The phosphorylation mechanism of mevalonate diphosphate decarboxylase: a QM/MM study.

Mevalonate diphosphate decarboxylase (MDD) catalyses a crucial step of the mevalonate pathway via Mg2+-ATP-dependent phosphorylation and decarboxylation reactions to ultimately produce isopentenyl diphosphate, the precursor of isoprenoids, which is essential to bacterial functions and provides ideal building blocks for the biosynthesis of isopentenols. However, the metal ion(s) in MDD has not been unambiguously resolved, which limits the understanding of the catalytic mechanism and the exploitation of enzymes for the development of antibacterial therapies or the mevalonate metabolic pathway for the biosynthesis of biofuels. Here by analogizing structurally related kinases and molecular dynamics simulations, we constructed a model of the MDD-substrate-ATP-Mg2+ complex and proposed that MDD requires two Mg2+ ions for maintaining a catalytically active conformation. Subsequent QM/MM studies indicate that MDD catalyses the phosphorylation of its substrate mevalonate diphosphate (MVAPP) via a direct phosphorylation reaction, instead of the previously assumed catalytic base mechanism. The results here would shed light on the active conformation of MDD-related enzymes and their catalytic mechanisms and therefore be useful for developing novel antimicrobial therapies or reconstructing mevalonate metabolic pathways for the biosynthesis of biofuels.

Catalytic mechanism of mevalonate kinase revisited, a QM/MM study.

Mevalonate Kinase (MVK) catalyses the ATP-Mg2+ mediated phosphate transfer of mevalonate to produce mevalonate 5-phosphate and is a key kinase in the mevalonate pathway in the biosynthesis of isopentenyl diphosphate, the precursor of isoprenoid-based biofuels. However, the crystal structure in complex with the native substrate mevalonate, ATP and Mg2+ has not been resolved, which has limited the understanding of its reaction mechanism and therefore its application in the production of isoprenoid-based biofuels. Here using molecular docking, molecular dynamics (MD) simulations and a hybrid QM/MM study, we revisited the location of Mg2+ resolved in the crystal structure of MVK and determined a catalytically competent MVK structure in complex with the native substrate mevalonate and ATP. We demonstrated that significant conformational change on a flexible loop connecting the α6 and α7 helix is induced by the substrate binding. Further, we found that Asp204 is coordinated to the Mg2+ ion. Arg241 plays a crucial role in organizing the triphosphoryl tail of ATP for in-line phosphate transfer and stabilizing the negative charge that accumulates at the ß,γ-bridging oxygen of ATP upon bond cleavage. Remarkably, we revealed that the phosphorylation of mevalonate catalyzed by MVK occurs via a direct phosphorylation mechanism, instead of the conventionally postulated catalytic base mechanism. The catalytically competent complex structure of MVK as well as the mechanism of reaction will pave the way for the rational engineering of MVK to exploit its applications in the production of biofuels.

Simvastatin inhibits CD44 fragmentation in chondrocytes.

In human osteoarthritic chondrocytes, the hyaluronan receptor CD44 undergoes proteolytic cleavage at the cell surface. CD44 cleavage is thought to require transit of CD44 into cholesterol-rich lipid rafts. The purpose of this study was to investigate whether statins exert a protective effect on articular chondrocytes due to diminution of cholesterol. Three model systems of chondrocytes were examined including human HCS-2/8 chondrosarcoma cells, human osteoarthritic chondrocytes and normal bovine articular chondrocytes. Treatment with IL-1ß + Oncostatin M resulted in a substantial increase in CD44 fragmentation in each of the three chondrocyte models. Pre-incubation with simvastatin prior to treatment with IL-1ß + Oncostatin M decreased the level of CD44 fragmentation, decreased the proportion of CD44 that transits into the lipid raft fractions, decreased ADAM10 activity and diminished the interaction between CD44 and ADAM10. In HCS-2/8 cells and bovine articular chondrocytes, fragmentation of CD44 was blocked by the knockdown of ADAM10. Inhibition of CD44 fragmentation by simvastatin also resulted in improved retention of pericellular matrix. Addition of cholesterol and farnesyl-pyrophosphate reversed the protective effects of simvastatin. Thus, the addition of simvastatin exerts positive effects on chondrocytes including reduced CD44 fragmentation and enhanced the retention of pericellular matrix.

The potential of the mevalonate pathway for enhanced isoprenoid production.

The cytosol-localised mevalonic acid (MVA) pathway delivers the basic isoprene unit isopentenyl diphosphate (IPP). In higher plants, this central metabolic intermediate is also synthesised by the plastid-localised methylerythritol phosphate (MEP) pathway. Both MVA and MEP pathways conspire through exchange of intermediates and regulatory interactions. Products downstream of IPP such as phytosterols, carotenoids, vitamin E, artemisinin, tanshinone and paclitaxel demonstrate antioxidant, cholesterol-reducing, anti-ageing, anticancer, antimalarial, anti-inflammatory and antibacterial activities. Other isoprenoid precursors including isoprene, isoprenol, geraniol, farnesene and farnesol are economically valuable. An update on the MVA pathway and its interaction with the MEP pathway is presented, including the improvement in the production of phytosterols and other isoprenoid derivatives. Such attempts are for instance based on the bioengineering of microbes such as Escherichia coli and Saccharomyces cerevisiae, as well as plants. The function of relevant genes in the MVA pathway that can be utilised in metabolic engineering is reviewed and future perspectives are presented.

De Novo Transcriptome and Expression Profile Analysis to Reveal Genes and Pathways Potentially Involved in Cantharidin Biosynthesis in the Blister Beetle Mylabris cichorii.

The dried body of Mylabris cichorii is well-known Chinese traditional medicine. The sesquiterpenoid cantharidin, which is secreted mostly by adult male beetles, has recently been used as an anti-cancer drug. However, little is known about the mechanisms of cantharidin biosynthesis. Furthermore, there is currently no genomic or transcriptomic information for M. cichorii. In this study, we performed de novo assembly transcriptome of M. cichorii using the Illumina Hiseq2000. A single run produced 9.19 Gb of clean nucleotides comprising 29,247 sequences, including 23,739 annotated sequences (about 81%). We also constructed two expression profile libraries (20-25 day-old adult males and 20-25 day-old adult females) and discovered 2,465 significantly differentially-expressed genes. Putative genes and pathways involved in the biosynthesis of cantharidin were then characterized. We also found that cantharidin biosynthesis in M. cichorii might only occur via the mevalonate (MVA) pathway, not via the methylerythritol 4-phosphate/deoxyxylulose 5-phosphate (MEP/DOXP) pathway or a mixture of these. Besides, we considered that cantharidin biosynthesis might be related to the juvenile hormone (JH) biosynthesis or degradation. The results of transcriptome and expression profiling analysis provide a comprehensive sequence resource for M. cichorii that could facilitate the in-depth study of candidate genes and pathways involved in cantharidin biosynthesis, and may thus help to improve our understanding of the mechanisms of cantharidin biosynthesis in blister beetles.

Negative Feedbacks by Isoprenoids on a Mevalonate Kinase Expressed in the Corpora Allata of Mosquitoes.

BACKGROUND: Juvenile hormones (JH) regulate development and reproductive maturation in insects. JHs are synthesized through the mevalonate pathway (MVAP), an ancient metabolic pathway present in the three domains of life. Mevalonate kinase (MVK) is a key enzyme in the MVAP. MVK catalyzes the synthesis of phosphomevalonate (PM) by transferring the γ-phosphoryl group from ATP to the C5 hydroxyl oxygen of mevalonic acid (MA). Despite the importance of MVKs, these enzymes have been poorly characterized in insects. RESULTS: We functionally characterized an Aedes aegypti MVK (AaMVK) expressed in the corpora allata (CA) of the mosquito. AaMVK displayed its activity in the presence of metal cofactors. Different nucleotides were used by AaMVK as phosphoryl donors. In the presence of Mg(2+), the enzyme has higher affinity for MA than ATP. The activity of AaMVK was regulated by feedback inhibition from long-chain isoprenoids, such as geranyl diphosphate (GPP) and farnesyl diphosphate (FPP). CONCLUSIONS: AaMVK exhibited efficient inhibition by GPP and FPP (Ki less than 1 µM), and none by isopentenyl pyrophosphate (IPP) and dimethyl allyl pyrophosphate (DPPM). These results suggest that GPP and FPP might act as physiological inhibitors in the synthesis of isoprenoids in the CA of mosquitoes. Changing MVK activity can alter the flux of precursors and therefore regulate juvenile hormone biosynthesis.

Sparse feature selection methods identify unexpected global cellular response to strontium-containing materials.

Despite the increasing sophistication of biomaterials design and functional characterization studies, little is known regarding cells' global response to biomaterials. Here, we combined nontargeted holistic biological and physical science techniques to evaluate how simple strontium ion incorporation within the well-described biomaterial 45S5 bioactive glass (BG) influences the global response of human mesenchymal stem cells. Our objective analyses of whole gene-expression profiles, confirmed by standard molecular biology techniques, revealed that strontium-substituted BG up-regulated the isoprenoid pathway, suggesting an influence on both sterol metabolite synthesis and protein prenylation processes. This up-regulation was accompanied by increases in cellular and membrane cholesterol and lipid raft contents as determined by Raman spectroscopy mapping and total internal reflection fluorescence microscopy analyses and by an increase in cellular content of phosphorylated myosin II light chain. Our unexpected findings of this strong metabolic pathway regulation as a response to biomaterial composition highlight the benefits of discovery-driven nonreductionist approaches to gain a deeper understanding of global cell-material interactions and suggest alternative research routes for evaluating biomaterials to improve their design.

Inhibition of bacterial mevalonate diphosphate decarboxylase by eriochrome compounds.

Mevalonate diphosphate decarboxylase (MDD; EC 4.1.1.33) catalyzes the irreversible decarboxylation of mevalonate diphosphate in the mevalonate pathway to form isopentenyl diphosphate, which is a precursor in the biosynthesis of many essential polyisoprenoid natural products, including sterols. In low G/C Gram-positive bacteria, which utilize the mevalonate pathway, MDD is required for cell viability and thus is a potential target for development of antibiotic drugs. To identify potential inhibitors of the enzyme, the National Cancer Institute's Mechanistic Diversity Set library of compounds was screened for inhibitors of Staphylococcus epidermidis MDD. From this screen, the compound Eriochrome Black A (EBA), an azo dye, was found to inhibit the enzyme with an IC50 value<5µM. Molecular docking of EBA into a crystal structure of S. epidermidis MDD suggested binding at the active site. EBA, along with the related Eriochrome B and T compounds, was evaluated for its ability to not only inhibit enzymatic activity but to inhibit bacterial growth as well. These compounds exhibited competitive inhibition towards the substrate mevalonate diphosphate, with Ki values ranging from 0.6 to 2.7µM. Non-competitive inhibition was observed versus ATP indicating binding of the inhibitor in the mevalonate diphosphate binding site, consistent with molecular docking predictions. Fluorescence quenching analyses also supported active site binding of EBA. These eriochrome compounds are effective at inhibiting S. epidermidis cell growth on both solid media and in liquid culture (MIC50 from 31 to 350µM) raising the possibility that they could be developed into antibiotic leads targeting pathogenic low-G/C Gram-positive cocci.

Sterol partitioning by HMGR and DXR for routing intermediates toward withanolide biosynthesis.

Withanolides biosynthesis in the plant Withania somnifera (L.) Dunal is hypothesized to be diverged from sterol pathway at the level of 24-methylene cholesterol. The conversion and translocation of intermediates for sterols and withanolides are yet to be characterized in this plant. To understand the influence of mevalonate (MVA) and 2-C-methyl-d-erythritol-4-phosphate (MEP) pathways on sterols and withanolides biosynthesis in planta, we overexpressed the WsHMGR2 and WsDXR2 in tobacco, analyzed the effect of transient suppression through RNAi, inhibited MVA and MEP pathways and fed the leaf tissue with different sterols. Overexpression of WsHMGR2 increased cycloartenol, sitosterol, stigmasterol and campesterol compared to WsDXR2 transgene lines. Increase in cholesterol was, however, marginally higher in WsDXR2 transgenic lines. This was further validated through transient suppression analysis, and pathway inhibition where cholesterol reduction was found higher due to WsDXR2 suppression and all other sterols were affected predominantly by WsHMGR2 suppression in leaf. The transcript abundance and enzyme analysis data also correlate with sterol accumulation. Cholesterol feeding did not increase the withanolide content compared to cycloartenol, sitosterol, stigmasterol and campesterol. Hence, a preferential translocation of carbon from MVA and MEP pathways was found differentiating the sterols types. Overall results suggested that MVA pathway was predominant in contributing intermediates for withanolides synthesis mainly through the campesterol/stigmasterol route in planta.

Mevalonate-dependent enzymatic synthesis of amorphadiene driven by an ATP-regeneration system using polyphosphate kinase.

Polyphosphate kinase (PPK), which can regenerate ATP from ADP, was utilized in the mevalonate-dependent enzymatic synthesis of amorphadiene. The activity of PPK, cloned from Escherichia coli, was determined by (31)P-NMR. The yield from the PPK-catalyzed synthesis was 25%, 2.5 times higher than that without PPK. The (31)P-NMR analysis of the final reaction mixture indicated no accumulation of intermediates.

NMR dynamics investigation of ligand-induced changes of main and side-chain arginine N-H's in human phosphomevalonate kinase.

Phosphomevalonate kinase (PMK) catalyzes phosphoryl transfer from adenosine triphosphate (ATP) to mevalonate 5-phosphate (M5P) on the pathway for synthesizing cholesterol and other isoprenoids. To permit this reaction, its substrates must be brought proximal, which would result in a significant and repulsive buildup of negative charge. To facilitate this difficult task, PMK contains 17 arginines and eight lysines. However, the way in which this charge neutralization and binding is achieved, from a structural and dynamics perspective, is not known. More broadly, the role of arginine side-chain dynamics in binding of charged substrates has not been experimentally defined for any protein to date. Herein we report a characterization of changes to the dynamical state of the arginine side chains in PMK due to binding of its highly charged substrates, ATP and M5P. These studies were facilitated by the use of arginine-selective labeling to eliminate spectral overlap. Model-free analysis indicated that while substrate binding has little effect on the arginine backbone dynamics, binding of either substrate leads to significant rigidification of the arginine side chains throughout the protein, even those that are >8 A from the binding site. Such a global rigidification of arginine side chains is unprecedented and suggests that there are long-range electrostatic interactions of sufficient strength to restrict the motion of arginine side chains on the picosecond-to-nanosecond time scale. It will be interesting to see whether such effects are general for arginine residues in proteins that bind highly charged substrates, once additional studies of arginine side-chain dynamics are reported.

Synthesis of ATP derivatives of compounds of the mevalonate pathway (isopentenyl di- and triphosphate; geranyl di- and triphosphate, farnesyl di- and triphosphate, and dimethylallyl diphosphate) catalyzed by T4 RNA ligase, T4 DNA ligase and other ligases Potential relationship with the effect of bisphosphonates on osteoclasts.

Compounds of the mevalonate pathway containing a terminal di- or triphosphate (mev-PP or mev-PPP) were tested as substrates of several enzyme ligases (T4 RNA ligase, T4 DNA ligase, firefly luciferase and other ligases) for the synthesis of ATP derivatives of the mev-pppA or mev-ppppA type. T4 RNA ligase, in the presence of ATP and the substrates: geranyl, farnesyl or isopentenyl triphosphates, and geranyl, farnesyl, dimethylallyl or isopentenyl diphosphates, all at 0.3 mM concentration, catalyzed the synthesis of the corresponding ATP derivatives at a relative rate of activity of: 7.6+/-1.4 mU/mg or 100%; 39%; 42%; 24%; 18%; 12% and 6%, respectively. Inhibition (%) of the synthesis by excess of substrate (0.8 mM vs. 0.3 mM) was observed with farnesyl diphosphate (99%); farnesyl triphosphate (96%) and geranyl triphosphate (32%). V(max), K(m), K(cat) and K(cat)/K(m) values were also determined. The K(cat)/K(m) values calculated were for: farnesyl triphosphate, 166; geranyl triphosphate, 52.2; farnesyl diphosphate, 12.1; geranyl diphosphate, 8.6; isopentenyl triphosphate, 6.7; dimethylallyl diphosphate, 3.1 and isopentenyl diphosphate, 0.9. Similar results were obtained with T4 DNA ligase. The above-mentioned compounds were also substrates of firefly luciferase synthesizing the mev-pppA or mev-ppppA derivatives. In our hands, neither the acyl- or acetyl-CoA synthetases nor the ubiquiting activating enzyme (E1) catalyzed the synthesis of ATP derivatives of these compounds. The results here presented could be related with the mechanism of action of bisphosphonates on osteoclasts or tumor cells.

Crystal structures of Trypanosoma brucei and Staphylococcus aureus mevalonate diphosphate decarboxylase inform on the determinants of specificity and reactivity.

Mevalonate diphosphate decarboxylase (MDD) catalyzes the ATP-dependent decarboxylation of mevalonate 5-diphosphate (MDP) to form isopentenyl pyrophosphate, a ubiquitous precursor for isoprenoid biosynthesis. MDD is a poorly understood component of this important metabolic pathway. Complementation of a temperature-sensitive yeast mutant by the putative mdd genes of Trypanosoma brucei and Staphylococcus aureus provides proof-of-function. Crystal structures of MDD from T. brucei (TbMDD, at 1.8 A resolution) and S. aureus (SaMDD, in two distinct crystal forms, each diffracting to 2.3 A resolution) have been determined. Gel-filtration chromatography and analytical ultracentrifugation experiments indicate that TbMDD is predominantly monomeric in solution while SaMDD is dimeric. The new crystal structures and comparison with that of the yeast Saccharomyces cerevisiae enzyme (ScMDD) reveal the structural basis for this variance in quaternary structure. The presence of an ordered sulfate in the structure of TbMDD reveals for the first time details of a ligand binding in the MDD active site and, in conjunction with well-ordered water molecules, comparisons with the related enzyme mevalonate kinase, structural and biochemical data derived on ScMDD and SaMDD, allows us to model a ternary complex with MDP and ATP. This model facilitates discussion of the molecular determinants of substrate recognition and contributions made by specific residues to the enzyme mechanism.

Pig liver phosphomevalonate kinase: kinetic mechanism.

Phosphomevalonate kinase catalyzes the phosphorylation of phosphomevalonate to diphosphomevalonate by ATP, one of the initial steps in the biosynthesis of steroids and isoprenoids. In previous studies, the enzyme from pig liver was purified and characterized, and preliminary work showed that the enzyme follows hyperbolic kinetics and a sequential mechanism. The present work is a more detailed analysis of its kinetic mechanism, using initial velocity and isotope exchange at equilibrium measurements. The results are compatible with a Bi Bi sequential ordered mechanism with phosphomevalonate as the first substrate and ADP the last product. The Km values estimated are 43+/-7 microM for Mg-ATP and 12+/-3 microM for phosphomevalonate, with a Vmax of 51+/-2 micromol min-1 mg of protein-1.

Inhibition of mevalonate 5-diphosphate decarboxylase by fluorinated substrate analogs.

Mevalonate 5-diphosphate decarboxylase (MDD) is a peroxisomal enzyme in the cholesterol biosynthetic pathway, which plays an important role in regulating cholesterol biosynthesis. In the present study, rat MDD was cloned and purified to apparent homogeneity. Two fluorinated MDD substrate analogs, P'-geranyl 2-fluoromevalonate 5-diphosphate (4) and 2-fluoromevalonate 5-diphosphate (6), were synthesized, and both were found to be irreversible inhibitors of rat MDD. These two inhibitors were characterized, and mechanisms of the inactivation process were proposed. Kinetic studies indicate both analogs only bind into mevalonate binding-site of MDD. Compound 4 shows competitive inhibition on mevalonate kinase (MVK), and its IC(50) value was determined to be comparable with that of geranyl diphosphate. Further kinetic studies indicate compound 4 only bind into ATP binding-site of MVK. These studies provide an example for a single inhibitor to carry out sequential blocking of two enzymes in cholesterol biosynthesis, which may provide useful information for drug discovery for the purpose of treating cardiovascular disease and cancer or for pest control.

Bifunctional inhibitors of mevalonate kinase and mevalonate 5-diphosphate decarboxylase.

[structure: see text] A bifunctional inhibitor of mevalonate kinase and mevalonate 5-diphosphate decarboxylase was synthesized. Both enzymes are in the cholesterol biosynthetic pathway and play an important role in regulating cholesterol biosynthesis. The molecule may become a useful lead compound for further development for treating cardiovascular disease and cancer. This study provides a novel example of a single inhibitor blocking two sequential steps simultaneously in the cholesterol biosynthetic pathway.

Targeting the mevalonate pathway inhibits the function of the epidermal growth factor receptor.

PURPOSE: The epidermal growth factor receptor (EGFR) is a key regulator of growth, differentiation, and survival of epithelial cancers. In a small subset of tumors, the presence of activating mutations within the ATP binding site confers increased susceptibility to gefitinib, a potent tyrosine kinase inhibitor of EGFR. Agents that can inhibit EGFR function through different mechanisms may enhance gefitinib activity in patients lacking these mutations. Mevalonate metabolites play significant roles in the function of the EGFR; therefore, mevalonate pathway inhibitors may potentiate EGFR-targeted therapies. EXPERIMENTAL DESIGN: In this study, we evaluated the effect of lovastatin on EGFR function and on gefitinib activity. Effects on EGFR function were analyzed by Western blot analysis using phosphospecific antibodies to EGFR, AKT, and extracellular signal-regulated kinase. Cytotoxic effects of lovastatin and/or gefitinib were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and flow cytometry. RESULTS: Lovastatin treatment inhibited EGF-induced EGFR autophosphorylation by 24 hours that was reversed by the coadministration of mevalonate. Combining lovastatin and gefitinib treatments showed enhanced inhibition of AKT activation by EGF in SCC9 cells. The combination of 10 mumol/L lovastatin and 10 mumol/L gefitinib treatments showed cooperative cytotoxicity in all 8 squamous cell carcinomas, 4 of 4 non-small cell lung carcinoma and 4 of 4 colon carcinoma cell lines tested. Isobologram and flow cytometric analyses of three representative cell lines with wild-type EGFR ATP binding sites confirmed that this combination was synergistic inducing a potent apoptotic response. CONCLUSIONS: Taken together, these results show that targeting the mevalonate pathway can inhibit EGFR function. They also suggest the potential utility of combining these clinically relevant therapeutic approaches.

Enterococcus faecalis mevalonate kinase.

Gram-positive pathogens synthesize isopentenyl diphosphate, the five-carbon precursor of isoprenoids, via the mevalonate pathway. The enzymes of this pathway are essential for the survival of these organisms, and thus may represent possible targets for drug design. To extend our investigation of the mevalonate pathway in Enterococcus faecalis, we PCR-amplified and cloned into pET-28b the mvaK1 gene thought to encode mevalonate kinase, the fourth enzyme of the pathway. Following transformation of the construct EFK1-pET28b into Escherichia coli BL21(DE3) cells, the expressed C-terminally hexahistidine-tagged protein was purified on a nickel affinity support to apparent homogeneity. The purified protein catalyzed the divalent ion-dependent phosphorylation of mevalonate to mevalonate 5-phosphate. The specific activity of the purified kinase was 24 micromole/min/mg protein. Based on sedimentation velocity data, E. faecalis mevalonate kinase exists in solution primarily as a monomer with a mass of 32.2 kD. Optimal activity occurred at pH 10 and at 37 degrees C. Delta H(a) was 22 kcal/mole. Kinetic analysis suggested that the reaction proceeds via a sequential mechanism. K(m) values were 0.33 mM (mevalonate), 1.1 mM (ATP), and 3.3 mM (Mg(2+)). Unlike mammalian mevalonate kinases, E. faecalis mevalonate kinase utilized all tested nucleoside triphosphates as phosphoryl donors. ADP, but not AMP, inhibited the reaction with a K(i) of 2.7 mM.

Molecular regulation of cholesterol biosynthesis: implications in carcinogenesis.

Cholesterol synthesis was demonstrated to be mandatory for cellular growth and serves to supply one of the necessary building blocks for new membranes demanded by dividing cells during growth. The mevalonate pathway, which is regulated through a finely tuned mechanism, is responsible mainly for cholesterol enrichment to cells. Among the various steps, the production of mevalonate from 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) is the most critically regulated step catalyzed by HMG-CoA reductase. The ability of sterols to regulate both the transcriptional rates of the reductase gene and the degradative machinery for the reductase protein provides a multilevel system for controlling the expression of this enzyme. Much convincing evidence indicates that cells manifest a higher flux through the mevalonate pathway when proliferating than when they are in the cell cycle arrest condition; furthermore, tumors undergo deregulated cholesterogenesis mainly at the critical rate-controlling juncture (i.e., the reaction catalyzed by HMG-CoA reductase). The mevalonate component of the cholesterol biosynthesis plays a key role in controlling cell proliferation by generating prenyl intermediates, particularly farnesyl and geranyl-geranyl moieties. These isoprenoids covalently modify and thus modulate the biological activity of signal transducing proteins, such as that of the Ras superfamily. The prenylated Ras-mediated signal transduction pathway provides much of the molecular information needed to trigger cell proliferation. Therefore, depletion of mevalonate can block both the processing and the transforming activities of Ras, indicating that drugs such as lovastatin and compactin, which had previously been exploited for lowering cholesterol levels, may be useful chemotherapeutic agents for treating tumors harboring oncogenic Ras mutation. In addition, Ras prenylation, which provides much of the molecular information needed to trigger cell proliferation, represents an inviting target for the design of chemotherapeutic drugs that would interrupt such signaling events and arrest tumor cell proliferation.