Characterization of induction of EPAS-1 and HIF-1α by hypoxia. Immunoblots of HeLa(B) cell whole-cell extracts (100 μg) with MoAb 190b (upper panels) and MoAb 28b (lower panels). (A) Cells were exposed to 1% oxygen for 30 to 180 minutes. (B) Cells were exposed to normoxia or 1% oxygen for 2 to 48 hours. (C) Cells were incubated in normoxia (N) or 1% oxygen (H) for 16 hours and harvested at different times following return to normoxia (Reoxygenation). (D) Cells were seeded at different densities and cultured under normoxic conditions. (E) Cells on gas-permeable dishes were exposed to different oxygen concentrations or 100 μmol/L DFO for 6 hours.