Sterol carrier protein-2 is involved in cholesterol transfer from the endoplasmic reticulum to the plasma membrane in human fibroblasts

The cellular mechanism of Cholesterol transport from the endoplasmic reticulum to the plasma membrane is currently unknown. To assess the possibility that sterol carrier protein-2 (SCP-2) is involved in this transport, we studied the time course of newly synthesized Cholesterol incorporation in the plasma membrane of normal and SCP-2-deficient (Zellweger syndrome) human fibroblasts. Cholesterol transfer was rapid, cytoskeleton-independent, and Golgi-independent in normal cells, but it was slower, cytoskeleton-dependent, and Golgi-dependent in SCP-2-deficient cells. After SCP-2 Antisense Oligonucleotides treatment of normal fibroblasts, the rapid transport was reduced by 81% with a simultaneous increase of the slower one. These results suggest that in normal fibroblasts the major fraction of newly synthesized Cholesterol is transported to the plasma membrane by a SCP-2-dependent mechanism. In contrast, in SCP-2-deficient cells, newly synthesized Cholesterol leaves the endoplasmic reticulum by a Cytoskeleton/Golgi-dependent mechanism.