title: BMI1-UBR5 axis regulates transcriptional repression at damaged chromatin.
abstract: BMI1 is a component of the Polycomb Repressive Complex 1 (PRC1), which plays a key role in maintaining epigenetic silencing during development. BMI1 also participates in gene silencing during DNA damage response, but the precise downstream function of BMI1 in gene silencing is unclear. Here we identified the UBR5 E3 ligase as a downstream factor of BMI1. We found that UBR5 forms damage-inducible nuclear foci in a manner dependent on the PRC1 components BMI1, RNF1 (RING1a), and RNF2 (RING1b). Whereas transcription is repressed at UV-induced lesions on chromatin, depletion of the PRC1 members or UBR5 alone derepressed transcription elongation at these sites, suggesting that UBR5 functions in a linear pathway with PRC1 in inducing gene silencing at lesions. Mass spectrometry (MS) analysis revealed that UBR5 associates with BMI1 as well as FACT components SPT16 and SSRP1. We found that UBR5 localizes to the UV-induced lesions along with SPT16. We show that UBR5 ubiquitinates SPT16, and depletion of UBR5 or BMI1 leads to an enlargement of SPT16 foci size at UV lesions, suggesting that UBR5 and BMI1 repress SPT16 enrichment at the damaged sites. Consistently, depletion of the FACT components effectively reversed the transcriptional derepression incurred in the UBR5 and BMI1 KO cells. Finally, UBR5 and BMI1 KO cells are hypersensitive to UV, which supports the notion that faulty RNA synthesis at damaged sites is harmful to the cell fitness. Altogether, these results suggest that BMI1 and UBR5 repress the polymerase II (Pol II)-mediated transcription at damaged sites, by negatively regulating the FACT-dependent Pol II elongation.
authors.affiliation: Department of Cell Biology, Microbiology, and Molecular Biology, College of Arts and Sciences, University of South Florida, Tampa, FL 33620.
authors.forename: Anthony
authors.initials: A
authors.lastname: Sanchez
authors.affiliation: Department of Cell Biology, Microbiology, and Molecular Biology, College of Arts and Sciences, University of South Florida, Tampa, FL 33620.
authors.forename: Angelo
authors.initials: A
authors.lastname: De Vivo
authors.affiliation: Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712.
authors.forename: Nadima
authors.initials: N
authors.lastname: Uprety
authors.affiliation: Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712.
authors.forename: Jonghwan
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Cell Biology, Microbiology, and Molecular Biology, College of Arts and Sciences, University of South Florida, Tampa, FL 33620.
authors.forename: Stanley M
authors.initials: SM
authors.lastname: Stevens
authors.affiliation: Department of Cell Biology, Microbiology, and Molecular Biology, College of Arts and Sciences, University of South Florida, Tampa, FL 33620; ykee@usf.edu.
authors.forename: Younghoon
authors.initials: Y
authors.lastname: Kee
mesh_terms: D002843:Chromatin / Q000378:metabolism*; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D063150:Polycomb Repressive Complex 1 / Q000378:metabolism*; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism*; D015398:Signal Transduction; D061805:Transcription Elongation, Genetic; D014158:Transcription, Genetic; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: C069077:BMI1 protein, human; D002843:Chromatin; D012097:Repressor Proteins; C117617:UBR5 protein, human; D063150:Polycomb Repressive Complex 1; C080355:RING1 protein, human; C489841:RNF2 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: BMI1; FACT; Polycomb; UBR5; transcription