Detection of histone H3 K27M mutation and post-translational modifications in pediatric diffuse midline glioma via tissue immunohistochemistry informs diagnosis and clinical outcomes.

Tina Huang,Nitin Wadhwani,Jin Qi,Ali Shilatifard,Amir Behdad,Roxanna Garcia,Amanda M Saratsis,Craig Horbinski,Rishi Lulla,Charles James

doi:10.18632/oncotarget.26430

Abstract

Pediatric diffuse midline glioma is a highly morbid glial neoplasm that may arise in the thalamus or brainstem (also known as diffuse intrinsic pontine glioma or DIPG). Because tumor anatomic location precludes surgical resection, diagnosis and treatment is based on MR imaging and analysis of biopsy specimens. Up to 80% of pediatric diffuse midline gliomas harbor a histone H3 mutation resulting in the replacement of lysine 27 with methionine (K27M) in genes encoding histone H3 variant H3.3 (H3F3A) or H3.1 (HIST1H3B). H3K27M mutant glioma responds more poorly to treatment and is associated with worse clinical outcome than wild-type tumors, so mutation detection is now diagnostic for a new clinical entity, diffuse midline glioma H3K27M mutant, as defined in the most recent WHO classification system. We previously reported patterns of histone H3 trimethylation (H3K27me3) and acetylation (H3K27Ac) associated with H3K27M mutation that impact transcription regulation and contribute to tumorigenesis. Given the clinical implications of the H3K27M mutation and these associated H3 post-translational modifications (PTMs), we set to determine whether they can be characterized via immunohistochemistry (IHC) in a cohort of pediatric glioma (n = 69) and normal brain tissue (n = 4) specimens. We observed 100% concordance between tissue IHC and molecular sequencing for detecting H3K27M mutation. In turn, H3K37M and H3K27me3 results, but not H3K27Ac staining patterns, were predictive of clinical outcomes. Our results demonstrate H3K27M and H3K27me3 staining of pediatric glioma tissue may be useful for diagnosis, stratification to epigenetic targeted therapies, and longitudinal monitoring of treatment response.

Highlights

Pediatric high-grade glioma (HGG) persists as the leading cause of cancer death in children
Somatic missense mutations in Histone histone 3 (H3).3 and H3.1 genes (H3F3A and HIST1H3B) occur in up to 80% of pediatric diffuse midline gliomas, including thalamic www.oncotarget.com and diffuse intrinsic pontine gliomas (DIPGs)
Because H3K27M mutation detection is more predictive of patient clinical outcome than traditional tumor morphologic features, molecular diagnosis of mutation status is required for all cases of diffuse midline glioma, and K27M mutant tumors are deemed World Health Organization (WHO) Grade IV irrespective of tumor histopathologic features [11]

Summary

Introduction

Pediatric high-grade glioma (HGG) persists as the leading cause of cancer death in children. Somatic mutations in histone 3 (H3) isoforms H3.3 and H3.1, resulting in substitution of methionine for lysine at residue 27 of the histone H3 N-terminal tail (p.Lys27Met or K27M), are detected in >80% of diffuse midline gliomas, including thalamic glioma and diffuse intrinsic pontine glioma (DIPG) [1,2,3,4] Due to this change in the amino acid sequence of the N-terminal tail of Histone H3, H3K27M mutant tumors harbor altered patterns of histone H3 post-translational modification (PTM). Since these H3K27M-associated changes in H3 marks significantly affect chromatin structure and function, resulting in distinct gene and protein expression, as well as DNA methylation patterns [1, 2, 5,6,7,8] and tumor phenotype [1, 3, 4, 9, 10], detection of changes in H3K27me and H3K27Ac over time may be important for assessing tumor response to epigenetic therapies

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