Journal of Lipid Research, Vol 26, 831-841, Copyright © 1985 by Lipid Research, Inc.
Role of mevalonate in regulation of cholesterol synthesis and 3-hydroxy- 3-methylglutaryl coenzyme A reductase in cultured cells and their cytoplasts
G Popjak, CF Clarke, C Hadley and A Meenan
H4-II-E-C3 hepatoma cells in culture respond to lipid-depleted media and to
mevinolin with increased sterol synthesis from [14C]acetate and rise of
3-hydroxy-3-methylglutaryl coenzyme A reductase levels. Mevalonate at 4 mM
concentration represses sterol synthesis and the reductase, and completely
abolishes the effects of mevinolin. Mevalonate has little or no effect on
sterol synthesis or reductase in enucleated hepatoma cells (cytoplasts) or
on reductase in cytoplasts of cultured Chinese hamster ovary (CHO) cells.
The sterol-synthesizing system of hepatoma cell cytoplasts and the
reductase in the cytoplasts of CHO cells were completely stable for at
least 4 hr. While reductase levels and sterol synthesis from acetate
followed parallel courses, the effects on sterol synthesis--both increases
and decreases--exceeded those on reductase. In vitro translation of
hepatoma cell poly(A)+RNAs under various culture conditions gave an
immunoprecipitable polypeptide with a mass of 97,000 daltons. The
poly(A)+RNA from cells exposed for 24 hr to lipid-depleted media plus
mevinolin (1 microgram/ml) contained 2.8 to 3.6 times more
reductase-specific mRNA than that of cells kept in full-growth medium, or
cells exposed to lipid-depleted media plus mevinolin plus mevalonate.
Northern blot hybridization of H4 cell poly(A)+RNAs with [32P]cDNA to the
reductase of CHO cells gave two 32P- labeled bands of 4.6 and 4.2 K-bases
of relative intensities 1.0, 0.61- 1.1, 2.56, and 1.79 from cells kept,
respectively, in full-growth medium, lipid-depleted medium plus mevinolin
plus mevalonate, lipid- depleted medium plus mevinolin, and lipid-depleted
medium. These values approximate the reductase levels of these cells. We
conclude that mevalonate suppresses cholesterol biosynthesis in part by
being a source of a product that decreases the level of reductase-specific
mRNA.
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