title: Dynamic Behavior of the RNA Polymerase II and the Ubiquitin Proteasome System During the Neuronal DNA Damage Response to Ionizing Radiation.
abstract: Neurons are highly vulnerable to genotoxic agents. To restore genome integrity upon DNA lesions, neurons trigger a DNA damage response (DDR) that requires chromatin modifications and transcriptional silencing at DNA damage sites. To study the reorganization of the active RNA polymerase II (Pol II), which transcribes all mRNA-encoding genes, and the participation of the ubiquitin-proteasome system (UPS) in the neuronal DDR, we have used rat sensory ganglion neurons exposed to X-rays (4 Gy) ionizing radiation (IR). In control neurons, Pol II appears concentrated in numerous chromatin microfoci identified as transcription factories by the incorporation of 5'-fluorouridine into nascent RNA. Upon IR treatment, numerous IR-induced foci (IRIF), which were immunoreactive for γH2AX and 53BP1, were observed as early as 30 min post-IR; their number progressively reduced at 3 h, 1 day, and 3 days post-IR. The formation of IRIF was associated with a decrease in Pol II levels by both immunofluorescence and Western blotting. Treatment with the proteasome inhibitor bortezomib strongly increased Pol II levels in both control and irradiated neurons, suggesting that proteasome plays a proteolytic role by clearing stalled Pol II complexes at DNA damage sites, as a prelude to DNA repair. Neuronal IRIF recruited ubiquitylated proteins, including ubiquitylated histone H2A (Ub-H2A), and the catalytic proteasome 20S. Ub-H2A has been associated with transcriptional silencing at DNA damage sites. On the other hand, the participation of UPS in neuronal DDR may be essential for the ubiquitylation of Pol II and other proteasome substrates of the DNA repair machinery and their subsequent proteasome-mediated degradation.
authors.affiliation: Department of Anatomy and Cell Biology and "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", University of Cantabria-IDIVAL, Cardenal Herrera Oria s/N, Santander, 39011, Spain.
authors.forename: Iñigo
authors.initials: I
authors.lastname: Casafont
authors.affiliation: Department of Anatomy and Cell Biology and "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", University of Cantabria-IDIVAL, Cardenal Herrera Oria s/N, Santander, 39011, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Palanca
authors.affiliation: Laboratorio de Inestabilidad Genómica, Centro Nacional de Investigaciones Oncológicas (CNIO), Madrid, Spain.
authors.forename: Vanesa
authors.initials: V
authors.lastname: Lafarga
authors.affiliation: Department of Anatomy and Cell Biology and "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", University of Cantabria-IDIVAL, Cardenal Herrera Oria s/N, Santander, 39011, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Mata-Garrido
authors.affiliation: Department of Anatomy and Cell Biology and "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", University of Cantabria-IDIVAL, Cardenal Herrera Oria s/N, Santander, 39011, Spain.
authors.forename: Maria T
authors.initials: MT
authors.lastname: Berciano
authors.affiliation: Department of Anatomy and Cell Biology and "Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)", University of Cantabria-IDIVAL, Cardenal Herrera Oria s/N, Santander, 39011, Spain. lafargam@unican.es.
authors.forename: Miguel
authors.initials: M
authors.lastname: Lafarga
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D015536:Down-Regulation / Q000528:radiation effects; D022041:Euchromatin / Q000378:metabolism; D008297:Male; D009474:Neurons / Q000378:metabolism / Q000473:pathology* / Q000528:radiation effects*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism*; D011839:Radiation, Ionizing; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000528:radiation effects; D025801:Ubiquitin / Q000378:metabolism*; D057149:Ubiquitinated Proteins / Q000378:metabolism
chemical_list: D022041:Euchromatin; D025801:Ubiquitin; D057149:Ubiquitinated Proteins; D012319:RNA Polymerase II; D046988:Proteasome Endopeptidase Complex
keywords: DNA damage; Neurons; RNA polymerase II; Transcription factories; Ubiquitin proteasome system