Pavlenko, E. | bioRxiv Science

bioRxiv2023

Activation of automethylated PRC2 by dimerization on chromatin

Polycomb Repressive Complex 2 (PRC2) is an epigenetic regulator that trimethylates lysine 27 of histone 3 (H3K27me3) and is essential for embryonic development and cellular differentiation. H3K27me3 is associated with transcriptionally repressed chromatin and is established when PRC2 is allosterically activated upon methyl-lysine binding by the regulatory subunit EED. Automethylation of the catalytic subunit EZH2 stimulates its activity by an unknown mechanism. Here, we show that PRC2 forms a dimer on chromatin in which an inactive, automethylated PRC2 protomer is the allosteric activator of a second PRC2 that is poised to methylate H3 of a substrate nucleosome. Functional assays support our model of allosteric trans-autoactivation via EED, suggesting a novel mechanism mediating context- dependent activation of PRC2. Our work showcases the molecular mechanism of auto- modification coupled dimerization in the regulation of chromatin modifying complexes.

biochemistry↗

bioRxiv2023

Remodelling of the endothelial cell transcriptional program via paracrine and DNA-binding activities of MPO

Myeloperoxidase (MPO) is an enzyme that functions in host defence by catalysing the formation of reactive oxygen intermediates. Synthesized majorly by myeloid progenitor cell types and neutrophils, MPO is released into the vascular lumen during inflammation, where it may adhere and subsequently enter endothelial cells coating vascular walls. Here, we show that MPO actually enters the nucleus of these endothelial cells and binds chromatin independently of its enzymatic activity to cause changes in chromatin structure. At its binding sites, MPO drives chromatin decondensation, while enhancing condensation at flanking regions. We further show that MPO binds loci relevant for the activation of the endothelial-to- mesenchymal transition (EndMT) and the migratory potential of ECs. Finally, MPO interacts with the RNA- binding factor ILF3 affecting its relative abundance between cytoplasm and nucleus. This leads to ILF3:MPO- driven transcriptional and post-transcriptional regulation. Accordingly, MPO-knockout mice show reduced EC numbers at scars formed after myocardial infarction, indicating reduced neovascularization. In summary, we describe a non-enzymatic role for MPO in coordinating EndMT and controlling the fate of endothelial cells through direct chromatin binding and association with such co-factors as ILF3.

genomics↗