RESUMO
DNA-protein crosslinks (DPCs) arise from enzymatic intermediates, metabolism or chemicals like chemotherapeutics. DPCs are highly cytotoxic as they impede DNA-based processes such as replication, which is counteracted through proteolysis-mediated DPC removal by spartan (SPRTN) or the proteasome. However, whether DPCs affect transcription and how transcription-blocking DPCs are repaired remains largely unknown. Here we show that DPCs severely impede RNA polymerase II-mediated transcription and are preferentially repaired in active genes by transcription-coupled DPC (TC-DPC) repair. TC-DPC repair is initiated by recruiting the transcription-coupled nucleotide excision repair (TC-NER) factors CSB and CSA to DPC-stalled RNA polymerase II. CSA and CSB are indispensable for TC-DPC repair; however, the downstream TC-NER factors UVSSA and XPA are not, a result indicative of a non-canonical TC-NER mechanism. TC-DPC repair functions independently of SPRTN but is mediated by the ubiquitin ligase CRL4CSA and the proteasome. Thus, DPCs in genes are preferentially repaired in a transcription-coupled manner to facilitate unperturbed transcription.
Assuntos
DNA Helicases , Enzimas Reparadoras do DNA , Reparo do DNA , Proteínas de Ligação a Poli-ADP-Ribose , Proteólise , RNA Polimerase II , Transcrição Gênica , Humanos , Proteínas de Transporte , DNA/metabolismo , DNA/genética , Dano ao DNA , DNA Helicases/metabolismo , DNA Helicases/genética , Enzimas Reparadoras do DNA/metabolismo , Enzimas Reparadoras do DNA/genética , Proteínas de Ligação a DNA/metabolismo , Proteínas de Ligação a DNA/genética , Células HEK293 , Proteínas de Ligação a Poli-ADP-Ribose/metabolismo , Proteínas de Ligação a Poli-ADP-Ribose/genética , Complexo de Endopeptidases do Proteassoma/metabolismo , Receptores de Interleucina-17 , RNA Polimerase II/metabolismo , RNA Polimerase II/genética , Fatores de Transcrição/metabolismo , Fatores de Transcrição/genética , Ubiquitina-Proteína Ligases/metabolismo , Ubiquitina-Proteína Ligases/genéticaRESUMO
The cohesin complex regulates higher order chromosome architecture through maintaining sister chromatid cohesion and folding chromatin by DNA loop extrusion. Impaired cohesin function underlies a heterogeneous group of genetic syndromes and is associated with cancer. Here, we mapped the genetic dependencies of human cell lines defective of cohesion regulators DDX11 and ESCO2. The obtained synthetic lethality networks are strongly enriched for genes involved in DNA replication and mitosis and support the existence of parallel sister chromatid cohesion establishment pathways. Among the hits, we identify the chromatin binding, BRCT-domain containing protein PAXIP1 as a novel cohesin regulator. Depletion of PAXIP1 severely aggravates cohesion defects in ESCO2 mutant cells, leading to mitotic cell death. PAXIP1 promotes global chromatin association of cohesin, independent of DNA replication, a function that cannot be explained by indirect effects of PAXIP1 on transcription or DNA repair. Cohesin regulation by PAXIP1 requires its binding partner PAGR1 and a conserved FDF motif in PAGR1. PAXIP1 co-localizes with cohesin on multiple genomic loci, including active gene promoters and enhancers. Possibly, this newly identified role of PAXIP1-PAGR1 in regulating cohesin occupancy on chromatin is also relevant for previously described functions of PAXIP1 in transcription, immune cell maturation and DNA repair.
