Multimerization and Retention of the Scavenger Receptor SR-B1 in the Plasma Membrane

• Published in: Developmental cell 2019-08, Vol.50 (3), p.283-295.e5
• Main Authors: Marques, Pedro E., Nyegaard, Steffen, Collins, Richard F., Troise, Fulvia, Freeman, Spencer A., Trimble, William S., Grinstein, Sergio
• Format: Article
• Language: English
• Subjects: Actin Cytoskeleton - metabolism; adrenal gland; Animals; atherosclerosis; Cell Membrane - metabolism; CHO Cells; cholesterol; Cricetinae; Cricetulus; Endocytosis; HDL; Hep G2 Cells; Humans; Leucine Zippers; liver; multimerization; Mutation; Protein Multimerization; retention; scavenger receptor; Scavenger Receptors, Class B - chemistry; Scavenger Receptors, Class B - genetics; Scavenger Receptors, Class B - metabolism; SR-B1
• ISSN: 1534-5807; 1878-1551
• DOI: 10.1016/j.devcel.2019.05.026

Scavenger receptor B1 (SR-B1), the main receptor for high-density lipoprotein (HDL), is key in preventing atherosclerosis. It removes cholesterol from HDL, returning the lipid-poor lipoprotein to the circulation. To study the mechanisms controlling SR-B1 dynamics at the plasma membrane and its internalization rate, we developed a single-chain variable fragment (ScFv) antibody to image the receptor in live cells and track the behavior of single SR-B1 molecules. Unlike transferrin receptors, cholera-toxin-binding gangliosides, and bulk membrane markers, SR-B1 was internalized only marginally over hours. Plasmalemmal retention was not attributable to its C-terminal PDZ-binding domain or to attachment to the cortical cytoskeleton. Instead, SR-B1 undergoes multimerization into large metastable clusters that, despite being mobile in the membrane, fail to enter endocytic pathways. SR-B1 multimerization was impaired by mutating its C-terminal leucine zipper and by disrupting actin polymerization, causing rapid receptor internalization. Multimerization and plasmalemmal retention are critical for SR-B1 function. [Display omitted] •SR-B1 behavior and internalization were assessed in live cells using an ScFv antibody•SR-B1 is retained at the plasma membrane of cells for several hours•Extensive SR-B1 multimerization allows the receptor to evade endocytosis•Disruption of multimerization impairs HDL binding and SR-B1 function at the membrane Marques et al. show that SR-B1, the main receptor for HDL, undergoes multimerization at the plasma membrane. Multimerization allows the receptor to evade endocytosis and is essential for selective lipid uptake from HDL. Multimerization and retention require the C-terminal leucine zipper of SR-B1 and an intact actin cytoskeleton.