Effects of overexpression of the amino-terminal fragment of apolipoprotein B on apolipoprotein B and lipoprotein production.
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-beta (which contains apoB-17 plus a small lipid-binding beta-sheet region of apoB, AdB-17beta) were produced. Hepatoma cells were infected with AdB17 or AdB17-beta with AdLacZ, an adenovirus expressing beta-galactosidase, as a control. Overexpression of apoB-17 and apoB-17-beta 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 beta-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
Z
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
Kako
Y
Y
Pang
L
L
Freeman
M W
MW
Glick
J M
JM
Wang
X
X
Goldberg
I J
IJ
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001055:Apolipoproteins B / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000097:blood; D008049:Lipase / Q000097:blood; D008074:Lipoproteins / Q000097:blood*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D014407:Tumor Cells, Cultured
D001055:Apolipoproteins B; D002352:Carrier Proteins; D008074:Lipoproteins; C106092:microsomal triglyceride transfer protein; D008049:Lipase