Abstract

Phospholipids form the matrix of plasmamebranes (PM) consisting of an asymmetric lipid bilayer. The high amounts of sphingolipids and cholesterol in the PM are furthermore the basis to form liquid-ordered domains / rafts by saturated long chain fatty acid interactions. Hence, the lipid trafficking pathways enabling the membrane biogenesis and lateral segregation into membrane compounds remain largely undefined. Here we could demonstrate that the scavenger receptor CD36 selectively mediates the lipid uptake of sphingomyelin (SM) and phosphatidylcholine (PC) into PM in an endocytosis independent way. In human monocytes we could further show that the selective phospholipid uptake for SM, PC and phosphatidylethanolamine was almost exclusively promoted by CD36 and SR-BI. Whereas CD36 was mainly localized in rafts, we found about 2/3rds of SR-BI located in non-rafts. Thereby, the main cell entrance for phospholipids and cholesterol was mediated by SR-BI into non-raft compartments. SR-BI was then internalized by clathrin-coated pits and promoted the formation of intracellular microdomains in early endosomes by recruitment of the newly acquired raft lipids. Thus, we propose a leading role for SR-BI in generating new rafts by the incorporation of the raft building lipids SM and cholesterol. These may provide a pool for the regeneration of raft domains within the PM.