Oxysterol-binding protein-related protein 1 variants have opposing cholesterol transport activities from the endolysosomes

Mol Biol Cell. 2020 Apr 1;31(8):793-802. doi: 10.1091/mbc.E19-12-0697. Epub 2020 Feb 5.

Abstract

OSBPL1 encodes the full-length oxysterol-binding protein-related protein ORP1L, which transports LDL-derived cholesterol at membrane contacts between the late endosomes/lysosomes (LEL) and the endoplasmic reticulum (ER). OSBPL1 also encodes the truncated variant ORP1S that contains only the C-terminal lipid binding domain. HeLa cells in which both variants were knocked out (ORP1-null) were used to determine the functional relationship between ORP1L and ORP1S with respect to cellular cholesterol localization and regulation. ORP1-null cells accumulated cholesterol in LEL and had reduced plasma membrane (PM) cholesterol. PM cholesterol was restored by expression of wild-type ORP1S or a phosphatidylinositol phosphate-binding mutant but not by a sterol-binding mutant. Expression of ORP2, another truncated variant, also restored PM cholesterol in ORP1-null cells. Consistent with a LEL-to-PM cholesterol transport activity, a small fraction of ORP1S was detected on the PM. As a consequence of reduced delivery of cholesterol to the PM in ORP1-null cells, cholesterol was diverted to the ER resulting in normalization of de novo cholesterol synthesis. The deficiency in PM cholesterol also reduced ABCA1-dependent cholesterol efflux and LDL receptor activity in ORP1-null cells. We conclude that ORP1S, which lacks discrete membrane-targeting motifs, transports cholesterol from LEL to the PM.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter 1 / metabolism
  • Acetyl-CoA C-Acetyltransferase / metabolism
  • Amino Acid Motifs
  • Biological Transport
  • CRISPR-Cas Systems
  • Cell Membrane / metabolism
  • Cholesterol / metabolism*
  • Endoplasmic Reticulum / metabolism
  • Endosomes / metabolism*
  • HeLa Cells
  • Humans
  • Intracellular Membranes / metabolism
  • Lysosomes / metabolism*
  • Membrane Lipids / metabolism
  • Oxysterol Binding Proteins
  • Protein Domains
  • Protein Isoforms / metabolism
  • Receptors, LDL / metabolism
  • Receptors, Steroid / deficiency
  • Receptors, Steroid / genetics
  • Receptors, Steroid / metabolism*
  • Sequence Deletion

Substances

  • ABCA1 protein, human
  • ATP Binding Cassette Transporter 1
  • Membrane Lipids
  • Protein Isoforms
  • Receptors, LDL
  • Receptors, Steroid
  • Oxysterol Binding Proteins
  • Cholesterol
  • Acetyl-CoA C-Acetyltransferase

Grants and funding