Effect of chylomicron remnants on apolipoprotein E synthesis in HepG2 cells.
The effect of chylomicron remnants (CM-R) on apolipoprotein (apo) E synthesis by HepG2 cells was studied. The accumulation rate of apo E in the medium was increased in cells incubated with CM-R (chylo-cells) compared with that in the control cells. However, the abundance of apo E mRNA was not greater in chylo-cells than in control cells. The time course of apo E accumulation in the medium showed that apo E increased in the chylo-cells linearly up to 24 hours, whereas it increased in the control cells linearly only up to 6 hours, when it reached a plateau. The results suggest that the secretion rate of apo E was not affected by incubation with CM-R, but that uptake of the newly secreted apo E by the cells may be depressed by incubation with CM-R. Autoradiography of newly synthesized apo E showed that chylo-cells produced much more "larger" apo E than did the control cells. Two-dimensional electrophoresis of the apo E newly synthesized by the chylo-cells showed that the larger apo E was slightly acidic even after treatment with neuraminidase. Pulse-chase labeling of apo E showed that the larger apo E was secreted by both control and chylo-cells equally and that the larger apo E was converted to regular apo E in the medium more effectively in control cells than in chylo-cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Teramoto
T
T
1st Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, Japan.
Matsushima
T
T
Kinoshita
M
M
Watanabe
T
T
Hashimoto
Y
Y
Tsukamoto
K
K
Katsuragawa
K
K
Okazaki
S
S
Yamanaka
M
M
D001057:Apolipoproteins E / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D001345:Autoradiography; D006528:Carcinoma, Hepatocellular / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology*; D002914:Chylomicrons / Q000494:pharmacology*; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D009439:Neuraminidase / Q000494:pharmacology; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D013997:Time Factors; D014407:Tumor Cells, Cultured
D001057:Apolipoproteins E; D002914:Chylomicrons; D012333:RNA, Messenger; D009439:Neuraminidase