Hypoxia-inducible factor 1 activation by aerobic glycolysis implicates the Warburg effect in carcinogenesis

Cancer cells display high rates of aerobic glycolysis, a phenomenon known historically as the Warburg effect. Lactate and pyruvate, the end products of glycolysis, are highly produced by cancer cells even in the presence of oxygen. Hypoxia-induced gene expression in cancer cells has been linked to malignant transformation. Here we provide evidence that lactate and pyruvate regulate hypoxia-inducible gene expression independently of hypoxia by stimulating the accumulation of hypoxia-inducible Factor 1alpha (HIF-1alpha). In human gliomas and other cancer cell lines, the accumulation of HIF-1alpha protein under aerobic conditions requires the metabolism of glucose to pyruvate that prevents the aerobic degradation of HIF-1alpha protein, activates HIF-1 DNA binding activity, and enhances the expression of several HIF-1-activated genes including erythropoietin, vascular endothelial growth factor, glucose transporter 3, and aldolase A. Our findings support a novel role for pyruvate in metabolic signaling and suggest a mechanism by which high rates of aerobic glycolysis can promote the malignant transformation and survival of cancer cells.     

Crosstalk of mTOR/PKM2 and STAT3/c-Myc signaling pathways regulate the energy metabolism and acidic microenvironment of gastric cancer

Cancer cells consume large amounts of glucose to produce lactate, even in the presence of ample oxygen. This phenomenon is called the Warburg effect. c-Myc is an important member of the Myc gene family and is involved in the development of various tumors. It plays an important role in the regulation of tumor energy metabolism, which can regulate glycolysis to promote the Warburg effect in a tumor. Our study aimed to improve the malignant biological behavior by controlling the energy metabolism of gastric cancer through the mTOR/PKM2 and signal transduction and activator 3 (STAT3)/c-Myc signaling pathways through a series of in vitro experiments. Human gastric cancer AGS and HGC-27 cells were treated with PKM2 and c-Myc lentivirus, and the effects of the knockdown of PKM2 and/or c-Myc were analyzed on cell proliferation, cell apoptosis, the ability of cell migration, and the growth signaling pathway in vitro. The expressions of PKM2, c-Myc, LDHA, STAT3, P-STAT3, GLUT-1 gene were identified by the quantitative real-time polymerase chain reaction and Western blot analysis. Lactate and glucose levels were tested by the corresponding kit. Our findings showed that PKM2 and c-Myc were upregulated in human gastric cancer. Knockdown of c-Myc in gastric cancer cells suppressed cell proliferation capacity and glycolysis level, and the inhibitory effects on gastric cancer cells upon co-knockdown of PKM2 and c-Myc were more obvious compared with knockout of PKM2 or c-Myc alone. And there was a correlation between the mTOR/PKM2 and the STAT3/c-Myc signaling pathways. Our results suggested that c-Myc might be considered a potential therapeutic target for gastric cancer and PKM2 combined with c-Myc could better inhibit the malignant biological behaviors of gastric cancer.     

Lactate promotes glutamine uptake and metabolism in oxidative cancer cells

Oxygenated cancer cells have a high metabolic plasticity as they can use glucose, glutamine and lactate as main substrates to support their bioenergetic and biosynthetic activities. Metabolic optimization requires integration. While glycolysis and glutaminolysis can cooperate to support cellular proliferation, oxidative lactate metabolism opposes glycolysis in oxidative cancer cells engaged in a symbiotic relation with their hypoxic/glycolytic neighbors. However, little is known concerning the relationship between oxidative lactate metabolism and glutamine metabolism. Using SiHa and HeLa human cancer cells, this study reports that intracellular lactate signaling promotes glutamine uptake and metabolism in oxidative cancer cells. It depends on the uptake of extracellular lactate by monocarboxylate transporter 1 (MCT1). Lactate first stabilizes hypoxia-inducible factor-2α (HIF-2α), and HIF-2α then transactivates c-Myc in a pathway that mimics a response to hypoxia. Consequently, lactate-induced c-Myc activation triggers the expression of glutamine transporter ASCT2 and of glutaminase 1 (GLS1), resulting in improved glutamine uptake and catabolism. Elucidation of this metabolic dependence could be of therapeutic interest. First, inhibitors of lactate uptake targeting MCT1 are currently entering clinical trials. They have the potential to indirectly repress glutaminolysis. Second, in oxidative cancer cells, resistance to glutaminolysis inhibition could arise from compensation by oxidative lactate metabolism and increased lactate signaling.     

Dysregulation of glucose transport, glycolysis, TCA cycle and glutaminolysis by oncogenes and tumor suppressors in cancer cells

A common set of functional characteristics of cancer cells is that cancer cells consume a large amount of glucose, maintain high rate of glycolysis and convert a majority of glucose into lactic acid even in the presence of oxygen compared to that of normal cells (Warburg's Effects). In addition, cancer cells exhibit substantial alterations in several energy metabolism pathways including glucose transport, tricarboxylic acid (TCA) cycle, glutaminolysis, mitochondrial respiratory chain oxidative phosphorylation and pentose phosphate pathway (PPP). In the present work, we focused on reviewing the current knowledge about the dysregulation of the proteins/enzymes involved in the key regulatory steps of glucose transport, glycolysis, TCA cycle and glutaminolysis by several oncogenes including c-Myc and hypoxia inducible factor-1 (HIF-1) and tumor suppressor, p53, in cancer cells. The dysregulation of glucose transport and energy metabolism pathways by oncogenes and lost functions of the tumor suppressors have been implicated as important biomarkers for cancer detection and as valuable targets for the development of new anticancer therapies.     

Huaier shows anti-cancer activities by inhibition of cell growth,migration and energy metabolism in lung cancer through PI3K/AKT/HIF-1α pathway

Huaier has been verified to have anti-cancer effects on many tumours. However, little information is available about the effects of Huaier on non-small cell lung cancer (NSCLC). We sought to probe the anti-cancer effects and related mechanisms of Huaier on lung cancer. A549 cells were pre-treated with 2, 4 and 8 mg/mL Huaier at different time points. Thereafter, cell viability was analysed by CCK-8 and the migration and invasion were detected by Scratch test and Transwell chamber migration assay. Moreover, ELISA, Western blot, shRNA transfection and RT-PCR were conducted to discover the related gene and protein expressions of energy metabolism and phosphatidylinositol 3-kinase (PI3K)/AKT/hypoxia-inducible factor 1α (HIF-1α) pathway. Furthermore, tumour xenografts were accomplished to inspect the anti-cancer effects of Huaier. Our consequences suggested that Huaier considerably repressed cell viability and migration in a dose-dependent way. In addition, Huaier statistically suppressed glycolysis, glucose transport and lactic acid (LA) accumulation. Besides, we detected that Huaier could inactivate the PI3K/AKT/HIF-1α pathway. The in vivo data confirmed that Huaier obviously decreased tumour volume and tumour growth, reduced the glycolysis, glucose transport and HIF-1α expression in the tumour-bearing tissues. Our results suggested Huaier revealed anti-tumour effects in both in vivo and in vitro possibly through PI3K/AKT/HIF-1α pathway.     

Damage-associated molecular patterns in the pathogenesis of osteoarthritis: potentially novel therapeutic targets

Albendazole (ABZ) has an anti-tumor ability and inhibits HIF-1α activity. HIF-1α is associated with glycolysis and vascular endothelial cell growth factor (VEGF) expression, which plays an important role in cancer progression. These clues indicate that ABZ exerts an anti-cancer effect by regulating glycolysis and VEGF expression. The aim of this study is to clarify the effects of ABZ on non-small cell lung cancer (NSCLC) cells and explore the underlying molecular mechanisms. The expression levels of HIF-1α and VEGF were detected using western blot analysis, and the effect of ABZ on glycolysis was evaluated by measuring the relative activities of hexokinase (HK), pyruvate kinase (PK), and lactate dehydrogenase (LDH) and detecting the production of lactate in A549 and H1299 cells. The results showed that ABZ decreased the expression levels of HIF-1α and VEGF and suppressed glycolysis in under hypoxia, but not normoxic condition. Inhibiting HIF-1α also suppressed glycolysis and VEGF expression. Additionally, ABZ inhibited the volume and weight, decreased the relative activities of HK, PK, and LDH, and reduced the levels of HIF-1α and VEGF of A549 xenografts in mouse models. In conclusion, ABZ inhibited growth of NSCLC cells by suppressing HIF-1α-dependent glycolysis and VEGF expression.     

Metabolic regulation of cancer cell side population by glucose through activation of the Akt pathway

Side population (SP) cells within tumors are a small fraction of cancer cells with stem-like properties that can be identified by flow cytometry analysis based on their high ability to export certain compounds such as Hoechst 33342 and chemotherapeutic agents. The existence of stem-like SP cells in tumors is considered as a key factor contributing to drug resistance, and presents a major challenge in cancer treatment. Although it has been recognized for some time that tumor tissue niches may significantly affect cancer stem cells (CSCs), the role of key nutrients such as glucose in the microenvironment in affecting stem-like cancer cells and their metabolism largely remains elusive. Here we report that SP cells isolated from human cancer cells exhibit higher glycolytic activity compared to non-SP cells. Glucose in the culture environment exerts a profound effect on SP cells as evidenced by its ability to induce a significant increase in the percentage of SP cells in the overall cancer cell population, and glucose starvation causes a rapid depletion of SP cells. Mechanistically, glucose upregulates the SP fraction through ATP-mediated suppression of AMPK and activation of the Akt pathway, leading to elevated expression of the ATP-dependent efflux pump ABCG2. Importantly, inhibition of glycolysis by 3-BrOP significantly reduces SP cells in vitro and impairs their ability to form tumors in vivo. Our data suggest that glucose is an essential regulator of SP cells mediated by the Akt pathway, and targeting glycolysis may eliminate the drug-resistant SP cells with potentially significant benefits in cancer treatment.     

Akt and c-Myc Differentially Activate Cellular Metabolic Programs and Prime Cells to Bioenergetic Inhibition

The high glucose consumption of tumor cells even in an oxygen-rich environment, referred to as the Warburg effect, has been noted as a nearly universal biochemical characteristic of cancer cells. Targeting the glycolysis pathway has been explored as an anti-cancer therapeutic strategy to eradicate cancer based on this fundamental biochemical property of cancer cells. Oncoproteins such as Akt and c-Myc regulate cell metabolism. Accumulating studies have uncovered various molecular mechanisms by which oncoproteins affect cellular metabolism, raising a concern as to whether targeting glycolysis will be equally effective in treating cancers arising from different oncogenic activities. Here, we established a dual-regulatable FL5.12 pre-B cell line in which myristoylated Akt is expressed under the control of doxycycline, and c-Myc, fused to the hormone-binding domain of the human estrogen receptor, is activated by 4-hydroxytamoxifen. Using this system, we directly compared the effect of these oncoproteins on cell metabolism in an isogenic background. Activation of either Akt or c-Myc leads to the Warburg effect as indicated by increased cellular glucose uptake, glycolysis, and lactate generation. When cells are treated with glycolysis inhibitors, Akt sensitizes cells to apoptosis, whereas c-Myc does not. In contrast, c-Myc but not Akt sensitizes cells to the inhibition of mitochondrial function. This is correlated with enhanced mitochondrial activities in c-Myc cells. Hence, although both Akt and c-Myc promote aerobic glycolysis, they differentially affect mitochondrial functions and render cells susceptible to the perturbation of cellular metabolic programs.     

Warburg-like Glycolysis and Lactate Shuttle in Mouse Decidua during Early Pregnancy

Decidualization is an essential process of maternal endometrial stromal cells to support pregnancy. Although it is known that enhanced glucose influx is critical for decidualization, the underlying mechanism in regulating glucose metabolism in decidua remains insufficiently understood. Here, we demonstrate that aerobic glycolysis-related genes and factors are all substantially induced during decidualization, indicating the existence of Warburg-like glycolysis in decidua. In vitro, progesterone activates hypoxia-inducible factor 1α (Hif1α) and c-Myc through Pi3k-Akt signaling pathway to maintain aerobic glycolysis in decidualizing cells. Knocking down of pyruvate kinase M2 (Pkm2) attenuates the induction of decidual marker gene. Decidual formation in vivo is also impaired by glycolysis inhibitor 3-bromopyruvate. Besides, lactate exporter monocarboxylate transporter 4 (Mct4) is induced in newly formed decidual cells, whereas lactate importer Mct1 and proliferation marker Ki-67 are complementarily located in the surrounding undifferentiated cells, which are supposed to consume lactate for proliferation. Hif1α activation is required for lactate-dependent proliferation of the undifferentiated cells. Inhibition of lactate flux leads to compromised decidualization and decelerated lactate-dependent proliferation. In summary, we reveal that Warburg-like glycolysis and local lactate shuttle are activated in decidua and play important roles for supporting early pregnancy.     

Hypoxia-inducible Factor-1-mediated Regulation of Semaphorin 4D Affects Tumor Growth and Vascularity

Tumor progression and metastasis depend on the ability of cancer cells to initiate angiogenesis to ensure delivery of oxygen, nutrients, and growth factors to tumor cells and provide access to the systemic circulation. Hypoxia-inducible factor-1 (HIF-1) can activate expression of a broad range of genes that mediate many of the adaptive responses to decreased oxygen concentration, such as enhanced glucose uptake and formation of new blood vessels. Acting through Plexin-B1 on endothelial cells, Semaphorin 4D (Sema4D) has been shown to promote angiogenesis and enhance invasive growth and proliferation in some tumors. Here we show that the gene for Sema4D, the product of which is elevated in head and neck squamous cell carcinoma (HNSCC) cells, contains upstream hypoxia response elements (HRE) and is strongly induced in hypoxia in a HIF-1-dependent manner. Knocking down Sema4D expression with short hairpin (sh) RNA reduces in vitro endothelial cell migration and growth and vascularity of HNSCC xenografts expressing a degradation resistant HIF-1α subunit. We also demonstrate a correlation between HIF-1 activity and Sema4D expression in HNSCC specimens. These findings indicate that Sema4D is induced by hypoxia in a HIF-1-dependent manner and influences endothelial cell migration and tumor vascularity. Expression of Sema4D may be a strategy by which carcinomas promote angiogenesis and therefore could represent a therapeutic target for these malignancies.