title: Absence of Smad3 confers radioprotection through modulation of ERK-MAPK in primary dermal fibroblasts.
abstract: BACKGROUND
  Transforming growth factor-beta1 (TGF-beta1), a key biological mediator following ionizing radiation, plays a role in a complex tissue reaction involved in local radiation-induced pathological damage. Knocking out Smad3 (S3KO), a downstream signaling intermediate in the TGF-beta pathway, in mice protects their skin from radiation damage as demonstrated by decreased epithelial acanthosis and dermal fibrosis as compared to Smad3 wild-type (S3WT) mice.
  
  
  OBJECTIVE
  The present study was designed to investigate the molecular mechanisms contributing to increased radioprotection in the absence of Smad3.
  
  
  METHODS
  Primary dermal fibroblasts derived from S3WT and KO mice were exposed to 5Gy ionizing radiation in vitro. Western blot analyses, immunocytochemistry, and reporter transfections were used to dissect the radiation-induced events.
  
  
  RESULTS
  There was increased phosphorylation of ERK-MAPK, p53 and H2A.X in S3KO compared to the S3WT fibroblasts, implicating them in a key signaling cascade in response of these cells to radiation. Pro-fibrotic gene expression was decreased in S3KO fibroblasts post-irradiation.
  
  
  CONCLUSIONS
  The absence of Smad3 may decrease radio-responsiveness by increasing activation of DNA damage sensing mechanisms and decreasing induction of pro-fibrotic genes.
authors.affiliation: Laboratory of Cell Regulation and Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA. arany@fas.harvard.edu
authors.forename: Praveen R
authors.initials: PR
authors.lastname: Arany
authors.forename: Kathleen C
authors.initials: KC
authors.lastname: Flanders
authors.forename: William
authors.initials: W
authors.lastname: DeGraff
authors.forename: John
authors.initials: J
authors.lastname: Cook
authors.forename: James B
authors.initials: JB
authors.lastname: Mitchell
authors.forename: Anita B
authors.initials: AB
authors.lastname: Roberts
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000528:radiation effects; D002478:Cells, Cultured; D004249:DNA Damage / Q000528:radiation effects; D020405:Dermis / Q000166:cytology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism* / Q000528:radiation effects*; D006657:Histones / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D011832:Radiation Injuries / Q000517:prevention & control; D011839:Radiation, Ionizing; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D048049:Extracellular Signal-Regulated MAP Kinases; D006657:Histones; D051900:Smad3 Protein; D016159:Tumor Suppressor Protein p53; C497791:Smad3 protein, mouse; C475961:gamma-H2AX protein, mouse