title: Different transport routes for high density lipoprotein and its associated free sterol in polarized hepatic cells.
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.
authors.affiliation: Department of Biochemistry, Weill Medical College of Cornell University, New York, NY 10021, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wüstner
authors.forename: Mousumi
authors.initials: M
authors.lastname: Mondal
authors.forename: Amy
authors.initials: A
authors.lastname: Huang
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Maxfield
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D045744:Cell Line, Tumor; D016764:Cell Polarity; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000378:metabolism; D004875:Ergosterol / Q000031:analogs & derivatives* / Q000378:metabolism; D005453:Fluorescence; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013261:Sterols / Q000378:metabolism*
chemical_list: D008075:Lipoproteins, HDL; D013261:Sterols; C010905:dehydroergosterol; D000255:Adenosine Triphosphate; D004875:Ergosterol