Antioxidant and Inhibitory Activities of Filipendula glaberrima Leaf Constituents against HMG-CoA Reductase and Macrophage Foam Cell Formation

In our search for bioactive components, various chromatographic separations of the organic fractions from Filipendula glaberrima leaves led to the isolation of a new ellagitannin and a triterpenoid, along with 26 known compounds. The structures of the isolates were determined based on their spectroscopic properties and chemical evidence, which were then evaluated for their antioxidant activities, inhibitory activities on 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and foam cell formation in THP-1 cells to prevent atherosclerosis. Rugosin B methyl ester (1) showed the best HMG-CoA reductase inhibition and significantly reduced ox-low-density lipoprotein-induced THP-1 macrophage-derived foam cell formation at 25 µM. In addition, no cytotoxicity was observed in THP-1 cells at 50 μg/mL of all extracts in the macrophage foam cell formation assay. Therefore, F. glaberrima extract containing 1 is promising in the development of dietary supplements due to its potential behavior as a novel source of nutrients for preventing and treating atherosclerosis.

Inhibitors of 3-Hydroxy-3-methylglutaryl Coenzyme A Reductase Decrease the Growth, Ergosterol Synthesis and Generation of petite Mutants in Candida glabrata and Candida albicans

Candida glabrata and Candida albicans, the most frequently isolated candidiasis species in the world, have developed mechanisms of resistance to treatment with azoles. Among the clinically used antifungal drugs are statins and other compounds that inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), resulting in decreased growth and ergosterol levels in yeasts. Ergosterol is a key element for the formation of the yeast cell membrane. However, statins often cause DNA damage to yeast cells, facilitating mutation and drug resistance. The aim of the current contribution was to synthesize seven series of compounds as inhibitors of the HMGR enzyme of Candida ssp., and to evaluate their effect on cellular growth, ergosterol synthesis and generation of petite mutants of C. glabrata and C. albicans. Compared to the reference drugs (fluconazole and simvastatin), some HMGR inhibitors caused lower growth and ergosterol synthesis in the yeast species and generated fewer petite mutants. Moreover, heterologous expression was achieved in Pichia pastoris, and compounds 1a, 1b, 6g and 7a inhibited the activity of recombinant CgHMGR and showed better binding energy values than for α-asarone and simvastatin. Thus, we believe these are good candidates for future antifungal drug development.

Ameliorations in dyslipidemia and atherosclerotic plaque by the inhibition of HMG-CoA reductase and antioxidant potential of phytoconstituents of an aqueous seed extract of Acacia senegal (L.) Willd in rabbits

The assigned work was aimed to examine the capability of phytoconstituents of an aqueous seed extract of Acacia senegal (L.) Willd to inhibit HMG-CoA reductase and regression of the atherosclerotic plaque. The chemical fingerprinting of the test extract was assessed by LC-MS/MS. Consequently, the analyses of in-vitro, in-vivo, and in-silico were executed by using the standard protocols. The in-vitro assessment of the test extract revealed 74.1% inhibition of HMG-CoA reductase. In-vivo assessments of the test extract indicated that treated hypercholesterolemic rabbits exhibited a significant (P≤0.001) amelioration in the biomarker indices of the dyslipidaemia i.e., atherogenic index, Castelli risk index(I&II), atherogenic coefficient along with lipid profile. Subsequently, significant reductions were observed in the atherosclerotic plaque and antioxidant levels. The in-silico study of molecular docking shown interactions capabilities of the leading phytoconstituents of the test extract i.e., eicosanoic acid, linoleic acid, and flavan-3-ol with target protein of HMG-CoA reductase. The values of RSMF and potential energy of top docked complexes were show significant interactions. Accordingly, the free energy of solvation, interaction angle, radius of gyration and SASA were shown significant stabilities of top docked complex. The cumulative data of results indicate phytoconstituents of an aqueous seed extract of Acacia senegal have capabilities to inhibit the HMG-CoA reductase and improve the levels of antioxidants.

The 3-hydroxy-3-methylglutaryl-coenzyme A reductase 5 gene from Malus domestica enhances oxidative stress tolerance in Arabidopsis thaliana

3-Hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) is the first rate-limiting enzyme regulating the synthesis of terpenoids upstream of the mevalonate (MVA) pathway. In higher plants, members of the HMGR genes families play an important role in plant growth and development and in response to various environmental stresses. In the present study, a novel HMGR gene, designated MdHMGR5, was isolated from apple (Malus domestica L.) and characterized. Expression of MdHMGR5 enhanced the activity of HMGR enzyme in transgenic Arabidopsis thaliana L. plants. Under oxidative stress, transgenic A. thaliana plants over-expressing MdHMGR5 had a higher germination rate, a longer main root length, higher chlorophyll and proline content, and higher activities of antioxidant enzymes. On the other hand, malondialdehyde (MDA) content, relative conductivity and reactive oxygen species (ROS) production rate were significantly lower than in wild type plants. These results indicated that over-expression of MdHMGR5 enhanced plant tolerance to oxidative stress by scavenging ROS in transgenic plants. Over-expression of MdHMGR5 also affected the expression levels of genes in mevalonic acid and 2C-methyl-D-erythritol 4-phosphate (MVA and MEP) pathways of A. thaliana plants. These results indicate that over-expression of MdHMGR5 enhances tolerance to oxidative stress by maintaining photosynthesis and scavenging ROS in transgenic A. thaliana plants.

Purification of brain peroxisomes and localization of 3-hydroxy-3-methylglutaryl coenzyme A reductase

At least three different subcellular compartments, including peroxisomes, are involved in cholesterol biosynthesis. Because proper CNS development depends on de novo cholesterol biosynthesis, peroxisomes must play a critical functional role in this process. Surprisingly, no information is available on the peroxisomal isoprenoid/cholesterol biosynthesis pathway in normal brain tissue or on the compartmentalization of isoprene metabolism in the CNS. This has been due mainly to the lack of a well-defined isolation procedure for brain tissue, and also to the presence of myelin in brain tissue, which results in significant contamination of subcellular fractions. As a first step in characterizing the peroxisomal isoprenoid pathway in the CNS, we have established a purification procedure to isolate peroxisomes and other cellular organelles from the brain stem, cerebellum and spinal cord of the mouse brain. We demonstrate by use of marker enzymes and immunoblotting with antibodies against organelle specific proteins that the isolated peroxisomes are highly purified and well separated from the ER and mitochondria, and are free of myelin contamination. The isolated peroxisomal fraction was purified at least 40-fold over the original homogenate. In addition, we show by analytical subcellular fractionation and immunoelectron microscopy that HMG-CoA reductase protein and activity are localized both in the ER and peroxisomes in the CNS.

Age-related changes in cholesterol metabolism in macrosomic offspring of rats with streptozotocin-induced diabetes

The aim of this study was to determine the impact of diabetic macrosomia on cholesterol and lipoprotein metabolism. Age-related changes in the activities of serum LCAT, hepatic HMG-CoA reductase, cholesterol 7alpha-hydroxylase, and ACAT, the major enzymes involved in cholesterol metabolism, were determined in macrosomic offspring of streptozotocin-induced diabetic rats. Hepatic, serum, and lipoprotein cholesterol contents were also examined. Mild hyperglycemia in pregnant rats was induced by intraperitoneal injection of streptozotocin (40 mg/kg body weight) on day 5 of gestation. Control pregnant rats were injected with citrate buffer. At birth, macrosomic pups had higher serum, LDL-HDL(1), and HDL(2-3) cholesterol levels (P < 0.05) associated with increased LCAT activity (+57%) compared with control values. At 1 and 2 months of life, serum and lipoprotein cholesterol concentrations in macrosomic rats were similar to those of controls, whereas LCAT activity remained elevated about 1.5-fold. In addition, there was no change in hepatic cholesterol contents but hepatic HMG-CoA reductase, cholesterol 7alpha-hydroxylase, and ACAT activities were higher in both macrosomic males and females than in their respective controls (P < 0.01). By 3 months, macrosomic rats had developed hypercholesterolemia with a rise in all lipoproteins. Enzyme activities were still increased in these mature macrosomic rats, and hepatic cholesteryl esters were higher only in macrosomic females. These data demonstrate an overproduction, combined with overutilization, of cholesterol during the phase of rapid growth in macrosomic rats. However, cholesterol oversynthesis exceeded its removal and was a major contributor to hypercholesterolemia in adult macrosomic rats. In conclusion, macrosomia was associated with alterations in cholesterol metabolism through adulthood.

3-Hydroxy-3-methylglutaryl Coenzyme A Reductase Is Sterol-Dependently Cleaved by Cathepsin L-Type Cysteine Protease in the Isolated Endoplasmic Reticulum

We have recently shown that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, an endoplasmic reticulum (ER) membrane protein, is degraded in ER membranes prepared from sterol pretreated cells and that such degradation is catalyzed by a cysteine protease within the reductase membrane domain. The use of various protease inhibitors suggested that degradation of HMG-CoA reductase in vitro is catalyzed by a cathepsin L-type cysteine protease. Purified ER contains E-64-sensitive cathepsin L activity whose inhibitor sensitivity was well matched to that of HMG-CoA reductase degradation in vitro. CLIK-148 (cathepsin L inhibitor) inhibited degradation of HMG-CoA reductase in vitro. Purified cathepsin L also efficiently cleaved HMG-CoA reductase in isolated ER preparations. To determine whether a cathepsin L-type cysteine protease is involved in sterol-regulated degradation of HMG-CoA reductase in vivo, we examined the effect of E-64d, a membrane-permeable cysteine protease inhibitor, in living cells. While lactacystin, a proteasome-specific inhibitor, inhibited sterol-dependent degradation of HMG-CoA reductase, E-64d failed to do so. In contrast, degradation of HMG-CoA reductase in sonicated cells was inhibited by E-64d, CLIK-148, and leupeptin but not by lactacystin. Our results indicate that HMG-CoA reductase is degraded by the proteasome under normal conditions in living cells and that it is cleaved by cathepsin L leaked from lysosomes during preparation of the ER, thus clarifying the apparently paradoxical in vivo and in vitro results. Cathepsin L-dependent proteolysis was observed to occur preferentially in sterol-pretreated cells, suggesting that sterol treatment results in conformational changes in HMG-CoA reductase that make it more susceptible to such cleavage.

Effect of exposure to a country liquor (Toddy) during gestation on lipid metabolism in rats

The objective of this study was to determine the effects of country liquor Toddy and its equivalent quantity of ethanol on lipid metabolism during gestation in rats. Female rats weighing an average of 125 g were exposed to Toddy (24.5 ml/body weight/day) and ethanol (0.52 ml/kg body weight/day) for 15 days before conception and throughout gestation. On the 19th day of gestation, altered liver function and hyperlipidemia was seen in both the treated groups. Altered liver function was evidenced by the increased activity of alcohol dehydrogenase, aldehyde dehydrogenase, glutamic oxaloacetic transaminase or aspartate amino transferase (GOT), glutamic pyruvic transaminase or alanine amino transferase (GPT) and gamma glutamyl transpeptidase (GGT). Hyperlipidemia was caused by increased biosynthesis and decreased degradation of lipids. The incorporation of 14C acetate in lipids and activities of HMG CoA reductase and lipogenic enzymes were elevated and activity of LPL and bile acids contents were decreased. Toddy treated rats were more severely affected than those receiving an equivalent quantity of ethanol. Toddy seemed to potentiate the toxicity induced by alcohol indicating the role of the nonethanolic portion. Hepatic functions were also affected.

Cloning and characterization of the gene encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase in melon (Cucumis melo L. reticulatus)

We have isolated a cDNA for Cm-HMGR, encoding 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in melon (Cucumis melo L. reticulatus; Genbank Accession No. AB021862). Cm-HMGR encodes a polypeptide of 588 amino acids that contains two transmembrane domains and a catalytic domain. Database searches revealed that Cm-HMGR shows homology to HMG1 (63.7%) and HMG2 (70.3%) of tomato, to HMG1 (77.2%) and HMG2 (69.4%) of Arabidopsis thaliana, and to HMGR of tobacco (72.6%). Functional expression in a HMG-CoA reductase-deficient mutant yeast showed that Cm-HMGR products mediate the synthesis of mevalonate. Northern analysis revealed that the level of Cm-HMGR mRNA in the fruit increased after pollination and markedly decreased at the end of fruit enlargement. During ripening, Cm-HMGR mRNA levels increased markedly in the fruit. In parallel with mRNA expression, Cm-HMGR activity increased after pollination, whereas no Cm-HMGR activity was detectable during fruit ripening. Our results suggest that Cm-HMGR is important during early post-pollination development of the fruit in melon.

[Phenotypic changes in transgenic tobacco plants with an antisense form of the hmg1 gene]

Tobacco plants were genetically transformed with the Arabidopsis thaliana heterologous hmg1 gene encoding 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme involved in the metabolism of terpenoid compounds. The hmg1 gene was inserted under the control of the 35S RNA double promoter from the cauliflower mosaic virus (CaMV 35S) both in direct and reverse orientation relative to the promoter. DNA analysis by polymerase chain reaction (PCR) and Southern blotting confirmed the transgenic nature of the tobacco plants obtained. DNA-RNA hybridization revealed expression of the hmg1 gene in these tobacco plants. The plants transformed with the antisense copy of the hmg1 gene differed from the control plants in delayed development and in flower color and shape.

Mapping and molecular characterization of five HMG1-related DNA sequences

Recently, the high mobility group (HMG) proteins have attracted a lot of interest since it was shown that some members of that group can causally be involved in tumorigenesis. One HMG protein gene member is HMG1 for which the number of related DNA sequences has been estimated to be approximately 20-30. Nevertheless, besides the gene for HMG1 only one retropseudogene has been molecularly characterized. It was the aim of this study to map and characterize further sequences related to HMG1. PCR-screening of a PAC library resulted in 25 very strongly positive clones apparently containing HMG1-like cDNA sequences. Of eight clones which were further investigated five were distinguishable from each other based on their chromosome assignment and DNA sequence. Due to their homology to the HMG1 gene the DNA sequences were designated as HMG1L1, HMG1L3, HMG1L4, HMG1L5, and HMG1L6. By FISH experiments they were assigned to 2q32, 2q35, 3p24, 15q22, and 20q13, respectively. Except for one sequence, they did not show mutations leading to a frame shift or a new termination codon. Thus, we cannot exclude that these four HMG1-related DNA sequences represent active genes or can at least be activated e.g. by chromosome rearrangements in tumor cells. So far, the existence of six genes encoding HMG proteins has been described but because of a high frequency of closely related DNA sequences in the human genome it can be assumed that some of them are either pseudogenes or very similar genes.

Molecular targets of a human HNF1 alpha mutation responsible for pancreatic beta-cell dysfunction

The reverse tetracycline-dependent transactivator system was employed in insulinoma INS-1 cells to achieve controlled inducible expression of hepatocyte nuclear factor-1 alpha (HNF1 alpha)-P291fsinsC, the most common mutation associated with subtype 3 of maturity-onset diabetes of the young (MODY3). Nuclear localized HNF1 alpha-P291fsinsC protein exerts its dominant-negative effects by competing with endogenous HNF1 alpha for the cognate DNA-binding site. HNF1 alpha controls multiple genes implicated in pancreatic beta-cell function and notably in metabolism- secretion coupling. In addition to reduced expression of the genes encoding insulin, glucose transporter-2, L-pyruvate kinase, aldolase B and 3-hydroxy-3-methylglutaryl coenzyme A reductase, induction of HNF1 alpha-P291fsinsC also significantly inhibits expression of mitochondrial 2-oxoglutarate dehydrogenase (OGDH) E1 subunit mRNA and protein. OGDH enzyme activity and [(14)C]pyruvate oxidation were also reduced. In contrast, the mRNA and protein levels of mitochondrial uncoupling protein-2 were dramatically increased by HNF1 alpha-P291fsinsC induction. As predicted from this altered gene expression profile, HNF1 alpha-P291fsinsC also inhibits insulin secretory responses to glucose and leucine, correlated with impaired nutrient-evoked mitochondrial ATP production and mitochondrial membrane hyperpolarization. These unprecedented results suggest the molecular mechanism of HNF1 alpha-P291fsinsC causing beta-cell dysfunction.

A gene cluster for the mevalonate pathway from Streptomyces sp. Strain CL190

A biosynthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1. 1.1.34), the rate-limiting enzyme of the mevalonate pathway for isopentenyl diphosphate biosynthesis, had previously been purified from Streptomyces sp. strain CL190 and its corresponding gene (hmgr) had been cloned (S. Takahashi, T. Kuzuyama, and H. Seto, J. Bacteriol. 181:1256-1263, 1999). Sequence analysis of the flanking regions of the hmgr gene revealed five new open reading frames, orfA to -E, which showed similarity to those encoding eucaryotic and archaebacterial enzymes for the mevalonate pathway. Feeding experiments with [1-(13)C]acetate demonstrated that Escherichia coli JM109 harboring the hmgr gene and these open reading frames used the mevalonate pathway under induction with isopropyl beta-D-thiogalactopyranoside. This transformant could grow in the presence of fosmidomycin, a potent and specific inhibitor of the nonmevalonate pathway, indicating that the mevalonate pathway, intrinsically absent in E. coli, is operating in the E. coli transformant. The hmgr gene and orfABCDE are thus unambiguously shown to be responsible for the mevalonate pathway and to form a gene cluster in the genome of Streptomyces sp. strain CL190.

Molecular cloning and structural analysis of 3-hydroxy-3-methylglutaryl coenzyme A reductase of the moth Agrotis ipsilon

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, which plays a key role in isoprenoid biosynthesis, catalyses the synthesis of mevalonate from HMG-CoA. Insects do not synthesize cholesterol de novo, rather mevalonate derivatives lead to non-sterol isoprenoids which are essential for development and reproduction. In this paper, we describe an HMG-CoA reductase of the moth Agrotis ipsilon and we report its expression in fat body, ovary, muscle, brain and corpora allata tissues of adult specimens. The analysis of the cDNA reveals that it encodes a polypeptide of 833 amino acids (Mr = 89785). Alignments of this HMG-CoA reductase from A. ipsilon with the homologous sequences of other eukaryotes shows a high degree of conservation in all species studied. Parsimony analysis based on these alignments produced dendrograms congruent with the current systematic schemes. This suggests that, during eukaryote evolution, HMG-CoA reductase diversified in parallel with taxonomic splitting.

Mutational analysis of the karmellae-inducing signal in Hmg1p, a yeast HMG-CoA reductase isozyme

In response to elevated levels of HMG-CoA reductase, an integral endoplasmic reticulum (ER) membrane protein, cells assemble novel ER arrays. These membranes provide useful models for exploration of ER structure and function, as well as general features of membrane biogenesis and turnover. Yeast express two functional HMG-CoA reductase isozymes, Hmg1p and Hmg2p, each of which induces morphologically different ER arrays. Hmg1p induces stacks of paired nuclear-associated membranes called karmellae. In contrast, Hmg2p induces peripheral ER membrane arrays and short nuclear-associated membrane stacks. In spite of their ability to induce different cellular responses, both Hmg1p and Hmg2p have similar structures, including a polytopic membrane domain containing eight predicted transmembrane helices. By examining a series of recombinant HMG-CoA reductase proteins, our laboratory previously demonstrated that the last ER-lumenal loop (Loop G) of the Hmg1p membrane domain contains a signal needed for proper karmellae assembly. Our goal was to examine the primary sequence requirements within Loop G that were critical for proper function of this signal. To this end, we randomly mutagenized the Loop G sequence, expressed the mutagenized Hmg1p in yeast, and screened for inability to generate karmellae at wild-type levels. Out of approximately 4000 strains with Loop G mutations, we isolated 57 that were unable to induce wild-type levels of karmellae assembly. Twenty-nine of these mutants contained one or more point mutations in the Loop G sequence, including nine single point mutants, four of which had severe defects in karmellae assembly. Comparison of these mutations to single point mutations that did not affect karmellae assembly did not reveal obvious patterns of sequence requirements. For example, both conservative and non-conservative changes were present in both groups and changes that altered the total charge of the Loop G region were observed in both groups. Our hypothesis is that Loop G serves as a karmellae-inducing signal by mediating protein-protein or protein-lipid interactions and that amino acids revealed by this analysis may be important for maintaining the proper secondary structure needed for these interactions.

A highly ordered structure in V(D)J recombination cleavage complexes is facilitated by HMG1

Central to understanding the process of V(D)J recombination is appreciation of the protein-DNA complex which assembles on the recombination signal sequences (RSS). In addition to RAG1 and RAG2, the protein HMG1 is known to stimulate the efficiency of the cleavage reaction. Using electrophoretic mobility shift analysis we show that HMG1 stimulates the in vitro assembly of a stable complex with the RAG proteins on each RSS. We use UV crosslinking studies of this complex with azido-phenacyl derivatized probes to map the contact sites between the RAG proteins, HMG1 derivatives and the RSS. We find that the RAG proteins make contacts at the nonamer, heptamer and adjacent coding region. The HMG1 protein by itself appears to localize at the 3' side of the nonamer, but a cooperative complex with the RAG proteins is positioned at the 3' side of the heptamer and adjacent spacer in the 12RSS. In the complex with RAG proteins, HMG1 is positioned primarily in the spacer of the 23RSS. We suggest that bends introduced into these DNA substrates at specific locations by the RAG proteins and HMG1 may help distinguish the 12RSS from the 23RSS and may therefore play an important role in the coordinated reaction.

Chinese green tea lowers cholesterol level through an increase in fecal lipid excretion

Lung Chen Tea, a Chinese green tea, has been found to lower serum and liver cholesterol. In this study, its dose response and mechanisms of action on cholesterol lowering in diet-induced hypercholesterolemic Sprague-Dawley rats were investigated. The activities of three major lipid metabolizing enzymes, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-Co A) reductase, cholesterol 7alpha-hydroxylase and fatty acid synthase (FAS), as well as fecal excretion of bile acids and cholesterol were examined. Lung Chen Tea administration for eight weeks significantly lowered the serum cholesterol in the 2% and 4% groups. The activities of the three enzymes were not affected by Lung Chen Tea, but the fecal bile acids and cholesterol excretions were significantly increased. These results demonstrated that Lung Chen Tea lowered plasma cholesterol by increasing fecal bile acids and cholesterol excretion. Further investigation is required to evaluate the exact mechanisms of action of Lung Chen Tea.

Salt stress affects sterol biosynthesis in the halophilic black yeast Hortaea werneckii

Hortaea werneckii is a black yeast recently isolated from salterns in Slovenia. Some of the adaptations of halophilic microorganisms to increased salinity and osmolarity of the environment are alterations in membrane properties. By modulating the fluidity, sterols play an important role as a component of eukaryotic biological membranes. We studied the regulation of sterol biosynthesis in H. werneckii through the activity and amount of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG R), a key regulatory enzyme in the biosynthesis of sterols. We found some differences in the characteristics of HMG R and in its regulation by different environmental salinities in H. werneckii when compared to the mesophilic baker's yeast, Saccharomyces cerevisiae. Our results suggest that halophilic black yeast regulates sterol biosynthesis through HMG R in a different way than mesophiles, which might be a consequence of the different ecophysiology of halophilic black yeasts. From this perspective, H. werneckii is an interesting novel model organism for studies on salt stress-responsive proteins as well as on sterol biosynthesis in eukaryotes.

Implication of recent trials with b-hydroxy-b-methylglutaryl coenzyme A reductase inhibitors for hypertension management

BACKGROUND

There is broad agreement that statin treatment should be targeted at absolute coronary heart disease (CHD) risk but no consensus on the level of risk to target. We have examined the implications of adopting three different treatment policies for the management of hypertensive patients in the UK using data from treated hypertensives aged 35-69 years included in the Health Survey for England (1993).

METHODS

We calculated the proportion of hypertensive patients with existing atherosclerotic cardiovascular disease requiring statin treatment for secondary prevention of CHD. For those without atherosclerotic cardiovascular disease (primary prevention), we estimated CHD risk from the Framingham equation and examined the proportion with CHD risk exceeding thresholds of 4.5, 3 and 1.5% per year.

RESULTS

Twenty-one percent of treated hypertensives would require statin treatment for secondary prevention of CHD. When the CHD event threshold for statin treatment was set at > or =4.5% per year [equivalent to a number needed to treat (NNT) in 5 years of 13] a further 0.6% of hypertensive patients were identified for treatment; at a threshold of 3.0% per year (NNT = 20) 5.5% of patients were identified for primary prevention; and at a threshold of 1.5% per year (NNT = 40) 28.5% of patients were identified for primary prevention.

CONCLUSIONS

Those needing secondary prevention are first priority for statins and 21% of hypertensive patients will require treatment Formulation of guidelines for primary prevention should take into account the NNT; the proportion of patients targeted for treatment; the cost-effectiveness and the total cost of treatment. Current British guidance will entail treating an additional 5.5% of hypertensive patients for primary prevention and therefore 27% of hypertensive patients.

A 'distributed degron' allows regulated entry into the ER degradation pathway

Protein degradation is employed in both regulation and quality control. Regulated degradation of specific proteins is often mediated by discrete regions of primary sequence known as degrons, whereas protein quality control involves recognition of structural features common to damaged or misfolded proteins, rather than specific features of an individual protein. The yeast HMG-CoA reductase isozyme Hmg2p undergoes stringently regulated degradation by machinery that is also required for ER quality control. The 523 residue N-terminal transmembrane domain of Hmg2p is necessary and sufficient for regulated degradation. To understand how Hmg2p undergoes regulated degradation by the ER quality control pathway, we analyzed over 300 mutants of Hmg2p. Regulated degradation of Hmg2p requires information distributed over the entire transmembrane domain. Accordingly, we refer to this determinant as a 'distributed' degron, which has functional aspects consistent with both regulation and quality control. The Hmg2p degron functions in the specific, regulated degradation of Hmg2p and can impart regulated degradation to fusion proteins. However, its recognition is based on dispersed structural features rather than primary sequence motifs. This mode of targeting has important consequences both for the prediction of degradation substrates and as a potential therapeutic strategy for targeted protein degradation using endogenous degradation pathways.

Activation of the cholesterol pathway and Ras maturation in response to stress

All cells depend on sterols and isoprenoids derived from mevalonate (MVA) for growth, differentiation, and maintenance of homeostatic functions. In plants, environmental insults like heat and sunlight trigger the synthesis of isoprene, also derived from MVA, and this phenomenon has been associated with enhanced tolerance to heat. Here, we show that in human prostate adenocarcinoma PC-3M cells heat shock leads to activation of the MVA pathway. This is characterized by a dose- and time-dependent elevation in 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) activity, enhanced sterol and isoprenoid synthesis, and increased protein prenylation. Furthermore, prenylation and subsequent membrane localization of Ras, a central player in cell signaling, was rapidly induced following heat stress. These effects were dose-dependent, augmented with repeated insults, and were prevented by culturing cells in the presence of lovastatin, a competitive inhibitor of HMGR. Enhanced Ras maturation by heat stress was also associated with a heightened activation of extracellular signal-regulated kinase (ERK), a key mediator of both mitogenic and stress signaling pathways, in response to subsequent growth factor stimulation. Thus, activation of the MVA pathway may constitute an important adaptive host response to stress, and have significant implications to carcinogenesis.

Epidermal growth factor stimulates 3-hydroxy-3-methylglutaryl-coenzyme A reductase expression via the ErbB-2 pathway in human breast adenocarcinoma cells

HMG-CoA reductase is the key enzyme for the biosynthesis of isoprenoid compounds essential for cell growth and differentiation. Its tyrosine kinase-dependent modulation has recently been suggested and described in the ErbB-2 overexpressing cell line SKBR-3 [Asslan et al. (1998) Biochem. J. 330, 241-246]. Epidermal growth factor (EGF) increased the HMG-CoA reductase activity, protein, and mRNA levels only in ErbB-2-expressing cells (SKBR-3 and MCF-7) but not in MDA-MB-468 cells that do not express ErbB-2 even though their EGF receptor was efficiently phosphorylated. Tyrphostin AG 879, a specific inhibitor of ErbB-2 tyrosine kinase activity, decreased HMG-CoA reductase activity only in cells that expressed ErbB-2. A functional EGF receptor appeared to be necessary since its inhibition by the specific tyrphostin AG 1478 abolished the EGF effects. Phosphatidylinositol 3-kinase (PI 3-kinase) might be a crucial enzyme in the signaling pathway since the specific inhibitor, LY 294002, was shown to inhibit HMG-CoA reductase activity and to completely abolish the stimulation by EGF in SKBR-3 cells.

Hmg-coA reductase gene family in cotton (Gossypium hirsutum L.): unique structural features and differential expression of hmg2 potentially associated with synthesis of specific isoprenoids in developing embryos

As a first step towards understanding the biosynthesis of isoprenoids that accumulate in specialized pigment glands of cotton at the molecular level, two full-length genes (hmg1 and hmg2) were characterized encoding hmg-coA reductase (HMGR; EC 1.1.1.34), the enzyme that catalyzes the formation of a key isoprenoid precursor. Cotton hmgr genes exhibited features typical of other plant genes, however, hmg2 encodes the largest of all plant HMGR enzymes described to date. HMG2 contains several novel features that may represent functional specialization of this particular HMGR isoform. Such features include a unique 42 amino acid sequence located in the region separating the N-terminal domain and C-terminal catalytic domain, as well as an N-terminal hydrophobic domain that is not found in HMG1 or other HMGR enzymes. DNA blot analysis revealed that hmg1 and hmg2 belong to small subfamilies that probably include homeologous loci in allotetraploid cotton (Gossypium hirsutum L.). Ribonuclease protection assays revealed that hmg1 and hmg2 are differentially expressed in a developmentally- and spatially-modulated manner during morphogenesis of specialized terpenoid-containing pigment glands in embryos. Induced expression of hmg2 coincided with a possible commitment to sesquiterpenoid biosynthesis in developing embryos, although other developmental processes also requiring HMGR cannot be excluded.

Structure of genes encoding chromosomal HMG1 proteins from maize

The high mobility group (HMG) proteins of the HMG1 family are architectural proteins in chromatin that are considered to facilitate the formation of complex nucleoprotein structures in various biological processes such as transcription and recombination. Plants express a variety of these non-sequence-specific DNA-bending proteins. The sequences encoding the maize HMGa and HMGc1 proteins were isolated from a genomic DNA library. Determination of the nucleotide sequences of these genes revealed that the coding region of both genes has a similar genomic structure, comprising seven exons and six introns. The positioning of the introns is conserved between the two genes, whereas the number of introns and their positions are entirely different in the related animal genes. In the 5' flanking region of the hmgc1 gene, a copia-like retrotransposon was identified. In addition to the genes encoding HMGa and HMGc1, several genomic fragments (retropseudo gene, fragments of the genes) were isolated and characterised.

3-Hydroxy-3-methylglutaryl coenzyme a reductase activity in liver of athymic mice with or without an implanted human carcinoma

Hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase activities and cholesterol content in the liver of athymic mice either bearing or not an implanted human lung mucoepidormoid carcinoma (HLMC) and in the neoplasic tissue, were analyzed. The properties of the HMG-CoA reductase of HLMC grown in nude mice and those ones found in the liver of these animals, sacrificed either at mid-light or mid-dark, were similar. The hepatic reductase activity was found to be four- to five-fold greater at mid-dark than at mid-light (462 +/- 141 vs. 123 +/- 22 pmol min-1 mg protein-1). Since the Km value was not modified, the mid-dark activity could be due to an increase in the amount of enzyme. In contrast, HLMC reductase activity and cholesterol content showed similar values at mid-light and mid-dark points. HLMC reductase does not appear to have any diurnal variation and the cholesterol synthesis and content seems to be independent of food intake. HLMC-bearing nude mice undergo several alterations in the biosynthesis and homeostasis of cholesterol. Hypocholesterolemia, lower hepatic cholesterol content and higher HMG-CoA reductase activity are characteristic of host mice.

Improvement in cholesterol metabolism in mice given chronic treatment of taurine and fed a high-fat diet

The effects of chronic treatment of taurine on hypercholesterolemia and atherosclerosis were examined in C57BL/6J mice fed a high-fat diet containing 15% fat and 1.25% cholesterol. Taurine was dissolved in drinking water at 1% (w/v) and was given to mice ad libitum during 6 months-feeding of a high-fat diet. Hypercholesterolemia occurred and lipid accumulation on the aortic valve was evident. Taurine treatment lowered serum LDL + VLDL cholesterol by 44% in mice fed a high-fat diet, while it elevated serum HDL cholesterol by 25%. As a result, the atherogenic index, the ratio of HDL to LDL + VLDL was markedly improved. Cholesterol content in the liver also decreased by 19% with taurine. Similar tendencies were seen in mice fed regular chow, but the changes were not significant. The area of aortic lipid accumulation, which served as an index of atherosclerosis, was reduced by 20% with taurine. In the liver, taurine doubled the activity of cholesterol 7alpha-hydroxylase. These observations, together with prior findings, suggest that the cholesterol-lowering action of taurine may relate to the increased conversion of cholesterol to bile acids via stimulation of cholesterol 7a-hydroxylase activity. Thus, chronic treatment of high-fat mice with taurine improves the abnormal profile of the serum lipoproteins, and thereby retards the progression of atherosclerosis.

Comparison of the effects of gemfibrozil and clofibric acid on peroxisomal enzymes and cholesterol synthesis of rat hepatocytes

We studied whether the peroxisomal proliferation, induction of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) and activation of cholesterol synthesis by gemfibrozil shown in whole body (Hashimoto F., Ishikawa T., Hamada S. and Hayashi H., Biochemical. Pharm., 49, 1213-1221 (1995)) is also detected at a culture cell level, and we made a comparative analysis of the effects of clofibric acid. Gemfibrozil at 0.25 mM increased the activity of some peroxisomal enzymes (catalase and the cyanide-insensitive fatty acyl-CoA oxidizing system) after incubation for 72 h. However, contrary to whole body experiments, gemfibrozil decreased the activity of HMG-CoA reductase and cholesterol synthesis from [14C]acetate. At 1 mM, gemfibrozil decreased not only the activity of HMG-CoA reductase and cholesterol synthesis, but also the protein content of the cells and peroxisomal enzyme activity, indicating nonspecific inhibition at this concentration. Clofibric acid (0.25 and 1 mM) increased the activity of peroxisomal enzymes, but decreased the activity of HMG-CoA reductase and cholesterol synthesis. With respect to the direct effect on HMG-CoA reductase in the cell homogenate, gemfibrozil at 0.25 mm did not affect the activity, but it clearly inhibited the activity at 2 mM and above. Clofibric acid at 2 mM hardly affected the activity, but it clearly decreased the activity at 5 mM and over. That is, gemfibrozil directly inhibited the activity more strongly than clofibric acid. The direct inhibition of the enzyme itself required higher concentrations of both agents than did inhibition at the culture cell level. These results suggest that the cytotoxicity of gemfibrozil is greater than that of clofibric acid, and that gemfibrozil, as well as clofibric acid, can induce peroxisomal enzymes in the culture cell level. In contrast to whole body results, gemfibrozil may suppress cholesterol synthesis from [14C]acetate through the inhibition of HMG-CoA reductase at the culture cell level. The decreases in the reductase activity caused by gemfibrozil and clofibric acid at the culture cell level may not be caused by the direct inhibition of the enzyme.

Sequence determinants for regulated degradation of yeast 3-hydroxy-3-methylglutaryl-CoA reductase, an integral endoplasmic reticulum membrane protein

The degradation rate of 3-hydroxy-3-methylglutaryl CoA reductase (HMG-R), a key enzyme of the mevalonate pathway, is regulated through a feedback mechanism by the mevalonate pathway. To discover the intrinsic determinants involved in the regulated degradation of the yeast HMG-R isozyme Hmg2p, we replaced small regions of the Hmg2p transmembrane domain with the corresponding regions from the other, stable yeast HMG-R isozyme Hmg1p. When the first 26 amino acids of Hmg2p were replaced with the same region from Hmg1p, Hmg2p was stabilized. The stability of this mutant was not due to mislocalization, but rather to an inability to be recognized for degradation. When amino acid residues 27-54 of Hmg2p were replaced with those from Hmg1p, the mutant was still degraded, but its degradation rate was poorly regulated. The degradation of this mutant was still dependent on the first 26 amino acid residues and on the function of the HRD genes. These mutants showed altered ubiquitination levels that were well correlated with their degradative phenotypes. Neither determinant was sufficient to impart regulated degradation to Hmg1p. These studies provide evidence that there are sequence determinants in Hmg2p necessary for degradation and optimal regulation, and that independent processes may be involved in Hmg2p degradation and its regulation.

Esterified cholesterol accumulation induced by aggregated LDL uptake in human vascular smooth muscle cells is reduced by HMG-CoA reductase inhibitors

Vascular smooth muscle cell (VSMC) proliferation is a key event in the development of atherosclerotic lesions. VSMCs synthesize extracellular matrix, where low density lipoproteins (LDLs) are trapped and become aggregated (agLDL). The objective of this study was to investigate the cholesterol uptake and accumulation triggered by agLDL in comparison with native LDL (nLDL) on unstimulated and platelet-derived growth factor-stimulated human aortic VSMCs and the role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on these processes. Esterified cholesterol (EC) accumulation induced by agLDL in VSMCs was correlated with the degree of aggregation and concentration. The EC content of VSMCs treated with 100 microg/mL of agLDL (80% aggregated) increased approximately 70-fold over that in VSMCs incubated with the same concentration of nLDL. Whereas nLDL-derived EC was increased approximately twofold in platelet-derived growth factor-stimulated VSMCs, there was no effect of platelet-derived growth factor (10(-9) mol/L) on the uptake of agLDL. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor simvastatin (5 micromol/L) reduced EC accumulation derived from agLDL uptake by 58% and 35% in platelet-derived growth factor-stimulated and unstimulated VSMCs, respectively. This inhibition was overcome by geranylgeraniol (10 micromol/L) and partially by farnesol (10 micromol/L). Fluorescence microscopy of the cellular internalization of agLDL labeled with the fluorochrome 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine demonstrated that simvastatin reduces EC accumulation derived from agLDL by inhibiting its endocytosis and that the effect is completely reversed by geranygeraniol. These results indicate that agLDLs are rapidly internalized by human VSMCs and that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors modulate EC accumulation. These data suggest a possible mechanism by which statins could contribute to the passivation and stabilization of actively growing atherosclerotic lesions.

Nitrogen-containing bisphosphonates inhibit the mevalonate pathway and prevent post-translational prenylation of GTP-binding proteins, including Ras

Bisphosphonates are currently the most important class of antiresorptive drugs used for the treatment of metabolic bone diseases. Although the molecular targets of bisphosphonates have not been identified, these compounds inhibit bone resorption by mechanisms that can lead to osteoclast apoptosis. Bisphosphonates also induce apoptosis in mouse J774 macrophages in vitro, probably by the same mechanisms that lead to osteoclast apoptosis. We have found that, in J774 macrophages, nitrogen-containing bisphosphonates (such as alendronate, ibandronate, and risedronate) inhibit post-translational modification (prenylation) of proteins, including the GTP-binding protein Ras, with farnesyl or geranylgeranyl isoprenoid groups. Clodronate did not inhibit protein prenylation. Mevastatin, an inhibitor of 3-hydroxy-3-methylglutatyl (HMG)-CoA reductase and hence the biosynthetic pathway required for the production of farnesyl pyrophosphate and geranylgeranyl pyrophosphate, also caused apoptosis in J774 macrophages and murine osteoclasts in vitro. Furthermore, alendronate-induced apoptosis, like mevastatin-induced apoptosis, could be suppressed in J774 cells by the addition of farnesyl pyrophosphate or geranylgeranyl pyrophosphate, while the effect of alendronate on osteoclast number and bone resorption in murine calvariae in vitro could be overcome by the addition of mevalonic acid. These observations suggest that nitrogen-containing bisphosphonate drugs cause apoptosis following inhibition of post-translational prenylation of proteins such as Ras. It is likely that these potent antiresorptive bisphosphonates also inhibit bone resorption by preventing protein prenylation in osteoclasts and that enzymes of the mevalonate pathway or prenyl protein transferases are the molecular targets of the nitrogen-containing bisphosphonates. Furthermore, the data support the view that clodronate acts by a different mechanism.

Age changes in the activity of liver 3-hydroxy-3-methylglutaryl-CoA reductase in female rats: influence of mammary pathology

Hydroxymethylglutaryl-Coenzyme A (HMG-CoA) reductase is a highly regulated enzyme which shows a marked circadian rhythmicity. We studied the impact of aging on this rhythm as well as the degree of correlation between age changes in circulating pituitary hormone levels and liver reductase activity in young (4 months) and old (33 months) Sprague-Dawley female rats. Lipid composition was also assessed in plasma and liver microsomes. The maximal activity (midnight) of HMG-CoA reductase fell from 864 +/- 28 pmol mevalonate/min/mg protein in the young rats to 552 +/- 45 pmol/min/mg protein in the old animals, whereas significant change was not observed in the basal (noon) activity levels of the enzyme. Noon serum cholesterol, but not midnight values, was significantly higher in the old rats. Liver cholesterol levels were similar in young and old rats. In old rats, fatty acid composition of liver microsomes revealed an increase in linoleic acid concurrently with a significant decrease in arachidonic acid (AA). A significant correlation was not detected between the age changes in pituitary hormone (GH, PRL, TSH, FSH) serum levels and those in reductase activity. On the other hand, a significant positive correlation was found in the old rats between hepatic reductase activity and the severity of mammary pathology. We conclude that, like most biological rhythms, HMG-CoA reductase circadian fluctuation decreases in amplitude with age. This change does not seem to be linked to the alterations of neuroendocrine function associated with the aging process. The presence of growing mammary tumors seems to stimulate liver reductase activity, which may constitute an adaptive response of the enzyme to cholesterol demand by the growing neoplastic tissue.

Genetic and biochemical analysis of the transmembrane domain of Arabidopsis 3-hydroxy-3-methylglutaryl coenzyme A reductase

We have examined the amino terminal membrane anchoring domain of Arabidopsis thaliana 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmg1p), a key enzyme of the isoprenoid biosynthetic pathway. Using both in vitro and in vivo approaches, we have analyzed a series of recombinant derivatives to identify key structural elements which play a role in defining Hmg1p transmembrane topology. Based on our results, we have proposed a topological model for Hmg1p in which the enzyme spans the lipid bilayer twice. We have shown the two transmembrane segments, designated TMS1 and TMS2, to be structurally and functionally inequivalent in their ability to direct the targeting and orientation of reporter proteins. Furthermore, we provide evidence indicating both the extreme amino terminal end and carboxyl terminal domain of the protein reside in the cytosol. This model therefore provides a key basis for the future examination of the role of the transmembrane domain in the targeting and regulation of Hmg1p in plant cells.

Effects of single administration of pravastatin sodium on hepatic cholesterol metabolism in rats

Pravastatin sodium, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, was administered to rats at 500 mg/kg, and the changes in several parameters concerning the metabolism of cholesterol in the liver were determined over 12 h. HMG-CoA reductase activity began to be induced 6 h after pravastatin dosage and continued to increase for an additional 6 h. A significant reduction of serum and liver microsomal cholesterol was observed only at 9 h. At this time point, the protein mass and activity of cholesterol 7 alpha-hydroxylase were significantly decreased by 31% and 34%, respectively. Hepatic low density lipoprotein (LDL) receptor expression was not affected by pravastatin throughout the experimental period. These results suggest that, in rats, the compensatory mechanism to restore the cholesterol balance after depletion of liver cholesterol produced by a single administration of pravastatin might primarily depend on the induction of HMG-CoA reductase and might be facilitated by a reduction in cholesterol 7 alpha-hydroxylase, without the induction of hepatic LDL receptor.

High mobility group proteins cHMG1a, cHMG1b, and cHMGI are distinctly distributed in chromosomes and differentially expressed during ecdysone dependent cell differentiation

The mammalian high mobility group proteins HMGI/Y and HMG1/2 are thought to play an architectural role in assembly of nucleoprotein structures. Counterparts to these proteins have recently been found in the cells of the Dipteran insect Chironomus. In this report we investigate the distribution of three abundant HMG proteins in interphase giant chromosomes of the midge, Chironomus. By means of the indirect immunofluorescence technique the cHMG1b and cHMGI proteins were localized in chromosomal puffs, suggesting their involvement in the organization of transcriptionally active chromatin. In contrast, the highly abundant protein cHMG1a was rather uniformly distributed in the chromosomes. The cHMGI protein, but not cHMG1a or cHMG1b, was detected in nucleoli, which may indicate a role in the transcription of ribosomal genes. The regions of the interphase chromosomes containing AT-rich DNA did not contain higher levels of the cHMGI and cHMG1b proteins. A correlation between the specific location of these proteins in chromatin and their synthesis and turnover rates was observed.

Remnant-like very-low-density lipoprotein isolated from hypertriglyceridemic patients by immunoaffinity chromatography suppressed 3-hydroxy-3-methylglutaryl coenzyme A activity of cultured human skin fibroblasts

It has been previously reported that VLDL unbound to monoclonal antibody against apoB-100 was rich in apoE, thus resembling remnant particles (J Lipid Res, 1993:33;369-380). In the current study, we have further analyzed the unbound VLDL fraction in plasma from hypertriglyceridemic patients using a mixture of monoclonal antibodies against apoB-100 and apoA-1. The unbound VLDL isolated from the plasma of hypertriglyceridemic patients was found to be rich in apoE, apoB-48, and triglyceride compared with the bound VLDL. Furthermore, these unbound VLDL, but not bound VLDL, significantly suppressed HMG CoA reductase activity of cultured human skin fibroblasts (-20 to -25%, P = 0.0022). The degree of suppression is significantly correlated with the apoE content of unbound VLDL (r = -0.769, P < 0.05). Unbound VLDL failed to suppress the activity of HMG CoA reductase of LDL receptor negative fibroblasts. These observations indicate a potential atherogenicity of remnant-like unbound VLDL by delivering more cholesterol through the LDL receptor dependent pathway with apoE as a ligand. In conclusion, this new immunoaffinity chromatography system is a useful method for directly quantifying atherogenic remnants in plasma.

Cloning and expression of solanidine UDP-glucose glucosyltransferase from potato

A cDNA encoding solanidine glucosyltransferase (SGT) was isolated from potato. The cDNA was selected from a yeast expression library using a positive selection based on the higher toxicity of steroidal alkaloid aglycons relative to their associated glycosylated forms. The cDNA contained an open reading frame encoding a 56 kDa polypeptide with regions of similarity to previously characterized UDP-glucosyltransferases. The enzyme activity and reaction products of recombinant SGT in yeast were consistent with those observed for the endogenous enzyme from potato. SGT mRNA and protein accumulated in tubers in response to wounding. The time course for SGT mRNA accumulation paralleled that of 3-hydroxy-3-methylglutaryl-coenzymeA isoform 1 (hmg1) mRNA. Steady-state SGT mRNA levels also increased transiently upon wounding of leaves.

Role of 26S proteasome and HRD genes in the degradation of 3-hydroxy-3-methylglutaryl-CoA reductase, an integral endoplasmic reticulum membrane protein

3-hydroxy-3-methylglutaryl-CoA reductase (HMG-R), a key enzyme of sterol synthesis, is an integral membrane protein of the endoplasmic reticulum (ER). In both humans and yeast, HMG-R is degraded at or in the ER. The degradation of HMG-R is regulated as part of feedback control of the mevalonate pathway. Neither the mechanism of degradation nor the nature of the signals that couple the degradation of HMG-R to the mevalonate pathway is known. We have launched a genetic analysis of the degradation of HMG-R in Saccharomyces cerevisiae using a selection for mutants that are deficient in the degradation of Hmg2p, an HMG-R isozyme. The underlying genes are called HRD (pronounced "herd"), for HMG-CoA reductase degradation. So far we have discovered mutants in three genes: HRD1, HRD2, and HRD3. The sequence of the HRD2 gene is homologous to the p97 activator of the 26S proteasome. This p97 protein, also called TRAP-2, has been proposed to be a component of the mature 26S proteasome. The hrd2-1 mutant had numerous pleiotropic phenotypes expected for cells with a compromised proteasome, and these phenotypes were complemented by the human TRAP-2/p97 coding region. In contrast, HRD1 and HRD3 genes encoded previously unknown proteins predicted to be membrane bound. The Hrd3p protein was homologous to the Caenorhabditis elegans sel-1 protein, a negative regulator of at least two different membrane proteins, and contained an HRD3 motif shared with several other proteins. Hrd1p had no full-length homologues, but contained an H2 ring finger motif. These data suggested a model of ER protein degradation in which the Hrd1p and Hrd3p proteins conspire to deliver HMG-R to the 26S proteasome. Moreover, our results lend in vivo support to the proposed role of the p97/TRAP-2/Hrd2p protein as a functionally important component of the 26S proteasome. Because the HRD genes were required for the degradation of both regulated and unregulated substrates of ER degradation, the HRD genes are the agents of HMG-R degradation but not the regulators of that degradation.

Increasing hepatic cholesterol 7alpha-hydroxylase reduces plasma cholesterol concentrations in normocholesterolemic and hypercholesterolemic rabbits

The effect of bile acid depletion and replacement with glycodeoxycholic acid on plasma cholesterol concentrations, hepatic low-density lipoprotein (LDL) receptor binding and messenger RNA (mRNA) levels, and hepatic activities and mRNA levels for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and cholesterol 7alpha-hydroxylase was investigated in 19 New Zealand white (NZW) and 15 Watanabe heritable hyperlipidemic (WHHL) rabbits. Bile acid depletion was produced by external bile drainage for 5 days, which maximized cholic acid synthesis. Replacement was achieved by infusing glycodeoxycholic acid intraduodenally for 24 hours so that the hepatic bile acid flux reached prefistula levels. Plasma and liver cholesterol concentrations were 13 times and 50% greater, respectively, hepatic LDL receptor-mediated binding was 26% less, and cholesterol 7alpha-hydroxylase activity and mRNA levels were 62% and 86% less in WHHL than NZW rabbits. After bile drainage, plasma cholesterol concentrations decreased 29% in NZW rabbits and 40% in WHHL rabbits and were associated with a 2.1-fold increase in hepatic LDL receptor-mediated binding in the NZW rabbits, but there was no change in the WHHL rabbits. Cholesterol 7alpha-hydroxylase activity and mRNA levels increased three and four times in NZW and WHHL rabbits, respectively, although liver cholesterol levels remained unchanged. Replacement with exogenous glycodeoxycholic acid increased plasma cholesterol concentrations 1.7 times in NZW rabbits and decreased enhanced cholesterol 7alpha-hydroxylase activity 54%, mRNA levels 86%, cholic acid synthesis 38%, and hepatic LDL receptor-mediated binding 57% in NZW rabbits. Bile acid depletion stimulated cholic acid synthesis by up-regulating cholesterol 7alpha-hydroxylase to use cholesterol and reduce plasma concentrations substantially in both NZW and WHHL rabbits, although LDL receptors did not function in WHHL rabbits. Glycodeoxycholic acid replacement inhibited elevated cholesterol 7alpha-hydroxylase, cholic acid synthesis, and hepatic LDL receptor binding to reestablish baseline plasma cholesterol levels in NZW rabbits. Hypercholesterolemia in WHHL rabbits was related to the combination of dysfunctional LDL receptors and inhibited cholesterol 7alpha-hydroxylase. Plasma cholesterol concentrations were reduced significantly when cholesterol 7alpha-hydroxylase was stimulated even in the absence of LDL receptor function.

The promoter for tomato 3-hydroxy-3-methylglutaryl coenzyme A reductase gene 2 has unusual regulatory elements that direct high-level expression

The promoter region of tomato (Lycopersicon esculentum) 3-hydroxy-3-methylglutaryl coenzyme A reductase gene 2 (HMG2) has been analyzed using the transient expression of HMG2-luciferase fusions in red fruit pericarp. The mRNA for HMG2 accumulates to high level during fruit ripening, in a pattern that coincides with the synthesis of the carotenoid lycopene. Unlike most promoters, the region that is upstream of the HMG2 TATA element is not required for high-level expression. The 180-bp region containing the TATA element, the 5' untranslated region, and the translation start site are comparable in strength of the full-length 35S cauliflower mosaic virus promoter. Pyrimidine-rich sequences present in the 5' untranslated leader are important in regulating expression. Also, the ATG start region has been found to increase translation efficiency by a factor of 4 to 10. An alternative hairpin secondary structure has been identified surrounding the HMG2 initiator ATG, which could participate in the translational regulation of this locus. HMG2 appears to be a novel class of strong plant promoters that incorporate unusual, positive regulators of gene expression.

Coordinated expression and activity of 3-hydroxy-3-methylglutaryl coenzyme A synthase and reductase in the fat body of Blattella germanica (L.) during vitellogenesis

Levels of mRNA for the two 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthases, (HMG-S1 and HMG-S2), and for HMG-CoA reductase (HMG-R) of Blattella germanica were analyzed in the fat body during the first gonadotrophic cycle. HMG-S2 and HMG-R showed the highest mRNA levels on day 0 and decreased thereafter, whereas HMG-S1, showed faint expression. Western blot using specific antibodies for HMG-S1 and HMG-S2 showed no detectable levels for HMG-S1 but a clear pattern for HMG-S2. Both results point to a very limited role for HMG-CoA synthase-1 in B. germanica fat body that the functional enzyme in this organ is HMG-CoA synthase-2. HMG-CoA reductase and synthase proteins shared a cyclic pattern (maximum levels at day 4 and minimum levels on days 0 and 8), which was coincident with the pattern of activity. The delay between gene transcription and protein synthesis suggests a finely regulated translation mechanism. Moreover, the pattern of mevalonate synthesis parallels that of vitellogenin production, suggesting a coordinate mechanism between the mevalonate pathway and the production of vitellogenin.

The human general co-factors

The human general co-factors were discovered during biochemical fractionation of mammalian nuclear extracts in functional in vitro assays. They appear to act in concert with other co-activators that bind tightly to the TATA-binding protein and RNA polymerase II. Several co-factors have been shown to interact with general transcription factors, leading either to activation or repression of transcription. At least one subgroup of co-factors that enhance the effects of activators on transcription are DNA-binding proteins located in the chromatin. In fact, one co-factor, the repressor NC2, is structurally related to histones. The understanding of the molecular interplay of such components of the initiation complex in the chromatin-including general co-factors, other co-factors, general factors and activators-will be a major challenge in the future.

Dietary alpha-tocopherol attenuates the impact of gamma-tocotrienol on hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in chickens

The concentration-dependent impact of gamma-tocotrienol on serum cholesterol can be traced to the posttranscriptional down-regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. gamma-Tocotrienol also suppresses tumor growth. Palmvitee, the tocopherol and tocotrienol-rich fraction of palm oil, is the sole commercial source of gamma-tocotrienol. Contrary to the universal findings of the efficacy of gamma-tocotrienol there are conflicting reports of the impact of Palmvitee on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, serum cholesterol concentrations and tumor development. These conflicting reports led us to examine the impact of alpha-tocopherol on the cholesterol-suppressive action of gamma-tocotrienol. Control and experimental diets were fed to groups of White Leghorn chickens (n = 10) for 26 d. The control diet was supplemented with 21 nmol alpha-tocopherol/g. All experimental diets provided 141 nmol of blended tocols/g diet. The alpha-tocopherol and gamma-tocotrienol concentrations of the experimental diets ranged from 21 to 141 and 0 to 120 nmol/g, respectively. We now report that including alpha-tocopherol in tocol blends containing adequate gamma-tocotrienol to suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase activity results in an attenuation of the tocotrienol action (P < 0.001). A summary of results from studies utilizing different Palmvitee preparations shows that effective preparations consist of 15-20% alpha-tocopherol and approximately 60% gamma- (and delta-) tocotrienol, whereas less effective preparations consist of > or = 30% alpha-tocopherol and 45% gamma- (and delta-) tocotrienol.

Low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA levels are coordinately reduced in human renal cell carcinoma

The current investigation aimed to determine if the gene expression of important structures in cholesterol metabolism is altered in a solid human tumor. For this purpose we determined low density lipoprotein (LDL) receptor and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) transcript levels and total tissue cholesterol in both tumors and normal kidney tissue in a series of samples from 29 patients with renal cell carcinoma. (RCC). LDL-receptor- and HMG-CoA reductase mRNA levels were reduced in tumor tissue as compared with normal kidney tissue (by 29%, P < 0.03, and 31%, P < 0.001 respectively). The LDL-receptor mRNA levels correlated significantly to the mRNA levels for HMG-CoA reductase in tumors (P < 0.0001) and normal kidney tissue (P < 0.03). The total tissue cholesterol levels in tumors were 5-fold elevated (P < 0.0001) as compared to normal kidney. We conclude that the mRNA levels for LDL-receptor and HMG-CoA reductase are regulated in parallel in human RCC and in normal kidney, and that these mRNA are generally reduced in human RCC. The data indicate that the accumulation of cholesterol in RCC may not be due to increased LDL receptor expression or de novo synthesis of cholesterol.

Hepatic HMG-CoA reductase gene expression during the course of puromycin-induced nephrosis

Increased production and depressed catabolism of lipoproteins play major roles in the pathogenesis of hypercholesterolemia of nephrotic syndrome (NS). However, the effect, if any, of NS on cholesterol biosynthetic capacity is uncertain. We examined the gene expression of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoAR, the rate limiting step in cholesterol biosynthesis) during the induction and chronic phase of puromycin (PAN)-induced NS in rats. The rats were randomized to NS (given i.p. puromycin aminonucleoside 130 mg/kg on day 1 and 60 mg/kg on day 14) and placebo-treated control groups. Subgroups of animals were sacrificed at days 5, 10, 20 and 30. The liver was harvested between 7 and 9 p.m. for measurements of HMG-CoAR and actin mRNAs, HMG-CoAR enzymatic activity and microsomal cholesterol concentration. In separate experiments, subgroups of animals with chronic NS (day 30) were studied in fed and 20-hour fasting states. A marked but transient rise in hepatic HMG-CoAR mRNA and HMG-CoAR enzymatic activity was observed following the onset and exacerbation of proteinuria within a few days after each puromycin injection. On each occasion, HMG-CoAR fell to the baseline level despite persistent severe hypercholesterolemia. In an attempt to examine the possible acute effect of PAN per se, experiments were repeated before and at short intervals (8 and 24 hr) after puromycin injection when proteinuria was absent and the drug exposure prominent. The HMG-CoAR mRNA and activity were virtually unchanged during this period, suggesting the lack of an acute effect of puromycin. Twenty-hour fasting led to a marked rise in HMG-CoAR mRNA and activity in animals with chronic NS but not in the controls. Microsomal cholesterol remained unchanged and comparable in the two groups at all points. Thus, the marked but transient rise in hepatic HMG-CoAR gene expression observed during the induction phase and with fasting during the chronic phase of PAN-induced NS may contribute to the generation and maintenance of hypercholesterolemia in this animal model.

Dual roles of HMG-CoA reductase inhibitors in solid organ transplantation: lipid lowering and immunosuppression

Hyperlipidemia has been associated with the development of transplant coronary vasculopathy (TCV) in heart transplant recipients and chronic rejection in kidney transplant recipients. HMG-CoA reductase inhibitors (HMGCoARIs) are effective in treating post-transplant hyperlipidemia, but their effects on patient and graft outcome remain unclear. In a prospective randomized trial investigating pravastatin (PVS) use early after heart transplantation, we observed that PVS treated patients had a decreased incidence of clinically severe acute rejection episodes resulting in a significant improvement in one year survival (94% vs. 78% in the control group, P = 0.02), and decreases in both the incidence and progression of TCV. This observation was validated in a prospective randomized study of kidney transplant recipients where we found that PVS reduced the incidence of acute rejection episodes (25% vs. 58% in the control group, P = 0.01). In both the heart and kidney transplant recipients, taking PVS, we noted decreases in natural killer cell (NKC) cytotoxicity. In vitro studies reveal that: PVS inhibits NKC cytotoxicity; PVS acts synergistically with cyclosporine to inhibit cytotoxic lymphocyte activity; and, other HMGCoARIs inhibit T-cell proliferation and monocyte chemotaxis. In conclusion, HMGCoARIs may have immunosuppressive properties in transplant recipients that could be useful in combating acute and chronic rejection.

A hydroxymethylglutaryl-CoA reductase inhibitor synthesized by yeasts

Screening of different yeast species showed that they are able to synthesize hydroxymethylglutaryl-CoA (HMGCoA) reductase inhibitors. Crude methanol extracts and the purified inhibitors from Pichia labacensis and Candida cariosilignicola were tested for their biological activity on the solubilized microsomal HMGCoA reductase from Chinese hamster ovary cells. Identification of the inhibitors was studied by thin layer chromatography, high pressure liquid chromatography and mass spectroscopy.