DIDO3 acts at the interface of RNAPII transcription and chromatin structure regulation

Chromatin structure and organization has a key role in gene expression regulation. Here, we integrated ChIP-seq, RNA-seq, Hi-C, epigenetic, and cancer-related mutations data to get insight into the role of Death Inducer Obliterator gene (Dido1) in RNA pol II (RNAPII) transcription and chromatin structure regulation. Analysis of ChIP-seq data of DIDO3, the largest protein isoform of Dido1, revealed binding-sites overlap about 70% with RNAPII and H3K36me3 in the mouse genome, but also significant overlap 10-30% with Polycomb, CTCF, H3K4me3, and H3K27ac. Based on this analysis we propose that DIDO3s PHD domain interacts with H3K36me3 posttranslational modification. Integrating multi-omics data we describe how DIDO3 potentially recruit several transcription factors, including RNAPII, and also regulates genes transcribing those same transcription factors. DIDO3 regulation of the genes traduced into proteins to which it binds puts DIDO3 in the center of intricate feedback loops. We showed, by using data from a DIDO3 mutant, that DIDO3 C-terminus is responsible for most of these transcriptional regulation, and is also implicated in other very important pathways by regulating genes encoding for Polycomb-accessory proteins, subunits of the SWI/SNF chromatin remodelling, or Set1/COMPASS chromatin modifier complexes. These multi-protein complexes control gene activation or silencing and also play a role in tumour development. DIDO3 C-terminus region and splice-site for alternative DIDO2/DIDO3 protein isoforms tended to accumulate recurrent truncating mutations identified in the TCGA Pan-Cancer dataset. We hypothesize that deregulation of DIDO3, as it happens with large epigenetic complexes and long-range interactions, leads to cell differentiation deficiency and cancer development. Overall, we propose here a molecular mechanism by which DIDO3, favour RNAPII pausing and long-range chromatin interactions.