High levels of homocysteine downregulate apolipoprotein E expression via nuclear factor kappa B

Figure 2 Homocysteine inhibits the activity of apolipoprotein E proximal promoter in either absence or presence of ME2 in RAW 264. 7 macrophages and HEK-293 cells. Transient transfection experiments were performed using (-500/+73) apoE proximal promoter (A, C) or ME2/(-500/+73) multienhancer/apoE promoter constructs (B, D) driving the luciferase reporter and the transfected cells were incubated with 50-500 μmol/L homocysteine for 24 h. Then, luciferase activity was assessed and normalized to the activity of the co-transfected β-galactosidase. Treatment of RAW 264.7 (A, B) and HEK-293 cells (C, D) with 500 μmol/L Hcy significantly decreased (^aP < 0.05 or ^bP< 0.01) apoE promoter activity, in the presence (B, D) or in the absence of ME2 (A, C). Low concentrations of Hcy (50 μmol/L) did not considerably decrease (P > 0.05) the activity of apoE promoter either in the absence (A, C) or in the presence of ME2 (B, D). MEK1/2: MAPK/ERK kinase; Hcy: Homocysteine; ApoE: Apolipoprotein E.