title: Persistence of γ-H2AX and 53BP1 foci in proliferating and non-proliferating human mammary epithelial cells after exposure to γ-rays or iron ions.
abstract: OBJECTIVE
  To investigate γ-H2AX (phosphorylated histone H2AX) and 53BP1 (tumour protein 53 binding protein No. 1) foci formation and removal in proliferating and non-proliferating human mammary epithelial cells (HMEC) after exposure to sparsely and densely ionising radiation under different cell culture conditions.
  
  
  METHODS
  HMEC cells were grown either as monolayers (2D) or in extracellular matrix to allow the formation of acinar structures in vitro (3D). Foci numbers were quantified by image analysis at various time points after exposure.
  
  
  RESULTS
  Our results reveal that in non-proliferating cells under 2D and 3D cell culture conditions, iron-ion induced γ-H2AX foci were still present at 72 h after exposure, although 53BP1 foci returned to control levels at 48 h. In contrast in proliferating HMEC, both γ-H2AX and 53BP1 foci decreased to control levels during the 24-48 h time interval after irradiation under 2D conditions. Foci numbers decreased faster after γ-ray irradiation and returned to control levels by 12 h regardless of marker, cell proliferation status, and cell culture condition.
  
  
  CONCLUSIONS
  The disappearance of radiation-induced γ-H2AX and 53BP1 foci in HMEC has different dynamics that depend on radiation quality and proliferation status. Notably, the general patterns do not depend on the cell culture condition (2D versus 3D). We speculate that the persistent γ-H2AX foci in iron-ion irradiated non-proliferating cells could be due to limited availability of double-strand break (DSB) repair pathways in G0/G1-phase, or that repair of complex DSB requires replication or chromatin remodelling.
authors.affiliation: Lawrence Berkeley National Laboratory, Life Sciences Division, Department of Cancer and DNA Damage Responses, Berkeley, CA 94720, USA. tgroesser@lbl.gov
authors.forename: Torsten
authors.initials: T
authors.lastname: Groesser
authors.forename: Hang
authors.initials: H
authors.lastname: Chang
authors.forename: Gerald
authors.initials: G
authors.lastname: Fontenay
authors.forename: James
authors.initials: J
authors.lastname: Chen
authors.forename: Sylvain V
authors.initials: SV
authors.lastname: Costes
authors.forename: Mary
authors.initials: M
authors.lastname: Helen Barcellos-Hoff
authors.forename: Bahram
authors.initials: B
authors.lastname: Parvin
authors.forename: Bjorn
authors.initials: B
authors.lastname: Rydberg
mesh_terms: D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D005720:Gamma Rays; D020450:Heavy Ions; D006657:Histones / Q000378:metabolism*; D006801:Humans; D007501:Iron; D042361:Mammary Glands, Human / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: C468783:H2AX protein, human; D006657:Histones; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D007501:Iron