title: Chronic hypoxia decreases synthesis of homologous recombination proteins to offset chemoresistance and radioresistance.
abstract: Hypoxic and/or anoxic tumor cells can have increased rates of mutagenesis and altered DNA repair protein expression. Yet very little is known regarding the functional consequences of any hypoxia-induced changes in the expression of proteins involved in DNA double-strand break repair. We have developed a unique hypoxic model system using H1299 cells expressing an integrated direct repeat green fluorescent protein (DR-GFP) homologous recombination (HR) reporter system to study HR under prolonged chronic hypoxia (up to 72 h under 0.2% O(2)) without bias from altered proliferation, cell cycle checkpoint activation, or severe cell toxicity. We observed decreased expression of HR proteins due to a novel mechanism involving decreased HR protein synthesis. Error-free HR was suppressed 3-fold under 0.2% O(2) as measured by the DR-GFP reporter system. This decrease in functional HR resulted in increased sensitivity to the DNA cross-linking agents mitomycin C and cisplatin but not to the microtubule-interfering agent, paclitaxel. Chronically hypoxic H1299 cells that had decreased functional HR were relatively radiosensitive [oxygen enhancement ratio (OER), 1.37] when compared with acutely hypoxic or anoxic cells (OER, 1.96-2.61). Using CAPAN1 cells isogenic for BRCA2 and siRNA to RAD51, we confirmed that the hypoxia-induced radiosensitivity was due to decreased HR capacity. Persistent down-regulation of HR function by the tumor microenvironment could result in low-fidelity DNA repair and have significant implications for response to therapy and genetic instability in human cancers.
authors.affiliation: Princess Margaret Hospital (University Health Network), University of Toronto, Toronto, Ontario, Canada.
authors.forename: Norman
authors.initials: N
authors.lastname: Chan
authors.forename: Marianne
authors.initials: M
authors.lastname: Koritzinsky
authors.forename: Helen
authors.initials: H
authors.lastname: Zhao
authors.forename: Ranjit
authors.initials: R
authors.lastname: Bindra
authors.forename: Peter M
authors.initials: PM
authors.lastname: Glazer
authors.forename: Simon
authors.initials: S
authors.lastname: Powell
authors.forename: Abdellah
authors.initials: A
authors.lastname: Belmaaza
authors.forename: Brad
authors.initials: B
authors.lastname: Wouters
authors.forename: Robert G
authors.initials: RG
authors.lastname: Bristow
mesh_terms: D015687:Cell Hypoxia / Q000502:physiology*; D049109:Cell Proliferation; D002470:Cell Survival; D045643:DNA Repair Enzymes / Q000096:biosynthesis* / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D006801:Humans; D010100:Oxygen / Q000494:pharmacology*; D051135:Rad51 Recombinase / Q000096:biosynthesis / Q000378:metabolism; D011836:Radiation Tolerance / Q000187:drug effects; D011995:Recombination, Genetic / Q000187:drug effects / Q000502:physiology; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D045643:DNA Repair Enzymes; D010100:Oxygen