Transport of Cholesterol from the Endoplasmic Reticulum to the Plasma Membrane

We have studied the transport of newly synthesized cholesterol from the endoplasmic reticulum to the plasma membrane in Chinese hamster ovary cells using a cell fractionation assay. We found that transport is dependent on metabolic energy, but that the maintenance of the high differential concentration of cholesterol in the plasma membrane is not an energy-requiring process. We have tested a variety of inhibitors for their effect on cholesterol transport and found that cytochalasin B, colchicine, monensin, cycloheximide, and NH4Cl did not have any effect. The cholesterol transport process shows a sharp temperature dependence; it ceases at 15°C, whereas cholesterol synthesis continues. When synthesis occurs at 15°C, the newly synthesized cholesterol accumulates in the endoplasmic reticulum and in a low density, lipid-rich vesicle fraction. These results suggest that cholesterol is transported via a vesicular system.