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Retroendocytosis of High Density Lipoproteins by the Human Hepatoma Cell Line, HepG2

Retroendocytosis of High Density Lipoproteins by the Human Hepatoma Cell Line, HepG2 When human HepG2 hepatoma cells were pulsed wtth 12S Nabeled high density lipoproteins (HDL) and chased In fresh medium, up to 65% of the radioactivity released was preclpltable with trlchloroacetlc acid. Cell-Internalized 12S I-HDL contributed to the release of acld-preclpitable material; when cells were treated with trypsln before the chase to remove 12S I-HDL bound to the outer cell membrane, 50% of the released material was still acld-preclpitable. Characterization of the radioactive material resecreted by trypsinlzed cells revealed the presence of particles that were similar In size and density to mature HDL and contained intact apollpoprotelns (apo) A-l and A-ll. The release of Internalized label occurred at 37°C but not at 4°C. Monensln, which Inhibits endosomal recycling of receptors, decreased the binding of 12S I-HDL to cells by 75%, Inhibited the release of Internalized radioactivity as acld-preclpitable material by 80%, and increased the release of acid-soluble material by 90%. In contrast, the lysosomal Inhibitor chloroqulne increased the association of 12 *I-HDL to cells by 25%, Inhibited the release of preclpltable material by 10%, and inhibited the release of acid-soluble radioactivity by 80%. Pre-lncubatlon with cholesterol caused a 50% Increase In the specific binding, Internallzatlon, and resecretion of HDL label. Cholesterol affected the release of acld-preclpitable label much more (+90%) than that of acid-soluble material (+20%). Taken together, these findings suggest that HepG2 cells can bind, Internalize, and resecrete HDL by a retroendocytotic process. Furthermore, the results wtth cholesterol and monensin Indicate that a regulated, recycling, receptor-like molecule Is Involved In the binding and Intracellular routing of HDL. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Arteriosclerosis Wolters Kluwer Health

Retroendocytosis of High Density Lipoproteins by the Human Hepatoma Cell Line, HepG2

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Copyright
© 1990 by American Heart Association, Inc.
ISSN
0276-5047

Abstract

When human HepG2 hepatoma cells were pulsed wtth 12S Nabeled high density lipoproteins (HDL) and chased In fresh medium, up to 65% of the radioactivity released was preclpltable with trlchloroacetlc acid. Cell-Internalized 12S I-HDL contributed to the release of acld-preclpitable material; when cells were treated with trypsln before the chase to remove 12S I-HDL bound to the outer cell membrane, 50% of the released material was still acld-preclpitable. Characterization of the radioactive material resecreted by trypsinlzed cells revealed the presence of particles that were similar In size and density to mature HDL and contained intact apollpoprotelns (apo) A-l and A-ll. The release of Internalized label occurred at 37°C but not at 4°C. Monensln, which Inhibits endosomal recycling of receptors, decreased the binding of 12S I-HDL to cells by 75%, Inhibited the release of Internalized radioactivity as acld-preclpitable material by 80%, and increased the release of acid-soluble material by 90%. In contrast, the lysosomal Inhibitor chloroqulne increased the association of 12 *I-HDL to cells by 25%, Inhibited the release of preclpltable material by 10%, and inhibited the release of acid-soluble radioactivity by 80%. Pre-lncubatlon with cholesterol caused a 50% Increase In the specific binding, Internallzatlon, and resecretion of HDL label. Cholesterol affected the release of acld-preclpitable label much more (+90%) than that of acid-soluble material (+20%). Taken together, these findings suggest that HepG2 cells can bind, Internalize, and resecrete HDL by a retroendocytotic process. Furthermore, the results wtth cholesterol and monensin Indicate that a regulated, recycling, receptor-like molecule Is Involved In the binding and Intracellular routing of HDL.

Journal

ArteriosclerosisWolters Kluwer Health

Published: Jul 1, 1990

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