The acetate/ACSS2 switch regulates HIF-2 stress signaling in the tumor cell microenvironment

HIF-2α expression and metabolic signaling require ACSS2 in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is an aggressive cancer driven by VHL loss and aberrant HIF-2α signaling. Identifying means to regulate HIF-2α thus has potential therapeutic benefit. Acetyl-CoA synthetase 2 (ACSS2) converts acetate to acetyl-CoA and is associated with poor patient prognosis in ccRCC. Here we tested the effects of ACSS2 on HIF-2α and cancer cell metabolism and growth in ccRCC models and clinical samples. ACSS2 inhibition reduced HIF-2α levels and suppressed ccRCC cell line growth in vitro, in vivo, and in cultures of primary ccRCC patient tumors. This treatment reduced glycolytic signaling, cholesterol metabolism, and mitochondrial integrity, all of which are consistent with loss of HIF-2α. Mechanistically, ACSS2 inhibition decreased chromatin accessibility and HIF-2α expression and stability. While HIF-2α protein levels are widely regulated through pVHL-dependent proteolytic degradation, we identify a potential pVHL-independent pathway of degradation via the E3 ligase MUL1. We show that MUL1 can directly interact with HIF-2α and that overexpression of MUL1 decreased HIF-2α levels in a manner partially dependent on ACSS2. These findings identify multiple mechanisms to regulate HIF-2α stability and ACSS2 inhibition as a strategy to complement HIF-2α-targeted therapies and deplete pathogenically stabilized HIF-2α.

Sodium acetate increases the productivity of HEK293 cells expressing the ECD-Her1 protein in batch cultures: experimental results and metabolic flux analysis

Human Embryonic Kidney cells (HEK293) are a popular host for recombinant protein expression and production in the biotechnological industry. This has driven within both, the scientific and the engineering communities, the search for strategies to increase their protein productivity. The present work is inserted into this search exploring the impact of adding sodium acetate (NaAc) into a batch culture of HEK293 cells. We monitored, as a function of time, the cell density, many external metabolites, and the supernatant concentration of the heterologous extra-cellular domain ECD-Her1 protein, a protein used to produce a candidate prostate cancer vaccine. We observed that by adding different concentrations of NaAc (0, 4, 6 and 8 mM), the production of ECD-Her1 protein increases consistently with increasing concentration, whereas the carrying capacity of the medium decreases. To understand these results we exploited a combination of experimental and computational techniques. Metabolic Flux Analysis (MFA) was used to infer intracellular metabolic fluxes from the concentration of external metabolites. Moreover, we measured independently the extracellular acidification rate and oxygen consumption rate of the cells. Both approaches support the idea that the addition of NaAc to the culture has a significant impact on the metabolism of the HEK293 cells and that, if properly tuned, enhances the productivity of the heterologous ECD-Her1 protein.

Novel metabolomics-biohumoral biomarkers model for predicting survival of metastatic soft-tissue sarcomas

Soft tissue sarcomas (STSs) are rare malignant tumors that are difficult to prognosticate using currently available instruments. Omics sciences could provide more accurate and individualized survival predictions for patients with metastatic STS. In this pilot, hypothesis-generating study, we integrated clinicopathological variables with proton nuclear magnetic resonance (1H NMR) plasma metabolomic and lipoproteomic profiles, capturing both tumor and host characteristics, to identify novel prognostic biomarkers of 2-year survival. Forty-five metastatic STS (mSTS) patients with prevalent leiomyosarcoma and liposarcoma histotypes receiving trabectedin treatment were enrolled. A score combining acetate, triglycerides low-density lipoprotein (LDL)-2, and red blood cell count was developed, and it predicts 2-year survival with optimal results in the present cohort (84.4% sensitivity, 84.6% specificity). This score is statistically significant and independent of other prognostic factors such as age, sex, tumor grading, tumor histotype, frailty status, and therapy administered. A nomogram based on these 3 biomarkers has been developed to inform the clinical use of the present findings.

Acetate acts as a metabolic immunomodulator by bolstering T-cell effector function and potentiating antitumor immunity in breast cancer

Acetate metabolism is an important metabolic pathway in many cancers and is controlled by acetyl-CoA synthetase 2 (ACSS2), an enzyme that catalyzes the conversion of acetate to acetyl-CoA. While the metabolic role of ACSS2 in cancer is well described, the consequences of blocking tumor acetate metabolism on the tumor microenvironment and antitumor immunity are unknown. We demonstrate that blocking ACSS2, switches cancer cells from acetate consumers to producers of acetate thereby freeing acetate for tumor-infiltrating lymphocytes to use as a fuel source. We show that acetate supplementation metabolically bolsters T-cell effector functions and proliferation. Targeting ACSS2 with CRISPR-Cas9 guides or a small-molecule inhibitor promotes an antitumor immune response and enhances the efficacy of chemotherapy in preclinical breast cancer models. We propose a paradigm for targeting acetate metabolism in cancer in which inhibition of ACSS2 dually acts to impair tumor cell metabolism and potentiate antitumor immunity.

HIF: a master regulator of nutrient availability and metabolic cross-talk in the tumor microenvironment

A role for hypoxia-inducible factors (HIFs) in hypoxia-dependent regulation of tumor cell metabolism has been thoroughly investigated and covered in reviews. However, there is limited information available regarding HIF-dependent regulation of nutrient fates in tumor and stromal cells. Tumor and stromal cells may generate nutrients necessary for function (metabolic symbiosis) or deplete nutrients resulting in possible competition between tumor cells and immune cells, a result of altered nutrient fates. HIF and nutrients in the tumor microenvironment (TME) affect stromal and immune cell metabolism in addition to intrinsic tumor cell metabolism. HIF-dependent metabolic regulation will inevitably result in the accumulation or depletion of essential metabolites in the TME. In response, various cell types in the TME will respond to these hypoxia-dependent alterations by activating HIF-dependent transcription to alter nutrient import, export, and utilization. In recent years, the concept of metabolic competition has been proposed for critical substrates, including glucose, lactate, glutamine, arginine, and tryptophan. In this review, we discuss how HIF-mediated mechanisms control nutrient sensing and availability in the TME, the competition for nutrients, and the metabolic cross-talk between tumor and stromal cells.

Acss2/HIF-2 signaling facilitates colon cancer growth and metastasis

The microenvironment of solid tumors is characterized by oxygen and glucose deprivation. Acss2/HIF-2 signaling coordinates essential genetic regulators including acetate-dependent acetyl CoA synthetase 2 (Acss2), Creb binding protein (Cbp), Sirtuin 1 (Sirt1), and Hypoxia Inducible Factor 2α (HIF-2α). We previously shown in mice that exogenous acetate augments growth and metastasis of flank tumors derived from fibrosarcoma-derived HT1080 cells in an Acss2/HIF-2 dependent manner. Colonic epithelial cells are exposed to the highest acetate levels in the body. We reasoned that colon cancer cells, like fibrosarcoma cells, may respond to acetate in a pro-growth manner. In this study, we examine the role of Acss2/HIF-2 signaling in colon cancer. We find that Acss2/HIF-2 signaling is activated by oxygen or glucose deprivation in two human colon cancer-derived cell lines, HCT116 and HT29, and is crucial for colony formation, migration, and invasion in cell culture studies. Flank tumors derived from HCT116 and HT29 cells exhibit augmented growth in mice when supplemented with exogenous acetate in an Acss2/HIF-2 dependent manner. Finally, Acss2 in human colon cancer samples is most frequently localized in the nucleus, consistent with it having a signaling role. Targeted inhibition of Acss2/HIF-2 signaling may have synergistic effects for some colon cancer patients.

Acss2 Deletion Reveals Functional Versatility via Tissue-Specific Roles in Transcriptional Regulation

The coordination of cellular biological processes is regulated in part via metabolic enzymes acting to match cellular metabolism to current conditions. The acetate activating enzyme, acyl-coenzyme A synthetase short-chain family member 2 (Acss2), has long been considered to have a predominantly lipogenic function. More recent evidence suggests that this enzyme has regulatory functions in addition to its role in providing acetyl-CoA for lipid synthesis. We used Acss2 knockout mice (Acss2-/-) to further investigate the roles this enzyme plays in three physiologically distinct organ systems that make extensive use of lipid synthesis and storage, including the liver, brain, and adipose tissue. We examined the resulting transcriptomic changes resulting from Acss2 deletion and assessed these changes in relation to fatty acid constitution. We find that loss of Acss2 leads to dysregulation of numerous canonical signaling pathways, upstream transcriptional regulatory molecules, cellular processes, and biological functions, which were distinct in the liver, brain, and mesenteric adipose tissues. The detected organ-specific transcriptional regulatory patterns reflect the complementary functional roles of these organ systems within the context of systemic physiology. While alterations in transcriptional states were evident, the loss of Acss2 resulted in few changes in fatty acid constitution in all three organ systems. Overall, we demonstrate that Acss2 loss institutes organ-specific transcriptional regulatory patterns reflecting the complementary functional roles of these organ systems. Collectively, these findings provide further confirmation that Acss2 regulates key transcription factors and pathways under well-fed, non-stressed conditions and acts as a transcriptional regulatory enzyme.

Metabolic adaptations of cancer in extreme tumor microenvironments

Cancer cells are highly heterogeneous to adapt to extreme tumor microenvironments (TMEs). TMEs challenge cancer cells via hypoxia, nutrition starvation, and acidic pH, promoting invasion and metastasis concomitant with genetic, epigenetic, and metabolic alterations. Metabolic adaptation to an extreme TME could allow cancer cells to evade cell death and immune responses, as well as resulting in drug resistance, recurrence, and poor patient prognosis. Therefore, elucidation of the metabolic adaptation of malignant cancer cells within TMEs is necessary, however, most are still elusive. Recently, adaptation of cancer cells within the TME can be analyzed via cell-cell interactions at the single-cell level. In addition, information into organelle-organelle interactions has recently been obtained. These cell-cell, and organelle-organelle interactions demonstrate the potential as new cancer therapy targets, as they play essential roles in the metabolic adaptation of cancer cells to the TME. In this manuscript, we review (1) metabolic adaptations within tumor microenvironments through (2) cell-to-cell, and (3) organelle-organelle metabolic interactions.

A cholesterogenic gene signature for predicting the prognosis of young breast cancer patients

Purpose

We aimed to establish a cholesterogenic gene signature to predict the prognosis of young breast cancer (BC) patients and then verified it using cell line experiments.

Methods

In the bioinformatic section, transcriptional data and corresponding clinical data of young BC patients (age ≤ 45 years) were downloaded from The Cancer Genome Atlas (TCGA) database for training set. Differentially expressed genes (DEGs) were compared between tumour tissue (n = 183) and normal tissue (n = 30). By using univariate Cox regression and multi COX regression, a five-cholesterogenic-gene signature was established to predict prognosis. Subgroup analysis and external validations of GSE131769 from the Gene Expression Omnibus (GEO) were performed to verify the signature. Subsequently, in experiment part, cell experiments were performed to further verify the biological roles of the five cholesterogenic genes in BC.

Results

In the bioinformatic section, a total of 97 upregulated genes and 124 downregulated cholesterogenic genes were screened as DEGs in the TCGA for training the model. A risk scoring signature contained five cholesterogenic genes (risk score = -1.169 × GRAMD1C -0.992 × NFKBIA + 0.432 × INHBA + 0.261 × CD24 -0.839 × ACSS2) was established, which could differentiate the prognosis of young BC patients between high-risk and low-risk group (<0.001). The prediction value of chelesterogenic gene signature in excellent with AUC was 0.810 in TCGA dataset. Then the prediction value of the signature was verified in GSE131769 with P = 0.033. In experiment part, although the downregulation of CD24, GRAMD1C and ACSS2 did not significantly affect cell viability, NFKBIA downregulation promoted the viability, colony forming ability and invasion capability of BC cells, while INHBA downregulation had the opposite effects.

Conclusion

The five-cholesterogenic-gene signature had independent prognostic value and robust reliability in predicting the prognosis of young BC patients. The cell experiment results suggested that NFKBIA played a protective role, while INHBA played the pro-cancer role in breast cancer.

Acetyl-CoA synthetase 2(ACSS2): a review with a focus on metabolism and tumor development

Acetyl-CoA synthetase 2 (ACSS2), an important member of the acetyl-CoA synthetase (ACSS) family, can catalyze the conversion of acetate to acetyl coenzyme A (acetyl-CoA). Currently, acetyl-CoA is considered an important intermediate metabolite in the metabolism of energy substrates. In addition, nutrients converge through acetyl-CoA into a common metabolic pathway, the tricarboxylic acid cycle and oxidative phosphorylation. Not only does ACSS2 play a crucial role in material energy metabolism, it is also involved in the regulation of various acetylation processes, such as regulation of histone and transcription factor acetylation. ACSS2-mediated regulation of acetylation is related to substance metabolism and tumorigenesis. In mammalian cells, ACSS2 utilizes intracellular acetate to synthesize acetyl-CoA, a step in the process of DNA and histone acetylation. In addition, studies in tumors have shown that cancer cells adapt to the growth conditions in the tumor microenvironment (TME) by activating or increasing the expression level of ACSS2 under metabolic stress. Therefore, this review mainly outlines the role of ACSS2 in substance metabolism and tumors and provides insights useful for investigating ACSS2 as a therapeutic target.

Acetyl-CoA Synthetase 2 as a Therapeutic Target in Tumor Metabolism

Simple Summary

Acetyl-CoA Synthetase 2 (ACSS2) is highly expressed in a variety of tumors, which is very important for tumor growth, proliferation, invasion, and metastasis in the nutritional stress microenvironment. Studies have proven that ACSS2 inhibitors can be effective in halting cancer growth and can be combined with other antineoplastic drugs to reduce drug resistance. This article mainly reviews the mechanism of ACSS2-promoting tumor growth from many aspects and the prospect of clinical application of targeted inhibitors.

Abstract

Acetyl-CoA Synthetase 2 (ACSS2) belongs to a member of the acyl-CoA short-chain synthase family, which can convert acetate in the cytoplasm and nucleus into acetyl-CoA. It has been proven that ACSS2 is highly expressed in glioblastoma, breast cancer, liver cancer, prostate cancer, bladder cancer, renal cancer, and other tumors, and is closely related to tumor stage and the overall survival rate of patients. Accumulating studies show that hypoxia and a low serum level induce ACSS2 expression to help tumor cells cope with this nutrient-poor environment. The potential mechanisms are associated with the ability of ACSS2 to promote the synthesis of lipids in the cytoplasm, induce the acetylation of histones in the nucleus, and facilitate the expression of autophagy genes. Novel-specific inhibitors of ACSS2 are developed and confirmed to the effectiveness in pre-clinical tumor models. Targeting ACSS2 may provide novel approaches for tumor treatment. This review summarizes the biological function of ACSS2, its relation to survival and prognosis in different tumors, and how ACSS2 mediates different pathways to promote tumor metastasis, invasion, and drug resistance.

Interplay Among Metabolism, Epigenetic Modifications, and Gene Expression in Cancer

Epigenetic modifications and metabolism are two fundamental biological processes. During tumorigenesis and cancer development both epigenetic and metabolic alterations occur and are often intertwined together. Epigenetic modifications contribute to metabolic reprogramming by modifying the transcriptional regulation of metabolic enzymes, which is crucial for glucose metabolism, lipid metabolism, and amino acid metabolism. Metabolites provide substrates for epigenetic modifications, including histone modification (methylation, acetylation, and phosphorylation), DNA and RNA methylation and non-coding RNAs. Simultaneously, some metabolites can also serve as substrates for nonhistone post-translational modifications that have an impact on the development of tumors. And metabolic enzymes also regulate epigenetic modifications independent of their metabolites. In addition, metabolites produced by gut microbiota influence host metabolism. Understanding the crosstalk among metabolism, epigenetic modifications, and gene expression in cancer may help researchers explore the mechanisms of carcinogenesis and progression to metastasis, thereby provide strategies for the prevention and therapy of cancer. In this review, we summarize the progress in the understanding of the interactions between cancer metabolism and epigenetics.

Regulation of Lipid Metabolism Under Stress and Its Role in Cancer

Within the tumor microenvironment, cancer cells are often exposed to oxygen and nutrient deficiency, leading to various changes in their lipid composition and metabolism. These alterations have important therapeutic implications as they affect the cancer cells' survival, membrane dynamics, and therapy response. This chapter provides an overview of recent insights into the regulation of lipid metabolism in cancer cells under metabolic stress. We discuss how this metabolic adaptation helps cancer cells thrive in a harsh tumor microenvironment.

Acetate Promotes a Differential Energy Metabolic Response in Human HCT 116 and COLO 205 Colon Cancer Cells Impacting Cancer Cell Growth and Invasiveness

Under dysbiosis, a gut metabolic disorder, short-chain carboxylic acids (SCCAs) are secreted to the lumen, affecting colorectal cancer (CRC) development. Butyrate and propionate act as CRC growth inhibitors, but they might also serve as carbon source. In turn, the roles of acetate as metabolic fuel and protein acetylation promoter have not been clearly elucidated. To assess whether acetate favors CRC growth through active mitochondrial catabolism, a systematic study evaluating acetate thiokinase (AcK), energy metabolism, cell proliferation, and invasiveness was performed in two CRC cell lines incubated with physiological SCCAs concentrations. In COLO 205, acetate (+glucose) increased the cell density (50%), mitochondrial protein content (3–10 times), 2-OGDH acetylation, and oxidative phosphorylation (OxPhos) flux (36%), whereas glycolysis remained unchanged vs. glucose-cultured cells; the acetate-induced OxPhos activation correlated with a high AcK activity, content, and acetylation (1.5–6-fold). In contrast, acetate showed no effect on HCT116 cell growth, OxPhos, AcK activity, protein content, and acetylation. However, a substantial increment in the HIF-1α content, HIF-1α-glycolytic protein targets (1–2.3 times), and glycolytic flux (64%) was observed. Butyrate and propionate decreased the growth of both CRC cells by impairing OxPhos flux through mitophagy and mitochondrial fragmentation activation. It is described, for the first time, the role of acetate as metabolic fuel for ATP supply in CRC COLO 205 cells to sustain proliferation, aside from its well-known role as protein epigenetic regulator. The level of AcK determined in COLO 205 cells was similar to that found in human CRC biopsies, showing its potential role as metabolic marker.

Fatty acid oxidation: driver of lymph node metastasis

Fatty acid oxidation (FAO) is the emerging hallmark of cancer metabolism because certain tumor cells preferentially utilize fatty acids for energy. Lymph node metastasis, the most common way of tumor metastasis, is much indispensable for grasping tumor progression, formulating therapy measure and evaluating tumor prognosis. There is a plethora of studies showing different ways how tumor cells metastasize to the lymph nodes, but the role of FAO in lymph node metastasis remains largely unknown. Here, we summarize recent findings and update the current understanding that FAO may enable lymph node metastasis formation. Afterward, it will open innovative possibilities to present a distinct therapy of targeting FAO, the metabolic rewiring of cancer to terminal cancer patients.

Acetate Induces Growth Arrest in Colon Cancer Cells Through Modulation of Mitochondrial Function

Acetate is one of the main short chain fatty acids produced in the colon when fermentable carbohydrates are digested. It has been shown to affect normal metabolism, modulating mitochondrial function, and fatty acid oxidation. Currently, there is no clear consensus regarding the effects of acetate on tumorigenesis and cancer metabolism. Here, we investigate the metabolic effects of acetate on colon cancer. HT29 and HCT116 colon cancer cell lines were treated with acetate and its effect on mitochondrial proliferation, reactive oxygen species, density, permeability transition pore, cellular bioenergetics, gene expression of acetyl-CoA synthetase 1 (ACSS1) and 2 (ACSS2), and lipid levels were investigated. Acetate was found to reduce proliferation of both cell lines under normoxia as well as reducing glycolysis; it was also found to increase both oxygen consumption and ROS levels. Cell death observed was independent of ACSS1/2 expression. Under hypoxic conditions, reduced proliferation was maintained in the HT29 cell line but no longer observed in the HCT116 cell line. ACSS2 expression together with cellular lipid levels was increased in both cell lines under hypoxia which may partly protect cells from the anti-proliferative effects of reversed Warburg effect caused by acetate. The findings from this study suggest that effect of acetate on proliferation is a consequence of its impact on mitochondrial metabolism and during normoxia is independent of ACCS1/2 expression.

Acetyl-CoA Metabolism and Histone Acetylation in the Regulation of Aging and Lifespan

Acetyl-CoA is a metabolite at the crossroads of central metabolism and the substrate of histone acetyltransferases regulating gene expression. In many tissues fasting or lifespan extending calorie restriction (CR) decreases glucose-derived metabolic flux through ATP-citrate lyase (ACLY) to reduce cytoplasmic acetyl-CoA levels to decrease activity of the p300 histone acetyltransferase (HAT) stimulating pro-longevity autophagy. Because of this, compounds that decrease cytoplasmic acetyl-CoA have been described as CR mimetics. But few authors have highlighted the potential longevity promoting roles of nuclear acetyl-CoA. For example, increasing nuclear acetyl-CoA levels increases histone acetylation and administration of class I histone deacetylase (HDAC) inhibitors increases longevity through increased histone acetylation. Therefore, increased nuclear acetyl-CoA likely plays an important role in promoting longevity. Although cytoplasmic acetyl-CoA synthetase 2 (ACSS2) promotes aging by decreasing autophagy in some peripheral tissues, increased glial AMPK activity or neuronal differentiation can stimulate ACSS2 nuclear translocation and chromatin association. ACSS2 nuclear translocation can result in increased activity of CREB binding protein (CBP), p300/CBP-associated factor (PCAF), and other HATs to increase histone acetylation on the promoter of neuroprotective genes including transcription factor EB (TFEB) target genes resulting in increased lysosomal biogenesis and autophagy. Much of what is known regarding acetyl-CoA metabolism and aging has come from pioneering studies with yeast, fruit flies, and nematodes. These studies have identified evolutionary conserved roles for histone acetylation in promoting longevity. Future studies should focus on the role of nuclear acetyl-CoA and histone acetylation in the control of hypothalamic inflammation, an important driver of organismal aging.

Olfactory receptor 78 regulates erythropoietin and cardiorespiratory responses to hypobaric hypoxia

Olfactory receptor (Olfr) 78 is expressed in the carotid bodies (CB) and participates in CB responses to acute hypoxia. Olfr78 is also expressed in the kidney, which is a major site of erythropoietin (Epo) production by hypoxia. The present study examined the role of Olfr78 in cardiorespiratory and renal Epo gene responses to hypobaric hypoxia (HH), simulating low O₂ condition experienced at high altitude. Studies were performed on adult, male wild-type (WT) and Olfr78 null mice treated with 18 h of HH (0.4 atmospheres). HH-treated WT mice exhibited increased baseline breathing, augmented hypoxic ventilatory response, elevated blood pressure, and plasma norepinephrine (NE) levels. These effects were associated with increased baseline CB sensory nerve activity and augmented CB sensory nerve response to subsequent acute hypoxia. In contrast, HH-treated Olfr78 null mice showed an absence of cardiorespiratory and CB sensory nerve responses, suggesting impaired CB-dependent cardiorespiratory adaptations. WT mice responded to HH with activation of the renal Epo gene expression and elevated plasma Epo levels, and these effects were attenuated or absent in Olfr78 null mice. The attenuated Epo activation by HH was accompanied with markedly reduced hypoxia-inducible factor (HIF)-2α protein and reduced activation of HIF-2 target gene Sod-1 in Olfr78 null mice, suggesting impaired transcriptional activation of HIF-2 contributes to attenuated Epo responses to HH. These results demonstrate a hitherto uncharacterized role for Olfr78 in cardiorespiratory adaptations and renal Epo gene activation by HH such as that experienced at high altitude.NEW & NOTEWORTHY In this study, we delineated a previously uncharacterized role for olfactory receptor 78 (Olfr78), a G-protein-coupled receptor in regulation of erythropoietin and cardiorespiratory responses to hypobaric hypoxia. Our results demonstrate a striking loss of cardiorespiratory adaptations accompanied by an equally striking absence of carotid body sensory nerve responses to hypobaric hypoxia in Olfr78 null mice. We further demonstrate a hitherto uncharacterized role for Olfr78 in erythropoietin activation by hypobaric hypoxia.

Targeting ACSS2 with a Transition-State Mimetic Inhibits Triple-Negative Breast Cancer Growth

Acetyl-CoA is a vitally important and versatile metabolite used for many cellular processes including fatty acid synthesis, ATP production, and protein acetylation. Recent studies have shown that cancer cells upregulate acetyl-CoA synthetase 2 (ACSS2), an enzyme that converts acetate to acetyl-CoA, in response to stresses such as low nutrient availability and hypoxia. Stressed cancer cells use ACSS2 as a means to exploit acetate as an alternative nutrient source. Genetic depletion of ACSS2 in tumors inhibits the growth of a wide variety of cancers. However, there are no studies on the use of an ACSS2 inhibitor to block tumor growth. In this study, we synthesized a small-molecule inhibitor that acts as a transition-state mimetic to block ACSS2 activity in vitro and in vivo. Pharmacologic inhibition of ACSS2 as a single agent impaired breast tumor growth. Collectively, our findings suggest that targeting ACSS2 may be an effective therapeutic approach for the treatment of patients with breast cancer. SIGNIFICANCE: These findings suggest that targeting acetate metabolism through ACSS2 inhibitors has the potential to safely and effectively treat a wide range of patients with cancer.

Activation of amino acid metabolic program in cardiac HIF1-alpha-deficient mice

HIF1-alpha expression defines metabolic compartments in the developing heart, promoting glycolytic program in the compact myocardium and mitochondrial enrichment in the trabeculae. Nonetheless, its role in cardiogenesis is debated. To assess the importance of HIF1-alpha during heart development and the influence of glycolysis in ventricular chamber formation, herein we generated conditional knockout models of Hif1a in Nkx2.5 cardiac progenitors and cardiomyocytes. Deletion of Hif1a impairs embryonic glycolysis without influencing cardiomyocyte proliferation and results in increased mitochondrial number and transient activation of amino acid catabolism together with HIF2α and ATF4 upregulation by E12.5. Hif1a mutants display normal fatty acid oxidation program and do not show cardiac dysfunction in the adulthood. Our results demonstrate that cardiac HIF1 signaling and glycolysis are dispensable for mouse heart development and reveal the metabolic flexibility of the embryonic myocardium to consume amino acids, raising the potential use of alternative metabolic substrates as therapeutic interventions during ischemic events.

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Loss of cardiac Hif1a does not preclude heart development or cardiac function

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Embryonic Hif1a-deficient hearts transiently upregulate amino acid catabolism

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Amino acid catabolism activation sustains heart growth in the absence of glycolysis

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HIF2α and ATF4 are transiently upregulated in the developing heart upon Hif1a loss

Chemotherapy-induced S100A10 recruits KDM6A to facilitate OCT4-mediated breast cancer stemness

Breast cancer stem cells (BCSCs) play a critical role in cancer recurrence and metastasis. Chemotherapy induces BCSC specification through increased expression of pluripotency factors, but how their expression is regulated is not fully understood. Here, we delineate a pathway controlled by hypoxia-inducible factor 1 (HIF-1) that epigenetically activates pluripotency factor gene transcription in response to chemotherapy. Paclitaxel induces HIF-1-dependent expression of S100A10, which forms a complex with ANXA2 that interacts with histone chaperone SPT6 and histone demethylase KDM6A. S100A10, ANXA2, SPT6, and KDM6A are recruited to OCT4 binding sites and KDM6A erases H3K27me3 chromatin marks, facilitating transcription of genes encoding the pluripotency factors NANOG, SOX2, and KLF4, which along with OCT4 are responsible for BCSC specification. Silencing of S100A10, ANXA2, SPT6, or KDM6A expression blocks chemotherapy-induced enrichment of BCSCs, impairs tumor initiation, and increases time to tumor recurrence after chemotherapy is discontinued. Pharmacological inhibition of KDM6A also impairs chemotherapy-induced BCSC enrichment. These results suggest that targeting HIF-1/S100A10-dependent and KDM6A-mediated epigenetic activation of pluripotency factor gene expression in combination with chemotherapy may block BCSC enrichment and improve clinical outcome.

The Evolving Landscape of Noncanonical Functions of Metabolic Enzymes in Cancer and Other Pathologies

Key pathological, including oncogenic, signaling pathways regulate the canonical functions of metabolic enzymes that serve the cellular metabolic needs. Importantly, these signaling pathways also confer a large number of metabolic enzymes to have noncanonical or nonmetabolic functions that are referred to as "moonlighting" functions. In this review, we highlight how aberrantly regulated metabolic enzymes with such activities play critical roles in the governing of a wide spectrum of instrumental cellular activities, including gene expression, cell-cycle progression, DNA repair, cell proliferation, survival, apoptosis, and tumor microenvironment remodeling, thereby promoting the pathologic progression of disease, including cancer.

Acetate Revisited: A Key Biomolecule at the Nexus of Metabolism, Epigenetics, and Oncogenesis - Part 2: Acetate and ACSS2 in Health and Disease

Acetate, the shortest chain fatty acid, has been implicated in providing health benefits whether it is derived from the diet or is generated from microbial fermentation of fiber in the gut. These health benefits range widely from improved cardiac function to enhanced red blood cell generation and memory formation. Understanding how acetate could influence so many disparate biological functions is now an area of intensive research. Protein acetylation is one of the most common post-translational modifications and increased systemic acetate strongly drives protein acetylation. By virtue of acetylation impacting the activity of virtually every class of protein, acetate driven alterations in signaling and gene transcription have been associated with several common human diseases, including cancer. In part 2 of this review, we will focus on some of the roles that acetate plays in health and human disease. The acetate-activating enzyme acyl-CoA short-chain synthetase family member 2 (ACSS2) will be a major part of that focus due to its role in targeted protein acetylation reactions that can regulate central metabolism and stress responses. ACSS2 is the only known enzyme that can recycle acetate derived from deacetylation reactions in the cytoplasm and nucleus of cells, including both protein and metabolite deacetylation reactions. As such, ACSS2 can recycle acetate derived from histone deacetylase reactions as well as protein deacetylation reactions mediated by sirtuins, among many others. Notably, ACSS2 can activate acetate released from acetylated metabolites including N-acetylaspartate (NAA), the most concentrated acetylated metabolite in the human brain. NAA has been associated with the metabolic reprograming of cancer cells, where ACSS2 also plays a role. Here, we discuss the context-specific roles that acetate can play in health and disease.

Acetate: Friend or foe against breast tumour growth in the context of obesity?

Acetate is reported as a regulator of fat mass but also as lipogenic source for cancer cells. Breast cancer is surrounded by adipose tissue and has been associated with obesity. However, whether acetate contributes to cancer cell metabolism as lipogenic substrate and/or by changing fat storage and eventually obesity‐induced breast cancer progression remains unknown. Therefore, we studied the contribution of acetate to breast cancer metabolism and progression. In vitro, we found that acetate is not a bioenergetic substrate under normoxia and did not result in a significant change of growth. However, by using lipidomic approaches, we discovered that acetate changes the lipid profiles of the cells under hypoxia. Moreover, while mice fed a high‐fat diet (HFD) developed bigger tumours than their lean counterparts, exogenous acetate supplementation leads to a complete abolishment of fat mass gain without reverting the HFD‐induced obesity‐driven tumour progression. In conclusion, although acetate protects against diet‐induced obesity, our data suggest that it is not affecting HFD‐driven tumour progression.

RNA-Seq Study of Hepatic Response of Yellow-Feather Chickens to Acute Heat Stress

The yellow-feather broiler is a popular poultry breed in Asia, particularly in China. In this study, we performed RNA-seq analysis to identify differentially expressed genes (deGs) in the liver of yellow-feather broilers that had been subjected to acute heat stress treatment (38±1°C for 4 h, recovery 2 h) and determine the response of the liver to high temperature and its effects on yellow-feather broiler physiology. We found that the cloacal temperature and respiratory rate of yellow-feather chickens were significantly increased immediately after the initiation of acute heat stress (38°c) treatment. And after recovery for 2 h, there was no difference in the cloacal temperature and respiratory rate between the acute heat stress and control groups. A total of 834 DEGs were observed in response to heat stress by RNA-seq. Almost half of the DEGs were involved in the lipid and energy metabolism, including fatty acid metabolism (ACOX1, ACACA, ACSL1, ACSL6, ACAA1, ACAA2, HADHB, and FASN) and propanoate metabolism (ACSS2, ALDH2, ACACA, DLAT, ALDH7A1, MDH1, ME1, ABAT, SUCLG2, and ACSS3). Our findings provide the context for RNA-seq studies in the liver of yellow-feather chickens and suggest that the liver of yellow-feather broilers has the lipid and energy metabolism physiological mechanisms activated in response to heat stress.

Modern Perspective on Metabolic Reprogramming in Malignant Neoplasms

Metabolic reprogramming is one of the central features of transformed cells. Elucidation of interactions between oncogenic signaling and cell metabolic processes has become the basis for extensive studies of metabolism reprogramming in tumor tissue. The review summarizes the key results of studies on the catabolic and anabolic rearrangements in tumor cells with special emphasis on carbohydrate, lipid, amino acid, and acetate metabolism determining the cancer phenotype of cells.

A substitution mutation in a conserved domain of mammalian acetate-dependent acetyl CoA synthetase 2 results in destabilized protein and impaired HIF-2 signaling

The response to environmental stresses by eukaryotic organisms includes activation of protective biological mechanisms, orchestrated in part by transcriptional regulators. The tri-member Hypoxia Inducible Factor (HIF) family of DNA-binding transcription factors include HIF-2, which is activated under conditions of oxygen or glucose deprivation. Although oxygen-dependent protein degradation is a key mechanism by which HIF-1 and HIF-2 activity is regulated, HIF-2 is also influenced substantially by the coupled action of acetylation and deacetylation. The acetylation/deacetylation process that HIF-2 undergoes employs a specific acetyltransferase and deacetylase. Likewise, the supply of the acetyl donor, acetyl CoA, used for HIF-2 acetylation originates from a specific acetyl CoA generator, acetate-dependent acetyl CoA synthetase 2 (Acss2). Although Acss2 is predominantly cytosolic, a subset of the Acss2 cellular pool is enriched in the nucleus following oxygen or glucose deprivation. Prevention of nuclear localization by a directed mutation in a putative nuclear localization signal in Acss2 abrogates HIF-2 acetylation and blunts HIF-2 dependent signaling as well as flank tumor growth for knockdown/rescue cancer cells expressing ectopic Acss2. In this study, we report generation of a novel mouse strain using CRISPR/Cas9 mutagenesis that express this mutant Acss2 allele in the mouse germline. The homozygous mutant mice have impaired induction of the canonical HIF-2 target gene erythropoietin and blunted recovery from acute anemia. Surprisingly, Acss2 protein levels are dramatically reduced in these mutant mice. Functional studies investigating the basis for this phenotype reveal multiple protein instability domains in the Acss2 carboxy terminus. The findings described herein may be of relevance in the regulation of native Acss2 protein as well as for humans carrying missense mutations in these domains.

Regulation of chromatin and gene expression by metabolic enzymes and metabolites

Metabolism and gene expression, which are two fundamental biological processes that are essential to all living organisms, reciprocally regulate each other to maintain homeostasis and regulate cell growth, survival and differentiation. Metabolism feeds into the regulation of gene expression via metabolic enzymes and metabolites, which can modulate chromatin directly or indirectly - through regulation of the activity of chromatin trans-acting proteins, including histone-modifying enzymes, chromatin-remodelling complexes and transcription regulators. Deregulation of these metabolic activities has been implicated in human diseases, prominently including cancer.

Metabolism and inflammation: implications for traumatic brain injury therapeutics

INTRODUCTION

Traumatic Brain Injury (TBI) is a leading cause of death and disability in young people, affecting 69 million people annually, worldwide. The initial trauma disrupts brain homeostasis resulting in metabolic dysfunction and an inflammatory cascade, which can then promote further neurodegenerative effects for months or years, as a 'secondary' injury. Effective targeting of the cerebral inflammatory system is challenging due to its complex, pleiotropic nature. Cell metabolism plays a key role in many diseases, and increased disturbance in the TBI metabolic state is associated with poorer patient outcomes. Investigating critical metabolic pathways, and their links to inflammation, can potentially identify supplements which alter the brain's long-term response to TBI and improve recovery. Areas covered: The authors provide an overview of literature on metabolism and inflammation following TBI, and from relevant pre-clinical and clinical studies, propose therapeutic strategies. Expert opinion: There is still no specific active drug treatment for TBI. Changes in metabolic and inflammatory states have been reported after TBI and appear linked. Understanding more about abnormal cerebral metabolism following TBI, and its relationship with cerebral inflammation, will provide essential information for designing therapies, with implications for neurocritical care and for alleviating long-term disability and neurodegeneration in post-TBI patients.

Hidden features: exploring the non-canonical functions of metabolic enzymes

The study of cellular metabolism has been rigorously revisited over the past decade, especially in the field of cancer research, revealing new insights that expand our understanding of malignancy. Among these insights is the discovery that various metabolic enzymes have surprising activities outside of their established metabolic roles, including in the regulation of gene expression, DNA damage repair, cell cycle progression and apoptosis. Many of these newly identified functions are activated in response to growth factor signaling, nutrient and oxygen availability, and external stress. As such, multifaceted enzymes directly link metabolism to gene transcription and diverse physiological and pathological processes to maintain cell homeostasis. In this Review, we summarize the current understanding of non-canonical functions of multifaceted metabolic enzymes in disease settings, especially cancer, and discuss specific circumstances in which they are employed. We also highlight the important role of subcellular localization in activating these novel functions. Understanding their non-canonical properties should enhance the development of new therapeutic strategies for cancer treatment.

Summary: This Review summarizes recent findings about multifaceted metabolic enzymes with non-canonical activities outside their core biochemical functions, and how they may provide new therapeutic strategies for cancers.

Spatiotemporal Control of Acetyl-CoA Metabolism in Chromatin Regulation

The epigenome is sensitive to the availability of metabolites that serve as substrates of chromatin-modifying enzymes. Links between acetyl-CoA metabolism, histone acetylation, and gene regulation have been documented, although how specificity in gene regulation is achieved by a metabolite has been challenging to answer. Recent studies suggest that acetyl-CoA metabolism is tightly regulated both spatially and temporally to elicit responses to nutrient availability and signaling cues. Here we discuss evidence that acetyl-CoA production is differentially regulated in the nucleus and cytosol of mammalian cells. Recent findings indicate that acetyl-CoA availability for site-specific histone acetylation is influenced through post-translational modification of acetyl-CoA-producing enzymes, as well as through dynamic regulation of the nuclear localization and chromatin recruitment of these enzymes.

Coordinate regulation of stress signaling and epigenetic events by Acss2 and HIF-2 in cancer cells

Survival of cancer cells in the harsh tumor microenvironment, characterized by oxygen and glucose deprivation, requires rapid initiation of cytoprotective measures. Metabolites whose levels change during stress are ideal signaling cues, particularly if used in post-translational modifications of stress-responsive signal transducers. In cancer cells exposed to oxygen or glucose deprivation, there is an increase in cellular levels of acetate, a substrate for acetate-dependent acetyl CoA synthetase 2 (Acss2) that also stimulates translocation of Acss2 from the cytosol to the nucleus. Nuclear, but not cytosolic, Acss2 promotes acetylation of the stress-responsive Hypoxia Inducible Factor 2α (HIF-2α) subunit by the acetyltransferase/coactivator Creb binding protein (Cbp), a process that facilitates stable Cbp/HIF-2α complex formation. In addition to promoting de novo transcription, Cbp and HIF-2α act in concert to regulate local histone 3 epigenetic marks. Exogenous acetate augments Acss2/HIF-2 dependent cancer growth and metastasis in cell culture and mouse models. Thus, an acetate switch in mammals links nutrient intake and stress signaling with tumor growth and metastasis.

Extracellular Acidic pH Activates the Sterol Regulatory Element-Binding Protein 2 to Promote Tumor Progression

Conditions of the tumor microenvironment, such as hypoxia and nutrient starvation, play critical roles in cancer progression. However, the role of acidic extracellular pH in cancer progression is not studied as extensively as that of hypoxia. Here, we show that extracellular acidic pH (pH 6.8) triggered activation of sterol regulatory element-binding protein 2 (SREBP2) by stimulating nuclear translocation and promoter binding to its targets, along with intracellular acidification. Interestingly, inhibition of SREBP2, but not SREBP1, suppressed the upregulation of low pH-induced cholesterol biosynthesis-related genes. Moreover, acyl-CoA synthetase short-chain family member 2 (ACSS2), a direct SREBP2 target, provided a growth advantage to cancer cells under acidic pH. Furthermore, acidic pH-responsive SREBP2 target genes were associated with reduced overall survival of cancer patients. Thus, our findings show that SREBP2 is a key transcriptional regulator of metabolic genes and progression of cancer cells, partly in response to extracellular acidification.

ATP-Citrate Lyase Controls a Glucose-to-Acetate Metabolic Switch

Mechanisms of metabolic flexibility enable cells to survive under stressful conditions and can thwart therapeutic responses. Acetyl-coenzyme A (CoA) plays central roles in energy production, lipid metabolism, and epigenomic modifications. Here, we show that, upon genetic deletion of Acly, the gene coding for ATP-citrate lyase (ACLY), cells remain viable and proliferate, although at an impaired rate. In the absence of ACLY, cells upregulate ACSS2 and utilize exogenous acetate to provide acetyl-CoA for de novo lipogenesis (DNL) and histone acetylation. A physiological level of acetate is sufficient for cell viability and abundant acetyl-CoA production, although histone acetylation levels remain low in ACLY-deficient cells unless supplemented with high levels of acetate. ACLY-deficient adipocytes accumulate lipid in vivo, exhibit increased acetyl-CoA and malonyl-CoA production from acetate, and display some differences in fatty acid content and synthesis. Together, these data indicate that engagement of acetate metabolism is a crucial, although partial, mechanism of compensation for ACLY deficiency.

A microfluidic oxygen gradient demonstrates differential activation of the hypoxia-regulated transcription factors HIF-1α and HIF-2α

Gas-perfused microchannels generated a linear oxygen gradient via diffusion across a 100 μm polydimethylsiloxane (PDMS) membrane. The device enabled exposure of a single monolayer of cells sharing culture media to a heterogeneous oxygen landscape, thus reflecting the oxygen gradients found at the microscale in the physiological setting and allowing for the real-time exchange of paracrine factors and metabolites between cells exposed to varying oxygen levels. By tuning the distance between two gas supply channels, the slope of the oxygen gradient was controlled. We studied the hypoxic activation of the transcription factors HIF-1α and HIF-2α in human endothelial cells within a spatial linear gradient of oxygen. Quantification of the nuclear to cytosolic ratio of HIF immunofluorescent staining demonstrated that the threshold for HIF-1α activation was below 2.5% O2 while HIF-2α was activated throughout the entire linear gradient. We show for the first time HIF-2α is subject to hyproxya, hypoxia by proxy, wherein hypoxic cells activate HIF in close-proximity normoxic cells. These results underscore the differences between HIF-1α and HIF-2α regulation and suggest that a microfluidic oxygen gradient is a novel tool for identifying distinct hypoxic signaling activation and interactions between differentially oxygenated cells.

Hypoxia-inducible factor-2α promotes tumor progression and has crosstalk with Wnt/β-catenin signaling in pancreatic cancer

Background

Pancreatic cancer is a devastating disease that is characterized by persistent hypoxia. The roles of hypoxia-inducible factor-2α (hif-2α) are different to those of hif-1α, although both are critical for tumor cells to adapt to the hypoxic microenvironment. However, unlike the well-studied hif-1α, the role of hif-2α in tumors, including pancreatic cancer, is poorly understood.

Methods

Herein, we used a mutated hif-2α (A530T) to figure out the problem that wild-type hif-2α is quickly degraded which limits the study of its function. Using several cell lines, mouse models, and human tissues, we obtained a general picture of hif-2α in pancreatic cancer progression.

Results

Functional assays revealed that hif-2α promotes epithelial-to-mesenchymal transition, enhances tumor proliferation and invasion, increases stemness, facilitates angiogenesis, and up-regulates aerobic glycolysis. We identified an interaction between hif-2α and β-catenin, and found that hif-2α/β-catenin complex formation increased the activity of β-catenin and the protein stability of hif-2α. In vivo study confirmed the pro-oncogenic role of hif-2α, whose expression correlated with those of E-cadherin, vimentin, Ki-67, and CD31, but not hif-1α. A human tissue study showed that hif-2α was associated with lymph node metastasis, pathological grade, stroma abundance, vascularization and patient survival. High expression of hif-2α was also identified as an independent indicator of poor prognosis in patients with pancreatic cancer.

Conclusions

Our systematic study revealed the roles of hif-2α in pancreatic cancer, and may provide a novel target for this highly malignant disease.

ACSS2 gene variant associated with cleft lip and palate in two independent Hispanic populations

OBJECTIVES/HYPOTHESIS

A candidate variant (p.Val496Ala) of the ACSS2 gene (T > C missense, rs59088485 variant at chr20: bp37 33509608) was previously found to consistently segregate with nonsyndromic cleft lip and/or palate (NSCLP) in three Honduran families. Objectives of this study were 1) to investigate the frequency of this ACSS2 variant in Honduran unrelated NSCLP patients and unrelated unaffected controls and 2) to investigate the frequency of this variant in Colombian unrelated affected NSCLP patients and unrelated unaffected controls.

STUDY DESIGN

Case-control studies.

METHODS

Sanger sequencing of 99 unrelated Honduran NSCLP patients and 215 unrelated unaffected controls for the p.Val496Ala ACSS2 variant was used to determine the carrier frequency in NSCLP patients and controls. Sanger sequencing of 230 unrelated Colombian NSCLP patients and 146 unrelated unaffected controls for the p.Val496Ala ACSS2 variant was used to determine the carrier frequency in NSCLP patients and controls.

RESULTS

In the Honduran population, the odds ratio of having NSCLP among carriers of the p.Val496Ala ACSS2 variant was 4.0 (P = .03), with a carrier frequency of seven of 99 (7.1%) in unrelated affected and four of 215 (1.9%) in unrelated unaffected individuals. In the Colombian population, the odds ratio of having NSCLP among carriers of the p.Val496Ala ACSS2 variant was 2.6 (P = .04), with a carrier frequency of 23 of 230 (10.0%) in unrelated affected and six of 146 (4.1%) in unrelated unaffected individuals.

CONCLUSIONS

These findings support the role of ACSS2 in NSCLP in two independent Hispanic populations from Honduras and Colombia.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:E336-E339, 2017.

Acyl-CoA synthetase short-chain family member 2 (ACSS2) is regulated by SREBP-1 and plays a role in fatty acid synthesis in caprine mammary epithelial cells

Sterol regulatory element binding protein 1 (SREBP-1) is well-known as the master regulator of lipogenesis in rodents. Acyl-CoA synthetase short-chain family member 2 (ACSS2) plays a key role in lipogenesis by synthesizing acetyl-CoA from acetate for lipogenesis. ATP citrate lyase (ACLY) catalyzes the conversion of citrate and coenzyme A to acetyl-CoA, hence, it is also important for lipogenesis. Although ACSS2 function in cancer cells has been elucidated, its essentiality in ruminant mammary lipogenesis is unknown. Furthermore, ACSS2 gene promoter and its regulatory mechanisms have not known. Expression of ACSS2 was high in lipid synthesizing tissues, and its expression increased during lactation compared with non-lactating period. Simultaneous knockdown of both ACSS2 and ACLY by siRNA in primary goat mammary epithelial cells decreased (p < 0.05) the mRNA abundance of genes associated with de novo fatty acid synthesis (FASN, ACACA, SCD1) and triacylglycerol (TAG) synthesis (DGAT1, DGAT2, GPAM, and AGPAT6). Genes responsible for lipid droplet formation and secretion (PLIN2 and PLIN3) and fatty acid oxidation (ATGL, HSL, ACOX, and CPT1A) all decreased (p < 0.05) after ACSS2 and ACLY knockdown. Total cellular TAG content and lipid droplet formation also decreased. Use of a luciferase reporter assay revealed a direct regulation of ACSS2 by SREBP-1. Furthermore, SREBP-1 interacted with an SRE (SREBP response element) spanning at -475 to -483 bp on the ACSS2 promoter. Taken together, our results revealed a novel pathway that SREBP-1 may regulate fatty acid and TAG synthesis by regulating the expression of ACSS2.

Decreased expression of acetyl-CoA synthase 2 promotes metastasis and predicts poor prognosis in hepatocellular carcinoma

Metastasis is a serious risk that may occur during the treatment of hepatocellular carcinoma (HCC), preventing many patients from being surgical candidates and contributing to poor prognosis. Hypoxia has been proved an important factor of metastasis through the epithelial–mesenchymal transition (EMT) pathway. Acetyl‐CoA synthase 2 (ACSS2) provides an acetyl group for the acetylation of hypoxia‐inducible factor (HIF)‐2α, and this epigenetic modification affects the activity of HIF‐2α and the subsequent EMT process. Here, we showed that ACSS2 expression was negatively correlated with HCC malignancy. Knockdown of ACSS2 increased the invasion and migration ability of HCC cells and promoted EMT without increasing the total protein level of HIF‐2α, even in hypoxic conditions. The immunoprecipitation assay revealed downregulated acetylation levels of HIF‐2α after ACSS2 knockdown in hypoxic conditions, which resulted in enhanced HIF‐2α activity. Finally, decreased expression of ACSS2 was found to be related to advanced stage and poor overall survival and disease‐free survival rates in a cohort of patients with HCC. In conclusion, ACSS2 plays an important role in the acetylation process of HIF‐2α, which effectively modifies the activity of HIF‐2α under hypoxic conditions and greatly impacts on the prognosis of patients with HCC.

Cold Inducible RNA Binding Protein Is Involved in Chronic Hypoxia Induced Neuron Apoptosis by Down-Regulating HIF-1α Expression and Regulated By microRNA-23a

Background: Neuron apoptosis mediated by hypoxia inducible factor 1α (HIF-1α) in hippocampus is one of the most important factors accounting for the chronic hypobaric hypoxia induced cognitive impairment. As a neuroprotective molecule that is up-regulated in response to various environmental stress, CIRBP was reported to crosstalk with HIF-1α under cellular stress. However, its function under chronic hypobaric hypoxia remains unknown. Objective: In this study, we tried to identify the role of CIRBP in HIF-1α mediated neuron apoptosis under chronic hypobaric hypoxia and find a possible method to maintain its potential neuroprotective in long-term high altitude environmental exposure. Methods: We established a chronic hypobaric hypoxia rat model as well as a tissue culture model where SH-SY5Y cells were exposed to 1% hypoxia. Based on these models, we measured the expressions of HIF-1α and CIRBP under hypoxia exposure and examined the apoptosis of neurons by TUNEL immunofluorescence staining and western blot analysis of apoptosis related proteins. In addition, by establishing HIF-1α shRNA and pEGFP-CIRBP plasmid transfected cells, we confirmed the role of HIF-1α in chronic hypoxia induced neuron apoptosis and identified the influence of CIRBP over-expression upon HIF-1α and neuron apoptosis in the process of exposure. Furthermore, we measured the expression of the reported hypoxia related miRNAs in both models and the influence of miRNAs' over-expression/knock-down upon CIRBP in the process of HIF-1α mediated neuron apoptosis. Results: HIF-1α expression as well as neuron apoptosis was significantly elevated by chronic hypobaric hypoxia both in vivo and in vitro. CIRBP was induced in the early stage of exposure (3d/7d); however as the exposure was prolonged (21d), CIRBP level of the hypoxia group became significantly lower than that of control. In addition, HIF-1α knockdown significantly decreased neuron apoptosis under hypoxia, suggesting HIF-1α may be pro-apoptotic in the process of exposure. CIRBP over-expression significantly suppressed HIF-1α up-regulation in hypoxia and inhibited HIF-1α mediated neuron apoptosis. Interestingly, miR-23a was also induced by hypoxia exposure and showed the same changing tendency with CIRBP (increasing in 3d/7d, decreasing in 21d). In addition, over-expressing miR-23a up-regulated CIRBP, down-regulated HIF-1α and attenuated neuron apoptosis. Conclusion: Cold inducible RNA binding protein is involved in chronic hypoxia induced neuron apoptosis by down-regulating HIF-1α expression, and MiR-23a may be an important tool to maintain CIRBP level and function.

Acetate as a Metabolic and Epigenetic Modifier of Cancer Therapy

Metabolic networks are significantly altered in neoplastic cells. This altered metabolic program leads to increased glycolysis and lipogenesis and decreased dependence on oxidative phosphorylation and oxygen consumption. Despite their limited mitochondrial respiration, cancer cells, nonetheless, derive sufficient energy from alternative carbon sources and metabolic pathways to maintain cell proliferation. They do so, in part, by utilizing fatty acids, amino acids, ketone bodies, and acetate, in addition to glucose. The alternative pathways used in the metabolism of these carbon sources provide opportunities for therapeutic manipulation. Acetate, in particular, has garnered increased attention in the context of cancer as both an epigenetic regulator of posttranslational protein modification, and as a carbon source for cancer cell biomass accumulation. However, to date, the data have not provided a clear understanding of the precise roles that protein acetylation and acetate oxidation play in carcinogenesis, cancer progression or treatment. This review highlights some of the major issues, discrepancies, and opportunities associated with the manipulation of acetate metabolism and acetylation-based signaling in cancer development and treatment.

The metabolic fate of acetate in cancer

Recent high-profile reports have reignited an interest in acetate metabolism in cancer. Acetyl-CoA synthetases that catalyse the conversion of acetate to acetyl-CoA have now been implicated in the growth of hepatocellular carcinoma, glioblastoma, breast cancer and prostate cancer. In this Review, we discuss how acetate functions as a nutritional source for tumours and as a regulator of cancer cell stress, and how preventing its (re)capture by cancer cells may provide an opportunity for therapeutic intervention.

Metabolic control of epigenetics in cancer

Alterations in the epigenome and metabolism both affect molecular rewiring in cancer cells and facilitate cancer development and progression. However, recent evidence suggests the existence of important bidirectional regulatory mechanisms between metabolic remodelling and the epigenome (specifically methylation and acetylation of histones) in cancer. Most chromatin-modifying enzymes require substrates or cofactors that are intermediates of cell metabolism. Such metabolites, and often the enzymes that produce them, can transfer into the nucleus, directly linking metabolism to nuclear transcription. We discuss how metabolic remodelling can contribute to tumour epigenetic alterations, thereby affecting cancer cell differentiation, proliferation and/or apoptosis, as well as therapeutic responses.

Tissue metabolic profiling of lymph node metastasis of colorectal cancer assessed by 1H NMR

Lymph node metastasis is a decisive prognostic and therapeutic staging factor for colorectal cancer (CRC), which is one of the most prevalent types of cancer and a malignant tumor. The metabolic profiling of tissue samples from a large cohort of lymph node non‑metastatic CRC patients (n=73), lymph node metastatic CRC patients (n=52) and normal controls (n=41) was performed using 1H nuclear magnetic resonance (NMR) together with multivariate statistical analyses. Excellent separation was obtained between CRC patients and normal controls, and CRC patients were also perfectly classified according to lymph node metastasis. Forty‑two distinguishing metabolites were identified, which revealed disturbance of glycolysis, glutaminolysis, fatty acid metabolism, choline metabolism and amino acids, suggesting that cellular functions in energy production, macromolecular synthesis, oxidative stress and immune escape of cancer cells are affected in CRC. In total, 10 tissue metabolites were significantly disturbed between non‑metastatic and metastatic CRC patients. The present study firstly staged CRC patients by lymph node metastasis by metabolomic approach. The identified metabolites may be associated with the neoplasia, invasion and metastasis of the tumor. The results suggest the promising application of these metabolites in clinical therapy, and further understanding of the related mechanism warrants further investigation.

Proteomic Alterations in Response to Hypoxia Inducible Factor 2α in Normoxic Neuroblastoma Cells

Hypoxia inducible factor (HIF)-2α protein expression in solid tumors promotes stem-like phenotype in cancer stem cells and increases tumorigenic potential in nonstem cancer cells. Recently, we have shown that HIF-1/2α gene expression is correlated to neuroblastoma (NB) poor survival and to undifferentiated tumor state; HIF-2α protein was demonstrated to enhance aggressive features of the disease. In this study, we used proteomic experiments on NB cells to investigate HIF-2α downstream-regulated proteins or pathways with the aim of providing novel therapeutic targets or bad prognosis markers. We verified that pathways mostly altered by HIF-2α perturbation are involved in tumor progression. In particular, HIF-2α induces alteration of central metabolism and splicing control pathways. Simultaneously, WNT, RAS/MAPK, and PI3K/AKT activity or expression are affected and may impact the sensitivity and the intensity of HIF-2α-regulated pathways. Furthermore, genes coding the identified HIF-2α-related markers built a signature able to stratify NB patients with unfavorable outcome. Taken together, our findings underline the relevance of dissecting the downstream effects of a poor survival marker in developing targeted therapy and improving patient stratification. Future prospective studies are needed to translate the use of these data into the clinical practice.

Targeting EPO and EPO receptor pathways in anemia and dysregulated erythropoiesis

INTRODUCTION

Recombinant human erythropoietin (rhEPO) is a first-line therapeutic for the anemia of chronic kidney disease, cancer chemotherapy, AIDS (Zidovudine therapy), and lower-risk myelodysplastic syndrome. However, rhEPO frequently elevates hypertension, is costly, and may affect cancer progression. Potentially high merit therefore exists for defining new targets for anti-anemia agents within erythropoietin (EPO) and EPO receptor (EPOR) regulatory circuits.

AREAS COVERED

EPO production by renal interstitial fibroblasts is subject to modulation by several regulators of hypoxia-inducible factor 2a (HIF2a) including Iron Response Protein-1, prolyl hydroxylases, and HIF2a acetylases, each of which holds potential as anti-anemia drug targets. The cell surface receptor for EPO (EPOR) preassembles as a homodimer, together with Janus Kinase 2 (JAK2), and therefore it remains attractive to develop novel agents that trigger EPOR complex activation (activating antibodies, mimetics, small-molecule agonists). Additionally, certain downstream transducers of EPOR/JAK2 signaling may be druggable, including Erythroferrone (a hepcidin regulator), a cytoprotective Spi2a serpin, and select EPOR-associated protein tyrosine phosphatases.

EXPERT OPINION

While rhEPO (and biosimilars) are presently important mainstay erythropoiesis-stimulating agents (ESAs), impetus exists for studies of novel ESAs that fortify HIF2a's effects, act as EPOR agonists, and/or bolster select downstream EPOR pathways to erythroid cell formation. Such agents could lessen rhEPO dosing, side effects, and/or costs.