d-cer-C6 treatment alters Golgi membrane organization. (A) HeLa cells expressing mannosidase II–GFP (MannII-GFP) were treated with ethanol, 20 µM l-cer-C6, or 20 µM d-cer-C6 for 4 h. The localization of the Golgi markers mannosidase II–GFP and GRASP65 was monitored by immunofluorescence microscopy. (B) HeLa cells were treated with ethanol, 20 µM l-cer-C6, or 20 µM d-cer-C6 for 4 h, and the localization of the TGN markers p230 and TGN46 was monitored by immunofluorescence microscopy. (C) HeLa cells were transfected with sialyltransferase-GFP (ST-GFP) and treated with ethanol, 20 µM l-cer-C6, or 20 µM d-cer-C6 for 4 h. The localization of ST-GFP and TGN46 was monitored by immunofluorescence microscopy. (D) Quantitation of the relative colocalization of the different proteins in the experiments shown in A–C, as measured by the Pearson’s correlation coefficient between the green and red channels. Bars show the mean values ± SEM of ≥10 cells counted from three independent experiments. Bars, 5 µm. **, P < 0.01.