INHIBITION OF PROTEIN-SYNTHESIS IN BABY-HAMSTER KIDNEY-CELLS BLOCKS OXYSTEROL-MEDIATED SUPPRESSION OF 3-HYDROXY-3-METHYLGLUTARYL-COA REDUCTASE MESSENGER-RNA AT A POSTTRANSCRIPTIONAL LEVEL
Jw. Choi et al., INHIBITION OF PROTEIN-SYNTHESIS IN BABY-HAMSTER KIDNEY-CELLS BLOCKS OXYSTEROL-MEDIATED SUPPRESSION OF 3-HYDROXY-3-METHYLGLUTARYL-COA REDUCTASE MESSENGER-RNA AT A POSTTRANSCRIPTIONAL LEVEL, Biochemical journal, 296, 1993, pp. 859-866
The effects of the protein-synthesis inhibitor cycloheximide on 25-hyd
roxycholesterol-mediated suppression of 3-hydroxy-3-methylglutaryl-CoA
(HMG-CoA) reductase mRNA levels were evaluated in the baby-hamster ki
dney cell line C100. Cells cultured in medium supplemented with delipi
dized fetal bovine serum and 25 muM lovastatin for 12-24- h had a 5-fo
ld higher level of HMG-CoA reductase mRNA than cells grown in medium s
upplemented with non-delipidized fetal bovine serum (FBS). The higher
level was due to increased transcription, as determined by run-on assa
ys with isolated nuclei. Addition of 25-hydroxycholesterol to lovastat
in-treated cells lowered HMGCoA reductase mRNA levels within 4 h of tr
eatment to those of cells grown in FBS-supplemented medium. This decre
ase was due in part to a decrease in gene transcription. Cycloheximide
added in conjunction with 25-hydroxycholesterol to lovastatin-treated
cells blocked the suppression of mRNA levels, but did not block oxyst
erol-mediated suppression of transcription. In addition, cycloheximide
added to cells grown in FBS-supplemented medium rapidly increased mRN
A levels by 10-fold relative to untreated cells, with no comparable in
crease in transcription. No comparable increase in either the mRNA lev
el or rate of transcription for beta-actin was observed under such con
ditions. These results indicate that cycloheximide specifically stabil
izes HMG-CoA reductase mRNA in the presence of oxysterols and suggests
that continuous synthesis of a short lived protein regulator is requi
red for oxysterol-mediated suppression of HMG-CoA reductase mRNA at a
post-transcriptional level.