Reduced expression of fumarate hydratase in clear cell renal cancer mediates HIF-2α accumulation and promotes migration and invasion

The Interplay between Dysregulated Metabolism and Epigenetics in Cancer

Cellular metabolism (or energetics) and epigenetics are tightly coupled cellular processes. It is arguable that of all the described cancer hallmarks, dysregulated cellular energetics and epigenetics are the most tightly coregulated. Cellular metabolic states regulate and drive epigenetic changes while also being capable of influencing, if not driving, epigenetic reprogramming. Conversely, epigenetic changes can drive altered and compensatory metabolic states. Cancer cells meticulously modify and control each of these two linked cellular processes in order to maintain their tumorigenic potential and capacity. This review aims to explore the interplay between these two processes and discuss how each affects the other, driving and enhancing tumorigenic states in certain contexts.

TMT-based comprehensive proteomic profiling identifies serum prognostic signatures of acute myeloid leukemia

Acute myeloid leukemia (AML) is classified into favorable-risk, intermediate-risk, and poor-risk subtypes. This study aimed to compare the serum proteomic signatures of the three AML subtypes and identify prognostic biomarkers for AML. Serum samples from patients with favorable-risk (n = 14), intermediate-risk (n = 19), and poor-risk AMLs (n = 18) were used for the analysis of tandem mass tag (TMT) labeling-based quantitative proteomics. Comparative analysis was performed to identify differentially expressed proteins (DEPs) between groups. Prognostic proteins were screened using binary logistics regression analysis. TMT-MS/MS proteomics analysis identified 138 DEPs. Fumarate hydratase (FH), isocitrate dehydrogenase 2 (IDH2), and enolase 1 (ENO1) were significantly upregulated in poor-risk patients compared with favorable-risk patients. ELISA assay confirmed that patients with poor-risk AMLs had higher levels of IDH2, ENO1, and FH compared with intermediate-risk AML patients. Logistics analysis identified that proteins 3-hydroxyacyl-CoA dehydrogenase type-2 (HADH, odds ratio (OR) = 1.035, p = 0.010), glutamine synthetase (GLUL, OR = 1.022, p = 0.039), and lactotransferrin (LTF, OR = 1.1224, p = 0.016) were associated with poor prognosis, and proteins ENO1 (OR = 1.154, p = 0.053), FH (OR = 1.043, p = 0.059), and IDH2 (OR = 3.350, p = 0.055) were associated with AML prognosis. This study showed that AML patients had elevated levels of FH, IDH2, ENO1, LTF, and GLUL proteins and might be at high risk of poor prognosis.

Parthenolide targets NF-κB (P50) to inhibit HIF-1α-mediated metabolic reprogramming of HCC

We focus on investigating the role of Parthenolide (Par), a small sesquiterpenoid molecule, in hepatocellular carcinoma (HCC) and its effective target.

Highly-metastatic HCC cells, MHCC97-H, were divided into the DMSO and the Par groups, of which the Par group was intervened at 5 and 10 mg/L doses. Cell viability was assessed by CCK-8 assay. Transwell chamber assay was performed to examine the metastatic and invasive abilities, while plate clone formation assay was conducted to detect the clone formation ability. For analysis of glucose uptake, glycolytic ability and lactate level, the glycolysis assay was employed. Brdu staining was performed to evaluate the cell proliferative potential. The P50 and HIF-1α levels were measured by immunofluorescence, while the expressions of p-P50 and HIF-1α were determined by Western-Blot. Small molecule–protein docking and Pull-down experiments were conducted to validate the Par–P50 binding model. After establishing the tumor-bearing mouse model, Par was administered by gavage to measure the tissue levels of P50 and HIF-1α, followed by plotting of tumor growth curves.

Par could inhibit the metastatic, invasive and clone formation abilities of MHCC97-H cells, reduce the cell proliferative potential, and suppress the glycolysis, as manifested by down-regulated level of lactate and reduced oxygen consumption. Meanwhile, Par inhibited the HIF-1α expression. We found that after silencing P50, the HIF-1α was down-regulated, the glycolytic ability decreased drastically, and the cellular metastatic and invasive abilities were suppressed. After P50 knockout, the effect of Par intervention on the MHCC97-H cells was reduced. In HCC-bearing mice, Par also exhibited an excellent anti-tumor effect, decreasing the tissue levels of P50 and HIF-1α.

This study discovers that Par can inhibit the HIF-1α-mediated glycolysis of HCC cells by targeting P50, thereby exerting an anti-tumor effect. P50 is a major effective target of Par.

Oncometabolites as Regulators of DNA Damage Response and Repair

Dysregulation of DNA damage response and repair (DDR) contributes to oncogenesis, yet also generates the potential for targeted cancer therapies by exploiting synthetic lethal interactions. Oncometabolites, small intermediates of metabolism overproduced in certain cancers, have emerged as a new mechanism of DDR modulation through their effects on multiple DNA repair pathways. Increasing evidence suggests that oncometabolite-induced DDR defects may offer the opportunity for tumor-selective chemo- and radio-sensitization. Here we review the biology of oncometabolites and diverse mechanisms by which they impact DDR, with a focus on emerging therapeutic strategies and ongoing clinical trials targeting oncometabolite-induced DDR defects in cancer.

Identification of hub genes with prognostic values in multiple myeloma by bioinformatics analysis

PURPOSE

Multiple myeloma (MM) is a malignant disease with abnormal proliferation of clonal plasma cells. Hypoxia is an important factor in the pathogenesis and development of MM. However, the underlying mechanisms are not fully understood.

MATERIAL & METHODS

To determine hub genes related to hypoxia in MM, this study took integrated bioinformatics analysis with two expression datasets (GSE80140 and GSE80545) downloaded from Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were filtrated under the condition of both p-value < 0.05 and [log2FoldChange (log2FC)] > 1. Then, gene ontology (GO) and Kyoto encyclopedia of genes and genomes enrichment (KEGG) analysis, and protein-protein interaction (PPI) network construction were utilized to further explore these DEGs. PrognoScan evaluated all the candidate hub genes for survival analysis.

RESULTS

In total, three hub genes, including FH, TSTA3, and POLR3G, were screened out to be related to hypoxia in MM. Patients with the lower expression level of FH, TSTA3, and POLR3G have statistically significantly longer disease- specific survival (Cox p < 0.05).

CONCLUSION

We identified FH, TSTA3, and POLR3G as hub genes which can affect MM patients'outcome and new biomarkers for diagnosis and prognosis of MM. Further functional and mechanistic studies are need to develop in order to make them as potential target for clinical treatment.

Metabolic reprogramming in renal cancer: Events of a metabolic disease

Recent studies have established that tumors can reprogram the pathways involved in nutrient uptake and metabolism to withstand the altered biosynthetic, bioenergetics and redox requirements of cancer cells. This phenomenon is called metabolic reprogramming, which is promoted by the loss of tumor suppressor genes and activation of oncogenes. Because of alterations and perturbations in multiple metabolic pathways, renal cell carcinoma (RCC) is sometimes termed as a "metabolic disease". The majority of metabolic reprogramming in renal cancer is caused by the inactivation of von Hippel-Lindau (VHL) gene and activation of the Ras-PI3K-AKT-mTOR pathway. Hypoxia-inducible factor (HIF) and Myc are other important players in the metabolic reprogramming of RCC. All types of RCCs are associated with reprogramming of glucose and fatty acid metabolism and the tricarboxylic acid (TCA) cycle. Metabolism of glutamine, tryptophan and arginine is also reprogrammed in renal cancer to favor tumor growth and oncogenesis. Together, understanding these modifications or reprogramming of the metabolic pathways in detail offer ample opportunities for the development of new therapeutic targets and strategies, discovery of biomarkers and identification of effective tumor detection methods.

Reprogramming of Metabolism in Kidney Cancer

Metabolic reprogramming is one of the major steps that tumor cells take during cancer progression. This process allows the cells to survive in a nutrient- and oxygen-deprived environment, to become stress tolerant, and to metastasize to different sites. Recent studies have shown that reprogramming happens in stromal cells and involves the cross-talk of the cancer cell/tumor microenvironment. There are similarities between the metabolic reprogramming that occurs in both noncancerous kidney diseases and renal cell carcinoma (RCC), suggesting that such reprogramming is a means by which renal epithelial cells survive injury and repair the tissue, and that RCC cells hijack this system. This article reviews reprogramming of major metabolism pathways in RCC, highlighting similarities and differences from kidney diseases and potential therapeutic strategies against it.

Isocitrate dehydrogenase 3A, a rate-limiting enzyme of the TCA cycle, promotes hepatocellular carcinoma migration and invasion through regulation of MTA1, a core component of the NuRD complex

The precise molecular mechanism of hepatocellular carcinoma (HCC) remains ambiguous. Isocitrate dehydrogenase 3A (IDH3A) is known as a subunit of the IDH3 heterotetramer. To the best of our knowledge, the biological effect of IDH3A in malignant tumors is unclear. Here, we report that IDH3A is significantly upregulated in HCC tissues; moreover, high expression of IDH3A is strongly associated with tumor size and the clinicopathologic stage of HCC. RNA-seq revealed that depletion of IDH3A affects the expression of metastasis associated 1 (MTA1), an oncogene which is related to the progression of numerous cancer types to the metastasis stage. Cell transfection was used to upregulate and downregulate the expression of IDH3A in HCC cells. The migration activity of HCC cells was assessed using wound healing assays. While transwell assays were carried out to detect the invasion of HCC cells. RNA-seq, RT-qPCR and western blot were used to validate MTA1 as a potential target gene. The present study suggested that IDH3A can upregulate MTA1 expression and promote epithelial-mesenchymal transition (EMT) in HCC by inducing MTA1 expression, thereby facilitating cell migration and invasion of HCC cells. Here, we demonstrated the importance of IDH3A in HCC progression. The identification of the IDH3A axis provides novel insight into the pathogenesis of HCC, and the IDH3A axis might represent a novel target for the treatment of HCC.

Role of the mitochondrial stress response in human cancer progression

IMPACT STATEMENT

Dysregulated mitochondria often occurred in cancers. Mitochondrial dysfunction might contribute to cancer progression. We reviewed several mitochondrial stresses in cancers. Mitochondrial stress responses might contribute to cancer progression. Several mitochondrion-derived molecules (ROS, Ca2+, oncometabolites, exported mtDNA, mitochondrial double-stranded RNA, humanin, and MOTS-c), integrated stress response, and mitochondrial unfolded protein response act as retrograde signaling pathways and might be critical in the development and progression of cancer. Targeting these mitochondrial stress responses may be an important strategy for cancer treatment.

Metabolic Heterogeneity of Cancer Cells: An Interplay between HIF-1, GLUTs, and AMPK

It has been long recognized that cancer cells reprogram their metabolism under hypoxia conditions due to a shift from oxidative phosphorylation (OXPHOS) to glycolysis in order to meet elevated requirements in energy and nutrients for proliferation, migration, and survival. However, data accumulated over recent years has increasingly provided evidence that cancer cells can revert from glycolysis to OXPHOS and maintain both reprogrammed and oxidative metabolism, even in the same tumor. This phenomenon, denoted as cancer cell metabolic plasticity or hybrid metabolism, depends on a tumor micro-environment that is highly heterogeneous and influenced by an intensity of vasculature and blood flow, oxygen concentration, and nutrient and energy supply, and requires regulatory interplay between multiple oncogenes, transcription factors, growth factors, and reactive oxygen species (ROS), among others. Hypoxia-inducible factor-1 (HIF-1) and AMP-activated protein kinase (AMPK) represent key modulators of a switch between reprogrammed and oxidative metabolism. The present review focuses on cross-talks between HIF-1, glucose transporters (GLUTs), and AMPK with other regulatory proteins including oncogenes such as c-Myc, p53, and KRAS; growth factor-initiated protein kinase B (PKB)/Akt, phosphatydyl-3-kinase (PI3K), and mTOR signaling pathways; and tumor suppressors such as liver kinase B1 (LKB1) and TSC1 in controlling cancer cell metabolism. The multiple switches between metabolic pathways can underlie chemo-resistance to conventional anti-cancer therapy and should be taken into account in choosing molecular targets to discover novel anti-cancer drugs.

Oncometabolites in renal cancer

The study of cancer metabolism has evolved vastly beyond the remit of tumour proliferation and survival with the identification of the role of 'oncometabolites' in tumorigenesis. Simply defined, oncometabolites are conventional metabolites that, when aberrantly accumulated, have pro-oncogenic functions. Their discovery has led researchers to revisit the Warburg hypothesis, first postulated in the 1950s, of aberrant metabolism as an aetiological determinant of cancer. As such, the identification of oncometabolites and their utilization in diagnostics and prognostics, as novel therapeutic targets and as biomarkers of disease, are areas of considerable interest in oncology. To date, fumarate, succinate, L-2-hydroxyglutarate (L-2-HG) and D-2-hydroxyglutarate (D-2-HG) have been characterized as bona fide oncometabolites. Extensive metabolic reprogramming occurs during tumour initiation and progression in renal cell carcinoma (RCC) and three oncometabolites - fumarate, succinate and L-2-HG - have been implicated in this disease process. All of these oncometabolites inhibit a superfamily of enzymes known as α-ketoglutarate-dependent dioxygenases, leading to epigenetic dysregulation and induction of pseudohypoxic phenotypes, and also have specific pro-oncogenic capabilities. Oncometabolites could potentially be exploited for the development of novel targeted therapies and as biomarkers of disease.

Rescue of TCA Cycle Dysfunction for Cancer Therapy

Mitochondrion, a maternally hereditary, subcellular organelle, is the site of the tricarboxylic acid (TCA) cycle, electron transport chain (ETC), and oxidative phosphorylation (OXPHOS)—the basic processes of ATP production. Mitochondrial function plays a pivotal role in the development and pathology of different cancers. Disruption in its activity, like mutations in its TCA cycle enzymes, leads to physiological imbalances and metabolic shifts of the cell, which contributes to the progression of cancer. In this review, we explored the different significant mutations in the mitochondrial enzymes participating in the TCA cycle and the diseases, especially cancer types, that these malfunctions are closely associated with. In addition, this paper also discussed the different therapeutic approaches which are currently being developed to address these diseases caused by mitochondrial enzyme malfunction.

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 key regulatory genes drive tumor initiation, growth, metastasis, and drug resistance. Instead, the advent of high-throughput technologies has revolutionized cancer research, allowing to investigate molecular alterations at multiple levels, including genome, epigenome, transcriptome, proteome, and metabolome and showing the multifaceted aspects of this disease. The multi-omics approaches revealed an intricate molecular landscape where different cellular functions are interconnected and cooperatively contribute to shaping the malignant phenotype. Recent evidence has brought to light how metabolism and epigenetics are highly intertwined, and their aberrant crosstalk can contribute to tumorigenesis. The oncogene-driven metabolic plasticity of tumor cells supports the energetic and anabolic demands of proliferative tumor programs and secondary can alter the epigenetic landscape via modulating the production and/or the activity of epigenetic metabolites. Conversely, epigenetic mechanisms can regulate the expression of metabolic genes, thereby altering the metabolome, eliciting adaptive responses to rapidly changing environmental conditions, and sustaining malignant cell survival and progression in hostile niches. Thus, cancer cells take advantage of the epigenetics-metabolism crosstalk to acquire aggressive traits, promote cell proliferation, metastasis, and pluripotency, and shape tumor microenvironment. Understanding this bidirectional relationship is crucial to identify potential novel molecular targets for the implementation of robust anti-cancer therapeutic strategies.

Non-canonical roles for metabolic enzymes and intermediates in malignant progression and metastasis

Metabolic alterations are established as a hallmark of cancer. Such hallmark changes in cancer metabolism are characterized by reprogramming of energy-producing pathways and increases in the generation of biosynthetic intermediates to meet the needs of rapidly proliferating tumor cells. Various metabolic phenotypes such as aerobic glycolysis, increased glutamine consumption, and lipolysis have also been associated with the process of metastasis. However, in addition to the energy and biosynthetic alterations, a number of secondary functions of enzymes and metabolites are emerging that specifically contribute to metastasis. Here, we describe atypical intracellular roles of metabolic enzymes, extracellular functions of metabolic enzymes, roles of metabolites as signaling molecules, and epigenetic regulation mediated by altered metabolism, all of which can affect metastatic progression. We highlight how some of these mechanisms are already being exploited for therapeutic purposes, and discuss how others show similar potential.

Oncogenic Metabolism Acts as a Prerequisite Step for Induction of Cancer Metastasis and Cancer Stem Cell Phenotype

Metastasis is a major obstacle to the efficient and successful treatment of cancer. Initiation of metastasis requires epithelial-mesenchymal transition (EMT) that is regulated by several transcription factors, including Snail and ZEB1/2. EMT is closely linked to the acquisition of cancer stem cell (CSC) properties and chemoresistance, which contribute to tumor malignancy. Tumor suppressor p53 inhibits EMT and metastasis by negatively regulating several EMT-inducing transcription factors and regulatory molecules; thus, its inhibition is crucial in EMT, invasion, metastasis, and stemness. Metabolic alterations are another hallmark of cancer. Most cancer cells are more dependent on glycolysis than on mitochondrial oxidative phosphorylation for their energy production, even in the presence of oxygen. Cancer cells enhance other oncogenic metabolic pathways, such as glutamine metabolism, pentose phosphate pathway, and the synthesis of fatty acids and cholesterol. Metabolic reprogramming in cancer is regulated by the activation of oncogenes or loss of tumor suppressors that contribute to tumor progression. Oncogenic metabolism has been recently linked closely with the induction of EMT or CSC phenotypes by the induction of several metabolic enzyme genes. In addition, several transcription factors and molecules involved in EMT or CSCs, including Snail, Dlx-2, HIF-1α, STAT3, TGF-β, Wnt, and Akt, regulate oncogenic metabolism. Moreover, p53 induces metabolic change by directly regulating several metabolic enzymes. The collective data indicate the importance of oncogenic metabolism in the regulation of EMT, cell invasion and metastasis, and adoption of the CSC phenotype, which all contribute to malignant transformation and tumor development. In this review, we highlight the oncogenic metabolism as a key regulator of EMT and CSC, which is related with tumor progression involving metastasis and chemoresistance. Targeting oncometabolism might be a promising strategy for the development of effective anticancer therapy.

Germline mutations of renal cancer predisposition genes and clinical relevance in Chinese patients with sporadic, early-onset disease

BACKGROUND

An inherited susceptibility to renal cancers is associated with multiple predisposing genes, but most screening tests are limited to patients with a family history. Next-generation sequencing (NGS)-based multigene panels provide an efficient and adaptable tool for investigating pathogenic germline mutations on a larger scale. This study investigated the frequency of pathogenic germline mutations in renal cancer predisposition genes in patients with sporadic, early-onset disease.

METHODS

An NGS-based panel of 23 known and potential renal cancer predisposition genes was used to analyze germline mutations in 190 unrelated Chinese patients under the age of 45 years who presented with renal tumors. The detected variants were filtered for pathogenicity, and then their frequencies were calculated and correlated with clinical features. Germline variants of the fumarate hydratase (FH) and BRCA1-associated protein 1 (BAP1) genes were comprehensively analyzed because of their aggressive potential.

RESULTS

In total, 18 patients (9.5%) had germline mutations in 10 genes. Twelve of these 18 patients had alterations in renal cancer predisposition genes (6.3%), and 6 patients had mutations in potential predisposition genes such as BRCA1/2. Notably, pathogenic mutation carriers had a significant family history in second-degree relatives in comparison with those without pathogenic mutations (P < .001). Variants of unknown clinical significance in FH and BAP1 demonstrated evidence of additional somatic loss in tumors.

CONCLUSIONS

In patients with early-onset disease, a multigene panel identified a high pathogenic germline mutation rate in renal cancer predisposition genes. This study emphasizes the importance of screening patients with early-onset disease for mutations in cancer predisposition genes. Germline screening should be encouraged in early-onset patients to provide personalized medicine and improve patient outcomes.

Emerging evidence for targeting mitochondrial metabolic dysfunction in cancer therapy

Mammalian cells use a complex network of redox-dependent processes necessary to maintain cellular integrity during oxidative metabolism, as well as to protect against and/or adapt to stress. The disruption of these redox-dependent processes, including those in the mitochondria, creates a cellular environment permissive for progression to a malignant phenotype and the development of resistance to commonly used anticancer agents. An extension of this paradigm is that when these mitochondrial functions are altered by the events leading to transformation and ensuing downstream metabolic processes, they can be used as molecular biomarkers or targets in the development of new therapeutic interventions to selectively kill and/or sensitize cancer versus normal cells. In this Review we propose that mitochondrial oxidative metabolism is altered in tumor cells, and the central theme of this dysregulation is electron transport chain activity, folate metabolism, NADH/NADPH metabolism, thiol-mediated detoxification pathways, and redox-active metal ion metabolism. It is proposed that specific subgroups of human malignancies display distinct mitochondrial transformative and/or tumor signatures that may benefit from agents that target these pathways.

Hemangioblastoma in Hereditary Leiomyomatosis and Renal Cell Cancer Syndrome: a phenotypic overlap between VHL and HLRCC Syndromes

Hemangioblastomas are rare vascularized central nervous system tumors, which can occur sporadically or be associated with von Hippel Lindau Syndrome. The pathogenesis of hemangioblastomas in von Hippel Lindau Syndrome is proposed to involve a pseudohypoxic intracellular state induced by dysregulation of hypoxia inducible factor alpha due to the absence of von Hippel Lindau protein complex mediated destruction. Dysregulation of fumarate hydratase, a tricarboxylic acid cycle enzyme, occurs in Hereditary Leiomyomatosis and Renal Cell Cancer Syndrome due to germline fumarate hydratase gene mutations, and also results in oncogenesis via hypoxia inducible factor alpha dysregulation. We present a case study of hemangioblastoma occurrence in a Hereditary Leiomyomatosis and Renal Cell Cancer Syndrome patient and propose it as possible evidence of a phenotypic overlap between von Hippel Lindau and Hereditary Leiomyomatosis and Renal Cell Cancer Syndromes due to their overlapping role in the biochemical regulation of hypoxia inducible factor alpha.

Leiomyoma with bizarre nuclei: a morphological, immunohistochemical and molecular analysis of 31 cases

Leiomyomas associated with hereditary leiomyomatosis and renal cell carcinoma syndrome and leiomyomas with bizarre nuclei often show overlapping morphological features, in particular cells with prominent eosinophilic nucleoli, perinucleolar halos, and eosinophilic cytoplasmic inclusions. Although hereditary leiomyomatosis and renal cell carcinoma syndrome is defined by fumarate hydratase (FH) germline mutations, resulting in S-(2-succino)-cysteine (2SC) formation, it is unknown whether leiomyomas with bizarre nuclei show similar alterations. In this study, we evaluated the morphology and FH/2SC immunoprofile of 31 leiomyomas with bizarre nuclei. DNA from tumor and normal tissues from 24 cases was subjected to massively parallel sequencing targeting 410 key cancer genes. Somatic genetic alterations were detected using state-of-the-art bioinformatics algorithms. No patient reported a personal history of renal neoplasia or cutaneous leiomyomas, but one had a family history of renal cell carcinoma while another had a family history of uterine leiomyomas. Aberrant FH/2SC expression was noted in 17 tumors (16 FH-negative/2SC-positive, 1 FH-positive/2SC-positive). On univariate analysis, staghorn vessels, eosinophilic cytoplasmic inclusions, diffuse distribution of prominent eosinophilic nucleoli with perinucleolar halos, and an 'alveolar pattern of edema' were associated with an abnormal immunoprofile, but only staghorn vessels remained significant on multivariate analysis. Massively parallel sequencing analysis (n=24) revealed that 13/14 tumors with aberrant FH/2SC immunoprofile harbored somatic FH somatic genetic alterations, including homozygous deletions (n=9), missense mutations coupled with loss of heterozygosity (n=3), and a splice site mutation (n=1), whereas no somatic FH mutations/deletions were found in tumors with normal immunoprofile (n=10; P<0.0001). Leiomyomas with bizarre nuclei with normal FH/2SC staining pattern more frequently harbored TP53 and/or RB1 alterations than those with aberrant FH/2SC immunoprofile (60 vs 14%; P=0.032). These data demonstrate that leiomyomas with bizarre nuclei are morphologically and genetically heterogeneous and that hereditary leiomyomatosis and renal cell carcinoma syndrome-related morphological features, abnormal FH/2SC staining, and somatic FH mutations/deletions can be seen in a subset of sporadic tumors.

Reprogramming of central carbon metabolism in cancer stem cells

Cancer metabolism has been studied for years and adopted in the clinic for monitoring disease progression and therapy response. Despite our growing knowledge of a distinctly altered metabolic behavior in cancer, drugs targeting cancer metabolism have remained less than promising. Recent efforts in cancer stem cell (CSC) biology suggest that a subpopulation of tumor-initiating cells within the tumor bulk represents the root of tumor recurrence and therapy resistance. In recent years, metabolic phenotype of CSCs of various tumor types has been identified. This breakthrough has shed light on the underlying mechanism by which CSCs maintain stemness, confer resistance to therapies and initiate tumor relapse. The distinct metabolic characteristics of CSCs compared to non-CSCs provide an opportunity to target CSCs more specifically and have become a major focus in cancer research in recent years with substantial efforts conducted towards discovering clinical targets. This perspective article summarizes the current knowledge of CSC metabolism in carcinogenesis and highlights the potential of targeting CSC metabolism for therapy.

Genetic alterations in Krebs cycle and its impact on cancer pathogenesis

Cancer cells exhibit alterations in many cellular processes, including oxygen sensing and energy metabolism. Glycolysis in non-oxygen condition is the main energy production process in cancer rather than mitochondrial respiration as in benign cells. Genetic and epigenetic alterations of Krebs cycle enzymes favour the shift of cancer cells from oxidative phosphorylation to anaerobic glycolysis. Mutations in genes encoding aconitase, isocitrate dehydrogenase, succinate dehydrogenase, fumarate hydratase, and citrate synthase are noted in many cancers. Abnormalities of Krebs cycle enzymes cause ectopic production of Krebs cycle intermediates (oncometabolites) such as 2-hydroxyglutarate, and citrate. These oncometabolites stabilize hypoxia inducible factor 1 (HIF1), nuclear factor like 2 (Nrf2), inhibit p53 and prolyl hydroxylase 3 (PDH3) activities as well as regulate DNA/histone methylation, which in turn activate cell growth signalling. They also stimulate increased glutaminolysis, glycolysis and production of reactive oxygen species (ROS). Additionally, genetic alterations in Krebs cycle enzymes are involved with increased fatty acid β-oxidations and epithelial mesenchymal transition (EMT) induction. These altered phenomena in cancer could in turn promote carcinogenesis by stimulating cell proliferation and survival. Overall, epigenetic and genetic changes of Krebs cycle enzymes lead to the production of oncometabolite intermediates, which are important driving forces of cancer pathogenesis and progression. Understanding and applying the knowledge of these mechanisms opens new therapeutic options for patients with cancer.

Metabolic changes associated with tumor metastasis, part 2: Mitochondria, lipid and amino acid metabolism

Metabolic alterations are a hallmark of cancer controlling tumor progression and metastasis. Among the various metabolic phenotypes encountered in tumors, this review focuses on the contributions of mitochondria, lipid and amino acid metabolism to the metastatic process. Tumor cells require functional mitochondria to grow, proliferate and metastasize, but shifts in mitochondrial activities confer pro-metastatic traits encompassing increased production of mitochondrial reactive oxygen species (mtROS), enhanced resistance to apoptosis and the increased or de novo production of metabolic intermediates of the TCA cycle behaving as oncometabolites, including succinate, fumarate, and D-2-hydroxyglutarate that control energy production, biosynthesis and the redox state. Lipid metabolism and the metabolism of amino acids, such as glutamine, glutamate and proline are also currently emerging as focal control points of cancer metastasis.

Role of mitochondrial dysfunction in cancer progression

Deregulated cellular energetics was one of the cancer hallmarks. Several underlying mechanisms of deregulated cellular energetics are associated with mitochondrial dysfunction caused by mitochondrial DNA mutations, mitochondrial enzyme defects, or altered oncogenes/tumor suppressors. In this review, we summarize the current understanding about the role of mitochondrial dysfunction in cancer progression. Point mutations and copy number changes are the two most common mitochondrial DNA alterations in cancers, and mitochondrial dysfunction induced by chemical depletion of mitochondrial DNA or impairment of mitochondrial respiratory chain in cancer cells promotes cancer progression to a chemoresistance or invasive phenotype. Moreover, defects in mitochondrial enzymes, such as succinate dehydrogenase, fumarate hydratase, and isocitrate dehydrogenase, are associated with both familial and sporadic forms of cancer. Deregulated mitochondrial deacetylase sirtuin 3 might modulate cancer progression by regulating cellular metabolism and oxidative stress. These mitochondrial defects during oncogenesis and tumor progression activate cytosolic signaling pathways that ultimately alter nuclear gene expression, a process called retrograde signaling. Changes in the intracellular level of reactive oxygen species, Ca(2+), or oncometabolites are important in the mitochondrial retrograde signaling for neoplastic transformation and cancer progression. In addition, altered oncogenes/tumor suppressors including hypoxia-inducible factor 1 and tumor suppressor p53 regulate mitochondrial respiration and cellular metabolism by modulating the expression of their target genes. We thus suggest that mitochondrial dysfunction plays a critical role in cancer progression and that targeting mitochondrial alterations and mitochondrial retrograde signaling might be a promising strategy for the development of selective anticancer therapy.

A holistic view of cancer bioenergetics: mitochondrial function and respiration play fundamental roles in the development and progression of diverse tumors

Since Otto Warburg made the first observation that tumor cells exhibit altered metabolism and bioenergetics in the 1920s, many scientists have tried to further the understanding of tumor bioenergetics. Particularly, in the past decade, the application of the state-of the-art metabolomics and genomics technologies has revealed the remarkable plasticity of tumor metabolism and bioenergetics. Firstly, a wide array of tumor cells have been shown to be able to use not only glucose, but also glutamine for generating cellular energy, reducing power, and metabolic building blocks for biosynthesis. Secondly, many types of cancer cells generate most of their cellular energy via mitochondrial respiration and oxidative phosphorylation. Glutamine is the preferred substrate for oxidative phosphorylation in tumor cells. Thirdly, tumor cells exhibit remarkable versatility in using bioenergetics substrates. Notably, tumor cells can use metabolic substrates donated by stromal cells for cellular energy generation via oxidative phosphorylation. Further, it has been shown that mitochondrial transfer is a critical mechanism for tumor cells with defective mitochondria to restore oxidative phosphorylation. The restoration is necessary for tumor cells to gain tumorigenic and metastatic potential. It is also worth noting that heme is essential for the biogenesis and proper functioning of mitochondrial respiratory chain complexes. Hence, it is not surprising that recent experimental data showed that heme flux and function are elevated in non-small cell lung cancer (NSCLC) cells and that elevated heme function promotes intensified oxygen consumption, thereby fueling tumor cell proliferation and function. Finally, emerging evidence increasingly suggests that clonal evolution and tumor genetic heterogeneity contribute to bioenergetic versatility of tumor cells, as well as tumor recurrence and drug resistance. Although mutations are found only in several metabolic enzymes in tumors, diverse mutations in signaling pathways and networks can cause changes in the expression and activity of metabolic enzymes, which likely enable tumor cells to gain their bioenergetic versatility. A better understanding of tumor bioenergetics should provide a more holistic approach to investigate cancer biology and therapeutics. This review therefore attempts to comprehensively consider and summarize the experimental data supporting our latest view of cancer bioenergetics.

Papillary renal cell carcinoma: A review of the current therapeutic landscape

Renal cell carcinoma (RCC) is the most common cancer of the kidney and accounts for 2-3% of all adult malignancies. Clear cell carcinoma represents the most common histologic subtype, while papillary Renal Cell Carcinoma (pRCC) accounts for 10-20% of all renal cell cancers. While the inactivation of VHL gene can be found in the majority of clear cell carcinomas, different molecular mechanisms are involved into pRCC biology. Mutations in the MET oncogene are an essential step into the pathogenesis of hereditary pRCC forms, but they can be found only in a small rate of sporadic cases. Several agents, including anti-VEGF drugs and mTOR inhibitors, are possible options in the treatment of advanced and metastatic pRCC, following the demonstration of efficacy obtained in clinical trials including all RCC histologic subtypes. However, data specifically obtained in the subgroup of patients affected by pRCC are limited and not conclusive. Several ongoing trials are evaluating the efficacy of targeted therapy in papillary form. However, more rationale approaches based on molecular studies would help improving the outcome of these patients. Among others, MET inhibitors and targeted immunotherapy are promising new strategies for hereditary and sporadic disease. This review summarizes current knowledge on pRCC tumorigenesis and discusses recent and ongoing clinical trials with new therapeutic agents.

OVCAR-3 spheroid-derived cells display distinct metabolic profiles

Introduction

Recently, multicellular spheroids were isolated from a well-established epithelial ovarian cancer cell line, OVCAR-3, and were propagated in vitro. These spheroid-derived cells displayed numerous hallmarks of cancer stem cells, which are chemo- and radioresistant cells thought to be a significant cause of cancer recurrence and resultant mortality. Gene set enrichment analysis of expression data from the OVCAR-3 cells and the spheroid-derived putative cancer stem cells identified several metabolic pathways enriched in differentially expressed genes. Before this, there had been little previous knowledge or investigation of systems-scale metabolic differences between cancer cells and cancer stem cells, and no knowledge of such differences in ovarian cancer stem cells.

Methods

To determine if there were substantial metabolic changes corresponding with these transcriptional differences, we used two-dimensional gas chromatography coupled to mass spectrometry to measure the metabolite profiles of the two cell lines.

Results

These two cell lines exhibited significant metabolic differences in both intracellular and extracellular metabolite measurements. Principal components analysis, an unsupervised dimensional reduction technique, showed complete separation between the two cell types based on their metabolite profiles. Pathway analysis of intracellular metabolomics data revealed close overlap with metabolic pathways identified from gene expression data, with four out of six pathways found enriched in gene-level analysis also enriched in metabolite-level analysis. Some of those pathways contained multiple metabolites that were individually statistically significantly different between the two cell lines, with one of the most broadly and consistently different pathways, arginine and proline metabolism, suggesting an interesting hypothesis about cancerous and stem-like metabolic phenotypes in this pair of cell lines.

Conclusions

Overall, we demonstrate for the first time that metabolism in an ovarian cancer stem cell line is distinct from that of more differentiated isogenic cancer cells, supporting the potential importance of metabolism in the differences between cancer cells and cancer stem cells.

Leiomyoma cutis: a focused review on presentation, management, and association with malignancy

Cutaneous leiomyomas (CLs) are rare, sporadic, or inherited tumors of smooth muscle origin associated with various disorders. Hereditary leiomyomatosis and renal cell cancer (HLRCC) is the primary tumor predisposition syndrome associated with inherited CLs, affecting 180 families worldwide, with significant mortality. CLs are subdivided into piloleiomyomas, genital leiomyomas, and angioleiomyomas based on their smooth muscle of origin, as well as their clinicopathologic features. Piloleiomyomas, derived from arrector pili muscle, are solitary or multiple firm papulonodules located typically on the extremities and trunk; genital leiomyomas, derived from dartoic, vulvar, or mammary smooth muscle, are solitary papulonodules or pedunculated papules located on the scrotum, vulva, or nipple; and angioleiomyomas, which include solid, cavernous, or venous subtypes, are derived from the tunica media of small arteries and veins and typically present on the extremities. Partial/excisional biopsy is required for diagnosing all CLs. Histology shows interlacing fascicles of spindle cells with moderate amounts of eosinophilic cytoplasm and a blunt-ended, elongated nucleus with perinuclear halos. Surgical excision is curative for CLs, with other management options including medical or destructive therapy; active surveillance is advised to monitor HLRCC-associated neoplasms, with pharmacological therapies under active research.

Targeting ABL1-mediated oxidative stress adaptation in fumarate hydratase-deficient cancer

Patients with germline fumarate hydratase (FH) mutation are predisposed to develop aggressive kidney cancer with few treatment options and poor therapeutic outcomes. Activity of the proto-oncogene ABL1 is upregulated in FH-deficient kidney tumors and drives a metabolic and survival signaling network necessary to cope with impaired mitochondrial function and abnormal accumulation of intracellular fumarate. Excess fumarate indirectly stimulates ABL1 activity, while restoration of wild-type FH abrogates both ABL1 activation and the cytotoxicity caused by ABL1 inhibition or knockdown. ABL1 upregulates aerobic glycolysis via the mTOR/HIF1α pathway and neutralizes fumarate-induced proteotoxic stress by promoting nuclear localization of the antioxidant response transcription factor NRF2. Our findings identify ABL1 as a pharmacologically tractable therapeutic target in glycolytically dependent, oxidatively stressed tumors.

Bioinformatics analysis and expression study of fumarate hydratase in lung cancer

BACKGROUND

As its etiology and pathogenesis is obscure, illustrating the molecular mechanism of lung cancer has become a serious and urgent task. Studies have shown that fumarate hydratase (FH) is a tumor suppressor related to tumorigenesis, development, and invasion. Our aim was to analyze the biological information of FH, and detect the messenger ribonucleic acid (mRNA) and protein expression of FH in lung cancer cells to explore its role in tumorigenesis and in the development of lung cancer.

METHOD

We analyzed the biological characteristics of FH, then utilized reverse transcription-polymerase chain reaction (RT-PCR) to study FH mRNA expression in A549 and 16 human bronchial epithelial (HBE) cell lines. The protein expression of FH was detected in 57 cases of human lung cancer tissues and 19 cases of normal lung tissues by immunohistochemistry.

RESULTS

1. Bioinformatic analysis: FH mainly exist in the mitochondria; the common structural elements of FH are mainly α-helix, random coil, β-turn, and extended strand; there are five possible transmembrane domains in the entire polypeptide chain; FH is a hydrophilic and soluble protein. 2. RT-PCR result: FH mRNA expression was downregulated in A549 cells compared with 16HBE cells. 3. Immunohistochemistry: FH protein expression was significantly lower in lung cancer cells than in normal lung tissues (P < 0.05), but was not correlated with the patients' age, gender, tumor size, pathological type, or lymph node, distant, or tumor node metastasis stage.

CONCLUSION

FH was under-expressed in lung cancer, suggesting that it may be an indicator of tumorigenesis and could be a potential target for therapies against lung cancer in the future.

Defects in mitochondrial metabolism and cancer

Cancer is a heterogeneous set of diseases characterized by different molecular and cellular features. Over the past decades, researchers have attempted to grasp the complexity of cancer by mapping the genetic aberrations associated with it. In these efforts, the contribution of mitochondria to the pathogenesis of cancer has tended to be neglected. However, more recently, a growing body of evidence suggests that mitochondria play a key role in cancer. In fact, dysfunctional mitochondria not only contribute to the metabolic reprogramming of cancer cells but they also modulate a plethora of cellular processes involved in tumorigenesis. In this review, we describe the link between mutations to mitochondrial enzymes and tumor formation. We also discuss the hypothesis that mutations to mitochondrial and nuclear DNA could cooperate to promote the survival of cancer cells in an evolving metabolic landscape.

The role of mitochondria in the oncogenic signal transduction

Mitochondria are intracellular organelles thought to have evolved from an alphaproteobacterium engulfed by the ancestor of the eukaryotic cell, an archeon, two billion years ago. Although mitochondria are frequently recognised as the "power plant" of the cell, the function of these organelles go beyond the simple generation of ATP. In fact, mounting evidence suggests that mitochondria are involved in several cellular processes, from regulation of cell death to signal transduction. Given this important role in cell physiology, mitochondrial dysfunction has been frequently associated with human diseases including cancer. Importantly, recent evidence suggests that mitochondrial function is directly regulated by oncogenes and tumour suppressors. However, the consequences of deregulation of mitochondrial function in tumour formation are still unclear. In this review, I propose that mitochondria play a pivotal role in shaping the oncogenic signalling cascade and that mitochondrial dysfunction, in some circumstances, is a required step for cancer transformation.

How does cancer cell metabolism affect tumor migration and invasion?

Cancer metastasis is the major cause of cancer-associated death. Accordingly, identification of the regulatory mechanisms that control whether or not tumor cells become "directed walkers" is a crucial issue of cancer research. The deregulation of cell migration during cancer progression determines the capacity of tumor cells to escape from the primary tumors and invade adjacent tissues to finally form metastases. The ability to switch from a predominantly oxidative metabolism to glycolysis and the production of lactate even when oxygen is plentiful is a key characteristic of cancer cells. This metabolic switch, known as the Warburg effect, was first described in 1920s, and affected not only tumor cell growth but also tumor cell migration. In this review, we will focus on the recent studies on how cancer cell metabolism affects tumor cell migration and invasion. Understanding the new aspects on molecular mechanisms and signaling pathways controlling tumor cell migration is critical for development of therapeutic strategies for cancer patients.

The proto-oncometabolite fumarate binds glutathione to amplify ROS-dependent signaling

The tricarboxylic acid cycle enzyme fumarate hydratase (FH) has been identified as a tumor suppressor in a subset of human renal cell carcinomas. Human FH-deficient cancer cells display high fumarate concentration and ROS levels along with activation of HIF-1. The underlying mechanisms by which FH loss increases ROS and HIF-1 are not fully understood. Here, we report that glutamine-dependent oxidative citric acid cycle metabolism is required to generate fumarate and increase ROS and HIF-1 levels. Accumulated fumarate directly bonds the antioxidant glutathione in vitro and in vivo to produce the metabolite succinated glutathione (GSF). GSF acts as an alternative substrate to glutathione reductase to decrease NADPH levels and enhance mitochondrial ROS and HIF-1 activation. Increased ROS also correlates with hypermethylation of histones in these cells. Thus, fumarate serves as a proto-oncometabolite by binding to glutathione which results in the accumulation of ROS.

Reversed argininosuccinate lyase activity in fumarate hydratase-deficient cancer cells

BACKGROUND

Loss of function of fumarate hydratase (FH), the mitochondrial tumor suppressor and tricarboxylic acid (TCA) cycle enzyme, is associated with a highly malignant form of papillary and collecting duct renal cell cancer. The accumulation of fumarate in these cells has been linked to the tumorigenic process. However, little is known about the overall effects of the loss of FH on cellular metabolism.

METHODS

We performed comprehensive metabolomic analyses of urine from Fh1-deficient mice and stable isotopologue tracing from human and mouse FH-deficient cell lines to investigate the biochemical signature of the loss of FH.

RESULTS

The metabolomics analysis revealed that the urea cycle metabolite argininosuccinate is a common metabolic biomarker of FH deficiency. Argininosuccinate was found to be produced from arginine and fumarate by the reverse activity of the urea cycle enzyme argininosuccinate lyase (ASL), making these cells auxotrophic for arginine. Depleting arginine from the growth media by the addition of pegylated arginine deiminase (ADI-PEG 20) decreased the production of argininosuccinate in FH-deficient cells and reduced cell survival and proliferation.

CONCLUSIONS

These results unravel a previously unidentified correlation between fumarate accumulation and the urea cycle enzyme ASL in FH-deficient cells. The finding that FH-deficient cells become auxotrophic for arginine opens a new therapeutic perspective for the cure of hereditary leiomyomatosis and renal cell cancer (HLRCC).

Multiple hits for the association of uterine fibroids on human chromosome 1q43

Uterine leiomyomas (or fibroids) are the most common tumors in women of reproductive age. Early studies of two familial cancer syndromes, the multiple cutaneous and uterine leiomyomatosis (MCUL1), and the hereditary leiomyomatosis and renal cell cancer (HLRCC), implicated FH, a gene on chromosome 1q43 encoding the tricarboxylic acid cycle fumarate hydratase enzyme. The role of this metabolic housekeeping gene in tumorigenesis is still a matter of debate and pseudo-hypoxia has been suggested as a pathological mechanism. Inactivating FH mutations have rarely been observed in the nonsyndromic and common form of fibroids; however, loss of heterozygosity across FH appeared as a significant event in the pathogenesis of a subset of these tumors. To assess the role of FH and the linked genes in nonsyndromic uterine fibroids, we explored a two-megabase interval spanning FH in the NIEHS Uterine fibroid study, a cross-sectional study of fibroids in 1152 premenopausal women. Association mapping with a dense set of single nucleotide polymorphisms revealed several peaks of association (p = 10(-2)-8.10(-5)) with the risk and/or growth of fibroids. In particular, genes encoding factors suspected (cytosolic FH) or known (EXO1 - exonuclease 1) to be involved in DNA mismatch repair emerged as candidate susceptibility genes whereas those acting in the autophagy/apoptosis (MAP1LC3C - microtubule-associated protein) or signal transduction (RGS7 - Regulator of G-protein and PLD5- Phospoholipase D) appeared to affect tumor growth. Furthermore, body mass index, a suspected confounder altered significantly but unpredictably the association with the candidate genes in the African and European American populations, suggesting the presence of a major obesity gene in the studied region. With the high potential for occult tumors in common conditions such as fibroids, validation of our data in family-based studies is needed.

Hyperpolarized 13C-pyruvate magnetic resonance reveals rapid lactate export in metastatic renal cell carcinomas

Renal cell carcinomas (RCC) are a heterogeneous group of tumors with a wide range of aggressiveness. Noninvasive methods to confidently predict the tumor biologic behavior and select appropriate treatment are lacking. Here, we investigate the dynamic metabolic flux in living RCC cells using hyperpolarized (13)C-pyruvate magnetic resonance spectroscopy (MRS) combined with a bioreactor platform and interrogated the biochemical basis of the MRS data with respect to cancer aggressiveness. RCC cells have significantly higher pyruvate-to-lactate flux than the normal renal tubule cells. Furthermore, a key feature distinguishing the localized from the metastatic RCC cells is the lactate efflux rate, mediated by the monocarboxylate transporter 4 (MCT4). The metastatic RCC cells have significantly higher MCT4 expression and corresponding higher lactate efflux, which is essential for maintaining a high rate of glycolysis. We show that such differential cellular transporter expression and associated metabolic phenotype can be noninvasively assessed via real-time monitoring of hyperpolarized (13)C-pyruvate-to-lactate flux.

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.

Tissue-based proteomics reveals FXYD3, S100A11 and GSTM3 as novel markers for regional lymph node metastasis in colon cancer

Regional lymph node metastasis negatively affects prognosis in colon cancer patients. The molecular processes leading to regional lymph node metastasis are only partially understood and proteomic markers for metastasis are still scarce. Therefore, a tissue-based proteomic approach was undertaken for identifying proteins associated with regional lymph node metastasis. Two complementary tissue-based proteomic methods have been employed. MALDI imaging was used for identifying small proteins (≤25 kDa) in situ and label-free quantitative proteomics was used for identifying larger proteins. A tissue cohort comprising primary colon tumours without metastasis (UICC II, pN0, n = 21) and with lymph node metastasis (UICC III, pN2, n = 33) was analysed. Subsequent validation of identified proteins was done by immunohistochemical staining on an independent tissue cohort consisting of primary colon tumour specimens (n = 168). MALDI imaging yielded ten discriminating m/z species, and label-free quantitative proteomics 28 proteins. Two MALDI imaging-derived candidate proteins (FXYD3 and S100A11) and one from the label-free quantitative proteomics (GSTM3) were validated on the independent tissue cohort. All three markers correlated significantly with regional lymph node metastasis: FXYD3 (p = 0.0110), S100A11 (p = 0.0071), and GSTM3 (p = 0.0173). FXYD3 and S100A11 were more highly expressed in UICC II patient tumour tissues. GSTM3 was more highly expressed in UICC III patient tumour tissues. By our tissue-based proteomic approach, we could identify a large panel of proteins which are associated with regional lymph node metastasis and which have not been described so far. Here we show that novel markers for regional lymph metastasis can be identified by MALDI imaging or label-free quantitative proteomics and subsequently validated on an independent tissue cohort.

HIF-1 versus HIF-2--is one more important than the other?

Hypoxia is a state where oxygen availability/delivery is below the level necessary to maintain physiological oxygen tension for a particular tissue. It is well-established that when tissue demand exceeds its oxygen supply, a cascade of intracellular events is activated, with the elevation of the expression of hypoxia-inducible factors (HIFs). As a consequence, the extensive transcriptional response regulating angiogenesis, glucose metabolism, cell growth, metastasis and others processes is induced. The discovery of differences between HIF isoforms has provided new insights into HIFs biology. Importantly, the opposite effects can be exerted by HIF-1 and HIF-2 on the regulation of angiogenic response. Although both isoforms may upregulate the expression of pro-angiogenic vascular endothelial growth factor (VEGF), HIF-1 diminished the expression of interleukin-8 (IL-8) by inhibition of the Nrf2 transcription factor whereas HIF-2 augmented expression of IL-8 in an Nrf2-independent way but via upregulation of SP-1 activity. Moreover, the opposite regulation of c-Myc transcription factor by both HIF isoforms may influence IL-8 regulation. Complexity of effects exerted by both HIF isoforms resulting from the cooperation with other transcription factors should be subjected to intensive investigation especially in the context of pro-and anti-angiogenic therapies.

Cancer and altered metabolism: potential importance of hypoxia-inducible factor and 2-oxoglutarate-dependent dioxygenases

Hypoxia-inducible factor (HIF) deregulation contributes to the Warburg effect. HIF consists of an unstable α subunit and a stable β subunit. In the presence of oxygen, HIFα becomes prolyl hydroxylated by members of the EglN (also called PHD) family, leading to its proteasomal degradation. Under hypoxic conditions, EglN activity is diminished and HIF levels rise. EglN1 is the primary HIF prolyl hydroxylase with EglN2 and EglN3 playing compensatory roles under certain conditions. EglN2 and EglN3 also appear to play HIF-independent roles in regulating cell proliferation and apoptosis, respectively. The EglNs belong to a large family of 2-oxoglutarate-dependent dioxygenases that includes the TET DNA hydroxymethylases and JmjC-containing histone demethylases. Members of this superfamily can be inhibited by endogenous metabolites, including fumarate and succinate, which accumulate in tumors that have fumarate hydratase (FH) or succinate dehydrogenase (SDH) mutations, respectively, as well as by the 2-hydroxyglutarate detected in isocitrate dehydrogenase (IDH) mutant tumors. 2-Oxoglutarate-dependent dioxygenases therefore provide a link between altered metabolism and cancer.