PFA ependymoma-associated protein EZHIP inhibits PRC2 activity through a H3 K27M-like mechanism
Bibliographic record
Abstract
ABSTRACT Polycomb group (PcG) proteins are essential for development and are frequently misregulated in human cancers. Polycomb Repressive Complexes (PRC1, PRC2) function in a collaborative epigenetic cross-talk with H3K27me3 to initiate and maintain transcriptional silencing. Diffuse intrinsic pontine gliomas (DIPGs) have extremely low H3K27me3 levels mediated by H3 K27M oncohistone. Posterior fossa type A (PFA) ependymomas also exhibit very low H3K27 methylation but lack the K27M oncohistone. Instead, PFA tumors express high levels of EZHIP (Enhancer of Zeste Homologs Inhibitory Protein, also termed CXORF67 ). We find that a highly conserved sequence within the C-terminus of EZHIP is necessary and sufficient to inhibit the catalytic activity of PRC2 in vitro and in vivo . Our biochemical experiments indicate that EZHIP directly interacts with the active site of the EZH2 subunit in a mechanism that is remarkably similar to the K27M oncohistone. Furthermore, expression of H3 K27M or EZHIP in cells promote similar chromatin profiles: loss of broad H3K27me3 domains, but retention of H3K27me3 at the sites of PRC2 recruitment. Importantly, we find that H3K27me3-mediated allosteric activation of PRC2 substantially increases the inhibition potential of EZHIP and H3 K27M, providing a potential mechanism for loss of H3K27me3 spreading from CpG islands in vivo . Our data indicate that PFA ependymoma and DIPG are driven in part by the action of peptidyl PRC2 inhibitors– the K27M oncohistone and the EZHIP ‘oncohistone-mimic’– that dysregulate gene silencing to promote tumorigenesis.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".