Radicicol binds and inhibits mammalian ATP citrate lyase

Synthesis, growth inhibitory activity against tumor cells, and structure-activity relationship of CGK733 and its analogs

CGK733 was reported as a compound that inhibited ATM/ATR kinase activities and blocked their checkpoint signaling pathways with great selectivity. However, this paper was subsequently retracted, and the truth about the activity of CGK733 remains unclear. We synthesized various analogs of CGK733 with a modification of the carboxylic acid moiety and/or the aniline derivative moiety to accumulate knowledge of the structure-activity relationship of this compound. Growth inhibitory activity of CGK733 and novel 35 analogs against HeLa S3 cells was evaluated, and the structure-activity relationship revealed that analogs with the 2-naphthyl or 4-fluorophenyl group instead of the benzhydryl group have activity comparable to CGK733 and that the 3-nitro group on the aniline moiety significantly affects the activity.

Recent advance of ATP citrate lyase inhibitors for the treatment of cancer and related diseases

ATP citrate lyase (ACLY), a strategic metabolic enzyme that catalyzes the glycolytic to lipidic metabolism, has gained increasing attention as an attractive therapeutic target for hyperlipidemia, cancers and other human diseases. Despite of continual research efforts, targeting ACLY has been very challenging. In this field, most reported ACLY inhibitors are "substrate-like" analogues, which occupied with the same active pockets. Besides, some ACLY inhibitors have been disclosed through biochemical screening or high throughput virtual screening. In this review, we briefly summarized the cancer-related functions and the recent advance of ACLY inhibitors with a particular focus on the SAR studies and their modes of action. We hope to provide a timely and updated overview of ACLY and the discovery of new ACLY inhibitors.

Targeting fatty acid uptake and metabolism in cancer cells: A promising strategy for cancer treatment

Despite scientific development, cancer is still a fatal disease. The development of cancer is thought to be significantly influenced by fatty acids. Several mechanisms that control fatty acid absorption and metabolism are reported to be altered in cancer cells to support their survival. Cancer cells can use de novo synthesis or uptake of extracellular fatty acid if one method is restricted. This factor makes it more difficult to target one pathway while failing to treat the disease properly. Side effects may also arise if several inhibitors simultaneously target many targets. If a viable inhibitor could work on several routes, the number of negative effects might be reduced. Comparative investigations against cell viability have found several potent natural and manmade substances. In this review, we discuss the complex roles that fatty acids play in the development of tumors and the progression of cancer, newly discovered and potentially effective natural and synthetic compounds that block the uptake and metabolism of fatty acids, the adverse side effects that can occur when multiple inhibitors are used to treat cancer, and emerging therapeutic approaches.

Following the design path of isoform-selective Hsp90 inhibitors: Small differences, great opportunities

The heat shock protein 90 (Hsp90) family consists of four highly conserved isoforms: the mitochondrial TRAP-1, the endoplasmic reticulum-localised Grp94, and the cytoplasmic Hsp90α and Hsp90β. Since the late 1990s, this family has been extensively studied as a potential target for the treatment of cancer, neurological disorders, and infectious diseases. The initial approach was to develop non-selective, so-called pan-Hsp90 ATP-competitive inhibitors of the N-terminal domain. Many of these agents were tested in clinical trials, mainly for the treatment of cancer, but none of them succeeded in the clinic. This was mainly due to the lack of efficacy and various toxicities associated with the induction of heat shock response (HSR). This lack of success has prompted a turn to new approaches of Hsp90 inhibition. Thus, inhibitors selective for a particular isoform of Hsp90 have been developed. These isoform-selective inhibitors do not induce HSR and have a more targeted effect because not all client proteins are equally dependent on all four paralogues of Hsp90. However, it is extremely difficult to develop such selective compounds because the family is highly conserved. Hsp90α and Hsp90β have an amazing 95% identity of the N-terminal ATP binding site, differing only in two amino acid residues. Therefore, the focus of this review is to fully elucidate the key structural features of the selective inhibitor classes in terms of binding site dissimilarities. In addition to a methodological characterisation of the structure-activity relationships, the main advantages of selective inhibition of the TRAP-1, Grp94, Hsp90α and Hsp90β isoforms are discussed.

Discovery and characterization of novel ATP citrate lyase inhibitors from natural products by a luminescence-based assay

ATP citrate lyase (ACLY) is a key enzyme in glucolipid metabolism with therapeutic prospect for treating hyperlipidemia and various cancers. Much effort has been put into discovering ACLY inhibitors. However, current screening approaches have limitations in sensitivity, portability and high-throughput. To develop a general screening assay, we investigated series of conditions affecting the enzymatic reaction based on the ADP-Glo luminescence assay. Bovine serum albumin (0.001%) added triggered strong and stable fluorescence signal. The optimized assay was validated and applied to screen our natural product library. Two novel inhibitors were identified with IC₅₀ values of 3.86 ± 0.62 μM (2) and 15.48 ± 2.51 μM (4). Their aggregations and target specificities were also examined. 2 was characterized as a noncompetitive inhibitor of ACLY, while 4 was a competitive inhibitor of CoA, which was also elucidated by docking studies. In anticancer activity evaluation, 2 with higher inhibition potency did not exhibit anticancer effect, probably owing to its insufficient cell-permeability. 4 showed moderate inhibition in the proliferation of A549 and PC3 cells. This study not only developed a general approach for ACLY inhibitor discovery, but also identified a new scaffold ACLY inhibitor, which could be served as a hit compound in drug design.

A Novel Metabolic Reprogramming Strategy for the Treatment of Diabetes-Associated Breast Cancer

Diabetes is directly related to the risk of breast cancer (BC) occurrence and worsened BC prognosis. Currently, there are no specific treatments for diabetes-associated BC. This paper aims to understand the fundamental mechanisms of diabetes-induced BC progression and to develop personalized treatments. It reports a metabolic reprogramming strategy (MRS) that pharmaceutical induction of glucose import and glycolysis with metformin and NF-κB inhibitor (NF-κBi) while blocking the export of excessive lactate via inhibiting monocarboxylate transporter 4 (MCT4) leads to a metabolic crisis within the cancer cells. It demonstrates that the MRS shifts the metabolism of BC cells toward higher production of lactate, blocks lactate secretion, prompts intracellular acidification and induces significant cytotoxicity. Moreover, a novel MCT4 inhibitor CB-2 has been identified by structure-based virtual screening. A triple combination of metformin, CB-2, and trabectedin, a drug that impedes NF-κB signaling, strongly inhibits BC cells. Compared to normal glucose condition, MRS elicits more potent cancer cell-killing effects under high glucose condition. Animal model studies show that diabetic conditions promote the proliferation and progression of BC xenografts in nude mice and that MRS treatment significantly inhibits HG-induced BC progression. Therefore, inhibition of MCT4 combined with metformin/NF-κBi is a promising cancer therapy, especially for diabetes-associated BC.

Lipogenesis inhibitors: therapeutic opportunities and challenges

Fatty acids are essential for survival, acting as bioenergetic substrates, structural components and signalling molecules. Given their vital role, cells have evolved mechanisms to generate fatty acids from alternative carbon sources, through a process known as de novo lipogenesis (DNL). Despite the importance of DNL, aberrant upregulation is associated with a wide variety of pathologies. Inhibiting core enzymes of DNL, including citrate/isocitrate carrier (CIC), ATP-citrate lyase (ACLY), acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), represents an attractive therapeutic strategy. Despite challenges related to efficacy, selectivity and safety, several new classes of synthetic DNL inhibitors have entered clinical-stage development and may become the foundation for a new class of therapeutics.

De novo lipogenesis (DNL) is vital for the maintenance of whole-body and cellular homeostasis, but aberrant upregulation of the pathway is associated with a broad range of conditions, including cardiovascular disease, metabolic disorders and cancers. Here, Steinberg and colleagues provide an overview of the physiological and pathological roles of the core DNL enzymes and assess strategies and agents currently in development to therapeutically target them.

Currently Available Strategies for Target Identification of Bioactive Natural Products

In recent years, biologically active natural products have gradually become important agents in the field of drug research and development because of their wide availability and variety. However, the target sites of many natural products are yet to be identified, which is a setback in the pharmaceutical industry and has seriously hindered the translation of research findings of these natural products as viable candidates for new drug exploitation. This review systematically describes the commonly used strategies for target identification via the application of probe and non-probe approaches. The merits and demerits of each method were summarized using recent examples, with the goal of comparing currently available methods and selecting the optimum techniques for identifying the targets of bioactive natural products.

Discovery of a new ATP-citrate lyase (ACLY) inhibitor identified by a pharmacophore-based virtual screening study

ATP citrate lyase (ACLY) is an important enzyme that catalyzes the conversion of citrate to acetyl-CoA in normal cells, facilitating the de novo fatty acid synthesis. Lipids and fatty acids were found to be accumulated in different types of tumors, such as brain, breast, rectal and ovarian cancer, representing a great source of energy for cancer cell growth and metabolism. Since ACLY-mediated conversion of citrate to acetyl-CoA constitutes the basis for fatty acid synthesis, ACLY seems to be quite an unexplored and promising therapeutic target for anticancer drug design. A pharmacophore-based virtual screening (VS) protocol with the aid of hierarchical docking, consensus docking (CD), molecular dynamics (MD) simulations and ligand-protein binding free energy calculations led to the identification of compound VS1, which showed a moderate but promising inhibitory activity, demonstrating to be 2.5 times more potent than reference inhibitor 2-hydroxycitrate. These results validate the reliability of our VS workflow and pave the way for the design of novel and more potent ACLY inhibitors.Communicated by Ramaswamy H. Sarma.

Target identification of natural medicine with chemical proteomics approach: probe synthesis, target fishing and protein identification

Natural products are an important source of new drugs for the treatment of various diseases. However, developing natural product-based new medicines through random moiety modification is a lengthy and costly process, due in part to the difficulties associated with comprehensively understanding the mechanism of action and the side effects. Identifying the protein targets of natural products is an effective strategy, but most medicines interact with multiple protein targets, which complicate this process. In recent years, an increasing number of researchers have begun to screen the target proteins of natural products with chemical proteomics approaches, which can provide a more comprehensive array of the protein targets of active small molecules in an unbiased manner. Typically, chemical proteomics experiments for target identification consist of two key steps: (1) chemical probe design and synthesis and (2) target fishing and identification. In recent decades, five different types of chemical proteomic probes and their respective target fishing methods have been developed to screen targets of molecules with different structures, and a variety of protein identification approaches have been invented. Presently, we will classify these chemical proteomics approaches, the application scopes and characteristics of the different types of chemical probes, the different protein identification methods, and the advantages and disadvantages of these strategies.

The vital role of ATP citrate lyase in chronic diseases

Chronic or non-communicable diseases are the leading cause of death worldwide; they usually result in long-term illnesses and demand long-term care. Despite advances in molecular therapeutics, specific biomarkers and targets for the treatment of these diseases are required. The dysregulation of de novo lipogenesis has been found to play an essential role in cell metabolism and is associated with the development and progression of many chronic diseases; this confirms the link between obesity and various chronic diseases. The main enzyme in this pathway-ATP-citrate lyase (ACLY), a lipogenic enzyme-catalyzes the critical reaction linking cellular glucose catabolism and lipogenesis. Increasing lines of evidence suggest that the modulation of ACLY expression correlates with the development and progressions of various chronic diseases such as neurodegenerative diseases, cardiovascular diseases, diabetes, obesity, inflammation, and cancer. Recent studies suggest that the inhibition of ACLY activity modulates the glycolysis and lipogenesis processes and stimulates normal physiological functions. This comprehensive review aimed to critically evaluate the role of ACLY in the development and progression of different diseases and the effects of its downregulation in the prevention and treatment of these diseases.

Transcriptional regulators involved in responses to volatile organic compounds in plants

Field studies have shown that plants growing next to herbivore-infested plants acquire higher resistance to herbivore damage. This increased resistance is partly due to regulation of plant gene expression by volatile organic compounds (VOCs) released by plants that sense environmental challenges such as herbivores. The molecular basis for VOC sensing in plants, however, is poorly understood. Here, we report the identification of TOPLESS-like proteins (TPLs) that have VOC-binding activity and are involved in VOC sensing in tobacco. While screening for volatiles that induce stress-responsive gene expression in tobacco BY-2 cells and tobacco plants, we found that some sesquiterpenes induce the expression of stress-responsive genes. These results provided evidence that plants sense these VOCs and motivated us to analyze the mechanisms underlying volatile sensing using tobacco as a model system. Using a pulldown assay with caryophyllene derivative-linked beads, we identified TPLs as transcriptional co-repressors that bind volatile caryophyllene analogs. Overexpression of TPLs in cultured BY-2 cells or tobacco leaves reduced caryophyllene-induced gene expression, indicating that TPLs are involved in the responses to caryophyllene analogs in tobacco. We propose that unlike animals, which use membrane receptors for sensing odorants, a transcriptional co-repressor plays a role in sensing and mediating VOC signals in plant cells.

Dehydrocurvularin is a potent antineoplastic agent irreversibly blocking ATP-citrate lyase: evidence from chemoproteomics

Dehydrocurvularin irreversibly inhibits human ATP-citrate lyase.

Methods to validate Hsp90 inhibitor specificity, to identify off-target effects, and to rethink approaches for further clinical development

The molecular chaperone Hsp90 is one component of a highly complex and interactive cellular proteostasis network (PN) that participates in protein folding, directs misfolded and damaged proteins for destruction, and participates in regulating cellular transcriptional responses to environmental stress, thus promoting cell and organismal survival. Over the last 20 years, it has become clear that various disease states, including cancer, neurodegeneration, metabolic disorders, and infection by diverse microbes, impact the PN. Among PN components, Hsp90 was among the first to be pharmacologically targeted with small molecules. While the number of Hsp90 inhibitors described in the literature has dramatically increased since the first such small molecule was described in 1994, it has become increasingly apparent that not all of these agents have been sufficiently validated for specificity, mechanism of action, and lack of off-target effects. Given the less than expected activity of Hsp90 inhibitors in cancer-related human clinical trials, a re-evaluation of potentially confounding off-target effects, as well as confidence in target specificity and mechanism of action, is warranted. In this commentary, we provide feasible approaches to achieve these goals and we discuss additional considerations to improve the clinical efficacy of Hsp90 inhibitors in treating cancer and other diseases.

New Perspectives on Chloroplast Protein Import

Virtually all chloroplasts in extant photosynthetic eukaryotes derive from a single endosymbiotic event that probably occurred more than a billion years ago between a host eukaryotic cell and a cyanobacterium-like ancestor. Many endosymbiont genes were subsequently transferred to the host nuclear genome, concomitant with the establishment of a system for protein transport through the chloroplast double-membrane envelope. Presently, 2,000-3,000 different nucleus-encoded chloroplast proteins must be imported into the chloroplast following their synthesis in the cytosol. The TOC (translocon at the outer envelope membrane of chloroplasts) and TIC (translocon at the inner envelope membrane of chloroplasts) complexes are protein translocation machineries at the outer and inner envelope membranes, respectively, that facilitate this chloroplast protein import with the aid of a TIC-associated ATP-driven import motor. All the essential components of this protein import system seemed to have been identified through biochemical analyses and subsequent genetic studies that initiated in the late 1990s. However, in 2013, the Nakai group reported a novel inner envelope membrane TIC complex, for which a novel ATP-driven import motor associated with this TIC complex is likely to exist. In this mini review, I will summarize these recent discoveries together with new, or reanalyzed, data presented by other groups in recent years. Whereas the precise concurrent view of chloroplast protein import is still a matter of some debate, it is anticipated that the entire TOC/TIC/ATP motor system, including any novel components, will be conclusively established in the next decade. Such findings may lead to an extensively revised view of the evolution and molecular mechanisms of chloroplast protein import.

Fatty Acids and Breast Cancer: Make Them on Site or Have Them Delivered

Brisk fatty acid (FA) production by cancer cells is accommodated by the Warburg effect. Most breast and other cancer cell types are addicted to fatty acids (FA), which they require for membrane phospholipid synthesis, signaling purposes, and energy production. Expression of the enzymes required for FA synthesis is closely linked to each of the major classes of signaling molecules that stimulate BC cell proliferation. This review focuses on the regulation of FA synthesis in BC cells, and the impact of FA, or the lack thereof, on the tumor cell phenotype. Given growing awareness of the impact of dietary fat and obesity on BC biology, we will also examine the less-frequently considered notion that, in addition to de novo FA synthesis, the lipolytic uptake of preformed FA may also be an important mechanism of lipid acquisition. Indeed, it appears that cancer cells may exist at different points along a "lipogenic-lipolytic axis," and FA uptake could thwart attempts to exploit the strict requirement for FA focused solely on inhibition of de novo FA synthesis. Strategies for clinically targeting FA metabolism will be discussed, and the current status of the medicinal chemistry in this area will be assessed. J. Cell. Physiol. 231: 2128-2141, 2016. © 2016 Wiley Periodicals, Inc.

Third generation photo-cross-linked small-molecule affinity matrix: a photoactivatable and photocleavable system enabling quantitative analysis of the photo-cross-linked small molecules and their target purification

The third generation of photoactivatable beads designed to capture bioactive small molecules in a chemo- and site-nonselective manner upon irradiation at 365 nm of UV light and release them as coumarin conjugates after exposure to UV light of 302 nm is described. These photoactivatable and photocleavable beads enable quantification of the amount and distribution of immobilized small molecules prior to the pull-down experiments to identify target protein(s) for the immobilized small molecules. The newly developed system was then used to analyze the functional group compatibility of the photo-cross-linking technology as well as the preferable nature of small molecules to be immobilized. As a result, compounds having a hydroxyl group, carboxylic acid, or aromatic ring were shown to give multiple conjugates, indicating that these compounds are well compatible with the photoactivatable beads system.

Structure-activity Relationship for FR901464: A Versatile Method for the Conversion and Preparation of Biologically Active Biotinylated Probes

The structure-activity relationship for FR901464, a potent cell-cycle inhibitor, was examined by synthesizing its analogs. A versatile method for converting FR901464 was devised. This method made it possible to synthesize biologically active FR901464-biotin conjugates which could be used to isolate the binding proteins.

Antinociceptive activity of CC44, a biotinylated improgan congener

Improgan, a non-opioid, antinociceptive drug, activates descending analgesic circuits following brain administration, but the improgan receptor remains unidentified. Since biotinylation of drugs can enhance drug potency or facilitate discovery of new drug targets, a biotinylated congener of improgan (CC44) and several related compounds were synthesized and tested for antinociceptive activity. In rats and mice, intracerebroventricular (i.c.v.) administration of CC44 produced dose-dependent reductions in thermal nociceptive (tail flick and hot plate) responses, with 5-fold greater potency than improgan. CC44 also robustly attenuated mechanical (tail pinch) nociception in normal rats and mechanical allodynia in a spinal nerve ligation model of neuropathic pain. Similar to the effects of improgan, CC44 antinociception was reversed by the GABAA agonist muscimol (consistent with activation of analgesic circuits), and was resistant to the opioid antagonist naltrexone (implying a non-opioid mechanism). Also like improgan, CC44 produced thermal antinociception when microinjected into the rostral ventromedial medulla (RVM). Unlike improgan, CC44 (i.c.v.) produced antinociception which was resistant to antagonism by the cannabinoid CB1 antagonist/inverse agonist rimonabant. CC44 was inactive in mice following systemic administration, indicating that CC44 does not penetrate the brain. Preliminary findings with other CC44 congeners suggest that the heteroaromatic nucleus (imidazole), but not the biotin moiety, is required for CC44's antinociceptive activity. These findings demonstrate that CC44 is a potent analgesic compound with many improgan-like characteristics. Since powerful techniques are available to characterize and identify the binding partners for biotin-containing ligands, CC44 may be useful in searching for new receptors for analgesic drugs.

The Warburg effect dictates the mechanism of butyrate-mediated histone acetylation and cell proliferation

Widespread changes in gene expression drive tumorigenesis, yet our knowledge of how aberrant epigenomic and transcriptome profiles arise in cancer cells is poorly understood. Here, we demonstrate that metabolic transformation plays an important role. Butyrate is the primary energy source of normal colonocytes and is metabolized to acetyl-CoA, which was shown to be important not only for energetics but also for HAT activity. Due to the Warburg effect, cancerous colonocytes rely on glucose as their primary energy source, so butyrate accumulated and functioned as an HDAC inhibitor. Although both mechanisms increased histone acetylation, different target genes were upregulated. Consequently, butyrate stimulated the proliferation of normal colonocytes and cancerous colonocytes when the Warburg effect was prevented from occurring, whereas it inhibited the proliferation of cancerous colonocytes undergoing the Warburg effect. These findings link a common metabolite to epigenetic mechanisms that are differentially utilized by normal and cancerous cells because of their inherent metabolic differences.

Detection of changes in gene regulatory patterns, elicited by perturbations of the Hsp90 molecular chaperone complex, by visualizing multiple experiments with an animation

Background

To make sense out of gene expression profiles, such analyses must be pushed beyond the mere listing of affected genes. For example, if a group of genes persistently display similar changes in expression levels under particular experimental conditions, and the proteins encoded by these genes interact and function in the same cellular compartments, this could be taken as very strong indicators for co-regulated protein complexes. One of the key requirements is having appropriate tools to detect such regulatory patterns.

Results

We have analyzed the global adaptations in gene expression patterns in the budding yeast when the Hsp90 molecular chaperone complex is perturbed either pharmacologically or genetically. We integrated these results with publicly accessible expression, protein-protein interaction and intracellular localization data. But most importantly, all experimental conditions were simultaneously and dynamically visualized with an animation. This critically facilitated the detection of patterns of gene expression changes that suggested underlying regulatory networks that a standard analysis by pairwise comparison and clustering could not have revealed.

Conclusions

The results of the animation-assisted detection of changes in gene regulatory patterns make predictions about the potential roles of Hsp90 and its co-chaperone p23 in regulating whole sets of genes. The simultaneous dynamic visualization of microarray experiments, represented in networks built by integrating one's own experimental with publicly accessible data, represents a powerful discovery tool that allows the generation of new interpretations and hypotheses.

Identification of ATP citrate lyase as a positive regulator of glycolytic function in glioblastomas

Glioblastomas, the most malignant type of glioma, are more glycolytic than normal brain tissue. Robust migration of glioblastoma cells has been previously demonstrated under glycolytic conditions and their pseudopodia contain increased glycolytic and decreased mitochondrial enzymes. Glycolysis is suppressed by metabolic acids, including citric acid which is excluded from mitochondria during hypoxia. We postulated that glioma cells maintain glycolysis by regulating metabolic acids, especially in their pseudopodia. The enzyme that breaks down cytosolic citric acid is ATP citrate lyase (ACLY). Our identification of increased ACLY in pseudopodia of U87 glioblastoma cells on 1D gels and immunoblots prompted investigation of ACLY gene expression in gliomas for survival data and correlation with expression of ENO1, that encodes enolase 1. Queries of the NIH's REMBRANDT brain tumor database based on Affymetrix data indicated that decreased survival correlated with increased gene expression of ACLY in gliomas. Queries of gliomas and glioblastomas found an association of upregulated ACLY and ENO1 expression by chi square for all probe sets (reporters) combined and correlation for numbers of probe sets indicating shared upregulation of these genes. Real-time quantitative PCR confirmed correlation between ACLY and ENO1 in 21 glioblastomas (p < 0.001). Inhibition of ACLY with hydroxycitrate suppressed (p < 0.05) in vitro glioblastoma cell migration, clonogenicity and brain invasion under glycolytic conditions and enhanced the suppressive effects of a Met inhibitor on cell migration. In summary, gene expression data, proteomics and functional assays support ACLY as a positive regulator of glycolysis in glioblastomas.

Drug-target identification from total cellular lysate by drug-induced conformational changes

Identification of drug targets is a key step in the development of novel pharmaceuticals. To this end, chemical probes or affinity matrices are often used, requiring substantial structure-activity relationship (SAR) studies. Here we report on the development of a novel technique for drug-target identification from total cellular lysate conducted independently of SAR information. This technique relies on binding of a drug to its target inducing a conformational change in target protein, thereby altering its susceptibility to proteolysis and resulting in specific degradation in some cases or in protection of target protein in others. As proof of concept, three drugs with identified targets were used. First, incubation of cellular lysates with okadaic acid elicited a specific protective effect on its target, protein phosphatase 2A catalytic subunit. Second, specific protection from exogenous protease of FKBP12 by FK506 and Hsp90 fragments by radicicol were observed. We then used the method to validate the targets of UCS15A, an Src signaling inhibitor. UCS15A induced proteolysis of a number of proteins, one of which was identified as Sam68. These studies suggest that the technology may be generally useful for identification and validation of drug targets.

Cooperation between BAT and WAT of rats in thermogenesis in response to cold, and the mechanism of glycogen accumulation in BAT during reacclimation

Rats were exposed to cold and then reacclimated at neutral temperature. Changes related to fatty acid and glucose metabolism in brown and white adipose tissues (BAT and WAT) and in muscle were then examined. Of the many proteins involved in the metabolic response, two lipogenic enzymes, acetyl-coenzyme A carboxylase (ACC) and ATP-citrate lyase, were found to play a pervasive role and studied in detail. Expression of the total and phosphorylated forms of both lipogenic enzymes in response to cold increased in BAT but decreased in WAT. Importantly, in BAT, only the phosphorylation of the ACC1 isoenzyme was enhanced, whereas that of ACC2 remained unchanged. The activities of these enzymes and the in vivo rate of FFA synthesis together suggested that WAT supplies BAT with FFA and glucose by decreasing its own synthetic activity. Furthermore, cold increased the glucose uptake of BAT by stimulating the expression of components of the insulin signaling cascade, as observed by the enhanced expression and phosphorylation of Akt and GSK-3. In muscle, these changes were observed only during reacclimation, when serum insulin also increased. Such changes may be responsible for the extreme glycogen accumulation in the BAT of rats reacclimated from cold.

A role for ATP-citrate lyase, malic enzyme, and pyruvate/citrate cycling in glucose-induced insulin secretion

In pancreatic beta-cells, metabolic coupling factors generated during glucose metabolism and pyruvate cycling through anaplerosis/cataplerosis processes contribute to the regulation of insulin secretion. Pyruvate/citrate cycling across the mitochondrial membrane leads to the production of malonyl-CoA and NADPH, two candidate coupling factors. To examine the implication of pyruvate/citrate cycling in glucose-induced insulin secretion (GIIS), different steps of the cycle were inhibited in INS 832/13 cells by pharmacological inhibitors and/or RNA interference (RNAi) technology: mitochondrial citrate export, ATP-citrate lyase (ACL), and cytosolic malic enzyme (ME1). The inhibitors of the di- and tri-carboxylate carriers, n-butylmalonate and 1,2,3-benzenetricarboxylate, respectively, reduced GIIS, indicating the importance of transmitochondrial transport of tri- and dicarboxylates in the action of glucose. To directly test the role of ACL and ME1 in GIIS, small hairpin RNA (shRNA) were used to selectively decrease ACL or ME1 expression in transfected INS 832/13 cells. shRNA-ACL reduced ACL protein levels by 67%, and this was accompanied by a reduction in GIIS. The amplification/K(ATP)-independent pathway of GIIS was affected by RNAi knockdown of ACL. The ACL inhibitor radicicol also curtailed GIIS. shRNA-ME1 reduced ME1 activity by 62% and decreased GIIS. RNAi suppression of either ACL or ME1 did not affect glucose oxidation. However, because ACL is required for malonyl-CoA formation, inhibition of ACL expression by shRNA-ACL decreased glucose incorporation into palmitate and increased fatty acid oxidation in INS 832/13 cells. Taken together, the results underscore the importance of pyruvate/citrate cycling in pancreatic beta-cell metabolic signaling and the regulation of GIIS.

Feasibility of pathways for transfer of acyl groups from mitochondria to the cytosol to form short chain acyl-CoAs in the pancreatic beta cell

The mitochondria of pancreatic beta cells are believed to convert insulin secretagogues into products that are translocated to the cytosol where they participate in insulin secretion. We studied the hypothesis that short chain acyl-CoA (SC-CoAs) might be some of these products by discerning the pathways of SC-CoA formation in beta cells. Insulin secretagogues acutely stimulated 1.5-5-fold increases in acetoacetyl-CoA, succinyl-CoA, malonyl-CoA, hydroxymethylglutaryl-CoA (HMG-CoA), and acetyl-CoA in INS-1 832/13 cells as judged from liquid chromatography-tandem mass spectrometry measurements. Studies of 12 relevant enzymes in rat and human pancreatic islets and INS-1 832/13 cells showed the feasibility of at least two redundant pathways, one involving acetoacetate and the other citrate, for the synthesis SC-CoAs from secretagogue carbon in mitochondria and the transfer of their acyl groups to the cytosol where the acyl groups are converted to SC-CoAs. Knockdown of two key cytosolic enzymes in INS-1 832/13 cells with short hairpin RNA supported the proposed scheme. Lowering ATP citrate lyase 88% did not inhibit glucose-induced insulin release indicating citrate is not the only carrier of acyl groups to the cytosol. However, lowering acetoacetyl-CoA synthetase 80% partially inhibited glucose-induced insulin release indicating formation of SC-CoAs from acetoacetate in the cytosol is important for insulin secretion. The results indicate beta cells possess enzyme pathways that can incorporate carbon from glucose into acetyl-CoA, acetoacetyl-CoA, and succinyl-CoA and carbon from leucine into these three SC-CoAs plus HMG-CoA in their mitochondria and enzymes that can form acetyl-CoA, acetoacetyl-CoA, malonyl-CoA, and HMG-CoA in their cytosol.

Inhibitors of nonhousekeeping functions of the apicoplast defy delayed death in Plasmodium falciparum

Targeting of apicoplast replication and protein synthesis in the apicomplexan Toxoplasma gondii has conventionally been associated with the typical "delayed death" phenotype, characterized by the death of parasites only in the generation following drug intervention. We demonstrate that antibiotics like clindamycin, chloramphenicol, and tetracycline, inhibitors of prokaryotic protein synthesis, invoke the delayed death phenotype in Plasmodium falciparum, too, as evident from a specific reduction of apicoplast genome copy number. Interestingly, however, molecules like triclosan, cerulenin, fops, and NAS-91, inhibitors of the recently discovered fatty acid synthesis pathway, and succinyl acetone, an inhibitor of heme biosynthesis that operates in the apicoplast of the parasite, display rapid and striking parasiticidal effects. Our results draw a clear distinction between apicoplast functions per se and the apicoplast as the site of metabolic pathways, which are required for parasite survival, and thus subserve the development of novel antimalarial therapy.

Epolactaene binds human Hsp60 Cys442 resulting in the inhibition of chaperone activity

Epolactaene is a microbial metabolite isolated from Penicillium sp., from which we synthesized its derivative ETB (epolactaene tertiary butyl ester). In the present paper, we report on the identification of the binding proteins of epolactaene/ETB, and the results of our investigation into its inhibitory mechanism. Using biotin-labelled derivatives of epolactaene/ETB, human Hsp (heat-shock protein) 60 was identified as a binding protein of epolactaene/ETB in vitro as well as in situ. In addition, we found that Hsp60 pre-incubated with epolactaene/ETB lost its chaperone activity. The in vitro binding study showed that biotin-conjugated epolactaene/ETB covalently binds to Hsp60. In order to investigate the binding site, binding experiments with alanine mutants of Hsp60 cysteine residues were conducted. As a result, it was suggested that Cys442 is responsible for the covalent binding with biotin-conjugated epolactaene/ETB. Furthermore, the replacement of Hsp60 Cys442 with an alanine residue renders the chaperone activity resistant to ETB inhibition, while the alanine replacement of other cysteine residues do not. These results indicate that this cysteine residue is alkylated by ETB, leading to Hsp60 inactivation.

Hsp90 inhibition accelerates cell lysis. Anti-Hsp90 ribozyme reveals a complex mechanism of Hsp90 inhibitors involving both superoxide- and Hsp90-dependent events

The 90 kDa heat shock protein, Hsp90, is an abundant molecular chaperone participating in the cytoprotection of eukaryotic cells. Here we analyzed the involvement of Hsp90 in the maintenance of cellular integrity using partial cell lysis as a measure. Inhibition of Hsp90 by geldanamycin, radicicol, cisplatin, and novobiocin induced a significant acceleration of detergent- and hypotonic shock-induced cell lysis. The concentration and time dependence of cell lysis acceleration was in agreement with the Hsp90 inhibition characteristics of the N-terminal inhibitors, geldanamycin and radicicol. Glutathione and other reducing agents partially blocked geldanamycin-induced acceleration of cell lysis but were largely ineffective with other inhibitors. Indeed, geldanamycin treatment led to superoxide production and a change in membrane fluidity. When Hsp90 content was diminished using anti-Hsp90 hammerhead ribozymes, an accelerated cell lysis was also observed. Hsp90 inhibition-induced cell lysis was more pronounced in eukaryotic (yeast, mouse red blood, and human T-lymphoma) cells than in bacteria. Our results indicate that besides the geldanamycin-induced superoxide production, and a consequent increase in cell lysis, inhibition or lack of Hsp90 alone can also compromise cellular integrity. Moreover, cell lysis after hypoxia and complement attack was also enhanced by any type of Hsp90 inhibition used, which shows that the maintenance of cellular integrity by Hsp90 is important in physiologically relevant lytic conditions of tumor cells.

Inhibitors of NF-kappaB signaling: design and synthesis of a biotinylated isopanepoxydone affinity reagent

A number of inhibitors of NF-kappaB signaling arising from our recent syntheses of isopanepoxydone and panepoxydone have been identified. Structure-activity data have been correlated to allow the design and synthesis of an affinity reagent for the isolation and identification of any relevant cellular target.

Inhibition of branched-chain alpha-keto acid dehydrogenase kinase and Sln1 yeast histidine kinase by the antifungal antibiotic radicicol

The 90-kDa heat shock family (HSP90) of protein and two-component histidine kinases, although quite distinct at the primary amino acid sequence level, share a common structural ATP-binding domain known as the Bergerat fold. The Bergerat fold is important for the ATPase activity and associated chaperone function of HSP90. Two-component histidine kinases occur in bacteria, yeast, and plants but have yet to be identified in mammalian cells. The antifungal antibiotic radicicol (Monorden) has been shown to bind to the Bergerat fold of HSP90 and to inhibit its ATPase activity. The structural similarity between the Bergerat fold of HSP90 and bacterial two-component histidine kinases prompted our inquiry into whether radicicol could be a potential inhibitor of histidine kinase-like proteins. Structural homology searches suggest that the ATP-binding domains of the yeast histidine kinase Sln1 and the mammalian, branched-chain alpha-keto acid dehydrogenase kinase are very similar to that of other Bergerat fold family members. On the basis of structural homology, we tested radicicol as a potential inhibitor of Sln1 and branched-chain alpha-keto acid dehydrogenase kinase (BCKDHK) and propose a mechanism of inhibition of these kinases. Although BCKDHK has been shown to have serine autophosphorylation activity, we speculate, based on the results from this study and other supporting evidence, that BCKDHK may also have intrinsic histidine kinase activity.

Critical role for cataplerosis via citrate in glucose-regulated insulin release

The molecular mechanisms mediating acute regulation of insulin release by glucose are partially known. The process involves at least two pathways that can be discriminated on basis of their (in)dependence of closure of ATP-sensitive potassium (K+(ATP)) channels. The mechanism of the K+(ATP) channel-independent pathway was proposed to involve cataplerosis, the export of mitochondrial intermediates into the cytosol and in the induction of fatty acid-derived signaling molecules. In the present article, we have explored in fluorescence-activated cell sorter (FACS)-purified rat beta-cells the molecular steps involved in chronic glucose regulation of the insulin secretory response. When compared with culture in 10 mmol/l glucose, 24 h culture in 3 mmol/l glucose shifts the phenotype of the cells into a state with low further secretory responsiveness to glucose, lower rates of glucose oxidation, and lower rates of cataplerosis. Microarray mRNA analysis indicates that this shift can be attributed to differences in expression of genes involved in the K+(ATP) channel-dependent pathway, in cataplerosis and in fatty acid/cholesterol biosynthesis. This response was paralleled by glucose upregulation of the transcription factor sterol regulatory element binding protein 1c (SREBP1c) (ADD1) and downregulation of peroxisome proliferator-activated receptor (PPAR)-alpha and PPAR-beta (PPARdelta). The functional importance of cataplerosis via citrate for glucose-induced insulin release was further supported by the observation that two ATP-citrate lyase inhibitors, radicicol and (-)-hydroxycitrate, block part of glucose-stimulated release in beta-cells. In conclusion, chronic glucose regulation of the glucose-responsive secretory phenotype is associated with coordinated changes in gene expression involved in the K+(ATP) channel-dependent pathway, in cataplerosis via citrate and in acyl CoA/cholesterol biosynthesis.

Drug receptor identification from multiple tissues using cellular-derived mRNA display libraries

The use of display technologies to identify small molecule receptors from proteome libraries would provide a significant advantage in drug discovery. We have used mRNA display to select, based on affinity, proteins that bind to a drug of interest. A library of mRNA-protein fusion molecules was constructed from human liver, kidney, and bone marrow transcripts and selected using an immobilized FK506-biotin conjugate. Three rounds of selection produced full-length FKBP12 (FK506 binding protein 12 kDa) as the dominant clone. An analogous method was also used to map the minimal drug binding domain within FKBP12. Using this approach, it is anticipated that mRNA display could eventually play a key role in the discovery and characterization of new drug receptor interactions.