Abstract
Oxygen availability has important effects on cell physiology. Although hyperoxic and hypoxic stresses have been well characterized, little is known about cellular functions in the oxygen levels commonly found in vivo. Here, we show that p53-dependent apoptosis in response to different DNA-damaging agents was reduced when normal and cancer cells were cultured at physiological oxygen tensions instead of the usual atmospheric levels. Different from what has been described in hypoxia, this was neither determined by decreases in p53 induction or its transactivation activity, nor by differences in the intracellular accumulation of reactive oxygen species. At these physiological oxygen levels, we found a constitutive activation of the ERK1/2 MAPK in all the models studied. Inhibition of this signaling pathway reversed the protective effect in some but not all cell lines. We conclude that a stress-independent constitutive activation of prosurvival pathways, including but probably not limited to MAPK, can protect cells in physiological oxygen tensions against genotoxic stress. Our results underscore the need of considering the impact of oxygen levels present in the tissue microenvironment when studying cell sensitivity to treatments such as chemotherapy and radiotherapy.
Highlights
Changes in oxygen levels are known to affect the life span of cultured cells
All of this suggests that low oxygen levels are beneficial for cells as long as they remain above the threshold of severe hypoxia and highlights the importance of studying cells in environments that are similar to those found in live tissues in the absence of stress or disease
We concluded that variations in the induction or the activity of p53 after DNA damage were not responsible for the reduction in apoptosis observed at 5% O2, which further stresses the differences between physiologically low oxygen tensions and hypoxia
Summary
Cell Culture—Cells were maintained in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum and penicillin-streptomycin (50 units/ml). IMR90 expressing a dominant negative p53 (IMR90 DNp53) were obtained using a R248W mutant of p53 subcloned with BamHI/AscI into a pBABE vector, as described [15]. Amphotropic virus stocks were generated by transient.
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