J. Biol. Chem., Vol. 258, Issue 15, 9220-9226, Aug, 1983
Effect of tunicamycin on 3-hydroxy-3-methylglutaryl coenzyme A reductase in C-6 glial cells
JJ Volpe and RI Goldberg
The effects of tunicamycin on 3-hydroxy-3-methylglutaryl coenzyme A
(HMG-CoA) reductase activity and cholesterol biosynthesis have been studied
in cultured C-6 glial cells. Depending on culture conditions, exposure to
tunicamycin caused either a marked inhibition of induction of HMG-CoA
reductase activity or, under steady state conditions, a marked reduction in
enzymatic activity. Incorporation of [14 C]acetate into sterols was
affected similarly. After a 24-h exposure, a 50% reduction in reductase
activity was observed with a concentration of 0.05 micrograms/ml, and a
maximal, 65-70% reduction occurred with 0.10 micrograms/ml of the drug. The
effect of tunicamycin on reductase activity and on sterol synthesis was
apparent 4 h after addition of the drug and nearly maximal after 6 h. The
relative specificity of the effect of tunicamycin was indicated by the
finding of no change in the activities of NADPH-cytochrome c reductase,
acetyl-CoA carboxylase, or fatty acid synthetase, in incorporation of
[3H]leucine into total protein, or in the rate of increase in cellular
protein and phospholipid at concentrations of tunicamycin that caused the
marked effect on HMG-CoA reductase. The reversibility of the effect of
tunicamycin was shown by observing total recovery of reductase activity
within 24 h after removal of the drug following a 24-h exposure. That the
effect of tunicamycin on reductase is related to the drug's effect on
glycoprotein synthesis was shown in two ways. First, the range of
concentrations over which tunicamycin led to the decrease in reductase
activity was essentially identical with the range over which the drug led
to a decrease in incorporation of [3H]mannose into protein. Second,
incubation of C-6 cells with N-acetylglucosamine simultaneously with
tunicamycin was accompanied by prevention of the drug's effect on both
HMG-CoA reductase and glycoprotein synthesis. These data suggest that
glycoprotein synthesis is necessary for the expression of HMG-CoA reductase
activity and, thereby, cholesterol synthesis in glial cells. Moreover, a
link between glycoprotein and cholesterol biosynthesis could play a role in
the mediation of certain maturational events in cells of neural origin.
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