Transport of cholesterol from the endoplasmic reticulum to the plasma membrane.

Abstract

We have studied the transport of newly synthesized cholesterol from the endo: plasmic 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 NH4CI 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.

On the relationship between the dual specificity of the bovine brain phosphatidylinositol transfer protein and membrane phosphatidylinositol levels

“…In chinese hamster ovary cells for instance, PC transport from the endoplasmic reticulum to the plasma membrane was shown to be extremely fast (halftime of 2 min at 25 o C), hardly temperature dependent, and not affected by energy poisons [7]. Cholesterol transport on the other hand, which is thought to occur by a vesicular mechanism, was found to be relatively slow (halftime of 26.5 min at 25 ° C), very temperature dependent and blocked by energy poisons [9]. A study on lipid transport in epithelial cells has indicated that the very rapid transport of PC and PI is in agreement with spontaneous, possibly protein-mediated, phospholipid transport rather than a membrane flow mechanism [10].…”

Nonvesicular Lipid Transfer from the Endoplasmic Reticulum

“…Both vesicular and nonvesicular lipid transport mediate intracellular lipid trafficking from the ER. Yet, inhibition of vesicular transport by pharmacological and genetic manipulations such as BFA or colchicine treatment, ATP depletion, and specific sec mutants (such as Sec18 mutant) has no effect on intracellular transport of certain lipid species (Kaplan and Simoni 1985b;Urbani and Simoni 1990;Heino et al 2000;Baumann et al 2005). Furthermore, imaging and biochemical studies using fluorescent lipid analogs, such as DHE (dehydroergosterol; a fluorescent cholesterol analog) and radioactive labels lipids, respectively, support the involvement of nonvesicular transport in intracellular lipid trafficking (Maxfield and Mondal 2006).…”

Dissecting the role of the Golgi complex and lipid rafts in biosynthetic transport of cholesterol to the cell surface

“…Transport of newly synthesized cholesterol from the ER to the plasma membrane has been shown to be temperature-dependent (12). We therefore tested whether the cyclodextrin extraction assay could be used to detect the inhibitory effect of 15°C incubation on cholesterol transport to the plasma membrane in BHK cells.…”

“…10). Instead, cholesterol transport from the ER to the cell surface was shown to be a rapid (t 1/2 ϭ 10-20 min), energy-and temperature-dependent process that bypasses the Golgi apparatus and does not require an intact cytoskeleton (10)(11)(12)(13). In addition, there is evidence that cytosolic carrier proteins, such as caveolin-1 (14,15) or sterol carrier protein-2 (16), may play a role in this process.…”