Regulation of synthesis and degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase by low density lipoprotein and 25-hydroxycholesterol in UT-1 cells.
UT-1 cells are a clone of Chinese hamster ovary cells that were selected to grow in the presence of compactin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase [mevalonate: NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34]. These cells have 100- to 1,000-fold more immunoprecipitable reductase than normal. The enzyme activity is rapidly decreased when low density lipoprotein (LDL) or 25-hydroxycholesterol is added to the culture medium. In this current study, a quantitative immunoprecipitation assay was used to determine whether LDL and 25-hydroxycholesterol inhibit the synthesis or stimulate the degradation of reductase in UT-1 cells. Each of these agents inhibited the incorporation of [35S]methionine into immunoprecipitable reductase by more than 98%. Pulse-chase experiments showed that reductase was degraded with a half-life of 10-13 hr in UT-1 cells and that the rate of degradation of preformed enzyme was increased 3-fold by the addition of either LDL or 25-hydroxycholesterol. We conclude that the predominant mechanism by which LDL and 25-hydroxycholesterol decrease reductase activity in UT-1 cells is a profound suppression of synthesis of the enzyme.
D000818:Animals; D000936:Antigen-Antibody Complex; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D006888:Hydroxycholesterols / Q000494:pharmacology*; D006903:Hydroxymethylglutaryl CoA Reductases / Q000096:biosynthesis / Q000378:metabolism*; D007074:Immunoglobulin G; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D010053:Ovary
D000936:Antigen-Antibody Complex; D006888:Hydroxycholesterols; D007074:Immunoglobulin G; D008077:Lipoproteins, LDL; C007997:25-hydroxycholesterol; D006903:Hydroxymethylglutaryl CoA Reductases