Regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase mRNA levels in rat liver.

Addition of cholestyramine or cholestyramine plus mevinolin to the diet has been reported to increase the activity and mass of rat liver 3-hydroxy-3-methylglutaryl-CoA reductase. The present data show that these same dietary manipulations cause an induction of functional reductase mRNA. RNA was isolated from rat livers and added to an in vitro translation system, and the reductase was immunoprecipitated and analyzed by polyacrylamide gel electrophoresis under denaturing conditions. One protein was specifically immunoprecipitated and was found to have a Mr of 90,000 on 0.5 M urea/sodium dodecyl sulfate/polyacrylamide gels and a Mr of 94,000 on 8 M urea/sodium dodecyl sulfate/polyacrylamide gels. In animals fed rat chow supplemented with 5% cholestyramine and 0.1% mevinolin, reductase mRNA levels were 5.7-fold higher than in animals fed rat chow with 5% cholestyramine and were 16-fold higher than in animals fed rat chow with 5% cholestyramine and given mevalonolactone by stomach intubation. RNA isolated from animals fed a normal diet and killed at the nadir of the diurnal cycle of enzyme activity contained no detectable amounts of reductase mRNA as determined by this assay.