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Cell-of-origin and Developmental Trajectories Cooperate to Determine Chromatin Landscapes in Histone-Mutant Diffuse Midline Gliomas

ABSTRACT: Diffuse midline gliomas (DMGs) are universally fatal pediatric brain tumors associated with mutations in genes encoding either histone H3.1 or histone 3.3, often substitution of methionine for lysine 27 (H3K27M). H3K27 is a critical determinant of chromatin state via methylation by Enhancer-of-Zeste-Homolog-2 (EZH2). Previous reports have suggested that the pathologically low levels of H3K27me3 found in histone-mutant DMGs result primarily from H3K27M inhibiting EZH2 directly, but recent reports have called this model into question. To better understand the chromatin landscape of DMGs, we applied CUT&RUN to patient-derived DMG cell lines. Remarkably, we find that the PRC2 activity is similar in DMGs and embryonic stem cells, suggesting a primitive cell-of-origin, despite transcriptionally active regions maintaining markers of both stem cells and differentiated cells. We also show that exogenous expression of H3.3M at physiological levels has little effect on H3K27me3 levels, that H3K27M can colocalize with H3K27me3 in vivo and that the H3.3K27M oncohistone does not show evidence of sequestering PRC2 components. Our results suggest that chromatin landscapes in DMGs are a consequence of a stem-like chromatin state that is retained despite activation of differentiation programs. Our findings have implications for understanding DMG gliomagenesis and therapeutic approaches centered on epigenome-modifying agents.

ORGANISM(S): Homo sapiens

PROVIDER: GSE118099 | GEO | 2020/09/08

REPOSITORIES: GEO

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