H3.3 G34R mutations in pediatric primitive neuroectodermal tumors of central nervous system (CNS-PNET) and pediatric glioblastomas: possible diagnostic and therapeutic implications?

Abstract

Pediatric glioblastomas recently have been exon sequenced with evidence that approximately 30 % of cases harbour mutations of the histone H3.3 gene. Although studies to determinate their role in risk stratification are on-going, it remains to be determined whether H3.3 mutations could be found in other tumors such as pediatric primitive neuroectodermal tumors of the central nervous system (CNS-PNETs) and whether the presence of H3.3 mutations in glioblastomas could be used as diagnostic tool in their differential diagnosis with CNS-PNETs. We performed a large mutational pyrosequencing-based screening on 123 pediatric glioblastomas and 33 CNS-PNET. The analysis revealed that 39/123 (31.7 %) glioblastomas carry H3.3 mutations. The K27M (AAG → ATG, lysine → methionine) mutation was found in 33 glioblastomas (26 %); the G34R (GGG → AGG, glycine → arginine) was observed in 6 glioblastomas (5.5 %). However, we also identified 4 of 33 cases (11 %) of CNS-PNETs harbouring a H3.3 G34R mutation. Multiplex ligation-dependent probe amplification analysis revealed PDGFR-alpha amplification and EGFR gain in two cases and N-Myc amplification in one case of H3.3 G34R mutated CNS-PNET. None of H3.3 mutated tumors presented a CDKN2A loss. In conclusion, because pediatric patients with glioblastoma and CNS-PNET are treated according to different therapeutic protocols, these findings may raise further concerns about the reliability of the histological diagnosis in the case of an undifferentiated brain tumor harbouring G34R H3.3 mutation. In this view, additional studies are needed to determine whether H3.3 G34 mutated CNS-PNET/glioblastomas may represent a defined tumor subtype.

The Histone Variant H3.3 in Transcriptional Regulation and Human Disease

“…Additional sequencing analyses with more patient samples revealed that these two types of mutations have distinct features. K27M mutations occur in younger patients (5–29 years), whereas G34R/V mutations appear in slightly older patients (9–42 years) [101–103]. The majority of tumors associated with H3K27M mutation are restricted to midline locations such as thalamus, pons, brainstem and the spinal cord [102].…”

Evaluation of a novel antibody to define histone 3.3 G34R mutant brain tumours

“…This represents one out of 64 cases, and may reflect the known challenges of diagnosis high grade supratentorial CNS malignancies in childhood which can now be facilitated by specific antibodies such as reported here in the light of recent proposal for reclassification of CNS PNETs [10]. Interestingly, Gessi et al have recently reported G34R mutations in 4/33 CNS-PNET cases by sequencing and suggested that these could be defined tumour subtype [7], supporting the potential of our G34R antibody to detect G34R mutation in various TMA cohorts. However, once again further tissue was also not available for our CNS-PNET case to histological review or sequence.…”

Adult Diffuse Astrocytoma in the Medulla Oblongata: Molecular Biological Analyses Including H3F3A Mutation of Histone H3.3

“…The mutation hotspot codons at K27 and G34 of the H3.3 genes (AAG → ATG; GGG → AGG; GGG → GTG) were screened by pyrosequencing according to a previous report. 9) Pyrosequencing was performed using PyroGold reagents (QIAGEN GmbH, Hilden, Germany) on the PSQ 96MA instrument (QIAGEN GmbH), according to the manufacturer’s instructions. Control oligonucleotides (QIAGEN GmbH) were used to detect the background signal.…”

“…2,4,5) Recently, recurrent H3F3A mutations of histone H3.3 have been identified as a frequent event in pediatric diffuse intrinsic brainstem gliomas (DIPGs) and thalamic glioblastomas (GBMs), associated with prognosis and survival. 6–9) However, due to its rarity, the relationship between the clinical course and molecular biological features in adult brain stem gliomas have still been poorly understood. …”