Glucose metabolism in cancer. Evidence that demethylation events play a role in activating type II hexokinase gene expression

Targeting the Warburg effect: A revisited perspective from molecular mechanisms to traditional and innovative therapeutic strategies in cancer

Cancer reprogramming is an important facilitator of cancer development and survival, with tumor cells exhibiting a preference for aerobic glycolysis beyond oxidative phosphorylation, even under sufficient oxygen supply condition. This metabolic alteration, known as the Warburg effect, serves as a significant indicator of malignant tumor transformation. The Warburg effect primarily impacts cancer occurrence by influencing the aerobic glycolysis pathway in cancer cells. Key enzymes involved in this process include glucose transporters (GLUTs), HKs, PFKs, LDHs, and PKM2. Moreover, the expression of transcriptional regulatory factors and proteins, such as FOXM1, p53, NF-κB, HIF1α, and c-Myc, can also influence cancer progression. Furthermore, lncRNAs, miRNAs, and circular RNAs play a vital role in directly regulating the Warburg effect. Additionally, gene mutations, tumor microenvironment remodeling, and immune system interactions are closely associated with the Warburg effect. Notably, the development of drugs targeting the Warburg effect has exhibited promising potential in tumor treatment. This comprehensive review presents novel directions and approaches for the early diagnosis and treatment of cancer patients by conducting in-depth research and summarizing the bright prospects of targeting the Warburg effect in cancer.

An integrative view on glucagon function and putative role in the progression of pancreatic neuroendocrine tumours (pNETs) and hepatocellular carcinomas (HCC)

Cancer metabolism research area evolved greatly, however, is still unknown the impact of systemic metabolism control and diet on cancer. It makes sense that systemic regulators of metabolism can act directly on cancer cells and activate signalling, prompting metabolic remodelling needed to sustain cancer cell survival, tumour growth and disease progression. In the present review, we describe the main glucagon functions in the control of glycaemia and of metabolic pathways overall. Furthermore, an integrative view on how glucagon and related signalling pathways can contribute for pancreatic neuroendocrine tumours (pNETs) and hepatocellular carcinomas (HCC) progression, since pancreas and liver are the major organs exposed to higher levels of glucagon, pancreas as a producer and liver as a scavenger. The main objective is to bring to discussion some glucagon-dependent mechanisms by presenting an integrative view on microenvironmental and systemic aspects in pNETs and HCC biology.

Histone Methyltransferase NSD2 Activates PKCα to Drive Metabolic Reprogramming and Lenalidomide Resistance in Multiple Myeloma

Multiple myeloma cells undergo metabolic reprogramming in response to the hypoxic and nutrient-deprived bone marrow microenvironment. Primary oncogenes in recurrent translocations might be able to drive metabolic heterogeneity to survive the microenvironment that can present new vulnerabilities for therapeutic targeting. t(4;14) translocation leads to the universal overexpression of histone methyltransferase NSD2 that promotes plasma cell transformation through a global increase in H3K36me2. Here, we identified PKCα as an epigenetic target that contributes to the oncogenic potential of NSD2. RNA sequencing of t(4;14) multiple myeloma cell lines revealed a significant enrichment in the regulation of metabolic processes by PKCα, and the glycolytic gene, hexokinase 2 (HK2), was transcriptionally regulated by PKCα in a PI3K/Akt-dependent manner. Loss of PKCα displaced mitochondria-bound HK2 and reversed sensitivity to the glycolytic inhibitor 3-bromopyruvate. In addition, the perturbation of glycolytic flux led to a metabolic shift to a less energetic state and decreased ATP production. Metabolomics analysis indicated lactate as a differential metabolite associated with PKCα. As a result, PKCα conferred resistance to the immunomodulatory drugs (IMiD) lenalidomide in a cereblon-independent manner and could be phenocopied by either overexpression of HK2 or direct supplementation of lactate. Clinically, t(4;14) patients had elevated plasma lactate levels and did not benefit from lenalidomide-based regimens. Altogether, this study provides insights into the epigenetic-metabolism cross-talk in multiple myeloma and highlights the opportunity for therapeutic intervention that leverages the distinct metabolic program in t(4;14) myeloma.

SIGNIFICANCE

Aberrant glycolysis driven by NSD2-mediated upregulation of PKCα can be therapeutically exploited using metabolic inhibitors with lactate as a biomarker to identify high-risk patients who exhibit poor response towards IMiD-based regimens.

DNA 5mC and RNA m6A modification successively facilitates the initiation and perpetuation stages of HSC activation in liver fibrosis progression

Hepatic stellate cells (HSC) are key effector cells in liver fibrosis. Upon stimulation, the quiescent HSC undergoes complex morphological and functional changes to transdifferentiate into activated collagen-producing myofibroblasts. DNA/RNA methylations (5mC/m6A) are both implicated to participate in hepatic fibrosis, yet their respective roles and specific targets in HSC activation remain elusive. Here, we demonstrate that 5mC is indispensable for the initiation stage of HSC activation (myofibroblast transdifferentiation), whereas m6A is essential for the perpetuation stage of HSC activation (excessive ECM production). Mechanistically, DNA 5mC hypermethylation on the promoter of SOCS3 and PPARγ genes leads to STAT3-mediated metabolic reprogramming and lipid loss in the initiation stage. RNA m6A hypermethylation on the transcripts of major collagen genes enhances the mRNA stability in a YTHDF1-dependent manner, which contributes to massive ECM production. Vitamin A-coupled YTHDF1 siRNA alleviates CCl4-induced liver fibrosis in mice through HSC-specific inhibition of collagen production. HIF-1α, which is transactivated by STAT3, serves as a bridge linking the initiation and the perpetuation stages through transactivating YTHDF1. These findings indicate successive roles of DNA 5mC and RNA m6A modification in the progression of HSC activation, which provides new drug targets for epigenetic therapy of liver fibrosis.

A novel small molecule glycolysis inhibitor WZ35 exerts anti-cancer effect via metabolic reprogramming

Background

Liver cancer is the fifth leading cause of cancer death worldwide, but early diagnosis and treatment of liver cancer remains a clinical challenge. How to screen and diagnose liver cancer early and prolong the survival rate is still the focus of researchers.

Methods

Cell experiments were used to detect the effect of WZ35 on the colony formation ability and proliferation activity of hepatoma cells, nude mouse experiment to observe the in vivo anticancer activity and toxic side effects of WZ35; metabolomics analysis, glucose metabolism experiment and Seahorse analysis of liver cancer cells treated with WZ35; cell experiments combined with bioinformatics analysis to explore the mechanism of WZ35-mediated metabolic reprogramming to exert anticancer activity; tissue microarray and case analysis to evaluate the clinical significance of biomarkers for early diagnosis, treatment and prognosis evaluation of liver cancer.

Results

WZ35 inhibited the proliferation activity of various cell lines of liver cancer, and showed good therapeutic effect in nude mice model of hepatocellular carcinoma without obvious toxic and side effects; WZ35 inhibited the absorption of glucose in hepatoma cells, and the drug effect glycolysis, phosphorylation and purine metabolism are relatively seriously damaged; WZ35 mainly inhibits YAP from entering the nucleus as a transcription factor activator by activating oxidative stress in liver cancer cells, reducing the transcription of GLUT1, and finally reducing its GLUT1. Tissue microarray and case analysis showed that GLUT1 and YAP were highly expressed and correlated in liver cancer patients, and were associated with poor patient prognosis. The GLUT1-YAP risk model had a high score in predicting prognosis.

Conclusion

The study confirms that WZ35 is a small molecule glycolysis inhibitor, and through its properties, it mediates metabolic reprogramming dominated by impaired glycolysis, oxidative phosphorylation and purine metabolism to inhibit the proliferation activity of liver cancer cells. Our findings present novel insights into the pathology of liver cancer and potential targets for new therapeutic strategies. GLUT1-YAP has important reference significance for predicting the stages of disease progression in liver cancer patients and have the potential to serve as novel biomarkers for the diagnosis and treatment of liver cancer.

The metabolic addiction of cancer stem cells

Cancer stem cells (CSC) are the minor population of cancer originating cells that have the capacity of self-renewal, differentiation, and tumorigenicity (when transplanted into an immunocompromised animal). These low-copy number cell populations are believed to be resistant to conventional chemo and radiotherapy. It was reported that metabolic adaptation of these elusive cell populations is to a large extent responsible for their survival and distant metastasis. Warburg effect is a hallmark of most cancer in which the cancer cells prefer to metabolize glucose anaerobically, even under normoxic conditions. Warburg's aerobic glycolysis produces ATP efficiently promoting cell proliferation by reprogramming metabolism to increase glucose uptake and stimulating lactate production. This metabolic adaptation also seems to contribute to chemoresistance and immune evasion, a prerequisite for cancer cell survival and proliferation. Though we know a lot about metabolic fine-tuning in cancer, what is still in shadow is the identity of upstream regulators that orchestrates this process. Epigenetic modification of key metabolic enzymes seems to play a decisive role in this. By altering the metabolic flux, cancer cells polarize the biochemical reactions to selectively generate "onco-metabolites" that provide an added advantage for cell proliferation and survival. In this review, we explored the metabolic-epigenetic circuity in relation to cancer growth and proliferation and establish the fact how cancer cells may be addicted to specific metabolic pathways to meet their needs. Interestingly, even the immune system is re-calibrated to adapt to this altered scenario. Knowing the details is crucial for selective targeting of cancer stem cells by choking the rate-limiting stems and crucial branch points, preventing the formation of onco-metabolites.

Stress Responses as Master Keys to Epigenomic Changes in Transcriptome and Metabolome for Cancer Etiology and Therapeutics

From initiation through progression, cancer cells are subjected to a magnitude of endogenous and exogenous stresses, which aid in their neoplastic transformation. Exposure to these classes of stress induces imbalance in cellular homeostasis and, in response, cancer cells employ informative adaptive mechanisms to rebalance biochemical processes that facilitate survival and maintain their existence. Different kinds of stress stimuli trigger epigenetic alterations in cancer cells, which leads to changes in their transcriptome and metabolome, ultimately resulting in suppression of growth inhibition or induction of apoptosis. Whether cancer cells show a protective response to stress or succumb to cell death depends on the type of stress and duration of exposure. A thorough understanding of epigenetic and molecular architecture of cancer cell stress response pathways can unveil a plethora of information required to develop novel anticancer therapeutics. The present view highlights current knowledge about alterations in epigenome and transcriptome of cancer cells as a consequence of exposure to different physicochemical stressful stimuli such as reactive oxygen species (ROS), hypoxia, radiation, hyperthermia, genotoxic agents, and nutrient deprivation. Currently, an anticancer treatment scenario involving the imposition of stress to target cancer cells is gaining traction to augment or even replace conventional therapeutic regimens. Therefore, a comprehensive understanding of stress response pathways is crucial for devising and implementing novel therapeutic strategies.

Reprogramming Carbohydrate Metabolism in Cancer and Its Role in Regulating the Tumor Microenvironment

Altered metabolism has become an emerging feature of cancer cells impacting their proliferation and metastatic potential in myriad ways. Proliferating heterogeneous tumor cells are surrounded by other resident or infiltrating cells, along with extracellular matrix proteins, and other secretory factors constituting the tumor microenvironment. The diverse cell types of the tumor microenvironment exhibit different molecular signatures that are regulated at their genetic and epigenetic levels. The cancer cells elicit intricate crosstalks with these supporting cells, exchanging essential metabolites which support their anabolic processes and can promote their survival, proliferation, EMT, angiogenesis, metastasis and even therapeutic resistance. In this context, carbohydrate metabolism ensures constant energy supply being a central axis from which other metabolic and biosynthetic pathways including amino acid and lipid metabolism and pentose phosphate pathway are diverged. In contrast to normal cells, increased glycolytic flux is a distinguishing feature of the highly proliferative cancer cells, which supports them to adapt to a hypoxic environment and also protects them from oxidative stress. Such rewired metabolic properties are often a result of epigenetic alterations in the cancer cells, which are mediated by several factors including, DNA, histone and non-histone protein modifications and non-coding RNAs. Conversely, epigenetic landscapes of the cancer cells are also dictated by their diverse metabolomes. Altogether, this metabolic and epigenetic interplay has immense potential for the development of efficient anti-cancer therapeutic strategies. In this book chapter we emphasize upon the significance of reprogrammed carbohydrate metabolism in regulating the tumor microenvironment and cancer progression, with an aim to explore the different metabolic and epigenetic targets for better cancer treatment.

Epigenetic Small-Molecule Modulators Targeting Metabolic Pathways in Cancer

Metabolic deregulation is a key factor in cancer progression. Epigenetic changes and metabolic rewiring are intertwined in cancer. Deregulated epigenetic modifiers cause metabolic aberrations by targeting the expression of metabolic enzymes. Conversely, metabolites and cofactors affect the expression and activity of epigenetic regulators. Small molecules are promising therapeutic approaches to target the epigenetic-metabolomic crosstalk in cancer. Here, we focus on the interplay between metabolic rewiring and epigenetic landscape in the context of tumourigenesis and highlight recent advances in the use of small-molecule drug targets for therapy.

Quantitative Expression of Key Cancer Markers in the AS-30D Hepatocarcinoma Model

Hepatocellular carcinoma is one of the cancers with the highest mortality rate worldwide. HCC is often diagnosed when the disease is already in an advanced stage, making the discovery and implementation of biomarkers for the disease a critical aim in cancer research. In this study, we aim to quantify the transcript levels of key signaling molecules relevant to different pathways known to participate in tumorigenesis, with special emphasis on those related to cancer hallmarks and epithelial-mesenchymal transition, using as a model the murine transplantable hepatocarcinoma AS-30D. Using qPCR to quantify the mRNA levels of genes involved in tumorigenesis, we found elevated levels for Tgfb1 and Spp1, two master regulators of EMT. A mesenchymal signature profile for AS-30D cells is also supported by the overexpression of genes encoding for molecules known to be associated to aggressiveness and metastatic phenotypes such as Foxm1, C-met, and Inppl1. This study supports the use of the AS-30D cells as an efficient and cost-effective model to study gene expression changes in HCC, especially those associated with the EMT process.

Metabostemness in cancer: Linking metaboloepigenetics and mitophagy in remodeling cancer stem cells

Cancer stem cells (CSCs) are rare populations of malignant cells with stem cell-like features of self-renewal, uninterrupted differentiation, tumorigenicity, and resistance to conventional therapeutic agents, and these cells have a decisive role in treatment failure and tumor relapse. The self-renewal potential of CSCs with atypical activation of developmental signaling pathways involves the maintenance of stemness to support cancer progression. The acquisition of stemness in CSCs has been accomplished through genetic and epigenetic rewiring following the metabolic switch. In this context, "metabostemness" denotes the metabolic parameters that essentially govern the epitranscriptional gene reprogramming mechanism to dedifferentiate tumor cells into CSCs. Several metabolites often referred to as oncometabolites can directly remodel chromatin structure and thereby influence the operation of epitranscriptional circuits. This integrated metaboloepigenetic dimension of CSCs favors the differentiated cells to move in dedifferentiated macrostates. Some metabolic events might perform as early drivers of epitranscriptional reprogramming; however, subsequent metabolic hits may govern the retention of stemness properties in the tumor mass. Interestingly, selective removal of mitochondria through autophagy can promote metabolic plasticity and alter metabolic states during differentiation and dedifferentiation. In this connection, novel metabostemness-specific drugs can be generated as potential cancer therapeutics to target the metaboloepigenetic circuitry to eliminate CSCs.

Inositol treatment inhibits medulloblastoma through suppression of epigenetic-driven metabolic adaptation

Deregulation of chromatin modifiers plays an essential role in the pathogenesis of medulloblastoma, the most common paediatric malignant brain tumour. Here, we identify a BMI1-dependent sensitivity to deregulation of inositol metabolism in a proportion of medulloblastoma. We demonstrate mTOR pathway activation and metabolic adaptation specifically in medulloblastoma of the molecular subgroup G4 characterised by a BMI1High;CHD7Low signature and show this can be counteracted by IP6 treatment. Finally, we demonstrate that IP6 synergises with cisplatin to enhance its cytotoxicity in vitro and extends survival in a pre-clinical BMI1High;CHD7Low xenograft model.

Estimation of serum pyruvic acid levels in oral squamous cell carcinoma

Introduction:

Cancer cells generally exhibit increased glycolysis for adenosine triphosphate generation (the Warburg effect) due to mitochondrial respiration injury and hypoxia, which are frequently associated with resistance to therapeutic agents. Pyruvic acid is produced as an end product of glycolysis along with lactic acid. At room temperature, lactic acid converts into pyruvic acid as it is chemically unstable.

Aim:

To evaluate the serum pyruvic acid levels in patients with oral squamous cell carcinoma (OSCC).

Materials and Methods:

Thirty clinically and histopathologically confirmed cases of OSCC were included in the study. The cases were staged clinically (tumor–node–metastasis staging) and graded histopathologically (modified Broder's classification). A control group of 30 age-matched individuals with no systemic diseases were selected and the serum levels of pyruvic acid were measured and the absorbance was read using a spectrophotometer at a wavelength of 540 nm. The results were evaluated statistically and discussed.

Results:

Pair-wise comparison of clinical stages and histological grades of OSCC was done using Tukey's multiple post hoc procedure. The increase in mean serum pyruvic acid levels between any two groups and grades was found to be statistically significant respectively (P<0.05).

Conclusion:

Serum pyruvic acid levels gradually increased from individuals without OSCC to individuals with OSCC. Higher levels of serum pyruvic acid were seen with increasing clinical stage and the mean serum pyruvic acid levels were also found to be significantly increasing with advancing histopathological grades of OSCC.

Caveolin-1 scaffolding domain peptide regulates glucose metabolism in lung fibrosis

Increased metabolism distinguishes myofibroblasts or fibrotic lung fibroblasts (fLfs) from the normal lung fibroblasts (nLfs). The mechanism of metabolic activation in fLfs has not been fully elucidated. Furthermore, the antifibrogenic effects of caveolin-1 scaffolding domain peptide CSP/CSP7 involving metabolic reprogramming in fLfs are unclear. We therefore analyzed lactate and succinate levels, as well as the expression of glycolytic enzymes and hypoxia inducible factor-1α (HIF-1α). Lactate and succinate levels, as well as the basal expression of glycolytic enzymes and HIF-1α, were increased in fLfs. These changes were reversed following restoration of p53 or its transcriptional target microRNA-34a (miR-34a) expression in fLfs. Conversely, inhibition of basal p53 or miR-34a increased glucose metabolism, glycolytic enzymes, and HIF-1α in nLfs. Treatment of fLfs or mice having bleomycin- or Ad-TGF-β1-induced lung fibrosis with CSP/CSP7 reduced the expression of glycolytic enzymes and HIF-1α. Furthermore, inhibition of p53 or miR-34a abrogated CSP/CSP7-mediated restoration of glycolytic flux in fLfs in vitro and in mice with pulmonary fibrosis and lacking p53 or miR-34a expression in fibroblasts in vivo. Our data indicate that dysregulation of glucose metabolism in fLfs is causally linked to loss of basal expression of p53 and miR-34a. Treatment with CSP/CSP7 constrains aberrant glucose metabolism through restoration of p53 and miR-34a.

Dysregulation of metabolic enzymes in tumor and stromal cells: Role in oncogenesis and therapeutic opportunities

Altered cellular metabolism is a hallmark of cancer. Metabolic rewiring in cancer cells occurs due to the activation of oncogenes, inactivation of tumor suppressor genes, and/or other adaptive changes in cell signaling pathways. Furthermore, altered metabolism is also reported in tumor-corrupted stromal cells as a result of their interaction with cancer cells or due to their adaptation in the dynamic tumor microenvironment. Metabolic alterations are associated with dysregulation of metabolic enzymes and tumor-stromal metabolic crosstalk is vital for the progressive malignant journey of the tumor cells. Therefore, several therapies targeting metabolic enzymes have been evaluated and/or are being investigated in preclinical and clinical studies. In this review, we discuss some important metabolic enzymes that are altered in tumor and/or stromal cells, and focus on their role in supporting tumor growth. Moreover, we also discuss studies carried out in various cancers to target these metabolic abnormalities for therapeutic exploitation.

Causes and Consequences of Variable Tumor Cell Metabolism on Heritable Modifications and Tumor Evolution

When cancer research advanced into the post-genomic era, it was widely anticipated that the sought-after cure will be delivered promptly. Instead, it became apparent that an understanding of cancer genomics, alone, is unable to translate the wealth of information into successful cures. While gene sequencing has significantly improved our understanding of the natural history of cancer and identified candidates for therapeutic targets, it cannot predict the impact of the biological response to therapies. Hence, patients with a common mutational profile may respond differently to the same therapy, due in part to different microenvironments impacting on gene regulation. This complexity arises from a feedback circuit involving epigenetic modifications made to genes by the metabolic byproducts of cancer cells. New insights into epigenetic mechanisms, activated early in the process of carcinogenesis, have been able to describe phenotypes which cannot be inferred from mutational analyses per se. Epigenetic changes can propagate throughout a tumor via heritable modifications that have long-lasting consequences on ensuing phenotypes. Such heritable epigenetic changes can be evoked profoundly by cancer cell metabolites, which then exercise a broad remit of actions across all stages of carcinogenesis, culminating with a meaningful impact on the tumor's response to therapy. This review outlines some of the cross-talk between heritable epigenetic changes and tumor cell metabolism, and the consequences of such changes on tumor progression.

Mitochondrial glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase abrogate p53 induced apoptosis in a yeast model: Possible implications for apoptosis resistance in cancer cells

BACKGROUND

Escape from apoptosis is an important hallmark of tumor progression and drug resistance in cancer cells. It is well demonstrated that over-expression of human wtp53 in Saccharomyces cerevisiae induces apoptosis by directly targeting the mitochondria. In this study, we showed that how S.cerevisiae escaped from p53 induced apoptosis in the presence of a fermentable carbon source (sucrose), but not on non-fermentable carbon source (glycerol).

METHODS

Mitochondrial fractions from yeast cultures grown in the presence of sucrose or glycerol with and without p53 expression were fractionated and analyzed by LC-MS/MS. Differentially expressed proteins were studied and detailed biochemical analysis for selected proteins was performed.The effect of mitochondrial HXK-2 over-expression induced by p53 in sucrose grown cells on cell survival was evaluated using gene deletion/tagging, co-localisation and mitochondrial ROS detection.

RESULTS

We observe that mitochondria isolated from p53 over-expressing cells accumulate Pentose phosphate Pathway (PPP) enzymes including glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) which led to enhanced mitochondrial NADPH production only when cells are cultured in sucrose but not glycerol. In contrast, mitochondria isolated from Δhxk2 p53 over-expressing cells grown in sucrose did not accumulate G6PDH and 6PGDH and resulted in defective growth.

CONCLUSIONS

Enhanced association of HXK2 with the mitochondria with the concomitant accumulation of G6PDG and 6PGDH results in increased NADPH that scavenges ROS and provides resistance to apoptosis.

GENERAL SIGNIFICANCE

Given the extensive similarity of aerobic glycolysis between humans and yeast, the phenomena described here could as well be responsible for the escape of apoptosis in cancer cells.

Dissociation of mitochondrial HK-II elicits mitophagy and confers cardioprotection against ischemia

Preservation of mitochondrial integrity is critical for maintaining cellular homeostasis. Mitophagy is a mitochondria-specific type of autophagy which eliminates damaged mitochondria thereby contributing to mitochondrial quality control. Depolarization of the mitochondrial membrane potential is an established mechanism for inducing mitophagy, mediated through PINK1 stabilization and Parkin recruitment to mitochondria. Hexokinase-II (HK-II) which catalyzes the first step in glucose metabolism, also functions as a signaling molecule to regulate cell survival, and a significant fraction of cellular HK-II is associated with mitochondria (mitoHK-II). We demonstrate here that pharmacological interventions and adenoviral expression of a mitoHK-II dissociating peptide which reduce mitoHK-II levels lead to robust increases in mitochondrial Parkin and ubiquitination of mitochondrial proteins in cardiomyocytes and in a human glioblastoma cell line 1321N1, independent of mitochondrial membrane depolarization or PINK1 accumulation. MitoHK-II dissociation-induced mitophagy was demonstrated using Mito-Keima in cardiomyocytes and in 1321N1 cells. Subjecting cardiomyocytes or the in vivo heart to ischemia leads to modest dissociation of mitoHK-II. This response is potentiated by expression of the mitoHK-II dissociating peptide, which increases Parkin recruitment to mitochondria and, importantly, provides cardioprotection against ischemic stress. These results suggest that mitoHK-II dissociation is a physiologically relevant cellular event that is induced by ischemic stress, the enhancement of which protects against ischemic damage. The mechanism which underlies the effects of mitoHK-II dissociation can be attributed to the ability of Bcl2-associated athanogene 5 (BAG5), an inhibitor of Parkin, to localize to mitochondria and form a molecular complex with HK-II. Overexpression of BAG5 attenuates while knockdown of BAG5 sensitizes the effect of mitoHK-II dissociation on mitophagy. We suggest that HK-II, a glycolytic molecule, can function as a sensor for metabolic derangements at mitochondria to trigger mitophagy, and modulating the intracellular localization of HK-II could be a novel way of regulating mitophagy to prevent cell death induced by ischemic stress.

Mechanisms and Implications of Metabolic Heterogeneity in Cancer

Tumors display reprogrammed metabolic activities that promote cancer progression. We currently possess a limited understanding of the processes governing tumor metabolism in vivo and of the most efficient approaches to identify metabolic vulnerabilities susceptible to therapeutic targeting. While much of the literature focuses on stereotyped, cell-autonomous pathways like glycolysis, recent work emphasizes heterogeneity and flexibility of metabolism between tumors and even within distinct regions of solid tumors. Metabolic heterogeneity is important because it influences therapeutic vulnerabilities and may predict clinical outcomes. This Review describes current concepts about metabolic regulation in tumors, focusing on processes intrinsic to cancer cells and on factors imposed upon cancer cells by the tumor microenvironment. We discuss experimental approaches to identify subtype-selective metabolic vulnerabilities in preclinical cancer models. Finally, we describe efforts to characterize metabolism in primary human tumors, which should produce new insights into metabolic heterogeneity in the context of clinically relevant microenvironments.

Metabolic Dysregulations and Epigenetics: A Bidirectional Interplay that Drives Tumor Progression

Cancer has been considered, for a long time, a genetic disease where mutations in keyregulatory genes drive tumor initiation, growth, metastasis, and drug resistance. Instead, theadvent of high-throughput technologies has revolutionized cancer research, allowing to investigatemolecular alterations at multiple levels, including genome, epigenome, transcriptome, proteome,and metabolome and showing the multifaceted aspects of this disease. The multi-omics approachesrevealed an intricate molecular landscape where different cellular functions are interconnected andcooperatively contribute to shaping the malignant phenotype. Recent evidence has brought to lighthow metabolism and epigenetics are highly intertwined, and their aberrant crosstalk can contributeto tumorigenesis. The oncogene-driven metabolic plasticity of tumor cells supports the energeticand anabolic demands of proliferative tumor programs and secondary can alter the epigeneticlandscape via modulating the production and/or the activity of epigenetic metabolites. Conversely,epigenetic mechanisms can regulate the expression of metabolic genes, thereby altering themetabolome, eliciting adaptive responses to rapidly changing environmental conditions, andsustaining malignant cell survival and progression in hostile niches. Thus, cancer cells takeadvantage of the epigenetics-metabolism crosstalk to acquire aggressive traits, promote cellproliferation, metastasis, and pluripotency, and shape tumor microenvironment. Understandingthis bidirectional relationship is crucial to identify potential novel molecular targets for theimplementation of robust anti-cancer therapeutic strategies.

miR‑185 regulates the growth of osteosarcoma cells via targeting Hexokinase 2

MicroRNAs (miRNAs) have been proposed as potential prognostic and diagnostic biomarkers in numerous types of cancer, including osteosarcoma (OS), which is the most common bone malignancy. The present study revealed that the expression of miR‑185 was downregulated in OS tissues and cells. Overexpression of miR‑185 significantly suppressed the proliferation and migration of OS cells. To further investigate the functional roles of miR‑185 in OS, the downstream targets of miR‑185 were predicted using the microRNA.org database. The results revealed that in cancer cells, hexokinase 2 (HK2), the rate‑limiting enzyme of glycolysis, was a potential target of miR‑185. Molecular analysis indicated that miR‑185 binds to the 3'‑untranslated region of HK2 mRNA. Overexpressed miR‑185 downregulated the mRNA and protein levels of HK2 in OS cells. In addition, an inverse correlation between the expression of miR‑185 and HK2 was reported in OS. Consistent with the downregulation of HK2 induced by miR‑185, overexpression of HK2 in OS cells significantly attenuated the inhibitory effects of miR‑185 on glucose consumption and lactate production, while depletion of miR‑185 promoted the glycolysis of OS cells. Additionally, restoration of HK2 abolished the inhibitory effects of miR‑185 on the proliferation of OS cells. In summary, these results revealed that miR‑185 suppressed the glucose metabolism of OS cells; thus, miR‑185 may be considered as a promising therapeutic target for the treatment of OS.

Connections between metabolism and epigenetics in cancers

In the past half century, our version on cancer, from tumor initiation, growth, to metastasis, is dominated by genetic mutation. The importance of metabolism and epigenetics was not recognized until most recently. Extensive cell proliferation is one of the hallmarks of cancers. To support the energetic and anabolic demands of enhanced proliferation, tumors reprogram the pathways of nutrient procurement and metabolism. In this context, a new link between metabolic alterations and cancer progression has been unraveled over the last decade by the studies conducted in the area of cancer cell metabolism. Cancer cells are known to alter their metabolic profile during the course of tumorigenesis and metastasis thereby exhibiting a tightly regulated program of metabolic plasticity. Noteworthy, certain metabolic alteration are known to occur at the epigenetic level, thus making epigenetics and metabolism highly interwoven in a reciprocal manner. Metabolites that are generated during metabolic pathways, such as in glycolytic cycle and oxidative phosphorylation, serve as cofactors or substrates for the enzymatic reactions that catalyze the epigenetic modifications and transcriptional regulation. Several studies also indicate that the epigenome is sensitive to cellular metabolism. Since many of the metabolic alterations and consequently aberrated epigenetic regulation are common to a wide range of cancer types, they serve as promising targets for anti-cancer therapies. Here we discuss the latest findings in cancer cell metabolism, elucidating the major anabolic, catabolic and energetic demands required for sustaining cancer growth, and the influence of altered metabolism on epigenetics and vice versa. A comprehensive research pertaining to metabolomic profiling and epigenome interactors/mediators in malignant neoplasias is imperative in deciphering the potential targets that can be exploited for the development of robust anti-cancer therapies.

Tristetraprolin-mediated hexokinase 2 expression regulation contributes to glycolysis in cancer cells

Hexokinase 2 (HK2) catalyzes the first step of glycolysis and is up-regulated in cancer cells. The mechanism has not been fully elucidated. Tristetraprolin (TTP) is an AU-rich element (ARE)-binding protein that inhibits the expression of ARE-containing genes by enhancing mRNA degradation. TTP expression is down-regulated in cancer cells. We demonstrated that TTP is critical for down-regulation of HK2 expression in cancer cells. HK2 mRNA contains an ARE within its 3'-UTR. TTP binds to HK2 3'-UTR and enhances degradation of HK2 mRNA. TTP overexpression decreased HK2 expression and suppressed the glycolytic capacity of cancer cells, measured as glucose uptake and production of glucose-6-phosphate, pyruvate, and lactate. TTP overexpression reduced both the extracellular acidification rate (ECAR) and the oxygen consumption rate (OCR) of cancer cells. Ectopic expression of HK2 in cancer cells attenuated the reduction in glycolytic capacity, ECAR, and OCR from TTP. Taken together, these findings suggest that TTP acts as a negative regulator of HK2 expression and glucose metabolism in cancer cells.

Metabolism and Epigenetic Interplay in Cancer: Regulation and Putative Therapeutic Targets

Alterations in the epigenome and metabolism affect molecular rewiring of cancer cells facilitating cancer development and progression. Modulation of histone and DNA modification enzymes occurs owing to metabolic reprogramming driven by oncogenes and expression of metabolism-associated genes is, in turn, epigenetically regulated, promoting the well-known metabolic reprogramming of cancer cells and, consequently, altering the metabolome. Thus, several malignant traits are supported by the interplay between metabolomics and epigenetics, promoting neoplastic transformation. In this review we emphasize the importance of tumour metabolites in the activity of most chromatin-modifying enzymes and implication in neoplastic transformation. Furthermore, candidate targets deriving from metabolism of cancer cells and altered epigenetic factors is emphasized, focusing on compounds that counteract the epigenomic-metabolic interplay in cancer.

Reciprocal Regulation of Metabolic Reprogramming and Epigenetic Modifications in Cancer

Cancer cells reprogram their metabolism to meet their demands for survival and proliferation. The metabolic plasticity of tumor cells help them adjust to changes in the availability and utilization of nutrients in the microenvironment. Recent studies revealed that many metabolites and metabolic enzymes have non-metabolic functions contributing to tumorigenesis. One major function is regulating epigenetic modifications to facilitate appropriate responses to environmental cues. Accumulating evidence showed that epigenetic modifications could in turn alter metabolism in tumors. Although a comprehensive understanding of the reciprocal connection between metabolic and epigenetic rewiring in cancer is lacking, some conceptual advances have been made. Understanding the link between metabolism and epigenetic modifications in cancer cells will shed lights on the development of more effective cancer therapies.

Anti-fibrosis activity of combination therapy with epigallocatechin gallate, taurine and genistein by regulating glycolysis, gluconeogenesis, and ribosomal and lysosomal signaling pathways in HSC-T6 cells

A previous study by our group indicated that combined treatment with taurine, epigallocatechin gallate (EGCG) and genistein protects against liver fibrosis. The aim of the present study was to elucidate the antifibrotic mechanism of this combination treatment using isobaric tag for relative and absolute quantification (iTRAQ)-based proteomics in an activated rat hepatic stellate cell (HSC) line. In the present study, HSC-T6 cells were incubated with taurine, EGCG and genistein, and cellular proteins were extracted and processed for iTRAQ labeling. Quantification and identification of proteins was performed using two-dimensional liquid chromatography coupled with tandem mass spectrometry. Proteomic analysis indicated that the expression of 166 proteins were significantly altered in response to combination treatment with taurine, EGCG and genistein. A total 76 of these proteins were upregulated and 90 were downregulated. Differentially expressed proteins were grouped according to their association with specific Kyoto Encyclopedia of Genes and Genomes pathways. The results indicated that the differentially expressed proteins hexokinase-2 and lysosome-associated membrane glycoprotein 1 were associated with glycolysis, gluconeogenesis and lysosome signaling pathways. The expression of these proteins was validated using western blot analysis; the expression of hexokinase-2 was significantly decreased and the expression of lysosome-associated membrane glycoprotein 1 was significantly increased in HSC-T6 cells treated with taurine, EGCG and genistein compared with the control, respectively (P<0.05). These results were in accordance with the changes in protein expression identified using the iTRAQ approach. Therefore, the antifibrotic effect of combined therapy with taurine, EGCG and genistein may be associated with the activation of several pathways in HSCs, including glycolysis, gluconeogenesis, and the ribosome and lysosome signaling pathways. The differentially expressed proteins identified in the current study may be useful for treatment of liver fibrosis in the future.

c-Myc targeted regulators of cell metabolism in a transgenic mouse model of papillary lung adenocarcinoma

c-Myc's role in pulmonary cancer metabolism is uncertain. We therefore investigated c-Myc activity in papillary lung adenocarcinomas (PLAC). Genomics revealed 90 significantly regulated genes (> 3-fold) coding for cell growth, DNA metabolism, RNA processing and ribosomal biogenesis and bioinformatics defined c-Myc binding sites (TFBS) at > 95% of up-regulated genes. EMSA assays at 33 novel TFBS evidenced DNA binding activity and ChIP-seq data retrieved from public repositories confirmed these to be c-Myc bound. Dual-luciferase gene reporter assays developed for RNA-Terminal-Phosphate-Cyclase-Like-1(RCL1), Ribosomal-Protein-SA(RPSA), Nucleophosmin/Nucleoplasmin-3(NPM3) and Hexokinase-1(HK1) confirmed c-Myc functional relevance and ChIP assays with HEK293T cells over-expressing ectopic c-Myc demonstrated enriched c-Myc occupancy at predicted TFBS for RCL1, NPM3, HK1 and RPSA. Note, c-Myc recruitment on chromatin was comparable to the positive controls CCND2 and CDK4. Computational analyses defined master regulators (MR), i.e. heterogeneous nuclear ribonucleoprotein A1, nucleolin, the apurinic/apyrimidinic endonuclease 1, triosephosphate-isomerase 1, folate transporter (SLC19A1) and nucleophosmin to influence activity of up to 90% of PLAC-regulated genes. Their expression was induced by 3-, 3-, 6-, 3-, 11- and 7-fold, respectively. STRING analysis confirmed protein-protein-interactions of regulated genes and Western immunoblotting of fatty acid synthase, serine hydroxyl-methyltransferase 1, arginine 1 and hexokinase 2 showed tumor specific induction. Published knock down studies confirmed these proteins to induce apoptosis by disrupting neoplastic lipogenesis, by endorsing uracil accumulation and by suppressing arginine metabolism and glucose-derived ribonucleotide biosynthesis. Finally, translational research demonstrated high expression of MR and of 47 PLAC up-regulated genes to be associated with poor survival in lung adenocarcinoma patients (HR 3.2 p < 0.001) thus, providing a rationale for molecular targeted therapies in PLACs.

New therapeutic strategies to treat human cancers expressing mutant p53 proteins

The tumor suppressor p53 plays a critical role to preserve DNA fidelity from diverse insults through the regulation of cell-cycle checkpoints, DNA repair, senescence and apoptosis. The TP53 is the most frequently inactivated gene in human cancers. This leads to the production of mutant p53 proteins that loose wild-type p53 tumor suppression functions and concomitantly acquire new oncogenic properties among which deregulated cell proliferation, increased chemoresistance, disruption of tissue architecture, promotion of migration, invasion and metastasis and several other pro-oncogenic activities. Mouse models show that the genetic reconstitution of the wild type p53 tumor suppression functions rescues tumor growth. This strongly supports the notion that either restoring wt-p53 activity or inhibiting mutant p53 oncogenic activity could provide an efficient strategy to treat human cancers. In this review we briefly summarize recent advances in the study of small molecules and compounds that subvert oncogenic activities of mutant p53 protein into wt-p53 tumor suppressor functions. We highlight inhibitors of signaling pathways aberrantly modulated by oncogenic mutant p53 proteins as promising therapeutic strategies. Finally, we consider the clinical applications of compounds targeting mutant p53 and the use of currently available drugs in the treatment of tumors expressing mutant p53 proteins.

Regulation of HK2 expression through alterations in CpG methylation of the HK2 promoter during progression of hepatocellular carcinoma

Hexokinase 2 (HK2) is a rate-determining enzyme in aerobic glycolysis, a process upregulated in tumor cells. HK2 expression is controlled by various transcription factors and epigenetic alterations and is heterogeneous in hepatocellular carcinomas (HCCs), though the cause of this heterogeneity is not known. DNA methylation in the HK2 promoter CpG island (HK2-CGI) and its surrounding regions (shore and shelf) has not previously been evaluated, but may provide clues about the regulation of HK2 expression. Here, we compared HK2 promoter methylation in HCCs and adjacent non-cancerous liver tissues using a HumanMethylation450 BeadChip array. We found that, while the HK2-CGI N-shore was hypomethylated, thereby enhancing HK2 expression, the HK2-CGI was itself hypermethylated in some HCCs. This hypermethylation suppressed HK2 expression by inhibiting interactions between HIF-1α and a hypoxia response element (HRE) located at -234/-230. HCCs that were HK2negative and had distinct promoter CGI methylation were denoted as having a HK2-CGI methylation phenotype (HK2-CIMP), which was associated with poor clinical outcome. These findings indicate that HK2-CGI N-shore hypomethylation and HK2-CGI hypermethylation affect HK2 expression by influencing the interaction between HIF 1α and HRE. HK2-CGI hypermethylation induces HK2-CIMP and could represent a prognostic biomarker for HCC.

Clear cell hepatocellular carcinoma: origin, metabolic traits and fate of glycogenotic clear and ground glass cells

Clear cell hepatocellular carcinoma (CCHCC) has hitherto been considered an uncommon, highly differentiated variant of hepatocellular carcinoma (HCC) with a relatively favorable prognosis. CCHCC is composed of mixtures of clear and/or acidophilic ground glass hepatocytes with excessive glycogen and/or fat and shares histology, clinical features and etiology with common HCCs. Studies in animal models of chemical, hormonal and viral hepatocarcinogenesis and observations in patients with chronic liver diseases prone to develop HCC have shown that the majority of HCCs are preceded by, or associated with, focal or diffuse excessive storage of glycogen (glycogenosis) which later may be replaced by fat (lipidosis/steatosis). In ground glass cells, the glycogenosis is accompanied by proliferation of the smooth endoplasmic reticulum, which is closely related to glycogen particles and frequently harbors the hepatitis B surface antigen (HBsAg). From the findings in animal models a sequence of changes has been established, commencing with preneoplastic glycogenotic liver lesions, often containing ground glass cells, and progressing to glycogen-poor neoplasms via various intermediate stages, including glycogenotic/lipidotic clear cell foci, clear cell hepatocellular adenomas (CCHCA) rich in glycogen and/or fat, and CCHCC. A similar process seems to take place in humans, with clear cells frequently persisting in CCHCC and steatohepatitic HCC, which presumably represent intermediate stages in the development rather than particular variants of HCC. During the progression of the preneoplastic lesions, the clear and ground glass cells transform into cells characteristic of common HCC. The sequential cellular changes are associated with metabolic aberrations, which start with an activation of the insulin signaling cascade resulting in pre-neoplastic hepatic glycogenosis. The molecular and metabolic changes underlying the glycogenosis/lipidosis are apparently responsible for the dramatic metabolic shift from gluconeogenesis to the pentose phosphate pathway and Warburg-type glycolysis, which provide precursors and energy for an ever increasing cell proliferation during progression.

Regulation of glycolysis in head and neck squamous cell carcinoma

Glycolysis is highly upregulated in head and neck squamous cell carcinoma (HNSCC). HNSCC glycolysis is an important contributor to disease progression and decreases sensitivity to radiation or chemotherapy. Despite therapeutic advances, the survival rates for HNSCC patients remain low. Understanding glycolysis regulation in HNSCC will facilitate the development of effective therapeutic strategies for this disease. In this review, we will evaluate the regulation of altered HNSCC glycolysis and possible therapeutic approaches by targeting glycolytic pathways.

Non-metabolic functions of glycolytic enzymes in tumorigenesis

Cancer cells reprogram their metabolism to meet the requirement for survival and rapid growth. One hallmark of cancer metabolism is elevated aerobic glycolysis and reduced oxidative phosphorylation. Emerging evidence showed that most glycolytic enzymes are deregulated in cancer cells and play important roles in tumorigenesis. Recent studies revealed that all essential glycolytic enzymes can be translocated into nucleus where they participate in tumor progression independent of their canonical metabolic roles. These noncanonical functions include anti-apoptosis, regulation of epigenetic modifications, modulation of transcription factors and co-factors, extracellular cytokine, protein kinase activity and mTORC1 signaling pathway, suggesting that these multifaceted glycolytic enzymes not only function in canonical metabolism but also directly link metabolism to epigenetic and transcription programs implicated in tumorigenesis. These findings underscore our understanding about how tumor cells adapt to nutrient and fuel availability in the environment and most importantly, provide insights into development of cancer therapy.

A causal link from ALK to hexokinase II overexpression and hyperactive glycolysis in EML4-ALK-positive lung cancer

A high rate of aerobic glycolysis is a hallmark of malignant transformation. Accumulating evidence suggests that diverse regulatory mechanisms mediate this cancer-associated metabolic change seen in a wide spectrum of cancer. The echinoderm microtubule associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion protein is found in approximately 3-7% of non-small cell lung carcinomas (NSCLC). Molecular evidence and therapeutic effectiveness of FDA-approved ALK inhibitors indicated that EML4-ALK is a driving factor of lung tumorigenesis. A recent clinical study showed that NSCLC harboring EML4-ALK rearrangements displayed higher glucose metabolism compared to EML4-ALK-negative NSCLC. In the current work, we presented evidence that EML4-ALK is coupled to overexpression of hexokinase II (HK2), one of the rate-limiting enzymes of the glycolytic pathway. The link from EML4-ALK to HK2 upregulation is essential for a high rate of glycolysis and proliferation of EML4-ALK-rearranged NSCLC cells. We identified hypoxia-inducible factor 1α (HIF1α) as a key transcription factor to drive HK2 gene expression in normoxia in these cells. EML4-ALK induced hypoxia-independent but glucose-dependent accumulation of HIF1α protein via both transcriptional activation of HIF1α mRNA and the PI3K-AKT pathway to enhance HIF1α protein synthesis. The EML4-ALK-mediated upregulation of HIF1α, HK2 and glycolytic metabolism was also highly active in vivo as demonstrated by FDG-PET imaging of xenografts grown from EML4-ALK-positive NSCLC cells. Our data reveal a novel EML4-ALK-HIF1α-HK2 cascade to enhance glucose metabolism in EML4-ALK-positive NSCLC.

The Warburg effect: molecular aspects and therapeutic possibilities

It has been about nine decades since the proposal of Otto Warburg on the metabolism of cancer cells. Unlike normal cells which undergo glycolysis and oxidative phosphorylation in the presence of oxygen, proliferating and cancer cells exhibit an increased uptake of glucose and increased rate of glycolysis and predominantly undergo lactic acid fermentation. Whether this phenomenon is the consequence of genetic dysregulation in cancer or is the cause of cancer still remains unknown. However, there is certainly a strong link between the genetic factors, epigenetic modulation, cancer immunosurveillance and the Warburg effect, which will be discussed in this review. Dichloroacetate and 3-bromopyruvate are among the substances that have been studied as potential cancer therapies. With our expanding knowledge of cellular metabolism, therapies targeting the Warburg effect appear very promising. This review discusses different aspects of these emerging therapies.

In vitro effects of some flavonoids and phenolic acids on human pyruvate kinase isoenzyme M2

Pyruvate kinase isoenzyme M2 (PKM2) is one of the most important control point enzyme in glycolysis pathway. Hence, its inhibitors and activators are currently considered as the potential anticancer agents. The effect of 28 polyphenolic compounds on the enzyme activity was investigated in vitro. Among these compounds, neoeriocitrin, (-)-catechin gallate, fisetin, (±)-taxifolin and (-)-epicatechin have the highest inhibition effect with IC50 value within 0.65-1.33 µM range. Myricetin and quercetin 3-β-D-glucoside exhibited the highest activation effect with 0.51 and 1.34 µM AC50 values, respectively. Twelve of the compounds showed inhibition effect within 7-38 µM range of IC50 value. Sinapinic acid and p-coumaric acid showed an activation effect with 26.2 and 22.2 µM AC50 values, respectively. The results propose that the polyphenolics may be the potential PKM2 inhibitors/activators, and they may be used as lead compounds for the synthesis of new inhibitors or activators of this enzyme.

Restoration of mitochondria function as a target for cancer therapy

Defective oxidative phosphorylation has a crucial role in the attenuation of mitochondrial function, which confers therapy resistance in cancer. Various factors, including endogenous heat shock proteins (HSPs) and exogenous agents such as dichloroacetate, restore respiratory and other physiological functions of mitochondria in cancer cells. Functional mitochondria might ultimately lead to the restoration of apoptosis in cancer cells that are refractory to current anticancer agents. Here, we summarize the key reasons contributing to mitochondria dysfunction in cancer cells and how restoration of mitochondrial function could be exploited for cancer therapeutics.

Evidence for heightened hexokinase II immunoexpression in hepatocyte dysplasia and hepatocellular carcinoma

BACKGROUND

Normal hepatocytes exhibit low-affinity hexokinase (glucokinase [HKIV]), but during oncogenesis, there is a switch from HKIV to HKII expression. The aims of this study were to compare the immunoexpression of HKII in non-dysplastic cirrhosis (NDC), liver cell change/dysplasia in cirrhosis (LCD), HCC, and normal liver control tissues, and to correlate HKII expression with clinical and histopathological parameters.

DESIGN

Immunohistochemistry was performed on a liver cancer progression tissue array consisting of specimens from explants with cirrhosis, including 45 tissue samples with HCC, 108 without HCC, 143 with LCD, and 8 normal liver control tissues. HKII expression was quantified as positive pixel counts/square millimeter (ppc/mm(2)) by image analysis.

RESULTS

There was a stepwise increase in HKII level from normal liver tissue to NDC, to LCD, and to HCC (p = 0.001). HKII levels were significantly higher in areas of LCD versus NDC (p ≤ 0.001), and in LCD and HCC versus NDC (p = 0.007). HKII levels were similar in LCD and HCC (p = 0.124). HKII levels were higher in grade 2-4 versus grade 1 HCCs (p = 0.044), and in pleomorphic versus non-pleomorphic HCC variants (p = 0.041). Higher levels of HKII expression in LCD and HCC versus NDC and in higher tumor grade remained significant in multivariate analysis.

CONCLUSIONS

Higher levels of HKII immunoexpression in LDC and HCC compared with NDC suggest that upregulation of HKII occurs during the process of hepatocarcinogenesis in humans. In HCC, higher levels of HKII are associated with more aggressive histological features.

Metabostemness: a new cancer hallmark

The acquisition of and departure from stemness in cancer tissues might not only be hardwired by genetic controllers, but also by the pivotal regulatory role of the cellular metabotype, which may act as a "starter dough" for cancer stemness traits. We have coined the term metabostemness to refer to the metabolic parameters causally controlling or functionally substituting the epitranscriptional orchestration of the genetic reprograming that redirects normal and tumor cells toward less-differentiated cancer stem cell (CSC) cellular states. Certain metabotypic alterations might operate as pivotal molecular events rendering a cell of origin susceptible to epigenetic rewiring required for the acquisition of aberrant stemness and, concurrently, of refractoriness to differentiation. The metabostemness attribute can remove, diminish, or modify the nature of molecular barriers present in Waddington's epigenetic landscapes, thus allowing differentiated cells to more easily (re)-enter into CSC cellular macrostates. Activation of the metabostemness trait can poise cells with chromatin states competent for rapid dedifferentiation while concomitantly setting the idoneous metabolic stage for later reprograming stimuli to finish the journey from non-cancerous into tumor-initiating cells. Because only a few permitted metabotypes will be compatible with the operational properties owned by CSC cellular states, the metabostemness property provides a new framework through which to pharmacologically resolve the apparently impossible problem of discovering drugs aimed to target the molecular biology of the cancer stemness itself. The metabostemness cancer hallmark generates a shifting oncology theory that should guide a new era of metabolo-epigenetic cancer precision medicine.

TRIM24 links glucose metabolism with transformation of human mammary epithelial cells

Tripartite motif 24 protein (TRIM24) is a plant homeodomain/bromodomain histone reader, recently associated with poor overall survival of breast-cancer patients. At a molecular level, TRIM24 is a negative regulator of p53 levels and a co-activator of estrogen receptor. However, the role of TRIM24 in breast tumorigenesis remains largely unknown. We used an isogenic human mammary epithelial cell (HMEC) culture model, derived from reduction mammoplasty tissue, and found that ectopic expression of TRIM24 in immortalized HMECs (TRIM24 iHMECs) greatly increased cellular proliferation and induced malignant transformation. Subcutaneous injection of TRIM24 iHMECs in nude mice led to growth of intermediate to high-grade tumors in 60-70% of mice. Molecular analysis of TRIM24 iHMECs revealed a glycolytic and tricarboxylic acid cycle gene signature, alongside increased glucose uptake and activated aerobic glycolysis. Collectively, these results identify a role for TRIM24 in breast tumorigenesis through reprogramming of glucose metabolism in HMECs, further supporting TRIM24 as a viable therapeutic target in breast cancer.

Hexokinase-II positively regulates glucose starvation-induced autophagy through TORC1 inhibition

Hexokinase-II (HK-II) catalyzes the first step of glycolysis and also functions as a protective molecule; however, its role in protective autophagy has not been determined. Results showed that inhibition of HK-II diminished, while overexpression of HK-II potentiated, autophagy induced by glucose deprivation in cardiomyocyte and noncardiomyocyte cells. Immunoprecipitation studies revealed that HK-II binds to and inhibits the autophagy suppressor, mTOR complex 1 (TORC1), and that this binding was increased by glucose deprivation. The TOS motif, a scaffold sequence responsible for binding TORC1 substrates, is present in HK-II, and mutating it blocked its ability to bind to TORC1 and regulate protective autophagy. The transition from glycolysis to autophagy appears to be regulated by a decrease in glucose-6 phosphate. We suggest that HK-II binds TORC1 as a decoy substrate and provides a previously unrecognized mechanism for switching cells from a metabolic economy, based on plentiful energy, to one of conservation, under starvation.

Tumor suppressor p53 and its mutants in cancer metabolism

Tumor-suppressor p53 plays a key role in tumor prevention. As a transcription factor, p53 transcriptionally regulates its target genes to initiate different biological processes in response to stress, including apoptosis, cell cycle arrest or senescence, to exert its function in tumor suppression. Recent studies have revealed that metabolic regulation is a novel function of p53. Metabolic changes have been regarded as a hallmark of tumors and a key contributor to tumor development. p53 regulates many different aspects of metabolism, including glycolysis, mitochondrial oxidative phosphorylation, pentose phosphate pathway, fatty acid synthesis and oxidation, to maintain the homeostasis of cellular metabolism, which contributes to the role of p53 in tumor suppression. p53 is frequently mutated in human tumors. In addition to loss of tumor suppressive function, tumor-associated mutant p53 proteins often gain new tumorigenic activities, termed gain-of-function of mutant p53. Recent studies have shown that mutant p53 mediates metabolic changes in tumors as a novel gain-of-function to promote tumor development. Here we review the functions and mechanisms of wild-type and mutant p53 in metabolic regulation, and discuss their potential roles in tumorigenesis.

Methylated DNA binding domain protein 2 (MBD2) coordinately silences gene expression through activation of the microRNA hsa-mir-496 promoter in breast cancer cell line

Methylated DNA binding protein 2 (MBD2) binds methylated promoters and suppresses transcription in cis through recruitment of a chromatin modification repressor complex. We show here a new mechanism of action for MBD2: suppression of gene expression indirectly through activation of microRNA hsa-mir-496. Overexpression of MBD2 in breast epithelial cell line MCF-10A results in induced expression and demethylation of hsa-mir-496 while depletion of MBD2 in a human breast cancer cell lines MCF-7 and MDA-MB231 results in suppression of hsa-mir-496. Activation of hsa-mir-496 by MBD2 is associated with silencing of several of its target genes while depletion of MBD2 leads to induction of hsa-mir-496 target genes. Depletion of hsa-mir-496 by locked nucleic acid (LNA) antisense oligonucleotide leads to activation of these target genes in MBD2 overexpressing cells supporting that hsa-mir-496 is mediating in part the effects of MBD2 on gene expression. We demonstrate that MBD2 binds the promoter of hsa-mir-496 in MCF-10A, MCF-7 and MDA-MB-231 cells and that it activates an in vitro methylated hsa-mir-496 promoter driving a CG-less luciferase reporter in a transient transfection assay. The activation of hsa-mir-496 is associated with reduced methylation of the promoter. Taken together these results describe a novel cascade for gene regulation by DNA methylation whereby activation of a methylated microRNA by MBD2 that is associated with loss of methylation triggers repression of downstream targets.

Epigenetics and cancer metabolism

Cancer cells adapt their metabolism to support proliferation and survival. A hallmark of cancer, this alteration is characterized by dysfunctional metabolic enzymes, changes in nutrient availability, tumor microenvironment and oncogenic mutations. Metabolic rewiring in cancer is tightly connected to changes at the epigenetic level. Enzymes that mediate epigenetic status of cells catalyze posttranslational modifications of DNA and histones and influence metabolic gene expression. These enzymes require metabolites that are used as cofactors and substrates to carry out reactions. This interaction of epigenetics and metabolism constitutes a new avenue of cancer biology and could lead to new insights for the development of anti-cancer therapeutics.

Mitochondrial retrograde signaling at the crossroads of tumor bioenergetics, genetics and epigenetics

Mitochondria play a central role not only in energy production but also in the integration of metabolic pathways as well as signals for apoptosis and autophagy. It is becoming increasingly apparent that mitochondria in mammalian cells play critical roles in the initiation and propagation of various signaling cascades. In particular, mitochondrial metabolic and respiratory states and status on mitochondrial genetic instability are communicated to the nucleus as an adaptive response through retrograde signaling. Each mammalian cell contains multiple copies of the mitochondrial genome (mtDNA). A reduction in mtDNA copy number has been reported in various human pathological conditions such as diabetes, obesity, neurodegenerative disorders, aging and cancer. Reduction in mtDNA copy number disrupts mitochondrial membrane potential (Δψm) resulting in dysfunctional mitochondria. Dysfunctional mitochondria trigger retrograde signaling and communicate their changing metabolic and functional state to the nucleus as an adaptive response resulting in an altered nuclear gene expression profile and altered cell physiology and morphology. In this review, we provide an overview of the various modes of mitochondrial retrograde signaling focusing particularly on the Ca(2+)/Calcineurin mediated retrograde signaling. We discuss the contribution of the key factors of the pathway such as Calcineurin, IGF1 receptor, Akt kinase and HnRNPA2 in the propagation of signaling and their role in modulating genetic and epigenetic changes favoring cellular reprogramming towards tumorigenesis.

p53 regulates glucose metabolism by miR-34a

Cancer cells rely mainly on glycolysis rather than mitochondrial respiration for energy production, which is called the Warburg effect. p53 mutations are observed in about half of cancer cases, and p53 controls the cell cycle and cell death in response to cellular stressors. p53 has been emphasized as a metabolic regulator involved in glucose, glutamine, and purine metabolism. Here, we demonstrated metabolic changes in cancer that occurred through p53. We found that p53-inducible microRNA-34a (miR-34a) repressed glycolytic enzymes (hexokinase 1, hexokinase 2, glucose-6-phosphate isomerase), and pyruvate dehydrogenase kinase 1. Treatment with an anti-miR-34a inhibitor relieved the decreased expression in these enzymes following DNA damage. miR-34a-mediated inhibition of these enzymes resulted in repressed glycolysis and enhanced mitochondrial respiration. The results suggest that p53 has a miR-34a-dependent integrated mechanism to regulate glucose metabolism.

Hepatitis B virus X protein-induced aberrant epigenetic modifications contributing to human hepatocellular carcinoma pathogenesis

Hepatocellular carcinoma (HCC) remains one of the most prevalent malignant diseases worldwide, and the majority of cases are related to hepatitis B virus (HBV) infection. Interactions between the HBV-encoded X (HBx) protein and host factors are known to play major roles in the onset and progression of HBV-related HCC. These dynamic molecular mechanisms are extremely complex and lead to prominent changes in the host genetic and epigenetic architecture. This review summarizes the current knowledge about HBx-induced epigenetic changes, including aberrations in DNA methylation, histone modifications, and microRNA expression, and their roles in HBV-infected liver cells and HBV-related HCC. Moreover, the HBx-mediated epigenetic control of HBV covalently closed circular DNA (cccDNA) is also discussed. Although this field of study is relatively new, the accumulated evidence has indicated that the epigenetic events induced by HBx play important roles in the development of HBV-related HCC. Ongoing research will help to identify practical applications of the HBV-related epigenetic signatures as biomarkers for early HCC detection or as potential targets to prevent and treat HBV-related HCC.

The Warburg effect: insights from the past decade

Several decades ago, Otto Warburg discovered that cancer cells produce energy predominantly by glycolysis; a phenomenon now termed "Warburg effect". Warburg linked mitochondrial respiratory defects in cancer cells to aerobic glycolysis; this theory of his gradually lost its importance with the lack of conclusive evidence confirming the presence of mitochondrial defects in cancer cells. Scientists began to believe that this altered mechanism of energy production in cancer cells was more of an effect than the cause. More than 50 years later, the clinical use of FDG-PET imaging in the diagnosis and monitoring of cancers rekindled the interest of the scientific community in Warburg's hypothesis. In the last ten years considerable progress in the field has advanced our understanding of the Warburg effect. However, it still remains unclear if the Warburg effect plays a causal role in cancers or it is an epiphenomenon in tumorigenesis. In this review we aim to discuss the molecular mechanisms associated with the Warburg effect with emphasis on recent advances in the field including the role of epigenetic changes, miRNAs and post-translational modification of proteins. In addition, we also discuss emerging therapeutic strategies that target the dependence of cancer cells on altered energy processing through aerobic glycolysis.

Interactions between epigenetics and metabolism in cancers

Cancer progression is accompanied by widespread transcriptional changes and metabolic alterations. While it is widely accepted that the origin of cancer can be traced to the mutations that accumulate over time, relatively recent evidence favors a similarly fundamental role for alterations in the epigenome during tumorigenesis. Changes in epigenetics that arise from post-translational modifications of histones and DNA are exploited by cancer cells to upregulate and/or downregulate the expression levels of oncogenes and tumor suppressors, respectively. Although the mechanisms behind these modifications, in particular how they lead to gene silencing and activation, are still being understood, most of the enzymatic machinery of epigenetics require metabolites as substrates or cofactors. As a result, their activities can be influenced by the metabolic state of the cell. The purpose of this review is to give an overview of cancer epigenetics and metabolism and provide examples of where they converge.

Cancer cachexia: mediators, signaling, and metabolic pathways

Cancer cachexia is characterized by a significant reduction in body weight resulting predominantly from loss of adipose tissue and skeletal muscle. Cachexia causes reduced cancer treatment tolerance and reduced quality and length of life, and remains an unmet medical need. Therapeutic progress has been impeded, in part, by the marked heterogeneity of mediators, signaling, and metabolic pathways both within and between model systems and the clinical syndrome. Recent progress in understanding conserved, molecular mechanisms of skeletal muscle atrophy/hypertrophy has provided a downstream platform for circumventing the variations and redundancy in upstream mediators and may ultimately translate into new targeted therapies.