Document Detail


Quantitative analysis of SR-BI-dependent HDL retroendocytosis in hepatocytes and fibroblasts.
MedLine Citation:
PMID:  16705213     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Previous studies have suggested that HDL retroendocytosis may play a role in scavenger receptor class B type I (SR-BI)-dependent selective lipid uptake in a cell-specific manner. To investigate this possibility, we developed methods to quantitatively measure HDL uptake and resecretion in fibroblast (COS-7) and hepatocyte (HepG2) cells expressing exogenous SR-BI. Approximately 17% and 24% of HDL associated in an SR-BI-dependent manner with COS-7 and HepG2 cells, respectively, accumulates intracellularly after a 10 min incubation. To determine whether this intracellular HDL undergoes retroendocytosis, we developed a pulse-chase assay whereby internalized biotinylated (125)I-HDL(3) secreted from cells is quantitatively precipitated from cell supernatants using immobilized streptavidin. Our results show a rapid secretion of a portion of intracellular HDL from both cell types (representing 4-7% of the total cell-associated HDL) that is almost complete within 30 min (half-life approximately 10 min). In COS-7 cells, the calculated rate of HDL secretion ( approximately 0.5 ng HDL/mg/min) was >30-fold slower than the rate of SR-BI-dependent selective cholesteryl ester (CE) uptake ( approximately 17 ng HDL/mg/min), whereas the rate of release of HDL from the cell surface ( approximately 19 ng HDL/mg/min) was similar to the rate of selective CE uptake. Notably, the rate of SR-BI-dependent HDL resecretion in COS-7 and HepG2 cells was similar. BLT1, a compound that inhibits selective CE uptake, does not alter the amount of SR-BI-mediated HDL retroendocytosis in COS-7 cells. From these data, we conclude that HDL retroendocytosis in COS-7 and HepG2 cells is similar and that the vast majority of SR-BI-dependent selective uptake occurs at the cell surface in both cell types.
Authors:
Bing Sun; Erik R M Eckhardt; Shoba Shetty; Deneys R van der Westhuyzen; Nancy R Webb
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2006-05-16
Journal Detail:
Title:  Journal of lipid research     Volume:  47     ISSN:  0022-2275     ISO Abbreviation:  J. Lipid Res.     Publication Date:  2006 Aug 
Date Detail:
Created Date:  2006-08-02     Completed Date:  2006-09-26     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0376606     Medline TA:  J Lipid Res     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1700-13     Citation Subset:  IM    
Affiliation:
Department of Internal Medicine, Graduate Center for Nutritional Sciences, University of Kentucky Medical Center, Lexington, 40536, USA.
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MeSH Terms
Descriptor/Qualifier:
Animals
Biotinylation
COS Cells
Cell Line, Tumor
Cercopithecus aethiops
Cholesterol Esters / metabolism
Endocytosis / physiology*
Fibroblasts / metabolism*
Hepatocytes / metabolism*
Humans
Lipid Metabolism
Lipoproteins, HDL / metabolism*,  secretion
Mice
Microscopy, Confocal
Scavenger Receptors, Class B / genetics,  metabolism*,  physiology
Grant Support
ID/Acronym/Agency:
HL-63763/HL/NHLBI NIH HHS
Chemical
Reg. No./Substance:
0/Cholesterol Esters; 0/Lipoproteins, HDL; 0/Scavenger Receptors, Class B

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