Different transport routes for high density lipoprotein and its associated free sterol in polarized hepatic cells

J Lipid Res. 2004 Mar;45(3):427-37. doi: 10.1194/jlr.M300440-JLR200. Epub 2003 Dec 16.

Abstract

We analyzed the intracellular transport of HDL and its associated free sterol in polarized human hepatoma HepG2 cells. Using pulse-chase protocols, we demonstrated that HDL labeled with Alexa 488 at the apolipoprotein (Alexa 488-HDL) was internalized by a scavenger receptor class B type I (SR-BI)-dependent process at the basolateral membrane and became enriched in a subapical/apical recycling compartment. Most Alexa 488-HDL was rapidly recycled to the basolateral cell surface and released from cells. Within 30 min of chase at 37 degrees C, approximately 3% of the initial cell-associated Alexa 488-HDL accumulated in the biliary canaliculus (BC) formed at the apical pole of polarized HepG2 cells. Even less Alexa 488-HDL was transported to late endosomes or lysosomes. The fluorescent cholesterol analog dehydroergosterol (DHE) incorporated into Alexa 488-HDL was delivered to the BC within a few minutes, independent of the labeled apolipoprotein. This transport did not require metabolic energy and could be blocked by antibodies against SR-BI. The fraction of cell-associated DHE transported to the BC was comparable when cells were incubated with either Alexa 488-HDL containing DHE or with DHE bound to methyl-beta-cyclodextrin. We conclude that rapid, nonvesicular transport of sterol to the BC and efficient recycling of HDL particles underlies the selective sorting of sterol from HDLs in hepatocytes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphate / pharmacology
  • Biological Transport / drug effects
  • Cell Line, Tumor
  • Cell Polarity*
  • Endocytosis / drug effects
  • Endosomes / metabolism
  • Ergosterol / analogs & derivatives*
  • Ergosterol / metabolism
  • Fluorescence
  • Hepatocytes / cytology*
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism*
  • Humans
  • Kinetics
  • Lipoproteins, HDL / metabolism*
  • Lysosomes / metabolism
  • Spectrometry, Fluorescence
  • Sterols / metabolism*

Substances

  • Lipoproteins, HDL
  • Sterols
  • dehydroergosterol
  • Adenosine Triphosphate
  • Ergosterol