BRPF3

BRPF3 is a chromatin scaffold protein that assembles a dedicated tetrameric complex with the HBO1/KAT7 (MYST2) histone acetyltransferase, distinguishing it from other MYST-family enzymes, and directs this complex to acetylate histone H3K14 (PMID:26677226, PMID:26620551). Genome-wide, the BRPF3-HBO1 complex is enriched at ORC1-binding replication origins near transcription start sites, where it deposits H3K14ac, and BRPF3 is required for efficient origin activation by promoting CDC45 recruitment downstream of MCM2-7 loading (PMID:26620551). Beyond its catalytic targeting role, BRPF3 stabilizes its partner enzyme by binding MYST2 and antagonizing HUWE1-mediated ubiquitination and proteasomal degradation, so that BRPF3 levels set MYST2 abundance and thereby influence cell-cycle progression and stem-cell differentiation (PMID:32555450). The BRPF3 bromodomain functions as an acetyl-lysine reader, recognizing H4K5ac and H4K5acK12ac marks (PMID:34448544). This reader-scaffold activity is functionally separable from H3K14 acetylation: BRPF3 supports PARP-inhibitor resistance in ovarian carcinoma cells through its bromodomain function rather than through HBO1-dependent H3K14ac (PMID:37493106), and in cardiac fibroblasts stabilized BRPF3 recruits KAT7 to the Celf1 promoter to drive H3K14ac and transcriptional activation, promoting fibrosis (PMID:41132846).

1. 2015 High

   Establishing which acetyltransferase BRPF3 partners with answered whether it has a dedicated enzymatic complex; it forms a specific tetramer with HBO1/KAT7 that acetylates H3K14, excluding other MYST enzymes.

   Evidence reciprocal Co-IP of endogenous proteins and biochemical complex characterization, replicated across two studies

   PMID:26620551 PMID:26677226

   Open questions at the time

   • Identity and contribution of the other two tetramer subunits not resolved
   • Structural basis of complex assembly not defined
2. 2015 High

   Mapping where the complex acts and what it does there showed BRPF3-HBO1 is enriched at replication origins near TSSs and is required for origin activation via CDC45 recruitment, placing it precisely in the replication pathway.

   Evidence RNAi knockdown with genome-wide ChIP-seq for BRPF3/HBO1/H3K14ac and CDC45 vs MCM2-7 chromatin recruitment assays

   PMID:26620551

   Open questions at the time

   • Mechanism linking H3K14ac to CDC45 loading not defined
   • Relative contribution of origin vs promoter functions unresolved
3. 2015 Medium

   Knockout analysis tested whether BRPF3 is developmentally essential; unlike paralogs Brpf1/Brpf2, Brpf3 loss produces no gross phenotype despite dynamic embryonic expression, functionally distinguishing the paralogs.

   Evidence LacZ reporter knock-in and knockout mouse phenotypic analysis

   PMID:26677226

   Open questions at the time

   • Possible redundancy with paralogs not directly tested
   • Subtle or stress-conditional phenotypes not assessed
4. 2020 Medium

   Identifying how BRPF3 controls its partner's abundance showed it binds MYST2 and antagonizes HUWE1-mediated ubiquitination, revealing a stabilizing rather than purely catalytic-targeting role.

   Evidence Co-IP, overexpression/knockdown of BRPF3 and HUWE1, and ubiquitination assays in mouse ESCs

   PMID:32555450

   Open questions at the time

   • Single lab without reciprocal validation in other cell types
   • Whether stabilization requires complex assembly or is direct competition with HUWE1 unclear
5. 2020 Medium

   Testing the consequence of excess BRPF3 demonstrated that overexpression elevates MYST2, dysregulating cell cycle and delaying lineage commitment, with HUWE1 rescue confirming the stabilization axis is causal.

   Evidence BRPF3/HUWE1 overexpression, embryoid body formation and cell-cycle assays in mouse ESCs

   PMID:32555450

   Open questions at the time

   • Phenotype from overexpression rather than physiological levels
   • Downstream targets driving differentiation delay not identified
6. 2021 Medium

   Defining the histone-mark specificity of the BRPF3 bromodomain established it as an acetyl-lysine reader recognizing H4K5ac and H4K5acK12ac, providing a chromatin-recruitment mechanism distinct from its H3K14ac deposition.

   Evidence histone peptide binding and pull-down assays from purified human histones with MD simulation

   PMID:34448544

   Open questions at the time

   • In vitro binding not validated by genome-wide reader occupancy in cells
   • Affinity and selectivity relative to other bromodomain readers not benchmarked
7. 2023 Medium

   Separating reader from catalytic function in cancer showed BRPF3 loss reduces PARPi resistance whereas HBO1 inhibition does not, implicating the bromodomain reader function independently of H3K14ac.

   Evidence siRNA and pharmacologic inhibition of BRPF3 vs HBO1 in isogenic PARPi-sensitive/resistant HGSOC lines with histone MS

   PMID:37493106

   Open questions at the time

   • Molecular pathway connecting BRPF3 reader function to PARPi resistance not defined
   • Single tumor type and cell-line model
8. 2025 Medium

   Linking BRPF3 to a disease pathway showed circ-CELF1 stabilizes BRPF3, which scaffolds KAT7 to the Celf1 promoter to drive H3K14ac and transcription, demonstrating gene-specific scaffolding in cardiac fibrosis.

   Evidence circRNA knockdown/overexpression, ubiquitination assays, ChIP for H3K14ac and protein interaction assays in cardiac fibroblasts

   PMID:41132846

   Open questions at the time

   • Single lab and model system
   • Generalizability of promoter-specific scaffolding beyond Celf1 not established

• How BRPF3's reader (bromodomain/PWWP/PHD) and catalytic-targeting activities are integrated to select between replication origins, specific promoters, and partner stabilization in different cell contexts remains unresolved.
• No structural model of the full BRPF3-HBO1 tetramer
• Determinants of locus selectivity unknown
• Endogenous loss-of-function phenotype in mammals remains mild and largely uncharacterized mechanistically