Chronic hypoxia decreases synthesis of homologous recombination proteins to offset chemoresistance and radioresistance.
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.
Chan
Norman
N
Princess Margaret Hospital (University Health Network), University of Toronto, Toronto, Ontario, Canada.
Koritzinsky
Marianne
M
Zhao
Helen
H
Bindra
Ranjit
R
Glazer
Peter M
PM
Powell
Simon
S
Belmaaza
Abdellah
A
Wouters
Brad
B
Bristow
Robert G
RG
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
C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D045643:DNA Repair Enzymes; D010100:Oxygen