The class B, type I scavenger receptor promotes the selective uptake of high density lipoprotein cholesterol ethers into caveolae

The uptake of cholesterol eaters from high density lipoproteins (HDLs) is c haracterized by the initial movement of cholesterol esters into a reversibl e plasma membrane pool. Cholesterol eaters are subsequently internalized to a nonreversible pool. Unlike the uptake of cholesterol from low density li poproteins, cholesterol ester uptake from HDL does not involve the internal ization and degradation of the particle and is therefore termed selective. The class B, type I scavenger receptor (SR-BI) has been identified as an HD L receptor and shown to mediate selective cholesterol ester uptake. SR-BI i s localized to cholesterol- and sphingomyelin-rich microdomains called cave olae, Caveolae are directly involved in cholesterol trafficking. Therefore, we tested the hypothesis that caveolae are accepters for HDL-derived chole sterol ether (CE), Our studies demonstrate that in Chinese hamster ovary ce lls expressing SR-BI, >80% of the plasma membrane associated CE is present in caveolae after 7.5 min of selective cholesterol ether uptake. We also sh ow that excess, unlabeled HDL can extract the radiolabeled CE from caveolae , demonstrating that caveolae constitute a reversible plasma membrane pool of CE. Furthermore, 50% of the caveolae-associated CE can be chased into a nonreversible pool. We conclude that caveolae are accepters for HDL-derived cholesterol ethers, and that caveolae constitute a reversible, plasma memb rane pool of cholesterol ethers.