BRAT1

BRAT1 is a scaffold protein that integrates DNA damage signaling, RNA processing, and neuronal differentiation programs. It binds BRCA1, ATM, DNA-PKcs, and SMC1 at DNA double-strand breaks and maintains PIKK kinase activation by inhibiting PP2A-mediated dephosphorylation; its nuclear translocation under genotoxic stress requires Ndfip1/Nedd4-dependent ubiquitination (PMID:16452482, PMID:25631046). BRAT1 forms a trimeric complex with Integrator subunits INTS9 and INTS11, recruiting INTS11 to promoters of REST-target neuronal genes to activate neuronal differentiation; disease-causing mutations that disrupt this interaction block neural differentiation, establishing BRAT1 loss-of-function as a cause of neurodevelopmental disease (PMID:36028512, PMID:38805275). BRAT1 also influences mitochondrial metabolism and Akt/mTOR signaling, as its depletion increases mitochondrial ROS, suppresses PDH activity, and reduces Akt/Erk phosphorylation (PMID:25070371, PMID:25657994).

1. 2006 High

   Identification of BRAT1 as a BRCA1- and ATM-binding protein that localizes to DSBs and is required for ATM activation established its entry point into the DNA damage response, resolving how ATM phosphorylation is sustained after irradiation — via BRAT1-mediated inhibition of PP2A dephosphorylation.

   Evidence Yeast two-hybrid screen, siRNA knockdown, in vitro phosphatase assay with purified BRAT1, okadaic acid rescue

   PMID:16452482

   Open questions at the time

   • Mechanism of PP2A inhibition at the structural level unknown
   • Whether BRAT1 acts catalytically or stoichiometrically on PP2A not determined
   • Contribution of BRAT1 to DSB repair outcomes not assessed
2. 2010 Medium

   Extending BRAT1's role beyond ATM, its binding to DNA-PKcs and SMC1 and requirement for their damage-induced phosphorylation established BRAT1 as a general scaffold for multiple PIKK kinases in early DNA damage signaling.

   Evidence Co-immunoprecipitation and siRNA knockdown with phosphorylation readouts for DNA-PKcs Ser2056 and SMC1 Ser966 after neocarzinostatin treatment; domain mapping

   PMID:21779444 PMID:22977523

   Open questions at the time

   • Direct vs. bridged interactions with DNA-PKcs not fully resolved
   • How BRAT1 coordinates ATM and DNA-PKcs activities at the same break is unknown
   • No in vivo validation of DNA-PKcs/SMC1 regulation by BRAT1
3. 2013 High

   Atomic-resolution structures of BRCA1 BRCT domains bound to the BRAT1 phosphopeptide defined the molecular basis of the BRCA1–BRAT1 interaction, showing pSer269 and Phe(+3) as key anchoring residues.

   Evidence X-ray crystallography at 2.2 Å resolution, isothermal titration calorimetry

   PMID:24073851

   Open questions at the time

   • Functional consequence of disrupting BRCA1–BRAT1 interaction in cells not tested in this study
   • Whether phosphorylation of Ser269 is damage-regulated is not established
   • No full-length structural information for BRAT1
4. 2014 Medium

   Demonstrating functions beyond DNA repair, BRAT1 depletion was shown to increase mitochondrial ROS, suppress PDH activity and Akt/Erk signaling, and impair mTOR stability, with Akt activator rescue placing BRAT1 upstream of Akt in growth signaling.

   Evidence Stable siRNA knockdown, glucose uptake, MitoSOX, PDH activity assay, Akt activator (SC79) rescue; conditional KO MEFs for mTOR analysis

   PMID:25070371 PMID:25657994

   Open questions at the time

   • Direct molecular mechanism linking BRAT1 to mTOR/Akt is unknown
   • Whether metabolic phenotypes are separable from DNA damage signaling defects not addressed
   • No identification of direct metabolic binding partners
5. 2015 High

   The discovery that Ndfip1-dependent Nedd4 ubiquitination of BRAT1 is required for its nuclear translocation under genotoxic stress resolved how BRAT1 gains access to nuclear DNA damage sites and connected the ubiquitin pathway to ATM signaling maintenance.

   Evidence Ndfip1 knockdown/overexpression, subcellular fractionation, immunofluorescence, in vivo brain injury model in neurons

   PMID:25631046

   Open questions at the time

   • Specific ubiquitination sites on BRAT1 not mapped
   • Whether ubiquitin chain type (K48/K63) matters for nuclear import not determined
   • Nuclear import receptor or mechanism downstream of ubiquitination unknown
6. 2022 High

   Identification of BRAT1 as a tight interactor of INTS9/INTS11 revealed a second major function: BRAT1 is required for Integrator-dependent 3′ end processing of UsnRNAs and snoRNAs and for proper expression of protein-coding genes, with defects recapitulated in patient-derived cells.

   Evidence Co-immunoprecipitation, RNA-seq, snRNA/snoRNA processing assays, ChIP, BRAT1 KO cells and patient-derived cell lines

   PMID:36028512

   Open questions at the time

   • Whether BRAT1 functions within the full Integrator complex or a distinct sub-complex is unclear
   • Structural basis of the BRAT1–INTS9/INTS11 interaction not resolved
   • Whether RNA processing defects drive the neurological phenotype or are parallel consequences is not established
7. 2024 High

   BRAT1 was shown to recruit INTS11 to REST-target neuronal gene promoters during differentiation, and disease-causing mutations (e.g. E522K) that disrupt the BRAT1–INTS11/INTS9 complex block neuronal differentiation, directly linking BRAT1 loss-of-function to neurodevelopmental disease.

   Evidence ChIP-seq, RNA-seq, BRAT1 KO mouse ESC differentiation assay with WT vs. disease-mutant rescue, NT2 differentiation assay

   PMID:38805275

   Open questions at the time

   • How BRAT1 displaces REST from promoters mechanistically is unknown
   • Whether the DNA damage and Integrator functions of BRAT1 are interdependent in neurons is not tested
   • No animal model of BRAT1 neurological disease with behavioral phenotyping
8. 2025 Medium

   Proteomic and functional analyses in glioblastoma demonstrated that BRAT1 depletion delays DSB repair and sensitizes to radiation, while pharmacological BRAT1 inhibition suppresses glioma stem cell migration and invasion, establishing BRAT1 as a therapeutic target in brain tumors.

   Evidence Stable shRNA depletion, proteomics/phosphoproteomics, γH2AX foci, ex vivo brain slice invasion assay, Curcusone D inhibitor

   PMID:39833546

   Open questions at the time

   • Curcusone D selectivity for BRAT1 versus off-target effects not fully characterized
   • Whether anti-invasion effects are mediated through Integrator or DDR functions is unknown
   • No clinical validation

• Key open questions include: (1) how the DNA damage scaffold and Integrator/neuronal differentiation functions of BRAT1 are coordinated or separated; (2) the structural basis of the BRAT1–INTS9/INTS11 trimeric complex; (3) the direct molecular mechanism connecting BRAT1 to Akt/mTOR and mitochondrial metabolism; and (4) whether BRAT1 has distinct functions in different cell types.
• No full-length structure of BRAT1 or its complexes
• Separation-of-function mutations distinguishing DDR from Integrator roles not generated
• In vivo animal models of BRAT1 disease with mechanistic characterization are lacking