The low-density lipoprotein receptor-related protein-1 associates transiently with lipid rafts

✍ Scribed by Lihua Wu; Steven L. Gonias

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 294 KB
• Volume: 96
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.20596

✦ Synopsis

Abstract

The low‐density lipoprotein receptor‐related protein‐1 (LRP‐1) is a multifunctional receptor that undergoes constitutive endocytosis and recycling. To identify LRP‐1 in lipid rafts, we biotin‐labeled cells using a membrane‐impermeable reagent and prepared Triton X‐100 fractions. Raft‐associated proteins were identified in streptavidin affinity‐precipitates of the Triton X‐100‐insoluble fraction. PDGF β‐receptor was identified exclusively in lipid rafts, whereas transferrin receptor was excluded. LRP‐1 distributed partially into rafts in murine embryonic fibroblasts (MEFs) and HT 1080 cells, but not in smooth muscle cells and CHO cells. LRP‐1 partitioning into rafts was not altered by ligands, including α~2~‐macroglobulin, platelet‐derived growth factor‐BB, and receptor‐associated protein (RAP). To examine LRP‐1 trafficking between membrane microdomains, we developed a novel method based on biotinylation and detergent fractionation. Association of LRP‐1 with rafts was transient; by 15 min, nearly all of the LRP‐1 that was initially raft‐associated exited this compartment. LRP‐1 in the Triton X‐100‐soluble fraction, which excludes lipid rafts, demonstrated complex kinetics, with phases reflecting import from rafts, endocytosis, and recycling. Potassium depletion blocked LRP‐1 endocytosis but did not inhibit trafficking of LRP‐1 from rafts into detergent‐soluble microdomains. Our data support a model in which LRP‐1 transiently associates with rafts but does not form a stable pool. Fluid movement of LRP‐1 between microdomains may facilitate its function in promoting the endocytosis of other plasma membrane proteins, such as the urokinase receptor, which localizes in lipid rafts. J. Cell. Biochem. © 2005 Wiley‐Liss, Inc.