Expression of normoxic and hypoxic EPAS-1 and HIF-1α protein in six human cell lines. Cells were cultured in parallel in normoxia (N) or 1% oxygen (H) for 4 hours. Whole-cell extracts (50 μg) were analyzed for EPAS-1 (MoAb 190b, top) and HIF-1α (MoAb 28b, bottom). Exposure time was 30 seconds for EPAS-1 and 120 seconds for HIF-1α, so that sensitivity of detection for the two proteins is approximately equal. The HeLa(B) hypoxic extract was independently shown to contain approximately equal amounts of EPAS-1 and HIF-1α by direct comparison with transfected COS-1 cell extracts.