Cancer cells exhibit an altered metabolism which is characterized by a preference for aerobic glycolysis more than mitochondrial oxidation of pyruvate. This provides anabolic support and selective growth advantage for cancer cells. Recently, a new concept has arisen suggesting that these metabolic changes may be due, in part, to an attenuated mitochondrial function which results from the inhibition of the pyruvate dehydrogenase complex (PDC). This mitochondrial complex links glycolysis to the Krebs cycle and the current understanding of its regulation involves the cyclic phosphorylation and dephosphorylation by specific pyruvate dehydrogenase kinases (PDKs) and pyruvate dehydrogenase phosphatases (PDPs).Here we review literature pertinent to provide an overview of the multiple levels of PDC regulation to allow cancer cells to adapt their metabolism to their bioenergetic demands. In particular, new post-translational modifications, such as phosphorylation, acetylation or succinylation of different PDC components have been highlighted and could act in a concerted manner to provide a high metabolic flexibility. In addition, we presented recent studies that underline the role of PDC in the control of cancer cell proliferation and metastasis.Finally, the therapeutic potential of PDK inhibitors is quickly regaining a forefront position in cancer. Several studies have shown that the decline in PDK activity either by pharmacological inhibition or a decreased expression leading to an enhanced PDC activity is associated with a reduction in tumor growth in vivo. The current understanding of properties of different inhibitors targeting PDKs which could have potential therapeutic effects in different types of cancer is presented.The mitochondrial pyruvate dehydrogenase complex (PDC) acts as a gatekeeper enzyme for energy metabolism by catalyzing irreversible decarboxylation of pyruvate into acetyl-CoA. The activity of PDC is highly regulated, at least in part, by reversible phosphorylation through pyruvate dehydrogenase kinases (PDKs) and pyruvate dehydrogenase phosphatases (PDPs) the functions of which are regulated by cellular nutrient cues. Here, we provide an overview of the complexities and peculiarities in the regulation of PDC for the control of substrate metabolism and flexibility in cancer cells. Particular attention is devoted to newly identified posttranslational modifications, such as phosphorylation, acetylation or succinylation, of the different PDC components and the mechanisms by which these modifications may act in concert to provide an optimal metabolic adaptation to sustain energy demands in cancer cells. We also discuss new pharmacological approaches used to develop effective PDK inhibitors as well as the properties and potential usefulness of these inhibitors for complex human diseases such as cancer. The Pyruvate Dehydrogenase Complex: A Crucial Role in the Regulation of Energy MetabolismThe multi-subunit mitochondrial PDC is at the center of glucose oxidative metabolism. PDC inserts pyruvate into the t...

OBJECTIVE-Pyruvate dehydrogenase complex (PDC) serves as the metabolic switch between glucose and fatty acid utilization. PDC activity is inhibited by PDC kinase (PDK). PDC shares the same substrate, i.e., pyruvate, as glyceroneogenesis, a pathway controlling fatty acid release from white adipose tissue (WAT). Thiazolidinediones activate glyceroneogenesis. We studied the regulation by rosiglitazone of PDK2 and PDK4 isoforms and tested the hypothesis that glyceroneogenesis could be controlled by PDK. RESEARCH DESIGN AND METHODS-Rosiglitazone was administered toZucker fa/fa rats, and then PDK4 and PDK2 mRNAs were examined in subcutaneous, periepididymal, and retroperitoneal WAT, liver, and muscle by real-time RT-PCR. Cultured WAT explants from humans and rats and 3T3-F442A adipocytes were rosiglitazone-treated before analyses of PDK2 and PDK4 mRNA and protein. Small interfering RNA (siRNA) was transfected by electroporation. Glyceroneogenesis was determined using [1-14 C]pyruvate incorporation into lipids.RESULTS-Rosiglitazone increased PDK4 mRNA in all WAT depots but not in liver and muscle. PDK2 transcript was not affected. This isoform selectivity was also found in ex vivotreated explants. In 3T3-F442A adipocytes, Pdk4 expression was strongly and selectively induced by rosiglitazone in a direct and transcriptional manner, with a concentration required for halfmaximal effect at 1 nmol/l. The use of dichloroacetic acid or leelamine, two PDK inhibitors, or a specific PDK4 siRNA demonstrated that PDK4 participated in glyceroneogenesis, therefore altering nonesterified fatty acid release in both basal and rosiglitazone-activated conditions.CONCLUSIONS-These data show that PDK4 upregulation in adipocytes participates in the hypolipidemic effect of thiazolidinediones through modulation of glyceroneogenesis. Diabetes

Butyrate, a short-chain fatty acid produced by the colonic bacterial fermentation is able to induce cell growth inhibition and differentiation in colon cancer cells at least partially through its capacity to inhibit histone deacetylases. Since butyrate is expected to impact cellular metabolic pathways in colon cancer cells, we hypothesize that it could exert its antiproliferative properties by altering cellular metabolism. We show that although Caco2 colon cancer cells oxidized both butyrate and glucose into CO 2 , they displayed a higher oxidation rate with butyrate as substrate than with glucose. Furthermore, butyrate pretreatment led to an increase cell capacity to oxidize butyrate and a decreased capacity to oxidize glucose, suggesting that colon cancer cells, which are initially highly glycolytic, can switch to a butyrate utilizing phenotype, and preferentially oxidize butyrate instead of glucose as energy source to produce acetyl coA. Butyrate pretreated cells displayed a modulation of glutamine metabolism characterized by an increased incorporation of carbons derived from glutamine into lipids and a reduced lactate production. The butyrate-stimulated glutamine utilization is linked to pyruvate dehydrogenase complex since dichloroacetate reverses this effect. Furthermore, butyrate positively regulates gene expression of pyruvate dehydrogenase kinases and this effect involves a hyperacetylation of histones at PDK4 gene promoter level. Our data suggest that butyrate exerts two distinct effects to ensure the regulation of glutamine metabolism: it provides acetyl coA needed for fatty acid synthesis, and it also plays a role in the control of the expression of genes involved in glucose utilization leading to the inactivation of PDC.Epidemiologic studies suggest that environmental factors including nutrients strongly influence the incidence of colon cancer. Dietary fibers found in cereals, vegetables and fruits undergo bacterial fermentation leading to the production of short-chain fatty acids (SCFAs) in the colon lumen. Butyrate is one of the most abundant SCFA and plays a key role in colonic epithelium homeostasis. It is oxidized to acetyl coA in mitochondria and represents the main fuel for normal colonocytes 1,2 as well as for colon cancer cells. 3 In human colon cancer cells, butyrate inhibits cell growth 3-5 and promotes differentiation. 6 Although the underlying mechanisms by which butyrate regulates cell proliferation and/or differentiation are not fully understood, it has been shown that butyrate action could involve various effects on gene expression, which are often attributed to its capacity to act as an inhibitor of histone deacetylases (HDACs). This effect leads to a hyperacetylation of histones and increased accessibility of transcription factors to promoters in the DNA. 7 Moreover, butyrate influences post-traductional modifications including DNA methylation, 8 histone methylation, 9 histone phosphorylation 10 and hyperacetylation of nonhistone proteins. 11 Those diverse effects may explain the i...

Cancer cells display alterations in many cellular processes. One core hallmark of cancer is the Warburg effect which is a glycolytic reprogramming that allows cells to survive and proliferate. Although the contributions of environmental contaminants to cancer development are widely accepted, the underlying mechanisms have to be clarified. Benzo[a]pyrene (B[a]P), the prototype of polycyclic aromatic hydrocarbons, exhibits genotoxic and carcinogenic effects, and it is a human carcinogen according to the International Agency for Research on Cancer. In addition to triggering apoptotic signals, B[a]P may induce survival signals, both of which are likely to be involved in cancer promotion. We previously suggested that B[a]P-induced mitochondrial dysfunctions, especially membrane hyperpolarization, might trigger cell survival signaling in rat hepatic epithelial F258 cells. Here, we further characterized these dysfunctions by focusing on energy metabolism. We found that B[a]P promoted a metabolic reprogramming. Cell respiration decreased and lactate production increased. These changes were associated with alterations in the tricarboxylic acid cycle which likely involve a dysfunction of the mitochondrial complex II. The glycolytic shift relied on activation of the Na+/H+ exchanger 1 (NHE1) and appeared to be a key feature in B[a]P-induced cell survival related to changes in cell phenotype (epithelial-to-mesenchymal transition and cell migration).

Resveratrol (RES), a polyphenol found in natural foods, displays anti-oxidant, anti-inflammatory and anti-proliferative properties potentially beneficial in cancers, in particular in the prevention of tumor growth. However, the rapid metabolism of resveratrol strongly limits its bioavailability. The molecular mechanisms sustaining the potential biological activity of low doses of resveratrol has not been extensively studied and, thus, needs better characterization. Here, we show that resveratrol (10 µM, 48 hr) induces both a cell growth arrest and a metabolic reprogramming in colon cancer cells. Resveratrol modifies the lipidomic profile, increases oxidative capacities and decreases glycolysis, in association with a decreased pentose phosphate activity and an increased ATP production. Resveratrol targets the pyruvate dehydrogenase (PDH) complex, a key mitochondrial gatekeeper of energy metabolism, leading to an enhanced PDH activity. Calcium chelation, as well as the blockade of the mitochondrial calcium uniport, prevents the resveratrol-induced augmentation in oxidative capacities and the increased PDH activity suggesting that calcium might play a role in the metabolic shift. We further demonstrate that the inhibition of the CamKKB or the downstream AMPK pathway partly abolished the resveratrol-induced increase of glucose oxidation. This suggests that resveratrol might improve the oxidative capacities of cancer cells through the CamKKB/AMPK pathway.

Succinate dehydrogenase (SDH) inhibitors (SDHIs) are used worldwide to limit the proliferation of molds on plants and plant products. However, as SDH, also known as respiratory chain (RC) complex II, is a universal component of mitochondria from living organisms, highly conserved through evolution, the specificity of these inhibitors toward fungi warrants investigation. We first establish that the human, honeybee, earthworm and fungal SDHs are all sensitive to the eight SDHIs tested, albeit with varying IC50 values, generally in the micromolar range. In addition to SDH, we observed that five of the SDHIs, mostly from the latest generation, inhibit the activity of RC complex III. Finally, we show that the provision of glucose ad libitum in the cell culture medium, while simultaneously providing sufficient ATP and reducing power for antioxidant enzymes through glycolysis, allows the growth of RC-deficient cells, fully masking the deleterious effect of SDHIs. As a result, when glutamine is the major carbon source, the presence of SDHIs leads to time-dependent cell death. This process is significantly accelerated in fibroblasts derived from patients with neurological or neurodegenerative diseases due to RC impairment (encephalopathy originating from a partial SDH defect) and/or hypersensitivity to oxidative insults (Friedreich ataxia, familial Alzheimer’s disease).

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Insulin and vanadate treatments have recently been shown to reverse the overexpression of the hepatic insulin receptor (IR) gene in streptozotocin-induced diabetic rats. To better understand the mechanisms underlying these effects, the abilities of insulin and vanadate to affect IR gene expression have been comparatively examined in Fao hepatoma cells, an insulin-responsive cell line. Exposure of Fao cells to insulin (1 microM) or vanadate (500 microM) for 24 h led to a 2-fold decrease in IR number in total cellular membranes. Insulin treatment did not affect IR messenger RNA (mRNA) level regardless of time of exposure and concentration. In contrast, vanadate treatment caused a time- and dose-dependent decrease in IR mRNA level, which was maximal (4-fold change) after a 24-h exposure to 500 microM vanadate and was fully reversible. Insulin treatment increased from 28 to 39% the relative expression of isotype A IR mRNA, but vanadate treatment did not significantly affect this parameter. Vanadate treatment did not modify mRNA half-life (3.5 h) in 5, 6 dichlorobenzimidazole riboside-treated cells but decreased by 4-fold the transcriptional activity of the IR gene. These data show for the first time that, although both insulin and vanadate decrease total cellular IR number in Fao cells, only vanadate decreases IR mRNA level. It does so by inhibiting transcription of the IR gene, suggesting an action on the gene promoter which could be mediated by changes in the level of expression and/or of phosphorylation of trans-acting factors.