MRGBP

MRGBP (C20orf20) is a subunit of the TRRAP/TIP60-containing NuA4 histone acetyltransferase complex that couples chromatin acetylation to transcriptional control and genome stability (PMID:20051959, PMID:33354938). Within this complex it interacts with BRD8 and bridges MRG15 to TIP60: recruited to active gene regions through MRG15 recognition of H3K4me1/3, MRGBP promotes TIP60 recruitment and acetylation of the histone variant H2A.Z at androgen receptor binding regions, thereby increasing AR occupancy and transactivation of target genes such as KLK3 and TMPRSS2 (PMID:30076933). In the context of DNA double-strand break repair, MRGBP acts as a general inhibitor that limits DNA-end resection, opposing the catalytic subunits of NuA4; its loss enhances early homologous recombination (PMID:33354938). Functionally, MRGBP supports cancer cell survival, as its depletion induces apoptosis and reduces xenograft tumor growth (PMID:21602893).

1. 2010 Medium

   Established MRGBP as a physical component of the TRRAP/TIP60 acetyltransferase machinery and identified its direct binding partner BRD8, placing it within a defined chromatin-modifying complex.

   Evidence Yeast two-hybrid screening and reciprocal co-immunoprecipitation

   PMID:20051959

   Open questions at the time

   • No reconstitution or structural validation of the interaction
   • Stoichiometry and architecture within the complex undefined
2. 2011 Low

   Demonstrated that MRGBP is functionally required for cancer cell survival, showing a phenotypic consequence of its loss before any molecular mechanism was known.

   Evidence siRNA knockdown with apoptosis assay and xenograft tumor model in cutaneous squamous cell carcinoma

   PMID:21602893

   Open questions at the time

   • No molecular mechanism linking knockdown to apoptosis identified
   • Single lab, single tumor type
3. 2018 Medium

   Resolved how MRGBP is targeted to chromatin and what it does there, defining a recruitment-to-acetylation axis that drives AR-dependent transcription.

   Evidence Co-immunoprecipitation, ChIP, and siRNA knockdown with gene expression readout in prostate cancer cells

   PMID:30076933

   Open questions at the time

   • Direct demonstration that MRGBP enzymatically enables H2A.Z acetylation versus stabilizing complex recruitment
   • Single lab, single cancer model
4. 2021 Medium

   Revealed an unexpected role for MRGBP in genome maintenance, showing it restrains DNA-end resection and thereby acts opposite to the catalytic NuA4 subunits in DSB repair.

   Evidence siRNA knockdown with DNA damage repair and homologous recombination assays

   PMID:33354938

   Open questions at the time

   • Molecular basis by which MRGBP limits resection unknown
   • Single lab, single study
5. 2022 Low

   Extended MRGBP's pro-tumorigenic function to Wnt/β-catenin and NF-κB signaling, linking it to EMT and metastasis.

   Evidence siRNA knockdown, overexpression, pathway inhibitor rescue, and in vitro/in vivo assays in colorectal cancer

   PMID:36208716

   Open questions at the time

   • Pathway placement inferred from inhibitor rescue without direct biochemical demonstration of the molecular link to DKK1 or p65
   • Single lab, single study

• How MRGBP's two opposing activities — promoting transcriptional acetylation versus inhibiting DSB-repair resection — are mechanistically partitioned within the same NuA4/TIP60 complex remains unresolved.
• No structural model of MRGBP within NuA4
• No biochemical reconstitution of its specific contribution to H2A.Z acetylation or resection control