title: Chronic hypoxia compromises repair of DNA double-strand breaks to drive genetic instability.
abstract: Hypoxic cells have been linked to genetic instability and tumor progression. However, little is known about the exact relationship between DNA repair and genetic instability in hypoxic cells. We therefore tested whether the sensing and repair of DNA double-strand breaks (DNA-dsbs) is altered in irradiated cells kept under continual oxic, hypoxic or anoxic conditions. Synchronized G0-G1 human fibroblasts were irradiated (0-10 Gy) after initial gassing with 0% O(2) (anoxia), 0.2% O(2) (hypoxia) or 21% O(2) (oxia) for 16 hours. The response of phosphorylated histone H2AX (γ-H2AX), phosphorylated ataxia telangiectasia mutated [ATM(Ser1981)], and the p53 binding protein 1 (53BP1) was quantified by intranuclear DNA repair foci and western blotting. At 24 hours following DNA damage, residual γ-H2AX, ATM(Ser1981) and 53BP1 foci were observed in hypoxic cells. This increase in residual DNA-dsbs under hypoxic conditions was confirmed using neutral comet assays. Clonogenic survival was also reduced in chronically hypoxic cells, which is consistent with the observation of elevated G1-associated residual DNA-dsbs. We also observed an increase in the frequency of chromosomal aberrations in chronically hypoxic cells. We conclude that DNA repair under continued hypoxia leads to decreased repair of G1-associated DNA-dsbs, resulting in increased chromosomal instability. Our findings suggest that aberrant DNA-dsb repair under hypoxia is a potential factor in hypoxia-mediated genetic instability.
authors.affiliation: Ontario Cancer Institute, Princess Margaret Hospital (University Health Network), Toronto, Ontario, Canada.
authors.forename: Ramya
authors.initials: R
authors.lastname: Kumareswaran
authors.forename: Olga
authors.initials: O
authors.lastname: Ludkovski
authors.forename: Alice
authors.initials: A
authors.lastname: Meng
authors.forename: Jenna
authors.initials: J
authors.lastname: Sykes
authors.forename: Melania
authors.initials: M
authors.lastname: Pintilie
authors.forename: Robert G
authors.initials: RG
authors.lastname: Bristow
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D015687:Cell Hypoxia; D002470:Cell Survival; D064447:Checkpoint Kinase 2; D043171:Chromosomal Instability; D002869:Chromosome Aberrations; D020552:Comet Assay; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism; D005347:Fibroblasts; D016193:G1 Phase; D006657:Histones / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016192:Resting Phase, Cell Cycle; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D000071857:Tumor Suppressor p53-Binding Protein 1
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D047908:Intracellular Signaling Peptides and Proteins; C498301:TP53BP1 protein, human; D025521:Tumor Suppressor Proteins; D000071857:Tumor Suppressor p53-Binding Protein 1; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases