Effect of a hypoxic enhancer on E-selectin promoter activity after retroviral delivery. Luciferase expression was measured in cells stably transfected with the retroviruses SEL and HRE-SEL. Cells were exposed to hypoxia (0.1% O2) and TNF-α (10 ng/ml) for 16 h. Values shown are the mean of six independent experiments. The differences between each culture condition are significant (P < 0.05). Differences between sEND cells and 3T3 are only significant in the case of the SEL, but not of the HRE-2-SEL infected cells. The absolute luciferase expression levels in sEND cells infected with SEL or HRE-2-SEL under normoxic conditions without TNF-α treatment are the same and normalised to a value of 1.