Endocytosis of apolipoprotein A-V by members of the low density lipoprotein receptor and the VPS10p domain receptor families

J Biol Chem. 2008 Sep 19;283(38):25920-7. doi: 10.1074/jbc.M802721200. Epub 2008 Jul 3.

Abstract

Apolipoprotein A-V (apoA-V) is present in low amounts in plasma and has been found to modulate triacylglycerol levels in humans and in animal models. ApoA-V displays affinity for members of the low density lipoprotein receptor (LDL-R) gene family, known as the classical lipoprotein receptors, including LRP1 and SorLA/LR11. In addition to LDL-A binding repeats, the mosaic receptor SorLA/LR11 also possesses a Vps10p domain. Here we show that apoA-V also binds to sortilin, a receptor from the Vsp10p domain gene family that lacks LDL-A repeats. Binding of apoA-V to sortilin was competed by neurotensin, a ligand that binds specifically to the Vps10p domain. To investigate the biological fate of receptor-bound apoA-V, binding experiments were conducted with cultured human embryonic kidney cells transfected with either SorLA/LR11 or sortilin. Compared with nontransfected cells, apoA-V binding to SorLA/LR11- and sortilin-expressing cells was markedly enhanced. Internalization experiments, live imaging studies, and fluorescence resonance energy transfer analyses demonstrated that labeled apoA-V was rapidly internalized, co-localized with receptors in early endosomes, and followed the receptors through endosomes to the trans-Golgi network. The observed decrease of fluorescence signal intensity as a function of time during live imaging experiments suggested ligand uncoupling in endosomes with subsequent delivery to lysosomes for degradation. This interpretation was supported by experiments with (125)I-labeled apoA-V, demonstrating clear differences in degradation between transfected and nontransfected cells. We conclude that apoA-V binds to receptors possessing LDL-A repeats and Vsp10p domains and that apoA-V is internalized into cells via these receptors. This could be a mechanism by which apoA-V modulates lipoprotein metabolism in vivo.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Vesicular Transport
  • Animals
  • Apolipoprotein A-V
  • Apolipoproteins A / chemistry*
  • CHO Cells
  • Cricetinae
  • Cricetulus
  • Endocytosis
  • Golgi Apparatus / metabolism
  • Humans
  • Kidney / embryology*
  • LDL-Receptor Related Proteins / chemistry*
  • Membrane Glycoproteins / chemistry
  • Membrane Transport Proteins / chemistry*
  • Nerve Tissue Proteins / chemistry
  • Protein Binding
  • Protein Structure, Tertiary
  • Receptors, Cell Surface / chemistry*
  • Receptors, LDL / chemistry*

Substances

  • APOA5 protein, human
  • Adaptor Proteins, Vesicular Transport
  • Apolipoprotein A-V
  • Apolipoproteins A
  • LDL-Receptor Related Proteins
  • Membrane Glycoproteins
  • Membrane Transport Proteins
  • Nerve Tissue Proteins
  • Receptors, Cell Surface
  • Receptors, LDL
  • SORL1 protein, human
  • sortilin