title: Accumulation of transferrin in Caco-2 cells: a possible mechanism of intestinal transferrin absorption.
abstract: Transferrin receptor (TfR)-mediated endocytosis and transcytosis in enterocyte-like Caco-2 cells was investigated in order to elucidate the transport mechanism of orally administered Tf-fusion proteins. Cellular uptake and pulse chase studies were performed in Caco-2, MCF-7 and bladder carcinoma (5637) cells using 125I-labeled Tf (125I-Tf). Co-localization studies of Rab 11 and FITC-Tf endocytosed at either the apical or basolateral membrane were performed in polarized Caco-2 cells grown on Transwells, using confocal laser scanning microscopy (LSM510, Zeiss). Unlike in MCF-7 or 5637 cells, where rapid recycling of Tf was observed, a significant amount of endocytosed 125I-Tf accumulated in Caco-2 cells. This accumulation was especially noticeable with the internalization of 125I-Tf from the apical membrane of polarized Caco-2 cells. Confocal microscopy studies showed that apically, but not basolaterally, endocytosed FITC-Tf was delivered to a Rab11-positive compartment. Our results suggest that a significant amount of apically endocytosed Tf in intestinal epithelial cells is transported to a Rab11-positive compartment, possibly a late endosomal and slow recycling compartment. The Rab11-positive compartment may control the release of apically internalized Tf for either slow recycling to apical membrane or processing to transcytotic compartments.
authors.affiliation: Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90033, USA.
authors.forename: Ching-Jou
authors.initials: CJ
authors.lastname: Lim
authors.forename: Fariba
authors.initials: F
authors.lastname: Norouziyan
authors.forename: Wei-Chiang
authors.initials: WC
authors.lastname: Shen
mesh_terms: D018938:Caco-2 Cells; D004705:Endocytosis; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D011990:Receptors, Transferrin / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*
chemical_list: D011990:Receptors, Transferrin; D011993:Recombinant Fusion Proteins; D014168:Transferrin