Coordinate regulation of 3-hydroxy-3-methylglutaryl-coenzyme A synthase, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and prenyltransferase synthesis but not degradation in HepG2 cells.
Human hepatoma HepG2 cells were used to demonstrate coordinate regulation of three enzymes of cholesterol synthesis under a variety of conditions. Addition of either delipidized serum and mevinolin or low density lipoprotein, 25-hydroxycholesterol, or mevalonic acid to HepG2 cells resulted in rapid changes both in the levels of the mRNAs and in the rates of synthesis of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase, HMG-CoA reductase, and farnesyl pyrophosphate synthetase (prenyltranferase). In all cases, the changes in mRNA levels were paralleled by changes in the rates of specific protein synthesis. Pulse-chase techniques were used to determine the half-lives of all three proteins. Addition of low density lipoprotein to the media during the chase increased the rate of degradation of HMG-CoA reductase 4.6-fold but had no affect on the half-lives of HMG-CoA synthase or prenyltransferase. Therefore, we conclude that the coordinate regulation of these three enzymes under a variety of conditions occurs at the level of enzyme synthesis and not at the level of protein stability.
Rosser
D S
DS
Department of Biological Chemistry, UCLA School of Medicine 90024.
Ashby
M N
MN
Ellis
J L
JL
Edwards
P A
PA
D002460:Cell Line; D004122:Dimethylallyltranstransferase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology; D006903:Hydroxymethylglutaryl CoA Reductases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D006904:Hydroxymethylglutaryl-CoA Synthase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000502:physiology; D008798:Mevalonic Acid / Q000494:pharmacology; D007652:Oxo-Acid-Lyases / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D014158:Transcription, Genetic / Q000187:drug effects; D014166:Transferases / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology
D006888:Hydroxycholesterols; D008077:Lipoproteins, LDL; D012333:RNA, Messenger; C007997:25-hydroxycholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D014166:Transferases; D006904:Hydroxymethylglutaryl-CoA Synthase; D004122:Dimethylallyltranstransferase; D007652:Oxo-Acid-Lyases; D008798:Mevalonic Acid