title: C/EBPβ-Thr217 phosphorylation signaling contributes to the development of lung injury and fibrosis in mice.
abstract: BACKGROUND
  Although C/EBPβ(ko) mice are refractory to Bleomycin-induced lung fibrosis the molecular mechanisms remain unknown. Here we show that blocking the ribosomal S-6 kinase (RSK) phosphorylation of the CCAAT/Enhancer Binding Protein (C/EBP)-β on Thr217 (a RSK phosphoacceptor) with either a single point mutation (Ala217), dominant negative transgene or a blocking peptide containing the mutated phosphoacceptor ameliorates the progression of lung injury and fibrosis induced by Bleomycin in mice.
  
  
  RESULTS
  Mice expressing the non-phosphorylatable C/EBPβ-Ala217 transgene had a marked reduction in lung injury on day-13 after Bleomycin exposure, compared to C/EBPβ(wt) mice, judging by the decrease of CD68(+) activated monocytes/macrophages, bone marrow-derived CD45(+) cells and lung cytokines as well as by the normal surfactant protein-C expression by lung pneumocytes. On day-21 after Bleomycin treatment, C/EBPβ(wt) mice but not mice expressing the dominant negative C/EBPβ-Ala217 transgene developed severe lung fibrosis as determined by quantitative collagen assays. All mice were of identical genetic background and back-crossed to the parental wild-type inbreed FVB mice for at least ten generations. Treatment of C/EBPβ(wt) mice with a cell permeant, C/EBPβ peptide that inhibits phosphorylation of C/EBPβ on Thr217 (40 µg instilled intracheally on day-2 and day-6 after the single Bleomycin dose) also blocked the progression of lung injury and fibrosis induced by Bleomycin. Phosphorylation of human C/EBPβ on Thr266 (human homologue phosphoacceptor) was induced in collagen-activated human lung fibroblasts in culture as well as in activated lung fibroblasts in situ in lungs of patients with severe lung fibrosis but not in control lungs, suggesting that this signaling pathway may be also relevant in human lung injury and fibrosis.
  
  
  CONCLUSIONS
  These data suggest that the RSK-C/EBPβ phosphorylation pathway may contribute to the development of lung injury and fibrosis.
authors: Department of Medicine, VA Healthcare Center, San Diego, California, United States of America.
authors: Martina
authors: M
authors: Buck
authors: Mario
authors: M
authors: Chojkier
mesh_terms: D000818:Animals; D001761:Bleomycin / Q000009:adverse effects; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D053181:Caspase 8 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D018450:Disease Progression; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D008168:Lung / Q000473:pathology; D055370:Lung Injury / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology* / Q000517:prevention & control; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D058628:Myofibroblasts / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011658:Pulmonary Fibrosis / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology* / Q000517:prevention & control; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013912:Threonine
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D010446:Peptide Fragments; D001761:Bleomycin; D013912:Threonine; D019893:Ribosomal Protein S6 Kinases; D053181:Caspase 8