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Journal of Lipid Research, Vol 29, 1215-1220, Copyright © 1988 by Lipid Research, Inc.
Apolipoprotein B synthesized by Hep G2 cells undergoes fatty acid acylation
JM Hoeg, MS Meng, R Ronan, SJ Demosky Jr, T Fairwell and HB Brewer Jr
Molecular Disease Branch, National Heart, Lung, and Blood Institute, Bethesda, MD 20892.
Apolipoprotein B is the principal protein associated with cholesterol
transport in the blood and has been proposed to play a central role in
human atherogenesis. The unique hydrophobic nature of this large (512 kDa),
glycosylated apolipoprotein differs from that of the other apolipoproteins.
Since another apolipoprotein, apolipoprotein A-I, has been recently shown
to have covalently bound fatty acids, potential fatty acid acylation of
apolipoprotein B was investigated. The human hepatoma cell line, Hep G2,
synthesizes apoB-100 and secretes the apolipoprotein into the culture
medium. After a 24-hr incubation with [14C]palmitate and [14C]stearate, the
label was incorporated into apoB- 100 when assessed by a sodium dodecyl
sulfate polyacrylamide gel electrophoresis, autoradiography, immunoblot
analysis, and immunoprecipitation. Hydroxylamine treatment, which
hydrolyzes ester and thioester bonds, removed the radiolabel. ApoB-100
isolated from Hep G2 cells by ultracentrifugation and preparative sodium
dodecyl sulfate gel electrophoresis was hydrolyzed and analyzed by
gas-liquid chromatography-mass spectrometry. In contrast to circulating
apoB in low density lipoproteins, both palmitate and stearate were present
in newly synthesized apoB-100. These results establish that newly
synthesized apoB-100 undergoes covalent acylation with palmitate and
stearate. The acylation of apoB may play an important role in lipoprotein
particle secretion. In addition, derangements in apoB fatty acid acylation
may lead to dyslipoproteinemia.

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Copyright © 1988 by the American Society for Biochemistry and Molecular Biology.
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