Role of ORPs in sterol transport from plasma membrane to ER and lipid droplets in mammalian cells.
In this study, we investigated the mechanisms of sterol transport from the plasma membrane (PM) to the endoplasmic reticulum (ER) and lipid droplets (LDs) in HeLa cells. By overexpressing all mammalian oxysterol-binding protein-related proteins (ORPs), we found that especially ORP1S and ORP2 enhanced PM-to-LD sterol transport. This reflected the stimulation of transport from the PM to the ER, rather than from the ER to LDs. Double knockdown of ORP1S and ORP2 inhibited sterol transport from the PM to the ER and LDs, suggesting a physiological role for these ORPs in the process. A two phenylalanines in an acidic tract (FFAT) motif in ORPs that mediates interaction with VAMP-associated proteins (VAPs) in the ER was not necessary for the enhancement of sterol transport by ORPs. However, VAP-A and VAP-B silencing slowed down PM-to-LD sterol transport. This was accompanied by enhanced degradation of ORP2 and decreased levels of several FFAT motif-containing ORPs, suggesting a role for VAPs in sterol transport by stabilization of ORPs.
Institute of Biomedicine, University of Helsinki, Finland.
Maurice
M
Jansen
Yuki
Y
Ohsaki
Laura Rita
LR
Rega
Robert
R
Bittman
Vesa M
VM
Olkkonen
Elina
E
Ikonen
D020816:Amino Acid Motifs; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D013261:Sterols / Q000378:metabolism*; D013329:Structure-Activity Relationship; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism; D000098825:Oxysterol Binding Proteins
D002352:Carrier Proteins; C461064:OSBPL2 protein, human; D011987:Receptors, Steroid; D013261:Sterols; C114051:VAPA protein, human; C496748:VAPB protein, human; D033921:Vesicular Transport Proteins; D000098825:Oxysterol Binding Proteins; D002784:Cholesterol