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Papers In Press, published online ahead of print March 3, 2008 J. Lipid Res., doi:10.1194/jlr.M700426-JLR200
Atherosclerosis Research Center, VA Healthcare System, Long Beach, Long Beach, CA 90822
Corresponding Author: linhua.zhang{at}va.gov;
Niacin is an effective agent for raising HDL, but its cellular target sites are largely unknown. We examined effects of niacin on the surface expression of ATP synthase ß chain, a newly described HDL/apoA-I receptor for HDL endocytosis, in HepG2 cells. Significant amount of immuno-detectable ß chain was observed on the surface of HepG2 cells, which was competitively displaced by apolipoprotain A-I. Niacin treatment reduced the surface expression of ß chain in HepG2 cells by ~27%, and decreased 125I-labeled HDL uptake up to ~35%. However, nicotinamide, a niacin metabolite that does not have clinical lipid effects, exhibited weaker inhibition on the ß chain cell surface expression, and failed to show inhibitory action on 125I-labeled HDL uptake. Furthermore, anti-ß chain antibody significantly reduced 125I-labeled HDL uptake, and abolished niacins inhibitory effect. Niacin did not change ß chain mRNA expression. These data suggest that niacin inhibits cell surface expression of the ATP synthase ß chain, leading to reduced hepatic removal of HDL protein, thus implicating a potential cellular target for niacin action to raise HDL.
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