Author Correction: Air pollution-derived particulate matter dysregulates hepatic Krebs cycle, glucose and lipid metabolism in mice.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Air pollution-derived particulate matter dysregulates hepatic Krebs cycle, glucose and lipid metabolism in mice.

Exposure to ambient air particulate matter (PM2.5) is well established as a risk factor for cardiovascular and pulmonary disease. Both epidemiologic and controlled exposure studies in humans and animals have demonstrated an association between air pollution exposure and metabolic disorders such as diabetes. Given the central role of the liver in peripheral glucose homeostasis, we exposed mice to filtered air or PM2.5 for 16 weeks and examined its effect on hepatic metabolic pathways using stable isotope resolved metabolomics (SIRM) following a bolus of 13C6-glucose. Livers were analyzed for the incorporation of 13C into different metabolic pools by IC-FTMS or GC-MS. The relative abundance of 13C-glycolytic intermediates was reduced, suggesting attenuated glycolysis, a feature found in diabetes. Decreased 13C-Krebs cycle intermediates suggested that PM2.5 exposure led to a reduction in the Krebs cycle capacity. In contrast to decreased glycolysis, we observed an increase in the oxidative branch of the pentose phosphate pathway and 13C incorporations suggestive of enhanced capacity for the de novo synthesis of fatty acids. To our knowledge, this is one of the first studies to examine 13C6-glucose utilization in the liver following PM2.5 exposure, prior to the onset of insulin resistance (IR).

Decoupling of Nrf2 Expression Promotes Mesenchymal State Maintenance in Non-Small Cell Lung Cancer.

Epithelial mesenchymal transition is a common mechanism leading to metastatic dissemination and cancer progression. In an effort to better understand this process we found an intersection of Nrf2/NLE2F2 (Nrf2), epithelial mesenchymal transition (EMT), and metabolic alterations using multiple in vitro and in vivo approaches. Nrf2 is a key transcription factor controlling the expression of redox regulators to establish cellular redox homeostasis. Nrf2 has been shown to exert both cancer inhibitory and stimulatory activities. Using multiple isogenic non-small cell lung cancer (NSCLC) cell lines, we observed a reduction of Nrf2 protein and activity in a prometastatic mesenchymal cell state and increased reactive oxygen species. Knockdown of Nrf2 promoted a mesenchymal phenotype and reduced glycolytic, TCA cycle and lipogenic output from both glucose and glutamine in the isogenic cell models; while overexpression of Nrf2 promoted a more epithelial phenotype and metabolic reactivation. In both Nrf2 knockout mice and in NSCLC patient samples, Nrf2low was co-correlated with markedly decreased expression of glycolytic, lipogenic, and mesenchymal RNAs. Conversely, Nrf2high was associated with partial mesenchymal epithelial transition and increased expression of metabolic RNAs. The impact of Nrf2 on epithelial and mesenchymal cancer cell states and metabolic output provide an additional context to Nrf2 function in cancer initiation and progression, with implications for therapeutic inhibition of Nrf2 in cancer treatment.

Inhibition of phosphoenolpyruvate carboxykinase blocks lactate utilization and impairs tumor growth in colorectal cancer.

BACKGROUND: Metabolic reprogramming is a key feature of malignant cells. While glucose is one of the primary substrates for malignant cells, cancer cells also display a remarkable metabolic flexibility. Depending on nutrient availability and requirements, cancer cells will utilize alternative fuel sources to maintain the TCA cycle for bioenergetic and biosynthetic requirements. Lactate was typically viewed as a passive byproduct of cancer cells. However, studies now show that lactate is an important substrate for the TCA cycle in breast, lung, and pancreatic cancer. METHODS: Metabolic analysis of colorectal cancer (CRC) cells was performed using a combination of bioenergetic analysis and 13C stable isotope tracing. RESULTS: We show here that CRC cells use lactate to fuel the TCA cycle and promote growth especially under nutrient-deprived conditions. This was mediated in part by maintaining cellular bioenergetics. Therefore targeting the ability of cancer cells to utilize lactate via the TCA cycle would have a significant therapeutic benefit. Phosphoenolpyruvate carboxykinase (PEPCK) is an important cataplerotic enzyme that promotes TCA cycle activity in CRC cells. Treatment of CRC cells with low micromolar doses of a PEPCK inhibitor (PEPCKi) developed for diabetes decreased cell proliferation and utilization of lactate by the TCA cycle in vitro and in vivo. Mechanistically, we observed that the PEPCKi increased nutrient stress as determined by decreased cellular bioenergetics including decreased respiration, ATP levels, and increased AMPK activation. 13C stable isotope tracing showed that the PEPCKi decreased the incorporation of lactate into the TCA cycle. CONCLUSIONS: These studies highlight lactate as an important substrate for CRC and the use of PEPCKi as a therapeutic approach to target lactate utilization in CRC cells.

Non-proteolytic ubiquitination of Hexokinase 2 by HectH9 controls tumor metabolism and cancer stem cell expansion.

Enormous efforts have been made to target metabolic dependencies of cancer cells for developing new therapies. However, the therapeutic efficacy of glycolysis inhibitors is limited due to their inability to elicit cell death. Hexokinase 2 (HK2), via its mitochondrial localization, functions as a central nexus integrating glycolysis activation and apoptosis resilience. Here we identify that K63-linked ubiquitination by HectH9 regulates the mitochondrial localization and function of HK2. Through stable isotope tracer approach and functional metabolic analyses, we show that HectH9 deficiency impedes tumor glucose metabolism and growth by HK2 inhibition. The HectH9/HK2 pathway regulates cancer stem cell (CSC) expansion and CSC-associated chemoresistance. Histological analyses show that HectH9 expression is upregulated and correlated with disease progression in prostate cancer. This work uncovers that HectH9 is a novel regulator of HK2 and cancer metabolism. Targeting HectH9 represents an effective strategy to achieve long-term tumor remission by concomitantly disrupting glycolysis and inducing apoptosis.

Tsc3 regulates SPT amino acid choice in Saccharomyces cerevisiae by promoting alanine in the sphingolipid pathway.

The generation of most sphingolipids (SPLs) starts with condensation between serine and an activated long-chain fatty acid catalyzed by serine palmitoyltransferase (SPT). SPT can also use other amino acids to generate small quantities of noncanonical SPLs. The balance between serine-derived and noncanonical SPLs is pivotal; for example, hereditary sensory and autonomic neuropathy type I results from SPT mutations that cause an abnormal accumulation of alanine-derived SPLs. The regulatory mechanism for SPT amino acid selectivity and physiological functions of noncanonical SPLs are unknown. We investigated SPT selection of amino acid substrates by measuring condensation products of serine and alanine in yeast cultures and SPT use of serine and alanine in a TSC3 knockout model. We identified the Tsc3 subunit of SPT as a regulator of amino acid substrate selectivity by demonstrating its primary function in promoting alanine utilization by SPT and confirmed its requirement for the inhibitory effect of alanine on SPT utilization of serine. Moreover, we observed downstream metabolic consequences to Tsc3 loss: serine influx into the SPL biosynthesis pathway increased through Ypk1-depenedent activation of SPT and ceramide synthases. This Ypk1-dependent activation of serine influx after Tsc3 knockout suggests a potential function for deoxy-sphingoid bases in modulating Ypk1 signaling.

De novo lipogenesis represents a therapeutic target in mutant Kras non-small cell lung cancer.

Oncogenic Kras mutations are one of the most common alterations in non-small cell lung cancer and are associated with poor response to treatment and reduced survival. Driver oncogenes, such as Kras are now appreciated for their ability to promote tumor growth via up-regulation of anabolic pathways. Therefore, we wanted to identify metabolic vulnerabilities in Kras-mutant lung cancer. Using the Kras LSL-G12D lung cancer model, we show that mutant Kras drives a lipogenic gene-expression program. Stable-isotope analysis reveals that mutant Kras promotes de novo fatty acid synthesis in vitro and in vivo. The importance of fatty acid synthesis in Kras-induced tumorigenesis was evident by decreased tumor formation in Kras LSL-G12D mice after treatment with a fatty acid synthesis inhibitor. Importantly, with gain and loss of function models of mutant Kras, we demonstrate that mutant Kras potentiates the growth inhibitory effects of several fatty acid synthesis inhibitors. These studies highlight the potential to target mutant Kras tumors by taking advantage of the lipogenic phenotype induced by mutant Kras.-Singh, A., Ruiz, C., Bhalla, K., Haley, J. A., Li, Q. K., Acquaah-Mensah, G., Montal, E., Sudini, K. R., Skoulidis, F., Wistuba, I. I., Papadimitrakopoulou, V., Heymach, J. V., Boros, L. G., Gabrielson, E., Carretero, J., Wong, K.-k., Haley, J. D., Biswal, S., Girnun, G. D. De novo lipogenesis represents a therapeutic target in mutant Kras non-small cell lung cancer.

Heme degradation enzyme biliverdin IXß reductase is required for stem cell glutamine metabolism.

Bioenergetic requirements of hematopoietic stem cells and pluripotent stem cells (PSCs) vary with lineage fate, and cellular adaptations rely largely on substrate (glucose/glutamine) availability and mitochondrial function to balance tricarboxylic acid (TCA)-derived anabolic and redox-regulated antioxidant functions. Heme synthesis and degradation converge in a linear pathway that utilizes TCA cycle-derived carbon in cataplerotic reactions of tetrapyrrole biosynthesis, terminated by NAD(P)H-dependent biliverdin reductases (IXα, BLVRA and IXß, BLVRB) that lead to bilirubin generation and cellular antioxidant functions. We now demonstrate that PSCs with targeted deletion of BLVRB display physiologically defective antioxidant activity and cellular viability, associated with a glutamine-restricted defect in TCA entry that was computationally predicted using gene/metabolite topological network analysis and subsequently validated by bioenergetic and isotopomeric studies. Defective BLVRB-regulated glutamine utilization was accompanied by exaggerated glycolytic accumulation of the rate-limiting hexokinase reaction product glucose-6-phosphate. BLVRB-deficient embryoid body formation (a critical size parameter of early lineage fate potential) demonstrated enhanced sensitivity to the pentose phosphate pathway (PPP) inhibitor 6-aminonicotinamide with no differences in the glycolytic pathway inhibitor 2-deoxyglucose. These collective data place heme catabolism in a crucial pathway of glutamine-regulated bioenergetic metabolism and suggest that early stages of lineage fate potential require glutamine anaplerotic functions and an intact PPP, which are, in part, regulated by BLVRB activity. In principle, BLVRB inhibition represents an alternative strategy for modulating cellular glutamine utilization with consequences for cancer and hematopoietic metabolism.

Analysis of sphingolipids, sterols, and phospholipids in human pathogenic Cryptococcus strains.

Cryptococcus species cause invasive infections in humans. Lipids play an important role in the progression of these infections. Independent studies done by our group and others provide some detail about the functions of these lipids in Cryptococcus infections. However, the pathways of biosynthesis and the metabolism of these lipids are not completely understood. To thoroughly understand the physiological role of these Cryptococcus lipids, a proper structure and composition analysis of Cryptococcus lipids is demanded. In this study, a detailed spectroscopic analysis of lipid extracts from Cryptococcus gattii and Cryptococcus grubii strains is presented. Sphingolipid profiling by LC-ESI-MS/MS was used to analyze sphingosine, dihydrosphingosine, sphingosine-1-phosphate, dihydrosphingosine-1-phosphate, ceramide, dihydroceramide, glucosylceramide, phytosphingosine, phytosphingosine-1-phosphate, phytoceramide, α-hydroxy phytoceramide, and inositolphosphorylceramide species. A total of 13 sterol species were identified using GC-MS, where ergosterol is the most abundant species. The 31P-NMR-based phospholipid analysis identified phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidyl-N,N-dimethylethanolamine, phosphatidyl-N-monomethylethanolamine, phosphatidylglycerol, phosphatidic acid, and lysophosphatidylethanolamine. A comparison of lipid profiles among different Cryptococcus strains illustrates a marked change in the metabolic flux of these organisms, especially sphingolipid metabolism. These data improve our understanding of the structure, biosynthesis, and metabolism of common lipid groups of Cryptococcus and should be useful while studying their functional significance and designing therapeutic interventions.

Oncogenic Myc Induces Expression of Glutamine Synthetase through Promoter Demethylation.

c-Myc is known to promote glutamine usage by upregulating glutaminase (GLS), which converts glutamine to glutamate that is catabolized in the TCA cycle. Here we report that in a number of human and murine cells and cancers, Myc induces elevated expression of glutamate-ammonia ligase (GLUL), also termed glutamine synthetase (GS), which catalyzes the de novo synthesis of glutamine from glutamate and ammonia. This is through upregulation of a Myc transcriptional target thymine DNA glycosylase (TDG), which promotes active demethylation of the GS promoter and its increased expression. Elevated expression of GS promotes cell survival under glutamine limitation, while silencing of GS decreases cell proliferation and xenograft tumor growth. Upon GS overexpression, increased glutamine enhances nucleotide synthesis and amino acid transport. These results demonstrate an unexpected role of Myc in inducing glutamine synthesis and suggest a molecular connection between DNA demethylation and glutamine metabolism in Myc-driven cancers.

PEPCK Coordinates the Regulation of Central Carbon Metabolism to Promote Cancer Cell Growth.

Phosphoenolpyruvate carboxykinase (PEPCK) is well known for its role in gluconeogenesis. However, PEPCK is also a key regulator of TCA cycle flux. The TCA cycle integrates glucose, amino acid, and lipid metabolism depending on cellular needs. In addition, biosynthetic pathways crucial to tumor growth require the TCA cycle for the processing of glucose and glutamine derived carbons. We show here an unexpected role for PEPCK in promoting cancer cell proliferation in vitro and in vivo by increasing glucose and glutamine utilization toward anabolic metabolism. Unexpectedly, PEPCK also increased the synthesis of ribose from non-carbohydrate sources, such as glutamine, a phenomenon not previously described. Finally, we show that the effects of PEPCK on glucose metabolism and cell proliferation are in part mediated via activation of mTORC1. Taken together, these data demonstrate a role for PEPCK that links metabolic flux and anabolic pathways to cancer cell proliferation.

The RUNX2 Transcription Factor Negatively Regulates SIRT6 Expression to Alter Glucose Metabolism in Breast Cancer Cells.

Activation of genes promoting aerobic glycolysis and suppression of mitochondrial oxidative phosphorylation is one of the hallmarks of cancer. The RUNX2 transcription factor mediates breast cancer (BC) metastasis to bone and is regulated by glucose availability. But, the mechanisms by which it regulates glucose metabolism and promotes an oncogenic phenotype are not known. RUNX2 expression in luminal BC cells correlated with lower estrogen receptor-α (ERα) levels, anchorage-independent growth, expression of glycolytic genes, increased glucose uptake, and sensitivity to glucose starvation, but not to inhibitors of oxidative phosphorylation. Conversely, RUNX2 knockdown in triple-negative BC cells inhibited mammosphere formation and glucose dependence. RUNX2 knockdown resulted in lower LDHA, HK2, and GLUT1 glycolytic gene expression, but upregulation of pyruvate dehydrogenase-A1 (PDHA1) mRNA and enzymatic activity, which was consistent with lower glycolytic potential. The NAD-dependent histone deacetylase, SIRT6, a known tumor suppressor, was a critical regulator of these RUNX2-mediated metabolic changes. RUNX2 expression resulted in elevated pAkt, HK2, and PDHK1 glycolytic protein levels that were reduced by ectopic expression of SIRT6. RUNX2 also repressed mitochondrial oxygen consumption rates (OCR), a measure of oxidative phosphorylation (respiration). Overexpression of SIRT6 increased respiration in RUNX2-positive cells, but knockdown of SIRT6 in cells expressing low RUNX2 decreased respiration. RUNX2 repressed SIRT6 expression at both the transcriptional and post-translational levels and endogenous SIRT6 expression was lower in malignant BC tissues or cell lines that expressed high levels of RUNX2. These results support a hypothesis whereby RUNX2-mediated repression of the SIRT6 tumor suppressor regulates metabolic pathways that promote BC progression.

Cyclin D1 represses gluconeogenesis via inhibition of the transcriptional coactivator PGC1α.

Hepatic gluconeogenesis is crucial to maintain normal blood glucose during periods of nutrient deprivation. Gluconeogenesis is controlled at multiple levels by a variety of signal transduction and transcriptional pathways. However, dysregulation of these pathways leads to hyperglycemia and type 2 diabetes. While the effects of various signaling pathways on gluconeogenesis are well established, the downstream signaling events repressing gluconeogenic gene expression are not as well understood. The cell-cycle regulator cyclin D1 is expressed in the liver, despite the liver being a quiescent tissue. The most well-studied function of cyclin D1 is activation of cyclin-dependent kinase 4 (CDK4), promoting progression of the cell cycle. We show here a novel role for cyclin D1 as a regulator of gluconeogenic and oxidative phosphorylation (OxPhos) gene expression. In mice, fasting decreases liver cyclin D1 expression, while refeeding induces cyclin D1 expression. Inhibition of CDK4 enhances the gluconeogenic gene expression, whereas cyclin D1-mediated activation of CDK4 represses the gluconeogenic gene-expression program in vitro and in vivo. Importantly, we show that cyclin D1 represses gluconeogenesis and OxPhos in part via inhibition of peroxisome proliferator-activated receptor γ coactivator-1α (PGC1α) activity in a CDK4-dependent manner. Indeed, we demonstrate that PGC1α is novel cyclin D1/CDK4 substrate. These studies reveal a novel role for cyclin D1 on metabolism via PGC1α and reveal a potential link between cell-cycle regulation and metabolic control of glucose homeostasis.

Transcription factor NRF2 regulates miR-1 and miR-206 to drive tumorigenesis.

The mechanisms by which deregulated nuclear factor erythroid-2-related factor 2 (NRF2) and kelch-like ECH-associated protein 1 (KEAP1) signaling promote cellular proliferation and tumorigenesis are poorly understood. Using an integrated genomics and ¹³C-based targeted tracer fate association (TTFA) study, we found that NRF2 regulates miR-1 and miR-206 to direct carbon flux toward the pentose phosphate pathway (PPP) and the tricarboxylic acid (TCA) cycle, reprogramming glucose metabolism. Sustained activation of NRF2 signaling in cancer cells attenuated miR-1 and miR-206 expression, leading to enhanced expression of PPP genes. Conversely, overexpression of miR-1 and miR-206 decreased the expression of metabolic genes and dramatically impaired NADPH production, ribose synthesis, and in vivo tumor growth in mice. Loss of NRF2 decreased the expression of the redox-sensitive histone deacetylase, HDAC4, resulting in increased expression of miR-1 and miR-206, and not only inhibiting PPP expression and activity but functioning as a regulatory feedback loop that repressed HDAC4 expression. In primary tumor samples, the expression of miR-1 and miR-206 was inversely correlated with PPP gene expression, and increased expression of NRF2-dependent genes was associated with poor prognosis. Our results demonstrate that microRNA-dependent (miRNA-dependent) regulation of the PPP via NRF2 and HDAC4 represents a novel link between miRNA regulation, glucose metabolism, and ROS homeostasis in cancer cells.

Rapid detection of an ABT-737-sensitive primed for death state in cells using microplate-based respirometry.

Cells that exhibit an absolute dependence on the anti-apoptotic BCL-2 protein for survival are termed "primed for death" and are killed by the BCL-2 antagonist ABT-737. Many cancers exhibit a primed phenotype, including some that are resistant to conventional chemotherapy due to high BCL-2 expression. We show here that 1) stable BCL-2 overexpression alone can induce a primed for death state and 2) that an ABT-737-induced loss of functional cytochrome c from the electron transport chain causes a reduction in maximal respiration that is readily detectable by microplate-based respirometry. Stable BCL-2 overexpression sensitized non-tumorigenic MCF10A mammary epithelial cells to ABT-737-induced caspase-dependent apoptosis. Mitochondria within permeabilized BCL-2 overexpressing cells were selectively vulnerable to ABT-737-induced cytochrome c release compared to those from control-transfected cells, consistent with a primed state. ABT-737 treatment caused a dose-dependent impairment of maximal O(2) consumption in MCF10A BCL-2 overexpressing cells but not in control-transfected cells or in immortalized mouse embryonic fibroblasts lacking both BAX and BAK. This impairment was rescued by delivering exogenous cytochrome c to mitochondria via saponin-mediated plasma membrane permeabilization. An ABT-737-induced reduction in maximal O(2) consumption was also detectable in SP53, JeKo-1, and WEHI-231 B-cell lymphoma cell lines, with sensitivity correlating with BCL-2:MCL-1 ratio and with susceptibility (SP53 and JeKo-1) or resistance (WEHI-231) to ABT-737-induced apoptosis. Multiplexing respirometry assays to ELISA-based determination of cytochrome c redistribution confirmed that respiratory inhibition was associated with cytochrome c release. In summary, cell-based respiration assays were able to rapidly identify a primed for death state in cells with either artificially overexpressed or high endogenous BCL-2. Rapid detection of a primed for death state in individual cancers by "bioenergetics-based profiling" may eventually help identify the subset of patients with chemoresistant but primed tumors who can benefit from treatment that incorporates a BCL-2 antagonist.

Metformin prevents liver tumorigenesis by inhibiting pathways driving hepatic lipogenesis.

A number of factors have been identified that increase the risk of hepatocellular carcinoma (HCC). Recently it has become appreciated that type II diabetes increases the risk of developing HCC. This represents a patient population that can be identified and targeted for cancer prevention. The biguanide metformin is a first-line therapy for the treatment of type II diabetes in which it exerts its effects primarily on the liver. A role of metformin in HCC is suggested by studies linking metformin intake for control of diabetes with a reduced risk of HCC. Although a number of preclinical studies show the anticancer properties of metformin in a number of tissues, no studies have directly examined the effect of metformin on preventing carcinogenesis in the liver, one of its main sites of action. We show in these studies that metformin protected mice against chemically induced liver tumors. Interestingly, metformin did not increase AMPK activation, often shown to be a metformin target. Rather metformin decreased the expression of several lipogenic enzymes and lipogenesis. In addition, restoring lipogenic gene expression by ectopic expression of the lipogenic transcription factor SREBP1c rescues metformin-mediated growth inhibition. This mechanism of action suggests that metformin may also be useful for patients with other disorders associated with HCC in which increased lipid synthesis is observed. As a whole these studies show that metformin prevents HCC and that metformin should be evaluated as a preventive agent for HCC in readily identifiable at-risk patients.

The diverse role of the PPARγ coactivator 1 family of transcriptional coactivators in cancer.

The critical role that altered cellular metabolism plays in promoting and maintaining the cancer phenotype has received considerable attention in recent years. For many years it was believed that aerobic glycolysis, also known as the Warburg Effect, played an important role in cancer. However, recent studies highlight the requirement of mitochondrial function, oxidative phosphorylation and biosynthetic pathways in cancer. This has promoted interest into mechanisms controlling these metabolic pathways. The PPARγ coactivator (PGC)-1 family of transcriptional coactivators have emerged as key regulators of several metabolic pathways including oxidative metabolism, energy homeostasis and glucose and lipid metabolism. While PGC-1s have been implicated in a number of metabolic diseases, recent studies highlight an important role in cancer. Studies show that PGC-1s have both pro and anticancer functions and suggests a dynamic role for the PGC-1s in cancer. We discuss in this review the links between PGC-1s and cancer, with a focus on the most well studied family member, PGC-1α.

N-Acetylfarnesylcysteine is a novel class of peroxisome proliferator-activated receptor γ ligand with partial and full agonist activity in vitro and in vivo.

The thiazolidedione (TZD) class of drugs is clinically approved for the treatment of type 2 diabetes. The therapeutic actions of TZDs are mediated via activation of peroxisome proliferator-activated receptor γ (PPARγ). Despite their widespread use, concern exists regarding the safety of currently used TZDs. This has prompted the development of selective PPARγ modulators (SPPARMs), compounds that promote glucose homeostasis but with reduced side effects due to partial PPARγ agonism. However, this also results in partial agonism with respect to PPARγ target genes promoting glucose homeostasis. Using a gene expression-based screening approach we identified N-acetylfarnesylcysteine (AFC) as both a full and partial agonist depending on the PPARγ target gene (differential SPPARM). AFC activated PPARγ as effectively as rosiglitazone with regard to Adrp, Angptl4, and AdipoQ, but was a partial agonist of aP2, a PPARγ target gene associated with increased adiposity. Induction of adipogenesis by AFC was also attenuated compared with rosiglitazone. Reporter, ligand binding assays, and dynamic modeling demonstrate that AFC binds and activates PPARγ in a unique manner compared with other PPARγ ligands. Importantly, treatment of mice with AFC improved glucose tolerance similar to rosiglitazone, but AFC did not promote weight gain to the same extent. Finally, AFC had effects on adipose tissue remodeling similar to those of rosiglitazone and had enhanced antiinflammatory effects. In conclusion, we describe a new approach for the identification of differential SPPARMs and have identified AFC as a novel class of PPARγ ligand with both full and partial agonist activity in vitro and in vivo.

PGC1α promotes tumor growth by inducing gene expression programs supporting lipogenesis.

Despite the role of aerobic glycolysis in cancer, recent studies highlight the importance of the mitochondria and biosynthetic pathways as well. PPARγ coactivator 1α (PGC1α) is a key transcriptional regulator of several metabolic pathways including oxidative metabolism and lipogenesis. Initial studies suggested that PGC1α expression is reduced in tumors compared with adjacent normal tissue. Paradoxically, other studies show that PGC1α is associated with cancer cell proliferation. Therefore, the role of PGC1α in cancer and especially carcinogenesis is unclear. Using Pgc1α(-/-) and Pgc1α(+/+) mice, we show that loss of PGC1α protects mice from azoxymethane-induced colon carcinogenesis. Similarly, diethylnitrosamine-induced liver carcinogenesis is reduced in Pgc1α(-/-) mice as compared with Pgc1α(+/+) mice. Xenograft studies using gain and loss of PGC1α expression showed that PGC1α also promotes tumor growth. Interestingly, while PGC1α induced oxidative phosphorylation and tricarboxylic acid cycle gene expression, we also observed an increase in the expression of two genes required for de novo fatty acid synthesis, ACC and FASN. In addition, SLC25A1 and ACLY, which are required for the conversion of glucose into acetyl-CoA for fatty acid synthesis, were also increased by PGC1α, thus linking the oxidative and lipogenic functions of PGC1α. Indeed, using stable (13)C isotope tracer analysis, we show that PGC1α increased de novo lipogenesis. Importantly, inhibition of fatty acid synthesis blunted these progrowth effects of PGC1α. In conclusion, these studies show for the first time that loss of PGC1α protects against carcinogenesis and that PGC1α coordinately regulates mitochondrial and fatty acid metabolism to promote tumor growth.

Liposomal doxorubicin increases radiofrequency ablation-induced tumor destruction by increasing cellular oxidative and nitrative stress and accelerating apoptotic pathways.

PURPOSE: To determine if oxidative and nitrative stress and/or apoptosis contribute to increased coagulation when combining radiofrequency (RF) ablation with liposomal doxorubicin. MATERIALS AND METHODS: Animal care committee approval was obtained. R3230 mammary adenocarcinomas in Fischer rats were treated with either RF ablation (n = 43), 1 mg of intravenously injected liposomal doxorubicin (n = 26), or combined therapy (n = 30) and were compared with control subjects (n = 11). A subset of animals receiving combination therapy (n = 24) were treated in the presence or absence of N-acetylcysteine (NAC) administered 24 hours and 1 hour before RF ablation. Tumors were analyzed 2 minutes to 72 hours after treatment to determine the temporal range of response by using immunohistochemical staining of the apoptosis marker cleaved caspase-3, phosphorylated gammaH2AX, and HSP70 and of markers of oxidative and nitrative stress (8-hydroxydeoxyguanosine [8-OHdG], 4-hydroxynonenal [4-HNE]-modified proteins, and nitrotyrosine [NT]). Statistical analyses, including t tests and analysis of variance for comparisons where appropriate, were performed. RESULTS: By 4 hours after RF ablation alone, a 0.48-mm +/- 0.13 (standard deviation) peripheral band with 57.0% +/- 7.3 cleaved caspase-3 positive cells was noted at the ablation margin, whereas a 0.73-mm +/- 0.18 band with 77.7% +/- 6.3 positivity was seen for combination therapy (P < .03 for both comparisons). Combination therapy caused increased and earlier staining for 4-HNE-modified proteins, 8-OHdG, NT, and gammaH2AX with colocalization to cleaved caspase-3 staining. A rim of increased HSP70 was identified peripheral to the area of cleaved caspase-3. Parameters of oxidative and nitrative stress were significantly inhibited by NAC 1 hour following RF ablation, resulting in decreased cleaved caspase-3 positivity (0.28-mm +/- 0.09 band of 25.9% +/- 7.4 positivity vs 0.59-mm +/- 0.11 band of 62.9% +/- 6.0 positivity, P < .001 for both comparisons). CONCLUSION: Combining RF ablation with liposomal doxorubicin increases cell injury and apoptosis in the zone of increased coagulation by using a mechanism that involves oxidative and nitrative stress that leads to accelerated apoptosis.