The lysosomal lipid transporter LIMP-2 is part of lysosome-ER STARD3-VAPB-dependent contact sites

Abstract

LIMP-2 (also known as SCARB2) is an abundant lysosomal membrane protein. Previous studies have shown that LIMP-2 functions as a virus receptor, a chaperone for lysosomal enzyme targeting and a lipid transporter. The large luminal domain of LIMP-2 contains a hydrophobic tunnel that enables transport of phospholipids, sphingosine and cholesterol from the lysosomal lumen to the membrane. The question about the fate of the lipids after LIMP-2-mediated transport is largely unexplored. To elucidate whether LIMP-2 is present at contact sites between lysosomes and the endoplasmic reticulum (ER), we performed a proximity-based interaction screen. This revealed that LIMP-2 interacts with the endosomal protein STARD3 and the ER-resident protein VAPB. Using imaging and co-immunoprecipitation, we demonstrated colocalization and physical interaction between LIMP-2 and these proteins. Moreover, we found that interaction of LIMP-2 with VAPB required the presence of STARD3. Our findings suggest that LIMP-2 is present at ER-lysosome contact sites, possibly facilitating cholesterol transport from the lysosomal to the ER membrane. This suggests a novel mechanism for inter-organelle communication and lipid trafficking mediated by LIMP-2.

Keywords: ER–lysosome contact sites; Endoplasmic reticulum; LIMP-2; Lipid transport; Lysosome; Membrane contact sites; SCARB2; STARD3; VAPB.