assembled HUSH not defined"]},{"year":2024,"claim":"Connected HUSH/MPP8 to PRC1.6 occupancy at a subset of silenced genes, indicating cross-talk between repressive complexes.","evidence":"Proximity labeling (C-BERST), forward genetic screen, and ChIP-seq with MPP8 loss-of-function (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint, single lab","Whether MPP8 directly recruits PRC1.6 or acts upstream not resolved"]},{"year":2025,"claim":"Extended MPP8/HUSH targets to interferon-stimulated genes and positioned MPP8 as a virally counteracted host restriction factor, implicating it in innate immune gene control.","evidence":"MPP8 depletion with RNA-seq and CUT&Tag in iPSCs for ISG repression; protein degradation and Co-IP with adenoviral E1B-55K/E4orf6 (preprints)","pmids":[],"confidence":"Low","gaps":["Both findings are preprints, single lab","Direct ubiquitylation of MPP8 by the viral E3 complex not biochemically defined","Mechanism distinguishing direct ISG repression from indirect effects not fully established"]},{"year":2026,"claim":"Identified a covalent labeling site (C99) adjacent to the methyl-lysine pocket, opening a route to chemical antagonists of the chromodomain.","evidence":"MALDI-TOF covalent fragment screening and glutathione reactivity selectivity assay","pmids":["41621721"],"confidence":"Medium","gaps":["Effect of C99 labeling on methyl-lysine binding not demonstrated","Cellular activity of the fragments not shown"]},{"year":null,"claim":"How MPP8's chromodomain-dependent methyl-mark reading and its chromodomain-independent HUSH/TASOR-scaffolding activities are partitioned across different target classes (E-cadherin, satellite repeats, LINE-1, ISGs) remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model reconciling chromatin-binding-dependent and -independent silencing","Direct MPP8–TASOR complex structure not determined","Rules governing locus-specific recruitment unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[0,2,3]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,10,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,13,10]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,4,10]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,9,16]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,10,6]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[0,9,13]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[4]}],"complexes":["HUSH complex"],"partners":["TASOR","SETDB1","ATF7IP","DNMT3A","GLP","G9A","SIRT1","HRP2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q99549","full_name":"M-phase phosphoprotein 8","aliases":["Two hybrid-associated protein 3 with RanBPM","Twa3"],"length_aa":860,"mass_kda":97.2,"function":"Heterochromatin component that specifically recognizes and binds methylated 'Lys-9' of histone H3 (H3K9me) and promotes recruitment of proteins that mediate epigenetic repression (PubMed:26022416, PubMed:28581500, PubMed:29211708). As part of the HUSH complex, promotes epigenetic repression of mobile genetic elements, such as retroviruses and transposable elements: the HUSH complex mainly represses LINE-1 (L1) retrotransposons that are still capable of transposition (PubMed:29211708). Silencing events often occur within introns of transcriptionally active genes, and lead to the down-regulation of host gene expression (PubMed:29211708). MPHOSPH8 mediates recruitment of the HUSH complex to H3K9me3 sites: the HUSH complex is recruited to genomic loci rich in H3K9me3 and is required to maintain transcriptional silencing by promoting recruitment of SETDB1, a histone methyltransferase that mediates further deposition of H3K9me3, as well as MORC2, a chromatin remodeler that compacts chromatin (PubMed:26022416, PubMed:28581500). The HUSH complex is also involved in the silencing of unintegrated retroviral DNA by being recruited by ZNF638: some part of the retroviral DNA formed immediately after infection remains unintegrated in the host genome and is transcriptionally repressed (PubMed:30487602). As part of the HUSH2 complex, promotes epigenetic repression of interferon-stimulated genes (PubMed:33144593, PubMed:39013473). Binds H3K9me and promotes DNA methylation by recruiting DNMT3A to target CpG sites; these can be situated within the coding region of the gene (PubMed:20871592). Mediates silencing of E-cadherin (CDH1) and protocadherin genes in the nervous system (PubMed:20871592)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q99549/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MPHOSPH8","classification":"Not Classified","n_dependent_lines":67,"n_total_lines":1208,"dependency_fraction":0.055463576158940396},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"HMGN5","stoichiometry":0.2},{"gene":"SSRP1","stoichiometry":0.2},{"gene":"TOP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/MPHOSPH8","total_profiled":1310},"omim":[{"mim_id":"621243","title":"TRANSCRIPTION ACTIVATION SUPPRESSOR FAMILY, MEMBER 2; TASOR2","url":"https://www.omim.org/entry/621243"},{"mim_id":"616661","title":"MORC FAMILY CW-TYPE ZINC FINGER PROTEIN 2; MORC2","url":"https://www.omim.org/entry/616661"},{"mim_id":"611626","title":"M-PHASE PHOSPHOPROTEIN 8; MPHOSPH8","url":"https://www.omim.org/entry/611626"},{"mim_id":"603854","title":"RAN-BINDING PROTEIN 9; RANBP9","url":"https://www.omim.org/entry/603854"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MPHOSPH8"},"hgnc":{"alias_symbol":["mpp8","HSMPP8"],"prev_symbol":[]},"alphafold":{"accession":"Q99549","domains":[{"cath_id":"2.40.50.40","chopping":"70-107","consensus_level":"medium","plddt":80.5747,"start":70,"end":107},{"cath_id":"1.25.40.20","chopping":"571-724","consensus_level":"medium","plddt":87.8617,"start":571,"end":724},{"cath_id":"2.60.120,2.60.120","chopping":"742-860","consensus_level":"high","plddt":59.2196,"start":742,"end":860}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99549","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99549-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99549-F1-predicted_aligned_error_v6.png","plddt_mean":56.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MPHOSPH8","jax_strain_url":"https://www.jax.org/strain/search?query=MPHOSPH8"},"sequence":{"accession":"Q99549","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99549.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99549/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99549"}},"corpus_meta":[{"pmid":"22086334","id":"PMC_22086334","title":"MPP8 mediates the interactions between DNA methyltransferase Dnmt3a and H3K9 methyltransferase GLP/G9a.","date":"2011","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/22086334","citation_count":118,"is_preprint":false},{"pmid":"20871592","id":"PMC_20871592","title":"Methyl-H3K9-binding protein MPP8 mediates E-cadherin gene silencing and promotes tumour cell motility and invasion.","date":"2010","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/20871592","citation_count":102,"is_preprint":false},{"pmid":"25870236","id":"PMC_25870236","title":"MPP8 and SIRT1 crosstalk in E-cadherin gene silencing and epithelial-mesenchymal transition.","date":"2015","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/25870236","citation_count":55,"is_preprint":false},{"pmid":"34031396","id":"PMC_34031396","title":"MPP8 is essential for sustaining self-renewal of ground-state pluripotent stem cells.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34031396","citation_count":52,"is_preprint":false},{"pmid":"30286792","id":"PMC_30286792","title":"Tri-methylation of ATF7IP by G9a/GLP recruits the chromodomain protein MPP8.","date":"2018","source":"Epigenetics & chromatin","url":"https://pubmed.ncbi.nlm.nih.gov/30286792","citation_count":50,"is_preprint":false},{"pmid":"22022377","id":"PMC_22022377","title":"Structural basis for specific binding of human MPP8 chromodomain to histone H3 methylated at lysine 9.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22022377","citation_count":43,"is_preprint":false},{"pmid":"21419134","id":"PMC_21419134","title":"Structural insights for MPP8 chromodomain interaction with histone H3 lysine 9: potential effect of phosphorylation on methyl-lysine binding.","date":"2011","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21419134","citation_count":41,"is_preprint":false},{"pmid":"34415726","id":"PMC_34415726","title":"A Peptidomimetic Ligand Targeting the Chromodomain of MPP8 Reveals HRP2's Association with the HUSH Complex.","date":"2021","source":"ACS chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/34415726","citation_count":17,"is_preprint":false},{"pmid":"31557926","id":"PMC_31557926","title":"The H3K9 Methylation Writer SETDB1 and its Reader MPP8 Cooperate to Silence Satellite DNA Repeats in Mouse Embryonic Stem Cells.","date":"2019","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/31557926","citation_count":17,"is_preprint":false},{"pmid":"29412790","id":"PMC_29412790","title":"Knockdown of MPP8 suppresses cell proliferation via regulation of HOXA5 in non-small cell lung cancer cells.","date":"2018","source":"Cellular and molecular biology (Noisy-le-Grand, France)","url":"https://pubmed.ncbi.nlm.nih.gov/29412790","citation_count":10,"is_preprint":false},{"pmid":"23416073","id":"PMC_23416073","title":"Mitotic phosphorylation of MPP8 by cyclin-dependent kinases regulates chromatin dissociation.","date":"2013","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/23416073","citation_count":7,"is_preprint":false},{"pmid":"25660450","id":"PMC_25660450","title":"Physical interaction between MPP8 and PRC1 complex and its implication for regulation of spermatogenesis.","date":"2015","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/25660450","citation_count":6,"is_preprint":false},{"pmid":"23532874","id":"PMC_23532874","title":"Humanin binds MPP8: mapping interaction sites of the peptide and protein.","date":"2013","source":"Journal of peptide science : an official publication of the European Peptide 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Cells.","date":"2023","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/37626833","citation_count":2,"is_preprint":false},{"pmid":"39638237","id":"PMC_39638237","title":"Structure and Methyl-lysine Binding Selectivity of the HUSH Complex Subunit MPP8.","date":"2024","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/39638237","citation_count":2,"is_preprint":false},{"pmid":"33893154","id":"PMC_33893154","title":"MPP8 Silences LINE-1 Retrotransposons to Promote Acute Myeloid Leukemia.","date":"2021","source":"Cancer discovery","url":"https://pubmed.ncbi.nlm.nih.gov/33893154","citation_count":0,"is_preprint":false},{"pmid":"41621721","id":"PMC_41621721","title":"Application of a MALDI mass spectrometry assay to identify covalent fragments targeting the methyl-lysine reader protein MPP8.","date":"2026","source":"SLAS discovery : advancing life sciences R & 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complex","date":"2024-07-19","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.17.602677","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13174,"output_tokens":4649,"usd":0.054629,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12675,"output_tokens":4432,"usd":0.087087,"stage2_stop_reason":"end_turn"},"total_usd":0.141716,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"MPP8 chromodomain directly binds methylated H3K9 (H3K9me2/me3) in vivo and in vitro, and MPP8 targets the E-cadherin gene promoter to repress it; knockdown reduces DNMT3A localization at the E-cadherin CpG island, decreasing DNA methylation there. MPP8 also physically interacts with H3K9 methyltransferases GLP and ESET, as well as DNMT3A.\",\n      \"method\": \"Chromodomain binding assays (in vitro and in vivo), ChIP, Co-immunoprecipitation, knockdown with reporter/methylation readout\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, ChIP, in vitro binding, and functional knockdown with defined molecular phenotype; independently replicated in subsequent papers\",\n      \"pmids\": [\"20871592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"G9a and GLP dimethylate Dnmt3a at K44 (mouse; equivalent to K47 human DNMT3A); the MPP8 chromodomain specifically recognizes this dimethylated Dnmt3a-K44me2. MPP8 also interacts with self-methylated GLP in a methylation-dependent manner. The MPP8 chromodomain forms a homodimer in solution and in crystals, suggesting a dimeric MPP8 bridges methylated Dnmt3a and GLP to form a Dnmt3a–MPP8–GLP/G9a silencing complex.\",\n      \"method\": \"In vitro methylation assay, crystal structure of MPP8 chromodomain dimer, Co-IP, peptide binding assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assay, crystal structure, and Co-IP with multiple orthogonal methods in one study\",\n      \"pmids\": [\"22086334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of human MPP8 chromodomain in complex with H3K9me3 peptide (residues 1–15) reveals a conserved aromatic cage (Phe59, Trp80, Tyr83) plus Asp87 that encloses the trimethyl-lysine, enabling discrimination of H3K9 from H3K27. The chromodomain forms a homodimer via domain-swapping of two β-strands. Modeled phosphorylation of cage residue Tyr83 is predicted to modulate methyl-lysine binding.\",\n      \"method\": \"X-ray crystallography, solution studies (dimerization), peptide binding affinity measurement\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — two independent crystal structures of MPP8 chromodomain–H3K9me3 complex reported (PMID 22022377 and 21419134), consistent findings\",\n      \"pmids\": [\"22022377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of MPP8 chromodomain–H3K9me3 peptide complex defines contacts with at least six H3 residues (Q5–S10); three aromatic residues (Phe59, Trp80, Tyr83) form a partial hydrophobic cage. MPP8 harbors an N-terminal chromodomain and C-terminal ankyrin repeat domain. Binding affinities for H3K9me3 and H3K9me2 are sub-micromolar.\",\n      \"method\": \"X-ray crystallography, fluorescence polarization binding assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus quantitative binding assay; consistent with independent structure from PMID 22022377\",\n      \"pmids\": [\"21419134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MPP8 is phosphorylated by cyclin B1–Cdk1 in vitro and in cells during mitosis; this phosphorylation causes MPP8 to dissociate from chromatin during metaphase-to-anaphase. An MPP8 STA mutant (all Cdk consensus sites substituted to Ala) fails to dissociate from chromatin during early mitosis, demonstrating that Cdk-dependent phosphorylation regulates MPP8 chromatin association.\",\n      \"method\": \"In vitro kinase assay (cyclin B1-Cdk1 + MPP8), site-directed mutagenesis (STA mutant), mitotic kinase inhibitor experiments, chromatin fractionation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis plus cellular fractionation in a single study\",\n      \"pmids\": [\"23416073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The mitochondrial peptide Humanin (HN) physically interacts with MPP8; co-immunoprecipitation confirmed the interaction. The MPP8-binding site on HN maps to residues 5–12, and the HN-binding domain on MPP8 maps to residues 431–560.\",\n      \"method\": \"Co-immunoprecipitation, peptide mapping, deletion analysis\",\n      \"journal\": \"Journal of peptide science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Co-IP and deletion mapping, no functional consequence established\",\n      \"pmids\": [\"23532874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MPP8 physically interacts with SIRT1 deacetylase. SIRT1 antagonizes PCAF-catalyzed acetylation of MPP8 at K439, protecting MPP8 from ubiquitin-proteasome degradation. Conversely, MPP8 recruits SIRT1 to target promoters for H4K16 deacetylation after MPP8 binds methyl-H3K9. Disrupting either MPP8 methyl-H3K9 binding or the SIRT1 interaction de-represses E-cadherin and reduces EMT phenotypes.\",\n      \"method\": \"Co-IP, site-directed mutagenesis (K439 acetylation site), ubiquitin-proteasome assay, ChIP, knockdown with EMT phenotype readout\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, mutagenesis, ChIP, and functional knockdown with mechanistic pathway defined in a single study\",\n      \"pmids\": [\"25870236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MPP8 physically interacts with PRC1 complex components in co-immunoprecipitation experiments. MPP8 knockdown in HeLa cells de-represses testis-specific genes, and depletion in murine ES cells induces mesoderm differentiation genes (Cdx2, Brachyury).\",\n      \"method\": \"Co-immunoprecipitation, shRNA knockdown with gene expression readout\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Co-IP and knockdown phenotype, limited mechanistic resolution\",\n      \"pmids\": [\"25660450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"G9a/GLP tri-methylates ATF7IP at an H3K9-like mimic motif in mouse embryonic stem cells; MPP8 recognizes this methylated ATF7IP via its chromodomain. SETDB1/MPP8-mediated reporter-provirus silencing is delayed in mESCs expressing an unmethylatable ATF7IP mutant, implicating ATF7IP methylation in SETDB1/MPP8-mediated transgene silencing.\",\n      \"method\": \"Comprehensive substrate screen (MS-based), in vitro methylation assay, chromodomain binding assay, unmethylatable mutant cell line, reporter-provirus silencing assay\",\n      \"journal\": \"Epigenetics & chromatin\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay, direct binding assay, and functional cell-based silencing assay with mutagenesis in one study\",\n      \"pmids\": [\"30286792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MPP8 physically interacts with SETDB1 in embryonic stem cells and co-regulates a significant number of common genomic targets, especially satellite DNA repeats, as shown by combined biochemical, transcriptomic, and genomic (ChIP/CUT&RUN) analyses.\",\n      \"method\": \"Co-immunoprecipitation, RNA-seq, ChIP-seq/genomic profiling\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus genome-wide co-occupancy and transcriptomic rescue, single lab\",\n      \"pmids\": [\"31557926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MPP8 is essential for ground-state pluripotency in mESCs; its depletion causes cell cycle arrest and spontaneous differentiation. SETDB1 recruits MPP8 to its genomic target loci. Unexpectedly, MPP8 lacking the chromodomain still efficiently represses LINE-1 elements, while the unannotated C-terminus is essential for function. MPP8 represses LINE1 elements through its association with the HUSH core complex, independently of detectable chromatin binding and maintenance of H3K9me3 levels.\",\n      \"method\": \"Auxin-inducible degron depletion, domain deletion mutants, ChIP-seq, RNA-seq, rescue experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — inducible depletion, domain-deletion rescue, and genome-wide profiling with orthogonal methods; replicated across multiple approaches\",\n      \"pmids\": [\"34031396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A peptidomimetic ligand (UNC5246) targeting the MPP8 chromodomain was developed; biotinylated UNC5246 in chemoproteomics studies revealed HRP2 (hepatoma-derived growth factor-related protein 2) as a novel MPP8-associated protein. HRP2 was shown to colocalize with MPP8 at the E-cadherin gene locus.\",\n      \"method\": \"One-bead one-compound (OBOC) combinatorial screening, chemoproteomics pulldown, ChIP colocalization\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, chemical pulldown and ChIP colocalization; novel interaction identified but mechanistic consequence not deeply characterized\",\n      \"pmids\": [\"34415726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MPP8 regulates the LIF/STAT3 signaling pathway activity and Nanog expression in mESCs. Induced degradation of MPP8 protein impairs mESC proliferation, colony formation, LIF/STAT3 pathway activity, and differentiation capacity.\",\n      \"method\": \"miniIAA7-tagged degron cell lines, auxin-induced degradation, reporter assays for STAT3 activity, colony formation assay\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — inducible degradation with defined signaling pathway readout, single lab, mechanistic link between MPP8 and STAT3 not fully resolved\",\n      \"pmids\": [\"37626833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Crystal structure of the MPP8 C-terminal domain (CTD) reveals five ankyrin repeats followed by a PINIT-domain-like fold. AlphaFold3 modeling predicts the MPP8 CTD interacts with SPOC and novel-fold domains in TASOR; point mutations at these predicted interfaces abolish HUSH-dependent transcriptional repression in a cell-based reporter assay. The MPP8 chromodomain binds sequences in SETDB1, ATF7IP, G9a, and GLP with similar or higher affinity than H3K9me3, suggesting MPP8 recruits H3K9 methyltransferases via its chromodomain.\",\n      \"method\": \"X-ray crystallography (MPP8 CTD), AlphaFold3 structural modeling, site-directed mutagenesis at predicted interfaces, cell-based HUSH reporter assay, binding affinity measurements\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus mutagenesis validated by functional reporter assay and quantitative binding measurements in a single study\",\n      \"pmids\": [\"39638237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Covalent fragment screening identified two acrylamide-containing fragments that covalently label MPP8 at cysteine 99 (C99), which is adjacent to the methyl-lysine binding pocket of the chromodomain, providing a site for potential covalent antagonist development.\",\n      \"method\": \"MALDI-TOF mass spectrometry covalent fragment screening, glutathione reactivity assay for selectivity\",\n      \"journal\": \"SLAS discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct MS identification of labeled residue, single lab, functional consequence on chromodomain binding not fully characterized in abstract\",\n      \"pmids\": [\"41621721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PRC1.6 complex colocalizes with the HUSH complex at active promoters genome-wide; PRC1.6 binding at a subset of HUSH-silenced genes is dependent on the core HUSH component MPP8, as shown by genome-wide chromatin profiling and loss-of-function experiments.\",\n      \"method\": \"Proximity labeling (C-BERST), forward genetic screen, ChIP-seq/genome-wide profiling, MPP8 loss-of-function\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — proximity proteomics plus genetic screen plus ChIP-seq, but preprint and single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In human iPSCs, MPP8 depletion (as a core HUSH component) induces expression of young LINE-1 elements and interferon-stimulated genes (ISGs) directly, without IFN signaling, suggesting MPP8 directly represses ISGs as transcriptional targets at the chromatin level. CUT&Tag confirmed MPP8 enrichment at HUSH-regulated ISGs.\",\n      \"method\": \"MPP8 depletion in iPSCs, RNA-seq, CUT&Tag chromatin profiling\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — CUT&Tag plus RNA-seq with depletion, preprint and single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MPP8 is targeted for proteasomal degradation by the adenoviral E3 ubiquitin ligase complex (E1B-55K and E4orf6) during HAdV infection, identifying MPP8 as a host restriction factor for adenovirus that the virus actively counteracts.\",\n      \"method\": \"Protein degradation assays, co-immunoprecipitation with viral proteins, proteasome inhibitor rescue\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, single lab, proteasomal degradation shown but mechanistic detail of ubiquitylation not fully characterized in abstract\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"MPP8 is a chromodomain-containing epigenetic reader protein that binds H3K9me2/3 marks (and methylated non-histone substrates including Dnmt3a-K44me2 and ATF7IP) via a structurally defined aromatic cage, and serves as a scaffold within the HUSH complex (with TASOR and Periphilin) to coordinate transcriptional silencing of retroelements, proviruses, and target genes by recruiting H3K9 methyltransferases (SETDB1, G9a/GLP, ESET) and DNMT3A through its chromodomain, while its C-terminal ankyrin-PINIT domain mediates TASOR interaction; MPP8 chromatin association is negatively regulated by Cdk1-cyclin B1-dependent phosphorylation during mitosis, and SIRT1 stabilizes MPP8 by removing PCAF-catalyzed K439 acetylation while MPP8 reciprocally recruits SIRT1 for H4K16 deacetylation at target loci.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MPHOSPH8 (MPP8) is a chromodomain-containing epigenetic reader that couples recognition of methylated histone and non-histone marks to transcriptional silencing of target genes and repeated genomic elements [#0, #10]. Its N-terminal chromodomain encloses trimethyl-lysine within a conserved aromatic cage (Phe59, Trp80, Tyr83 plus Asp87) that discriminates H3K9me3 from H3K27 and binds H3K9me2/me3 with sub-micromolar affinity, and the domain forms a domain-swapped homodimer [#2, #3]. Beyond histones, the chromodomain reads methylated marks on silencing-machinery components—Dnmt3a-K44me2, self-methylated GLP, and G9a/GLP-trimethylated ATF7IP—and binds methyltransferase sequences (SETDB1, ATF7IP, G9a, GLP) with affinity comparable to or exceeding H3K9me3, allowing MPP8 to bridge DNMT3A with G9a/GLP and to recruit H3K9 methyltransferases [#1, #8, #13]. MPP8 represses the E-cadherin promoter, where it directs DNMT3A-dependent CpG methylation and recruits SIRT1 for H4K16 deacetylation, thereby promoting EMT; SIRT1 reciprocally stabilizes MPP8 by reversing PCAF-catalyzed K439 acetylation that otherwise targets MPP8 for proteasomal degradation [#0, #6]. As a core subunit of the HUSH complex, MPP8 silences LINE-1 elements and proviruses through its unannotated C-terminus—a five-ankyrin-repeat plus PINIT-like fold that engages TASOR—independently of its chromodomain and of detectable chromatin binding [#10, #13]. MPP8 is essential for ground-state pluripotency in mouse ES cells, where its loss causes cell cycle arrest, spontaneous differentiation, and impaired LIF/STAT3 signaling [#10, #12]. Its chromatin association is cell-cycle-regulated: cyclin B1–Cdk1 phosphorylates MPP8 during mitosis to drive its dissociation from chromatin at the metaphase-to-anaphase transition [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established MPP8 as an H3K9 methyl-mark reader that physically links a chromatin signal to DNA methylation, defining its core role as a silencing scaffold.\",\n      \"evidence\": \"Chromodomain binding assays, ChIP, Co-IP, and knockdown with methylation readout at the E-cadherin promoter\",\n      \"pmids\": [\"20871592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis of methyl-lysine recognition\", \"Did not establish whether MPP8 acts within a defined multiprotein complex\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined the atomic basis of methyl-lysine discrimination and showed the chromodomain reads methylated non-histone substrates, extending MPP8 reading beyond H3K9.\",\n      \"evidence\": \"Crystal structures of MPP8 chromodomain with H3K9me3, fluorescence polarization binding, in vitro methylation, and Co-IP for Dnmt3a-K44me2 and self-methylated GLP\",\n      \"pmids\": [\"22086334\", \"22022377\", \"21419134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional importance of chromodomain homodimerization in cells not established\", \"Predicted Tyr83 phosphorylation modulating binding not experimentally verified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed MPP8 chromatin association is cell-cycle-controlled by mitotic phosphorylation, revealing dynamic regulation of the silencing reader.\",\n      \"evidence\": \"In vitro cyclin B1–Cdk1 kinase assay, STA phospho-site mutant, and chromatin fractionation through mitosis\",\n      \"pmids\": [\"23416073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The phosphatase reversing this modification is unidentified\", \"Functional consequence for silencing of specific target loci not measured\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified a physical interaction between MPP8 and the mitochondrial peptide Humanin, mapping the reciprocal binding regions.\",\n      \"evidence\": \"Co-IP, peptide mapping, and deletion analysis localizing the HN-binding site to MPP8 residues 431–560\",\n      \"pmids\": [\"23532874\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence of the interaction established\", \"Single lab, no reciprocal or structural validation\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected MPP8 to an acetylation-controlled stability switch and to histone deacetylation at target loci, integrating it into EMT regulation.\",\n      \"evidence\": \"Co-IP, K439 acetylation mutant, ubiquitin-proteasome assay, ChIP, and knockdown with EMT readout for SIRT1/PCAF; Co-IP and knockdown for PRC1 components\",\n      \"pmids\": [\"25870236\", \"25660450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which acetylation triggers degradation not resolved\", \"PRC1 interaction lacks structural or reciprocal validation\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated that methylation of ATF7IP, not only histones, is read by MPP8 and is required for SETDB1/MPP8 provirus silencing, broadening the methyl-mark reading model.\",\n      \"evidence\": \"MS substrate screen, in vitro methylation, chromodomain binding, and unmethylatable ATF7IP mutant in a reporter-provirus silencing assay\",\n      \"pmids\": [\"30286792\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not quantify contribution of ATF7IP methylation versus H3K9me at endogenous loci\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed genome-wide co-occupancy and functional co-regulation of MPP8 with SETDB1, especially at satellite repeats, establishing repeat-element silencing as a shared genomic program.\",\n      \"evidence\": \"Co-IP, RNA-seq, and ChIP-seq/CUT&RUN co-occupancy analysis in ES cells\",\n      \"pmids\": [\"31557926\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Directionality of recruitment between MPP8 and SETDB1 not resolved here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed that MPP8 represses LINE-1 via the HUSH complex through its C-terminus independently of the chromodomain and detectable chromatin binding, and that MPP8 is essential for pluripotency.\",\n      \"evidence\": \"Auxin-inducible degron depletion, domain-deletion rescue, ChIP-seq, and RNA-seq in mESCs; chemoproteomics with the chromodomain ligand UNC5246 identifying HRP2\",\n      \"pmids\": [\"34031396\", \"34415726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the C-terminal HUSH interaction not defined here\", \"Functional role of HRP2 interaction not characterized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Linked MPP8 to LIF/STAT3 signaling and Nanog expression, connecting its silencing activity to pluripotency-maintaining signaling.\",\n      \"evidence\": \"miniIAA7 degron depletion with STAT3 reporter, colony formation, and differentiation assays in mESCs\",\n      \"pmids\": [\"37626833\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between MPP8 chromatin function and STAT3 activity unresolved\", \"Direct versus indirect effect on Nanog not distinguished\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided the structural basis for MPP8's chromodomain-independent function, defining the C-terminal ankyrin-PINIT fold that engages TASOR and showing the chromodomain directly binds methyltransferase sequences.\",\n      \"evidence\": \"Crystal structure of MPP8 CTD, AlphaFold3 modeling of the TASOR interface, interface mutagenesis validated in a HUSH reporter assay, and binding affinity measurements\",\n      \"pmids\": [\"39638237\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct experimental structure of the MPP8 CTD–TASOR complex not solved\", \"Stoichiometry of MPP8 within assembled HUSH not defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected HUSH/MPP8 to PRC1.6 occupancy at a subset of silenced genes, indicating cross-talk between repressive complexes.\",\n      \"evidence\": \"Proximity labeling (C-BERST), forward genetic screen, and ChIP-seq with MPP8 loss-of-function (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab\", \"Whether MPP8 directly recruits PRC1.6 or acts upstream not resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended MPP8/HUSH targets to interferon-stimulated genes and positioned MPP8 as a virally counteracted host restriction factor, implicating it in innate immune gene control.\",\n      \"evidence\": \"MPP8 depletion with RNA-seq and CUT&Tag in iPSCs for ISG repression; protein degradation and Co-IP with adenoviral E1B-55K/E4orf6 (preprints)\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Both findings are preprints, single lab\", \"Direct ubiquitylation of MPP8 by the viral E3 complex not biochemically defined\", \"Mechanism distinguishing direct ISG repression from indirect effects not fully established\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified a covalent labeling site (C99) adjacent to the methyl-lysine pocket, opening a route to chemical antagonists of the chromodomain.\",\n      \"evidence\": \"MALDI-TOF covalent fragment screening and glutathione reactivity selectivity assay\",\n      \"pmids\": [\"41621721\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effect of C99 labeling on methyl-lysine binding not demonstrated\", \"Cellular activity of the fragments not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MPP8's chromodomain-dependent methyl-mark reading and its chromodomain-independent HUSH/TASOR-scaffolding activities are partitioned across different target classes (E-cadherin, satellite repeats, LINE-1, ISGs) remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model reconciling chromatin-binding-dependent and -independent silencing\", \"Direct MPP8–TASOR complex structure not determined\", \"Rules governing locus-specific recruitment unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 10, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 13, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 4, 10]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 9, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 10, 6]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 9, 13]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\"HUSH complex\"],\n    \"partners\": [\"TASOR\", \"SETDB1\", \"ATF7IP\", \"DNMT3A\", \"GLP\", \"G9a\", \"SIRT1\", \"HRP2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}