TOPORS, a tumor suppressor protein, maintains higher-order chromatin organization in mouse hepatocytes [PML ChIP-seq]

Within mammalian nuclear space, chromosomes are hierarchically folded into active (A) and inactive (B) compartments composed of topologically associating domains (TADs). Genomic regions interact with nuclear lamina, termed lamina-associated domains (LADs), associated with transcriptional repression. However, the molecular mechanisms underlying these 3D chromatin architectures remain undeciphered. Here, we demonstrate the role of a potential tumor suppressor, TOP1 Binding Arginine/Serine Rich Protein (TOPORS), in genome organization. Topors knockdown in mouse hepatocytes results in cell proliferation and migration promotion, as well as arrest in the S phase of the cell cycle. RNA-seq analysis shows that 373 genes are up-regulated, some of which are associated with nuclear structure, and 316 genes exhibit down-regulated, many related to metabolic process. Chromatin accessibility is inclined to alter in the intergenic regions, including enhancers. Chromatin-lamina interactions decrease globally, and the coverage of LADs reduces from 53.31% to 46.52%. Furthermore, Topors knockdown leads to significantly increasing interactions between A and B compartments in cis and in trans. Correspondingly, strength of TAD boundaries located at A/B borders is weakened. Collectively, our data reveal that TOPORS functions as a regulator in chromosome folding, providing novel insights into the architectural role of tumor suppressors in higher-order genome organization. Overall design: PML ChIP-seq data in Ctrl and Topors KD AML12 cells.