title: Effect of Cu,Zn superoxide dismutase on cholesterol metabolism in human hepatocarcinoma (HepG2) cells.
abstract: The microsomal enzyme 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase and the low density lipoprotein (LDL) receptor pathway carry out a key role on cholesterol homeostasis in eucaryotic cells. The HMG-CoA reductase is sensitive to oxidative inactivation and to phosphorylation by many kinases that are able to inactivate the protein and increase its susceptibility to proteolysis. We previously demonstrated that a calf thymus Cu,Zn SOD affects cholesterol metabolism. This protein binds with rat hepatocyte cell membrane by a specific surface membrane receptor. The involvement of Cu,Zn SOD in cholesterol metabolism is confirmed further by the presence of this antioxidant enzyme in circulating serum lipoproteins. We studied the effect of native human Cu,Zn SOD, metal-free SOD (apo SOD), and SOD-inactivated with hydrogen peroxide on cholesterol metabolism in human hepatocarcinoma HepG2 cells. Results showed that all forms of SODs used, at the concentration of 150 ng/ml, are able to affect cholesterol metabolism decreasing both HMG-CoA reductase activity and its protein levels; this inhibitory effect is accompanied by reduced cholesterol synthesis measured as [14C]acetate incorporation into [14C]cholesterol and by an increased [125I]LDL binding to HepG2 cells. Furthermore, the inhibitory effect of Cu,Zn SOD on cholesterol synthesis was completely abolished when the cells were incubated with Cu,Zn SOD in the presence of bisindoilmaleimide (BDM), an inhibitor of protein kinase C (PKC); moreover, we demonstrated that Cu,Zn SOD as well as apo SOD was able to increase PKC activity. Overall, data demonstrate that Cu,Zn SOD affects cholesterol metabolism independently from its dismutase activity and its metal content and that the inhibitory action on cholesterol synthesis is mediated by an activation of protein kinase C.
authors.affiliation: Dipartimento di Neuroscienze e Scienze del Comportamento, Sezione di Fisiologia, Università degli Studi di Napoli, Federico II, Via S. Pansini, 5, 80131 Naples, Italy. mondola@unina.it
authors.forename: Paolo
authors.initials: P
authors.lastname: Mondola
authors.forename: Rosalba
authors.initials: R
authors.lastname: Serù
authors.forename: Mariarosaria
authors.initials: M
authors.lastname: Santillo
authors.forename: Simona
authors.initials: S
authors.lastname: Damiano
authors.forename: Maurizio
authors.initials: M
authors.lastname: Bifulco
authors.forename: Chiara
authors.initials: C
authors.lastname: Laezza
authors.forename: Pietro
authors.initials: P
authors.lastname: Formisano
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Rotilio
authors.forename: Maria Rosa
authors.initials: MR
authors.lastname: Ciriolo
mesh_terms: D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D003720:Densitometry; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000378:metabolism; D008301:Maleimides / Q000494:pharmacology; D008670:Metals / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D013482:Superoxide Dismutase / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D004791:Enzyme Inhibitors; D007211:Indoles; D008077:Lipoproteins, LDL; D008301:Maleimides; D008670:Metals; D002784:Cholesterol; D006861:Hydrogen Peroxide; D006903:Hydroxymethylglutaryl CoA Reductases; D013482:Superoxide Dismutase; D011493:Protein Kinase C; C088060:bisindolylmaleimide