SIRT2-Mediated Deacetylation and Tetramerization of Pyruvate Kinase Directs Glycolysis and Tumor Growth

Metabolic Roles of Androgen Receptor and Tip60 in Androgen-Dependent Prostate Cancer

Androgen receptor (AR)-mediated signaling is essential for the growth and differentiation of the normal prostate and is the primary target for androgen deprivation therapy in prostate cancer. Tat interactive protein 60 kDa (Tip60) is a histone acetyltransferase that is critical for AR activation. It is well known that cancer cells rewire their metabolic pathways in order to sustain aberrant proliferation. Growing evidence demonstrates that the AR and Tip60 modulate key metabolic processes to promote the survival of prostate cancer cells, in addition to their classical roles. AR activation enhances glucose metabolism, including glycolysis, tricarboxylic acid cycle and oxidative phosphorylation, as well as lipid metabolism in prostate cancer. The AR also interacts with other metabolic regulators, including calcium/calmodulin-dependent kinase kinase 2 and mammalian target of rapamycin. Several studies have revealed the roles of Tip60 in determining cell fate indirectly by modulating metabolic regulators, such as c-Myc, hypoxia inducible factor 1α (HIF-1α) and p53 in various cancer types. Furthermore, Tip60 has been shown to regulate the activity of key enzymes in gluconeogenesis and glycolysis directly through acetylation. Overall, both the AR and Tip60 are master metabolic regulators that mediate cellular energy metabolism in prostate cancer, providing a framework for the development of novel therapeutic targets in androgen-dependent prostate cancer.

The Clinical Significance of SIRT2 in Malignancies: A Tumor Suppressor or an Oncogene?

Sirtuin 2 (SIRT2) is a member of the sirtuin protein family. It is a Class III histone deacetylase (HDACs) and predominantly localized to the cytosol. SIRT2 deacetylates histones and a number of non-histone proteins and plays a pivotal role in various physiologic processes. Previously, SIRT2 has been considered indispensable during carcinogenesis; however, there is now a significant controversy regarding whether SIRT2 is an oncogene or a tumor suppressor. The purpose of this review is to summarize the physiological functions of SIRT2 and its mechanisms in cancer. We will focus on five malignancies (breast cancer, non-small cell lung cancer, hepatocellular carcinoma, colorectal cancer, and glioma) to describe the current status of SIRT2 research and discuss the clinical evaluation of SIRT2 expression and the use of SIRT2 inhibitors.

Sirt2 Inhibition Enhances Metabolic Fitness and Effector Functions of Tumor-Reactive T Cells

Dysregulated metabolism is a key driver of maladaptive tumor-reactive T lymphocytes within the tumor microenvironment. Actionable targets that rescue the effector activity of antitumor T cells remain elusive. Here, we report that the Sirtuin-2 (Sirt2) NAD⁺-dependent deacetylase inhibits T cell metabolism and impairs T cell effector functions. Remarkably, upregulation of Sirt2 in human tumor-infiltrating lymphocytes (TILs) negatively correlates with response to TIL therapy in advanced non-small-cell lung cancer. Mechanistically, Sirt2 suppresses T cell metabolism by targeting key enzymes involved in glycolysis, tricarboxylic acid-cycle, fatty acid oxidation, and glutaminolysis. Accordingly, Sirt2-deficient murine T cells exhibit increased glycolysis and oxidative phosphorylation, resulting in enhanced proliferation and effector functions and subsequently exhibiting superior antitumor activity. Importantly, pharmacologic inhibition of Sirt2 endows human TILs with these superior metabolic fitness and effector functions. Our findings unveil Sirt2 as an unexpected actionable target for reprogramming T cell metabolism to augment a broad spectrum of cancer immunotherapies.

Emerging roles and the regulation of aerobic glycolysis in hepatocellular carcinoma

Liver cancer has become the sixth most diagnosed cancer and the fourth leading cause of cancer death worldwide. Hepatocellular carcinoma (HCC) is responsible for up to 75–85% of primary liver cancers, and sorafenib is the first targeted drug for advanced HCC treatment. However, sorafenib resistance is common because of the resultant enhancement of aerobic glycolysis and other molecular mechanisms. Aerobic glycolysis was firstly found in HCC, acts as a hallmark of liver cancer and is responsible for the regulation of proliferation, immune evasion, invasion, metastasis, angiogenesis, and drug resistance in HCC. The three rate-limiting enzymes in the glycolytic pathway, including hexokinase 2 (HK2), phosphofructokinase 1 (PFK1), and pyruvate kinases type M2 (PKM2) play an important role in the regulation of aerobic glycolysis in HCC and can be regulated by many mechanisms, such as the AMPK, PI3K/Akt pathway, HIF-1α, c-Myc and noncoding RNAs. Because of the importance of aerobic glycolysis in the progression of HCC, targeting key factors in its pathway such as the inhibition of HK2, PFK or PKM2, represent potential new therapeutic approaches for the treatment of HCC.

SIRT2 protects peripheral neurons from cisplatin-induced injury by enhancing nucleotide excision repair

Platinum-based chemotherapy-induced peripheral neuropathy is one of the most common causes of dose reduction and discontinuation of life-saving chemotherapy in cancer treatment; it often causes permanent impairment of quality of life in cancer patients. The mechanisms that underlie this neuropathy are not defined, and effective treatment and prevention measures are not available. Here, we demonstrate that SIRT2 protected mice against cisplatin-induced peripheral neuropathy (CIPN). SIRT2 accumulated in the nuclei of dorsal root ganglion sensory neurons and prevented neuronal cell death following cisplatin treatment. Mechanistically, SIRT2, an NAD+-dependent deacetylase, protected neurons from cisplatin cytotoxicity by promoting transcription-coupled nucleotide excision repair (TC-NER) of cisplatin-induced DNA cross-links. Consistent with this mechanism, pharmacological inhibition of NER using spironolactone abolished SIRT2-mediated TC-NER activity in differentiated neuronal cells and protection of neurons from cisplatin-induced cytotoxicity and CIPN in mice. Importantly, SIRT2's protective effects were not evident in lung cancer cells in vitro or in tumors in vivo. Taken together, our results identified SIRT2's function in the NER pathway as a key underlying mechanism of preventing CIPN, warranting future investigation of SIRT2 activation-mediated neuroprotection during platinum-based cancer treatment.

Inhibition of kras-derived exosomes downregulates immunosuppressive BACH2/GATA-3 expression via RIP-3 dependent necroptosis and miR-146/miR-210 modulation

Immunosuppressive chemoresistance is a major challenge in lung cancer treatment. Exosomes present in the tumor microenviroment are implicated in chemoresistant-related immune suppression, and metastasis but the exact pathogenic role of lung-derived exosomes is still uncertain. Recent reports reveal that lung cancer pathogenesis is strictly associated with a exosomal tumor supportive status and a dysfunctional immune system. In this study, we investigate the role of Kras-derived exosomes in chemoresistant immunosuppression in which neoplastic cells create a metabolic-sustained microenvironment. Findings reveal that Kras-derived exosomes induce regulation of SMARCE1/NCOR1 chromatin remodeling genes promoting pre-metastatic niche formation in naive mice and consequently increase lung metastatic burden. Furthermore, exosomal Kras inhibition downregulated transcription factor BACH2/GATA-3 expression in lung tumor tissues by shifting pyruvate/PKM2 dependent metabolism, contributing to a tumor-restraining status. Further co-treatment with carboplatin triggered RIP3/TNFa dependent necroptosis in ex vivo cells accompanied by differential expression of immunosuppressive miR-146/miR-210 regulators in metastatic lung cancer patients. Overall, these findings demonstrate the multifaceted roles of Kras-derived exosomes in sustaining lung immunosuppressive metastasis and provide new opportunities for effective metastasis inhibition, especially in chemoresistant tumors.

Low-Level Saturated Fatty Acid Palmitate Benefits Liver Cells by Boosting Mitochondrial Metabolism via CDK1-SIRT3-CPT2 Cascade

Saturated fatty acids (SFAs) (the "bad" fat), especially palmitate (PA), in the human diet are blamed for potential health risks such as obesity and cancer because of SFA-induced lipotoxicity. However, epidemiological results demonstrate a latent benefit of SFAs, and it remains elusive whether a certain low level of SFAs is physiologically essential for maintaining cell metabolic hemostasis. Here, we demonstrate that although high-level PA (HPA) indeed induces lipotoxic effects in liver cells, low-level PA (LPA) increases mitochondrial functions and alleviates the injuries induced by HPA or hepatoxic agent carbon tetrachloride (CCl₄). LPA treatment in mice enhanced liver mitochondrial activity and reduced CCl₄ hepatotoxicity with improved blood levels of aspartate aminotransferase (AST), alanine transaminase (ALT), and mitochondrial aspartate transaminase (m-AST). LPA-mediated mitochondrial homeostasis is regulated by CDK1-mediated SIRT3 phosphorylation, which in turn deacetylates and dimerizes CPT2 to enhance fatty acid oxidation. Thus, an advantageous effect is suggested by the consumption of LPA that augments mitochondrial metabolic homeostasis via CDK1-SIRT3-CPT2 cascade.

SIRT2: Controversy and multiple roles in disease and physiology

Sirtuin 2 (SIRT2) is an NAD+-dependent deacetylase that was under studied compared to other sirtuin family members. SIRT2 is the only sirtuin protein which is predominantly found in the cytoplasm but is also found in the mitochondria and in the nucleus. Recently, accumulating evidence has uncovered a growing number of substrates and additional detailed functions of SIRT2 in a wide range of biological processes, marking its crucial role. Here, we give a comprehensive profile of the crucial physiological functions of SIRT2 and its role in neurological diseases, cancers, and other diseases. This review summarizes the functions of SIRT2 in the nervous system, mitosis regulation, genome integrity, cell differentiation, cell homeostasis, aging, infection, inflammation, oxidative stress, and autophagy. SIRT2 inhibition rescues neurodegenerative disease symptoms and hence SIRT2 is a potential therapeutic target for neurodegenerative disease. SIRT2 is undoubtedly dysfunctional in cancers and plays a dual-faced role in different types of cancers, and although its mechanism is unresolved, SIRT2 remains a promising therapeutic target for certain cancers. In future, the continued rapid growth in SIRT2 research will help clarify its role in human health and disease, and promote the progress of this target in clinical practice.

The Molecular Effects of Sulforaphane and Capsaicin on Metabolism upon Androgen and Tip60 Activation of Androgen Receptor

Androgen receptor (AR) stimulators, such as androgen and Tip60, play a pivotal role in prostatic carcinogenesis as androgen receptor signaling is critical for the growth and transformation of the prostate gland. Moreover, androgen and Tip60 promotes HIF-1α activation, involved in metabolic reprogramming by increasing glycolysis, a hallmark in cancer initiation and development. In this study we evaluated the effect of androgen and Tip60 stimulus in AR pathway activation and HIF-1α stabilization, in terms of proliferation and cell metabolism in androgen-sensitive LNCaP cells. The protective role of the bioactive compounds sulforaphane and capsaicin against the effect of these stimuli leading to pro-carcinogenic features was also addressed. Sulforaphane and capsaicin decreased nuclear AR, prostate specific antigen and Bcl-XL levels, and cell proliferation induced by androgen and Tip60 in LNCaP cells. These bioactive compounds prevented the increase in glycolysis, hexokinase and pyruvate kinase activity, and reduced HIF-1α stabilization induced by androgen and Tip60 in LNCaP cells. The protective role of sulforaphane and capsaicin on prostate cancer may rely on mechanisms involving the inhibition of Tip60, AR and HIF-1α effects.

SIRT2 and Lysine Fatty Acylation Regulate the Activity of RalB and Cell Migration

Protein lysine fatty acylation is increasingly recognized as a prevalent and important protein post-translation modification. Recently, it has been shown that K-Ras4a, R-Ras2, and Rac1 are regulated by lysine fatty acylation. Here, we investigated whether other members of the Ras superfamily could also be regulated by lysine fatty acylation. Several small GTPases exhibit hydroxylamine resistant fatty acylation, suggesting they may also have protein lysine fatty acylation. We further characterized one of these GTPases, RalB. We show that RalB has C-terminal lysine fatty acylation, with the predominant modification site being Lys200. The lysine acylation of RalB is regulated by SIRT2, a member of the sirtuin family of nicotinamide adenine dinucleotide (NAD)-dependent protein lysine deacylases. Lysine fatty acylated RalB exhibited enhanced plasma membrane localization and recruited its known effectors Sec5 and Exo84, members of the exocyst complex, to the plasma membrane. RalB lysine fatty acylation did not affect the proliferation or anchorage-independent growth but did affect the trans-well migration of A549 lung cancer cells. This study thus identified an additional function for protein lysine fatty acylation and the deacylase SIRT2.

The sirtuin family in cancer

Sirtuins are a family of protein deacylases and ADP-ribosyl-transferases, homologs to the yeast SIR2 protein. Seven sirtuin paralogs have been described in mammals, with different subcellular locations, targets, enzymatic activities, and regulatory mechanisms. All sirtuins share NAD+ as substrate, placing them as central metabolic hubs with strong relevance in lifespan, metabolism, and cancer development. Much effort has been devoted to studying the roles of sirtuins in cancer, providing a wealth of data on sirtuins roles in mouse models and humans. Also, extensive data are available on the effects of pharmacological modulation of sirtuins in cancer development. Here, we present a comprehensive and organized resume of all the existing evidence linking every sirtuin with cancer development. From our analysis, we conclude that sirtuin modulation after tumor initiation results in unpredictable outcomes in most tumor types. On the contrary, all genetic and pharmacological models indicate that sirtuins activation prior to tumor initiation can constitute a powerful preventive strategy.

A Glycoconjugated SIRT2 Inhibitor with Aqueous Solubility Allows Structure-Based Design of SIRT2 Inhibitors

Small molecule inhibitors for SIRT2, a member of the sirtuin family of nicotinamide adenine dinucleotide-dependent protein lysine deacylases, have shown promise in treating cancer and neurodegenerative diseases. Developing SIRT2-selective inhibitors with better pharmacological properties is key to further realize the therapeutic potential of targeting SIRT2. One of the best SIRT2-selective inhibitors reported is a thiomyristoyl lysine compound called TM, which showed promising anticancer activity in mouse models without much toxicity to normal cells. The main limitations of TM, however, are the low aqueous solubility and lack of X-ray crystal structures to aid future drug design. Here, we designed and synthesized a glucose-conjugated TM (glucose-TM) analog with superior aqueous solubility. Although glucose-TM is not cell permeable, the excellent aqueous solubility allowed us to obtain a crystal structure of SIRT2 in complex with it. The structure enabled us to design several new TM analogs, one of which, NH4-6, showed superior water solubility and better anticancer activity in cell culture. The results of these studies provided important insights that will further fuel the future development of improved SIRT2 inhibitors as promising therapeutics for treating cancer and neurodegeneration.

Enzymatic and nonenzymatic protein acetylations control glycolysis process in liver diseases

Impaired glycolysis has pathologic effects on the occurrence and progression of liver diseases, and it appears that glycolysis is increased to different degrees in different liver diseases. As an important post-translational modification, reversible lysine acetylation regulates almost all cellular processes, including glycolysis. Lysine acetylation can occur enzymatically with acetyltransferases or nonenzymatically with acetyl-coenzyme A. Accompanied by the progression of liver diseases, there seems to be a temporal and spatial variation between enzymatic and nonenzymatic acetylations in the regulation of glycolysis. Here, we summarize the most recent findings on the functions and targets of acetylation in controlling glycolysis in the different stages of liver diseases. In addition, we discuss the differences and causes between enzymatic and nonenzymatic acetylations in regulating glycolysis throughout the progression of liver diseases. Then, we review these new discoveries to provide the potential implications of these findings for therapeutic interventions in liver diseases.-Li, J., Wang, T., Xia, J., Yao, W., Huang, F. Enzymatic and nonenzymatic protein acetylations control glycolysis process in liver diseases.

Subcellular compartmentalization of NAD+ and its role in cancer: A sereNADe of metabolic melodies

Nicotinamide adenine dinucleotide (NAD+) is an essential biomolecule involved in many critical processes. Its role as both a driver of energy production and a signaling molecule underscores its importance in health and disease. NAD+ signaling impacts multiple processes that are dysregulated in cancer, including DNA repair, cell proliferation, differentiation, redox regulation, and oxidative stress. Distribution of NAD+ is highly compartmentalized, with each subcellular NAD+ pool differentially regulated and preferentially involved in distinct NAD+-dependent signaling or metabolic events. Emerging evidence suggests that targeting NAD+ metabolism is likely to repress many specific mechanisms underlying tumor development and progression, including proliferation, survival, metabolic adaptations, invasive capabilities, heterotypic interactions with the tumor microenvironment, and stress response including notably DNA maintenance and repair. Here we provide a comprehensive overview of how compartmentalized NAD+ metabolism in mitochondria, nucleus, cytosol, and extracellular space impacts cancer formation and progression, along with a discussion of the therapeutic potential of NAD+-targeting drugs in cancer.

Acetylome profiling reveals extensive involvement of lysine acetylation in the conversion of muscle to meat

Protein lysine acetylation is an post-translational modification that regulates gene expression, metabolism, cell signaling, and diseases, but its implication in the postmortem (PM) meat quality development is basically unclear. In the present study, a quantitative proteomic analysis was conducted to profile acetylome in porcine muscle within 24 h PM. In total 595 acetylation sites assigned to 163 proteins were identified in porcine muscle, of which 460 sites distributing to 110 proteins significantly changed in acetylation levels in the conversion of muscle to meat. The dynamic acetylation/deacetylaion of muscle proteins was closely associated with critical chemical-biophysical changes in PM muscle. Bioinformatic analysis revealed that protein lysine acetylation likely regulated postmortem meat quality development by regulating glycolysis and muscle pH, cell stress reponse and apoptosis, muscle contraction and rigor mortis, calcium signaling and proteolysis, IMP synthesis and meat flavor development, and even the stability of pigment proteins and meat color. This study provided the first overview of protein lysine acetylation in PM muscle and revealed its significance in the conversion of muscle to meat. Future exploration of the exact role of protein lysine acetylation at specific sites will further our understanding regarding the underlying mechanisms and be helpful for meat quality control. SIGNIFICANCE: This is the first analysis of acetylome in farm animal and postmortem muscle. Our data showed that the dynamic acetylation/deacetylation of muscle proteins was closely related to the postmortem changes of muscle that affect the final quality of raw meat. Proteins related to glucose metabolism and muscle contraction were the two largest clusters of acetylproteins identified in postmortem porcine muscle. Networks of acetylproteins involved in apoptosis, calcium signaling and IMP synthesis were identified in postmortem porcine muscle at the same time. Our results revealed that protein lysine acetylation regulated the conversion of muscle to meat. It likely regulated meat quality development by regulating postmortem glycolysis, mitochondrion initiated cell apoptosis, calcium signaling, rigor mortis, meat flavor compound sysnthesis and meat tenderization. Our study broadened our understanding of the biochemistry regulating the postmortem conversion of muscle to meat and final meat quality development, which may be helpful for future meat quality control.

Sirtuin-mediated deacetylation of hnRNP A1 suppresses glycolysis and growth in hepatocellular carcinoma

Tumor cells undergo a metabolic shift in order to adapt to the altered microenvironment, although the underlying mechanisms have not been fully explored. HnRNP A1 is involved in the alternative splicing of the pyruvate kinase (PK) mRNA, allowing tumor cells to specifically produce the PKM2 isoform. We found that the acetylation status of hnRNP A1 in hepatocellular carcinoma (HCC) cells was dependent on glucose availability, which affected the PKM2-dependent glycolytic pathway. In the glucose-starved HCC cells, SIRT1 and SIRT6, members of deacetylase sirtuin family, were highly expressed and deacetylated hnRNP A1 after direct binding. We identified four lysine residues in hnRNP A1 that were deacetylated by SIRT1 and SIRT6, resulting in significant inhibition of glycolysis in HCC cells. Deacetylated hnRNP A1 reduced PKM2 and increased PKM1 alternative splicing in HCC cells under normal glucose conditions, thereby reducing the metabolic activity of PK and the non-metabolic PKM2-β-catenin signaling pathway. However, under glucose starvation, the low levels of acetylated hnRNP A1 reduced HCC cell metabolism to adapt to the nutrient deficiency. Taken together, sirtuin-mediated hnRNP A1 deacetylation inhibits HCC cell proliferation and tumorigenesis in a PKM2-dependent manner. These findings point to the metabolic reprogramming induced by hnRNP A1 acetylation in order to adapt to the nutritional status of the tumor microenvironment.

Identification of a novel small molecule that inhibits deacetylase but not defatty-acylase reaction catalysed by SIRT2

SIRT2 is a member of the human sirtuin family of proteins and possesses NAD⁺-dependent lysine deacetylase/deacylase activity. SIRT2 has been implicated in carcinogenesis in various cancers including leukaemia and is considered an attractive target for cancer therapy. Here, we identified NPD11033, a selective small-molecule SIRT2 inhibitor, by a high-throughput screen using the RIKEN NPDepo chemical library. NPD11033 was largely inactive against other sirtuins and zinc-dependent deacetylases. Crystallographic analysis revealed a unique mode of action, in which NPD11033 creates a hydrophobic cavity behind the substrate-binding pocket after a conformational change of the Zn-binding small domain of SIRT2. Furthermore, it forms a hydrogen bond to the active site histidine residue. In addition, NPD11033 inhibited cell growth of human pancreatic cancer PANC-1 cells with a concomitant increase in the acetylation of eukaryotic translation initiation factor 5A, a physiological substrate of SIRT2. Importantly, NPD11033 failed to inhibit defatty-acylase activity of SIRT2, despite its potent inhibitory effect on its deacetylase activity. Thus, NPD11033 will serve as a useful tool for both developing novel anti-cancer agents and elucidating the role of SIRT2 in various cellular biological processes.This article is part of a discussion meeting issue 'Frontiers in epigenetic chemical biology'.

Updates on the epigenetic roles of sirtuins

Sirtuins are a class of enzyme with NAD⁺-dependent protein lysine deacylase activities. They were initially discovered to regulate transcription and life span via histone deacetylase activities. Later studies expanded their activities to other proteins and acyl lysine modifications. Through deacylating various substrate proteins, they regulate many biological processes, including transcription, DNA repair and genome stability, metabolism, and signal transduction. Here, we review recent understandings of the epigenetic functions (broadly defined to include transcriptional, post-transcriptional regulation, and DNA repair) of mammalian sirtuins. Because of the important functions of sirtuins, their own regulation is of great interest and is also discussed.

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

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

Sirtuin 2-mediated deacetylation of cyclin-dependent kinase 9 promotes STAT1 signaling in type I interferon responses

Type I interferons (IFNs) induce expression of multiple genes that control innate immune responses to invoke both antiviral and antineoplastic activities. Transcription of these interferon-stimulated genes (ISGs) occurs upon activation of the canonical Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathways. Phosphorylation and acetylation are both events crucial to tightly regulate expression of ISGs. Here, using mouse embryonic fibroblasts and an array of biochemical methods including immunoblotting and kinase assays, we show that sirtuin 2 (SIRT2), a member of the NAD-dependent protein deacetylase family, is involved in type I IFN signaling. We found that SIRT2 deacetylates cyclin-dependent kinase 9 (CDK9) in a type I IFN-dependent manner and that the CDK9 deacetylation is essential for STAT1 phosphorylation at Ser-727. We also found that SIRT2 is subsequently required for the transcription of ISGs and for IFN-driven antiproliferative responses in both normal and malignant cells. These findings establish the existence of a previously unreported signaling pathway whose function is essential for the control of JAK-STAT signaling and the regulation of IFN responses. Our findings suggest that targeting sirtuin activities may offer an avenue in the development of therapies for managing immune-related diseases and cancer.

MicroRNA 675 cooperates PKM2 to aggravate progression of human liver cancer stem cells induced from embryonic stem cells

Both miR675 and pyruvate kinase M2 (PKM2) contribute to malignant progression of tumor, but its functions in liver cancer stem cells remain unclear. Herein, our findings indicate that miR675 plus PKM2 strongly promotes the growth of liver cancer stem cells. Mechanistically, miR675 plus PKM2 enhances the transcriptional activity of SUV39h2. On the other hand, the excessive SUV39h2 binds to more substrate histone H3, triggering an increase of tri-methylation of histone H3 on the ninth lysine. Furthermore, the tri-methylation of histone 3 on the ninth lysine (H3K9me3)-heterochromatin protein 1 alpha (HP1α) complex is increased when the complex occupancy ability on the C-myc promoter region is raised, recruiting CREB, P300, and RNApolII to the special position that results in C-myc high abundance. Therefore, miR675 plus PKM2 triggered the upregulation of C-myc by increasing the interaction between H3K9me3 and HP1α. Understanding the signaling pathways that miR675 plus PKM2 epigenetically possesses during the malignant transformation of liver cancer stem cells will contribute to more effective liver cancer therapies.

Sirtuins and Immuno-Metabolism of Sepsis

Sepsis and septic shock are the leading causes of death in non-coronary intensive care units worldwide. During sepsis-associated immune dysfunction, the early/hyper-inflammatory phase transitions to a late/hypo-inflammatory phase as sepsis progresses. The majority of sepsis-related deaths occur during the hypo-inflammatory phase. There are no phase-specific therapies currently available for clinical use in sepsis. Metabolic rewiring directs the transition from hyper-inflammatory to hypo-inflammatory immune responses to protect homeostasis during sepsis inflammation, but the mechanisms underlying this immuno-metabolic network are unclear. Here, we review the roles of NAD+ sensing Sirtuin (SIRT) family members in controlling immunometabolic rewiring during the acute systemic inflammatory response associated with sepsis. We discuss individual contributions among family members SIRT 1, 2, 3, 4 and 6 in regulating the metabolic switch between carbohydrate-fueled hyper-inflammation to lipid-fueled hypo-inflammation. We further highlight the role of SIRT1 and SIRT2 as potential "druggable" targets for promoting immunometabolic homeostasis and increasing sepsis survival.

PKM2, a potential target for regulating cancer

Aberrated glucose metabolism is a key future of cancer cells. Unlike normal cells, tumor cells favor glycolysis even in the presence of sufficient oxygen. Pyruvate kinase (PK), a key glucose metabolic enzyme, converts phosphoenolpyruvate (PEP) to pyruvate by transferring the high-energy phosphate group to adenosine diphosphate (ADP) to produce adenosine triphosphate (ATP). Pyruvate kinase M2 (PKM2), one of the four isozyme of PK, which universally expressed in rapidly proliferating cells such as embryonic cells and cancer cells. Recent years, more and more research suggested PKM2 plays a crucial role in cancer progression through both metabolic and non-metabolic pathways. On the one hand, the middle product of glycolysis, such as amino acids, nucleotides, lipids is necessary to rapid growth of cancer cells. On the other hand, PKM2 supports tumor growth through regulating the expression of gene that involved in cell proliferation, migration and apoptosis. In this article, we review the recent advances to further understand the regulation and function of PKM2 in tumorigenesis. Given its multiple effects on cancer, PKM2 may be a potential target for cancer diagnosis and treatment.

SIRT2 and Akt mediate NAD+-induced and NADH-induced increases in the intracellular ATP levels of BV2 microglia under basal conditions

NAD replenishment can restore ATP levels and rescue premature aging in Cockayne syndrome mice. However, there has been no mechanistic study regarding the effects of NAD and NADH on intracellular ATP levels under basal conditions. In our current study, we used BV2 microglia to test our hypothesis that NAD and NADH can increase intracellular ATP levels under basal conditions. We found that both NAD and NADH significantly increased the intracellular ATP levels of BV2 microglia, which were attenuated by SIRT2 siRNA, the SIRT2 inhibitor AGK2, and the phosphatidylinositol 3-kinase/Akt inhibitor LY294002. Our study has also suggested that SIRT2 mediates the NAD-induced and NADH-induced increase in Akt phosphorylation in BV2 microglia. Collectively, our study has suggested that SIRT2 mediates both NAD-induced and NADH-induced increases in the intracellular ATP levels of BV2 microglia by modulating Akt phosphorylation.

Dichloroacetic acid (DCA) synergizes with the SIRT2 inhibitor Sirtinol and AGK2 to enhance anti-tumor efficacy in non-small cell lung cancer

Combination chemotherapy is a potentially promising approach to enhance anticancer activity, overcome drug resistance, and improve disease-free and overall survival. The current study investigates the antitumor activity of sodium dichloroacetic acid (DCA) in combination with SIRT2 inhibitor Sirtinol and AGK2. We found that combining DCA with Sirtinol produced a synergistic therapeutic benefit in A549 and H1299 NSCLC cells in vitro and in a mouse A549 xenograft model. Synergistic potentiation of oxidative phosphorylation (OXPHOS) was observed, including decreased glucose consumption, decreased lactate production, increased OCR and increased ROS generation, possibly via co-targeting pyruvate dehydrogenase alpha 1(PDHA1). Mechanically, AGK2 and Sirtinol were found to increase the lysine-acetylation and decrease the serine-phosphorylation of PDHA1, which enabled the two inhibitors to synergize with DCA to further activate PDHA1. Besides, a AMPKα-ROS feed-forward loop was notably activated after the combined treatments compared with mono-therapy. Our results indicate that the combination of DCA and SIRT2 inhibitor may provide a promising therapeutic strategy to effectively kill cancer cells.

SIRT2 Promotes the Migration and Invasion of Gastric Cancer through RAS/ERK/JNK/MMP-9 Pathway by Increasing PEPCK1-Related Metabolism

Metastasis is the most important feature of gastric cancer (GC) and the most widely recognized reason for GC-related deaths. Unfortunately, the underlying mechanism behind this metastasis remains unknown. Mounting evidence suggests the dynamic regulatory role of sirtuin2 (SIRT2), a histone deacetylase (HDAC), in cell migration and invasion. The present study aims to evaluate the biological function of SIRT2 in GC and identify the target of SIRT2 as well as evaluate its therapeutic efficacy. We found that SIRT2 was upregulated in GC tissues compared to adjacent normal tissues, and this was correlated with reduced patient survival. Although CCK8 and colony-formation assays showed that SIRT2 overexpression marginally promoted proliferation in GC cell lines, SIRT2 knockdown or treatment with SirReal2 decreased the migration and invasion of GC cells. We demonstrated both in vitro and in vivo that SirReal2 could inhibit the deacetylation activity of SIRT2 and its downstream target PEPCK1, which is related to mitochondrial metabolism and RAS/ERK/JNK/MMP-9 pathway. Taken together, these results demonstrate for the first time that SirReal2 selectively targets SIRT2 and decreases migration as well as invasion in human GC cells. SirReal2 therefore shows promise as a new drug candidate for GC therapy.

Overexpression of Pyruvate Kinase Type M2 (PKM2) Promotes Ovarian Cancer Cell Growth and Survival Via Regulation of Cell Cycle Progression Related with Upregulated CCND1 and Downregulated CDKN1A Expression

BACKGROUND Many findings have shown that pyruvate kinase type M2 (PKM2) plays crucial roles in regulating the occurrence and development of various human cancers; however, its roles in ovarian cancer oncogenesis remain to be determined. MATERIAL AND METHODS The expression intensity of PKM2 in ovarian cancer tissues was examined by immunohistochemistry (IHC), and was then correlated to patient clinicopathologic characteristics. The roles of PKM2 in ovarian cancer cell proliferation, growth, and survival were examined by CCK-8, colony forming, and flow cytometry assays. The potentially involved molecular were then investigated by Western blot analysis. RESULTS IHC results showed that PKM2 was overexpressed in 100 of 114 (87.7%) serous ovarian cancer tissues as compared with 50 cases of non-cancerous ovarian tissues, and was associated with tumor size ≥7.5 cm and <7.5 cm (p<0.05). Overexpression of PKM2 in SKOV3 and HEY ovarian cancer cells by transfection with PKM2 lentivirus vector led to increased cell proliferation, growth, and survival, which may be related with PKM2 being able to increase cell cycle progress: G1 stage decreased, whereas S stage significantly increased. In contrast, all functions of SKOV3 and HEY cells described above were reversed by knocked down PKM2 expression using siRNA. Further data showed that overexpressed PKM2 led to increased CCND1 and decreased CDKN1A expression, whereas underexpressed PKM2 led to decreased CCND1 and increased CDKN1A expression in ovarian cancer cells. CONCLUSIONS PKM2 may play important roles in ovarian cancer development and may be a treatment target for this cancer.

Lysine Deacetylases and Regulated Glycolysis in Macrophages

Regulated cellular metabolism has emerged as a fundamental process controlling macrophage functions, but there is still much to uncover about the precise signaling mechanisms involved. Lysine acetylation regulates the activity, stability, and/or localization of metabolic enzymes, as well as inflammatory responses, in macrophages. Two protein families, the classical zinc-dependent histone deacetylases (HDACs) and the NAD-dependent HDACs (sirtuins, SIRTs), mediate lysine deacetylation. We describe here mechanisms by which classical HDACs and SIRTs directly regulate specific glycolytic enzymes, as well as evidence that links these protein deacetylases to the regulation of glycolysis-related genes. In these contexts, we discuss HDACs and SIRTs as key control points for regulating immunometabolism and inflammatory outputs from macrophages.

Long noncoding RNA MEG3 suppresses liver cancer cells growth through inhibiting β-catenin by activating PKM2 and inactivating PTEN

Maternally expressed gene 3 (MEG3) encodes an lncRNA which is suggested to function as a tumor suppressor and has been showed to involve in a variety of cancers. Herein, our findings demonstrate that MEG3 inhibits the malignant progression of liver cancer cells in vitro and in vivo. Mechanistically, MEG3 promotes the expression and maturition of miR122 which targets PKM2. Therefore, MEG3 decreases the expression and nuclear location of PKM2 dependent on miR122. Furthermore, MEG3 also inhibits CyclinD1 and C-Myc via PKM2 in liver cancer cells. On the other hand, MEG3 promotes β-catenin degradation through ubiquitin-proteasome system dependent on PTEN. Strikingly, MEG3 inhibits β-catenin activity through PKM2 reduction and PTEN increase. Significantly, we also found that excessive β-catenin abrogated the effect of MEG3 in liver cancer. In conclusion, our study for the first time demonstrates that MEG3 acts as a tumor suppressor by negatively regulating the activity of the PKM2 and β-catenin signaling pathway in hepatocarcinogenesis and could provide potential therapeutic targets for the treatment of liver cancer.

Posttranslational Modifications of Pyruvate Kinase M2: Tweaks that Benefit Cancer

Cancer cells rewire metabolism to meet biosynthetic and energetic demands. The characteristic increase in glycolysis, i.e., Warburg effect, now considered as a hallmark, supports cancer in various ways. To attain such metabolic reshuffle, cancer cells preferentially re-express the M2 isoform of pyruvate kinase (PKM2, M2-PK) and alter its quaternary structure to generate less-active PKM2 dimers. The relatively inactive dimers cause the accumulation of glycolytic intermediates that are redirected into anabolic pathways. In addition, dimeric PKM2 also benefits cancer cells through various non-glycolytic moonlight functions, such as gene transcription, protein kinase activity, and redox balance. A large body of data have shown that several distinct posttranslation modifications (PTMs) regulate PKM2 in a way that benefits cancer growth, e.g., formation of PKM2 dimers. This review discusses the recent advancements in our understanding of various PTMs and the benefits they impart to the sustenance of cancer. Understanding the PTMs in PKM2 is crucial to assess their therapeutic potential and to design novel anticancer strategies.

Functional genetic variants within the SIRT2 gene promoter in acute myocardial infarction

Coronary artery disease (CAD), including acute myocardial infarction (AMI) is the complication of atherosclerosis. Recently, genome-wide association studies have identified a large number of CAD-related genetic variants. However, only 10% of CAD cases could be explained. Low frequent and rare genetic variants have been recently proposed to be main causes for CAD. SIRT2 is a member of sirtuin family, NAD(+)-dependent class III deacetylases. SIRT2 is involved in genomic stability, metabolism, inflammation, oxidative stress and autophagy, as well as in platelet function. Thus, we hypothesized that genetic variants in SIRT2 gene may contribute to AMI. In this study, SIRT2 gene promoter was analyzed in large cohorts of AMI patients (n = 375) and ethnic-matched controls (n = 377). Three novel heterozygous DSVs (g.38900888_91delTAAA, g.38900270A>G and g.38899853C>T) were identified in three AMI patients, but in none of controls. These DSVs significantly altered the transcriptional activity of the SIRT2 gene promoter (P<0.05) in both HEK-293 and H9c2 cells. Five novel heterozygous DSVS (g.38900562C>T, g.38900413A>C, g.38900030G>A, g.38899925A>C and g.38899852C>T) were only found in controls, which did not significantly affected SIRT2 gene promoter activity (P>0.05). In addition, four novel heterozygous DSVs and five SNPs were found in both AMI patients and control with similar frequencies (P>0.05), two SNPs of which were examined and did not affect SIRT2 gene promoter activity (P>0.05). Taken together, the DSVs identified in AMI patients may change SIRT2 level by affecting the transcriptional activity of SIRT2 gene promoter, contributing to the AMI development as a rare risk factor.

Identification of a multienzyme complex for glucose metabolism in living cells

Sequential metabolic enzymes in glucose metabolism have long been hypothesized to form multienzyme complexes that regulate glucose flux in living cells. However, it has been challenging to directly observe these complexes and their functional roles in living systems. In this work, we have used wide-field and confocal fluorescence microscopy to investigate the spatial organization of metabolic enzymes participating in glucose metabolism in human cells. We provide compelling evidence that human liver-type phosphofructokinase 1 (PFKL), which catalyzes a bottleneck step of glycolysis, forms various sizes of cytoplasmic clusters in human cancer cells, independent of protein expression levels and of the choice of fluorescent tags. We also report that these PFKL clusters colocalize with other rate-limiting enzymes in both glycolysis and gluconeogenesis, supporting the formation of multienzyme complexes. Subsequent biophysical characterizations with fluorescence recovery after photobleaching and FRET corroborate the formation of multienzyme metabolic complexes in living cells, which appears to be controlled by post-translational acetylation on PFKL. Importantly, quantitative high-content imaging assays indicated that the direction of glucose flux between glycolysis, the pentose phosphate pathway, and serine biosynthesis seems to be spatially regulated by the multienzyme complexes in a cluster-size-dependent manner. Collectively, our results reveal a functionally relevant, multienzyme metabolic complex for glucose metabolism in living human cells.

Thienopyrimidinone Based Sirtuin-2 (SIRT2)-Selective Inhibitors Bind in the Ligand Induced Selectivity Pocket

Sirtuins (SIRTs) are NAD-dependent deacylases, known to be involved in a variety of pathophysiological processes and thus remain promising therapeutic targets for further validation. Previously, we reported a novel thienopyrimidinone SIRT2 inhibitor with good potency and excellent selectivity for SIRT2. Herein, we report an extensive SAR study of this chemical series and identify the key pharmacophoric elements and physiochemical properties that underpin the excellent activity observed. New analogues have been identified with submicromolar SIRT2 inhibtory activity and good to excellent SIRT2 subtype-selectivity. Importantly, we report a cocrystal structure of one of our compounds (29c) bound to SIRT2. This reveals our series to induce the formation of a previously reported selectivity pocket but to bind in an inverted fashion to what might be intuitively expected. We believe these findings will contribute significantly to an understanding of the mechanism of action of SIRT2 inhibitors and to the identification of refined, second generation inhibitors.

The Antibiotic Drug Tigecycline: A Focus on its Promising Anticancer Properties

Tigecycline (TIG), the first member of glycylcycline bacteriostatic agents, has been approved to treat complicated infections in the clinic because of its expanded-spectrum antibiotic potential. Recently, an increasing number of studies have emphasized the anti-tumor effects of TIG. The inhibitory effects of TIG on cancer depend on several activating signaling pathways and abnormal mitochondrial function in cancer cells. The aim of this review is to summarize the cumulative anti-tumor evidence supporting TIG activity against different cancer types, including acute myeloid leukemia (AML), glioma, non-small cell lung cancer (NSCLC), among others. In addition, the efficacy and side effects of TIG in cancer patients are summarized in detail. Future clinical trials are also to be discussed that will evaluate the security and validate the underlying the tumor-killing properties of TIG.