Caveolin-1-mediated apolipoprotein A-I membrane binding sites are not required for cholesterol efflux

PLoS One. 2011;6(8):e23353. doi: 10.1371/journal.pone.0023353. Epub 2011 Aug 12.

Abstract

Caveolin-1 (Cav1), a structural protein required for the formation of invaginated membrane domains known as caveolae, has been implicated in cholesterol trafficking and homeostasis. Here we investigated the contribution of Cav1 to apolipoprotein A-I (apoA-I) cell surface binding and intracellular processing using mouse embryonic fibroblasts (MEFs) derived from wild type (WT) or Cav1-deficient (Cav1(-/-)) animals. We found that cells expressing Cav1 have 2.6-fold more apoA-I binding sites than Cav1(-/-) cells although these additional binding sites are not associated with detergent-free lipid rafts. Further, Cav1-mediated binding targets apoA-I for internalization and degradation and these processes are not correlated to cholesterol efflux. Despite lower apoA-I binding, cholesterol efflux from Cav1(-/-) MEFs is 1.7-fold higher than from WT MEFs. Stimulation of ABCA1 expression with an LXR agonist enhances cholesterol efflux from both WT and Cav1(-/-) cells without increasing apoA-I surface binding or affecting apoA-I processing. Our results indicate that there are at least two independent lipid binding sites for apoA-I; Cav1-mediated apoA-I surface binding and uptake is not linked to cholesterol efflux, indicating that membrane domains other than caveolae regulate ABCA1-mediated cholesterol efflux.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter 1
  • ATP-Binding Cassette Transporters / metabolism
  • Algorithms
  • Animals
  • Apolipoprotein A-I / metabolism*
  • Binding Sites
  • Binding, Competitive
  • Biological Transport
  • Blotting, Western
  • Caveolin 1 / deficiency
  • Caveolin 1 / genetics
  • Caveolin 1 / metabolism*
  • Cell Membrane / metabolism*
  • Cells, Cultured
  • Cholesterol / metabolism*
  • Embryo, Mammalian / cytology
  • Fibroblasts / cytology
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism
  • Hydrocarbons, Fluorinated / pharmacology
  • Kinetics
  • Liver X Receptors
  • Membrane Microdomains / metabolism
  • Mice
  • Mice, Knockout
  • Orphan Nuclear Receptors / agonists
  • Protein Binding
  • Sulfonamides / pharmacology
  • Temperature

Substances

  • ATP Binding Cassette Transporter 1
  • ATP-Binding Cassette Transporters
  • Apolipoprotein A-I
  • Caveolin 1
  • Hydrocarbons, Fluorinated
  • Liver X Receptors
  • Orphan Nuclear Receptors
  • Sulfonamides
  • T0901317
  • Cholesterol