Sterol carrier protein-2 expression in mouse L-cell fibroblasts alters cholesterol uptake

Despite the progress made on the possible functions of sterol carrier protein (SCP-2) using assays in vitro, very little is known regarding the role of SCP-2 in intact cells. To further elucidate this role, mouse L-cell fibroblasts were transfected with cDNA encoding for mouse 15 kDa or 13.2 kDa SCP-2. The data show for the first time, that SCP-2 expression increases cholesterol uptake into transfected L-cell fibroblasts. Untransfected L-cells expressed SCP-2 at levels near or below the lower limit of detectability. SCP-2 immunoreactive protein levels were 0.030 +/- 0.004% and 0.036 +/- 0.002% of total cytosolic proteins in the 15 and 13.2 kDa stable transfectants, respectively. Both the 15 and 13.2 kDa SCP-2 expressions products were found as 13.2 kDa proteins, consistent with rapid post-translational cleavage of the putative amino terminal mitochondrial targeting sequence from the 15 kDa SCP-2. The effect of expressing either form of SCP-2 on [3H]cholesterol uptake was determined. Expression of the 15 kDa form, but not the 13.2 kDa form of SCP-2, enhanced the rate and extent of [3H]cholesterol uptake compared to control or mock-transfected L-cells. The [3H]cholesterol uptake rate in 15 kDa SCP-2 expressing cells was increased 1.3-fold, while the extent of [3H]cholesterol uptake was increased 1.4-fold after 12 h of uptake compared to control L-cells. The differences in cholesterol uptake between the cells expressing the 13.2 versus the 15 kDa protein, suggest that the 15 kDa form of SCP-2 is functionally localized within the cell, while the 13.2 kDa product is not.