The ER UDPase ENTPD5 promotes protein N-glycosylation, the Warburg effect, and proliferation in the PTEN pathway

The role of low-level lactate production in airway inflammation in asthma

Warburg and coworkers (Warburg O, Posener K, Negelein E. Z Biochem 152: 319, 1924) first reported that cancerous cells switch glucose metabolism from oxidative phosphorylation to aerobic glycolysis, and that this switch is important for their proliferation. Nothing is known about aerobic glycolysis in T cells from asthma. The objective was to study aerobic glycolysis in human asthma and the role of this metabolic pathway in airway hyperreactivity and inflammation in a mouse model of asthma. Human peripheral blood and mouse spleen CD4 T cells were isolated by negative selection. T cell proliferation was measured by thymidine incorporation. Cytokines and serum lactate were measured by ELISA. Mouse airway hyperreactivity to inhaled methacholine was measured by a FlexiVent apparatus. The serum lactate concentration was significantly elevated in clinically stable asthmatic subjects compared with healthy and chronic obstructive pulmonary disease controls, and negatively correlated with forced expiratory volume in 1 s. Proliferating CD4 T cells from human asthma and a mouse model of asthma produced higher amounts of lactate upon stimulation, suggesting a heightened glycolytic activity. Lactate stimulated and inhibited T cell proliferation at low and high concentrations, respectively. Dichloroacetate (DCA), an inhibitor of aerobic glycolysis, inhibited lactate production, proliferation of T cells, and production of IL-5, IL-17, and IFN-γ, but it stimulated production of IL-10 and induction of Foxp3. DCA also inhibited airway inflammation and hyperreactivity in a mouse model of asthma. We conclude that aerobic glycolysis is increased in asthma, which promotes T cell activation. Inhibition of aerobic glycolysis blocks T cell activation and development of asthma.

Metabolic flux and the regulation of mammalian cell growth

The study of normal mammalian cell growth and the defects that contribute to disease pathogenesis links metabolism to cell growth. Here, we visit several aspects of growth-promoting metabolism, emphasizing recent advances in our understanding of how alterations in glucose metabolism affect cytosolic and mitochondrial redox potential and ATP generation. These alterations drive cell proliferation not only through supporting biosynthesis, energy metabolism, and maintaining redox potential but also through initiating signaling mechanisms that are still poorly characterized. The evolutionary basis of these additional layers of growth control is also discussed.

Metabolic state of glioma stem cells and nontumorigenic cells

Gliomas contain a small number of treatment-resistant glioma stem cells (GSCs), and it is thought that tumor regrowth originates from GSCs, thus rendering GSCs an attractive target for novel treatment approaches. Cancer cells rely more on glycolysis than on oxidative phosphorylation for glucose metabolism, a phenomenon used in 2-[(18)F]fluoro-2-deoxy-D-glucose positron emission tomography imaging of solid cancers, and targeting metabolic pathways in cancer cells has become a topic of considerable interest. However, if GSCs are indeed important for tumor control, knowledge of the metabolic state of GSCs is needed. We hypothesized that the metabolism of GSCs differs from that of their progeny. Using a unique imaging system for GSCs, we assessed the oxygen consumption rate, extracellular acidification rate, intracellular ATP levels, glucose uptake, lactate production, PKM1 and PKM2 expression, radiation sensitivity, and cell cycle duration of GSCs and their progeny in a panel of glioma cell lines. We found GSCs and progenitor cells to be less glycolytic than differentiated glioma cells. GSCs consumed less glucose and produced less lactate while maintaining higher ATP levels than their differentiated progeny. Compared with differentiated cells, GSCs were radioresistant, and this correlated with a higher mitochondrial reserve capacity. Glioma cells expressed both isoforms of pyruvate kinase, and inhibition of either glycolysis or oxidative phosphorylation had minimal effect on energy production in GSCs and progenitor cells. We conclude that GSCs rely mainly on oxidative phosphorylation. However, if challenged, they can use additional metabolic pathways. Therefore, targeting glycolysis in glioma may spare GSCs.

The JAK2V617F oncogene requires expression of inducible phosphofructokinase/fructose-bisphosphatase 3 for cell growth and increased metabolic activity

Myeloproliferative neoplasms are characterized by overproduction of myeloid lineage cells with frequent acquisition of oncogenic JAK2V617F kinase mutations. The molecular mechanisms that regulate energy requirements in these diseases are poorly understood. Transformed cells tend to rely on fermentation instead of more efficient oxidative phosphorylation for energy production. Our data in JAK2V617F-transformed cells show that growth and metabolic activity were strictly dependent on the presence of glucose. Uptake of glucose and cell surface expression of the glucose transporter Glut1 required the oncogenic tyrosine kinase. Importantly, JAK2V617F as well as active STAT5 increased the expression of the inducible rate-limiting enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3), which controls glycolytic flux through 6-phosphofructo-1-kinase. PFKFB3 was required for JAK2V617F-dependent lactate production, oxidative metabolic activity and glucose uptake. Targeted knockdown of PFKFB3 also limited cell growth under normoxic and hypoxic conditions and blocked in vivo tumor formation in mice. Overall, these data suggest that inducible PFKFB3 is required for increased growth, metabolic activity and is regulated through active JAK2 and STAT5. Novel therapies that specifically block PFKFB3 activity or expression would, therefore, be expected to inhibit JAK2/STAT5-dependent malignancies and related cancers.

Heat shock transcription factor 1 is a key determinant of HCC development by regulating hepatic steatosis and metabolic syndrome

Hepatocellular carcinoma (HCC) occurrence and progression are linked tightly to progressive hepatic metabolic syndrome associated with insulin resistance, hepatic steatosis, and chronic inflammation. Heat shock transcription factor 1 (HSF1), a major transactivator of stress proteins, increases survival by protecting cells against environmental stressors. It has been implicated in the pathogenesis of cancer, but specific mechanisms by which HSF1 supports cancer development remain elusive. We propose a pathogenic mechanism whereby HSF1 activation promotes growth of premalignant cells and HCC development by stimulating lipid biosynthesis and perpetuating chronic hepatic metabolic disease induced by carcinogens. Our work shows that inactivation of HSF1 impairs cancer progression, mitigating adverse effects of carcinogens on hepatic metabolism by enhancing insulin sensitivity and sensitizing activation of AMP-activated protein kinase (AMPK), an important regulator of energy homeostasis and inhibitor of lipid synthesis. HSF1 is a potential target for the control of hepatic steatosis, hepatic insulin resistance, and HCC development.

Mitochondrial recoupling: a novel therapeutic strategy for cancer?

Recent findings link metabolic transformation of cancer cells to aberrant functions of mitochondrial uncoupling proteins (UCPs). By inducing proton leak, UCPs interfere with mitochondrial synthesis of adenosine 5'-triphosphate, which is also a key determinant of glycolytic pathways. In addition, UCP suppress the generation of superoxide, a byproduct of mitochondrial electron transport and a major source of oxidative stress. The near ubiquitous UCP2 becomes highly abundant in some cancers and may advance metabolic reprogramming, further disrupt tumour suppression, and promote chemoresistance. Here we review current evidence to suggest that inhibition of mitochondrial uncoupling may eliminate these responses and reveal novel anti-cancer strategies.

ER stress modulates cellular metabolism

Changes in metabolic processes play a critical role in the survival or death of cells subjected to various stresses. In the present study, we have investigated the effects of ER (endoplasmic reticulum) stress on cellular metabolism. A major difficulty in studying metabolic responses to ER stress is that ER stress normally leads to apoptosis and metabolic changes observed in dying cells may be misleading. Therefore we have used IL-3 (interleukin 3)-dependent Bak-/-Bax-/- haemopoietic cells which do not die in the presence of the ER-stress-inducing drug tunicamycin. Tunicamycin-treated Bak-/-Bax-/- cells remain viable, but cease growth, arresting in G1-phase and undergoing autophagy in the absence of apoptosis. In these cells, we used NMR-based SIRM (stable isotope-resolved metabolomics) to determine the metabolic effects of tunicamycin. Glucose was found to be the major carbon source for energy production and anabolic metabolism. Following tunicamycin exposure, glucose uptake and lactate production are greatly reduced. Decreased 13C labelling in several cellular metabolites suggests that mitochondrial function in cells undergoing ER stress is compromised. Consistent with this, mitochondrial membrane potential, oxygen consumption and cellular ATP levels are much lower compared with untreated cells. Importantly, the effects of tunicamycin on cellular metabolic processes may be related to a reduction in cell-surface GLUT1 (glucose transporter 1) levels which, in turn, may reflect decreased Akt signalling. These results suggest that ER stress exerts profound effects on several central metabolic processes which may help to explain cell death arising from ER stress in normal cells.

Metabolism strikes back: metabolic flux regulates cell signaling

Mammalian cells depend on growth factor signaling to take up nutrients; however, coordination of glucose and glutamine uptake has been a mystery. In this issue of Genes & Development, Wellen and colleagues (pp. 2784-2799) show that glucose flux through the hexosamine biosynthesis pathway regulates growth factor receptor glycosylation and enables glutamine consumption. This mechanism ensures that cells do not engage in anabolic metabolism when nutrients are limiting, and highlights how substrate availability for protein modifications can modulate cell signaling.

Regulation of cancer cell metabolism

Interest in the topic of tumour metabolism has waxed and waned over the past century of cancer research. The early observations of Warburg and his contemporaries established that there are fundamental differences in the central metabolic pathways operating in malignant tissue. However, the initial hypotheses that were based on these observations proved inadequate to explain tumorigenesis, and the oncogene revolution pushed tumour metabolism to the margins of cancer research. In recent years, interest has been renewed as it has become clear that many of the signalling pathways that are affected by genetic mutations and the tumour microenvironment have a profound effect on core metabolism, making this topic once again one of the most intense areas of research in cancer biology.

2010: signaling breakthroughs of the year

Members of the Editorial Board nominated as signaling breakthroughs insights gained from the "mega"--large-scale systems analyses--and the "micro"--protein structures--along with new findings in metabolism and genetics. In addition, research studies that may lead to new therapeutic avenues for cancer, diabetes, and Alzheimer's disease were selected as breakthroughs, along with the identification of unexpected heterogeneity of innate immune cells.