Histone H3F3A and HIST1H3B K27M mutations define two subgroups of diffuse intrinsic pontine gliomas with different prognosis and phenotypes

Abstract

Diffuse intrinsic pontine glioma (DIPG) is the most severe paediatric solid tumour, with no significant therapeutic progress made in the past 50 years. Recent studies suggest that diffuse midline glioma, H3-K27M mutant, may comprise more than one biological entity. The aim of the study was to determine the clinical and biological variables that most impact their prognosis. Ninety-one patients with classically defined DIPG underwent a systematic stereotactic biopsy and were included in this observational retrospective study. Histone H3 genes mutations were assessed by immunochemistry and direct sequencing, whilst global gene expression profiling and chromosomal imbalances were determined by microarrays. A full description of the MRI findings at diagnosis and at relapse was integrated with the molecular profiling data and clinical outcome. All DIPG but one were found to harbour either a somatic H3-K27M mutation and/or loss of H3K27 trimethylation. We also discovered a novel K27M mutation in HIST2H3C, and a lysine-to-isoleucine substitution (K27I) in H3F3A, also creating a loss of trimethylation. Patients with tumours harbouring a K27M mutation in H3.3 (H3F3A) did not respond clinically to radiotherapy as well, relapsed significantly earlier and exhibited more metastatic recurrences than those in H3.1 (HIST1H3B/C). H3.3-K27M-mutated DIPG have a proneural/oligodendroglial phenotype and a pro-metastatic gene expression signature with PDGFRA activation, while H3.1-K27M-mutated tumours exhibit a mesenchymal/astrocytic phenotype and a pro-angiogenic/hypoxic signature supported by expression profiling and radiological findings. H3K27 alterations appear as the founding event in DIPG and the mutations in the two main histone H3 variants drive two distinct oncogenic programmes with potential specific therapeutic targets.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-015-1478-0) contains supplementary material, which is available to authorized users.

S -adenosyl methionine is necessary for inhibition of the methyltransferase G9a by the lysine 9 to methionine mutation on histone H3

“…Our studies to date indicate that K-to-M oncohistones decrease levels of histone methylation through a trans mechanism, suggesting that the oncohistone concentration rather than the genomic location is important for oncogenic potential. Indeed, the K27M mutation has been observed to occur in genes encoding all forms of histone H3 (H3.1, H3.2, and H3.3) in human glioma (1,10,24). Our study reveals a critical role for SAM in the sequestration of lysine methyltransferases by these inhibitory mutant histones.…”

“…Unmodified H3 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] peptide (23 μM) was incubated with 25 nM G9a-SET in the presence of 50 μM SAM (radioactive: nonradioactive molar ratio = 0.016) in a buffer containing 50 mM Hepes (pH 7.9), 0.5 mM DTT, 0.25 mM PMSF, and 2 mM MgCl 2 . Where applicable, different H3 1-20 K9X peptides (Tufts University Peptide Synthesis Core) were present in the reaction.…”

“…Previously, we found that only long, unbranched hydrophobic side chains containing methionine (M) and isoleucine (I) at lysine 27 (K27M and K27I) were capable of inhibiting PRC2 in vitro and decreasing H3K27me3 when expressed ectopically in cultured cells (7). The recent identification of K27I histone H3 mutations in a small number of diffuse intrinsic pontine glioma samples further links the inhibition of PRC2 and loss of K27me3 to the likely oncogenic activity of histone H3K27 mutations (10). Additionally, histone H3 peptides that contained unbranched hydrophobic lysine Significance Recent exome sequencing studies have uncovered high-frequency histone H3 driver mutations in pediatric cancers.…”

Positron emission tomography imaging in diffuse intrinsic pontine glioma

“…Usually, DIPG are surgically not resectable and may display histological features ranging from grade II to grade IV of the World Health Organization (WHO) classification for gliomas. They frequently harbor a K27M mutation in one or other histone variant (2), with H3.1 mutant tumors displaying a younger patient age, distinct clinicopathological and radiological features, and a slightly longer survival time (3,4). Generally, DIPG are incurable; no significant therapeutic progress has been made in the past 50 years (4).…”

“…They frequently harbor a K27M mutation in one or other histone variant (2), with H3.1 mutant tumors displaying a younger patient age, distinct clinicopathological and radiological features, and a slightly longer survival time (3,4). Generally, DIPG are incurable; no significant therapeutic progress has been made in the past 50 years (4). In clinical trials, numerous experimental therapeutic approaches have been evaluated; however, none of them showed a survival benefit compared to standard external fractionated radiotherapy (5).…”