SIRT6 deacetylates PKM2 to suppress its nuclear localization and oncogenic functions

The Role of Pyruvate Kinase M2 Posttranslational Modification in the Occurrence and Development of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the deadly malignant tumors that directly leads to the death of nearly one million people worldwide every year, causing a serious burden on society. In the presence of sufficient oxygen, HCC cells rapidly generate energy through aerobic glycolysis, which promotes tumor cell proliferation, immune evasion, metastasis, angiogenesis, and drug resistance. Pyruvate kinase M2 (PKM2) is a key rate-limiting enzyme in glycolysis. In recent years, studies have found that PKM2 not only exerts pyruvate kinase activity in the process of glucose metabolism, but also exerts protein kinase activity in non-metabolic pathways to affect tumor cell processes, and its activity is flexibly regulated by various posttranslational modifications such as acetylation, phosphorylation, lactylation, ubiquitination, SUMOylation, and so forth. This review summarizes the role of posttranslational modifications of PKM2-related sites in the development of HCC.

Suppressing SENP1 inhibits esophageal squamous carcinoma cell growth via SIRT6 SUMOylation

PURPOSE

Esophageal squamous cell carcinoma (ESCC) is a prevalent tumor in the gastrointestinal tract, but our understanding of the molecular mechanisms underlying ESCC remains incomplete. Existing studies indicate that SUMO specific peptidase 1 (SENP1) plays a crucial role in the development and progression of various malignant tumors through diverse molecular mechanisms. However, the functional mechanism and clinical implications of SENP1 in the progression of ESCC remain unclear.

METHODS

Bulk RNA-Sequencing (RNA-seq) was used to compare potential genes in the esophageal tissues of mice with ESCC to the control group. The up-regulated SENP1 was selected. The protein level of SENP1 in ESCC patient samples was analyzed by immunohistochemistry and western blot. The potential prognostic value of SENP1 on overall survival of ESCC patients was examined using tissue microarray analysis and the Kaplan-Meier method. The biological function was confirmed through in vitro and in vivo knockdown approaches of SENP1. The role of SENP1 in cell cycle progression and apoptosis of ESCC cells was analyzed by flow cytometry and western blot. The downstream signaling pathways regulated by SENP1 were investigated via using RNA-Seq. SENP1-associated proteins were identified through immunoprecipitation. Overexpression of Sirtuin 6 (SIRT6) wildtype and mutant was performed to investigate the regulatory role of SENP1 in ESCC progression in vitro.

RESULTS

Our study discovered that SENP1 was upregulated in ESCC tissues and served as a novel prognostic factor. Moreover, SENP1 enhanced cell proliferation and migration of ESCC cell lines in vitro, as well as promoted tumor growth in vivo. Thymidine kinase 1 (TK1), Geminin (GMNN), cyclin dependent kinase 1(CDK1), and cyclin A2 (CCNA2) were identified as downstream genes of SENP1. Mechanistically, SENP1 deSUMOylated SIRT6 and subsequently inhibited SIRT6-mediated histone 3 lysine 56 (H3K56) deacetylation on those downstream genes. SIRT6 SUMOylation mutant (4KR) rescued the growth inhibition upon SENP1 depletion.

CONCLUSIONS

SENP1 promotes the malignant progression of ESCC by inhibiting the deacetylase activity of SIRT6 pathway through deSUMOylation. Our findings suggest that SENP1 may serve as a valuable biomarker for prognosis and a target for therapeutic intervention in ESCC.

Pyruvate Kinase M2: A Potential Regulator of Cardiac Injury Through Glycolytic and Non-glycolytic Pathways

ABSTRACT

Adult animals are unable to regenerate heart cells due to postnatal cardiomyocyte cycle arrest, leading to higher mortality rates in cardiomyopathy. However, reprogramming of energy metabolism in cardiomyocytes provides a new perspective on the contribution of glycolysis to repair, regeneration, and fibrosis after cardiac injury. Pyruvate kinase (PK) is a key enzyme in the glycolysis process. This review focuses on the glycolysis function of PKM2, although PKM1 and PKM2 both play significant roles in the process after cardiac injury. PKM2 exists in both low-activity dimer and high-activity tetramer forms. PKM2 dimers promote aerobic glycolysis but have low catalytic activity, leading to the accumulation of glycolytic intermediates. These intermediates enter the pentose phosphate pathway to promote cardiomyocyte proliferation and heart regeneration. Additionally, they activate adenosine triphosphate (ATP)-sensitive K + (K ATP ) channels, protecting the heart against ischemic damage. PKM2 tetramers function similar to PKM1 in glycolysis, promoting pyruvate oxidation and subsequently ATP generation to protect the heart from ischemic damage. They also activate KDM5 through the accumulation of αKG, thereby promoting cardiomyocyte proliferation and cardiac regeneration. Apart from glycolysis, PKM2 interacts with transcription factors like Jmjd4, RAC1, β-catenin, and hypoxia-inducible factor (HIF)-1α, playing various roles in homeostasis maintenance, remodeling, survival regulation, and neovascularization promotion. However, PKM2 has also been implicated in promoting cardiac fibrosis through mechanisms like sirtuin (SIRT) 3 deletion, TG2 expression enhancement, and activation of transforming growth factor-β1 (TGF-β1)/Smad2/3 and Jak2/Stat3 signals. Overall, PKM2 shows promising potential as a therapeutic target for promoting cardiomyocyte proliferation and cardiac regeneration and addressing cardiac fibrosis after injury.

Rutaecarpine Alleviates Early Brain Injury-Induced Inflammatory Response Following Subarachnoid Hemorrhage via SIRT6/NF-[Formula: see text]B Pathway

Subarachnoid hemorrhage (SAH), a specific subtype of cerebrovascular accident, is characterized by the extravasation of blood into the interstice between the brain and its enveloping delicate tissues. This pathophysiological phenomenon can precipitate an early brain injury (EBI), which is characterized by inflammation and neuronal death. Rutaecarpine (Rut), a flavonoid compound discovered in various plants, has been shown to have protective effects against SAH-induced cerebral insult in rodent models. In our study, we used a rodent SAH model to evaluate the effect of Rut on EBI and investigated the effect of Rut on the inflammatory response and its regulation of SIRT6 expression in vitro. We found that Rut exerts a protective effect on EBI in SAH rats, which is partly due to its ability to inhibit the inflammatory response. Notably, Rut up-regulated Sirtuin 6 (SIRT6) expression, leading to an increase in H3K9 deacetylation and inhibition of nuclear factor-kappa B (NF-[Formula: see text]B) transcriptional activation, thereby mediating the inflammatory response. In addition, further data showed that SIRT6 was proven to mediate the regulation of Rut on the microglial inflammatory response. These findings highlight the importance of SIRT6 in the regulation of inflammation and suggest a potential mechanism for the protective effect of Rut on EBI. In summary, Rut may have the potential to prevent and treat SAH-induced brain injury by interacting with SIRT6. Our findings may provide a new therapeutic strategy for the treatment of SAH-induced EBI.

The role and therapeutic potential of SIRTs in sepsis

Sepsis is a life-threatening organ dysfunction caused by the host's dysfunctional response to infection. Abnormal activation of the immune system and disturbance of energy metabolism play a key role in the development of sepsis. In recent years, the Sirtuins (SIRTs) family has been found to play an important role in the pathogenesis of sepsis. SIRTs, as a class of histone deacetylases (HDACs), are widely involved in cellular inflammation regulation, energy metabolism and oxidative stress. The effects of SIRTs on immune cells are mainly reflected in the regulation of inflammatory pathways. This regulation helps balance the inflammatory response and may lessen cell damage and organ dysfunction in sepsis. In terms of energy metabolism, SIRTs can play a role in immunophenotypic transformation by regulating cell metabolism, improve mitochondrial function, increase energy production, and maintain cell energy balance. SIRTs also regulate the production of reactive oxygen species (ROS), protecting cells from oxidative stress damage by activating antioxidant defense pathways and maintaining a balance between oxidants and reducing agents. Current studies have shown that several potential drugs, such as Resveratrol and melatonin, can enhance the activity of SIRT. It can help to reduce inflammatory response, improve energy metabolism and reduce oxidative stress, showing potential clinical application prospects for the treatment of sepsis. This review focuses on the regulation of SIRT on inflammatory response, energy metabolism and oxidative stress of immune cells, as well as its important influence on multiple organ dysfunction in sepsis, and discusses and summarizes the effects of related drugs and compounds on reducing multiple organ damage in sepsis through the pathway involving SIRTs. SIRTs may become a new target for the treatment of sepsis and its resulting organ dysfunction, providing new ideas and possibilities for the treatment of this life-threatening disease.

PP4R1 promotes glycolysis and gallbladder cancer progression through facilitating ERK1/2 mediated PKM2 nuclear translocation

Gallbladder cancer (GBC) is a common solid tumor of the biliary tract with a high mortality rate and limited curative benefits from surgical resection. Here, we aimed to elucidate the pathogenesis of GBC from the perspective of molecular mechanisms and determined that protein phosphatase 4 regulator subunit 1 (PP4R1) is overexpressed in GBC tissues and contributes to poor prognosis. Through a series of in vitro and in vivo experiments, we demonstrated that PP4R1 overexpression improved tumorigenesis in GBC cells. Further mechanistic exploration revealed that PP4R1 directly interacts with pyruvate kinase-M2 (PKM2), a key regulator of glycolysis. PP4R1 promotes the extracellular signal-related kinase 1 and 2 (ERK1/2)-mediated PKM2 nuclear translocation, thereby participating in the regulation of tumor glycolysis. Interestingly, we determined that PP4R1 strengthens the interaction between ERK1/2 and PKM2. Furthermore, PP4R1 enhanced the suppressive effects of the ERK inhibitor SCH772984 on GBC. In conclusion, our data showed that PP4R1 is a promising biomarker associated with GBC and confirmed that PP4R1 regulates PKM2-mediated tumor glycolysis, which provides a metabolic growth advantage to GBC cells, thereby promoting GBC tumor growth and metastasis1.

Sirt6 ablation in the liver causes fatty liver that increases cancer risky by upregulating Serpina12

Non-alcoholic fatty liver disease is a chronic liver abnormality that exhibits high variability and can lead to liver cancer in advanced stages. Hepatic ablation of SIRT6 results in fatty liver disease, yet the potential mechanism of SIRT6 deficiency, particularly in relation to downstream mediators for NAFLD, remains elusive. Here we identify Serpina12 as a key gene regulated by Sirt6 that plays a crucial function in energy homeostasis. Specifically, Sirt6 suppresses Serpina12 expression through histone deacetylation at its promoter region, after which the transcription factor, Cebpα, binds to and regulates its expression. Sirt6 deficiency results in an increased expression of Serpina12 in hepatocytes, which enhances insulin signaling and promotes lipid accumulation. Importantly, CRISPR-Cas9 mediated Serpina12 knockout in the liver ameliorated fatty liver disease caused by Sirt6 ablation. Finally, we demonstrate that Sirt6 functions as a tumor suppressor in the liver, and consequently, deletion of Sirt6 in the liver leads to not only the spontaneous development of tumors but also enhanced tumorigenesis in response to DEN treatment or under conditions of obesity.

The Role of Sirtuin 6 in the Deacetylation of Histone Proteins as a Factor in the Progression of Neoplastic Disease

SIRT6 is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase, predominantly located in the nucleus, that is involved in the processes of histone modification, DNA repair, cell cycle regulation, and apoptosis. Disturbances in SIRT6 expression levels have been observed in the development and progression of various types of cancer. Therefore, it is important to better understand the role of SIRT6 in biochemical pathways and assign it specific biological functions. This review aims to summarize the role of SIRT6 in carcinogenesis and tumor development. A better understanding of the factors influencing SIRT6 expression and its biological role in carcinogenesis may help to develop novel anti-cancer therapeutic strategies. Moreover, we discuss the anti-cancer effects and mechanism of action of small molecule SIRT6 modulators (both activators and inhibitors) in different types of cancer.

Role in posttranslational modification of M2type pyruvate kinase in tumorigenesis and development

PKM2, also known as M2-type pyruvate kinase, has attracted significant attention due to its crucial role in glycolysis and its abnormal expression in various tumors. With the discovery of PKM2's non-metabolic functions, the transition between its pyruvate kinase activity (in the tetrameric form in the cytoplasm) and protein kinase activity (in the dimeric form in the nucleus) has once again made PKM2 a target of interest in cancer research. Studies have shown that PKM2 is a protein susceptible to various post-translational modifications, and different post-translational modifications play important regulatory roles in processes such as PKM2 cellular localization, structure, and enzyme activity conversion. In this review, we focused on the recent progress of multiple post-translational modifications of PKM2 and their important roles in tumor initiation and development. For example, phosphorylation and acetylation promote nuclear translocation by altering PKM2 cell localization; glycosylation and ubiquitination can promote the formation of dimer structure by affecting the structural transformation of PKM2; succinylation and redox modification promoted the enhancement of PKM2 kinase activity by affecting the transformation of kinase activity. Both changes affect the structure and cell localization of PKM2 and they play a role in promoting or inhibiting tumor development via altering its kinase activity.

Nuclear transport proteins: structure, function, and disease relevance

Proper subcellular localization is crucial for the functioning of biomacromolecules, including proteins and RNAs. Nuclear transport is a fundamental cellular process that regulates the localization of many macromolecules within the nuclear or cytoplasmic compartments. In humans, approximately 60 proteins are involved in nuclear transport, including nucleoporins that form membrane-embedded nuclear pore complexes, karyopherins that transport cargoes through these complexes, and Ran system proteins that ensure directed and rapid transport. Many of these nuclear transport proteins play additional and essential roles in mitosis, biomolecular condensation, and gene transcription. Dysregulation of nuclear transport is linked to major human diseases such as cancer, neurodegenerative diseases, and viral infections. Selinexor (KPT-330), an inhibitor targeting the nuclear export factor XPO1 (also known as CRM1), was approved in 2019 to treat two types of blood cancers, and dozens of clinical trials of are ongoing. This review summarizes approximately three decades of research data in this field but focuses on the structure and function of individual nuclear transport proteins from recent studies, providing a cutting-edge and holistic view on the role of nuclear transport proteins in health and disease. In-depth knowledge of this rapidly evolving field has the potential to bring new insights into fundamental biology, pathogenic mechanisms, and therapeutic approaches.

Nuclear translocation of PKM2 mediates keratinocyte metabolic reprogramming in psoriasis

PKM2 mediates the Warburg effects and is crucial for tumorigenesis, but its role in hyperplastic skin disorders remains elusive. In this study, we investigated the function of PKM2 in psoriatic keratinocytes. We found that PKM2 expression and its nuclear translocation were induced in the epidermis of psoriasis patients, contributing to aerobic glycolysis and cell growth. Moreover, mass spectrometry combined with immunoprecipitation analysis revealed that PKM2 could interact with TRIM33, an E3 ubiquitin ligase in the nucleus, and this interaction is critical for the nuclear retention of PKM2. As a result of TRIM33-mediated ubiquitination, PKM2 nuclear protein kinase function is promoted, thus leading to the phosphorylation of STAT3. In addition, blocking PKM2 nuclear translocation abrogated TRIM33-triggered glycolysis and cell proliferation in keratinocytes. Taken together, our experiments demonstrate that ubiquitination regulates the nuclear retention of PKM2 in keratinocytes. Moreover, our results highlight a novel mechanism accounting for the metabolic reprogramming of keratinocytes in psoriasis patients.

The Role of NAD+, SIRTs Interactions in Stimulating and Counteracting Carcinogenesis

The World Health Organization has identified oncological diseases as one of the most serious health concerns of the current century. Current research on oncogenesis is focused on the molecular mechanisms of energy-biochemical reprogramming in cancer cell metabolism, including processes contributing to the Warburg effect and the pro-oncogenic and anti-oncogenic roles of sirtuins (SIRTs) and poly-(ADP-ribose) polymerases (PARPs). However, a clear understanding of the interaction between NAD⁺, SIRTs in cancer development, as well as their effects on carcinogenesis, has not been established, and literature data vary greatly. This work aims to provide a summary and structure of the available information on NAD⁺, SIRTs interactions in both stimulating and countering carcinogenesis, and to discuss potential approaches for pharmacological modulation of these interactions to achieve an anticancer effect.

20-Hydroxyecdysone inhibits inflammation via SIRT6-mediated NF-κB signaling in endothelial cells

20-Hydroxyecdysone (20E) is known to have numerous pharmacological activities and can be used to treat diabetes and cardiovascular diseases. However, the protective effects of 20E against endothelial dysfunction and its targets remain unclear. In the present study, we revealed that 20E treatment could modulate the release of the endothelium-derived vasomotor factors NO, PGI₂ and ET-1 and suppress the expression of ACE in TNF-α-induced 3D-cultured HUVECs. In addition, 20E suppressed the expression of CD40 and promoted the expression of SIRT6 in TNF-α-induced 3D-cultured HUVECs. The cellular thermal shift assay (CETSA), drug affinity responsive target stability (DARTS) and molecular docking results demonstrated that 20E binding increased SIRT6 stability, indicating that 20E directly bound to SIRT6 in HUVECs. Further investigation of the underlying mechanism showed that 20E could upregulate SIRT6 levels and that SIRT6 knockdown abolished the regulatory effect of 20E on CD40 in TNF-α-induced HUVECs, while SIRT6 overexpression further improved the effect of 20E. Moreover, we found that 20E could reduce the acetylation of NF-κB p65 (K310) through SIRT6, but the catalytic inactive mutant SIRT6 (H133Y) did not promote the deacetylation of NF-κB p65, suggesting that the inhibitory effect of 20E on NF-κB p65 was dependent on SIRT6 deacetylase activity. Additionally, our results indicated that 20E inhibited NF-κB via SIRT6, and the expression of CD40 was increased in HUVECs treated with SIRT6 siRNA and NF-κB inhibitor. In conclusion, the present study demonstrates that 20E exerts its effect through SIRT6-mediated deacetylation of NF-κB p65 (K310) to inhibit CD40 expression in ECs, and 20E may have therapeutic potential for the treatment of cardiovascular diseases.

Sirtuin-dependent metabolic and epigenetic regulation of macrophages during tuberculosis

Macrophages are the preeminent phagocytic cells which control multiple infections. Tuberculosis a leading cause of death in mankind and the causative organism Mycobacterium tuberculosis (MTB) infects and persists in macrophages. Macrophages use reactive oxygen and nitrogen species (ROS/RNS) and autophagy to kill and degrade microbes including MTB. Glucose metabolism regulates the macrophage-mediated antimicrobial mechanisms. Whereas glucose is essential for the growth of cells in immune cells, glucose metabolism and its downsteam metabolic pathways generate key mediators which are essential co-substrates for post-translational modifications of histone proteins, which in turn, epigenetically regulate gene expression. Herein, we describe the role of sirtuins which are NAD+-dependent histone histone/protein deacetylases during the epigenetic regulation of autophagy, the production of ROS/RNS, acetyl-CoA, NAD+, and S-adenosine methionine (SAM), and illustrate the cross-talk between immunometabolism and epigenetics on macrophage activation. We highlight sirtuins as emerging therapeutic targets for modifying immunometabolism to alter macrophage phenotype and antimicrobial function.

SIRT6 regulates endothelium-dependent relaxation by modulating nitric oxide synthase 3 (NOS3)

BACKGROUND AND OBJECTIVE

SIRT6, an NAD⁺-dependent protein deacetylase, is a key modulator of various biological functions. However, the precise role of SIRT6 in the regulation of endothelial function is still not fully understood. The current study sought to determine whether SIRT6 modulates NOS3 activity to regulate endothelium-dependent relaxations in the arterial wall and, if so, to investigate the potential underlying mechanism (s).

METHODS

ApoE^-/- mice and Sprague-Dawley rats had their aortic rings isolated for a vascular reactivity assay. Endothelial cells were cultured before qRT-PCR, western blot, immunoprecipitation, NO bioavailability, and acetylation/deacetylation assays were performed.

RESULTS

SIRT6 expression was significantly reduced in the aorta of ApoE^-/- mice fed a high-cholesterol diet, as was endothelium-dependent relaxation. Endothelial dysfunction could be corrected by delivering a SIRT6 overexpression construct via an adenovirus. In cultured endothelial cells, siRNA knockdown of SIRT6 decreased NOS3 catalytic activity, whereas adenoviral overexpression of SIRT6 increased NOS3-derived nitric oxide (NO) generation. SIRT6 interacted with and deacetylated human NOS3 at lysines 494, 497, and 504 of the calmodulin-binding domain, allowing calmodulin to bind to NOS3 and stimulate NOS3 activity. SIRT6 knockdown also reduced NOS3 expression by inhibiting Kruppel-Like Factor 2 (KLF2).

CONCLUSIONS

We identified SIRT6 as a new regulator of the activity of NOS3, with functional implications for endothelial-dependent relaxation.

Sirtuin 6-A Key Regulator of Hepatic Lipid Metabolism and Liver Health

Sirtuin 6 (SIRT6) is an NAD-dependent deacetylase/deacylase/mono-ADP ribosyltransferase, a member of the sirtuin protein family. SIRT6 has been implicated in hepatic lipid homeostasis and liver health. Hepatic lipogenesis is driven by several master regulators including liver X receptor (LXR), carbohydrate response element binding protein (ChREBP), and sterol regulatory element binding protein 1 (SREBP1). Interestingly, these three transcription factors can be negatively regulated by SIRT6 through direct deacetylation. Fatty acid oxidation is regulated by peroxisome proliferator activated receptor alpha (PPARα) in the liver. SIRT6 can promote fatty acid oxidation by the activation of PPARα or the suppression of miR-122. SIRT6 can also directly modulate acyl-CoA synthetase long chain family member 5 (ACSL5) activity for fatty acid oxidation. SIRT6 also plays a critical role in the regulation of total cholesterol and low-density lipoprotein (LDL)-cholesterol through the regulation of SREBP2 and proprotein convertase subtilisin/kexin type 9 (PCSK9), respectively. Hepatic deficiency of Sirt6 in mice has been shown to cause hepatic steatosis, inflammation, and fibrosis, hallmarks of alcoholic and nonalcoholic steatohepatitis. SIRT6 can dampen hepatic inflammation through the modulation of macrophage polarization from M1 to M2 type. Hepatic stellate cells are a key cell type in hepatic fibrogenesis. SIRT6 plays a strong anti-fibrosis role by the suppression of multiple fibrogenic pathways including the transforming growth factor beta (TGFβ)-SMAD family proteins and Hippo pathways. The role of SIRT6 in liver cancer is quite complicated, as both tumor-suppressive and tumor-promoting activities have been documented in the literature. Overall, SIRT6 has multiple salutary effects on metabolic homeostasis and liver health, and it may serve as a therapeutic target for hepatic metabolic diseases. To date, numerous activators and inhibitors of SIRT6 have been developed for translational research.

Sirtuin 1 activator alleviated lethal inflammatory injury via promotion of autophagic degradation of pyruvate kinase M2

Upregulation of pyruvate kinase M2 (PKM2) is critical for the orchestration of metabolism and inflammation in critical illness, while autophagic degradation is a recently revealed mechanism that counter-regulates PKM2. Accumulating evidence suggests that sirtuin 1 (SIRT1) function as a crucial regulator in autophagy. The present study investigated whether SIRT1 activator would downregulate PKM2 in lethal endotoxemia via promotion of its autophagic degradation. The results indicated that lethal dose of lipopolysaccharide (LPS) exposure decreased the level of SIRT1. Treatment with SRT2104, a SIRT1 activator, reversed LPS-induced downregulation of LC3B-II and upregulation of p62, which was associated with reduced level of PKM2. Activation of autophagy by rapamycin also resulted in reduction of PKM2. The decline of PKM2 in SRT2104-treated mice was accompanied with compromised inflammatory response, alleviated lung injury, suppressed elevation of blood urea nitrogen (BUN) and brain natriuretic peptide (BNP), and improved survival of the experimental animals. In addition, co-administration of 3-methyladenine, an autophagy inhibitor, or Bafilomycin A1, a lysosome inhibitor, abolished the suppressive effects of SRT2104 on PKM2 abundance, inflammatory response and multiple organ injury. Therefore, promotion of autophagic degradation of PKM2 might be a novel mechanism underlying the anti-inflammatory benefits of SIRT1 activator.

SIRT6 in Aging, Metabolism, Inflammation and Cardiovascular Diseases

As an important NAD⁺-dependent enzyme, SIRT6 has received significant attention since its discovery. In view of observations that SIRT6-deficient animals exhibit genomic instability and metabolic disorders and undergo early death, SIRT6 has long been considered a protein of longevity. Recently, growing evidence has demonstrated that SIRT6 functions as a deacetylase, mono-ADP-ribosyltransferase and long fatty deacylase and participates in a variety of cellular signaling pathways from DNA damage repair in the early stage to disease progression. In this review, we elaborate on the specific substrates and molecular mechanisms of SIRT6 in various physiological and pathological processes in detail, emphasizing its links to aging (genomic damage, telomere integrity, DNA repair), metabolism (glycolysis, gluconeogenesis, insulin secretion and lipid synthesis, lipolysis, thermogenesis), inflammation and cardiovascular diseases (atherosclerosis, cardiac hypertrophy, heart failure, ischemia-reperfusion injury). In addition, the most recent advances regarding SIRT6 modulators (agonists and inhibitors) as potential therapeutic agents for SIRT6-mediated diseases are reviewed.

Histone acetylation modifications: A potential targets for the diagnosis and treatment of papillary thyroid cancer

Thyroid cancer is a common malignancy of the endocrine system, with papillary thyroid cancer (PTC) being the most common type of pathology. The incidence of PTC is increasing every year. Histone acetylation modification is an important part of epigenetics, regulating histone acetylation levels through histone acetylases and histone deacetylases, which alters the proliferation and differentiation of PTC cells and affects the treatment and prognosis of PTC patients. Histone deacetylase inhibitors induce histone acetylation, resulting in the relaxation of chromatin structure and activation of gene transcription, thereby promoting differentiation, apoptosis, and growth arrest of PTC cells.

Targeting the acetylation signaling pathway in cancer therapy

Acetylation represents one of the major post-translational protein modifications, which introduces an acetyl functional group into amino acids such as the lysine residue to yield an acetate ester bond, neutralizing its positive charge. Regulation of protein functions by acetylation occurs in multiple ways, such as affecting protein stability, activity, localization, and interaction with other proteins or DNA. It has been well documented that the recruitment of histone acetyltransferases (HATs) and histone deacetylases (HDACs) to the transcriptional machinery can modulate histone acetylation status, which is directly involved in the dynamic regulation of genes controlling cell proliferation and division. Dysregulation of gene expression is involved in tumorigenesis and aberrant activation of histone deacetylases has been reported in several types of cancer. Moreover, there is growing body of evidence showing that acetylation is widely involved in non-histone proteins to impact their roles in various cellular processes including tumorigenesis. As such, small molecular compounds inhibiting HAT or HDAC enzymatic activities have been developed and investigated for therapeutic purpose. Here we review the recent progress in our understanding of protein acetylation and discuss the therapeutic potential of targeting the acetylation signaling pathway in cancer.

Quantitative acetylomics reveals dynamics of protein lysine acetylation in mouse livers during aging and upon the treatment of nicotinamide mononucleotide

Lysine acetylation is a reversible and dynamic post-translational modification that play vital roles in regulating multiple cellular processes including aging. However, acetylome-wide analysis in the aging process remains poorly studied in mammalian tissues. Nicotinamide adenine dinucleotide (NAD⁺), a hub metabolite, benefits healthspan at least in part due to the activation of Sirtuins, a family of NAD⁺-consuming deacetylases, indicating changes in acetylome. Here, we combine two antibodies for the enrichment of acetylated peptides and perform label-free quantitative acetylomic analysis of mouse livers during natural aging and upon the treatment of beta-nicotinamide mononucleotide (NMN), a NAD⁺ booster. Our study describes previously unknown acetylation sites and reveals the acetylome-wide dynamics with age as well as upon the treatment of NMN. We discover protein acetylation events as potential aging biomarkers. We demonstrate that the life-beneficial effect of NMN could be partially reflected by the changes in age-related protein acetylation. Our quantitative assessment indicates that NMN has mild effects on acetylation sites previously reported as substrates of Sirtuins. Collectively, our data analyzes protein acetylation with age, laying critical foundation for the functional study of protein post-translational modification essential for healthy aging and perhaps disease conditions.

The Role of HDACs in the Response of Cancer Cells to Cellular Stress and the Potential for Therapeutic Intervention

Throughout the process of carcinogenesis, cancer cells develop intricate networks to adapt to a variety of stressful conditions including DNA damage, nutrient deprivation, and hypoxia. These molecular networks encounter genomic instability and mutations coupled with changes in the gene expression programs due to genetic and epigenetic alterations. Histone deacetylases (HDACs) are important modulators of the epigenetic constitution of cancer cells. It has become increasingly known that HDACs have the capacity to regulate various cellular systems through the deacetylation of histone and bounteous nonhistone proteins that are rooted in complex pathways in cancer cells to evade death pathways and immune surveillance. Elucidation of the signaling pathways involved in the adaptive responses to cellular stress and the role of HDACs may lead to the development of novel therapeutic agents. In this article, we overview the dominant stress types including metabolic, oxidative, genotoxic, and proteotoxic stress imposed on cancer cells in the context of HDACs, which guide stress adaptation responses. Next, we expose a closer view on the therapeutic interventions and clinical trials that involve HDACs inhibitors, in addition to highlighting the impact of using HDAC inhibitors in combination with stress-inducing agents for the management of cancer and to overcome the resistance to current cancer therapy.

Characterizing the Effect of the Lysine Deacetylation Modification on Enzyme Activity of Pyruvate Kinase I and Pathogenicity of Vibrio alginolyticus

Pyruvate kinase I (PykF) is one of the key enzymes of glycolysis and plays a crucial role in bacterial metabolism. Several acetylation sites of Vibrio alginolyticus PykF were reported in previous studies and then 11 sites were first verified in this study, however, the specific roles of PykF acetylation remains unclear. Overlap-PCR and homologous recombination were implied to delete V. alginolyticus pykF gene and constructed complementary strains of site-directed mutagenesis for the further research focus on the deacetylation regulation on PykF. The results showed that the pyruvate kinase activity was sharply suppressed in the deacetylation status of K52, K68, and K317 of PykF, as well as the extracellular protease activity was significantly decreased in the deacetylation status of K52 and K68, but not induced with K317. Moreover, the growth rates of V. alginolyticus were not influenced with these three deacetylation sites. The ΔpykF mutant exhibited a 6-fold reduction in virulence to zebrafish. Site-directed mutations of K52R and K68R also showed reduced virulence while mutations of K317R didn't. The in vitro experiments showed that PykF was acetylated by acetyl phosphate (AcP), with the increase of incubation time by AcP, the acetylation level of PykF increased while the enzyme activity of PykF decreased correspondingly. Besides, PykF was deacetylated by CobB deacetylase and in result that the deacetylation was significantly down-regulated while the pyruvate kinase activity of PykF increased. Moreover, deletion of cobB gene had no significant difference in pyruvate kinase activity. These results confirm that CobB can regulate the acetylation level and pyruvate kinase activity of PykF. In summary, the results of this study provide a theoretical basis for further understanding of the deacetylation modification of PykF. It provides a new idea for the prevention and cure of vibriosis.

SIRT6 mediates multidimensional modulation to maintain organism homeostasis

As a member of the silent information regulators (sirtuins) family, SIRT6 can regulate a variety of biological processes, including DNA repair, glucose and lipid metabolism, oxidative stress and lifespan, and so forth. SIRT6 maintains organism homeostasis in a variety of phenotypes by mediating epigenetic regulation and posttranslational modification of functional proteins. In this review, we outline the structural basis of SIRT6 enzyme activity and its mechanism of maintaining organism homeostasis in a variety of phenotypes, with an emphasis on the upstream that regulates SIRT6 expression and the downstream substrates. And how SIRT6 achieves multidimensional coordination to maintain organism homeostasis and even extend lifespan. We try to understand the regulatory mechanism of SIRT6 in different phenotypes from the perspective of protein interaction.

SIRT6 Widely Regulates Aging, Immunity, and Cancer

SIRT6 is a member of the Sir2-like family in mammals. Recent structural and biochemical studies have characterized SIRT6 as having deacetylation, defatty-acylation, and mono-ADP-ribosylation activities, which determine its important regulatory roles during physiological and pathological processes. This review focuses mainly on the regulatory functions of SIRT6 in aging, cancer, and, especially, immunity. Particular attention is paid to studies illustrating the critical role of SIRT6 in the regulation of immune cells from the viewpoints of immunesenescence, immunometabolism, and tumor immunology. Owing to its role in regulating the function of the immune system, SIRT6 can be considered to be a potential therapeutic target for the treatment of diseases.

Role of sirtuins in esophageal cancer: Current status and future prospects

Esophageal cancer (EC) is a malignant cancer that still has a poor prognosis, although its prognosis has been improving with the development of multidisciplinary treatment modalities such as surgery, chemotherapy and radiotherapy. Therefore, identifying specific molecular markers that can be served as biomarkers for the prognosis and treatment response of EC is highly desirable to aid in the personalization and improvement of the precision of medical treatment. Sirtuins are a family of nicotinamide adenine dinucleotide (NAD+)-dependent proteins consisting of seven members (SIRT1-7). These proteins have been reported to be involved in the regulation of a variety of biological functions including apoptosis, metabolism, stress response, senescence, differentiation and cell cycle progression. Given the variety of functions of sirtuins, they are speculated to be associated in some manner with cancer progression. However, while the role of sirtuins in cancer progression has been investigated over the past few years, their precise role remains difficult to characterize, as they have both cancer-promoting and cancer-suppressing properties, depending on the type of cancer. These conflicting characteristics make research into the nature of sirtuins all the more fascinating. However, the role of sirtuins in EC remains unclear due to the limited number of reports concerning sirtuins in EC. We herein review the current findings and future prospects of sirtuins in EC.

Sirtuin 6 is a negative regulator of FcεRI signaling and anaphylactic responses

BACKGROUND

Binding IgE to a cognate allergen causes aggregation of Fcε receptor I (FcεRI) in mast cells, resulting in activation of receptor-associated Src family tyrosine kinases, including Lyn and Syk. Protein tyrosine phosphatase, receptor type C (PTPRC), also known as CD45, has emerged as a positive regulator of FcεRI signaling by dephosphorylation of the inhibitory tyrosine of Lyn.

OBJECTIVE

Sirtuin 6 (Sirt6), a NAD+-dependent deacetylase, exhibits an anti-inflammatory property. It remains to be determined, however, whether Sirt6 attenuates mast cell-associated diseases, including anaphylaxis.

METHODS

FcεRI signaling and mast cell degranulation were measured after IgE cross-linking in murine bone marrow-derived mast cells (BMMCs) and human cord blood-derived mast cells. To investigate the function of Sirt6 in mast cell activation in vivo, we used mast cell-dependent animal models of passive systemic anaphylaxis (PSA) and passive cutaneous anaphylaxis (PCA).

RESULTS

Sirt6-deficient BMMCs augmented IgE-FcεRI-mediated signaling and degranulation compared to wild-type BMMCs. Reconstitution of mast cell-deficient KitW-sh/W-sh mice with BMMCs received from Sirt6 knockout mice developed more severe PSA and PCA compared to mice engrafted with wild-type BMMCs. Similarly, genetic overexpression or pharmacologic activation of Sirt6 suppressed mast cell degranulation and blunted responses to PCA. Mechanistically, Sirt6 deficiency increased PTPRC transcription via acetylating histone H3, leading to enhanced aggregation of FcεRI in BMMCs. Finally, we recapitulated the Sirt6 regulation of PTPRC and FcεRI signaling in human mast cells.

CONCLUSIONS

Sirt6 acts as a negative regulator of FcεRI signaling cascade in mast cells by suppressing PTPRC transcription. Activation of Sirt6 may therefore represent a promising and novel therapeutic strategy for anaphylaxis.

Sirtuin 6 Is a Critical Epigenetic Regulator of Cancer

Sirtuin 6 (SIRT6) is a member of the mammalian sirtuin family with deacetylase, deacylase, and mono-ADP-ribosyl-transferase activities. It is a multitasking chromatin-associated protein regulating different cellular and physiological functions in cells. Specifically, SIRT6 dysfunction is implicated in several aging-related human diseases, including cancer. Studies indicate that SIRT6 has a tumor-specific role, and it is considered a tumor suppressor as well as a tumor growth inducer, depending on the type of cancer. In this chapter, we review the role of SIRT6 in metabolism, genomic stability, and cancer. Further, we provide an insight into the interplay of the tumor-suppressing and oncogenic roles of SIRT6 in cancer. Additionally, we discuss the use of small-molecule SIRT6 modulators as potential therapeutics.

Deubiquitinase OTUB2 exacerbates the progression of colorectal cancer by promoting PKM2 activity and glycolysis

Aberrant regulation of ubiquitination often leads to metabolic reprogramming in tumor cells. However, the underlying mechanisms are not fully understood. Here we demonstrate that OTUB2, an OTU deubiquitinase, is upregulated in colorectal cancer (CRC) and exacerbates the progression of CRC through modulating the aerobic glycolysis. Mechanistically, OTUB2 directly interacts with pyruvate kinase M2 (PKM2) and inhibits its ubiquitination by blocking the interaction between PKM2 and its ubiquitin E3 ligase Parkin, thereby enhancing PKM2 activity and promoting glycolysis. In response to glucose starvation stress, the effect of OTUB2 on PKM2 is enhanced, which confers metabolic advantage to CRC cells. Moreover, OTUB2 depletion reduces glucose consumption, lactate production, and cellular ATP production. OTUB2-knockout CRC cells exhibit attenuated proliferation and migration, as well as an elevated level of apoptosis and increased sensitivity to chemotherapy drugs. Furthermore, in vivo assays show that knockout of OTUB2 inhibits tumor growth in mice. Taken together, these findings reveal the critical role of OTUB2 in the regulation of glycolysis and illustrate the molecular mechanism underlying its role as a negative regulator of PKM2 ubiquitination in CRC, establishing a bridge between OTUB2-regulated PKM2 ubiquitination and altered metabolic patterns in CRC and suggesting that OTUB2 is a promising target for CRC treatment.

Protein acetylation effects on enzyme activity and metabolic pathway fluxes

Acetylation of proteins seems a widespread process found in the three domains of life. Several studies have shown that besides histones, acetylation of lysine residues also occurs in non-nuclear proteins. Hence, it has been suggested that this covalent modification is a mechanism that might regulate diverse metabolic pathways by modulating enzyme activity, stability, and/or subcellular localization or interaction with other proteins. However, protein acetylation levels seem to have low correlation with modification of enzyme activity and pathway fluxes. In addition, the results obtained with mutant enzymes that presumably mimic acetylation have frequently been over-interpreted. Moreover, there is a generalized lack of rigorous enzyme kinetic analysis in parallel to acetylation level determinations. The purpose of this review is to analyze the current findings on the impact of acetylation on metabolic enzymes and its repercussion on metabolic pathways function/regulation.

Pyruvate kinase M2 (PKM2) interacts with activating transcription factor 2 (ATF2) to bridge glycolysis and pyroptosis in microglia

Pyruvate kinase M2 (PKM2), a glycolytic rate-limiting enzyme, reportedly plays an important role in tumorigenesis and the inflammatory response by regulating the metabolic reprogramming. However, its contribution to microglial activation during neuroinflammation is still unknown. In this study, we observed an enhanced glycolysis level in the lipopolysaccharide (LPS)-activated microglia. Utilizing the glycolysis inhibitor 2-DG, we proved that LPS requires glycolysis to induce microglial pyroptosis. Moreover, the protein expression, dimer/monomer formation, phosphorylation and nuclear translocation of PKM2 were all increased by LPS. Silencing PKM2 or preventing its nuclear translocation by TEPP-46 significantly alleviated the LPS-induced inflammatory response and pyroptosis in microglia. Employing biological mass spectrometry combined with immunoprecipitation technology, we identified for the first time that PKM2 interacts with activating transcription factor 2 (ATF2) in microglia. Inhibition of glycolysis or preventing PKM2 nuclear aggregation significantly reduced the phosphorylation and activation of ATF2. Furthermore, knocking down ATF2 reduced the LPS-induced pyroptosis of microglia. In vivo, we showed the LPS-induced pyroptosis in the cerebral cortex tissues of mice, and first found that an increased PKM2 expression was co-localized with ATF2 in the inflamed mice brain. Collectively, our data suggested for the first time that PKM2, a key rate-limiting enzyme of the Warburg effect, directly interacts with the pro-inflammatory transcription factor ATF2 to bridge glycolysis and pyroptosis in microglia, which might be a pivotal crosstalk between metabolic reprogramming and neuroinflammation in the CNS.

Glutathione-S-transferase P promotes glycolysis in asthma in association with oxidation of pyruvate kinase M2

BACKGROUND

Interleukin-1-dependent increases in glycolysis promote allergic airways disease in mice and disruption of pyruvate kinase M2 (PKM2) activity is critical herein. Glutathione-S-transferase P (GSTP) has been implicated in asthma pathogenesis and regulates the oxidation state of proteins via S-glutathionylation. We addressed whether GSTP-dependent S-glutathionylation promotes allergic airways disease by promoting glycolytic reprogramming and whether it involves the disruption of PKM2.

METHODS

We used house dust mite (HDM) or interleukin-1β in C57BL6/NJ WT or mice that lack GSTP. Airway basal cells were stimulated with interleukin-1β and the selective GSTP inhibitor, TLK199. GSTP and PKM2 were evaluated in sputum samples of asthmatics and healthy controls and incorporated analysis of the U-BIOPRED severe asthma cohort database.

RESULTS

Ablation of Gstp decreased total S-glutathionylation and attenuated HDM-induced allergic airways disease and interleukin-1β-mediated inflammation. Gstp deletion or inhibition by TLK199 decreased the interleukin-1β-stimulated secretion of pro-inflammatory mediators and lactate by epithelial cells. 13C-glucose metabolomics showed decreased glycolysis flux at the pyruvate kinase step in response to TLK199. GSTP and PKM2 levels were increased in BAL of HDM-exposed mice as well as in sputum of asthmatics compared to controls. Sputum proteomics and transcriptomics revealed strong correlations between GSTP, PKM2, and the glycolysis pathway in asthma.

CONCLUSIONS

GSTP contributes to the pathogenesis of allergic airways disease in association with enhanced glycolysis and oxidative disruption of PKM2. Our findings also suggest a PKM2-GSTP-glycolysis signature in asthma that is associated with severe disease.

Protocatechuic aldehyde protects cardiomycoytes against ischemic injury via regulation of nuclear pyruvate kinase M2

Rescuing cells from stress damage emerges a potential therapeutic strategy to combat myocardial infarction. Protocatechuic aldehyde (PCA) is a major phenolic acid in Chinese herb Danshen (Salvia miltiorrhiza root). This study investigated whether PCA regulated nuclear pyruvate kinase isoform M2 (PKM2) function to protect cardiomyocytes. In rats subjected to isoprenaline, PCA attenuated heart injury and protected cardiomyocytes from apoptosis. Through DARTS and CETSA assays, we identified that PCA bound and promoted PKM2 nuclear translocation in cardiomyocytes exposed to oxygen/glucose deprivation (OGD). In the nucleus, PCA increased the binding of PKM2 to β-catenin via preserving PKM2 acetylation, and the complex, in cooperation with T-cell factor 4 (TCF4), was required for transcriptional induction of genes encoding anti-apoptotic proteins, contributing to rescuing cardiomyocyte survival. In addition, PCA ameliorated mitochondrial dysfunction and prevented mitochondrial apoptosis dependent on PKM2. Consistently, PCA increased the binding of PKM2 to β-catenin, improved heart contractive function, normalized heart structure and attenuated oxidative damage in mice subjected to artery ligation, but the protective effects were lost in Pkm2-deficient heart. Together, we showed that PCA regulated nuclear PKM2 function to rescue cardiomyocyte survival via β-catenin/TCF4 signaling cascade, suggesting the potential of pharmacological intervention of PKM2 shuttle to protect the heart.

Role of PKM2-Mediated Immunometabolic Reprogramming on Development of Cytokine Storm

The cytokine storm is a marker of severity of various diseases and increased mortality. The altered metabolic profile and energy generation of immune cells affects their activation, exacerbating the cytokine storm. Currently, the emerging field of immunometabolism has highlighted the importance of specific metabolic pathways in immune regulation. The glycolytic enzyme pyruvate kinase M2 (PKM2) is a key regulator of immunometabolism and bridges metabolic and inflammatory dysfunction. This enzyme changes its conformation thus walks in different fields including metabolism and inflammation and associates with various transcription factors. This review summarizes the vital role of PKM2 in mediating immunometabolic reprogramming and its role in inducing cytokine storm, with a focus on providing references for further understanding of its pathological functions and for proposing new targets for the treatment of related diseases.

SIRT6 Through the Brain Evolution, Development, and Aging

During an organism's lifespan, two main phenomena are critical for the organism's survival. These are (1) a proper embryonic development, which permits the new organism to function with high fitness, grow and reproduce, and (2) the aging process, which will progressively undermine its competence and fitness for survival, leading to its death. Interestingly these processes present various similarities at the molecular level. Notably, as organisms became more complex, regulation of these processes became coordinated by the brain, and failure in brain activity is detrimental in both development and aging. One of the critical processes regulating brain health is the capacity to keep its genomic integrity and epigenetic regulation-deficiency in DNA repair results in neurodevelopmental and neurodegenerative diseases. As the brain becomes more complex, this effect becomes more evident. In this perspective, we will analyze how the brain evolved and became critical for human survival and the role Sirt6 plays in brain health. Sirt6 belongs to the Sirtuin family of histone deacetylases that control several cellular processes; among them, Sirt6 has been associated with the proper embryonic development and is associated with the aging process. In humans, Sirt6 has a pivotal role during brain aging, and its loss of function is correlated with the appearance of neurodegenerative diseases such as Alzheimer's disease. However, Sirt6 roles during brain development and aging, especially the last one, are not observed in all species. It appears that during the brain organ evolution, Sirt6 has gained more relevance as the brain becomes bigger and more complex, observing the most detrimental effect in the brains of Homo sapiens. In this perspective, we part from the evolution of the brain in metazoans, the biological similarities between brain development and aging, and the relevant functions of Sirt6 in these similar phenomena to conclude with the evidence suggesting a more relevant role of Sirt6 gained in the brain evolution.

Mammalian SIRT6 Represses Invasive Cancer Cell Phenotypes through ATP Citrate Lyase (ACLY)-Dependent Histone Acetylation

The modulation of dynamic histone acetylation states is key for organizing chromatin structure and modulating gene expression and is regulated by histone acetyltransferase (HAT) and histone deacetylase (HDAC) enzymes. The mammalian SIRT6 protein, a member of the Class III HDAC Sirtuin family of NAD+-dependent enzymes, plays pivotal roles in aging, metabolism, and cancer biology. Through its site-specific histone deacetylation activity, SIRT6 promotes chromatin silencing and transcriptional regulation of aging-associated, metabolic, and tumor suppressive gene expression programs. ATP citrate lyase (ACLY) is a nucleo-cytoplasmic enzyme that produces acetyl coenzyme A (acetyl-CoA), which is the required acetyl donor for lysine acetylation by HATs. In addition to playing a central role in generating cytosolic acetyl-CoA for de novo lipogenesis, a growing body of work indicates that ACLY also functions in the nucleus where it contributes to the nutrient-sensitive regulation of nuclear acetyl-CoA availability for histone acetylation in cancer cells. In this study, we have identified a novel function of SIRT6 in controlling nuclear levels of ACLY and ACLY-dependent tumor suppressive gene regulation. The inactivation of SIRT6 in cancer cells leads to the accumulation of nuclear ACLY protein and increases nuclear acetyl-CoA pools, which in turn drive locus-specific histone acetylation and the expression of cancer cell adhesion and migration genes that promote tumor invasiveness. Our findings uncover a novel mechanism of SIRT6 in suppressing invasive cancer cell phenotypes and identify acetyl-CoA responsive cell migration and adhesion genes as downstream targets of SIRT6.

Nuclear Pyruvate Kinase M2 (PKM2) Contributes to Phosphoserine Aminotransferase 1 (PSAT1)-Mediated Cell Migration in EGFR-Activated Lung Cancer Cells

Simple Summary

Alternative functions for metabolic proteins have recently been shown to drive cancer growth. These may include differential enzymatic activity or novel protein associations. Phosphoserine aminotransferase 1 (PSAT1) participates in cellular serine synthesis and has been observed to be elevated in different tumor types. In this study, we aimed to identify new putative PSAT1 activities and determine their contribution to lung tumor progression. We found a direct association for PSAT1 with another enzyme, pyruvate kinase M2. While this appears not to affect PKM2’s metabolic activity, PSAT1 is required for the specific cellular localization of PKM2 upon tumorigenic signaling. Further, the depletion of PSAT1 suppresses lung cancer cell movement that can be partially restored by the compartment expression of PKM2. These findings reveal a novel mechanism that is able to promote the spread of this deadly disease.

Abstract

An elevated expression of phosphoserine aminotransferase 1 (PSAT1) has been observed in multiple tumor types and is associated with poorer clinical outcomes. Although PSAT1 is postulated to promote tumor growth through its enzymatic function within the serine synthesis pathway (SSP), its role in cancer progression has not been fully characterized. Here, we explore a putative non-canonical function of PSAT1 that contributes to lung tumor progression. Biochemical studies found that PSAT1 selectively interacts with pyruvate kinase M2 (PKM2). Amino acid mutations within a PKM2-unique region significantly reduced this interaction. While PSAT1 loss had no effect on cellular pyruvate kinase activity and PKM2 expression in non-small-cell lung cancer (NSCLC) cells, fractionation studies demonstrated that the silencing of PSAT1 in epidermal growth factor receptor (EGFR)-mutant PC9 or EGF-stimulated A549 cells decreased PKM2 nuclear translocation. Further, PSAT1 suppression abrogated cell migration in these two cell types whereas PSAT1 restoration or overexpression induced cell migration along with an elevated nuclear PKM2 expression. Lastly, the nuclear re-expression of the acetyl-mimetic mutant of PKM2 (K433Q), but not the wild-type, partially restored cell migration in PSAT1-silenced cells. Therefore, we conclude that, in response to EGFR activation, PSAT1 contributes to lung cancer cell migration, in part, by promoting nuclear PKM2 translocation.

Posttranslational modification of pyruvate kinase type M2 (PKM2): novel regulation of its biological roles to be further discovered

PKM2, pyruvate kinase type M2, has been shown to play a key role in aerobic glycolysis and to regulate the malignant behaviors of cancer cells. Recently, PKM2 has been revealed to hold dual metabolic and nonmetabolic roles. Working as both a pyruvate kinase with catalytic activity and a protein kinase that phosphorylates its substrates, PKM2 stands at the crossroads of glycolysis and tumor growth. Recently, it was revealed that the catalytic activity of PKM2 can be regulated by its posttranslational modification (PTM). Several PTM types, including phosphorylation, methylation, acetylation, oxidation, hydroxylation, succinylation, and glycylation, have been gradually identified on different amino acid residues of the PKM2 coding sequence. In this review, we highlight the recent advancements in understanding PKM2 PTMs and the regulatory roles conferred by PTMs during anaerobic glycolysis in tumors.

Multiple functions of pyruvate kinase M2 in various cell types

Glucose metabolism is a mechanism by which energy is produced in form of adenosine triphosphate (ATP) by mitochondria and precursor metabolites are supplied to enable the ultimate enrichment of mature metabolites in the cell. Recently, glycolytic enzymes have been shown to have unconventional but important functions. Among these enzymes, pyruvate kinase M2 (PKM2) plays several roles including having conventional metabolic enzyme activity, and also being a transcriptional regulator and a protein kinase. Compared with the closely related PKM1, PKM2 is highly expressed in cancer cells and embryos, whereas PKM1 is dominant in mature, differentiated cells. Posttranslational modifications such as phosphorylation and acetylation of PKM2 change its cellular functions. In particular, PKM2 can translocate to the nucleus, where it regulates the transcription of many target genes. It is notable that PKM2 also acts as a protein kinase to phosphorylate several substrate proteins. Besides cancer cells and embryonic cells, astrocytes also highly express PKM2, which is crucial for lactate production via expression of lactate dehydrogenase A (LDHA), while mature neurons predominantly express PKM1. The lactate produced in cancer cells promotes tumor progress and that in astrocytes can be supplied to neurons and may act as a major source for neuronal ATP energy production. Thereby, we propose that PKM2 along with its different posttranslational modifications has specific purposes for a variety of cell types, performing unique functions.

Emerging Therapeutic Potential of SIRT6 Modulators

Sirtuin 6 (SIRT6) is an NAD⁺-dependent protein deacylase and mono-ADP-ribosyltransferase of the sirtuin family with a wide substrate specificity. In vitro and in vivo studies have indicated that SIRT6 overexpression or activation has beneficial effects for cellular processes such as DNA repair, metabolic regulation, and aging. On the other hand, SIRT6 has contrasting roles in cancer, acting either as a tumor suppressor or promoter in a context-specific manner. Given its central role in cellular homeostasis, SIRT6 has emerged as a promising target for the development of small-molecule activators and inhibitors possessing a therapeutic potential in diseases ranging from cancer to age-related disorders. Moreover, specific modulators allow the molecular details of SIRT6 activity to be scrutinized and further validate the enzyme as a pharmacological target. In this Perspective, we summarize the current knowledge about SIRT6 pharmacology and medicinal chemistry and describe the features of the activators and inhibitors identified so far.

Oxygen sensing, mitochondrial biology and experimental therapeutics for pulmonary hypertension and cancer

The homeostatic oxygen sensing system (HOSS) optimizes systemic oxygen delivery. Specialized tissues utilize a conserved mitochondrial sensor, often involving NDUFS2 in complex I of the mitochondrial electron transport chain, as a site of pO₂-responsive production of reactive oxygen species (ROS). These ROS are converted to a diffusible signaling molecule, hydrogen peroxide (H₂O₂), by superoxide dismutase (SOD2). H₂O₂ exits the mitochondria and regulates ion channels and enzymes, altering plasma membrane potential, intracellular Ca²⁺ and Ca²⁺-sensitization and controlling acute, adaptive, responses to hypoxia that involve changes in ventilation, vascular tone and neurotransmitter release. Subversion of this O₂-sensing pathway creates a pseudohypoxic state that promotes disease progression in pulmonary arterial hypertension (PAH) and cancer. Pseudohypoxia is a state in which biochemical changes, normally associated with hypoxia, occur despite normal pO₂. Epigenetic silencing of SOD2 by DNA methylation alters H₂O₂ production, activating hypoxia-inducible factor 1α, thereby disrupting mitochondrial metabolism and dynamics, accelerating cell proliferation and inhibiting apoptosis. Other epigenetic mechanisms, including dysregulation of microRNAs (miR), increase pyruvate dehydrogenase kinase and pyruvate kinase muscle isoform 2 expression in both diseases, favoring uncoupled aerobic glycolysis. This Warburg metabolic shift also accelerates cell proliferation and impairs apoptosis. Disordered mitochondrial dynamics, usually increased mitotic fission and impaired fusion, promotes disease progression in PAH and cancer. Epigenetic upregulation of dynamin-related protein 1 (Drp1) and its binding partners, MiD49 and MiD51, contributes to the pathogenesis of PAH and cancer. Finally, dysregulation of intramitochondrial Ca²⁺, resulting from impaired mitochondrial calcium uniporter complex (MCUC) function, links abnormal mitochondrial metabolism and dynamics. MiR-mediated decreases in MCUC function reduce intramitochondrial Ca²⁺, promoting Warburg metabolism, whilst increasing cytosolic Ca²⁺, promoting fission. Epigenetically disordered mitochondrial O₂-sensing, metabolism, dynamics, and Ca²⁺ homeostasis offer new therapeutic targets for PAH and cancer. Promoting glucose oxidation, restoring the fission/fusion balance, and restoring mitochondrial calcium regulation are promising experimental therapeutic strategies.

A short review on cross-link between pyruvate kinase (PKM2) and Glioblastoma Multiforme

Pyruvate kinase (PK) catalyzes the last irreversible reaction of glycolysis pathway, generating pyruvate and ATP, from Phosphoenol Pyruvate (PEP) and ADP precursors. In mammals, four different tissue-specific isoforms (M1, M2, L and R) of PK exist, which are translated from two genes (PKL and PKR). PKM2 is the highly expressed isoform of PK in cancers, which regulates the aerobic glycolysis via reprogramming cancer cell's metabolic pathways to provide an anabolic advantage to the tumor cells. In addition to the established role of PKM2 in aerobic glycolysis of multiple cancer types, various recent findings have highlighted the non-metabolic functions of PKM2 in brain tumor development. Nuclear PKM2 acts as a co-activator and directly regulates gene transcription. PKM2 dependent transactivation of various oncogenic genes is instrumental in the progression and aggressiveness of Glioblastoma Multiforme (GBM). Also, PKM2 acts as a protein kinase in histone modification which regulates gene expression and tumorigenesis. Ongoing research has explored novel regulatory mechanisms of PKM2 and its association in GBM progression. This review enlists and summarizes the metabolic and non-metabolic roles of PKM2 at the cellular level, and its regulatory function highlights the importance of the nuclear functions of PKM2 in GBM progression, and an emerging role of PKM2 as novel cancer therapeutics.

The Two-Faced Role of SIRT6 in Cancer

Simple Summary

Cancer therapy relies on the employment of different strategies aimed at inducing cancer cell death through different mechanisms, including DNA damage and apoptosis induction. One of the key regulators of these pathways is the epigenetic enzyme SIRT6, which has been shown to have a dichotomous function in cell fate determination and, consequently, cancer initiation and progression. In this review, we aim to summarize the current knowledge on the role of SIRT6 in cancer. We show that it can act as both tumor suppressor and promoter, even in the same cancer type, depending on the biological context. We then describe the most promising modulators of SIRT6 which, through enzyme activation or inhibition, may impair tumor growth. These molecules can also be used for the elucidation of SIRT6 function, thereby advancing the current knowledge on this crucial protein.

Abstract

Sirtuin 6 (SIRT6) is a NAD⁺-dependent nuclear deacylase and mono-ADP-ribosylase with a wide spectrum of substrates. Through its pleiotropic activities, SIRT6 modulates either directly or indirectly key processes linked to cell fate determination and oncogenesis such as DNA damage repair, metabolic homeostasis, and apoptosis. SIRT6 regulates the expression and activity of both pro-apoptotic (e.g., Bax) and anti-apoptotic factors (e.g., Bcl-2, survivin) in a context-depending manner. Mounting evidence points towards a double-faced involvement of SIRT6 in tumor onset and progression since the block or induction of apoptosis lead to opposite outcomes in cancer. Here, we discuss the features and roles of SIRT6 in the regulation of cell death and cancer, also focusing on recently discovered small molecule modulators that can be used as chemical probes to shed further light on SIRT6 cancer biology and proposed as potential new generation anticancer therapeutics.

Is nuclear sirtuin SIRT6 a master regulator of immune function?

The ability to ward off pathogens with minimal damage to the host determines the immune system's robustness. Multiple factors, including pathogen processing, identification, secretion of mediator and effector molecules, and immune cell proliferation and differentiation into various subsets, constitute the success of mounting an effective immune response. Cellular metabolism controls all of these intricate processes. Cells utilize diverse fuel sources and switch back and forth between different metabolic pathways depending on their energy needs. The three most critical metabolic pathways on which immune cells depend to meet their energy needs are oxidative metabolism, glycolysis, and glutaminolysis. Dynamic switching between these metabolic pathways is needed for optimal function of the immune cells. Moreover, switching between these metabolic pathways needs to be tightly regulated to achieve the best results. Immune cells depend on the Warburg effect for their growth, proliferation, secretory, and effector functions. Here, we hypothesize that the sirtuin, SIRT6, could be a negative regulator of the Warburg effect. We also postulate that SIRT6 could act as a master regulator of immune cell metabolism and function by regulating critical signaling pathways.

Emerging roles of SIRT6 in human diseases and its modulators

The biological functions of sirtuin 6 (SIRT6; e.g., deacetylation, defatty-acylation, and mono-ADP-ribosylation) play a pivotal role in regulating lifespan and several fundamental processes controlling aging such as DNA repair, gene expression, and telomeric maintenance. Over the past decades, the aberration of SIRT6 has been extensively observed in diverse life-threatening human diseases. In this comprehensive review, we summarize the critical roles of SIRT6 in the onset and progression of human diseases including cancer, inflammation, diabetes, steatohepatitis, arthritis, cardiovascular diseases, neurodegenerative diseases, viral infections, renal and corneal injuries, as well as the elucidation of the related signaling pathways. Moreover, we discuss the advances in the development of small molecule SIRT6 modulators including activators and inhibitors as well as their pharmacological profiles toward potential therapeutics for SIRT6-mediated diseases.