Intracellular transport of high-density lipoprotein 3 in intestinal epithelial cells (Caco-2) is tubulin associated

Background: A retroendocytotic pathway for high-density lipoprotein 3 (HDL3 ) in cultured intestinal epithelial cell lines has been described, In small intestinal crypt cells and Caco-2, HDL3 is internalized, transported to li pid droplets and, after solubilization of these lipid droplets, resecreted. In the present study we examined the mechanisms of intracellular transport of HDL3 in the Caco-2 cell line. Methods: Apolipoprotein E free HDL3 was g old labeled for transmission electron microscopy and 1,1'-dioctadecyl-3,3,3 ',3'-tetramethylindocarbocyanine iodide [DiI(3)] labeled for fluorescence a nd confocal laser scanning microscopy. For tubulin desintegration Caco-2 ce lls were incubated with taxol, colchicine and beta- and gamma-lumicolchicin e. Tubulin staining was performed using a FITC labeled antibody. Uptake of HDL3 was quantified by FACS analysis. Results: HDL3 was rapidly internalize d and found to be in contact with lipid droplets in the perinuclear region after 10 min. By transmission electron microscopy a frequent colocalization of HDL3-containing vesicles and tubular structures was demonstrated. The c lose association of HDL3-containing vesicles with fluorescence stained tubu lin could be confirmed by confocal laser scanning microscopy. Preincubation of the cells with taxol and colchicine did not completely prevent internal ization but reduced it during a 2-hour incubation period to less than 50% o f the control cells. The transport of DiI(3)-labeled HDL3 to the lipid drop lets in the perinuclear region was almost completely blocked by taxol and c olchicine. Conclusion: Internalization and intracellular transport of HDL3 in intestinal epithelial cells (Caco-2) is dependent on a tubulin-mediated mechanism. Copyright (C) 2000 S. Karger AG, Basel.