Ligand-dependent localization and function of ORP-VAP complexes at membrane contact sites

Cell Mol Life Sci. 2015 May;72(10):1967-87. doi: 10.1007/s00018-014-1786-x. Epub 2014 Nov 25.

Abstract

Oxysterol-binding protein/OSBP-related proteins (ORPs) constitute a conserved family of sterol/phospholipid-binding proteins with lipid transporter or sensor functions. We investigated the spatial occurrence and regulation of the interactions of human OSBP/ORPs or the S. cerevisiae orthologs, the Osh (OSBP homolog) proteins, with their endoplasmic reticulum (ER) anchors, the VAMP-associated proteins (VAPs), by employing bimolecular fluorescence complementation and pull-down set-ups. The ORP-VAP interactions localize frequently at distinct subcellular sites, shown in several cases to represent membrane contact sites (MCSs). Using established ORP ligand-binding domain mutants and pull-down assays with recombinant proteins, we show that ORP liganding regulates the ORP-VAP association, alters the subcellular targeting of ORP-VAP complexes, or modifies organelle morphology. There is distinct protein specificity in the effects of the mutants on subcellular targeting of ORP-VAP complexes. We provide evidence that complexes of human ORP2 and VAPs at ER-lipid droplet interfaces regulate the hydrolysis of triglycerides and lipid droplet turnover. The data suggest evolutionarily conserved, complex ligand-dependent functions of ORP-VAP complexes at MCSs, with implications for cellular lipid homeostasis and signaling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amine Oxidase (Copper-Containing) / metabolism*
  • Cell Adhesion Molecules / metabolism*
  • Cell Line, Tumor
  • Endoplasmic Reticulum / metabolism*
  • Fluorescent Antibody Technique
  • Genetic Complementation Test
  • Humans
  • Hydrolysis
  • Lipid Droplets / metabolism*
  • Microscopy, Electron, Transmission
  • Microscopy, Fluorescence
  • Multiprotein Complexes / metabolism*
  • RNA Interference
  • Receptors, Steroid / metabolism*
  • Recombinant Proteins / metabolism*
  • Triglycerides / metabolism*
  • Yeasts

Substances

  • Cell Adhesion Molecules
  • Multiprotein Complexes
  • OSBPL2 protein, human
  • Receptors, Steroid
  • Recombinant Proteins
  • Triglycerides
  • AOC3 protein, human
  • Amine Oxidase (Copper-Containing)