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Divergent Pathogenic PR-DUB Complex Variants Converge Functionally Via PRC2 Displacement From Chromatin

Doyle, E. J.; Boyce, M.; Buggle, S.; Smith, T.; Dillon, E.; McElligott, A. M.; Orfali, N.; Coughlan, A. Y.; Pasini, D.; Conway, E.

2026-07-26 genetics
10.64898/2026.07.23.740410 bioRxiv
Show abstract

The PR-DUB complex is responsible for erasing the repressive histone modification, H2AK119ub1. ASXL1-3 proteins are mutually exclusive catalytic partners of BAP1 in the PR-DUB complex. Somatic heterozygous ASXL1-3 variants are associated with cancer, including myeloid malignancies, while de novo germline variants cause neurodevelopmental disorders such as Bohring-Opitz syndrome. These pathogenic variants are almost exclusively nonsense and frameshift and have been proposed to act as gain-of-function. However, the precise catalytic impact and mechanism of variant ASXL1-3 remains elusive. Using an isogenic embryonic stem cell model we have discovered that ASXL1 BOS variants drive reductions - but not global ablations - in H2AK119ub1, consistent with gain-of-function. This catalytic change occurs through the production of a truncated ASXL1 protein with enhanced stability. Hyper-stabilised ASXL1 drives a stoichiometric shift in PR-DUB assembly away from ASXL2 complexes. The drop in H2AK119ub1 levels ultimately reduces PRC2 binding and H3K27me3 deposition. Surprisingly, this phenotype is shared across PR-DUB loss-of-function models and indeed is emerging as a common phenotype across genetically and mechanistically distinct Polycomb-related chromatinopathies.

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