Fig. 1.

Hypoxia stimulates proliferation of A549 cells. A: DNA synthesis was evaluated in A549 cells by the Click-iT EdU Assay on days 0, 1, 3, and 5 of exposure to normoxia or hypoxia (1% O₂). Fresh 5-ethynyl-2′-deoxyuridine (EdU; 10 μm) was added to the culture medium 24 h before each time point/EdU fluorescence measurement. EdU incorporation values are expressed as means ± SE from 3 independent experiments with 8 wells per condition. *P < 0.001, compared with day 0; **P < 0.001, compared with day 3 normoxia and day 1 hypoxia; #P < 0.001, compared with day 5 normoxia and day 3 hypoxia. B: cells exposed to either normoxia or hypoxia (1% O₂) for up to 5 days, were trypsinized, and enumerated hemocytometrically on days 0, 1, 3, and 5 of exposure. *P < 0.05, compared with say 0; **P < 0.05, compared with day 3 normoxia; #P < 0.05, compared with day 5 normoxia.