Affinage

HP1BP3

Heterochromatin protein 1-binding protein 3 · UniProt Q5SSJ5

Length
553 aa
Mass
61.2 kDa
Annotated
2026-06-10
13 papers in source corpus 12 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

HP1BP3 is a linker histone H1-like chromatin protein that organizes higher-order chromatin and couples chromatin state to gene regulation, cell proliferation, and organismal physiology (PMID:20042602, PMID:25662603, PMID:40140990). It binds the nucleosome core particle in a 1:1 stoichiometry to form a chromatosome, contacting linker DNA at the nucleosomal entry/exit site through a central globular domain whose fold resembles that of canonical linker histones, while its N- and C-terminal regions and an embedded HP1-binding motif support chromatin engagement and direct binding to HP1 (PMID:20042602, PMID:25662603). Unlike canonical H1, its nucleosome occupancy is governed by the histone chaperones NPM1 and TAF-I and by cell-cycle-dependent post-translational modifications, and it preferentially loads at genomic loci bearing active H3 marks rather than inactive chromatin (PMID:25662603, PMID:40140990). Through this chromatin activity HP1BP3 maintains heterochromatin integrity during G1-S progression and sets G1 duration to control proliferative capacity (PMID:24830416). A distinct function couples chromatin to RNA processing: HP1BP3 associates with the Drosha-DGCR8 microprocessor at actively transcribed miRNA loci and retains nascent pri-miRNAs on chromatin to promote co-transcriptional miRNA biogenesis (PMID:27425409). It additionally cooperates with PGC7 at the Meg3 imprinted DMR to antagonize DNMT3A and preserve DNA methylation and chromatin condensation (PMID:39422314). In vivo, Hp1bp3-null mice show ~60% neonatal lethality, lifelong growth retardation driven non-cell-autonomously through the endocrine IGF-1 axis, and deficits in maternal behavior, anxiety, and cognitive aging (PMID:25662603, PMID:26402843, PMID:27470444, PMID:27460150).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2009 High

    Established the structural basis for HP1BP3 as a chromatin protein by showing its middle region forms a chromatosome-like structure on nucleosomes and that it directly binds HP1, defining it as a linker-histone-like, heterochromatin-associated factor.

    Evidence NMR structure of the globular domain, MNase protection on reconstituted mononucleosomes, in vitro direct binding assays

    PMID:20042602

    Open questions at the time
    • Did not establish full-length nucleosome binding stoichiometry
    • Functional consequence of HP1 binding in cells not addressed
  2. 2014 Medium

    Connected HP1BP3 chromatin dynamics to the cell cycle, showing it maintains heterochromatin integrity through G1-S and regulates G1 length and proliferation.

    Evidence Partial MNase digestion with iTRAQ chromatin proteomics and siRNA knockdown with cell-cycle analysis

    PMID:24830416

    Open questions at the time
    • Molecular targets controlling G1 duration not identified
    • Link to a specific transcriptional program unresolved
  3. 2014 Medium

    Extended chromatin function to stress physiology, showing HP1BP3-mediated chromatin condensation under hypoxia promotes tumor cell survival, therapy resistance, and self-renewal.

    Evidence DNase I partial digestion with iTRAQ chromatome profiling and loss/gain-of-function functional assays

    PMID:25100860

    Open questions at the time
    • Mechanism linking condensation to resistance phenotypes unclear
    • Upstream hypoxic signal to HP1BP3 unknown
  4. 2015 Medium

    Defined HP1BP3 domain architecture and demonstrated organismal requirement, mapping cell-cycle/PTM-regulated chromatin binding and revealing neonatal lethality and growth retardation in knockout mice.

    Evidence FRAP, microarray transcriptional profiling, domain/sequence analysis, and Hp1bp3-/- mouse phenotyping

    PMID:25662603

    Open questions at the time
    • Specific PTMs regulating binding not identified
    • Direct transcriptional targets among the 383 altered genes not mechanistically resolved
  5. 2015 Medium

    Identified the basis of the growth phenotype as non-cell-autonomous, implicating HP1BP3 in transcriptional control of the endocrine IGF-1 axis.

    Evidence Hp1bp3-/- mouse microCT, primary osteoblast/osteoclast differentiation, serum IGF-1/IGFBP ELISA, hepatic transcript quantification

    PMID:26402843

    Open questions at the time
    • Direct chromatin binding at Igf1/Igfbp loci not demonstrated
    • Tissue source of the primary defect not pinpointed
  6. 2016 High

    Revealed a chromatin-to-RNA-processing function: HP1BP3 retains nascent pri-miRNAs on chromatin and delivers them to the Drosha-DGCR8 microprocessor for co-transcriptional processing.

    Evidence Reciprocal Co-IP, ChIP-seq co-localization with Drosha, RIP for pri-miRNAs, and knockdown miRNA profiling

    PMID:27425409

    Open questions at the time
    • How HP1BP3 physically retains transcripts on chromatin not defined
    • Selectivity for particular miRNA loci unexplained
  7. 2016 Medium

    Demonstrated specific in vivo behavioral roles, with knockout females failing pup retrieval and showing altered anxiety without broader behavioral deficits.

    Evidence Hp1bp3-/- pup retrieval, open-field, elevated-plus-maze assays, and co-fostering rescue

    PMID:27470444

    Open questions at the time
    • Neural circuits and gene targets underlying behavior unknown
    • Relation to chromatin/miRNA functions not established
  8. 2016 Medium

    Linked HP1BP3 to cognitive aging, with knockout recapitulating age-associated memory deficits.

    Evidence Hp1bp3-/- cognitive behavioral testing and systems genetics in a genetically diverse mouse population

    PMID:27460150

    Open questions at the time
    • Molecular pathway connecting HP1BP3 to memory not identified
    • Whether effect is chromatin- or miRNA-dependent unresolved
  9. 2021 Medium

    Provided a downstream effector axis in cancer, with HP1BP3 upregulating miR-23a, which represses TRAF5 to drive esophageal tumor growth and metastasis.

    Evidence Knockdown/overexpression in cell lines and xenografts, miR-23a profiling, and TRAF5 3'UTR luciferase reporter

    PMID:34249436

    Open questions at the time
    • How HP1BP3 selectively induces miR-23a not shown
    • Generality beyond esophageal carcinoma untested
  10. 2022 Medium

    Identified an EZH2-HP1BP3 interaction that impairs H3K9 methylation and co-activates WNT7B to drive glioblastoma stemness and drug resistance.

    Evidence Co-IP/mass spectrometry, transcriptomics, gain/loss-of-function assays, and WNT inhibitor (LGK974) rescue

    PMID:36517590

    Open questions at the time
    • Direct vs indirect effect on H3K9 methylation not resolved
    • Whether HP1BP3 binds WNT7B chromatin directly unknown
  11. 2024 Medium

    Defined a cooperative HP1BP3-PGC7 mechanism at an imprinted DMR, antagonizing DNMT3A to maintain DNA methylation and chromatin condensation.

    Evidence Co-IP with domain mapping, ChIP, DNMT3A enrichment assays, and bisulfite sequencing under knockdown

    PMID:39422314

    Open questions at the time
    • Whether this extends to other imprinted loci unknown
    • Mechanism of DNMT3A exclusion not biochemically resolved
  12. 2025 High

    Established HP1BP3 as a bona fide linker histone variant with chaperone-regulated, activity-biased nucleosome binding, distinguishing it from canonical H1.

    Evidence In vitro chromatosome reconstitution with 1:1 NCP binding, NPM1/TAF-I interaction mapping, and ChIP-seq under chaperone knockdown

    PMID:40140990

    Open questions at the time
    • How chaperone regulation integrates with cell-cycle PTMs unresolved
    • Mechanism directing preference for active chromatin not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unknown how HP1BP3's linker-histone chromatin activity mechanistically unifies its diverse downstream roles in miRNA biogenesis, imprinting, IGF-1 signaling, and behavior.
  • No single model connects chromatin occupancy to specific transcriptional/miRNA outputs
  • PTMs and chaperone control not linked to in vivo phenotypes
  • Direct genomic targets driving organismal phenotypes unidentified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3 GO:0003677 DNA binding 2 GO:0042393 histone binding 2 GO:0140110 transcription regulator activity 2 GO:0003723 RNA binding 1
Localization
GO:0005694 chromosome 4 GO:0005634 nucleus 2
Pathway
R-HSA-4839726 Chromatin organization 3 R-HSA-1640170 Cell Cycle 1 R-HSA-8953854 Metabolism of RNA 1
Partners
DGCR8DROSHAEZH2HP1NPM1PGC7TAF-I
Complex memberships
Drosha-DGCR8 microprocessorchromatosome

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2009 HP1BP3 (HP1-BP74) middle region (residues Lys97–Lys274) associates with linker DNA at the entry/exit site of nucleosomal DNA, forming a chromatosome-like structure that protects ~25 bp of linker DNA from MNase digestion. The globular domain (Met153–Thr237) within this region adopts a structure similar to the globular domain of linker histones as determined by NMR. Full-length HP1BP3 directly binds HP1 (heterochromatin protein 1), with exact HP1-binding sites identified. NMR structure determination, MNase protection assay with reconstituted mononucleosomes, in vitro direct binding assays The Journal of biological chemistry High 20042602
2014 HP1BP3 dynamically associates with chromatin during interphase progression; it maintains heterochromatin integrity during G1-S progression and regulates the duration of G1 phase to influence cell proliferative capacity. Partial MNase digestion coupled with iTRAQ quantitative proteomics, biochemical fractionation, functional cell-cycle assays (siRNA knockdown with cell-cycle analysis) Molecular & cellular proteomics : MCP Medium 24830416
2014 HP1BP3 mediates chromatin condensation during hypoxia, leading to increased tumor cell viability, radio-resistance, chemo-resistance, and self-renewal. Its chromatin association topology changes under hypoxic versus normoxic conditions. DNase I partial digestion with iTRAQ quantitative proteomics, functional assays (cell viability, clonogenic survival, sphere formation under knockdown/overexpression) Molecular & cellular proteomics : MCP Medium 25100860
2015 HP1BP3 is structurally related to the linker histone H1 family, containing three globular domains and a positively charged C-terminal domain. FRAP studies demonstrate that chromatin binding depends on both its C- and N-terminal regions and is regulated by cell cycle stage and post-translational modifications. HP1BP3 contains functional motifs absent from canonical H1, including an acidic stretch and a consensus HP1-binding motif. Knockdown in HeLa cells alters expression of 383 genes. Hp1bp3−/− mice exhibit 60% neonatal lethality and lifelong ~20% growth retardation. FRAP (live-cell imaging), transcriptional profiling (microarray), mouse knockout phenotyping, domain analysis/sequence comparison Nucleic acids research Medium 25662603
2015 Hp1bp3−/− mice are proportionate dwarfs with severely impaired cortical and trabecular bone development. Primary osteoblast and osteoclast cultures from Hp1bp3−/− mice showed normal differentiation, indicating the growth defect is non-cell-autonomous. These mice exhibit ~60% reduction in circulating IGF-1 and ~4-fold increase in IGFBP-1 and IGFBP-2, with corresponding changes in hepatic transcripts of Igf1, Igfbp1, and Igfbp2, implicating HP1BP3 in transcriptional regulation of the endocrine IGF-1 axis. Hp1bp3−/− mouse knockout, microCT bone analysis, primary cell culture differentiation assays, ELISA for serum IGF-1/IGFBPs, hepatic transcript quantification Endocrinology Medium 26402843
2016 HP1BP3 specifically associates with the Drosha-DGCR8 microprocessor complex, co-localizes genome-wide with Drosha at actively transcribed miRNA loci (by ChIP), binds endogenous pri-miRNAs, and facilitates the Drosha/pri-miRNA association in vivo. Knockdown of HP1BP3 causes premature release of nascent pri-miRNAs from chromatin, impairing global miRNA biogenesis. HP1BP3 thus functions as a chromatin retention factor for co-transcriptional miRNA processing. Co-immunoprecipitation (Co-IP), chromatin immunoprecipitation (ChIP-seq), RNA immunoprecipitation (RIP), siRNA knockdown with miRNA profiling Molecular cell High 27425409
2016 Deletion of Hp1bp3 in female mice causes failure to retrieve pups and reduced anxiety-like behavior without deficits in social behavior, depression, motor coordination, or olfactory capability, identifying a specific role for HP1BP3 in maternal and anxiety-related behavior. Hp1bp3−/− mouse knockout, pup retrieval behavioral assay, open-field and elevated-plus-maze tests, co-fostering rescue experiment Genes, brain, and behavior Medium 27470444
2016 Deletion of functional Hp1bp3 in mice recapitulates memory deficits characteristic of aged impaired mice and humans, establishing HP1BP3 as a modulator of cognitive aging. Hp1bp3−/− mouse knockout, cognitive behavioral testing (memory assays), systems genetics using genetically diverse mouse population Neurobiology of aging Medium 27460150
2021 HP1BP3 promotes tumor growth and metastasis in esophageal squamous cell carcinoma by upregulating miR-23a, which directly binds to the 3′UTR of TRAF5, thereby altering cell survival and proliferation downstream. HP1BP3 knockdown/overexpression in cancer cell lines and xenograft models, miR-23a profiling, 3′UTR luciferase reporter assay for TRAF5 American journal of cancer research Medium 34249436
2022 EZH2 physically interacts with HP1BP3 in glioma stem cells, and this interaction impairs H3K9 methylation. EZH2 and HP1BP3 co-activate WNT7B expression, promoting temozolomide resistance and stemness in glioblastoma cells. Co-immunoprecipitation (Co-IP) followed by mass spectrometry, transcriptomic analysis, overexpression/knockdown functional assays, WNT pathway inhibitor (LGK974) rescue Oncogene Medium 36517590
2024 HP1BP3 interacts with PGC7 through its central globular domain (PGC7 binds via its C-terminal tail). HP1BP3 recruits PGC7 to the Meg3 differentially methylated region (DMR) in the Dlk1-Dio3 imprinted domain. Cooperative binding of PGC7 and HP1BP3 antagonizes DNMT3A enrichment at the Meg3-DMR, maintaining DNA methylation status. Depletion of either HP1BP3 or PGC7 leads to chromosome decondensation at this region. Co-immunoprecipitation, domain-mapping interaction assays, ChIP, DNMT3A enrichment assays, bisulfite sequencing for DNA methylation, knockdown phenotyping Journal of cellular biochemistry Medium 39422314
2025 HP1BP3 functions as a linker histone variant: it efficiently binds to nucleosome core particles (NCPs) forming a chromatosome, with a single HP1BP3 molecule binding a single NCP. Its NCP binding activity is regulated by linker histone chaperones NPM1 and TAF-I, which interact with the globular domains and C-terminal disordered region of HP1BP3. ChIP-seq shows HP1BP3 preferentially associates with genomic loci enriched for active histone H3 modification marks, in contrast to linker histone H1.2 which prefers inactive loci; these preferences are diminished upon NPM1 or TAF-I knockdown. Biochemical NCP-binding assays, chromatosome reconstitution, co-immunoprecipitation for chaperone interactions, ChIP-seq, siRNA knockdown Epigenetics & chromatin High 40140990

Source papers

Stage 0 corpus · 13 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2014 Profiling of the Chromatin-associated Proteome Identifies HP1BP3 as a Novel Regulator of Cell Cycle Progression. Molecular & cellular proteomics : MCP 43 24830416
2014 Quantitative profiling of chromatome dynamics reveals a novel role for HP1BP3 in hypoxia-induced oncogenesis. Molecular & cellular proteomics : MCP 38 25100860
2016 Systems genetics identifies Hp1bp3 as a novel modulator of cognitive aging. Neurobiology of aging 32 27460150
2016 HP1BP3, a Chromatin Retention Factor for Co-transcriptional MicroRNA Processing. Molecular cell 29 27425409
2015 HP1BP3 is a novel histone H1 related protein with essential roles in viability and growth. Nucleic acids research 27 25662603
2022 EZH2 interacts with HP1BP3 to epigenetically activate WNT7B that promotes temozolomide resistance in glioblastoma. Oncogene 22 36517590
2009 The middle region of an HP1-binding protein, HP1-BP74, associates with linker DNA at the entry/exit site of nucleosomal DNA. The Journal of biological chemistry 22 20042602
2015 Proportionate Dwarfism in Mice Lacking Heterochromatin Protein 1 Binding Protein 3 (HP1BP3) Is Associated With Alterations in the Endocrine IGF-1 Pathway. Endocrinology 14 26402843
2016 HP1BP3 expression determines maternal behavior and offspring survival. Genes, brain, and behavior 11 27470444
2021 HP1BP3 promotes tumor growth and metastasis by upregulating miR-23a to target TRAF5 in esophageal squamous cell carcinoma. American journal of cancer research 10 34249436
2017 The novel transcriptional factor HP1BP3 negatively regulates Hsp70 transcription in Crassostrea hongkongensis. Scientific reports 5 28469151
2025 Function of HP1BP3 as a linker histone is regulated by linker histone chaperones, NPM1 and TAF-I. Epigenetics & chromatin 1 40140990
2024 Interaction of PGC7 and HP1BP3 Maintains Meg3-DMR Methylation by Regulating Chromatin Configuration. Journal of cellular biochemistry 1 39422314

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