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Abstract
The mammalian cell continuously adjusts its sterol content by regulating levels of key sterol synthetic enzymes and levels of LDL receptors that mediate uptake of cholesterol-laden particles. Control is brought about by sterol-regulated transcription of relevant genes and by regulated degradation of the committed step enzyme HMG-CoA reductase (HMGR). Current work has revealed that proteolysis is at the heart of each of these mechanistically distinct axes. Transcriptional control is effected by regulated cleavage of the membrane-bound transcription factor sterol regulatory element binding protein (SREBP), and HMGR degradation is brought about by ubiquitin-mediated degradation. In each case, ongoing cell biological processes are being harnessed to bring about regulation. The secretory pathway plays a central role in allowing sterol-mediated control of transcription. The constitutively active endoplasmic reticulum (ER) quality control apparatus is employed to bring about regulated destruction of HMGR. This review describes the methods and results of various studies to understand the mechanisms and molecules involved in these distinct but interrelated aspects of sterol regulation and the intriguing similarities that appear to exist at the levels of protein sequence and cell biology.
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Affiliation(s)
- Randolph Y Hampton
- Section of Cell and Developmental Biology, Division of Biology, University of California, San Diego, La Jolla 92093-0347, USA.
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2
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Gardner RG, Shan H, Matsuda SP, Hampton RY. An oxysterol-derived positive signal for 3-hydroxy- 3-methylglutaryl-CoA reductase degradation in yeast. J Biol Chem 2001; 276:8681-94. [PMID: 11134013 DOI: 10.1074/jbc.m007888200] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sterol synthesis by the mevalonate pathway is modulated, in part, through feedback-regulated degradation of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR). In mammals, both a non-sterol isoprenoid signal derived from farnesyl diphosphate (FPP) and a sterol-derived signal appear to act together to positively regulate the rate of HMGR degradation. Although the nature and number of sterol-derived signals are not clear, there is growing evidence that oxysterols can serve in this capacity. In yeast, a similar non-sterol isoprenoid signal generated from FPP acts to positively regulate HMGR degradation, but the existence of any sterol-derived signal has thus far not been revealed. We now demonstrate, through the use of genetic and pharmacological manipulation of oxidosqualene-lanosterol cyclase, that an oxysterol-derived signal positively regulated HMGR degradation in yeast. The oxysterol-derived signal acted by specifically modulating HMGR stability, not endoplasmic reticulum-associated degradation in general. Direct biochemical labeling of mevalonate pathway products confirmed that oxysterols were produced endogenously in yeast and that their levels varied appropriately in response to genetic or pharmacological manipulations that altered HMGR stability. Genetic manipulation of oxidosqualene-lanosterol cyclase did result in the buildup of detectable levels of 24,25-oxidolanosterol by gas chromatography, gas chromatography-mass spectroscopy, and NMR analyses, whereas no detectable amounts were observed in wild-type cells or cells with squalene epoxidase down-regulated. In contrast to mammalian cells, the yeast oxysterol-derived signal was not required for HMGR degradation in yeast. Rather, the function of this second signal was to enhance the ability of the FPP-derived signal to promote HMGR degradation. Thus, although differences do exist, both yeast and mammalian cells employ a similar strategy of multi-input regulation of HMGR degradation.
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Affiliation(s)
- R G Gardner
- Section of Cell and Developmental Biology, Division of Biology, University of California at San Diego, La Jolla, California 92093 , USA
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Cattel L, Ceruti M. Inhibitors of 2,3-oxidosqualene cyclase as tools for studying the mechanism and function of the enzyme. Crit Rev Biochem Mol Biol 1998; 33:353-73. [PMID: 9827705 DOI: 10.1080/10409239891204378] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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4
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Affiliation(s)
- E I Mercer
- Department of Biochemistry, University of Wales, Aberystwyth, Dyfed, U.K
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5
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Abstract
The mechanism of each of the reactions in the post-squalene segment of the fungal and higher plant sterol biosynthetic pathway is outlined. The inhibitors of the enzymes catalyzing the reactions are described and how inhibition is brought about is explained in the areas where it is known.
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Affiliation(s)
- E I Mercer
- Department of Biochemistry, University College of Wales, Aberystwyth, Dyfed, United Kingdom
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6
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Kelly R, Miller SM, Lai MH, Kirsch DR. Cloning and characterization of the 2,3-oxidosqualene cyclase-coding gene of Candida albicans. Gene 1990; 87:177-83. [PMID: 2185141 DOI: 10.1016/0378-1119(90)90299-7] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
2,3-Oxidosqualene (OS) cyclase (OSC) catalyzes the conversion of OS to lanosterol, an essential step in the biosynthesis of sterols. The Candida albicans gene (ERG7) encoding OSC was cloned by complementation of a Saccharomyces cerevisiae OSC mutant (erg7). Two different Erg+ clones were isolated that contain a common overlapping region. The minimum region required for complementation was determined to be approx. 3.2 kb and a single 2.7-kb ERG7 transcript was detected. The cloned Candida ERG7 DNA complemented an additional nonconditional erg7 allele and a temperature-sensitive erg7 mutation. OSC activity was restored in the mutants as determined by [14C]acetate incorporation in vivo as well as incorporation in vitro in cell-free extracts using either [14C]isopentenyl pyrophosphate or [3H]OS as substrate. The level of OSC produced from expression of a single copy of the Candida ERG7 sequence was sufficient to allow growth of the S. cerevisiae erg7 mutants in the absence of exogenous ergosterol. These data support the contention that the Candida ERG7 sequence is the structural gene for OSC.
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Affiliation(s)
- R Kelly
- Squibb Institute for Medical Research, Department of Microbial Biochemistry and Genetics, Princeton, NJ 08543-4000
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Popják G, Meenan A, Parish EJ, Nes WD. Inhibition of Cholesterol Synthesis and Cell Growth by 24(R, S),25-Iminolanosterol and Triparanol in Cultured Rat Hepatoma Cells. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83338-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Balliano G, Viola F, Ceruti M, Cattel L. Inhibition of sterol biosynthesis in Saccharomyces cerevisiae by N,N-diethylazasqualene and derivatives. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 959:9-19. [PMID: 3278744 DOI: 10.1016/0005-2760(88)90144-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The ability of some azasqualene derivatives to inhibit yeast cell growth was compared with their inhibition activity on squalene-2,3-oxide cyclase (EC 5.4.99.7) both in living cells and in microsome preparations. Among the compounds tested, N,N-diethylazasqualene showed the best correlation between the activity on squalene-2,3-oxide cyclase and its inhibition of yeast growth. The N-oxide derivative, N,N-diethylazasqualene N-oxide, which was as active as the amine in microsomes, was much less active in living cells, probably because it could not easily penetrate the cell wall. Kinetic analysis of the inhibitory activity of compounds on squalene-2,3-oxide cyclase revealed a sharp difference between N,N-diethylazasqualene and its N-oxide; the former showed a non-competitive-type inhibition, whereas the latter behaved as a competitive inhibitor.
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Affiliation(s)
- G Balliano
- Istituto di Chimica Farmaceutica Applicata, Torino, Italy
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Lorenz RT, Parks LW. Regulation of ergosterol biosynthesis and sterol uptake in a sterol-auxotrophic yeast. J Bacteriol 1987; 169:3707-11. [PMID: 3301810 PMCID: PMC212455 DOI: 10.1128/jb.169.8.3707-3711.1987] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Inhibition of sterol uptake in Saccharomyces cerevisiae sterol auxotroph FY3 (alpha hem1 erg7 ura) by delta-aminolevulinic acid (ALA) is dependent on the ability of the organism to synthesize heme from ALA. Sterol-depleted cells not exposed to ALA or strain PFY3 cells, with a double heme mutation, exposed to ALA did not exhibit inhibition of sterol uptake. Addition of ALA to sterol-depleted FY3 stimulated production of a high endogenous concentration of 2,3-oxidosqualene (25.55 micrograms mg-1 [dry weight]) at 24 h, whereas FY3 not exposed to ALA or PFY3 exposed to ALA did not accumulate 2,3-oxidosqualene. The high concentration of 2,3-oxidosqualene in FY3 with ALA decreased, and 2,3;22,23-dioxidosqualene increased to a very high level. The elevation of 2,3-oxidosqualene by ALA was correlated with a fivefold increase in the activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (EC 1.1.1.34). The enhanced activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase was prevented by cycloheximide but not chloramphenicol and was dependent on a fermentative energy source. Inhibition of sterol uptake could not be attributed to 2,3-oxidosqualene or 2,3;22,23-dioxidosqualene but was due to a nonsaturating level of ergosterol produced as a consequence of heme competency through a leaky erg7 mutation.
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Ceruti M, Balliano G, Viola F, Cattel L, Gerst N, Schuber F. Synthesis and biological activity of azasqualenes, bis-azasqualenes and derivatives. Eur J Med Chem 1987. [DOI: 10.1016/0223-5234(87)90050-x] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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11
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Sterol Biosynthesis in Fungi, a Target for Broad Spectrum Fungicides. CHEMISTRY OF PLANT PROTECTION 1986. [DOI: 10.1007/978-3-642-69790-6_1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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12
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Duriatti A, Bouvier-Nave P, Benveniste P, Schuber F, Delprino L, Balliano G, Cattel L. In vitro inhibition of animal and higher plants 2,3-oxidosqualene-sterol cyclases by 2-aza-2,3-dihydrosqualene and derivatives, and by other ammonium-containing molecules. Biochem Pharmacol 1985; 34:2765-77. [PMID: 4015713 DOI: 10.1016/0006-2952(85)90578-7] [Citation(s) in RCA: 86] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
2-Aza-2,3-dihydrosqualene and related molecules, a series of new compounds designed as analogues of the transient carbocationic high energy intermediate, occurring in the oxirane ring opening during the cyclization of 2,3-oxidosqualene, were tested in vitro as inhibitors of the microsomal 2,3-oxidosqualene cyclase of animals (rat liver) and of higher plants (maize, pea). These molecules proved to be good and specific inhibitors for the cyclases of both phyla. The inhibition is due to positively charged species and is sensitive to the steric hindrance around the nitrogen-atom. 4,4,10 beta-Trimethyl-trans-decal-3 beta-ol and 4,10 beta-dimethyl-trans-decal-3 beta-ol, which have previously been described (J.A. Nelson et al., J. Am. chem. Soc. 100, 4900 (1978] as inhibitors of the 2,3-oxidosqualene cyclase of chinese hamster ovary cells, were found to be non-competitive inhibitors of the rat liver microsomal enzyme and presented no activity towards the higher plants cyclases. Aza derivatives of these decalines (A. Rahier et al., Phytochemistry, in press), which were aimed to mimic the C-8 carbocationic intermediate occurring during later steps of the 2,3-oxidosqualene cyclization did not inhibit the cyclases. This result underlines the theoretical limitations of the high energy analogues concept in designing enzyme inhibitors. Amongst other molecules tested, 2,3-epiminosqualene was found to be a reversible, non-competitive inhibitor of the cyclases; similarly U18666A was a very potent inhibitor of the microsomal cyclases. In contrast AMO 1618, a known anticholesterolemic agent reported previously to act at the level of the 2,3-oxidosqualene cyclization step, was not found per se to act on the cyclases.
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Hosokawa G, Patterson GW, Lusby WR. Effects of triarimol, tridermorph and triparanol on sterol biosynthesis in carrot, tobacco and soybean suspension cultures. Lipids 1984. [DOI: 10.1007/bf02537407] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Chang T, Schiavoni E, McCrae K, Nelson J, Spencer T. Inhibition of cholesterol biosynthesis in Chinese hamster ovary cells by 4,4,10 beta-trimethyl-trans-decal-3 beta-ol. A specific 2,3-oxidosqualene cyclase inhibitor. J Biol Chem 1979. [DOI: 10.1016/s0021-9258(19)86479-7] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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15
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Field RB, Holmlund CE, Whittaker NF. The effects of the hypocholesteremic compound 3 beta-(beta-dimethylaminoethoxy)-androst-5-en-17-one on the sterol and steryl ester composition of Saccharomyces cerevisiae. Lipids 1979; 14:741-7. [PMID: 393929 DOI: 10.1007/bf02533900] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
When yeast was grown in the presence of 10(-4) M 3 beta-(beta-dimethylaminoethoxy)-androst-5-en-17-one (DMAE-DHA), the compound 2,3;22,23-dioxidosqualene (DOS) accumulated. Total free sterol was reduced by about 30%, whereas almost no steryl esters were found. The same drug at lower concentration (3 x 10(-6) M) caused a slight increase in steryl ester production, and a 24% reduction in free sterol content. The marked accumulation of ergostra-5,7,22,24(28)-tetraen-3 beta-ol with 3 x 10(-6) M DMAE-DHA indicated that the C24-28 reductase is especially sensitive to the action of the drug.
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Ramsey RB. Effect of hypocholesterolemic agents on central nervous system cholesterol biosynthesis III. Zuclomiphene in combination with AY9944 and triparanol. Biochem Pharmacol 1978; 27:1637-40. [PMID: 81057 DOI: 10.1016/0006-2952(78)90172-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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18
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Campagnoni C, Holmlund CE, Whittaker N. The effect of triparanol on the composition of free and esterified sterols of Saccharomyces cerevisiae. Arch Biochem Biophys 1977; 184:555-60. [PMID: 339844 DOI: 10.1016/0003-9861(77)90465-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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19
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Sobus MT, Holmlund CE, Whittaker NF. Effects of the hypocholesteremic agent trifluperidol on the sterol, steryl ester, and fatty acid metabolism of Saccharomyces cerevisiae. J Bacteriol 1977; 130:1310-6. [PMID: 324983 PMCID: PMC235355 DOI: 10.1128/jb.130.3.1310-1316.1977] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Trifluperidol (TFP), at a concentration of 100 muM, inhibited the 24-h growth of Saccharomyces cerevisiae by about 30%. Effects on lipid metabolism were investigated by monitoring the incorporation of [1-14C]sodium acetate into various lipid fractions after 4 and 24 h of growth in the presence of several concentrations of TFP. Although little effect was noted on the amount of free sterols, 24-h incorporation of label into steryl esters was increased two- to fourfold by 100 muM TFP. Major sterol components of the steryl ester fraction isolated from an untreated culture were zymosterol (48%) and ergosterol (24%), whereas from the TFP-treated culture delta8,24(28)-ergostadienol (66.6%) and delta8-ergostenol (14.7%) were most abundant. Free sterols present in the highest concentration in the untreated culture were ergosterol (78.2%) and lanosterol (13%); whereas delta8,22-ergostadienol (38.5%), delta8-ergostenol (35.4%), and delta8,24(28)-ergostadienol (25.4%) were the most abundant free sterols obtained from the TFP-treated culture. Thus, the major block in the sterol biosynthetic pathway in yeast appears to be delta8 leads to delta7 isomerization. In these same cultures the relative amounts of C12 and C14 acids isolated from both steryl ester and miscellaneous lipid fractions were increased more than threefold over controls.
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Gollub EG, Liu KP, Dayan J, Adlersberg M, Sprinson DB. Yeast mutants deficient in heme biosynthesis and a heme mutant additionally blocked in cyclization of 2,3-oxidosqualene. J Biol Chem 1977. [DOI: 10.1016/s0021-9258(17)40440-6] [Citation(s) in RCA: 176] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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21
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Field RB, Holmlund CE. Isolation of 2,3;22,23-dioxidosqualene and 24,25-oxidolanosterol from yeast. Arch Biochem Biophys 1977; 180:465-71. [PMID: 327938 DOI: 10.1016/0003-9861(77)90061-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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