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Vol. 15, Issue 1, 132-141, January 2004

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Lipid-dependent Bidirectional Traffic of Apolipoprotein B in Polarized Enterocytes

Unité Mixte de Recherche, Institut National de la Santé et de la Recherche Médicale U505, Université Pierre et Marie Curie, Laboratoire de Pharmacologie Cellulaire et Moléculaire de l'EPHE, 75006 Paris, France

Submitted April 8, 2003; Revised September 19, 2003; Accepted September 19, 2003
Monitoring Editor: Randy Schekman

Enterocytes are highly polarized cells that transfer nutrients across the intestinal epithelium from the apical to the basolateral pole. Apolipoprotein B (apoB) is a secretory protein that plays a key role in the transepithelial transport of dietary fatty acids as triacylglycerol. The evaluation of the control of apoB traffic by lipids is therefore of particular interest. To get a dynamic insight into this process, we used the enterocytic Caco-2 cells cultured on microporous filters, a system in which the apical and basal compartments can be delimited. Combining biochemical and morphological approaches, our results showed that, besides their role in protection from degradation, lipids control the intracellular traffic of apoB in enterocytes. A supply of fatty acids and cholesterol is sufficient for the export of apoB from the endoplasmic reticulum and its post-Golgi traffic up to the apical brush-border domain, where it remains until an apical supply of complex lipid micelles signals its chase down to the basolateral secretory domain. This downward traffic of apoB involves a microtubule-dependent process. Our results demonstrate an enterocyte-specific bidirectional process for the lipid-dependent traffic of a secretory protein.

Abbreviations used: apoB, apolipoprotein B; BBD brush border domain; BSA, bovine serum albumin; CHX, cycloheximide; FA, fatty acid; FCS, fetal calf serum; FITC, fluorescein isothiocyanate; ITS, insulin transferrin selenium; ITS/L, insulin transferrin selenium and lipids; MTP, microsomal transfer protein; SAC, subapical compartment; SI, sucrase-isomaltase; TAG, triacyl-glycerol; TGN, trans-Golgi network; TRL, triacylglycerol-rich lipoprotein; WGA, wheat germ agglutinin.

^* Corresponding author. E-mail address: fransisco.delers-u505{at}bhdc.jussieu.fr.

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