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Journal of Lipid Research, Vol. 49, 1195-1201, June 2008
Copyright © 2008 by American Society for Biochemistry and Molecular Biology

Niacin inhibits surface expression of ATP synthase β chain in HepG2 cells: implications for raising HDL

Lin-Hua Zhang¹, Vaijinath S. Kamanna, Michael C. Zhang and Moti L. Kashyap¹

Atherosclerosis Research Center, Veterans Administration Healthcare System, Long Beach, CA; and Department of Medicine, University of California, Irvine, CA

This study was supported by grants from the Southern California Institute for Research and Education.

Published, JLR Papers in Press, March 3, 2008.

¹ To whom correspondence should be addressed. e-mail: Linhua.zhang{at}va.gov (L-H.Z.); Moti.Kashyap{at}va.gov (M.L.K.)

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 β chain, a newly described HDL/apolipoprotein A-I (apoA-I) receptor for HDL endocytosis, in HepG2 cells. A significant amount of immunodetectable β chain was observed on the surface of HepG2 cells, which was competitively displaced by apoA-I. Niacin treatment reduced the surface expression of β 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 β chain cell surface expression, and failed to show inhibitory action on ¹²⁵I-labeled HDL uptake. Furthermore, anti-β chain antibody significantly reduced ¹²⁵I-labeled HDL uptake and abolished the inhibitory effect of niacin. Niacin did not change β chain mRNA expression. These data suggest that niacin inhibits cell surface expression of the ATP synthase β chain, leading to reduced hepatic removal of HDL protein, thus implicating a potential cellular target for niacin action to raise HDL.

Supplementary key words hepatocytes • HDL receptor • nicotinic acid • flow cytometry

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