Apolipoprotein A-I stimulates the transport of intracellular cholesterol to cell-surface cholesterol-rich domains (caveolae)

We have studied the effect of lipid-free human plasma apolipoprotein A-1 (a poA-1) on the transport of newly synthesized cholesterol to cell-surface ch olesterol-rich domains, which in human skin fibroblasts are mainly represen ted by caveolae. Changes in transport of newly synthesized cholesterol were assessed after labelling cells with [C-14]acetate at 15 degreesC and warmi ng cells to permit the transfer of cholesterol, followed by the selective o xidation of cholesterol in cholesterol-rich domains (caveolae) in the plasm a membrane before their partial purification, ApoA-1, but not BSA added in an equimolar concentration, enhanced the transport of cholesterol to the ca veolae up to 5-fold in a dose- and time-dependent manner. The effect of apo A-1 on cholesterol transport exceeded its effect on cholesterol efflux, res ulting in an accumulation of intracellular cholesterol in caveolae. Methyl- beta -cyclodextrin, added at a concentration promoting cholesterol efflux t o the same extent as apoA-1, also stimulated cholesterol trafficking, but w as 3-fold less effective than apoA-1. Progesterone inhibited the transport of newly synthesized cholesterol to the caveolac. Treatment of cells with a poA-1 stimulated the expression of caveolin, increasing the amount of caveo lin protein and mRNA by approx. 2-fold. We conclude that apoA-1 induces the transport of intracellular cholesterol to cell-surface caveolac, possibly in part through the stimulation of caveolin expression.