title: Endocytosis is not required for the selective lipid uptake mediated by murine SR-BI.
abstract: The scavenger receptor class B, type I (SR-BI) mediates the cellular selective uptake of cholesteryl esters and other lipids from high-density lipoproteins (HDL) and low-density lipoproteins (LDL). This process, unlike classical receptor-mediated endocytosis, does not result in lipoprotein degradation. Instead, the lipid depleted particles are released into the medium. Here we show that selective lipid uptake mediated by murine SR-BI can be uncoupled from the endocytosis of HDL or LDL particles. We found that blocking selective lipid uptake by incubating cells with the small chemical inhibitors BLT-1 or BLT-4 did not affect endocytosis of HDL. Similarly, blocking endocytosis by hyperosmotic sucrose or K+ depletion did not prevent selective lipid uptake from HDL or LDL. These findings suggest that mSR-BI-mediated selective uptake occurs at the cell surface upon the association of lipoproteins with mSR-BI and does not require endocytosis of HDL or LDL particles.
authors.affiliation: Department of Cell Biology, Harvard Medical School and The CBR Institute for Biomedical Research, 200 Longwood Avenue, Room 134, Boston, MA 02115, USA.
authors.forename: Thomas J F
authors.initials: TJ
authors.lastname: Nieland
authors.forename: Marcelo
authors.initials: M
authors.lastname: Ehrlich
authors.forename: Monty
authors.initials: M
authors.lastname: Krieger
authors.forename: Tomas
authors.initials: T
authors.lastname: Kirchhausen
mesh_terms: D000818:Animals; D018955:CD36 Antigens; D016466:CHO Cells; D006224:Cricetinae; D004705:Endocytosis / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D050356:Lipid Metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D051379:Mice; D009281:Naphthalenes / Q000494:pharmacology*; D009997:Osmotic Pressure / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism*; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D013395:Sucrose / Q000494:pharmacology; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: C496792:(1-(2-methoxy-phenyl)-3-naphthalen-2-yl-urea); D018955:CD36 Antigens; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D009281:Naphthalenes; D011971:Receptors, Immunologic; D051116:Receptors, Scavenger; C495124:SCARB1 protein, human; D051122:Scavenger Receptors, Class B; D013395:Sucrose; D014508:Urea; D011188:Potassium