Specific cPRC1 complexes are co-opted to mediate oncogenic gene repression in H3K27M-mutant diffuse midline glioma.

ABSTRACT: Diffuse midline glioma (DMG) is a fatal childhood brain tumour characterised primarily by mutant histone H3 (H3K27M). H3K27M causes a global reduction in Polycomb Repressive Complex 2 (PRC2)-mediated H3K27me3 by inhibiting the enzymatic activity of the complex. Paradoxically, PRC2 histone methyltransferase activity is essential in for oncogenic gene repression in DMG tumour cells though downstream molecular mechanisms that are poorly understood. Here, we discover that this oncogenic gene repression is mediated by specific canonical PRC1 (cPRC1) formations containing CBX4. By combining CRISPR screening, biochemical and chromatin mapping approaches with functional perturbations we show that cPRC1 complexes containing CBX4-cPRC1 is co-opted to drive repression downstream of H3K27me3 in DMG cells. Remarkably, the altered H3K27me3 landscape characteristic of H3K27M-mutant DMG rewires the distribution of distinct cPRC1 complexes such that CBX4-cPRC1 accumulates at sites of H3K27me3 while other cPRC1 formations are reduced. Despite CBX4-cPRC1 accounting for less than 5% all cPRC1 H3K27M-mutant DMG, it acts as the predominant repressor of (Polycomb target) neural differentiation genes in this setting. Our findings link the altered distribution of H3K27me3 with imbalances of CBX-cPRC1 functions and consequent oncogenic gene repression, revealing new disease mechanisms and potential therapeutic opportunities in this incurable childhood brain tumour.

INSTRUMENT(S):

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Brain

DISEASE(S): Diffuse Midline Glioma

SUBMITTER: Pascal Jansen  

LAB HEAD: Michiel Vermeulen

PROVIDER: PXD047401 | Pride | 2025-06-24

REPOSITORIES: Pride