The influence of particle size and multiple apoprotein E-receptor interactions on the endocytic targeting of beta-VLDL in mouse peritoneal macrophages.
Low density lipoprotein (LDL) and beta-very low density lipoprotein (beta-VLDL) are internalized by the same receptor in mouse peritoneal macrophages and yet their endocytic patterns differ; beta-VLDL is targeted to both widely distributed and perinuclear vesicles, whereas LDL is targeted almost entirely to perinuclear lysosomes. This endocytic divergence may have important metabolic consequences since beta-VLDL is catabolized slower than LDL and is a more potent stimulator of acyl-CoA/cholesterol acyl transferase (ACAT) than LDL. The goal of this study was to explore the determinants of beta-VLDL responsible for its pattern of endocytic targeting. Fluorescence microscopy experiments revealed that large, intestinally derived, apoprotein (Apo) E-rich beta-VLDL was targeted mostly to widely distributed vesicles, whereas small, hepatically derived beta-VLDL was targeted more centrally (like LDL). Furthermore, the large beta-VLDL had a higher ACAT-stimulatory potential than the smaller beta-VLDL. The basis for these differences was not due to fundamental differences in the means of uptake; both large and small beta-VLDL were internalized by receptor-mediated endocytosis (i.e., not phagocytosis) involving the interaction of Apo E of the beta-VLDL with the macrophage LDL receptor. However, large beta-VLDL was much more resistant to acid-mediated release from LDL receptors than small beta-VLDL. Furthermore, partial neutralization of the multiple Apo Es on these particles by immunotitration resulted in a more perinuclear endocytic pattern, a lower ACAT-stimulatory potential, and an increased sensitivity to acid-mediated receptor release. These data are consistent with the hypothesis that the interaction of the multivalent Apo Es of large beta-VLDL with multiple macrophage LDL receptors leads to a diminished or retarded release of the beta-VLDL from its receptor in the acidic sorting endosome which, in turn, may lead to the widely distributed endocytic pattern of large beta-VLDL. These findings may represent a physiologically relevant example of a previously described laboratory phenomenon whereby receptor cross-linking by multivalent ligands leads to a change in receptor targeting.
Tabas
I
I
Department of Medicine, Columbia University, New York 10032.
Myers
J N
JN
Innerarity
T L
TL
Xu
X X
XX
Arnold
K
K
Boyles
J
J
Maxfield
F R
FR
D000818:Animals; D001057:Apolipoproteins E / Q000378:metabolism / Q000648:ultrastructure; D002850:Chromatography, Gel; D003571:Cytochalasin B / Q000494:pharmacology; D004285:Dogs; D004705:Endocytosis; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008079:Lipoproteins, VLDL / Q000378:metabolism* / Q000648:ultrastructure; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR; D008856:Microscopy, Fluorescence; D009500:Neutralization Tests; D010316:Particle Size; D011956:Receptors, Cell Surface / Q000378:metabolism*; D002785:Sterol O-Acyltransferase / Q000378:metabolism
D001057:Apolipoproteins E; D008079:Lipoproteins, VLDL; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011956:Receptors, Cell Surface; D003571:Cytochalasin B; D002785:Sterol O-Acyltransferase