Constitutive activation of one or more kinase signaling pathways is a hallmark of many cancers. Here we extend the previously described mass spectrometry-based KAYAK approach by monitoring kinase activities from multiple signaling pathways simultaneously. This improved single-reaction strategy, which quantifies the phosphorylation of 90 synthetic peptides in a single mass spectrometry run, is compatible with nanogram to microgram amounts of cell lysate. Furthermore, the approach enhances kinase monospecificity through substrate competition effects, faithfully reporting the signatures of many signaling pathways after mitogen stimulation or of basal pathway activation differences across a panel of well-studied cancer cell lines. Hierarchical clustering of activities from related experiments groups peptides phosphorylated by similar kinases together and, when combined with pathway alteration using pharmacological inhibitors, distinguishes underlying differences in potency, off-target effects and genetic backgrounds. Finally, we introduce a strategy to identify the kinase, and even associated protein complex members, responsible for phosphorylation events of interest.

Background: Atherosclerosis is a complex pathological condition caused by a number of mechanisms including the accelerated proliferation of vascular smooth muscle cells (VSMCs). Diabetes is likely to be an important risk factor for atherosclerosis, as hyperglycemia induces vascular smooth muscle cell (VSMC) proliferation and migration and may thus contribute to the formation of atherosclerotic lesions. This study was performed to investigate whether PGC-1 alpha, a PPAR gamma coactivator and metabolic master regulator, plays a role in regulating VSMC proliferation and migration induced by high glucose.Methodology/Principal Findings: PGC-1 alpha mRNA levels are decreased in blood vessel media of STZ-treated diabetic rats. In cultured rat VSMCs, high glucose dose-dependently inhibits PGC-1 alpha mRNA expression. Overexpression of PGC-1 alpha either by infection with adenovirus, or by stimulation with palmitic acid, significantly reduces high glucose-induced VSMC proliferation and migration. In contrast, suppression of PGC-1 alpha by siRNA mimics the effects of glucose on VSMCs. Finally, mechanistic studies suggest that PGC-1 alpha-mediated inhibition of VSMC proliferation and migration is regulated through preventing ERK1/2 phosphorylation.Conclusions/Significance: These results indicate that PGC-1 alpha is a key regulator of high glucose-induced proliferation and migration in VSMCs, and suggest that elevation of PGC-1 alpha in VSMC could be a useful strategy in preventing the development of diabetic atherosclerosis.

PURPOSE:For many tumor cells, de novo lipogenesis is a requirement for growth and survival. A considerable body of work suggests that inhibition of this pathway may be a powerful approach to antineoplastic therapy. It has recently been shown that inhibition of various steps in the lipogenic pathway individually can induce apoptosis or loss of viability in tumor cells. However, it is not clear whether quantitative differences exist in the ability of lipogenic enzymes to control tumor cell survival. We present a systematic approach that allows for a direct comparison of the control of lipogenic pathway enzymes over tumor cell growth and apoptosis using different cancer cells.EXPERIMENTAL DESIGN:RNA interference-mediated, graded down-regulation of fatty acid synthase (FAS) pathway enzymes was employed in combination with measurements of lipogenesis, apoptosis, and cell growth.RESULTS:In applying RNA interference titrations to two lipogenic enzymes, acetyl-CoA carboxylase 1 (ACC1) and FAS, we show that ACC1 and FAS both significantly control cell growth and apoptosis in HCT-116 cells. These results also extend to PC-3 and A2780 cancer cells.CONCLUSIONS:Control of tumor cell survival by different steps in de novo lipogenesis can be quantified. Because ACC1 and FAS both significantly control tumor cell growth and apoptosis, we propose that pharmacologic inhibitors of either enzyme might be useful agents in targeting cancer cells that critically rely on fatty acid synthesis. The experimental approach described here may be extended to other targets or disease-relevant pathways to identify steps suitable for therapeutic intervention.

4473 De novo fatty acid synthesis is critical for tumor cell survival, and small molecule inhibitors of this pathway may be useful anti-cancer agents. In this report we sought to evaluate the contributions of two pathway enzymes, acetyl-CoA carboxylase 1 (ACC1) and fatty acid synthase (FAS) on the survival of HCT-116 colon cancer cells. To this end, we performed a kinetic analysis of FAS and ACC1 inhibition using siRNA transfections with two oligonucleotide sequences per target at various concentrations (0, 30 and 60 nM). Cell death (by apoptosis) and viability were assessed and plotted as a function of lipogenesis under the various transfection conditions in order to obtain a specific kinetic profile for knockdown of each enzyme. The resulting curves allowed for a direct comparison of FAS and ACC1 in terms of their significance in maintaining tumor cell viability. A gradual decrease of lipid biosynthesis by as much as 50% was achieved with siRNA-mediated knockdown of either FAS or ACC1 in HCT-116 cells. Reduced lipid biosynthesis correlated well with the expression of either FAS or ACC1. Furthermore, the changes in apoptosis and viability induced by the siRNA titrations, when plotted against lipogenesis, revealed an identical kinetic profile for both FAS and ACC1. For example, following a reduction in lipid biosynthesis by 25%, about 20% of cells stained positive for apoptosis compared to about 3% in control cells, irrespective of which target was knocked down. These findings strongly support the concept that a decrease in de novo lipogenesis, rather than perturbations in pathway intermediates, causes apoptosis in tumor cells when the FAS pathway is inhibited. It is generally difficult to compare targets in a pathway by using single-point siRNA transfections. One reason for this is that knockdown efficiency, and therefore the resulting functional effects, are likely to vary between different targets. Here, we have applied a kinetic approach using siRNA titrations, which allowed us to directly compare enzymes in the FAS pathway with respect to their role in controlling lipogenesis and tumor cell viability. Our results show that FAS and ACC1 are equally important enzymes for controlling lipogenesis and viability in cultured HCT-116 cancer cells.

Uncoupling protein 2 (UCP2) negatively regulates insulin secretion. UCP2 deficiency (by means of gene knockout) improves obesity- and high glucose-induced beta cell dysfunction and consequently improves type 2 diabetes in mice. In the present study, we have discovered that the small molecule, genipin, rapidly inhibits UCP2-mediated proton leak. In isolated mitochondria, genipin inhibits UCP2-mediated proton leak. In pancreatic islet cells, genipin increases mitochondrial membrane potential, increases ATP levels, closes K(ATP) channels, and stimulates insulin secretion. These actions of genipin occur in a UCP2-dependent manner. Importantly, acute addition of genipin to isolated islets reverses high glucose- and obesity-induced beta cell dysfunction. Thus, genipin and/or chemically modified variants of genipin are useful research tools for studying biological processes thought to be controlled by UCP2. In addition, these agents represent lead compounds that comprise a starting point for the development of therapies aimed at treating beta cell dysfunction.

A series of 3-aryl-4-hydroxyquinolin-2(1H)-ones with fatty acid synthase inhibitory activity was prepared. Starting from a derivative with an IC(50) = 1.4 microM, SAR studies led to compounds with more than 70-fold increase in potency (IC(50) < 20 nM).

PGC-1 beta is a transcriptional coactivator that potently stimulates mitochondrial biogenesis and respiration of cells. Here, we have generated mice lacking exons 3 to 4 of the Pgc-1 beta gene (Pgc-1 beta(E3,4-/E3,4-) mice). These mice express a mutant protein that has reduced coactivation activity on a subset of transcription factors, including ERR alpha, a major target of PGC-1 beta in the induction of mitochondrial gene expression. The mutant mice have reduced expression of OXPHOS genes and mitochondrial dysfunction in liver and skeletal muscle as well as elevated liver triglycerides. Euglycemic-hyperinsulinemic clamp and insulin signaling studies show that PGC-1 beta mutant mice have normal skeletal muscle response to insulin but have hepatic insulin resistance. These results demonstrate that PGC-1 beta is required for normal expression of OXPHOS genes and mitochondrial function in liver and skeletal muscle. Importantly, these abnormalities do not cause insulin resistance in skeletal muscle but cause substantially reduced insulin action in the liver.

Uncoupling protein(UCP)1 is an integral membrane protein that is located in the mitochondrial inner membrane of brown adipocytes. Its physiological role is to mediate a regulated, thermogenic proton leak. UCP2 and UCP3 are recently identified UCP1 homologues. They also mediate regulated proton leak, and might function to control the production of superoxide and other downstream reactive oxygen species. However, their role in normal physiology remains unknown. Recent studies have shown that UCP2 has an important part in the pathogenesis of type-2 diabetes. The obscure roles of the UCP homologues in normal physiology, together with their emerging role in pathophysiology, provide exciting potential for further investigation.

Loss-of-function mutations in parkin are the predominant cause of familial Parkinson's disease. We previously reported that parkin-/- mice exhibit nigrostriatal deficits in the absence of nigral degeneration. Parkin has been shown to function as an E3 ubiquitin ligase. Loss of parkin function, therefore, has been hypothesized to cause nigral degeneration via an aberrant accumulation of its substrates. Here we employed a proteomic approach to determine whether loss of parkin function results in alterations in abundance and/or modification of proteins in the ventral midbrain of parkin-/- mice. Two-dimensional gel electrophoresis followed by mass spectrometry revealed decreased abundance of a number of proteins involved in mitochondrial function or oxidative stress. Consistent with reductions in several subunits of complexes I and IV, functional assays showed reductions in respiratory capacity of striatal mitochondria isolated from parkin-/- mice. Electron microscopic analysis revealed no gross morphological abnormalities in striatal mitochondria of parkin-/- mice. In addition, parkin-/- mice showed a delayed rate of weight gain, suggesting broader metabolic abnormalities. Accompanying these deficits in mitochondrial function, parkin-/- mice also exhibited decreased levels of proteins involved in protection from oxidative stress. Consistent with these findings, parkin-/- mice showed decreased serum antioxidant capacity and increased protein and lipid peroxidation. The combination of proteomic, genetic, and physiological analyses reveal an essential role for parkin in the regulation of mitochondrial function and provide the first direct evidence of mitochondrial dysfunction and oxidative damage in the absence of nigral degeneration in a genetic mouse model of Parkinson's disease.

OBJECTIVE:Uncoupling of isolated mitochondria by nonsteroidal antiinflammatory drugs (NSAIDs) has been considered relevant to the development of gastrointestinal (GI) side effects. We investigated the occurrence of NSAID-induced uncoupling of mitochondria in intact cells (rat thymocytes) compared with the effects of a selective cyclooxygenase 2 (COX-2) inhibitor.METHODS:Oxygen consumption and mitochondrial membrane potential were simultaneously measured amperometrically and by distribution of radioactive tracer molecules, respectively, in the presence and absence of pharmacologically relevant concentrations of the NSAIDs indomethacin and diclofenac and the selective COX-2 inhibitor SC-236. Analysis of data by a technique related to top-down elasticity analysis permitted assessment of the influence of these compounds on individual components of cellular energy metabolism.RESULTS:Indomethacin, diclofenac, and SC-236 increased proton leak in isolated mitochondria. Both diclofenac and SC-236 significantly stimulated proton leak in intact cells and simultaneously inhibited substrate oxidation and ATP turnover. Oxygen consumption rates of isolated cells remained unchanged over a wide concentration range of the drugs, despite significant effects on subsystems of cellular energy metabolism.CONCLUSION:NSAIDs and selective COX-2 inhibitors have significant and equally directed effects on cellular energy metabolism. They both uncouple mitochondrial respiration and inhibit substrate oxidation and ATP turnover. However, the topical effect and selective COX-2 inhibition may not be sufficient to cause NSAID-like damage to the GI tract.

Objective: To investigate whether activity and glucocorticoid treatment of rheumatic diseases are reflected by selected parameters of cellular energy metabolism of peripheral blood mononuclear cells (PBMC). Methods: PBMC were obtained from 30 healthy volunteers, 28 patients (16 inactive; 12 active) with rheumatoid arthritis, systemic lupus erythematosus, vasculitis, or other autoimmune diseases, and five patients with infectious diseases. Patients with active rheumatic diseases were examined before and 4–5 days after starting, restarting, or increasing the dose of glucocorticoids. Cellular oxygen consumption (as a measure of ATP production), bioenergetic ability to be stimulated, and major ATP consuming processes were measured amperometrically with a Clark electrode. Results: A normal value for oxygen consumption of 3.84 (SEM 0.1) (all data in nmol O2/min/107 cells) independent of sex was found. In patients with inactive disease the respiration rate was slightly higher, but was significantly increased in active patients to 4.82 (SEM 0.33) (p<0.001). PBMC from active patients showed a significantly lower bioenergetic response to a mitogenic stimulus than controls (p<0.05). In stimulated cells from active patients there was a significant reduction in cation transport and protein synthesis. All parameters above were almost normalised within 4–5 days upon optimised treatment with glucocorticoids. For comparison, PBMC from patients with active infectious diseases also showed an increased respiration rate; their response to mitogenic stimulation was even higher. Conclusions: This study shows for the first time that parameters describing the cellular function of PBMC in bioenergetic terms are suitable for (a) describing semiquantitatively the activity of a rheumatic disease and (b) assessing the therapeutic effect on the disease.

Glycolysis and apoptosis are considered major but independent pathways that are critical for cell survival1,2,3,4. The activity of BAD, a pro-apoptotic BCL-2 family member, is regulated by phosphorylation in response to growth/survival factors5,6,7,8. Here we undertook a proteomic analysis to assess whether BAD might also participate in mitochondrial physiology. In liver mitochondria, BAD resides in a functional holoenzyme complex together with protein kinase A7 and protein phosphatase 1 (PP1) catalytic units9, Wiskott–Aldrich family member WAVE-1 as an A kinase anchoring protein10, and glucokinase (hexokinase IV)11. BAD is required to assemble the complex in that Bad-deficient hepatocytes lack this complex, resulting in diminished mitochondria-based glucokinase activity and blunted mitochondrial respiration in response to glucose. Glucose deprivation results in dephosphorylation of BAD, and BAD-dependent cell death. Moreover, the phosphorylation status of BAD helps regulate glucokinase activity. Mice deficient for BAD or bearing a non-phosphorylatable BAD(3SA) mutant12 display abnormal glucose homeostasis including profound defects in glucose tolerance. This combination of proteomics, genetics and physiology indicates an unanticipated role for BAD in integrating pathways of glucose metabolism and apoptosis.

Failure to secrete adequate amounts of insulin in response to increasing concentrations of glucose is an important feature of type 2 diabetes. The mechanism for loss of glucose responsiveness is unknown. Uncoupling protein 2 (UCP2), by virtue of its mitochondrial proton leak activity and consequent negative effect on ATP production, impairs glucose-stimulated insulin secretion. Of interest, it has recently been shown that superoxide, when added to isolated mitochondria, activates UCP2-mediated proton leak. Since obesity and chronic hyperglycemia increase mitochondrial superoxide production, as well as UCP2 expression in pancreatic beta cells, a superoxide-UCP2 pathway could contribute importantly to obesity- and hyperglycemia-induced beta cell dysfunction. This study demonstrates that endogenously produced mitochondrial superoxide activates UCP2-mediated proton leak, thus lowering ATP levels and impairing glucose-stimulated insulin secretion. Furthermore, hyperglycemia- and obesity-induced loss of glucose responsiveness is prevented by reduction of mitochondrial superoxide production or gene knockout of UCP2. Importantly, reduction of superoxide has no beneficial effect in the absence of UCP2, and superoxide levels are increased further in the absence of UCP2, demonstrating that the adverse effects of superoxide on beta cell glucose sensing are caused by activation of UCP2. Therefore, superoxide-mediated activation of UCP2 could play an important role in the pathogenesis of beta cell dysfunction and type 2 diabetes.

Peroxisome proliferator-activated receptor gamma coactivator (PGC)-1alpha is a coactivator of nuclear receptors and other transcription factors that regulates several components of energy metabolism, particularly certain aspects of adaptive thermogenesis in brown fat and skeletal muscle, hepatic gluconeogenesis, and fiber type switching in skeletal muscle. PGC-1alpha has been shown to induce mitochondrial biogenesis when expressed in muscle cells, and preliminary analysis has suggested that this molecule may specifically increase the fraction of uncoupled versus coupled respiration. In this paper, we have performed detailed bioenergetic analyses of the function of PGC-1alpha and its homolog PGC-1beta in muscle cells by monitoring simultaneously oxygen consumption and membrane potential. Cells expressing PGC-1alpha or PGC-1beta display higher proton leak rates at any given membrane potential than control cells. However, cells expressing PGC-1alpha have a higher proportion of their mitochondrial respiration linked to proton leak than cells expressing PGC-1beta. Although these two proteins cause a similar increase in the expression of many mitochondrial genes, PGC-1beta preferentially induces certain genes involved in the removal of reactive oxygen species, recently recognized as activators of uncoupling proteins. Together, these data indicate that PGC-1alpha and PGC-1beta profoundly alter mitochondrial metabolism and suggest that these proteins are likely to play different physiological functions.

The primary aim of this paper was to calculate and report flux control coefficients for mitochondrial outer-membrane carnitine palmitoyltransferase (CPT I) over hepatic ketogenesis because its role in controlling this pathway during the neonatal period is of academic importance and immediate clinical relevance. Using hepatocytes isolated from suckling rats as our model system, we measured CPT I activity and carbon flux from palmitate to ketone bodies and to CO2 in the absence and presence of a range of concentrations of etomoxir. (This is converted in situ to etomoxir-CoA which is a specific inhibitor of the enzyme.) From these data we calculated the individual flux control coefficients for CPT I over ketogenesis, CO2 production and total carbon flux (0.51 +/- 0.03; -1.30 +/- 0.26; 0.55 +/- 0.07, respectively) and compared them with equivalent coefficients calculated by similar analyses [Drynan, L., Quant, P.A. & Zammit, V.A. (1996) Biochem. J. 317, 791-795] in hepatocytes isolated from adult rats (0.85 +/- 0.20; 0.23 +/- 0.06; 1.06 +/- 0.29). CPT I exerts significantly less control over ketogenesis in hepatocytes isolated from suckling rats than those from adult rats. In the suckling systems the flux control coefficients for CPT I over ketogenesis specifically and over total carbon flux (< 0.6) are not consistent with the enzyme being rate-limiting. Broadly similar results were obtained and conclusions drawn by reanalysis of previous data {from experiments in mitochondria isolated from suckling or adult rats [Krauss, S., Lascelles, C.V., Zammit, V.A. & Quant, P.A. (1996) Biochem. J. 319, 427-433]} using a different approach of control analysis, although it is not strictly valid to compare flux control coefficients from different systems. Our overall conclusion is that flux control coefficients for CPT I over oxidative fluxes from palmitate (or palmitoyl-CoA) differ markedly according to (a) the metabolic state, (b) the stage of development, (c) the specific pathway studied and (d) the model system.

Conference Abstract| October 01 2001 UCP2, expressed at endogenous levels, mediates mitochondrial proton leak in mammalian cells S. Krauss; S. Krauss 1Division of Endocrinology, Beth Israel Deaconess Medical Center and Harvard Medical School, 99 Brookline Ave., Boston, MA 02215, U.S.A Search for other works by this author on: This Site PubMed Google Scholar C.Y. Zhang; C.Y. Zhang 1Division of Endocrinology, Beth Israel Deaconess Medical Center and Harvard Medical School, 99 Brookline Ave., Boston, MA 02215, U.S.A Search for other works by this author on: This Site PubMed Google Scholar B.B. Lowell B.B. Lowell 1Division of Endocrinology, Beth Israel Deaconess Medical Center and Harvard Medical School, 99 Brookline Ave., Boston, MA 02215, U.S.A Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (2001) 29 (5): A120. https://doi.org/10.1042/bst029a120c Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation S. Krauss, C.Y. Zhang, B.B. Lowell; UCP2, expressed at endogenous levels, mediates mitochondrial proton leak in mammalian cells. Biochem Soc Trans 1 October 2001; 29 (5): A120. doi: https://doi.org/10.1042/bst029a120c Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 2001 Biochemical Society2001 Article PDF first page preview Close Modal You do not currently have access to this content.

Immune cells are in constant need of energy for both basic housekeeping and specific immune functions. Increased energy demand during lymphocyte stimulation is coordinated by signal transduction pathways. This review explores the interface between lymphocyte signaling and energy metabolism. In particular, it discusses recent work that allows weighing signaling routes with respect to their role in the regulation of energy metabolism during lymphocyte activation.

Abstract Mitochondria fulfill various important roles in cellular metabolism. Of note they play a central role in cellular energy metabolism.