The effect of apo E secretion on lipoprotein uptake in transfected cells.
To investigate the role of apolipoprotein E (apo E) secreted by peripheral tissues in local lipoprotein metabolism, we developed a cell strain that constitutively produced and secreted apo E. A fusion plasmid containing rat apo E genomic DNA under control of mouse metallothionein promotor was constructed and transfected into Chinese hamster ovary cells. A stable transformant designated CHO-MAEII constitutively secreted rat apo E mainly in the form of sialylated free protein. The secretion was further enhanced by metal induction up to 1 micrograms apo E/ml per 12 h. When incubated with 125I-labeled very low density lipoprotein (125I-VLDL) at 37 degrees C, CHO-MAEII took up and degraded 125I-VLDL with higher affinity than control cells. Furthermore, considerable amount of methylated 125I-VLDL was degraded by CHO-MAEII, while no methylated 125I-VLDL was degraded by control cells. No significant differences were found in the uptake of 125I-LDL. The data indicated that apo E molecules secreted by CHO-MAEII were transferred to 125-VLDL particles, which caused a higher affinity of these particles for LDL receptors on the cells. It is suggested that apo E secreted from peripheral tissues enhances the uptake of lipoproteins by themselves or by surrounding cells in the local environment which demand cholesterol and express LDL receptors. CHO-MAEII was a good model for these 'auto- or paracrine-like functions' of apo E.
Shimano
H
H
Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Fukazawa
C
C
Shibasaki
Y
Y
Mori
N
N
Gotoda
T
T
Harada
K
K
Shimada
M
M
Yamada
N
N
Yazaki
Y
Y
Takaku
F
F
D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism*; D001161:Arteriosclerosis / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D007700:Kinetics; D008074:Lipoproteins / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008745:Methylation; D051379:Mice; D051381:Rats; D011973:Receptors, LDL / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D001057:Apolipoproteins E; D008074:Lipoproteins; D008077:Lipoproteins, LDL; D008079:Lipoproteins, VLDL; D011973:Receptors, LDL; D011994:Recombinant Proteins