Knockout of GGPPS1 restrains rab37-mediated autophagy in response to ventilator-induced lung injury

Mechanical ventilation may cause ventilator-induced lung injury (VILI) in patients requiring ventilator support. Inhibition of autophagy is an important approach to ameliorate VILI as it always enhances lung injury after exposure to various stress agents. This study aimed to further reveal the potential mechanisms underlying the effects of geranylgeranyl diphosphate synthase large subunit 1 (GGPPS1) knockout and autophagy in VILI using C57BL/6 mice with lung-specific GGPPS1 knockout that were subjected to mechanical ventilation. The results demonstrate that GGPPS1 knockout mice exhibit significantly attenuated VILI based on the histologic score, the lung wet-to-dry ratio, total protein levels, neutrophils in bronchoalveolar lavage fluid, and reduced levels of inflammatory cytokines. Importantly, the expression levels of autophagy markers were obviously decreased in GGPPS1 knockout mice compared with wild-type mice. The inhibitory effects of GGPPS1 knockout on autophagy were further confirmed by measuring the ultrastructural change of lung tissues under transmission electron microscopy. In addition, knockdown of GGPPS1 in RAW264.7 cells reduced cyclic stretch-induced inflammation and autophagy. The benefits of GGPPS1 knockout for VILI can be partially eliminated through treatment with rapamycin. Further analysis revealed that Rab37 was significantly downregulated in GGPPS1 knockout mice after mechanical ventilation, while it was highly expressed in the control group. Simultaneously, Rab37 overexpression significantly enhances autophagy in cells that are treated with cyclin stretch, including GGPPS1 knockout cells. Collectively, our results indicate that GGPPS1 knockout results in reduced expression of Rab37 proteins, further restraining autophagy and VILI.

The Genetics of Atypical Femur Fractures-a Systematic Review

PURPOSE OF REVIEW

Atypical femur fractures (AFFs) are rare subtrochanteric or diaphyseal fractures regarded as side effects of bisphosphonates (BPs), possibly with a genetic background. Here, we summarize the most recent knowledge about genetics of AFFs.

RECENT FINDINGS

AFF has been reported in 57 patients with seven different monogenic bone disorders including hypophosphatasia and osteogenesis imperfecta; 56.1% had never used BPs, while 17.5% were diagnosed with the disorder only after the AFF. Gene mutation finding in familial and sporadic cases identified possible AFF-related variants in the GGPS1 and ATRAID genes respectively. Functional follow-up studies of mutant proteins showed possible roles in AFF. A recent small genome-wide association study on 51 AFF cases did not identify significant hits associated with AFF. Recent findings have strengthened the hypothesis that AFFs have underlying genetic components but more studies are needed in AFF families and larger cohorts of sporadic cases to confirm previous results and/or find novel gene variants involved in the pathogenesis of AFFs.

Cloning and Characterization of Farnesyl Diphosphate Synthase from the Rubber-Producing MushroomLactarius chrysorrheus

Farnesyl diphosphate is involved in rubber biosynthesis as an initiating substrate for both polyprenol and mushroom rubber. So far, we have isolated the cDNA of a farnesyl diphosphate synthase (FPS) for the first time from a rare rubber-producing mushroom, Lactarius chrysorrheus, by the degenerate RT-PCR technique based on sequence information of FPS genes from fungi and yeasts. The open reading frame was clarified to encode a protein of 381 amino acid residues with a calculated molecular weight of 42.9 kDa. The deduced amino acid sequence of L. chrysorrheus FPS showed about 50% identity with those of other fungi and yeasts as well as plants. We expressed the cDNA of L. chrysorrheus FPS in Escherichia coli as a glutathione-S-transferase (GST)-fusion protein. The purified obtained protein showed FPS activity in which geranyl diphosphate (GPP) served as primary substrate, with a 2.4-fold higher k(cat)/K(m) value for GPP than for dimethylallyl diphosphate (DMAPP).

Farnesyl diphosphate synthase activity affects ergosterol level and proliferation of yeastSaccharomyces cerevisae

The yeast farnesyl diphosphate synthase (FPPS) gene was engineered so as to construct allelic forms giving various activities of the enzyme. One of the substitutions was F96W in the chain length determination region. The other, K197, conserved within a consensus sequence found in the majority of FPP and GGPP synthases, was substituted by R, E and V. An intricate correlation has been found between the FPPS activity, the amount of ergosterol synthesized and cell growth of a mutant strain defective in FPPS. About 40% of wt FPPS activity was sufficient to support normal growth of the mutant. With further decline of FPPS activity (20 down to 3%) the amount of ergosterol remained unchanged at approximately 0.16% (vs dry weight), whereas growth yield decreased and lag times increased. We postulate that, in addition to ergosterol initiating and maintaining growth of yeast cells, FPP and/or its derivatives participate in these processes.

Engineered gene over-expression as a method of drug target identification

The proposed target of aminobisphosphonate (aBP) bone resorption inhibitors, both in mammalian osteoclasts and in Dictyostelium, is the enzyme farnesyl diphosphate synthase (FDP synthase). The genetic evidence, obtained with Dictyostelium, derives from variant strains that over-express FDP synthase and that are relatively resistant to aBPs. We show that forced FDP synthase over-expression also leads to aBP resistance; by placing FDP synthase under control of a semi-constitutive promoter, transforming it into Dictyostelium cells and selecting with the aBP alendronate. This combination of drug and dominant selectable marker provides a novel selection system for transformation. We further show that, when a population of Dictyostelium cells expressing an entire growth stage cDNA library is placed under alendronate selection, FDP synthase is the only cDNA insert that confers drug resistance. This confirms FDP synthase as the primary target of aBPs and suggests a general method of drug target identification based upon engineered gene over-expression.

Biochemical changes of mevalonate pathway in human colorectal cancer

BACKGROUND

Alterations in the mevalonate pathway may contribute to malignant cell growth. There are differences in the aetiology, clinical behaviour, pathological and genetic features in cancer of the right versus the left colon. Here, 3-hydroxy-3-methylglutatyl coenzyme A (HMG-CoA) reductase, farnesylpyrophosphate (FPP) synthase and farnesyltransferase (Ftase) activities were measured in human colorectal cancer (CRC) and normal mucosa in order to evaluate their role as potential markers of malignancy, also in relation to cancer location.

PATIENTS AND METHODS

HMG-CoA reductase, FPP synthase and Ftase activities were determined in CRC and normal mucosa of 90 patients by radiochemical assay.

RESULTS

The enzymatic activities were higher in cancer than in normal mucosa. The tumours located at the left side showed higher HMG-CoA reductase activity, whereas the right side tumours showed higher levels of Ftase and FPP synthase activity.

CONCLUSION

The determination of mevalonate pathway enzymes in relation to CRC location may be clinically relevant in designing anticancer targeted therapies.

Disruption of the structural gene for farnesyl diphosphate synthase in Escherichia coli

The chromosomal ispA gene encoding farnesyl diphosphate synthase of Escherichia coli was disrupted by inserting a neo gene cassette. The null ispA mutants were viable. The growth yield of the mutants was 70% to 80% of that of the wild-type strain under aerobic conditions, and was almost the same as the wild-type under anaerobic conditions. The levels of ubiquinone-8 and menaquinone-8 were both significantly lower (less than 13% and 18% of normal, respectively) in the mutants than in the wild-type. The undecaprenyl phosphate level in the mutants was modestly lower (40% to 70% of normal) than in the wild-type strain. Thus the synthesis of all-E-octaprenyl diphosphate, the precursor of ubiquinone-8 and menaquinone-8, was decreased more severely than that of Z,E-mixed undecaprenyl diphosphate, the precursor of undecaprenyl monophosphates, under the conditions where the synthesis of farnesyl diphosphate was decreased. The condensation of isopentenyl diphosphate with dimethylallyl diphosphate was detected in the cell-free extracts of the mutants, although it was 5% of that in the wild-type strain. A low level of farnesyl diphosphate seems to be synthesized in the mutants by other prenyltransferases such as octaprenyl diphosphate synthase or undecaprenyl diphosphate synthase.

Hepatic farnesyl diphosphate synthase expression is suppressed by polyunsaturated fatty acids

Dietary vegetable oils and fish oils rich in PUFA (polyunsaturated fatty acids) exert hypocholesterolaemic and hypotriglyceridaemic effects in rodents. The plasma cholesterol-lowering properties of PUFA are due partly to a diminution of cholesterol synthesis and of the activity of the rate-limiting enzyme HMG-CoA reductase (3-hydroxy-3-methylglutaryl-CoA reductase). To better understand the mechanisms involved, we examined how tuna fish oil and individual n-3 and n-6 PUFA affect the expression of hepatic FPP synthase (farnesyl diphosphate synthase), a SREBP (sterol regulatory element-binding protein) target enzyme that is subject to negative-feedback regulation by sterols, in co-ordination with HMG-CoA reductase. Feeding mice on a tuna fish oil diet for 2 weeks decreased serum cholesterol and triacylglycerol levels, by 50% and 60% respectively. Hepatic levels of FPP synthase and HMG-CoA reductase mRNAs were also decreased, by 70% and 40% respectively. Individual n-3 and n-6 PUFA lowered FPP synthase and HMG-CoA reductase mRNA levels in H4IIEC3 rat hepatoma cells to a greater extent than did stearate and oleate, with the largest inhibitory effects occurring with arachidonate, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). We observed a similar inhibitory effect on protein levels of FPP synthase. The suppressive effect of PUFA on the FPP synthase mRNA level was not due to a decrease in mRNA stability, but to transcription inhibition. Moreover, a lower nuclear availability of both SREBP-1 and SREBP-2 mature forms was observed in HepG2 human hepatoblastoma cells treated with arachidonate, EPA or DHA. Taken together, these data suggest that PUFA can down-regulate hepatic cholesterol synthesis through inhibition of HMG-CoA reductase and FPP synthase, at least in part through impairment of the SREBP pathway.

Bisphosphonate Inhibitors ofToxoplasmagondiGrowth: In Vitro,QSAR, and In Vivo Investigations

We have investigated the activity of 60 bisphosphonates against the replication of Toxoplasma gondii in vitro and of three of the most active compounds, in vivo. The two most active compounds found were n-alkyl bisphosphonates containing long (n = 9 or 10) hydrocarbon chains, not the nitrogen-containing species used in bone resorption therapy. The target of all of the most active bisphosphonates appears to be the isoprene biosynthesis pathway enzyme farnesyl pyrophosphate synthase (FPPS), as indicated by the correlations between T. gondii growth inhibition and FPPS (human and Leishmania major) enzyme inhibition and by the fact that a T. gondii strain engineered to overexpress FPPS required considerably higher levels of bisphosphonates to achieve 50% growth inhibition, while the IC(50) for atovaquone (which does not inhibit FPPS) remained the same in the overexpressing strain. The phosphonate inhibitor of the non-mevalonate pathway, fosmidomycin, which inhibits the enzyme 1-deoxyxylulose-5-phosphate reductoisomerase, had no effect on T. gondii growth. To investigate structure-activity relationships (SARs) in more detail, we used two three-dimensional quantitative SAR methods: comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA), to investigate all 60 bisphosphonates. Both the CoMFA and CoMSIA models indicated a 60-70% contribution from steric interactions and a 30-40% contribution from electrostatic interactions and using four N = 55 training sets for each method, we found on average between a factor of 2 and 3 error in IC(50) prediction. The three most active compounds found in vitro were tested in vivo in a Smith-Webster mouse model and the two most active bisphosphonates were found to provide up to an 80% protection from death, a considerable improvement over that found previously with nitrogen-containing bisphosphonates. This effect may originate in the much higher therapeutic indices of these alkyl bisphosphonates, as deduced from in vitro assays using LD(50) values for growth inhibition of a human cell line. Overall, these results indicate that alkyl bisphosphonates are promising compounds for further development as agents against Toxoplasma gondii growth, in vivo.

Cloning and expression of a farnesyl diphosphate synthase in Centella asiatica (L.) Urban

A cDNA encoding farnesyl diphosphate synthase (FPS; EC2.5.1.1/EC2.5.1.10) was isolated from Centella asiacita (L.) Urban, using degenerate primers based on two highly conserved domains. A full-length cDNA clone was subsequently isolated by rapid amplification of cDNA ends (RACE) PCR. The sequence of the CaFPS (C. asiatica farnesyl diphosphate synthase) cDNA contains an open reading frame of 1029 nucleotides encoding 343 amino acids with a molecular mass of 39.6 kDa. The deduced CaFPS amino acid sequence exhibits 84, 79, and 72%, identity to the FPSs of Artemisia annua, Arabidopsis thaliana, and Oryza sativa, respectively. Southern blot analysis suggested that the C. asiatica genome contains only one FPS gene. An artificially expressed soluble form of the CaFPS was identified by SDS-PAGE. It had high specific activity and produced farnesyl diphosphate as the major isoprenoid.

Pyridinium-1-yl Bisphosphonates Are Potent Inhibitors of Farnesyl Diphosphate Synthase and Bone Resorption

We report the design, synthesis and testing of a series of novel bisphosphonates, pyridinium-1-yl-hydroxy-bisphosphonates, based on the results of comparative molecular similarity indices analysis and pharmacophore modeling studies of farnesyl diphosphate synthase (FPPS) inhibition, human Vgamma2Vdelta2 T cell activation and bone resorption inhibition. The most potent molecules have high activity against an expressed FPPS from Leishmania major, in Dictyostelium discoideum growth inhibition, in gammadelta T cell activation and in an in vitro bone resorption assay. As such, they represent useful new leads for the discovery of new bone resorption, antiinfective and anticancer drugs.

Higher farnesyl diphosphate synthase activity in human colorectal cancer inhibition of cellular apoptosis

OBJECTIVE

Farnesyl diphosphate synthase (FPPs) produces FPP which is considered a branch-point intermediate in the synthesis of sterols and isoprenylated cellular metabolites. In this study we investigated whether detectable FPPs activity was present in human colorectal cancer (CRC), also evaluating in vitro the role of this enzyme in the growth and apoptosis of CRC cells by using Pamidronate (PAM), a FPPs activity inhibitor.

METHODS

The activity level of FPPs was determined in CRC and the normal surrounding mucosa of 50 patients by radiochemical assay. The FPPs mRNA expression was investigated in 15 of 50 patients by quantitative reverse transcriptase polymerase chain reaction (RT-PCR). K-ras mutation was evaluated using PCR and restriction enzyme analysis. Cell growth and apoptosis, after PAM treatment, in human CRC cell line DLD-1 were measured by MTT test and DNA fragmentation, respectively.

RESULTS

FPPs activity was detectable in human CRC. FPPs activity and its mRNA were significantly more abundant in cancer samples than in normal mucosa. In vitro PAM resulted in a significant reduction of cell growth and also gave rise to a marked proapoptotic effect.

CONCLUSIONS

This study provides the first evidence of the presence of FPPs activity in human CRC. Moreover, FPPs enzyme was found to play a significant role in colon cancer proliferation.

Temperature-dependent modulation of farnesyl diphosphate/geranylgeranyl diphosphate synthase from hyperthermophilic archaea

Enzyme characteristics of trans-prenyl diphosphate synthase (Tk-IdsA) from Thermococcus kodakaraensis, which catalyzes the consecutive trans-condensation of isopentenyl diphosphate (C(5)) units with allylic diphosphate, were examined. Product analysis revealed that Tk-IdsA is a bifunctional enzyme, farnesyl diphosphate (FPP, C(15))/geranylgeranyl diphosphate (GGPP, C(20)) synthase, and mainly yields both C(15) and C(20). The FPP/GGPP product ratio increases with the rise of the reaction temperature. The kinetic parameters obtained at 70 and 90 degrees C demonstrated that the rise of the temperature elevates the k(0) value for the C(10) allylic substrate to more than those for the C(5) and C(15) allylic substrates. These data suggest that Tk-IdsA contributes to adjust the membrane composition to the cell growth temperature by modulating its substrate and product specificities. Mutation study indicated that the aromatic side chain of Tyr-81 acts as a steric hindrance to terminate the chain elongation and defines the final product length.

Directed evolution of Escherichia coli farnesyl diphosphate synthase (IspA) reveals novel structural determinants of chain length specificity

Directed evolution of farnesyl diphosphate (FPP, C15) synthase (IspA) of Escherichia coli was carried out by error-prone PCR with a color complementation screen utilizing C40 carotenoid pathway enzymes. This allowed IspA mutants with enhanced production of the C40 carotenoid precursor geranylgeranyl diphosphate (GGPP, C20) to be readily identified. Analysis of these mutants was carried out in order to better understand the mechanisms of product chain length specificity in this enzyme. The 12 evolved clones having enhanced C20 GGPP production have characteristic mutations in the conserved regions of prenyl diphosphate synthases (designated regions I through VII). Some of these mutations (I76T, Y79S, Y79H, C75Y, H83Y, and H83Q) are found near or before the conserved first aspartate rich motif (FARM), which is involved in the mechanism for chain elongation reaction of all prenyl synthases. Molecular modeling suggested a mechanism for chain length determination for these mutations including substitutions at the 1st and 9th amino acids upstream of the FARM that have not been reported previously. In addition, a mutation on a helix adjacent to the FARM within the substrate-binding pocket (D115G) suggests a novel mechanism for chain length determination. One mutant IspA clone carries a mutation of C155G at the 2nd amino acid upstream of conserved region IV (GQxxDL), which was recently found to be an important region controlling the chain elongation of a Type III GGPP synthase. One IspA clone carries mutations (T234A and T249I) near the conserved second aspartate rich motif (SARM). As a verification of the in vivo activity of the mutant clones (represented as C40 carotenoid formation), we confirmed the product distribution of wild-type and mutant IspA using an in vitro assay.

Farnesyl diphosphate synthase; regulation of product specificity

Farnesyl diphosphate synthase (FPPS) is a key enzyme in isoprenoid biosynthesis which supplies sesquiterpene precursors for several classes of essential metabolites including sterols, dolichols, ubiquinones and carotenoids as well as substrates for farnesylation and geranylgeranylation of proteins. It catalyzes the sequential head-to-tail condensation of two molecules of isopentenyl diphosphate with dimethylallyl diphosphate. The enzyme is a homodimer of subunits, typically having two aspartate-rich motifs with two sets of substrate binding sites for an allylic diphosphate and isopentenyl diphosphate per homodimer. The synthase amino-acid residues at the 4th and 5th positions before the first aspartate rich motif mainly determine product specificity. Hypothetically, type I (eukaryotic) and type II (eubacterial) FPPSs evolved from archeal geranylgeranyl diphosphate synthase by substitutions in the chain length determination region. FPPS belongs to enzymes encoded by gene families. In plants this offers the possibility of differential regulation in response to environmental changes or to herbivore or pathogen attack.

Inhibition of isoprene biosynthesis pathway enzymes by phosphonates, bisphosphonates, and diphosphates

We have investigated the docking of a variety of inhibitors and substrates to the isoprene biosynthesis pathway enzymes farnesyl diphosphate synthase (FPPS), isopentenyl diphosphate/dimethylallyl diphosphate isomerase (IPPI) and deoxyxylulose-5-phosphate reductoisomerase (DXR) using the Lamarckian genetic alogorithm program, AutoDock. The docked ligand structures are predicted with a approximately 0.8 A rms deviation from the structures determined crystallographically. The errors found are a function of the number of atoms in the ligand (R = 0.91, p < 0.0001) and, to a lesser extent, on the resolution of the crystallographic structure (R = 0.70, p < 0.008). The structures of three isoprenoid diphosphates docked to the FPPS enzyme reveal strong electrostatic interactions with Mg(2+), lysine and arginine active site residues. Similar results are obtained with the docking of four IPPI inhibitors to the IPPI enzyme. The DXR substrate, deoxyxylulose-5-phosphate, is found to dock to Mn(2+)-NADPH-DXR in an almost identical manner as does the inhibitor fosimdomycin to Mn(2+)-DXR (ligand heavy atom rms deviation = 0.90 A) and is poised to interact with NADPH. Bisphosphonate inhibitors are found to bind to the allylic binding sites in both eukaryotic and prokaryotic FPPSs, in good accord with recent crystallographic results (a 0.4 A rms deviation from the X-ray structure with the E. coli enzyme). Overall, these results show for the first time that the geometries of a broad variety of phosphorus-containing inhibitors and substrates of isoprene biosynthesis pathway enzymes can be well predicted by using computational methods, which can be expected to facilitate the design of novel inhibitors of these enzymes.

Cloning and functional analysis of a cDNA encoding Ginkgo biloba farnesyl diphosphate synthase

Farnesyl diphosphate synthase (FPS; EC2.5.1.1/EC2. 5.1.10) catalyzes the synthesis of farnesyl diphosphate, and provides precursor for biosynthesis of sesquiterpene and isoprenoids containing more than 15 isoprene units in Ginkgo biloba. Here we report the cloning, characterization and functional analysis of a new cDNA encoding FPS from G. biloba. The full-length cDNA (designated GbFPS) had 1731 bp with an open reading frame of 1170 bp encoding a polypeptide of 390 amino acids. The deduced GbFPS was similar to other known FPSs and contained all the conserved regions of trans-prenyl chain-elongating enzymes. Structural modeling showed that GbFPS had the typical structure of FPS, the most prominent feature of which is the arrangement of 13 core helices around a large central cavity. Southern blot analysis revealed a small FPS gene family in G. biloba. Expression analysis indicated that GbFPS expression was high in roots and leaves, and low in stems. Functional complementation of GbFPS in an FPS-deficient strain confirmed that GbFPS mediates farnesyl diphosphate biosynthesis.

The metabolic imbalance underlying lesion formation in Arabidopsis thaliana overexpressing farnesyl diphosphate synthase (isoform 1S) leads to oxidative stress and is triggered by the developmental decline of endogenous HMGR activity

Overexpression of Arabidopsis thaliana farnesyl diphosphate synthase isoform 1S (FPS1S) in transgenic A. thaliana (L.) Heynh. leads to necrotic lesion formation in leaves in planta and to premature senescence in detached leaves [A. Masferrer et al. (2002) Plant J 30:123-132]. Here we report that leaves of plants overexpressing FPS1S with symptoms of necrosis show increased H2O2 formation and induction of both the pathogenesis-related 1 (PR-1) and the alternative oxidase 1a (AOX1a) genes. These findings indicate that plants overexpressing FPS1S should be considered as lesion-mimic mutants and lead us to propose that H2O2 is the main inducing agent of necrosis in these plants. The onset of necrosis appears in a developmentally regulated manner that correlates with the developmental decline of endogenous 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity. Accordingly, constitutive overexpression of HMGR in plants overexpressing FPS1S prevents both necrosis and premature senescence. These observations demonstrate that both phenotypes are due to an insufficient supply of mevalonic acid and support the notion that the metabolic imbalance associated with FPS1S overexpression is, in fact, triggered by the developmental decline of HMGR activity. We also show that overexpression of FPS1S alleviates growth inhibition caused by overexpression of the catalytic domain of isoform HMGR1S. Overall, our results reinforce the view that the levels of specific intermediates of the mevalonic acid pathway must be strictly controlled, particularly those located at branch-point positions, in order to avoid deleterious effects on plant growth and development.

Crystallization and preliminary X-ray diffraction study of the farnesyl diphosphate synthase fromTrypanosoma brucei

Farnesyl diphosphate synthase (FPPS) catalyses the formation of farnesyl diphosphate from dimethylallyl diphosphate and isopentenyl diphosphate and is an RNAi-validated drug target in Trypanosoma brucei, the causative agent of African sleeping sickness. A T. brucei FPPS (390 amino acids) has been expressed in Escherichia coli and the recombinant protein has been crystallized in the absence and presence of the bisphosphonate inhibitor minodronate. Diffraction data were collected at 100 K using synchrotron radiation from both crystal types. Crystals obtained in the absence of minodronate belong to space group I222, with unit-cell parameters a = 61.43, b = 118.12, c = 120.04 A, while crystals grown in the presence of minodronate belong to space group C2, with unit-cell parameters a = 131.98, b = 118.10, c = 63.25 A, beta = 112.48 degrees. An initial model of the drug-free protein has been built using a homology model with the molecular-replacement method and refined to 3.3 A resolution. It shows mostly helical structure and resembles the structure of avian farnesyl diphosphate synthase, but with the addition of two loop regions.

Nitrogen-containing bisphosphonate mechanism of action

The current paradigm for drug discovery requires the identification of a target involved in the disease process (e.g. enzyme or receptor) and the development of an appropriate ligand (activator, inhibitor or selective modulator). Selection of ligands for clinical development is based on the therapeutic window between efficacy vs. safety and ADME (absorption, distribution, metabolism and elimination) considerations. For bisphosphonates (BPs) the process has not followed that paradigm. BPs have very low absorption and are retained in bone, their target tissue. A few have been used on a limited basis for over 20 years in diseases of rapid bone destruction (e.g. post-menopausal osteoporosis, Paget's disease, bone metastases, etc.), without understanding their molecular mechanism of action. The nitrogen-containing BPs (N-BPs) are the latest and most potent addition to this family of compounds and have the widest use. They have high potency, are specifically targeted to the osteoclast on bone and are used at very low doses (5-10 mg clinically). Over the last four years, there was significant progress in elucidating the mechanism of action of BPs, both lacking and containing nitrogen. This review will focus on the mechanism of action of the N-BPs, specifically alendronate (ALN) and risedronate (RIS), the two agents most widely used. For these and all other N-BPs, the molecular target is the isoprenoid biosynthetic enzyme, farnesyl diphosphate synthase, in the cholesterol biosynthesis pathway. Although inhibition of this enzyme by N-BPs results in the suppression of sterol biosynthesis, it is actually disruption of a branch pathway, isoprenylation, that is responsible for N-BP pharmacological activity. Isoprenylation involves covalent linkage of the 15 or 20 carbon isoprene moiety farnesyl diphosphate or geranylgeranyl diphosphate, respectively, to the carboxy-terminus of regulatory proteins, including the small GTPases Ras, Rac, Rho and Cdc42. The latter three, as well as numerous others, are geranylgeranylated and play a rate-limiting role in the activity of the bone-resorbing osteoclast. This targeted osteoclast inhibition accounts for the potency of the N-BPs and for their ability to elicit the desired therapeutic response of suppressing bone turnover. The occasional gastrointestinal irritation caused by N-BPs appears to be mechanism-based and is also briefly reviewed.

Antiparasitic activity of risedronate in a murine model of acute Chagas' disease

We report the results of a study on the activity of the farnesyl-pyrophosphate synthase inhibitor risedronate (Ris) in a murine model of acute Chagas' disease. This compound displays rapid, cytocidal activity in vitro against Trypanosoma cruzi, but its in vivo activity had not been investigated previously. A murine model of acute Chagas' disease was used, in which experimental animals were infected with 10(3) trypomastigotes and intravenous treatment was started 24 h post-infection. In this model, Ris, at doses as low as 1 mg/kg per day given for 7 days, induced > 90% reductions in parasitaemia and increased very significantly (P = 0.001) the survival of treated animals. Higher doses (up to 10 mg/kg per day) led to further reductions in parasitaemia and mortality, with no deleterious effects on weight gain and general physical condition of the treated animals. There was no relapse of parasitaemia after discontinuation of treatment, suggesting trypanocidal, rather than trypanostatic, activity. This interpretation was confirmed by the almost complete disappearance of amastigote nests in the hearts of treated animals. However, no parasitological cures were observed in infected animals that received the bisphosphonate, probably due to the short treatment period. Taken together, these results indicate that Ris could be a useful lead compound for the development of new drugs effective against Chagas' disease.

Investigation of factors influencing production of the monocyclic carotenoid torulene in metabolically engineered Escherichia coli

Factors influencing production of the monocyclic carotenoid torulene in recombinant Escherichia coli were investigated by modulating enzyme expression level, culture conditions, and engineering of the isoprenoid precursor pathway. The gene dosage of in vitro evolved lycopene cyclase crtY2 significantly changed the carotenoid profile. A culture temperature of 28 degrees C showed better production of torulene than 37 degrees C while initial culture pH had no significant effect on torulene production. Glucose-containing LB, 2xYT, TB and MR media significantly repressed the production of torulene, and the other carotenoids lycopene, tetradehydrolycopene, and beta-carotene, in E. coli. In contrast, glycerol-containing LB, 2xYT, TB, and MR media enhanced torulene production. Overexpression of dxs, dxr, idi and/or ispA, individually and combinatorially, enhanced torulene production up to 3.1-3.3 fold. High torulene production was observed in a high dissolved oxygen level bioreactor in TB and MR media containing glycerol. Lycopene was efficiently converted into torulene during aerobic cultures, indicating that the engineered torulene synthesis pathway is well coordinated, and maintains the functionality and integrity of the carotenogenic enzyme complex.

Identification of a novel class of omega,E,E-farnesyl diphosphate synthase from Mycobacterium tuberculosis

We have identified an omega,E,E-farnesyl diphosphate (omega,E,E-FPP) synthase, encoded by the open reading frame Rv3398c, from Mycobacterium tuberculosis that is unique among reported FPP synthases in that it does not contain the type I (eukaryotic) or the type II (eubacterial) omega,E,E-FPP synthase signature motif. Instead, it has a structural motif similar to that of the type I geranylgeranyl diphosphate synthase found in Archaea. Thus, the enzyme represents a novel class of omega,E,E-FPP synthase. Rv3398c was cloned from the M. tuberculosis H37Rv genome and expressed in Mycobacterium smegmatis using a new mycobacterial expression vector (pVV2) that encodes an in-frame N-terminal affinity tag fusion with the protein of interest. The fusion protein was well expressed and could be purified to near homogeneity, allowing facile kinetic analysis of recombinant Rv3398c. Of the potential allylic substrates tested, including dimethylallyl diphosphate, only geranyl diphosphate served as an acceptor for isopentenyl diphosphate. The enzyme has an absolute requirement for divalent cation and has a K(m) of 43 microM for isopentenyl diphosphate and 9.8 microM for geranyl diphosphate and is reported to be essential for the viability of M. tuberculosis.

Formation of monoterpenes in Antirrhinum majus and Clarkia breweri flowers involves heterodimeric geranyl diphosphate synthases

The precursor of all monoterpenes is the C10 acyclic intermediate geranyl diphosphate (GPP), which is formed from the C5 compounds isopentenyl diphosphate and dimethylallyl diphosphate by GPP synthase (GPPS). We have discovered that Antirrhinum majus (snapdragon) and Clarkia breweri, two species whose floral scent is rich in monoterpenes, both possess a heterodimeric GPPS like that previously reported from Mentha piperita (peppermint). The A. majus and C. breweri cDNAs encode proteins with 53% and 45% amino acid sequence identity, respectively, to the M. piperita GPPS small subunit (GPPS.SSU). Expression of these cDNAs in Escherichia coli yielded no detectable prenyltransferase activity. However, when each of these cDNAs was coexpressed with the M. piperita GPPS large subunit (GPPS.LSU), which shares functional motifs and a high level of amino acid sequence identity with geranylgeranyl diphosphate synthases (GGPPS), active GPPS was obtained. Using a homology-based cloning strategy, a GPPS.LSU cDNA also was isolated from A. majus. Its coexpression in E. coli with A. majus GPPS.SSU yielded a functional heterodimer that catalyzed the synthesis of GPP as a main product. The expression in E. coli of A. majus GPPS.LSU by itself yielded active GGPPS, indicating that in contrast with M. piperita GPPS.LSU, A. majus GPPS.LSU is a functional GGPPS on its own. Analyses of tissue-specific, developmental, and rhythmic changes in the mRNA and protein levels of GPPS.SSU in A. majus flowers revealed that these levels correlate closely with monoterpene emission, whereas GPPS.LSU mRNA levels did not, indicating that the levels of GPPS.SSU, but not GPPS.LSU, might play a key role in regulating the formation of GPPS and, thus, monoterpene biosynthesis.

Quantitative structure-activity relationships for gammadelta T cell activation by bisphosphonates

gammadelta T cells are the first line of defense against many infectious organisms and are also involved in tumor cell surveillance and killing. They are stimulated by a broad range of small, phosphorus-containing antigens (phosphoantigens) as well as by the bisphosphonates commonly used in bone resorption therapy, such as pamidronate and risedronate. Here, we report the activation of gammadelta T cells by a broad range of bisphosphonates and develop a pharmacophore model for gammadelta T cell activation, in addition to using a comparative molecular similarity index analysis (CoMSIA) approach to make quantitative relationships between gammadelta T cell activation by bisphosphonates and their three-dimensional structures. The CoMSIA analyses yielded R(2) values of approximately 0.8-0.9 and q(2) values of approximately 0.5-0.6 for a training set of 45 compounds. Using an external test set, the activities (IC(50) values) of 16 compounds were predicted within a factor of 4.5, on average. The CoMSIA fields consisted of approximately 40% hydrophobic, approximately 40% electrostatic, and approximately 20% steric interactions. Since bisphosphonates are known to be potent, nanomolar inhibitors of the mevalonate/isoprene pathway enzyme farnesyl pyrophosphate synthase (FPPS), we also compared the pharmacophores for gammadelta T cell activation with those for FPPS inhibition, using the Catalyst program. The pharmacophores for gammadelta T cell activation and FPPS inhibition both consisted of two negative ionizable groups, a positive charge feature and an endocyclic carbon feature, all having very similar spatial dispositions. In addition, the CoMSIA fields were quite similar to those found for FPPS inhibition by bisphosphonates. The activities of the bisphosphonates in gammadelta T cell activation were highly correlated with their activities in FPPS inhibition: R = 0.88, p = 0.002, versus a human recombinant FPPS (N = 9 compounds); R = 0.82, p < 0.0001, for an expressed Leishmania major FPPS (N = 45 compounds). The bisphosphonate gammadelta T cell activation pharmacophore differs considerably, however, from that reported previously for gammadelta T cell activation by phosphoantigens (Gossman, W.; Oldfield, E. J. Med. Chem. 2002, 45, 4868-4874), suggesting different primary targets for the two classes of compounds. The ability to quite accurately predict the activity of bisphosphonates as gammadelta T cell activators by using 3D QSAR techniques can be expected to help facilitate the design of additional bisphosphonates for potential use in immunotherapy.

Selective in vitro effects of the farnesyl pyrophosphate synthase inhibitor risedronate on Trypanosoma cruzi

We present the results of the first detailed study of the molecular and cellular basis of the antiproliferative effects of the bisphosphonate risedronate (Ris) on Trypanosoma cruzi, the causative agent of Chagas' disease. Ris and related compounds, which block poly-isoprenoid biosynthesis at the level of farnesyl pyrophosphate synthase, are currently used for the treatment of bone resorption disorders, but also display selective activity against trypanosomatid and apicomplexan parasites. Ris induced a dose-dependent effect on growth of the extracellular epimastigote form of T. cruzi; complete growth arrest and cell lysis ensued at 150 microM. Growth inhibition was associated with depletion of the parasite's endogenous sterols, but complete growth arrest and loss of cell viability took place before full depletion of these compounds, suggesting that disappearance of other essential poly-isoprenoids is involved in its anti-parasitic action. Ris had a variety of effects on cellular ultrastructure, including mitochondrial swelling, disorganisation of other organelles, such as reservosomes and the kinetoplast, together with the appearance of autophagic vesicles and progressive vacuolization of the cytoplasm. Ris had selective antiproliferative effects against the clinically relevant amastigote form of T. cruzi, and at 100 microM, was able to prevent completely the development of T. cruzi infection of murine muscle heart or Vero cells, and to cure cultures which were already infected. Ris induced drastic ultrastructural alterations in the intracellular parasites and blocked amastigote to trypomastigote differentiation, with no biochemical or ultrastructural effects on the host cells, which fully recovered their normal structure and activity after treatment. Ris is, therefore, a promising lead compound for the development of new drugs against T. cruzi.

Peroxisome proliferator-activated receptor alpha (PPARalpha) activators induce hepatic farnesyl diphosphate synthase gene expression in rodents

Fibrates are hypolipidemic drugs that exert multiple effects on lipid metabolism by activating peroxisome proliferator-activated receptor alpha (PPARalpha) and modulating the expression of many target genes. In order to investigate the link between PPARalpha and cholesterol synthesis, we analysed the effect of fibrates on expression of the farnesyl diphosphate synthase (FPP synthase) gene, known to be regulated by sterol regulatory element-binding proteins (SREBPs), in conjunction with HMG-CoA reductase. In wild-type mice, both fenofibrate and WY 14,643 induced FPP synthase gene expression, an effect impaired in PPARalpha-null mice. A three-fold induction was observed in ciprofibrate-treated rat hepatocytes, in primary culture. This effect was decreased in presence of 5,6-dichlorobenzimidazole riboside (DRB) and cycloheximide (CHX), transcription and translation inhibitors, respectively. Acyl-CoA oxidase (AOX), a bona fide PPARalpha target gene, was induced by ciprofibrate but slower and more strongly than FPP synthase. In addition, induction of FPP synthase gene expression was abolished in the presence of 25-hydroxycholesterol (25-OH Chol). Thus, activation of PPARalpha by fibrates induced FPP synthase gene expression in both hepatocytes in culture and in mouse liver. This effect is likely to be dependent on cellular sterol level, possibly through SREBP-mediated transcriptional activation.

Statins prevent bisphosphonate-induced gamma,delta-T-cell proliferation and activation in vitro

The acute phase response is the major adverse effect of intravenously administered N-BPs. In this study we show that N-BPs cause gamma,delta-T-cell activation and proliferation in vitro by an indirect mechanism through inhibition of FPP synthase, an effect that can be overcome by inhibiting HMG-CoA reductase with a statin. These studies clarify the probable initial cause of the acute phase response to N-BP drugs and suggest a possible way of preventing this phenomenon.

INTRODUCTION

The acute phase response is the major adverse effect of intravenously administered nitrogen-containing bisphosphonate drugs (N-BPs), used in the treatment of metabolic bone diseases. This effect has recently been attributed to their action as non-peptide antigens and direct stimulation of gamma,delta-T-cells. However, because N-BPs are potent inhibitors of farnesyl diphosphate (FPP) synthase, they could cause indirect activation of gamma,delta-T-cells owing to the accumulation of intermediates upstream of FPP synthase in the mevalonate pathway, such as isopentenyl diphosphate/dimethylallyl diphosphate, which are known gamma,delta-T-cell agonists.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated from healthy volunteers and treated with N-BP, statin, or intermediates/inhibitors of the mevalonate pathway for 7 days in the presence of interleukin (IL)-2. Flow cytometric analysis of the T-cell-gated population was used to quantify the proportion of gamma,delta-T-cells in the CD3+ population.

RESULTS AND CONCLUSIONS

The ability of N-BPs to stimulate proliferation of CD3+ gamma,delta-T-cells in human PBMC cultures matched the ability to inhibit FPP synthase. Gamma,delta-T-cell proliferation and activation (interferon gamma [IFNgamma] and TNFalpha release) was prevented by mevastatin or lovastatin, which inhibit HMG-CoA reductase upstream of FPP synthase and prevent the synthesis of isopentenyl diphosphate/dimethylallyl diphosphate. Desoxolovastatin, an analog of lovastatin incapable of inhibiting HMG-CoA reductase, did not overcome the stimulatory effect of N-BP. Furthermore, statins did not prevent the activation of gamma,delta-T-cells by a synthetic gamma,delta-T-cell agonist or by anti-CD3 antibody. Together, these observations show that N-BPs indirectly stimulate the proliferation and activation of gamma,delta-T-cells caused by inhibition of FPP synthase and intracellular accumulation of isopentenyl diphosphate/ dimethylallyl diphosphate in PBMCs. Because activation of gamma,delta-T-cells could be the initiating event in the acute phase response to bisphosphonate therapy, co-administration of a statin could be an effective approach to prevent this adverse effect.

Mono and diterpene production inEscherichia coli

Mono- and diterpenoids are of great industrial and medical value as specialty chemicals and pharmaceuticals. Production of these compounds in microbial hosts, such as Escherichia coli, can be limited by intracellular levels of the polyprenyl diphosphate precursors, geranyl diphosphate (GPP), and geranylgeranyl diphosphate (GGPP). To alleviate this limitation, we constructed synthetic operons that express three key enzymes for biosynthesis of these precursors: (1). DXS,1-deoxy-d-xylulose-5-phosphate synthase; (2). IPPHp, IPP isomerase from Haematococcus pluvialis; and (3). one of two variants of IspA, FPP synthase that produces either GPP or GGPP. The reporter plasmids pAC-LYC and pACYC-IB, which encode enzymes that convert either FPP or GGPP, respectively, to the pigment lycopene, were used to demonstrate that at full induction, the operon encoding the wild-type FPP synthase and mutant GGPP synthase produced similar levels of lycopene. To synthesize di- or monoterpenes in E. coli using the GGPP and GPP encoding operons either a diterpene cyclase [casbene cyclase (Ricinus communis L) and ent-kaurene cyclase (Phaeosphaeria sp. L487)] or a monoterpene cyclase [3-carene cyclase (Picea abies)] was coexpressed with their respective precursor production operon. Analysis of culture extracts or headspace by gas chromatography-mass spectrometry confirmed the in vivo production of the diterpenes casbene, kaur-15-ene, and kaur-16-ene and the monoterpenes alpha-pinene, myrcene, sabinene, 3-carene, alpha-terpinene, limonene, beta-phellandrene, alpha-terpinene, and terpinolene. Construction and functional expression of GGPP and GPP operons provides an in vivo precursor platform host for the future engineering of di- and monoterpene cyclases and the overproduction of terpenes in bacteria.

Lipid Metabolism in Zebrafish

Forward genetics is an unbiased methodology to discover new genes or functions of genes. At the present, the zebrafish is one of the few vertebrate systems where large-scale forward genetic studies are practical. Fluorescent lipid labeling of zebrafish larvae derived from families created from ENU-mutagenized fish enabled us to perform a large scale in vivo screen to identify mutants with perturbed lipid processing. With the aid of the zebrafish genome project, positional cloning of mutated genes with abnormal lipid metabolism can be accelerated. MO- and gripNA-based transient gene silencing is feasible in zebrafish embryos and provides a reverse genetic screening strategy to search for important lipid regulators. The advantages of using zebrafish as a vertebrate model to study lipid metabolism include its rapid external development and its optical clarity that enables the monitoring of biological processes. Large scale, high-throughput drug screening in vivo, especially for drugs that inhibit lipid absorption, can be easily achieved in this model. These zebrafish-based assays are important tools to understand aspects of lipid biology with significant clinical implications.

Structural basis for bisphosphonate-mediated inhibition of isoprenoid biosynthesis

Farnesyl pyrophosphate synthetase (FPPS) synthesizes farnesyl pyrophosphate through successive condensations of isopentyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. Nitrogen-containing bisphosphonate drugs used to treat osteoclast-mediated bone resorption and tumor-induced hypercalcemia are potent inhibitors of the enzyme. Here we present crystal structures of substrate and bisphosphonate complexes of FPPS. The structures reveal how enzyme conformational changes organize conserved active site residues to exploit metal-induced ionization and substrate positioning for catalysis. The structures further demonstrate how nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme. Together, these FPPS complexes provide a structural template for the design of novel inhibitors that may prove useful for the treatment of osteoporosis and other clinical indications including cancer.

Bisphosphonates derived from fatty acids are potent inhibitors of Trypanosoma cruzi farnesyl pyrophosphate synthase

Studies on the mode of action of a series of bisphosphonates derived from fatty acids, which had previously proved to be potent inhibitors against Trypanosoma cruzi proliferation in in vitro assays, have been performed. Some of these drugs proved to be potent inhibitors against the intracellular form of the parasite, exhibiting IC(50) values at the low micromolar level. As bisphosphonates are FDA clinically approved for treatment of bone resorption disorders, their potential innocuousness makes them good candidates to control tropical diseases.

Scale-up of Artemisia annua L. hairy root cultures produces complex patterns of terpenoid gene expression

Hairy roots grow quickly, reach high densities, and can produce significant amounts of secondary metabolites, yet their scale-up to bioreactors remains challenging. Artemisia annua produces a rich array of terpenoids, including the sesquiterpene, artemisinin, and transformed roots of this species provide a good model for studying terpenoid production. These cultures were examined in shake flasks and compared with cultures grown in two types of bioreactors, a mist reactor and a bubble column reactor, which provide very different environments for the growing roots. Mist reactors have been shown previously to result in cultures that produce significantly more artemisinin per gram fresh weight of culture, while bubble column reactors have produced greater biomass. We have compared expression levels of four key terpenoid biosynthetic genes: 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), 1-deoxy-D-xylulose-5-phosphate synthase (DXS), 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), and farnesyl diphosphate synthase (FPS) in the three culture conditions. In shake flasks we found that although all four genes showed temporal regulation, only FPS expression correlated with artemisinin production. Light also affected the transcription of all four genes. Although expression in reactors was equivalent to or greater than that of roots grown in shake flasks, no correlation was found between expression level within six different zones of each reactor and their respective oxygen levels, light, and root-packing density. Surprisingly, transcriptional regulation of HMGR, DXS, DXR, and FPS was greatly affected by the position of the roots in each reactor. Thus, relying on a single reactor sample to characterize the gene activity in a whole reactor can be misleading, especially if the goal is to examine the difference between reactor types or operating parameters, steps essential in scaling up cultures for production.

Transcriptional regulation of farnesyl pyrophosphate synthase by liver X receptors

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that are involved in cholesterol and lipid metabolism. In addition to liver, the brain is another site where LXRs may control cholesterol homeostasis. In the brain, the regulation of cholesterol homeostasis is independent from other parts of the body, and its disturbance is associated with neurodegenerative disorders, such as Alzheimer's disease. We have used PCR-based suppressive subtractive cloning to identify new LXR target genes in brain cells. In this report, we show that farnesyl pyrophosphate synthase (FPPS) is a new target gene for LXR in astrocytes and neurons. Farnesyl pyrophosphate is an obligate intermediate for de novo cholesterol synthesis and a substrate for protein farnesylation. Stimulation of FPPS mRNA synthesis by an LXR agonist, Hypocholamide, was observed in several cell lines from the central nervous system. We identified a single putative direct repeat 4 (DR4) LXR response element in the FPPS promoter. In a reporter gene assay, LXR transactivated a reporter gene bearing a truncated FPPS promoter containing this DR4 cis-element but not if the DR4 element was mutated. Using gel-mobility shift assay, we further demonstrated the direct interaction between the LXR/retinoid X receptor (RXR) heterodimer and the response element. Taken together, our results indicate that LXRs directly regulate FPPS gene expression, and thus may play a role in modulating cholesterol synthesis in the brain.

Enzymes encoded by the farnesyl diphosphate synthase gene family in the Big Sagebrush Artemisia tridentata ssp. spiciformis

Farnesyl diphosphate synthase catalyzes the sequential head-to-tail condensation of two molecules of isopentenyl diphosphate with dimethylallyl diphosphate. In plants the presence of farnesyl diphosphate synthase isozymes offers the possibility of differential regulation. Three full-length cDNAs encoding putative isoprenoid synthases, FDS-1, FDS-2, and FDS-5, with greater than 89% similarity were isolated from a Big Sagebrush Artemisia tridentata cDNA library using a three-step polymerase chain reaction protocol. One of the open reading frames, FDS-5, encoded a protein with an N-terminal amino acid extension that was identified as a plastidial targeting peptide. Recombinant histidine-tagged versions of three proteins were purified, and their enzymatic properties were characterized. FDS-1 and FDS-2 synthesized farnesyl diphosphate as the final chain elongation product, but their kinetic behavior varied. FDS-1 prefers geranyl diphosphate over dimethylallyl diphosphate as an allylic substrate and is active at acidic pH values compared with FDS-2. In contrast, FDS-5 synthesized two irregular monoterpenoids, chrysanthemyl diphosphate and lavandulyl diphosphate, when incubated with dimethylallyl diphosphate and an additional product, the regular monoterpene geranyl diphosphate, when incubated with isopentenyl diphosphate and dimethylallyl diphosphate. Specific cellular functions are proposed for each of the three enzymes, and a scenario for evolution of isoprenyl synthases in plants is presented.

Androgens stimulate coordinated lipogenic gene expression in normal target tissues in vivo

In prostate cancer cell lines in culture androgens cause a marked and coordinated upregulation of the expression of several lipogenic genes. Here, using castrated male Wistar rats as an experimental paradigm, we investigated whether coordinated androgen stimulation of lipogenic gene expression represents a more general physiological regulation in non-cancerous androgen-responsive cells as well. In typical target tissues for androgen action such as the ventral prostate and the lacrimal gland, androgen deprivation resulted in a marked reduction in the mRNA and protein levels of genes involved in fatty acid (fatty acid synthase and acetyl-CoA-carboxylase) and cholesterol synthesis (HMG-CoA-reductase and farnesyl diphosphate synthase). Readministration of testosterone immediately following orchidectomy restored the expression of all four genes. Substitution of testosterone by the non-aromatizable androgen dihydrotestosterone gave rise to comparable changes in the mRNA and protein levels of the lipogenic genes under investigation, confirming the involvement of the androgen receptor in the observed effects. In support of the coordinate nature of this regulation, androgen-induced upregulation of lipogenic gene expression is accompanied by an increase in the nuclear content of SREBP, a key lipogenic transcription factor. Taken together, these findings provide evidence for a coordinate regulation of lipogenic gene expression not only in prostate cancer cell lines in culture but also in non-cancerous androgen-responsive tissues in vivo.

How myeloma cells escape bisphosphonate-mediated killing: development of specific resistance with preserved sensitivity to conventional chemotherapeutics

Although amino-bisphosphonates (N-BPs) induce apoptosis of myeloma cells in vitro, most in-vivo studies fail to demonstrate a corresponding antitumour effect. This discrepancy might reflect the development of resistance to the antitumour effects of N-BP in myeloma cells when they are exposed to N-BP for a prolonged time. To test this hypothesis, two N-BP-sensitive human myeloma cell lines were continuously exposed to increasing concentrations of the N-BP alendronate for 6 weeks. During this treatment period, 10 out of 10 sublines developed reduced apoptotic and antiproliferative responses to alendronate treatment. This de novo alendronate resistance was accompanied by resistance to another N-BP (zoledronate) but not to an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase or Fas ligand. Importantly, N-BP-resistant myeloma cells also remained sensitive to conventional myeloma chemotherapeutics (melphalan, doxorubicin and vincristine). Further analysis of the N-BP-resistant cells revealed an increased activity of the N-BP-specific target enzyme farnesyl pyrophosphate synthase, without upregulation of its gene transcription. Our results suggest that continuous exposure of myeloma cells to alendronate leads to the development of N-BP resistance. This is associated with an increased activity of farnesyl pyrophosphate synthase and does not evolve from defective apoptotic pathways. Importantly, the antitumour effects of conventional myeloma chemotherapeutics are preserved in the N-BP-resistant myeloma cells.

Chrysanthemyl diphosphate synthase. The relationship among chain elongation, branching, and cyclopropanation reactions in the isoprenoid biosynthetic pathway

The genes for chrysanthemyl diphosphate (CPP) synthase and farnesyl diphosphate (FPP) synthase from sagebrush, Artemisia tridentata spiciformis, were used to prepare a series of chimeric proteins to investigate the 1'-4 chain elongation, 1'-2 branching, and c1'-2-3 cyclopropanation reactions that join isoprenoid units to build more complex structures. The two genes were modified by site-directed mutagenesis to generate an identical set of six unique restriction sites at identical locations. The locations were selected to place a restriction site between each of the five conserved regions found in prenyltransferases that catalyze chain elongation. A series of chimeric proteins were generated by replacing amino acids in FPP synthase, beginning at the N-terminus of the enzyme, with increasing stretches of peptide from CPP synthase. An analysis of the products produced by the chimeras revealed a transition from 1'-4 chain elongation, to 1'-2 branching, and ultimately to c1'-2-3 cyclopropanation. These results demonstrate that the catalytic site for chain elongation, with minor modifications in its architecture, also catalyzes 1'-2 branching and c1'-2-3 cyclopropanation, and suggest that the branching and cyclopropanation reactions, in analogy to chain elongation, are electrophilic alkylations.

Mechanism of action of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the causative agent of Chagas' disease

We investigated the molecular basis of the activity of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the etiological agent of Chagas' disease. We found that growth inhibition of T. cruzi epimastigotes induced by this compound was associated with a reduction in the content of the parasite's endogenous sterols due to a specific blockade of their de novo synthesis at the level of squalene synthase.

Farnesyl pyrophosphate synthase is an essential enzyme in Trypanosoma brucei. In vitro RNA interference and in vivo inhibition studies

We report the cloning and sequencing of a gene encoding the farnesyl pyrophosphate synthase (FPPS) of Trypanosoma brucei. The protein (TbFPPS) is an attractive target for drug development because the growth of T. brucei has been shown to be inhibited by analogs of its substrates, the nitrogen containing bisphosphonates currently in use in bone resorption therapy. The protein predicted from the nucleotide sequence of the gene has 367 amino acids and a molecular mass of 42 kDa. Several sequence motifs found in other FPPSs are present in TbFPPS, including an 11-mer peptide insertion present also in the Trypanosoma cruzi FPPS. Heterologous expression of TbFPPS in Escherichia coli produced a functional enzyme that was inhibited by several nitrogen-containing bisphosphonates, such as pamidronate and risedronate. Risedronate was active in vivo against T. brucei infection in mice (giving a 60% survival rate), but pamidronate was not effective. The essential nature of TbFPPS was studied using RNA interference (RNAi) to inhibit the expression of the gene. Expression of TbFPPS double-stranded RNA in procyclic trypomastigotes caused specific degradation of mRNA. After 4 days of RNAi, the parasite growth rate declined and the cells subsequently died. Similar results were obtained with bloodstream form trypomastigotes, except that the RNAi system in this case was leaky and mRNA levels and parasites recovered with time. Molecular modeling and structure-activity investigations of enzyme and in vitro growth inhibition data resulted in similar pharmacophores, further validating TbFPPS as the target for bisphosphonates. These results establish that FPPS is essential for parasite viability and validate this enzyme as a target for drug development.

Molecular characterization of three 3-hydroxy-3-methylglutaryl-CoA reductase genes including pathogen-induced Hmg2 from pepper (Capsicum annuum)

Sesquiterpene phytoalexins, a class of plant defense metabolites, are synthesized from the cytosolic acetate/mevalonate pathway in isoprenoids biosynthetic system of plants. The 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes the synthesis of mevalonate, which is the specific precursor of this pathway, as a multi gene family. Three kinds of cDNA clones encoding HMGR were isolated from Korean red pepper (Capsicum annuum L. cv. NocKwang) and the HMGR2 gene (Hmg2) was especially obtained from a cDNA library constructed with Phytophthora capsici-infected pepper root RNAs. The Hmg2 encoding a 604-amino-acid peptide had typical features as an elicitor-induced isoform among HMGRs on its gene structure and had a predicted amino acid sequence homology. In addition, the expression of Hmg2 was rapidly induced within 1 h in response to a fungal pathogen and continuously increased up to 48 h. Together with sesquiterpene cyclase gene that was strongly induced 24 h after pathogen-infection, the Hmg2 and farnesyl pyrophosphate synthase gene were coordinately and sequentially regulated for the biosynthesis of defense-related sesquiterpene phytoalexins in pepper.

Interconversion of the product specificity of type I eubacterial farnesyl diphosphate synthase and geranylgeranyl diphosphate synthase through one amino acid substitution

Prenyltransferases catalyze the sequential condensation of isopentenyl diphosphate into prenyl diphosphates with specific chain lengths. Pioneering studies demonstrated that the product specificities of type I prenyltransferases were mainly determined by the amino acid residues at the 4th and 5th positions before the first aspartate-rich motif (FARM) of the prenyltransferases. We previously cloned a type I geranylgeranyl diphosphate synthase (GGDPSase) gene from Streptomyces griseolosporeus MF730-N6 [Hamano, Y., Dairi, T., Yamamoto, M., Kawasaki, T., Kaneda, K., Kuzuyama, T., Itoh, N., and Seto, H. (2001) BIOSCI: Biotechnol. Biochem. 65, 1627-1635]. In this study, a prenyltransferase gene was cloned from Streptomyces argenteolus A-2 and was confirmed to encode a type I farnesyl diphosphate synthase (FDPSase). Interestingly, the amino acid residues at the 4th and 5th positions before the FARM were the same in these two enzymes. To identify the amino acid that determines the product chain length, mutated enzymes, GGDPSase (L-50S), FDPSase (S-50L), GGDPSase (V-8A), FDPSase (A-8V), GGDPSase (A+57L), and FDPSase (L+58A), in which the amino acid residue at the -50th, -8th, and +57th (58th) position before or after the FARM was substituted with the corresponding amino acid of the other enzyme, were constructed. The GGDPSase (A+57L) and FDPSase (L+58A) produced farnesyl diphosphate and geranylgeranyl diphosphate, respectively. On the other hand, the other mutated enzymes produced prenyl diphosphates with the same chain lengths as the wild type enzymes did. These results showed that the amino acid residue at the 57th (58th) position after the FARM also played an important role in determination of the product specificity.

Farnesyl diphosphate synthase gene of three phototrophic bacteria and its use as a phylogenetic marker

Farnesyl diphosphate (FPP) synthase is essential not only for phototrophic bacteria in carotenoid biosynthesis, but also for non-phototrophic bacteria in the biosynthesis of physiologically important compounds. The gene encoding FPP synthase was assessed as a molecular marker to investigate the intermingled relationship between the phototropic and non-phototropic bacteria in the alpha-Proteobacteria based on 16S rRNA analysis. The FPP synthase amino acid sequences from three phototropic bacteria, Rhodobacter sphaeroides ATCC 11167(T), Rhodobacter capsulatus ATCC 11166(T) and Rhodovulum sulfidophilum W4(T), were determined and used in conjunction with sequences of other representative members of the alpha-, gamma- and epsilon-Proteobacteria and the low-G+C Gram-positive bacteria for phylogenetic analyses by the neighbour-joining and maximum-likelihood methods. The overall topology of the FPP synthase gene tree is consistent with that of the 16S rRNA tree, producing a distinct cluster of the three phototropic bacteria. A minor discordance between the two trees was observed in the cluster of the non-phototrophic Bradyrhizobiumjaponicum USDA 110 and Mesorhizobium loti MAFF 303099; the FPP synthase genes of these two rhizobial species are highly homologous as compared with their respective 16S rRNA. The results suggest that the FPP synthase and 16S rRNA genes have the same evolutionary pattern, evolving vertically from each common ancestral gene; the FPP synthase gene, therefore, could possibly be used for further study on the molecular systematics of photosynthetic bacteria.

Bisphosphonates and primary hyperparathyroidism

Bisphosphonates (BP) are pyrophosphate analogs that include very potent inhibitors of bone resorption. BPs act directly on the osteoclast, suppressing isoprenylation by inhibiting farnesyl diphosphate synthase in the cholesterol pathway, which causes osteoclast inactivation. BPs should therefore reduce the bone loss produced by any cause, including hyperparathyroidism and hypercalcemia of malignancy (MIH), caused by parathyroid hormone (PTH) and PTH-related protein (PTHrP), respectively. BPs at higher doses than used in osteoporosis are indeed the treatment of choice for malignancy-induced hypercalcemia. Limited, but convincing, data show that BPs at doses effective in osteoporosis also reverse bone loss associated with mild primary hyperparathyroidism (PHPT).

A novel role for farnesyl pyrophosphate synthase in fibroblast growth factor-mediated signal transduction

Farnesyl pyrophosphate synthase (FPPS) catalyses the formation of a key cellular intermediate in isoprenoid metabolic pathways. Here we describe a novel role for this enzyme in fibroblast growth factor (FGF)-mediated signalling. We demonstrate the binding of FPPS to FGF receptors (FGFRs) using the yeast two-hybrid assay, pull-down assays and co-immunoprecipitation. The interaction between FPPS and FGFR is regulated by the cellular metabolic state and by treatment with FGF-2. Overexpression of FPPS inhibits FGF-2-induced cell proliferation, accompanied by a failure of the FGF-2-mediated induction of cyclins D1 and E. Overexpression of FPPS in fibroblasts also promotes increased farnesylation of Ras, and temporally extends FGF-2-stimulated activation of the Ras/ERK (extracellular-signal-regulated kinase) cascade. These data suggest that, in addition to its role in isoprenoid biosynthesis, FPPS may function as a modulator of the cellular response to FGF treatment.

Partial purification of a farnesyl diphosphate synthase from whole-body Manduca sexta

Farnesyl diphosphate synthase (FPP synthase) is a ubiquitous enzyme that is required for the biosynthesis of sesquiterpenes, dolichols ubiquinones, and prenylated proteins in insects. We report on the partial purification and characterization of an FPP synthase, obtained from whole-body preparations of the lepidopteran insect, Manduca sexta. The larval enzyme was separated from isopentenyl diphosphate (IPP) isomerase, phosphatase, and GGPP synthase by preparative isoelectric focusing, and was further purified by DEAE Sepharose, hydroxyapatite, and size exclusion chromatography. Whole-body M. sexta FPP synthase has a native molecular weight of 60.5+/-3.5 kDa and consists of two subunits of 28.5+/-0.5 kDa. As seen with other prenyltransferases, the enzyme has an absolute requirement for divalent cation and both Mn(2+) and Mg(2+) stimulated activity, although the former was inhibitory at higher concentrations. Insect FPP synthase catalyzes the condensation of IPP (K(m)=2.9+/-1.2 microM) with both dimethylallyl diphosphate and geranyl diphosphate (K(m)=0.8+/-0.4 microM). The enzyme requires the presence of detergent, glycerol, and non-specific protein-protein interactions for stability and maximum catalytic activity.

Dolichol biosynthesis in the yeast Saccharomyces cerevisiae: an insight into the regulatory role of farnesyl diphosphate synthase

Dolichol, an isoprenoid lipid, known mainly for its function in protein glycosylation, is synthesised in the mevalonate pathway. The pathway is highly regulated, on multiple levels, by sterol and non-sterol derivatives of mevalonic acid. Farnesyl diphosphate (FPP) and/or FPP-derived molecules have been identified as the main non-sterol compounds regulating degradation of 3-hydroxy-3-methylglutaryl-CoA reductase, one of the regulatory enzymes in the mevalonate pathway. In the present review we concentrate on the effect of overexpression of farnesyl diphosphate synthase on dolichol biosynthesis in yeast. In this context the role of the Yta7 protein, belonging to the AAA ATPase family, in the regulation of FPP flux to the dolichol branch of the mevalonate pathway is discussed, and the effect of FPP and/or derived molecules on the transcription of genes encoding the first enzyme committed to dolichol biosynthesis, i.e. cis-prenyl transferase.

An investigation of bone resorption and Dictyostelium discoideum growth inhibition by bisphosphonate drugs

We report the results of 3D-QSAR/CoMFA investigations of the activity of bisphosphonate drugs, farnesyl pyrophosphate synthase (FPPSase) inhibitors, in the inhibition of bone resorption as well as the growth of Dictyostelium discoideum. In the case of D. discoideum, we find an experimental versus QSAR predicted pIC(50) R(2) value of 0.94 for 16 bisphosphonates over the 9-1200 microM range of IC(50) values, a cross-validated R(2) = 0.90, and a bootstrapped R(2) = 0.94, and we demonstrate that this approach has predictive utility (a 0.18 pIC(50) rms error for three test sets of 3 predictions). In bone resorption, we find an experimental versus predicted pLED (lowest effective dose) R(2) = 0.79 for 35 bisphosphonates over the 0.0001-1 mg of P/kg LED range, a cross-validated R(2) = 0.75, and a bootstrapped R(2) = 0.79. Two sets of 31 compounds were used as training sets for the predicted pLED values for two sets of 4 compounds which have an rms error of 0.44, larger than that found with D. discoideum. However, this can be attributed to the rather large uncertainties in the experimental bone resorption data which are almost all reported in decade steps (DeltapLED = 1). The CoMFA predicted (rat) bone antiresorptive pLED values are in agreement with literature (human recombinant) FPPSase inhibition results with an rms error of 0.45 (a factor of 2.8 error in activity prediction). We also report the single-crystal X-ray crystallographic structure of the compound most active in D. discoideum growth inhibition, 2-(3-picolyl)-aminomethylene-1,1-bisphosphonic acid. The structure clearly shows the presence of bond length alternation in the picolyl ring and a planar amino group linked by a very short (1.346 A) bond to the picolyl group, an amidinium-like structure which is also expected to occur in other highly active species such as minodronate and zoledronate. Overall, these results show that it is now possible to predict the activity of bisphosphonates using 3D-QSAR/CoMFA methods, although bone resorption studies should benefit from additional, accurate information on enzyme inhibition.