Surprising Phenotypic Diversity of Cancer-associated mutations of Gly 34 in the Histone H3 tail

Abstract

Sequencing of cancer genomes has identified recurrent somatic mutations in histones, termed oncohistones, which are frequently poorly understood. Previously we showed that fission yeast expressing only the H3.3G34R mutant identified in aggressive pediatric glioma had reduced H3K36 trimethylation and acetylation, increased genomic instability and replicative stress, and defective homology-dependent DNA damage repair (Yadav et al., 2017). Here we show that surprisingly distinct phenotypes result from G34V (also in glioma) and G34W (giant cell tumors of bone) mutations, differentially affecting H3K36 modifications, subtelomeric silencing, genomic stability, sensitivity to irradiation, alkylating agents, hydroxyurea and influencing DNA repair. In cancer, only one of thirty alleles encoding H3 is mutated. Whilst co-expression of wild-type H3 rescues most G34 mutant phenotypes, G34R causes dominant hydroxyurea sensitivity and homologous recombination defects, and dominant subtelomeric silencing. Together, these studies demonstrate the complexity associated with different substitutions at even a single residue in H3 and highlight the utility of genetically tractable systems for their analysis.

A DNA Repair and Cell Cycle Gene Expression Signature in Pediatric High-Grade Gliomas: Prognostic and Therapeutic Value

“…We started with previously established signatures of adult glioblastomas, composed of key effectors of the cell cycle as well as components of crucial DNA repair factors [ 22 ]. Although our data show that the signatures established in aGBMs can indeed capture features related to cell cycle and DNA repair in pHGG tumors, the observed segregation did not correlate with underlying driver mutations affecting histones, as shown in previous studies [ 18 , 20 , 21 , 31 , 32 , 33 ]. Our efforts to identify a specific DNA repair and cell cycle gene expression signature of pHGGs led to a 28-gene expression signature that was able to cluster the sus-tentorial and thalamic pHGG group effectively.…”

“…Of note, we were able to link histone mutated tumors to a more proliferative group displaying upregulation of the gene components of our signature. Previous studies have shown that the H3.3 G34 mutations impact several aspects of the DDR [ 20 , 21 , 34 ]. Intriguingly, we could not segregate H3.3- and H3.1-mutated DIPG.…”

“…In those DIPG, histone H3 demethylase inhibition using GSK-14 enhanced the efficiency of IR by inhibiting DSB repair by HR [ 19 ]. In contrast, H3.3 G34 mutants were found to display increased genomic instability and replicative stress, as well as a defective HR-mediated repair [ 20 , 21 ]. In aGBM, a novel classification was recently achieved using unique DNA repair and cell cycle gene expression signatures exposing vulnerabilities to DNA damaging agents and inhibitors of the DNA damage response [ 22 ].…”

Subtelomeric Chromatin in the Fission Yeast S. pombe

“…Further evidence supporting the involvement of acetylation status of H3K36 in knob formation came from study of a nearby residue in histone H3, H3-G34, which is mutated in pediatric high-grade glioma [ 88 , 89 , 90 , 91 ]. Both histone H3-G34R and H3-G34V mutations led to reduced H3K36me3, accumulation of H3K36me2, and transcriptional repression of ST domains.…”

“…Both histone H3-G34R and H3-G34V mutations led to reduced H3K36me3, accumulation of H3K36me2, and transcriptional repression of ST domains. Further, H3-G34R also prevented H3K36 acetylation [ 88 ] and caused an increase in knob formation [ 91 ], whereas H3-G34V did not affect either H3K36 acetylation or knob formation [ 91 ]. These data support the hypothesis that histone H3-G34R induces knob formation through reducing H3K36 acetylation levels.…”