title: X-box Binding Protein 1 Regulates Unfolded Protein, Acute-Phase, and DNA Damage Responses During Regeneration of Mouse Liver.
abstract: Liver regeneration after partial hepatectomy (PH) increases the protein folding burden at the endoplasmic reticulum of remnant hepatocytes, resulting in induction of the unfolded protein response. We investigated the role of the core unfolded protein response transcription factor X-box binding protein 1 (XBP1) in liver regeneration using genome-wide chromatin immunoprecipitation analysis.
  
  
  
  We performed studies with C57Bl6-J (control) and interleukin 6-knockout mice. Mice underwent PH or sham surgeries. In some mice, hepatic expression of XBP1 was knocked down by injection of adenoviral vectors encoding small hairpin RNAs against Xbp1 messenger RNA. Liver tissues were collected before surgery and at 6 and 48 hours after surgery and analyzed by chromatin immunoprecipitation followed by sequencing. We also performed functional analyses of HepG2 cells.
  
  
  
  Expression of XBP1 by hepatocytes increased immediately after PH (priming phase of liver regeneration) in control mice, but this effect was delayed in interleukin 6-deficient mice. In mice with knockdown of XBP1, we observed of liver tissue persistent endoplasmic reticulum stress, defects in acute-phase response, and increased hepatocellular damage, compared with control mice. Chromatin immunoprecipitation analyses of liver tissue showed that at 6 hours after PH, liver XBP1 became bound to a large set of genes implicated in proteostasis, the acute-phase response, metabolism, and the DNA damage response (DDR). At this time point, XBP1 bound the promoter of the signal transducer and activator of transcription 3 gene (Stat3). Livers of XBP1-knockdown mice showed reduced expression of STAT3 and had lower levels of STAT3 phosphorylation at Ser727, a modification that promotes cell proliferation and the DDR. Regenerating livers from XBP1-knockdown mice expressed high levels of a marker of DNA double-strand breaks, phosphorylated histone 2A, member X (H2AX), compared with control mice. The inhibition of XBP1 expression caused a reduced up-regulation of DDR messenger RNAs in regenerating hepatocytes.
  
  
  
  In livers of mice, we found that PH induces expression of XBP1, and that this activity requires interleukin 6. XBP1 expression regulates the unfolded protein response, acute-phase response, and DDR in hepatocytes. In regenerating livers, XBP1 deficiency leads to endoplasmic reticulum stress and DNA damage.
authors.affiliation: Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain.
authors.forename: Josepmaria
authors.initials: J
authors.lastname: Argemí
authors.affiliation: Center for Genomic Science of IIT@SEMM, Fondazione Istituto Italiano di Tecnologia (IIT), and Department of Experimental Oncology, European Institute of Oncology (IEO), Milan, Italy.
authors.forename: Theresia R
authors.initials: TR
authors.lastname: Kress
authors.affiliation: Department of Hepatology, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain.
authors.forename: Haisul C Y
authors.initials: HCY
authors.lastname: Chang
authors.affiliation: Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain.
authors.forename: Roberto
authors.initials: R
authors.lastname: Ferrero
authors.affiliation: Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Bértolo
authors.affiliation: Department of Hepatology, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain.
authors.forename: Haritz
authors.initials: H
authors.lastname: Moreno
authors.affiliation: Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain; Navarra Research Institute (IdisNa), Pamplona, Spain.
authors.forename: Manuela
authors.initials: M
authors.lastname: González-Aparicio
authors.affiliation: Department of Hepatology, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain; CiberEhd, Pamplona, Spain.
authors.forename: Iker
authors.initials: I
authors.lastname: Uriarte
authors.affiliation: Navarra Research Institute (IdisNa), Pamplona, Spain; Morphology Core Facility, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain; Department of Histology and Pathology, University of Navarra, Pamplona, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Guembe
authors.affiliation: Bioinformatics Service, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain.
authors.forename: Víctor
authors.initials: V
authors.lastname: Segura
authors.affiliation: Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain; Navarra Research Institute (IdisNa), Pamplona, Spain.
authors.forename: Rubén
authors.initials: R
authors.lastname: Hernández-Alcoceba
authors.affiliation: Department of Hepatology, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain; CiberEhd, Pamplona, Spain.
authors.forename: Matías A
authors.initials: MA
authors.lastname: Ávila
authors.affiliation: Center for Genomic Science of IIT@SEMM, Fondazione Istituto Italiano di Tecnologia (IIT), and Department of Experimental Oncology, European Institute of Oncology (IEO), Milan, Italy.
authors.forename: Bruno
authors.initials: B
authors.lastname: Amati
authors.affiliation: CiberEhd, Pamplona, Spain; Hepatology Unit, Clinica Universidad de Navarra, Pamplona, Navarra, Spain. Electronic address: jprieto@unav.es.
authors.forename: Jesús
authors.initials: J
authors.lastname: Prieto
authors.affiliation: Department of Gene Therapy and Regulation of Gene Expression, Center for Applied Medical Research (CIMA), University of Navarra, Pamplona, Spain. Electronic address: taragon@unav.es.
authors.forename: Tomás
authors.initials: T
authors.lastname: Aragón
mesh_terms: D000210:Acute-Phase Reaction / Q000235:genetics*; D000818:Animals; D004249:DNA Damage / Q000235:genetics*; D059865:Endoplasmic Reticulum Stress / Q000235:genetics*; D056945:Hep G2 Cells; D006498:Hepatectomy; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics; D008099:Liver / Q000378:metabolism*; D008115:Liver Regeneration / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D050796:STAT3 Transcription Factor / Q000378:metabolism; D056811:Unfolded Protein Response / Q000235:genetics*; D000071717:X-Box Binding Protein 1 / Q000235:genetics*
chemical_list: D015850:Interleukin-6; D050796:STAT3 Transcription Factor; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; C577686:interleukin-6, mouse
keywords: APR; ChIP-seq; DDR; Tissue Regeneration