A, effect of hypoxia and hypoxia mimics on MAPK activity. HeLa cells were maintained in normoxia or exposed to hypoxia (2% O2), Dfx (130 μM), or DOG (1 mM) for 6 h. 50 μg of whole cell lysates were applied to an SDS-PAGE. The total and activated ERK1/2 (pERK1/2) were measured by immunoblotting. B, effect of overexpression of MEK1 on HIF-1α activity and its responsiveness to hypoxia. 2 μg of pCMV.MEK1 or vector alone were co-transfected with 2 μg of pG4.H1α744–826 and 2 μg of pRR-Luc into HeLa cells in 100-mm culture dishes. 24 h after transfection, cells were trypsinized and evenly split into 12-well culture plates. 12 h after seeding, cells were switched to the indicated culture condition or exposed to the indicated chemicals for 6 h before analyses. Luciferase activity was normalized to co-transfected 0.5 μg of pCMV.β-gal. RLU, relative light units.