The LXR/RXR heterodimer activates the apoE ME.1 and ME.2 enhancers.
(A) LXRα/RXRα activates the −890-bp apoE proximal
promoter fused to either ME.1 or ME.2. HepG2 cells were transfected
with pGL-890, pGL-890-ME.1, or pGL-890-ME.2 with or without CMX-mLXRα
and CMX-RXRα and CMV-β-galactosidase. After transfection, cells
were incubated for 24 h in MEM supplemented with 10% (vol/vol)
LPDS and 22(R)HC (5.0 μg/ml), LG268 (50 nM), or
vehicle control. Luciferase activity was normalized for transfection
efficiency with the use of β-galactosidase activity. The data are
expressed as fold activation in the presence of the indicated ligand
versus in the absence of ligand and represent the average of triplicate
experiments. (B) VP16-LXRα activates the apoE proximal
promoter fused to either ME.1 or ME.2. Transient transfections were
performed by using CMX-VP16-LXRα and CMX-RXRα as indicated. The
results are shown as normalized luciferase units. (C)
ME.1 and ME.2 function as LXRα/RXR-responsive enhancers when fused
to a heterologous promoter. Transfections were performed with the use
of pTK-Luc, pTK-ME.1-Luc, or pTK-ME.2-Luc reporters. (D)
ME.1 and ME.2 are activated by VP16-LXRα. Transfections were
performed with the use of pTK-Luc, pTK-ME.1-Luc, or pTK-ME.2-Luc along
with CMX-VP16-LXRα and CMX-RXRα.