Avtor/Urednik		Plemenitaš, Ana; Watson, John A
Naslov		Down-regulation of mammalian 3-hydroxy-3-methylglutaryl coenzyme A reductase activity with highly purified liposomal cholesterol
Tip		članek
Vir		Eur J Biochem
Vol. in št.		Letnik 266, št. 2
Leto izdaje		1999
Obseg		str. 317-26
Jezik		eng
Abstrakt		Chinese hamster ovary-215 cells (CHO-215) cannot synthesize C27 and C28 sterols because of a defect in the reaction that decarboxylates 4-carboxysterols (Plemenitas, A., Havel, C.M. and Watson, J.A. (1990) J. Biol. Chem.265, 17012-17017). Thus, CHO-215 cell growth is dependent on an exogenous metabolically functional source of cholesterol. We used CHO-215 cells to (a) determine whether highly purified (>99.5%) cholesterol, in egg lecithin liposomes, could down-regulate derepressed 3-hydroxy-3 methyglutary coenzyme A (HMG-Coa) reductase activity and if so (b) determine wheter the loss in reductase catalytic correlated kinetically with the synthesis and accumulation of detectable oxycholesterol derivates. Liposomal cholesterol (26-39 uM) supported maximum CHO-215 growth and initiated suppression of HMG-CoA reductase activity at concentrations greater than 50uM. Maximum suppresion (50-60%) of reductase activity was achived with 181.3 uM liposomal cholesterol in 6 h. Also, regulatory concentrations of highly purified liposomal (3H) cholesterol were not converted (biologically or chemically) to detectable levels of oxy (3H) cholesterol derivatives during 3-6 h incubations. Lastly, a broad-spectrum cytochrome P450 inhibitor (miconazole) had no effect on liposomal cholesterol-mediated suppression of HMG-CoA reductase activity. These observations established that (a) highly purified cholesterol, incorporated into egg lecithin liposomes, can signal the down-regulation of derepressed mammalin cell HMG-CoA reductase activity and (b) if oxycholesterol synthesis was reqired for liposomal cholesterol-mediated down-regulated, the products had to be more potent than 24-, 25- or 26-/27 hydroxycholesterol.
Deskriptorji		HYDROXYMETHYLGLUTARYL COA REDUCTASES CHOLESTEROL LIPOSOMES HAMSTERS CELL LINE