title: Phosphorylation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase and modulation of its enzymic activity by calcium-activated and phospholipid-dependent protein kinase.
abstract: A calcium-activated and phospholipid-dependent protein kinase (protein kinase C) catalyzes the phosphorylation of both insoluble microsomal (Mr approximately 100,000) and purified soluble (Mr = 53,000) 3-hydroxy-3-methylglutaryl coenzyme A reductase. The phosphorylation and concomitant inactivation of enzymic activity of HMG-CoA reductase was absolutely dependent on Ca2+, phosphatidylserine, and diolein. Dephosphorylation of phosphorylated HMG-CoA reductase was associated with the loss of protein bound radioactivity and reactivation of enzymic activity. Maximal phosphorylation of purified HMG-CoA reductase was associated with the incorporation of 1.05 +/- 0.016 mol of phosphate/mol of native form of HMG-CoA reductase (Mr approximately 100,000). The apparent Km for purified HMG-CoA reductase and histone H1 was 0.08 mg/ml, and 0.12 mg/ml, respectively. The tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate stimulated the protein kinase C-catalyzed phosphorylation of HMG-CoA reductase. Increased phosphorylation of HMG-CoA reductase by phorbol 12-myristate 13-acetate suggests a possible in vivo protein kinase C-mediated mechanism for the short-term regulation of HMG-CoA reductase activity. The identification of the protein kinase C system in addition to the reductase kinase-reductase kinase kinase bicyclic cascade systems for the modulation of the enzymic activity of HMG-CoA reductase may provide new insights into the molecular mechanisms involved in the regulation of cholesterol biosynthesis.
authors.forename: Z H
authors.initials: ZH
authors.lastname: Beg
authors.forename: J A
authors.initials: JA
authors.lastname: Stonik
authors.forename: H B
authors.initials: HB
authors.lastname: Brewer
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004075:Diglycerides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D008862:Microsomes, Liver / Q000201:enzymology*; D008970:Molecular Weight; D010718:Phosphatidylserines / Q000494:pharmacology; D010743:Phospholipids / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004075:Diglycerides; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D010718:Phosphatidylserines; D010743:Phospholipids; D000255:Adenosine Triphosphate; D006903:Hydroxymethylglutaryl CoA Reductases; D011494:Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; C013965:diolein