Expression of ABCA1-EGFP fusion proteins in HEK 293 cells. (A) Confocal sections of transiently transfected HEK 293 cells expressing wild-type ABCA1-EGFP (left) and ABCA1 R1925Q-EGFP (middle and right). EGFP fluorescence is shown in green and DAPI staining of nuclear DNA in blue. The mutation caused severe alteration in ABCA1 trafficking to the plasma membrane as compared to the wild type (WT). (B) HEK 293 cells expressing wild-type ABCA1-EGFP and ABCA1 R1925Q-EGFP were stained for SERCA 2 (red) as marker for the ER. The same confocal sections are shown for EGFP (green, left column), SERCA 2 (red, middle column) and colocalization of EGFP and SERCA 2 in the overlay (yellow, right column). Colocalization of ABCA1-SERCA2 was observed in cells transfected with mutant ABCA1, implying retention of R1925Q in the ER. In contrast, wild-type ABCA1-EGFP localized predominantly to the plasma membrane and no colocalization was detected. Scale bar indicates 10 μm.