UBR5 Forms Ligand-Dependent Complexes on Chromatin to Regulate Nuclear Hormone Receptor Binding [ChIP-Seq]

Nuclear hormone receptors (NRs) are ligand-binding transcription factors that are important therapeutic targets in malignancy. Hormone binding triggers NR activation and their subsequent proteasomal degradation through unknown ligand-dependent ubiquitin ligase machinery. NR degradation is therapeutically relevant: the oncogenic PML-RARA fusion between PML and the retinoic acid receptor (RARA) drives acute promyelocytic leukemia and degradation of PML-RARA induced by all-trans-retinoic acid (ATRA) is required for anti-tumor activity. We identify a Leu-X-X-Leu-Leu (LxxLL) binding motif that associates with a conserved degron in RARA. A high-resolution crystal structure of the RARA ligand binding domain in complex with this LxxLL motif shows how UBR5 binding is mutually exclusive with nuclear co-activator engagement. Our work establishes UBR5-driven NR degradation as an integral regulator of transcriptional signaling by nuclear hormones. Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) was performed for RARA and UBR5 in NB4 cells and GR and UBR5 in A549 cells. Control samples for each cell type (DMSO) as well as treatment samples following application of ATRA and DEX in NB4 and A549 cells respectively. Separate preparations of DEX treated A549 cells were sequenced both 15 minutes and 24 hours post-treatment. Samples of the NB4 cell conditions were prepared in biological duplicate. Fractions of each sample were sequenced absent precipitation as matched input datasets.