MRGBP

MRGBP is a subunit of the NuA4/TIP60 histone acetyltransferase complex that functions as a chromatin-dependent transcriptional co-regulator and modulator of DNA damage repair. It is recruited to H3K4me1/me3-marked active chromatin through interaction with MRG15, where it promotes TIP60-mediated acetylation of histone variant H2A.Z, thereby facilitating androgen receptor occupancy and transactivation of target genes such as KLK3 and TMPRSS2 (PMID:30076933). Within the NuA4 complex, MRGBP paradoxically opposes DNA double-strand break repair by restricting DNA-end resection during homologous recombination, acting counter to the main NuA4 catalytic subunits (PMID:33354938). MRGBP also promotes epithelial–mesenchymal transition and metastasis in colorectal cancer through suppression of DKK1 to activate Wnt/β-catenin signaling and enhancement of NF-κB/p65 acetylation (PMID:36208716).

1. 2010 Medium

   Establishing MRGBP as a bona fide subunit of the TRRAP/TIP60 complex and identifying BRD8 as a direct interaction partner placed MRGBP within the NuA4 chromatin-remodeling machinery.

   Evidence Yeast two-hybrid screening with co-immunoprecipitation validation in human cells

   PMID:20051959

   Open questions at the time

   • Interaction with BRD8 confirmed by a single lab without reciprocal pull-down from BRD8 bait
   • Functional consequence of BRD8–MRGBP interaction not tested
   • No chromatin-level readout performed
2. 2011 Medium

   Demonstrating that MRGBP depletion induces apoptosis and suppresses tumor growth established a pro-survival role but left the underlying mechanism unresolved.

   Evidence siRNA knockdown in cutaneous squamous cell carcinoma cells with in vitro apoptosis assays and in vivo xenograft models

   PMID:21602893

   Open questions at the time

   • No downstream pathway or target genes identified
   • Apoptosis mechanism (intrinsic vs. extrinsic) not determined
   • Specificity of phenotype to NuA4 complex function not tested
3. 2018 High

   Defining the MRG15→MRGBP→TIP60 recruitment cascade on H3K4me-marked chromatin and linking it to H2A.Z acetylation and androgen receptor transactivation provided the first complete mechanistic pathway for MRGBP's transcriptional co-activator function.

   Evidence Co-immunoprecipitation, ChIP at AR target loci, siRNA knockdown with gene expression and histone modification readouts in prostate cancer cells

   PMID:30076933

   Open questions at the time

   • Direct biochemical reconstitution of the recruitment cascade not performed
   • Whether MRGBP functions analogously at non-AR target genes remains untested
   • Structural basis of MRG15–MRGBP interaction unknown
4. 2021 Medium

   Revealing that MRGBP restricts DNA-end resection during homologous recombination uncovered a surprising inhibitory role within the otherwise repair-promoting NuA4 complex, indicating subunit-specific regulatory functions.

   Evidence siRNA knockdown with DNA damage repair and homologous recombination/resection assays

   PMID:33354938

   Open questions at the time

   • Single-lab study; independent confirmation needed
   • Biochemical mechanism by which MRGBP antagonizes NuA4 catalytic activity at break sites not elucidated
   • Whether the repair phenotype depends on TIP60 catalytic activity or a distinct MRGBP function is unclear
5. 2022 Medium

   Identifying DKK1 suppression/Wnt activation and NF-κB/p65 acetylation as dual downstream effectors of MRGBP in colorectal cancer EMT extended its functional scope beyond NuA4-intrinsic chromatin regulation to oncogenic signaling pathways.

   Evidence Knockdown/overexpression, pathway inhibitor validation, xenograft metastasis models, EMT marker analysis in colorectal cancer cells

   PMID:36208716

   Open questions at the time

   • Whether MRGBP acetylates p65 directly via TIP60 or through an indirect mechanism is unresolved
   • No direct chromatin occupancy data (ChIP) at the DKK1 locus provided
   • Generalizability to non-colorectal cancer contexts not addressed

• The structural basis of MRGBP's integration into the NuA4 complex, its mechanism for opposing DNA-end resection, and how its transcriptional and repair functions are coordinated genome-wide remain open questions.
• No structural model of MRGBP within the NuA4 complex
• No genome-wide occupancy map (ChIP-seq) for MRGBP
• Mechanism by which MRGBP restricts resection while residing in a repair-promoting complex is unknown