The relative function of the 15 and 13.2 kDa forms of SCP-2 in cholesterol trafficking and metabolism was assessed using L-cell fibroblasts permanently transfected with the cDNA encoding for either the mouse 15 kDa or 13.2 kDa SCP-2. Expression of the 15 kDa, but not the 13.2 kDa SCP-2 increased [3H]cholesteryl ester formation from medium derived cholesterol by 30% compared to control cells. In both SCP-2 expressing cell lines, sphingomyelinase treatment increased the initial rate of [3 H]cholesteryl ester formation from plasma membrane derived cholesterol more than 11-fold and elevated [3H]cholesteryl ester levels 1.5-fold compared to control cells. Expression of both proteins resulted in nearly a 1.5-fold increase in [3H]oleic acid esterification into cholesteryl esters, although [3H]oleic acid esterification into triacylglycerols was also increased in the 13.2 kDa SCP-2 expressing cells relative to control. In both transfected cell lines, the cholesteryl ester mass was increased nearly 2-fold compared to control cells, consistent with increased cholesteryl ester synthesis. Similarly, triacylglycerol levels were increased 1.3-fold in the 13.2 kDa SCP-2 expressing cells which is consistent with the increased [3H]oleic acid esterification into triacylglycerol. In the 15 kDa SCP-2 expressing cells, triacylglycerol levels were decreased 60%, but free cholesterol levels were increased 1.2-fold relative to control cells. Thus, only the 15 kDa expression product, containing the putative targeting sequence, specifically enhanced cholesteryl ester formation from either plasma membrane or medium-derived cholesterol. In contrast, the 13.2 kDa expression product, lacking the putative targeting sequence, stimulated an increase in [3H]oleic acid esterification into both cholesterol and triacylglycerol pools, suggesting a non-specific stimulation of fatty acid esterification.
