Relation of the size and intracellular sorting of apoB to the formation of VLDL 1 and VLDL 2.
In this study, we tested the hypothesis that two separate pathways, the two-step process and an apolipoprotein B (apoB) size-dependent lipidation process, give rise to different lipoproteins. Expression of apoB-100 and C-terminally truncated forms of apoB-100 in McA-RH7777 cells demonstrated that VLDL particles can be assembled by apoB size-dependent linear lipidation, resulting in particles whose density is inversely related to the size of apoB. This lipidation results in a LDL-VLDL 2 particle containing apoB-100. VLDL 1 is assembled by the two-step process by apoB-48 and larger forms of apoB but not to any significant amount by apoB-41. The major amount of intracellular apoB-80 and apoB-100 banded with a mean density of 1.10 g/ml. Its formation was dependent on the sequence between apoB-72 and apoB-90. This dense particle, which is retained in the cell, possibly by chaperones or association with the microsomal membrane, is a precursor of secreted VLDL 1. The intracellular LDL-VLDL 2 particles formed during size-dependent lipidation appear to be the precursors of intracellular VLDL 1. We propose that the dense apoB-100 intracellular particle is converted to LDL-VLDL 2 by size-dependent lipidation. LDL-VLDL 2 is secreted or converted to VLDL 1 by the uptake of the major amount of triglycerides.
Stillemark-Billton
Pia
P
Department of Medical Biochemistry and the Wallenberg Laboratory for Cardiovascular Research, University of Göteborg, Göteborg, Sweden.
Beck
Caroline
C
Borén
Jan
J
Olofsson
Sven-Olof
SO
D000818:Animals; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000378:metabolism*; D045744:Cell Line, Tumor; D047468:Immunoprecipitation; D008079:Lipoproteins, VLDL / Q000096:biosynthesis*; D008099:Liver / Q000166:cytology; D051379:Mice; D018832:Molecular Chaperones; D010316:Particle Size; D021381:Protein Transport; D051381:Rats; D014162:Transfection; D014280:Triglycerides / Q000378:metabolism; D014461:Ultracentrifugation
D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D008079:Lipoproteins, VLDL; D018832:Molecular Chaperones; D014280:Triglycerides