Hormonal regulation during secretion of alpha-fetoprotein in hepatoma cells grown in synthetic medium.
The variant cell line of H4-II-E-C3 cells derived from the Reuber H-35 hepatoma cells has been established using protein- and lipid-free synthetic medium. This H4-II-E-C3-V line can synthesize and secrete considerable amounts of alpha-fetoprotein (AFP) and albumin. The addition of 5 X 10(-7) M dexamethasone to the medium stimulated the excretion of AFP without increasing total AFP synthesis, whereas 8.7 X 10(-8) M insulin inhibited the excretion of AFP without a significant inhibition of intracellular AFP synthesis. However, neither dexamethasone nor insulin altered either the cellular or secreted levels of albumin. Cells were pulse labeled with [35S]methionine and then chased after addition of excess unlabeled methionine. AFP appeared in the medium after 10 min, and 50% of the protein was secreted after 110 min. The rate of secretion of AFP was much slower than that of albumin, 50% of which was secreted after 25 min. Dexamethasone, 5 X 10(-7) M, caused a marked enhancement in the rate of AFP secretion, with 50% released after 75 min. Insulin, 8.7 X 10(-8) M, by contrast, caused a marked delay in AFP secretion with only 20% released after 180 min and then a plateau was approached. Since the intracellular AFP was excreted 55% after 180 min the remaining 25% of newly made AFP was suggested to be degraded during secretion. The kinetics of movement of AFP during secretion and endoglycosidase H treatment of intracellular and secreted AFP suggested that insulin impeded the transport of AFP from the rough endoplasmic reticulum to the Golgi apparatus.
Tsukada
Y
Y
Hibi
N
N
Ohkawa
K
K
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004261:DNA Replication / Q000187:drug effects; D004273:DNA, Neoplasm / Q000032:analysis; D003907:Dexamethasone / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism; D051381:Rats; D000509:alpha-Fetoproteins / Q000378:metabolism*
D004273:DNA, Neoplasm; D007328:Insulin; D000509:alpha-Fetoproteins; D003907:Dexamethasone; D008715:Methionine