Affinage

BTBD2

BTB/POZ domain-containing protein 2 · UniProt Q9BX70

Length
525 aa
Mass
55.9 kDa
Annotated
2026-06-09
11 papers in source corpus 6 papers cited in narrative 7 extracted findings
Cross-family judge faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

BTBD2 is a BTB-domain adaptor protein that couples Topoisomerase I (TOP1) to the cellular ubiquitin–proteasome machinery, governing both the turnover of damaged TOP1 and TOP1-dependent chromatin remodeling (PMID:11818025, PMID:36490343). It binds the core domain of human TOP1 directly (an interaction mapped to TOP1 residues 215–329 and requiring residues 236–237) without itself altering TOP1's supercoil-relaxation or cleavage activity in vitro (PMID:11818025, PMID:21092135). Functioning as a substrate-recognition adaptor for the CUL3–RBX1 E3 ubiquitin ligase, BTBD2 (with BTBD1) targets trapped TOP1 cleavage complexes for ubiquitination and proteasomal degradation; NEDDylation of CUL3 activates this pathway, and disabling CUL3 or NEDDylation sensitizes cancer cells to TOP1 inhibitors (PMID:36490343). The same TOP1-bridging activity is deployed during mitosis, where BTBD2 links HNF1β to TOP1 to drive DNA relaxation at bookmarked chromatin sites and enable post-mitotic gene reactivation (PMID:39388351). BTBD2 additionally assembles into cytoplasmic bodies scaffolded by TRIM5δ and modestly restricts HIV-1 infection (PMID:12878161, PMID:21092135).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2002 High

    Established that BTBD2 is a direct TOP1-binding protein, raising the question of whether it modulates topoisomerase activity or serves another function.

    Evidence Yeast two-hybrid, co-precipitation and GST-pulldown from HeLa cells, with deletion mapping and in vitro topoisomerase assays

    PMID:11818025

    Open questions at the time
    • Did not explain the functional consequence of the interaction, since TOP1 enzymatic activity was unaffected in vitro
    • No E3 ligase or ubiquitination role yet identified
  2. 2003 Medium

    Defined the subcellular context of BTBD2, showing it concentrates in TRIM5δ-scaffolded cytoplasmic bodies and can co-localize with TOP1, indicating a regulated compartmentalization.

    Evidence Immunofluorescence, GFP-fusion colocalization, TRIM5δ domain/point mutants, and compartment-redirecting truncation constructs in mouse and human cells

    PMID:11818025 PMID:12878161

    Open questions at the time
    • Functional role of cytoplasmic body assembly not established
    • Whether TOP1 co-localization reflects a physiological pool versus overexpression artifact unclear
  3. 2010 Medium

    Connected BTBD2 to a biological readout by pinpointing the TOP1 residues (236–237) required for binding and showing BTBD2 modestly restricts HIV-1 infection.

    Evidence Site-directed mutagenesis of TOP1, co-immunoprecipitation, and RNAi knockdown with HIV-1 infectivity assays in AGM and 293T cells

    PMID:21092135

    Open questions at the time
    • Mechanism linking the TOP1 interaction to viral restriction not defined
    • Effect size was modest (two- to three-fold)
  4. 2016 Medium

    Provided the first functional assignment of BTBD2 as a CUL3-pathway substrate adaptor, via its C. elegans ortholog acting in non-apoptotic developmental cell death.

    Evidence Genetic epistasis in C. elegans placing BTBD-2 with CUL-3, RBX-1 and SIAH-1 downstream of HSF-1 in the linker-cell death pathway

    PMID:26952214

    Open questions at the time
    • Relevant ubiquitination substrate in the LCD pathway not identified
    • Conservation of the adaptor role to human BTBD2 not directly tested here
  5. 2022 High

    Unified the prior observations into a mechanism: BTBD2 serves as a CUL3 substrate adaptor that ubiquitinates trapped TOP1 cleavage complexes for degradation, with therapeutic implications for TOP1 inhibitors.

    Evidence Ubiquitination and proteasomal degradation assays, siRNA depletion, NEDDylation inhibition, and cell viability assays in cancer cells

    PMID:36490343

    Open questions at the time
    • Relative contributions of BTBD1 versus BTBD2 to substrate recognition not separated
    • Structural basis of TOP1-cc recognition not resolved
  6. 2024 Medium

    Extended the TOP1-bridging function to a non-degradative, mitosis-specific role in chromatin bookmarking.

    Evidence Crosslinking ChIP, protein interaction assays, TOP1 activity assays on mitotic chromatin, and mutational analysis of the HNF1β–TOP1 interaction in mitotic cells

    PMID:39388351

    Open questions at the time
    • How BTBD2 switches between degradative (CUL3) and activating (HNF1β–TOP1) roles is unclear
    • Genome-wide scope of HNF1β bookmarking dependent on BTBD2 not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How BTBD2's distinct activities — CUL3-dependent TOP1-cc degradation, mitotic HNF1β–TOP1 activation, cytoplasmic body assembly, and HIV restriction — are coordinated within a single cell remains unresolved.
  • No structural model of BTBD2 bound to TOP1 or CUL3
  • Regulatory signals that partition BTBD2 between cytoplasmic bodies and nuclear/chromatin functions unknown
  • Whether cytoplasmic body localization relates mechanistically to the degradation or bookmarking roles is untested

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 3 GO:0140096 catalytic activity, acting on a protein 1
Localization
GO:0031410 cytoplasmic vesicle 2 GO:0005634 nucleus 1
Pathway
R-HSA-392499 Metabolism of proteins 1 R-HSA-4839726 Chromatin organization 1 R-HSA-73894 DNA Repair 1
Partners
BTBD1CUL3HNF1ΒRBX1TOP1TRIM5Δ
Complex memberships
CUL3-RBX1 E3 ubiquitin ligase complexTRIM5δ cytoplasmic bodies

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 BTBD2 physically interacts with the core domain of human topoisomerase I (TOP1); the interaction was confirmed by co-precipitation assays from HeLa cells, and the TOP1 sequences sufficient to bind BTBD2 were mapped to residues 215–329. Co-incubation of BTBD2 with TOP1 in vitro affected supercoil relaxation and DNA cleavage activities little or not at all. Two-hybrid screening, co-precipitation (pulldown) from HeLa cells, deletion mapping by two-hybrid and GST-pulldown, in vitro topoisomerase activity assay BMC genomics High 11818025
2003 BTBD2 (and BTBD1) colocalize to punctate or elongated cytoplasmic bodies in mouse and human cells. TRIM5δ (a RING-containing RBCC/TRIM family member) colocalizes with BTBD1/2 and serves as a scaffold for assembly of endogenous BTBD1/2 proteins at these bodies; deletion of TRIM5δ's coiled-coil region or mutation of its RING domain abolished colocalization. Immunofluorescence microscopy, GFP-fusion colocalization, expression of deletion/point mutants of TRIM5δ Experimental cell research Medium 12878161
2003 Epitope-tagged BTBD2 localizes to cytoplasmic bodies; when truncated versions of BTBD2 and TOP1 were co-transfected to direct both proteins to the same compartment (nucleus or cytoplasm), co-localization of BTBD2 and TOP1 was demonstrated in HeLa cells. Subcellular localization by fluorescence microscopy, co-transfection with compartment-targeting truncation constructs BMC genomics Medium 11818025
2010 The interaction of BTBD2 with TOP1 requires human TOP1 residues 236 and 237 (the same residues that enhance HIV-1 virion infectivity). RNAi-mediated knockdown of BTBD2 in AGM and human 293T target cells increased permissiveness to HIV-1 infection two- to three-fold, indicating a modest restriction role. Mutagenesis of TOP1 residues 236–237, co-immunoprecipitation, RNAi knockdown with HIV-1 infectivity assay Virology journal Medium 21092135
2016 In C. elegans, the BTBD-2 protein functions as an E3 substrate-adaptor component (together with CUL-3, RBX-1, and SIAH-1) downstream of HSF-1 in the ubiquitin–proteasome system to promote linker-cell-type (non-apoptotic) developmental cell death; genetic epistasis placed BTBD-2 in the LCD execution pathway. Genetic epistasis (C. elegans mutant analysis), molecular-genetic pathway delineation of LCD eLife Medium 26952214
2022 BTBD2 (together with BTBD1) acts as an adaptor protein for the E3-RING Cullin 3 (CUL3) ligase complex that ubiquitinates TOP1 cleavage complexes (TOP1-ccs), promoting their proteasomal degradation. NEDDylation of CUL3 activates this pathway, and depletion of CUL3 or inhibition of NEDDylation sensitizes cancer cells to TOP1 inhibitors. Genomic occupancy analysis, ubiquitination assays, proteasomal degradation assays, siRNA depletion, NEDDylation inhibition with small molecules, cell viability assays Science advances High 36490343
2024 BTBD2 interacts with HNF1β and enables the interaction and activation of Topoisomerase 1 (TOP1) specifically during mitosis, facilitating DNA relaxation around HNF1β mitotic chromatin sites and contributing to chromatin remodeling and gene reactivation after mitotic exit (bookmarking). Crosslinking-based chromatin immunoprecipitation, protein–protein interaction assay, TOP1 activity assay on mitotic chromatin, mutational analysis of HNF1β–TOP1 interaction domain Cell reports Medium 39388351

Source papers

Stage 0 corpus · 11 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2010 Polymorphisms of LIG4, BTBD2, HMGA2, and RTEL1 genes involved in the double-strand break repair pathway predict glioblastoma survival. Journal of clinical oncology : official journal of the American Society of Clinical Oncology 97 20368557
2003 BTBD1 and BTBD2 colocalize to cytoplasmic bodies with the RBCC/tripartite motif protein, TRIM5delta. Experimental cell research 89 12878161
2002 Characterization of BTBD1 and BTBD2, two similar BTB-domain-containing Kelch-like proteins that interact with Topoisomerase I. BMC genomics 43 11818025
2016 HSF-1 activates the ubiquitin proteasome system to promote non-apoptotic developmental cell death in C. elegans. eLife 31 26952214
2022 NEDDylated Cullin 3 mediates the adaptive response to topoisomerase 1 inhibitors. Science advances 17 36490343
2001 Identification and characterization of BTBD1, a novel BTB domain containing gene on human chromosome 15q24. Gene 15 11179693
2003 Gene and peptide analyses of newly defined lung cancer antigens recognized by HLA-A2402-restricted tumor-specific cytotoxic T lymphocytes. Cancer research 14 12782588
2024 HNF1β bookmarking involves Topoisomerase 1 activation and DNA topology relaxation in mitotic chromatin. Cell reports 5 39388351
2023 Identification of the transcriptome signatures and immune-inflammatory responses in postmenopausal osteoporosis. Heliyon 5 38187229
2010 Human TOP1 residues implicated in species specificity of HIV-1 infection are required for interaction with BTBD2, and RNAi of BTBD2 in old world monkey and human cells increases permissiveness to HIV-1 infection. Virology journal 2 21092135
2006 Identification and isolation of a BTB-POZ-containing gene expressed in oocytes and early embryos of the zebrafish Danio rerio. Genome 2 16936789

Missed literature

Know a paper Affinage missed for BTBD2? Flag it for the maintainers and the community.

No submissions yet.