Affinage

MBD6

Methyl-CpG-binding domain protein 6 · UniProt Q96DN6

Length
1003 aa
Mass
101.2 kDa
Annotated
2026-06-10
13 papers in source corpus 7 papers cited in narrative 7 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MBD6 is a heterochromatin-associated chromatin regulator that functions principally as an accessory subunit of the mammalian PR-DUB (BAP1/ASXL) Polycomb deubiquitinase complex (PMID:24634419, PMID:36180891). Although it carries an MBD domain that drives heterochromatic localization, this domain does not bind methylated DNA; its localization persists when DNA methylation is depleted, indicating a non-canonical recognition mode (PMID:20700456). Instead, the MBD domain is necessary and sufficient to mediate interaction with PR-DUB by docking onto the C-terminal PHD fingers of the ASXL1-3 scaffold subunits, forming an interface with a composite zinc-binding site [PMID:24634419, PMID:36180891, PMID:bio_10.1101_2024.12.08.627434]. Within this complex MBD6 stabilizes BAP1 occupancy genome-wide, and its depletion causes loss of BAP1 chromatin binding, reduced BAP1-dependent gene expression, and impaired growth of BAP1-dependent cancers (PMID:36180891). MBD6 contributes to repressive chromatin regulation, with haploinsufficiency derepressing genes genome-wide while downregulating mitochondrial loci such as COX17 and impairing mitochondrial respiration (PMID:41548483). MBD6 is additionally recruited to sites of DNA damage independently of PR-DUB (PMID:24634419) and binds m5C-modified chromatin-associated RNA, a contact required for proper H2AK119ub deubiquitination at chromatin [PMID:bio_10.1101_2025.06.24.661348].

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2010 Medium

    Established that MBD6's MBD domain governs heterochromatic targeting through a mechanism independent of DNA methylation, overturning the assumption that MBD-family proteins read methylated DNA.

    Evidence Colocalization imaging, MBD domain mutant analysis, and in vitro DNA binding assays in cultured cells with reduced methylation

    PMID:20700456

    Open questions at the time
    • The actual chromatin ligand recognized by the MBD domain was not identified
    • No protein partner was implicated at this stage
  2. 2014 High

    Identified the PR-DUB (BAP1/ASXL) complex as the physical partner of MBD6, reframing MBD6 as a Polycomb-associated factor and revealing a separable DNA-damage recruitment function.

    Evidence Reciprocal Co-IP, domain deletion mapping, ChIP for shared targets, and laser-induced DNA damage recruitment in cells

    PMID:24634419

    Open questions at the time
    • The molecular basis of the MBD6-ASXL contact was not resolved
    • Functional consequence of MBD6 loss on PR-DUB activity was untested
    • Mechanism of DNA-damage recruitment unknown
  3. 2022 High

    Defined MBD6 as a stabilizer of BAP1 chromatin occupancy by binding the ASXL1-3 C-terminal PHD fingers, establishing a functional and therapeutic dependency in BAP1-driven cancers.

    Evidence Co-IP, ChIP for BAP1 occupancy, knockdown, and in vitro/in vivo tumor growth assays

    PMID:36180891

    Open questions at the time
    • Structural detail of the PHD-MBD6 interface not resolved
    • Whether MBD6 directly modulates deubiquitinase catalysis not shown
  4. 2024 Medium

    Provided the structural rationale for the MBD6-ASXL interaction, showing the ASXL PHD is an atypical single-zinc, non-histone-binding domain that forms a composite zinc-binding interface with MBD6.

    Evidence In vitro reconstitution, AlphaFold3 modeling, and zinc chelation assays (preprint)

    PMID:bio_10.1101_2024.12.08.627434

    Open questions at the time
    • No experimental high-resolution structure
    • Preprint, single lab, in vitro only
    • Functional validation of the composite zinc site in cells absent
  5. 2025 Medium

    Linked MBD6 to RNA-mediated chromatin regulation by showing it binds m5C-modified chromatin-associated RNA, a contact required for proper H2AK119ub deubiquitination.

    Evidence caRNA pulldown, 5-azaC treatment, NSUN2 knockdown, and H2AK119ub measurement (preprint)

    PMID:bio_10.1101_2025.06.24.661348

    Open questions at the time
    • The RNA-binding determinant within MBD6 not mapped
    • Preprint, single lab
    • Whether caRNA binding and ASXL binding are coordinated is unknown
  6. 2026 Medium

    Demonstrated a repressive, dosage-sensitive role for MBD6 at chromatin with a specific physiological output in mitochondrial gene regulation and respiration.

    Evidence CRISPR heterozygous knockout, microarray transcriptomics, qRT-PCR, Seahorse flux assays, and public ChIP-seq co-localization at COX17 in SH-SY5Y cells

    PMID:41548483

    Open questions at the time
    • Direct causal link between MBD6/BAP1 occupancy and mitochondrial gene repression not proven mechanistically
    • Confined to one neuroblastoma line
    • Functional redundancy with MBD5 not dissected

Open questions

Synthesis pass · forward-looking unresolved questions
  • How MBD6's distinct activities — PR-DUB stabilization, DNA-damage recruitment, and m5C-caRNA binding — are integrated and regulated at chromatin remains unresolved.
  • No integrated structure of the MBD6-containing PR-DUB on chromatin
  • The chromatin ligand recognized by the MBD domain remains unidentified
  • Whether the same MBD6 pool performs all functions or distinct subpopulations exist is unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 2 GO:0140110 transcription regulator activity 2 GO:0003723 RNA binding 1
Localization
GO:0005634 nucleus 2 GO:0000228 nuclear chromosome 1
Pathway
R-HSA-4839726 Chromatin organization 2 R-HSA-74160 Gene expression (Transcription) 2
Partners
ASXL1ASXL2ASXL3BAP1FOXK2
Complex memberships
PR-DUB (BAP1/ASXL) complex

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2010 MBD6 colocalizes with heterochromatin in cultured cells, and this localization requires the integrity of its MBD domain. However, heterochromatic localization is maintained even in cells with severely decreased DNA methylation levels. In vitro, MBD6 does not bind methylated DNA sequences tested. Cell imaging/colocalization, domain mutant analysis, in vitro DNA binding assay PloS one Medium 20700456
2014 MBD6 interacts with the mammalian PR-DUB Polycomb protein complex (BAP1/ASXL), and this interaction is mediated by the MBD domain alone (necessary and sufficient). MBD6 and FOXK2/PR-DUB share genomic target genes by ChIP. MBD6, but not MBD5, is recruited to sites of DNA damage independently of PR-DUB. Co-immunoprecipitation, domain deletion/mutant analysis, chromatin immunoprecipitation (ChIP), laser-induced DNA damage recruitment assay Proteomics High 24634419
2022 MBD6 binds to the C-terminal PHD fingers of scaffold subunits ASXL1-3 and stabilizes the BAP1 (PR-DUB) complex at chromatin. Depletion of MBD6 leads to global loss of BAP1 occupancy at chromatin, reduced BAP1-dependent gene expression, and reduced tumor growth in vitro and in vivo in BAP1-dependent cancers (e.g., small cell lung cancer). Co-immunoprecipitation, ChIP, siRNA/shRNA knockdown, in vitro and in vivo tumor growth assays Genome biology High 36180891
2024 The ASXL PHD domain forms a stable complex with MBD6 (and MBD5) in vitro, and the interface between the ASXL PHD and MBD6 contains a composite zinc-binding site. The isolated ASXL PHD chelates a single zinc ion (atypical for PHD domains), and the ASXL PHD lacks features required for canonical histone H3 tail recognition. In vitro reconstitution, AlphaFold3 structural modeling, zinc chelation assay bioRxivpreprint Medium bio_10.1101_2024.12.08.627434
2026 Haploinsufficiency of MBD6 (and MBD5) in human neuroblastoma SH-SY5Y cells causes predominant upregulation of genes genome-wide (consistent with repressive roles), downregulation of mitochondrial genes (e.g., COX17), and impaired mitochondrial respiration (reduced basal and ATP-linked oxygen consumption) without changes in mitochondrial content. ChIP-seq data showed co-localization of MBD6 and BAP1 complex components at the COX17 promoter, suggesting direct chromatin-mediated regulation. CRISPR genome editing (heterozygous KO), microarray transcriptomics, qRT-PCR, Seahorse metabolic flux assay, public ChIP-seq analysis Biochemical and biophysical research communications Medium 41548483
2025 MBD6 binds chromatin-associated RNA (caRNA) containing 5-methylcytosine (m5C), and depletion of m5C in caRNA (by 5-azaC or NSUN2 loss) impairs MBD6 binding and consequently disrupts H2AK119ub deubiquitination at chromatin. 5-azaC treatment, NSUN2 knockdown, m5C depletion assays, H2AK119ub measurement, caRNA pulldown/binding assay bioRxivpreprint Medium bio_10.1101_2025.06.24.661348
2012 MBD6 is a direct transcriptional target of Oct4 in human adipose tissue-derived stem cells (hATSCs). Knockdown of MBD6 attenuates cell proliferation and induces cell death. MBD6 promotes transdifferentiation into neural and endodermal lineages while attenuating mesodermal differentiation, and acts by repressing MBD2 and MBD3. ChIP (Oct4 binding to MBD6 locus), siRNA knockdown, cell proliferation and differentiation assays Cellular and molecular life sciences Low 23052207

Source papers

Stage 0 corpus · 13 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2010 The human proteins MBD5 and MBD6 associate with heterochromatin but they do not bind methylated DNA. PloS one 88 20700456
2014 MBD5 and MBD6 interact with the human PR-DUB complex through their methyl-CpG-binding domain. Proteomics 80 24634419
2012 The expanding role of MBD genes in autism: identification of a MECP2 duplication and novel alterations in MBD5, MBD6, and SETDB1. Autism research : official journal of the International Society for Autism Research 75 23055267
2021 MBD5 and MBD6 couple DNA methylation to gene silencing through the J-domain protein SILENZIO. Science (New York, N.Y.) 68 34083448
2001 A novel mouse beta-defensin, mBD-6, predominantly expressed in skeletal muscle. The Journal of biological chemistry 31 11408484
2022 Single-nucleus RNA-seq reveals that MBD5, MBD6, and SILENZIO maintain silencing in the vegetative cell of developing pollen. Cell reports 26 36417865
2012 MBD6 is a direct target of Oct4 and controls the stemness and differentiation of adipose tissue-derived stem cells. Cellular and molecular life sciences : CMLS 21 23052207
2010 Extra views on RNA-dependent DNA methylation and MBD6-dependent heterochromatin formation in nucleolar dominance. Nucleus (Austin, Tex.) 20 21327072
2022 MBD5 and MBD6 stabilize the BAP1 complex and promote BAP1-dependent cancer. Genome biology 17 36180891
2023 ACD15, ACD21, and SLN regulate the accumulation and mobility of MBD6 to silence genes and transposable elements. Science advances 15 37967186
2019 The Expression of MBD6 Is Associated with Tumor Size in Uterine Leiomyomas. Genetic testing and molecular biomarkers 3 31313936
2023 ACD15, ACD21 and SLN regulate accumulation and mobility of MBD6 to silence genes and transposable elements. bioRxiv : the preprint server for biology 2 37662299
2026 Haploinsufficiency of MBD5 and MBD6 impairs mitochondrial respiration through chromatin-mediated gene regulation. Biochemical and biophysical research communications 0 41548483

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