DOT1L shapes ncPRC1-target gene repression to maintain cell identity of DLBCL [RNA-Seq]

To explore the mechanisms underlying the co-dependency between DOT1L and EZH2 in GCB-DLBCL, we performed an EZH2 inhibition (EZH2i)-anchored genome-wide CRISPR interference screen and identified multiple candidate genes encoding components of non-canonical (nc) PRC1 complexes, including USP7, KDM2B, RING1, and PCGF1.

We identified USP7 as potential direct target of DOT1L, whose downregulation was associated with increased EZH2i sensitivity in multiple GCB-DLBCL cell lines. Furthermore, we observed that DOT1L influences the composition of chromatin-bound ncPRC1 complexes and regulates, in part, the deposition of H2AK119 monoubiquitination (H2AK119ub1) at gene promoters co-occupied by H3K27me3, here defined as PRC1/2 target genes. These PRC1/2 targets were specifically enriched in PC signature genes, whose derepression was associated with DOT1L inhibition (DOT1Li)-mediated loss of H2AK119ub1.