Journal of Lipid Research, Vol 31, 1937-1946, Copyright © 1990 by Lipid Research, Inc.
Apolipoprotein B-100: immunolocalization and synthesis in human intestinal mucosa
E Levy, C Rochette, I Londono, CC Roy, RW Milne, YL Marcel and M Bendayan
Department of Nutrition, University of Montreal, Quebec, Canada.
Despite the evidence that the human small intestine produces two separate
species of apoB mRNA encoding for B-100 and B-48, there is a paucity of
data concerning the expression of the latter form in this organ. Using a
high resolution immunogold approach, with specific polyclonal antibodies
and a panel of monoclonal antibodies (2D8, 3A10, 4G3), both forms of apoB
(B-48 and B-100) were revealed over enterocytes of pediatric intestinal
samples. Intense labeling was observed over microvilli, apical smooth
membrane vesicles, multivesicular bodies, the basolateral membrane, as well
as the trans Golgi region. Only low labeling was found over the rough
endoplasmic reticulum (rER). Similar patterns of apoB distribution
characterized both duodenal and jejunal regions. The presence of labeling
over the Golgi apparatus and rER suggests a synthetic activity of both
forms of apoB by the epithelial cells. To test this hypothesis, human
intestine was incubated with [3H]leucine, homogenized, and subjected to
immunoprecipitation for apoB. Immunoprecipitates contained radioactivity
mainly in apoB-48 with relatively small amounts in apoB- 100 when examined
by NaDodSO4-polyacrylamide gel electrophoresis. These findings were further
supported by the biochemical determination of apoB-100 and apoB-48 in
chylomicron particles isolated from thoracic duct lymph of a human donor.
Taken together, our data suggest that the human intestine is able to
synthesize and to express the apoB-100.