title: ERCC1/ERCC4 5'-endonuclease activity as a determinant of hypoxic cell radiosensitivity.
abstract: In this study, the relationships between cellular oxygen enhancement ratios (OER) and nucleotide excision repair capability were examined using the UV20 mutant cell line (which has a defective ERCC1 gene). Using a clonogenic survival assay, the OER for the killing of wild-type AA8 cells was 3.2 +/- 0.1, whereas that for UV20 cells was only 2.35 +/- 0.05; the decreased OER of UV20 cells was the result of their significantly greater radiosensitivity relative to wild-type cells under hypoxic conditions. In AA8 cells, hypoxia protected against DNA double-strand break (dsb) induction (determined by pulsed-field gel electrophoresis) by a factor 3.5 +/- 0.3; i.e. to a similar extent that it modulated cell killing. However, this correlation was not apparent in UV20 cells, where hypoxia protected against dsb induction to a similar extent as in wild-type cells (approximately 3.2-fold). Stably transfected UV20 cells over-expressing a full-length ERCC1 cDNA clone displayed a normal OER (3.5 +/- 0.1) in addition to wild-type resistance to UV light. Our data suggest that the hypoxic radiosensitivity of UV20 cells is a direct result of their ERCC1 deficiency and reflects their inability to process some type of DNA damage (not dsbs) that is induced preferentially in hypoxic cells.
authors.affiliation: Radiobiology Program, Cross Cancer Institute, Edmonton, Alberta, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Murray
authors.forename: A
authors.initials: A
authors.lastname: Macann
authors.forename: J
authors.initials: J
authors.lastname: Hanson
authors.forename: E
authors.initials: E
authors.lastname: Rosenberg
mesh_terms: D000818:Animals; D016466:CHO Cells; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D003114:Colony-Forming Units Assay; D006224:Cricetinae; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D004720:Endonucleases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011836:Radiation Tolerance / Q000235:genetics / Q000502:physiology*; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; D011506:Proteins; C095888:xeroderma pigmentosum group F protein; C071447:ERCC1 protein, human; D004720:Endonucleases; D010100:Oxygen