Effects of overexpression of the amino-terminal fragment of apolipoprotein B on apolipoprotein B and lipoprotein production

Abstract

In vitro studies have shown that the binding site for microsomal triglyceride transfer protein (MTP) is within the first 17% of apoB (apoB-17). Expression of apoB-48 in McArdle cells decreases endogenous lipoprotein production; however, overexpression of human apoB in transgenic mice does not decrease endogenous mouse apoB expression. To assess this inconsistency, adenoviruses expressing human apoB-17 (AdB17) or apoB-17-β (which contains apoB-17 plus a small lipid-binding β-sheet region of apoB, AdB-17β) were produced. Hepatoma cells were infected with AdB17 or AdB17-β with AdLacZ, an adenovirus expressing β-galactosidase, as a control. Overexpression of apoB-17 and apoB-17-β in hepatoma cells to levels 2- to 3-fold greater than that of endogenous apoB did not alter endogenous apoB production. This was also true in the presence of oleic acid and N-acetyl-leucyl-leucyl-norleucinal. High levels of apoB-17 or β-galactosidase expression reduced apoB-100 production; however, control protein production was also reduced. To assess the effects of apoB-17 expression in vivo, mice of three different strains were injected with AdB17. Two days after injection, plasma apoB-17 was approximately 24 times the amount of endogenous apoB in the C57BL/6 mice, 2 times the apoB-100 in human apoB transgenic mice, and 4 times the apoB-48 in apoE knockout mice. Overexpression of apoB-17 did not decrease apoB-100 or apoB-48 concentrations in mouse plasma as assessed by Western blot analysis. These results demonstrate that although the apoB-17 binds to MTP in vitro, it does not alter endogenous apoB expression in mice or in hepatoma cells.—Li, Z., Y. Kako, L. Pang, M. W. Freeman, J. M. Glick, X. Wang, and I. J. Goldberg. Effects of overexpression of the amino-terminal fragment of apolipoprotein B on apolipoprotein B and lipoprotein production. J. Lipid Res. 2000. 41: 1912–1920.

Keywords

• adenovirus
• microsomal triglyceride transfer protein
• lipoprotein lipase
• very low density lipoproteins
• chylomicrons