scholarly journals Stimulation of liver cholesterol synthesis by actinomycin D

1968 ◽  
Vol 109 (5) ◽  
pp. 775-785 ◽  
Author(s):  
F. De Matteis
Keyword(s):  
Actinomycin D ◽  
Ketone Bodies ◽  
Cholesterol Biosynthesis ◽  
Mevalonic Acid ◽  
Liver Cholesterol ◽  
Tenfold Increase ◽  
Coa Reductase ◽  
Rate Limiting ◽  
Stimulation Of

1. An eightfold increase in the incorporation of [2−14C]acetate into liver cholesterol in vivo was observed 24hr. after starved rats had been given actinomycin D (0·5mg./kg. of body wt.). Liver cholesterol radioactivity declined faster in the treated animals, suggesting a greater rate of cholesterol turnover. 2. Liver slices from treated animals showed a tenfold increase in the incorporation of [2−14C]acetate into cholesterol; conversion into CO2 and into fatty acids was less markedly increased, and conversion into ketone bodies was not significantly affected. 3. The patterns of conversion into liver cholesterol in vivo of the lactone and the sodium salt of mevalonic acid differed markedly. The former was converted at a faster rate and to a greater extent than the latter. Treatment with actinomycin D increased the conversion of both forms of mevalonic acid into liver cholesterol, but only to a small extent. 4. Stimulation of the incorporation of acetate into cholesterol occurred at 4hr. after the administration of actinomycin D but not at 2hr. The response was abolished by the simultaneous administration of dl-ethionine or puromycin. 5. Pre-feeding with a cholesterol-rich diet greatly diminished the stimulation of conversion of acetate into cholesterol caused by actinomycin D, though it did not completely suppress it. Adrenalectomized animals responded to the drug, but much less markedly. 6. It is concluded that actinomycin D stimulates the synthesis of cholesterol in the liver at a stage in the pathway before mevalonic acid, by a mechanism that probably requires protein synthesis. A likely site would be the β-hydroxy-β-methylglutaryl-CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis. Some possible mechanisms by which the drug may lead to increased activity of this enzyme are considered.

scholarly journals ENZYME-MEMBRANE RELATIONSHIP IN PHENOBARBITAL INDUCTION OF SYNTHESIS OF DRUG-METABOLIZING ENZYME SYSTEM AND PROLIFERATION OF ENDOPLASMIC MEMBRANES

1966 ◽  
Vol 28 (2) ◽  
pp. 181-198 ◽  
Author(s):  
Sten Orrenius ◽  
Jan L. E. Ericsson
Keyword(s):  
Actinomycin D ◽  
Enzyme System ◽  
Drug Metabolizing Enzyme ◽  
Induction Process ◽  
Autophagic Activity ◽  
Metabolizing Enzyme ◽  
Parenchymal Cells ◽  
Phenobarbital Induction ◽  
Stimulation Of

The enzyme-membrane relationship in phenobarbital induction of synthesis of drug-metabolizing enzyme system and proliferation of endoplasmic membranes has been further studied. Ultrastructural observations suggest that newly formed endoplasmic membranes in rat liver parenchymal cells arise through continuous outgrowth and budding off from pre-existing cisternae and tubules of rough-surfaced endoplasmic reticulum. The membranes induced by phenobarbital treatment persist in the cytoplasm of the hepatocyte for up to 15 days after the last of a series of 5 phenobarbital injections; the phase of regression of the induced enzymes lasts for only 5 days. Disappearance of the membranes is gradual and does not seem to be associated with increased autophagic activity in the cell. A second series of injections of phenobarbital to previously induced rats—exhibiting normal drug-hydroxylating activity but an excess of liver endoplasmic membranes—is associated with a stimulation of the rate of Pi32 incorporation into microsomal phospholipid in vivo, similar to that found during the original induction process. Administration of Actinomycin D following a single phenobarbital injection delays the regression of the enhanced drug-hydroxylating activity. Finally, the effects of Actinomycin D and puromycin on the stimulated membrane formation are discussed.

scholarly journals Regulation of hepatic cholesterol biosynthesis. Effects of a cytochrome P-450 inhibitor on the formation and metabolism of oxygenated sterol products of lanosterol

1989 ◽  
Vol 264 (2) ◽  
pp. 495-502 ◽  
Author(s):  
J Iglesias ◽  
G F Gibbons
Keyword(s):  
Reductase Activity ◽  
Cholesterol Biosynthesis ◽  
Mevalonic Acid ◽  
Subcellular Fractions ◽  
Hmg Coa Reductase ◽  
Hepatocyte Cultures ◽  
C 32 ◽  
Lanosterol Demethylase ◽  
Cholesterol Precursor ◽  
Coa Reductase

The involvement of oxygenated cholesterol precursors in the regulation of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was studied by examining the effect of ketoconazole on the metabolism of mevalonic acid, lanosterol and the lanosterol metabolites, lanost-8-ene-3 beta,32-diol,3 beta-hydroxylanost-8-en-32-al and 4,4-dimethylcholesta-8,14-dien-3 beta-ol, in liver subcellular fractions and hepatocyte cultures. Inhibition of cholesterol synthesis from mevalonate by ketoconazole at concentrations up to 30 microM was due exclusively to a suppression of cytochrome P-450LDM (LDM = lanosterol demethylase) activity, resulting in a decreased rate of lanosterol 14 alpha-demethylation. No enzyme after the 14 alpha-demethylase step was affected. When [14C]mevalonate was the cholesterol precursor, inhibition of cytochrome P450LDM was accompanied by the accumulation of several labelled oxygenated sterols, quantitatively the most important of which was the C-32 aldehyde derivative of lanosterol. There was no accumulation of the 24,25-oxide derivative of lanosterol, nor of the C-32 alcohol. Under these conditions the activity of HMG-CoA reductase declined. The C-32 aldehyde accumulated to a far greater extent when lanost-8-ene-3 beta,32-diol rather than mevalonate was used as the cholesterol precursor in the presence of ketoconazole. With both precursors, this accumulation was reversed at higher concentrations of ketoconazole in liver subcellular fractions. A similar reversal was not observed in hepatocyte cultures.

scholarly journals Regulation of the synthesis of lutropin-induced protein in rat testis Leydig cells

1978 ◽  
Vol 170 (1) ◽  
pp. 9-15 ◽  
Author(s):  
Felix H. A. Janszen ◽  
Brian A. Cooke ◽  
Maria J. A. Van Driel ◽  
Henk J. Van Der Molen
Keyword(s):  
Protein Synthesis ◽  
Cyclic Amp ◽  
Leydig Cells ◽  
Actinomycin D ◽  
Polyacrylamide Gel Electrophoresis ◽  
Phosphodiesterase Inhibitor ◽  
Dibutyryl Cyclic Amp ◽  
Rat Testis ◽  
Stimulation Of

The mechanism of action of lutropin on the stimulation of the synthesis of a specific lutropin-induced protein in rat testis Leydig cells was investigated. Lutropin-induced protein has a mol.wt. of approx. 21000 and is detected by labelling the Leydig-cell proteins with [35S]methionine, followed by separation by polyacrylamide-gel electrophoresis and radioautography of the dried gel. The incorporation of35S into lutropin-induced protein was used as an estimate for the synthesis of the protein. Incubation of Leydig cells with dibutyryl cyclic AMP or cholera toxin also resulted in the stimulation of synthesis of the protein. Synthesis of lutropin-induced protein, when maximally stimulated with 100ng of lutropin/ml, could not be stimulated further by addition of dibutyryl cyclic AMP. Addition of 3-isobutyl-1-methylxanthine, a phosphodiesterase inhibitor, further increased synthesis of the protein in the presence of a submaximal dose of lutropin (10ng/ml) but not in the absence of lutropin or with maximal amounts of lutropin (100 and 1000ng/ml). Actinomycin D prevented the effect of lutropin on the stimulation of lutropin-induced protein synthesis when added immediately or 1h after the start of the incubation, but not when added after 5–6h. This is interpreted as reflecting that, after induction of mRNA coding for lutropin-induced protein, lutropin had no influence on the synthesis of the protein in the presence of actinomycin D. Synthesis of the protein was also stimulated in vivo by injection of choriogonadotropin into rats 1 day after hypophysectomy, and the time course of this stimulation of lutropin-induced protein synthesis in vivo was similar to that obtained by incubating Leydig cells in vitro with lutropin. From these results it is concluded that stimulation of lutropin-induced protein synthesis by lutropin is most probably mediated by cyclic AMP and involves synthesis of mRNA.

The regulated degradation of a 3-hydroxy-3-methylglutaryl-coenzyme A reductase reporter construct occurs in the endoplasmic reticulum

1994 ◽  
Vol 107 (9) ◽  
pp. 2635-2642
Author(s):  
L.W. Lecureux ◽  
B.W. Wattenberg
Keyword(s):  
Endoplasmic Reticulum ◽  
Coenzyme A ◽  
Cholesterol Biosynthesis ◽  
Mevalonic Acid ◽  
Dna Encoding ◽  
Hmg Coa Reductase ◽  
Steady State Levels ◽  
Coa Reductase ◽  
Membrane Anchoring ◽  
Beta Galactosidase

The rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG CoA) reductase, is regulated at a number of levels. One important mechanism is regulation of the half-life of the protein by a controlled proteolytic system. This comes about in response to downstream products of the sterol biosynthetic pathway. Little is known about this system, including where in the cell this regulated degradation occurs. HMG CoA reductase resides in the endoplasmic reticulum. To localize the site of regulated degradation of HMG CoA reductase, we used a construct that fuses the N-terminal membrane-anchoring domain of HMG CoA reductase in-frame with beta-galactosidase as a reporter domain (HM-Gal). HM-Gal has previously been shown to reproduce faithfully the degradative properties of native HMG CoA reductase (Chun et al. (1990) J. Biol. Chem. 265, 22004–22010). CHO cells transfected with DNA encoding HM-Gal were exposed to mevalonic acid, which enhances the rate of HMG CoA reductase degradation several fold, and leads to the reduction of the steady state levels of HM-Gal by 80–90%. To accumulate HMG CoA reductase at the site of degradation, cells were simultaneously treated with N-acetyl-leucyl-leucyl-norleucinal (ALLN), which inhibits the protease responsible for reductase degradation. HM-Gal was localized morphologically by immunofluorescence and biochemically by measuring beta-galactosidase activity in Percoll gradients of cellular homogenates. Using either technique HM-Gal localization was indistinguishable from that of ER markers in both control cells and in cells treated to accumulate HMG CoA reductase at the site of degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals A discoordinate increase in the cellular amount of 3-hydroxy-3-methylglutaryl-CoA reductase results in the loss of rate-limiting control over cholesterogenesis in a tumour cell-free system

1989 ◽  
Vol 258 (2) ◽  
pp. 421-425 ◽  
Author(s):  
N I Azrolan ◽  
P S Coleman
Keyword(s):  
Cholesterol Biosynthesis ◽  
Normal Liver ◽  
Preliminary Evidence ◽  
Free System ◽  
Normal Rat ◽  
Morris Hepatoma ◽  
Coa Reductase ◽  
Rate Limiting ◽  
Hydroxymethylglutaryl Coa Reductase ◽  
Tumour System

Cholesterol biosynthesis was characterized in cell-free post-mitochondrial supernatant systems prepared from both normal rat liver and Morris hepatoma 3924A. The rate of cholesterol synthesis per cell was 9-fold greater in the tumour system than in that from normal liver, and the tumour systems showed the loss of rate-limiting control at the hydroxymethylglutaryl-CoA reductase (HMGR)-catalysed step. The apparent absence of rate-limiting control over cell-free tumour cholesterogenesis was traced primarily to a discoordinate and dramatic increase in the amount of HMGR in the tumour relative to the liver system. Preliminary evidence for an altered control of the post-lanosterol portion of the pathway was also obtained with the tumour system.

Stimulation of inflammatory responses in vitro and in vivo by lipophilic HMG-CoA reductase inhibitors

2001 ◽  
Vol 1 (1) ◽  
pp. 105-118 ◽  
Author(s):  
Peter A Kiener ◽  
Patricia M Davis ◽  
Judy L Murray ◽  
Sonia Youssef ◽  
Bruce M Rankin ◽  
...  
Keyword(s):  
Inflammatory Responses ◽  
Hmg Coa Reductase ◽  
Reductase Inhibitors ◽  
Hmg Coa Reductase Inhibitors ◽  
Coa Reductase ◽  
Stimulation Of

scholarly journals Corticotropin regulation of the synthesis of a specific rat adrenal cytosolic protein. Effects of hypophysectomy and actinomycin D

1979 ◽  
Vol 182 (3) ◽  
pp. 717-725 ◽  
Author(s):  
Alice Dazord ◽  
Dominique Gallet ◽  
Helene Cohen ◽  
Jose M. Saez
Keyword(s):  
Protein Synthesis ◽  
Cyclic Amp ◽  
Total Protein ◽  
Actinomycin D ◽  
Polyacrylamide Gel Electrophoresis ◽  
Cytosolic Protein ◽  
And Control ◽  
Corticotropin Stimulation ◽  
Stimulation Of

The mechanism of corticotropin stimulation of the synthesis of a specific rat adrenal cytosolic protein was investigated. This protein (protein E) has a mol.wt. of approx. 30000. It is detected by polyacrylamide-gel electrophoresis of cytosol prepared from adrenal slices from rats treated with corticotropin in vivo and control rats, the slices being incubated with [3H]- and [14C]-leucine respectively. In rats 1–15 days after hypophysectomy, corticotropin, like dibutyryl cyclic AMP, induces an increase in protein E similar to that induced in control rats, even though both compounds no longer stimulate total protein synthesis. Corticotropin stimulation of protein E synthesis is mediated by cyclic AMP but not by corticosterone, since aminoglutethimide, a steroidogenic inhibitor, does not affect corticotropin stimulation, and dexamethasone alone has no effect. Actinomycin D, when injected in vivo 1h before or after corticotropin injection, prevents the effect of corticotropin on protein E synthesis, which is interpreted as evidence that mRNA synthesis is necessary for the stimulation of protein E synthesis. When injected more than 2h after corticotropin, actinomycin D does not prevent corticotropin stimulation of protein E synthesis, but completely blocks corticotropin stimulation of total protein synthesis. This is interpreted as meaning that, after stimulation of mRNA coding for protein E, corticotropin has no effect on the synthesis of protein E. On the other hand, corticotropin stimulation of protein E synthesis persists after hypophysectomy even though it no longer stimulates total protein synthesis. These data suggest that the factor(s) involved in the synthesis of protein E are more stable than those involved in total protein synthesis.

scholarly journals High-Risk Polymorphisms Associated with the Molecular Function of Human HMGCR Gene Infer the Impedance of Cholesterol Biosynthesis

2021 ◽  
Author(s):  
Keshob Chandra Das ◽  
Mohammad Uzzal Hossain ◽  
Md Moniruzzaman ◽  
Md Salimullah ◽  
Sharif Akhteruzzaman
Keyword(s):  
Solvent Accessibility ◽  
Cholesterol Biosynthesis ◽  
Functional Domain ◽  
Nucleotide Polymorphisms ◽  
Single Nucleotide ◽  
Functional Instability ◽  
Structural Evaluation ◽  
Coa Reductase ◽  
Rate Limiting ◽  
Major Target

Abstract Background: HMG-CoA reductase or HMGCR (3-Hydroxy-3-methylglutaryl-CoA reductase) is a rate-limiting enzyme involved in cholesterol biosynthesis. HMGCR plays an important role in the possible occurrence of hypercholesterolemia leading to atherosclerosis and coronary heart disease. This enzyme is a major target for cholesterol lowering drugs such as “statins” which blocks the synthesis of mevalonate, a precursor for cholesterol biosynthesis. This study aims to characterize deleterious mutations and classify functional Single Nucleotide Polymorphisms (SNPs) of the HMGCR gene through analysis of functional and structural evaluation, domain association, solvent accessibility, and energy minimization studies. Results: Among 6,815 SNP entries from different databases, approximately 388 SNPs were found to be missense. Analysis showed that seven missense SNPs are more likely to have deleterious effects. A tertiary model of the mutant protein was constructed to determine the functional and structural effects of the HMGCR mutation. In addition, the location of the mutations suggests that they may have deleterious effects because most of the mutations are resides in the functional domain of the protein. The findings from the bunch of bioinformatics tools predicted that rs147043821 and rs193026499 missense SNPs could cause significant structural and functional instability in the mutated proteins of the HMGCR gene. Conclusion: Therefore, the results of the current study would undoubtedly be accommodating in future endeavors concerning drug discovery and therapeutics against hypercholesterolemia.

Sign in / Sign up

Export Citation Format

Share Document