Scavenger receptor BI (SR-BI) mediates free cholesterol flux independentlyof HDL tethering to the cell surface

In addition to its effect on high density lipoprotein (HDL) cholesteryl est er (CE) uptake, scavenger receptor BI (SR-BI) was recently reported to stim ulate free cholesterol (FC) flux from Chinese hamster ovary (CHO) cells sta bly expressing mouse SR-BI, a novel function of SR-BI that may play a role in cholesterol removal from the vessel wall where the receptor can be found . It is possible that SR-BI stimulates flux simply by tethering acceptor HD L particles in close apposition to the cell surface thereby facilitating th e movement of cholesterol between the plasma membrane and HDL. To test this , we used transiently transfected cells and compared the closely related cl ass B scavenger receptors mouse SR-BI and rat CD36 for their ability to sti mulate cholesterol efflux as both receptors bind HDL with high affinity. Th e results showed that, although acceptor binding to SR-BI may contribute to efflux to a modest extent, the major stimulation of FC efflux occurs indep endently of acceptor binding to cell surface receptors, Instead our data in dicate that SR-BI mediates alterations to membrane FC domains which provoke enhanced bidirectional FC flux between cells and extracellular acceptors.- de la Llera-Moya, M., G. H. Rothblat, M. A. Connelly, G. Kellner-Weibel, S. W. Sakr, M. C. Phillips, and D. L. Williams. Scavenger receptor BI (SR-BI) mediates free cholesterol flux independently of HDL tethering to the cell surface.