MRG15 Is a Novel PALB2-interacting Factor Involved in Homologous Recombination

Abstract

PALB2 is an integral component of the BRCA complex important for recombinational DNA repair. However, exactly how this activity is regulated in vivo remains unexplored. Here we provide evidence to show that MRG15 is a novel PALB2-associated protein that ensures regulated recombination events. We found that the direct interaction between MRG15 and PALB2 is mediated by an evolutionarily conserved region on PALB2. Intriguingly, although damage-induced RAD51 foci formation and mitomycin C sensitivity appeared normal in MRG15-binding defective PALB2 mutants, these cells exhibited a significant increase in gene conversion rates. Consistently, we found that abrogation of the PALB2-MRG15 interaction resulted in elevated sister chromatid exchange frequencies. Our results suggest that loss of the PALB2-MRG15 interaction relieved the cells with the suppression of sister chromatid exchange and therefore led to a hyper-recombination phenotype in the gene conversion assay. Together, our study indicated that although PALB2 is required for proficient homologous recombination, it could also govern the choice of templates used in homologous recombination repair.

MRG15 is required for pre-mRNA splicing and spermatogenesis

“…Some other proteins or modifications might participate in the regulation of splicing events of Tpm1, Prm1, and Prm2 mRNAs. Because MRG15 can interact with HAT, HDAC complexes, and other histone modifications, such as methylated H4K20, localization of MRG15 on the genome may be regulated by not only H3K36me3 but also, other histone modifications and/or protein complexes (13)(14)(15)(16)(17)(18)(19)(20)(21)26). PTBPs are known to antagonize exon definition; therefore, those retained sequences could be recognized as an exon on the absence of MRG15 (44).…”

“…During spermatogenesis, histone H4 is highly acetylated before replacement of nucleosomal proteins from histones to TNPs to protamines (27). Because MRG15 is found in both HAT and HDAC complexes (13)(14)(15)(16)(17)(18)(19)(20)(21), MRG15 may be essential for postmeiotic events. To investigate whether MRG15 is involved in histone acetylation in postmeiotic spermatogenesis, acetylated histones were analyzed.…”

“…Because MRG15 plays an essential role during homology-directed DNA damage repair, SCP1, γH2AX, and ubiquitylated H2A were analyzed in spermatocytes to examine whether MRG15 is required for meiotic homologous recombination (20,21,24). However, there were no significant differences in localizations of meiosis regulating proteins between control and Mrg15 null testes (SI Appendix, Figs.…”

“…MRG15 specifically recognizes the methylated H3K36 and recruits polypyrimidine tract binding protein (PTB) at intronic splicing silencer elements near an exon to suppress exon insertions into mRNA (7). MRG15 is also a component of histone acetyltransferase (HAT) and histone deacetylase (HDAC) complexes and regulates transcription by balancing histone acetylation (7,(13)(14)(15)(16)(17)(18)(19)(20)(21). During spermatogenesis, before histones are replaced with transition proteins and protamines, histone H4 is highly acetylated, and the acetylation of histones is required for histone removal.…”

ATM-dependent Phosphorylation of the Fanconi Anemia Protein PALB2 Promotes the DNA Damage Response

“…Plasmids and siRNAs-HA-FLAG, Myc, and streptavidin binding peptide-FLAG (SFB)-tagged PALB2 or BRCA1 expression constructs were previously described (21,24,25). For RNAi-mediated depletion experiments, cells were transfected twice with either non-targeting control or target siRNAs (Dharmacon) using Oligofectamine according to the manufacturer's instructions (Invitrogen).…”