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Showing PHF21A — BHC80 is a alias.

PHF21A

PHD finger protein 21A · UniProt Q96BD5

Length
680 aa
Mass
74.9 kDa
Annotated
2026-06-10
25 papers in source corpus 11 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PHF21A (BHC80) is a chromatin-reader scaffold of the LSD1-CoREST/BRAF-HDAC (BHC) repression complex that couples recognition of unmodified chromatin to transcriptional silencing of neuronal genes (PMID:17687328, PMID:15325272). Its C-terminal PHD finger specifically binds unmethylated histone H3K4 (H3K4me0) and is sterically excluded by H3K4 methylation, with a crystal structure defining the basis of this recognition (PMID:17687328). This PHD/H3K4me0 engagement is functionally essential: PHF21A and LSD1 reciprocally depend on one another for chromatin association, and a PHD-finger point mutant that cannot bind H3 fails to restore repression of LSD1 target genes (PMID:17687328). Through the same PHD region PHF21A contacts each of the other BHC subunits, organizing the complex as a scaffold (PMID:15325272), and it stabilizes LSD1 occupancy at specific neuronal targets such as SCN3A, whose de-repression accompanies PHF21A haploinsufficiency in patient cells (PMID:22770980). PHF21A also negatively modulates REST-mediated repression of neurosecretion genes (PMID:19439607) and is required for full cAMP/CRE-driven immediate-early gene induction (PMID:28571721). A neuron-specific microexon isoform (PHF21A-n) loses AT-hook-dependent DNA binding while retaining H3K4me0 recognition, generating a hypomorphic LSD1 complex with reduced nucleosome engagement (PMID:37904995); expression of this neuronal isoform precedes the neuronal LSD1 isoform during differentiation, and through new partners including MYT1-family transcription factors and VIRMA the resulting enzymatically attenuated complex limits excess synapse formation during brain development (PMID:39395799). Disruption of PHF21A causes cognitive impairment, with disease-associated splice/missense variants acting through reduced PHF21A dosage (PMID:22770980, PMID:40622422).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2004 Medium

    Before its molecular role was defined, it was unclear how the BHC repression complex was organized; this established PHF21A as the scaffold that directly contacts every other BHC subunit.

    Evidence Direct pulldown binding assays with BHC components and transcriptional repression assays in cultured cells

    PMID:15325272

    Open questions at the time
    • Isoform-specific HDAC1/HDAC2 binding differences not mechanistically resolved
    • Single-lab binding data without structural mapping of subunit contacts
  2. 2006 Medium

    The in vivo requirement for PHF21A was unknown; knockout established it is essential for neonatal survival.

    Evidence Targeted gene knockout in mouse with phenotypic analysis

    PMID:16684532

    Open questions at the time
    • No detectable tissue developmental defect, leaving the lethal cause undefined
    • Does not connect survival phenotype to a specific molecular target
  3. 2007 High

    How PHF21A is targeted to chromatin and links to active repression was unresolved; the PHD finger was shown to read H3K4me0 and to be required for LSD1-complex repression.

    Evidence Crystal structure of PHD finger on H3 peptide, in vitro binding, plus RNAi/ChIP epistasis and PHD-mutant rescue

    PMID:17687328

    Open questions at the time
    • Does not address how DNA-binding or non-histone contacts contribute to targeting
    • Genome-wide target spectrum not defined
  4. 2009 Medium

    The relationship between PHF21A and the neuronal master repressor REST was unknown; PHF21A was shown to act as a negative modulator of REST-mediated repression at neurosecretion gene promoters.

    Evidence Cell fusion, transfection, ChIP, and immunodepletion in PC12 cells

    PMID:19439607

    Open questions at the time
    • Mechanism of how PHF21A antagonizes rather than reinforces repression at these loci unclear
    • Effect was only partial de-repression in a single cell system
  5. 2012 Medium

    Whether human PHF21A dosage controls LSD1 chromatin occupancy at defined genes was untested; haploinsufficiency was shown to reduce LSD1 occupancy and de-repress SCN3A.

    Evidence ChIP in patient-derived lymphoblastoid lines with PHF21A-disrupting balanced translocations

    PMID:22770980

    Open questions at the time
    • Limited to one target gene
    • Causality between SCN3A de-repression and patient phenotype not established
  6. 2017 Medium

    PHF21A had been characterized as a repressor; this placed it in active cAMP/CRE signaling by showing it is required for full immediate-early gene induction.

    Evidence RNA-seq, CRE-luciferase reporter, and IEG RT-qPCR after forskolin stimulation in patient-derived cells

    PMID:28571721

    Open questions at the time
    • Molecular basis of a repressor-scaffold promoting CRE induction unexplained
    • Direct CRE-promoter occupancy by PHF21A not shown
  7. 2019 Medium

    Functions beyond nuclear repression were unknown; a cytoplasmic splice variant was shown to drive MyD88-p38-TTP signaling and cytokine mRNA stabilization to promote proliferation.

    Evidence Subcellular localization, pathway inhibition, proliferation assays, and xenografts

    PMID:30910347

    Open questions at the time
    • Mechanism connecting isoform localization to pathway activation unresolved
    • Relationship of this cytoplasmic role to chromatin function unclear
  8. 2023 Medium

    How a neuron-specific isoform alters complex activity was unknown; the microexon-containing PHF21A-n was shown to lose AT-hook DNA binding while retaining H3K4me0 reading, yielding a hypomorphic demethylase complex.

    Evidence In vitro reconstitution of canonical vs. neuronal PHF21A-LSD1 complexes, AT-hook mutagenesis, DNA binding and splicing analysis (preprint)

    PMID:37904995

    Open questions at the time
    • Preprint not yet peer-reviewed
    • In vivo consequence of reduced nucleosome engagement not established in this study
  9. 2024 High

    The developmental purpose of neuronal PHF21A splicing was unknown; asynchronous isoform switching was shown to stepwise deactivate the LSD1-PHF21A complex and to restrain excess synapse formation via new partners.

    Evidence Unbiased proteomics, Phf21a mutant mice, co-IP, and neuron differentiation time-course

    PMID:39395799

    Open questions at the time
    • Functional contribution of MYT1-family and VIRMA interactions to synapse control not dissected
    • How catalytic inactivation translates to limiting synaptogenesis mechanistically unresolved
  10. 2025 Medium

    The pathogenic mechanism of a disease-associated variant was ambiguous; characterization showed it reduces neuronal-isoform splicing while preserving DNA binding, implicating dosage rather than binding defect.

    Evidence mRNA splicing analysis and DNA binding assays of the c.1285G>A variant

    PMID:40622422

    Open questions at the time
    • Single-individual variant characterization
    • Direct demonstration of dosage-dependent neuronal phenotype not provided

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved how PHF21A's chromatin-repressor scaffold function, its cytoplasmic signaling isoform, and its non-catalytic neuronal complex partners are mechanistically integrated to control neurodevelopment.
  • No structure of the full PHF21A-LSD1 complex on a nucleosome
  • Genome-wide target map and partner-specific functions undefined
  • Causal chain from variant dosage to cognitive/synaptic phenotype incomplete

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 2 GO:0042393 histone binding 2 GO:0140110 transcription regulator activity 2 GO:0060090 molecular adaptor activity 1
Localization
GO:0005634 nucleus 1 GO:0005829 cytosol 1
Pathway
R-HSA-4839726 Chromatin organization 3 R-HSA-74160 Gene expression (Transcription) 3 R-HSA-1266738 Developmental Biology 1
Partners
HDAC1HDAC2KDM1AMYT1RESTVIRMA
Complex memberships
BRAF-HDAC (BHC) complexLSD1-CoREST complex

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2007 The PHD finger of BHC80/PHF21A specifically binds unmethylated histone H3K4 (H3K4me0), and this interaction is abrogated by methylation of H3K4. Crystal structure of the PHD finger bound to an unmodified H3 peptide revealed the structural basis of H3K4me0 recognition. Crystal structure determination, in vitro binding assays, PHD-finger mutagenesis Nature High 17687328
2007 BHC80/PHF21A and LSD1 depend reciprocally on one another to associate with chromatin; knockdown of BHC80 de-represses LSD1 target genes, and repression is restored by wild-type BHC80 but not a PHD-finger mutant unable to bind H3, establishing that BHC80 PHD-finger/H3K4me0 recognition is required for LSD1-complex-mediated gene repression. RNA interference knockdown, ChIP, reintroduction of wild-type vs. PHD mutant BHC80 Nature High 17687328
2004 The C-terminal PHD zinc-finger domain of BHC80/PHF21A binds directly to each of the five other components of the BRAF-HDAC complex (BHC), and BHC80 organizes the BHC complex that mediates transcriptional repression; two isoforms differ in reduced binding to HDAC1 and HDAC2 despite retaining the PHD finger, suggesting BHC80 acts as a scaffold protein. Direct binding assays (pulldown), isoform analysis, transcriptional repression assays in cultured cells Biochemical and biophysical research communications Medium 15325272
2006 Bhc80 knockout mice die neonatally without nursing, demonstrating that BHC80/PHF21A is essential for neonatal survival in vivo, though no developmental defect in neuronal or non-neuronal tissues was detected. Targeted gene knockout in mouse, phenotypic analysis FEBS letters Medium 16684532
2009 BHC80/PHF21A acts as a negative modulator of REST-mediated repression: BHC80 associates with REST at promoters of neurosecretion genes (chromograninB, SNAP25) in low-REST but not high-REST cells; overexpression of BHC80 in high-REST defective PC12 cells partially de-represses neurosecretion mRNAs, an effect augmented by attenuation of REST DNA binding. Cell fusion, transient transfection, chromatin immunoprecipitation, immunodepletion The Journal of neuroscience Medium 19439607
2012 PHF21A haploinsufficiency in patient lymphoblastoid cell lines causes de-repression of the neuronal gene SCN3A and reduced LSD1 occupancy at the SCN3A promoter, directly linking PHF21A function to LSD1 chromatin occupancy at a specific target gene in human cells. ChIP in patient-derived lymphoblastoid cell lines with balanced translocations disrupting PHF21A American journal of human genetics Medium 22770980
2019 An alternative splice variant BHC80-2 localizes to the cytoplasm (unlike the canonical nuclear BHC80-1) and activates the MyD88-p38-TTP pathway, increasing RNA stability of tumor-promoting cytokines and stimulating cell proliferation independently of androgen receptor signaling. Subcellular fractionation/localization, pathway inhibition, cell proliferation assays, xenograft models European urology Medium 30910347
2017 PHF21A is required for full induction of cAMP-responsive element (CRE)-driven transcription; PHF21A-deficient patient cells show delayed induction of immediate early genes following forskolin/cAMP stimulation, placing PHF21A in the cAMP signaling pathway relevant to learning and memory. RNA-seq in patient-derived cells, CRE-luciferase reporter assay, RT-qPCR of immediate early genes after forskolin stimulation Neuroscience Medium 28571721
2023 Canonical PHF21A (PHF21A-c) binds DNA via its AT-hook motif; the neuron-specific isoform PHF21A-n (which includes a neuronal microexon) lacks this DNA-binding function yet retains H3K4me0 recognition. In vitro reconstitution showed the neuronal PHF21A-LSD1 complex is a hypomorphic H3K4 demethylating machinery with reduced nucleosome engagement. An autism-associated missense variant c.1285G>A at the last nucleotide of exon 13 impairs splicing of PHF21A-n. In vitro reconstitution of canonical vs. neuronal PHF21A-LSD1 complexes, AT-hook mutagenesis, DNA binding assays, splicing analysis bioRxiv (preprint)preprint Medium 37904995
2024 Neuronal PHF21A isoform expression precedes neuronal LSD1 isoform expression during human neuron differentiation and mouse brain development; this asynchronous splicing results in stepwise deactivation of the LSD1-PHF21A complex. The enzymatically inactive (neuronal) LSD1-PHF21A complex interacts with neuron-specific binding partners including MYT1-family transcription factors and VIRMA mRNA processing protein; these interactions do not require the PHF21A microexon. Using Phf21a mutant mice, neuronal PHF21A splicing was shown to prevent excess synapse formation. Proteomics (unbiased MS), Phf21a mutant mouse models, co-immunoprecipitation, neuron differentiation time-course analysis The Journal of biological chemistry High 39395799
2013 BHC80 knockdown in zebrafish embryos causes abnormal cardiac phenotype including imbalanced ventricle-to-atrium proportion, incomplete D-loop, tubular heart morphology, slow heart rate, and cardiac dysfunction, revealing a role for PHF21A in early cardiac development. Morpholino antisense knockdown in zebrafish, fluorescence microscopy in vmhc:GFP transgenic zebrafish, RT-PCR Acta physiologica Sinica Low 24129737
2025 The disease-associated missense variant c.1285G>A significantly reduces splicing efficiency of PHF21A neuronal isoforms while maintaining DNA binding capability of the resulting protein, indicating that reduced PHF21A dosage (rather than impaired DNA binding) is the likely pathogenic mechanism for cognitive impairment in this individual. mRNA splicing analysis, DNA binding assays, systematic variant characterization Cellular and molecular neurobiology Medium 40622422

Source papers

Stage 0 corpus · 25 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2007 Recognition of unmethylated histone H3 lysine 4 links BHC80 to LSD1-mediated gene repression. Nature 358 17687328
2012 Translocations disrupting PHF21A in the Potocki-Shaffer-syndrome region are associated with intellectual disability and craniofacial anomalies. American journal of human genetics 62 22770980
2004 Characterization of BHC80 in BRAF-HDAC complex, involved in neuron-specific gene repression. Biochemical and biophysical research communications 47 15325272
2019 Disruption of PHF21A causes syndromic intellectual disability with craniofacial anomalies, epilepsy, hypotonia, and neurobehavioral problems including autism. Molecular autism 38 31649809
2019 RNA Splicing of the BHC80 Gene Contributes to Neuroendocrine Prostate Cancer Progression. European urology 27 30910347
2009 The rest repression of the neurosecretory phenotype is negatively modulated by BHC80, a protein of the BRAF/HDAC complex. The Journal of neuroscience : the official journal of the Society for Neuroscience 24 19439607
2018 De novo truncating variants in PHF21A cause intellectual disability and craniofacial anomalies. European journal of human genetics : EJHG 18 30487643
2006 A component of BRAF-HDAC complex, BHC80, is required for neonatal survival in mice. FEBS letters 17 16684532
2015 A microdeletion encompassing PHF21A in an individual with global developmental delay and craniofacial anomalies. American journal of medical genetics. Part A 16 26333423
2017 Potocki-Shaffer syndrome in a child without intellectual disability-The role of PHF21A in cognitive function. American journal of medical genetics. Part A 12 28127865
2017 Transcriptome Analysis Revealed Impaired cAMP Responsiveness in PHF21A-Deficient Human Cells. Neuroscience 10 28571721
2022 PHF21A Related Disorder: Description of a New Case. International journal of molecular sciences 7 36555772
2024 Neuronal splicing of the unmethylated histone H3K4 reader, PHF21A, prevents excessive synaptogenesis. The Journal of biological chemistry 6 39395799
2023 The PHF21A neurodevelopmental disorder: an evaluation of clinical data from 13 patients. Clinical dysmorphology 4 36876344
2023 De novo variants in PHF21A cause intellectual developmental disorder with behavioral abnormalities and craniofacial dysmorphism with or without seizures: A case report and literature review. Seizure 4 37633153
2022 Novel Pathogenic Variant (c.1171A>T) in PHF21A in a Female with Intellectual Disability and Craniofacial Anomalies. Molecular syndromology 4 36158052
2024 Naturally occurring splice variants dissect the functional domains of BHC80 and emphasize the need for RNA analysis. American journal of medical genetics. Part A 3 38264805
2024 CircRNA-Phf21a_0002 promotes pyroptosis to aggravate hepatic ischemia/ reperfusion injury by sponging let-7b-5p. Heliyon 2 39262995
2023 A neuron-specific microexon ablates the novel DNA-binding function of a histone H3K4me0 reader PHF21A. bioRxiv : the preprint server for biology 2 37904995
2025 A zebrafish model unravels the role of PHF21A in neurodevelopment and epilepsy. Neuroscience 1 40784402
2024 Asynchronous microexon splicing of LSD1 and PHF21A during neurodevelopment. bioRxiv : the preprint server for biology 1 38562691
2023 A novel de novo variant in the PHF21A causes craniofacial abnormalities, intellectual disability and skeletal manifestations. Clinical genetics 1 36843358
2025 Molecular Consequences of a Missense PHF21A Variant, c.1285G > A, Associated With Syndromic Neurodevelopmental Disorder. Cellular and molecular neurobiology 0 40622422
2023 [A case of intellectual developmental disorder with behavioral abnormalities and craniofacial dysmorphism with or without seizures caused by PHF21A gene variation and review of literature]. Zhonghua er ke za zhi = Chinese journal of pediatrics 0 37528014
2013 [Impaired effect of BHC80 gene knock-down on the cardiac development in zebrafish]. Sheng li xue bao : [Acta physiologica Sinica] 0 24129737

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