Phosphatidylinositide 3-kinase activity is required for stabilin-1-mediated endosomal transport of acLDL

Immunobiology. 2005;210(2-4):161-73. doi: 10.1016/j.imbio.2005.05.022.

Abstract

Stabilin-1 is a type 1 transmembrane receptor specifically expressed by tissue macrophages and sinusoidal endothelial cells. We recently demonstrated that stabilin-1 is involved in the endocytic/recycling pathway and shuttles between the endosomal system and the trans-Golgi network (TGN) in human macrophages. In the present study, we designed a model cell system to study the mechanisms of stabilin-1-mediated endocytosis. Using CHO-K1 cells stably transfected with stabilin-1, we demonstrated that acetylated low-density lipoprotein (acLDL) induces recruitment of stabilin-1 into the endocytic pathway. Stabilin-1 mediates internalisation of acLDL and its delivery to early endosomes, and it is translocated together with its ligand to the late endosomal compartment. Treatment with wortmannin, a specific inhibitor of phosphatidylinositide 3-kinase (PI3K), did not block stabilin-1 mediated internalisation of acLDL as well as its trafficking to early endosomes, whereas it induced enlargement of stabilin-1/acLDL positive endosomes as well as partial dissociation of EEA1 from these structures. The major effect of wortmannin was the abrogation of stabilin-1/acLDL trafficking into the late endocytic pathway. In stabilin-1 positive human type 2 macrophages, wortmannin treatment resulted in formation of both enlarged and small stabilin-1 positive endosomes. This effect, however, was significantly weaker in macrophages as compared to CHO-stabilin-1 cells. Our data indicate that PI3K activity is required for the transfer of stabilin-1 and its ligand acLDL from early to late endosomal compartments.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Androstadienes / pharmacology
  • Animals
  • Biological Transport / physiology
  • Blotting, Western
  • CHO Cells
  • Cricetinae
  • Endocytosis / drug effects
  • Endocytosis / physiology*
  • Endosomes / drug effects
  • Endosomes / metabolism*
  • Flow Cytometry
  • Humans
  • Lipoproteins, LDL / metabolism*
  • Macrophages / drug effects
  • Macrophages / metabolism*
  • Microscopy, Confocal
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Protein Kinase Inhibitors / pharmacology
  • Transfection
  • Wortmannin
  • trans-Golgi Network / metabolism

Substances

  • Androstadienes
  • Lipoproteins, LDL
  • Protein Kinase Inhibitors
  • acetyl-LDL
  • Phosphatidylinositol 3-Kinases
  • Wortmannin