Induction of 3-hydroxy-3-methylglutaryl coenzyme A reductase in HeLa cells by glucocorticoids.
The activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase, EC 1.1.1.34) has been demonstrated both in homogenates and microsomes of the S3G strain of HeLa cells. It was increased 8- to 10-fold by the removal of serum from the growth medium. The presence of steroids, specifically of the glucocorticoid series, in the serum-less growth medium elicited an additional 100 to 345% increase over the serum-less control, whereas the addition of N6,O2'-dibutyryl adenosine 3':5'-monophosphate to the medium or dexamethasone to the assay mixture was without any stimulatory effect. Both inductions were blocked by cycloheximide and actinomycin D, suggesting a protein synthesis-dependent elevation of enzyme activity. Glucocorticoids were effective in the induction at concentrations ranging from 10(-6) to 10(-8) M and there was a demonstrated parallel between the magnitude of enzyme induction and glucocorticoid potency. The HMG-CoA reductase activities from steroid-induced and control cultures had identical assay characteristics (pH optima and apparent Km values for both NADPH and HMG-CoA). This induction of the rate-controlling enzyme of cholesterogenesis occurred despite the observation that glucocorticoids specifically depress the rate of acetate or water, but not mevalonate, incorporation into cholesterol.
D000429:Alcohol Oxidoreductases / Q000096:biosynthesis*; D001769:Blood; D003470:Culture Media; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D006367:HeLa Cells / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D006903:Hydroxymethylglutaryl CoA Reductases / Q000096:biosynthesis*; D007700:Kinetics; D013261:Sterols / Q000096:biosynthesis; D013329:Structure-Activity Relationship
D003470:Culture Media; D005938:Glucocorticoids; D013261:Sterols; D003609:Dactinomycin; D003907:Dexamethasone; D003513:Cycloheximide; D000429:Alcohol Oxidoreductases; D006903:Hydroxymethylglutaryl CoA Reductases