Journal of Lipid Research, Vol 31, 2257-2264, Copyright © 1990 by Lipid Research, Inc.
Perinatal hepatocyte/hepatoma hybrids: construction of clones that express the developmentally regulated monoacyglycerol acyltransferase activity [published erratum appears in J Lipid Res 1991 Aug;32(8):1390]
RA Coleman and ES Bardes
Department of Pediatrics, Duke University Medical Center, Durham, NC 27710.
Microsomal monoacyglycerol acyltransferase is a developmentally expressed
enzyme that catalyzes the synthesis of sn-1,2-diacylglycerol from
sn-2-monoacylglycerol and palmitoyl-CoA. The activity is present in liver
from fetal and suckling rats but is absent in the adult. In order to obtain
a stable permanent cell line that expresses this activity, Fao rat hepatoma
cells and hepatocytes from 8-day-old baby rats were hybridized and clones
were selected. Two hybrids (HA1 and HA7) expressed monoacylglycerol
acyltransferase activity. Like fetal hepatocytes, but unlike hepatocytes
from postnatal rats, the HA cells had high rates of [14C]acetate
incorporation into glycerolipids, cholesterol, and cholesteryl esters, and
they secreted triacylglycerol into the media. Monoacylglycerol
acyltransferase specific activity increased 2.5-fold as the cells divided
in culture, suggesting growth- dependent regulation. The specific
activities of glycerol-P acyltransferase, the committed step of the
microsomal pathway of glycerolipid synthesis, and diacylglycerol
acyltransferase, the activity unique to triacylglycerol biosynthesis, were
comparable to the levels of the corresponding activities in fetal
hepatocytes. Addition of insulin or dexamethasone to the media increased
the incorporation of [14C]oleate into triacyglycerol about 1.7-fold within
2 h, but had little effect on [14C]oleate incorporation into phospholipid.
These hormonally responsive rat-hepatoma/hepatocyte hybrids reflect the
fetal stage of hepatocyte development in five major aspects of lipid
metabolism: sterol, fatty acid, and triacylglycerol biosynthesis,
glycerolipid secretion, and the presence of the developmentally expressed
monoacylglycerol pathway.
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