NPM1 mislocalization mediated by RNA Pol I inhibition alters chromatin landscape

RNA polymerase I inhibition affects rRNA synthesis from rDNA clusters residing in nucleolar organizer regions (NORs). Here we have demonstrated RNA Pol I inhibition disrupts nucleolar architecture, NPM1 localization, and alters the chromatin landscape using coordinated eraser and writer enzymes. siRNA mediated depletion or dissociation of NPM1 allows HDAC1 loading on the chromatin. HDAC1 mediated deacetylation of H3K9ac creates H3K9 that undegoes SUV39H1-mediated methylation. The stripping of active histone marks leads to enrichment of repressive H3K9me3 in the genome. These altered chromatin landscape corroborates with loss of genome-wide chromatin accessibility and DNA hypermethylation mediated by DNMT1. Chromatin architectural analysis revealed disrupted nucleolar associated domains (NADs) transforming to lamin associated domains (LADs) with specific histone signatures and repressive states. The 3D nuclear architecture was remodeled by A/B compartments reorganization and loss of Hi-C loops at the H3K9ac depleted sites.