The emerging and diverse roles of sirtuins in cancer: a clinical perspective

Propofol inhibits colon cancer cell stemness and epithelial-mesenchymal transition by regulating SIRT1, Wnt/β-catenin and PI3K/AKT/mTOR signaling pathways

BACKGROUND

Propofol is a common sedative-hypnotic drug used for general anesthesia. Recent studies have drawn attention to the antitumor effects of propofol, but the potential mechanism by which propofol suppresses colon cancer stemness and epithelial-mesenchymal transition (EMT) has not been fully elucidated.

METHODS

For the in vitro experiments, we used propofol to treat LOVO and SW480 cells and Cell Counting Kit-8 (CCK-8) to detect proliferation. Self-renewal capacity, cell invasion and migration, flow cytometry analysis, qPCR and Western blotting were performed to detect the suppression of propofol to colon cancer cells and the underlying mechanism. Tumorigenicity and immunohistochemistry experiments were performed to confirm the role of propofol in vivo.

RESULT

We observed that propofol could suppressed stem cell-like characteristics and EMT-related behaviors, including self-renewal capacity, cell invasion and migration in colon cancer cells, and even suppressed tumorigenicity in vivo. Furthermore, investigations of the underlying mechanism revealed that propofol treatment downregulated SIRT1. SIRT1 overexpression or knockdown affected the stemness and EMT of colon cancer cells. Additionally, propofol reversed stemness and EMT in cells with overexpressing SIRT1 and subsequently inhibited the Wnt/β-catenin and PI3K/AKT/mTOR signaling pathways. Wnt/β-catenin pathway inhibitor and PI3K/AKT/mTOR pathway inhibitor blocked the propofol-induced reduction of sphere-formation and cell invasion-migration.

CONCLUSION

Propofol inhibits LOVO and SW480 cell stemness and EMT by regulating SIRT1 and the Wnt/β-catenin and PI3K/AKT/mTOR signaling pathways. Our findings indicate that propofol inhibits SIRT1 in cancer and is advantageous in colon cancer surgical treatment of patients with high SIRT1 expression.

SIRT1/APE1 promotes the viability of gastric cancer cells by inhibiting p53 to suppress ferroptosis

Gastric cancer (GC) is a common cancer worldwide with high mortality. Sirtuin 1 (SIRT1) and apurinic/apyrimidinic endodeoxyribonuclease 1 (APE1) are abnormally expressed in GC cells and related to p53, which is involved in ferroptosis. Thus, we explore the mechanism via which SIRT1, APE1, and p53 impact ferroptosis in GC cells. Specifically, GC cells were transfected with small-interfering RNA for SIRT1 (SiSIRT1) or small-interfering RNA for APE1 (SiAPE1) or with short-hairpin RNA for p53, and the cell viability, Fe²⁺, malondialdehyde (MDA), and glutathione (GSH) contents were detected by cell counting kit-8 assay and enzyme-linked immunosorbent assay. Western blot, immunofluorescence, and quantitative real-time polymerase chain reaction were conducted to quantify SIRT1, APE1, p53, solute carrier family 7 member 11 (SLC7A11), and glutathione peroxidase 4 (GPX4) levels in GC cells. Silencing of SIRT1 decreased viability, GSH content, and expressions of GPX4 and SLC7A11, while increased Fe²⁺, MDA content, and p53 expression in GC cells. Such aforementioned effects were reversed by APE1 overexpression. Also, SiAPE1 generated the same effects as SiSIRT1 on the above aspects, which was offset by p53 silencing. In short, SIRT1/APE1 promotes the growth of GC cells by targeting p53 to inhibit ferroptosis.

The Bile Acid Membrane Receptor TGR5 in Cancer: Friend or Foe?

The G-protein-coupled bile acid receptor, Gpbar1 or TGR5, is characterized as a membrane receptor specifically activated by bile acids. A series of evidence shows that TGR5 induces protein kinase B (AKT), nuclear factor kappa-B (NF-κB), extracellular regulated protein kinases (ERK1/2), signal transducer and activator of transcription 3 (STAT3), cyclic adenosine monophosphate (cAMP), Ras homolog family member A (RhoA), exchange protein activated by cAMP (Epac), and transient receptor potential ankyrin subtype 1 protein (TRPA1) signaling pathways, thereby regulating proliferation, inflammation, adhesion, migration, insulin release, muscle relaxation, and cancer development. TGR5 is widely distributed in the brain, lung, heart, liver, spleen, pancreas, kidney, stomach, jejunum, ileum, colon, brown adipose tissue (BAT), white adipose tissue (WAT), and skeletal muscle. Several recent studies have demonstrated that TGR5 exerts inconsistent effects in different cancer cells upon activating via TGR5 agonists, such as INT-777, ursodeoxycholic acid (UDCA), and taurolithocholic acid (TLCA). In this review, we discuss both the ‘friend’ and ‘foe’ features of TGR5 by summarizing its tumor-suppressing and oncogenic functions and mechanisms.

Inhibition of cell invasion and migration by targeting matrix metalloproteinase-9 expression via sirtuin 6 silencing in human breast cancer cells

Sirtuin 6 (SIRT6) regulation is involved in carcinogenesis. However, its role in breast cancer (BC) metastasis remains unclear. We investigated the effects of SIRT6 on protein kinase C activator- and cytokine-mediated cancer cell invasion and migration in MCF-7 and MDA-MB-231 cells and the association between SIRT6 and matrix metalloproteinase-9 (MMP-9) expression. To assess MMP-9 and SIRT6 expression in patients, protein levels in BC tissues were analyzed. MCF-7 and MDA-MB-231 cell viability was analyzed using MTT assays. SIRT6 was silenced in both cell lines and protein secretion, expression, and mRNA levels were analyzed. Transcription factor DNA activity was investigated using luciferase assays. Matrigel invasion assays were used to assess the effects of SIRT6 in both cell lines. SIRT6 and MMP-9 expression in cancer tissues was significantly higher than in paired normal breast tissues. 12-O-tetradecanoylphorbol-13-acetate (TPA) or tumor necrosis factor-α (TNF-α) increased MMP-9 expression and cell invasion and migration, but SIRT6 knockdown abolished these effects. SIRT6 overexpression additively increased TPA- and TNF-α-induced MMP-9 expression. SIRT6 knockdown suppressed the mitogen-activated protein kinase (MAPK) signaling pathway and thus TPA- and TNF-α-induced MMP-9 expression. SIRT6 silencing suppressed TPA- and TNF-α-induced nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) expressions in both cell lines, and treatment with MAPK, NF-κB, and AP-1 inhibitors reduced MMP-9 expression. The anti-invasive effects of SIRT6 in BC cells might be mediated by suppression of MAPK phosphorylation and reduction in NF-κB and AP-1 DNA activities, leading to MMP-9 downregulation, suggesting that SIRT6 modulation has the potential to target BC metastasis.

Flavonoids as Sirtuin Modulators

Sirtuins (SIRTs) are described as NAD+-dependent deacetylases, also known as class III histone deacetylases. So far, seven sirtuin genes (SIRTS 1-7) have been identified and characterized in mammals and also known to occur in bacteria and eukaryotes. SIRTs are involved in various biological processes including endocrine system, apoptosis, aging and longevity, diabetes, rheumatoid arthritis, obesity, inflammation, etc. Among them, the best characterized one is SIRT1. Actually, small molecules seem to be the most effective SIRT modulators. Flavonoids have been reported to possess many positive effects favrable for human health, while a relatively less research has been reported so far on their funcions as SIRT modulation mechanisms. In this regard, we herein aimed to focus on modulatory effects of flavonoids on SIRTs as the most common secondary metabolites in natural products. Our literature survey covering the years of 2006-2021 pointed out that flavonoids frequently interact with SIRT1 and SIRT3 followed by SIRT6. It can be also concluded that some popular flavonoid derivatives, e.g. resveratrol, quercetin, and catechin derivatives came forward in terms of SIRT modulation.

Assessment of Pharmacological Interactions between SIRT2 Inhibitor AGK2 and Paclitaxel in Different Molecular Subtypes of Breast Cancer Cells

Breast carcinoma (BC) is the most commonly diagnosed type of cancer in women in the world. Although the advances in the treatment of BC patients are significant, numerous side effects, severe toxicity towards normal cells as well as the multidrug resistance (MDR) phenomenon restrict the effectiveness of the therapies used. Therefore, new active compounds which decrease the MDR, extend disease-free survival, thereby ameliorating the effectiveness of the current treatment regimens, are greatly needed. Histone deacetylase inhibitors (HDIs), including sirtuin inhibitors (SIRTi), are the epigenetic antitumor agents which induce a cytotoxic effect in different types of cancer cells, including BC cells. Currently, combined forms of therapy with two or even more chemotherapeutics are promising antineoplastic tools to obtain a better response to therapy and limit adverse effects. Thus, on the one hand, much more effective chemotherapeutics, e.g., sirtuin inhibitors (SIRTi), are in demand; on the other hand, combinations of accepted cytostatics are trialed. Thus, the aim of our research was to examine the combination effects of a renowned cytotoxic drug paclitaxel (PAX) and SIRT2 inhibitor AGK2 on the proliferation and viability of the T47D, MCF7, MDA-MB-231, MDA-MB-468, BT-549 and HCC1937 BC cells. Moreover, cell cycle arrest and apoptosis induction were explored. The type of pharmacological interactions between AGK2 and PAX in different molecular subtypes of BC cells was assessed using the advanced isobolographic method. Our findings demonstrated that the tested active agents singly inhibited viability and proliferation of BC cells as well as induced cell cycle arrest and apoptosis in the cell-dependent context. Additionally, AGK2 increased the antitumor effect of PAX in most BC cell lines. We observed that, depending on the BC cell lines, the combinations of tested drugs showed synergistic, additive or antagonistic pharmacological interaction. In conclusion, our studies demonstrated that the consolidated therapy with the use of AGK2 and PAX can be considered as a potential therapeutic regimen in the personalized cure of BC patients in the future.

Novel CDK9 inhibitor oroxylin A promotes wild-type P53 stability and prevents hepatocellular carcinoma progression by disrupting both MDM2 and SIRT1 signaling

Hepatocellular carcinoma (HCC) is one of the most lethal tumours worldwide. However, the effects of first-line sorafenib treatment in advanced HCC fail to prolong patients' survival due to the highly heterogeneous characteristics of HCC etiology. Cyclin-dependent kinase 9 (CDK9) is an important target in the continuous development of cancer therapy. Here, we demonstrate that CDK9 is closely associated with the progression of HCC and can serve as an HCC therapeutic target by modulating the recovery of wild-type p53 (wt-p53) function. We prove that mouse double minute 2 homologue (MDM2) and Sirtuin 1 (SIRT1) are phosphorylated by CDK9 at Ser166 and Ser47, respectively. Inhibition of CDK9 not only reduces the MDM2-mediated ubiquitination and degradation of wt-p53 but also increases wt-p53 stability by suppressing deacetylase activity of SIRT1. Thus, inhibition of CDK9 promotes the wt-p53 stabilization and prevents HCC progression. However, excessive inhibition by high concentrations of specific CDK9 inhibitors counteracts the promotion of p53 stability and reduces their anti-HCC activity because of extreme general transcription repression. The effects of a novel CDK9 inhibitor named oroxylin A (OA) from Scutellaria baicalensis are explored, with the results indicating that OA shows moderate and controlled inhibition of CDK9 activity and expression, and stabilizes wt-p53 by inhibiting CDK9-regulated MDM2 and SIRT1 signaling. These outcomes indicate the high therapeutic potential of OA against HCC and its low toxicity in normal tissue. This study demonstrates a novel mechanism for the regulation of wt-p53 by CDK9 and indicates that OA is a potential candidate for HCC therapy.

Kaempferol and Apigenin suppresses the stemness properties of TNBC cells by modulating Sirtuins

Sirtuins (SIRTs) overexpression serves as a potential therapeutic target for TNBC because it is associated with bioactivities of cancer stem cells (CSCs), resistance to chemotherapy, and metastasis. Irrespective of the availability of synthetic SIRT inhibitors, new SIRT inhibitors with enhanced potency and lesser side effects serve as current unmet needs. Therefore, bioactive dietary compounds; kaempferol (KMP) and apigenin (API) were investigated for their anti-SIRTs potential. We observed KMP and API inhibits cellular proliferation by DNA damage and S-phase cell cycle arrest in TNBC Cells. They also suppress stemness properties in TNBCs as observed in experiments of mammosphere formation and clonogenic potential. Our mechanistic approach indicated that KMP and API inhibited SIRT3 and SIRT6 proteins, as evidenced by our in silico and in vitro experiment. Collectively, our studies suggest that KMP and API are promising candidates to be further developed as sirtuin modulators against TNBCs.

Role of Circulating Biomarkers in Platinum-Resistant Ovarian Cancer

Ovarian cancer (OC) is the second most common cause of death in women with gynecological cancer. Considering the poor prognosis, particularly in the case of platinum-resistant (PtR) disease, a huge effort was made to define new biomarkers able to help physicians in approaching and treating these challenging patients. Currently, most data can be obtained from tumor biopsy samples, but this is not always available and implies a surgical procedure. On the other hand, circulating biomarkers are detected with non-invasive methods, although this might require expensive techniques. Given the fervent hope in their value, here we focused on the most studied circulating biomarkers that could play a role in PtR OC.

SYT8 promotes pancreatic cancer progression via the TNNI2/ERRα/SIRT1 signaling pathway

Pancreatic cancer is a highly lethal malignancy due to failures of early detection and high metastasis in patients. While certain genetic mutations in tumors are associated with severity, the molecular mechanisms responsible for cancer progression are still poorly understood. Synaptotagmin-8 (SYT8) is a membrane protein that regulates hormone secretion and neurotransmission, and its expression is positively regulated by the promoter of the insulin gene in pancreatic islet cells. In this study, we identified a previously unknown role of SYT8 in altering tumor characteristics in pancreatic cancer. SYT8 levels were upregulated in patient tumors and contributed towards increased cell proliferation, migration, and invasion in vitro and in vivo. Increased SYT8 expression also promoted tumor metastasis in an in vivo tumor metastasis model. Furthermore, we showed that SYT8-mediated increase in tumorigenicity was regulated by SIRT1, a protein deacetylase previously known to alter cell metabolism in pancreatic lesions. SIRT1 expression was altered by orphan nuclear receptor ERRα and troponin-1 (TNNI2), resulting in cell proliferation and migration in an SYT8-dependent manner. Together, we identified SYT8 to be a central regulator of tumor progression involving signaling via the SIRT1, ERRα, and TNNI2 axis. This knowledge may provide the basis for the development of therapeutic strategies to restrict tumor metastasis in pancreatic cancer.

Therapeutic Role of Sirtuins Targeting Unfolded Protein Response, Coagulation, and Inflammation in Hypoxia-Induced Thrombosis

Thrombosis remains one of the leading causes of morbidity and mortality across the world. Many pathological milieus in the body resulting from multiple risk factors escort thrombosis. Hypoxic condition is one such risk factor that disturbs the integrity of endothelial cells to cause an imbalance between anticoagulant and procoagulant proteins. Hypoxia generates reactive oxygen species (ROS) and triggers inflammatory pathways to augment the coagulation cascade. Hypoxia in cells also activates unfolded protein response (UPR) signaling pathways in the endoplasmic reticulum (ER), which tries to restore ER homeostasis and function. But the sustained UPR linked with inflammation, generation of ROS and apoptosis stimulates the severity of thrombosis in the body. Sirtuins, a group of seven proteins, play a vast role in bringing down inflammation, oxidative and ER stress and apoptosis. As a result, sirtuins might provide a therapeutic approach towards the treatment or prevention of hypoxia-induced thrombosis. Sirtuins modulate hypoxia-inducible factors (HIFs) and counteract ER stress-induced apoptosis by attenuating protein kinase RNA-like endoplasmic reticulum kinase (PERK)/Eukaryotic translation initiation factor 2α (eIF2α) pathway activation. It prevents ER-stress mediated inflammation by targeting X-Box Binding Protein 1 (XBP1) and inhibiting nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κβ) signaling through deacetylation. Sirtuins also obstruct nucleotide-binding domain, leucine-rich-containing family, pyrin domain containing 3 (NLRP3) inflammasome activation to reduce the expression of several pro-inflammatory molecules. It protects cells against oxidative stress by targeting nuclear factor erythroid 2-related factor 2 (Nrf2), glutathione (GSH), forkhead box O3 (FOXO3), superoxide dismutase (SOD), catalase (CAT), peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), glucose-6-phosphate dehydrogenase (G6PD), phosphoglucomutase-2 (PGAM2), and NF-κB, to name few. This review, thus, discusses the potential role of sirtuins as a new treatment for hypoxia-induced thrombosis that involves an intersection of UPR and inflammatory pathways in its pathological manifestation.

Silent Information Regulator 1 Promotes Proliferation, Migration, and Invasion of Cervical Cancer Cells and Is Upregulated by Human Papillomavirus 16 E7 Oncoprotein

OBJECTIVE

Silent information regulator 1 (SIRT1), an NAD+-dependent III class histone deacetylase, plays crucial roles in cell proliferation, apoptosis, senescence, metabolism, and stress responses. Nevertheless, the role of SIRT1 in tumorigenesis remains unclear.

METHODS

In the present study, we measured expression levels of SIRT1 and HPV16 E7 protein in cervical cancer (CC) tissue and calculated their correlations. We measured the effect of silencing SIRT1 on the proliferation, migration, invasion, and apoptosis in human CC SiHa cells.

RESULTS

Immunohistochemistry results revealed that the expression of SIRT1 was upregulated with progression from CIN II-III to CC, but was not expressed in normal cervical tissues and CIN I. There was a positive correlation between SIRT1 expression and HPV16 E7 expression in CC tissues, and silencing of HPV16 E7 downregulated the expression of SIRT1. Depletion of SIRT1 downregulated SIRT1 expression, and inhibited proliferation, migration, and invasion of SiHa cells, inducing apoptosis.

CONCLUSIONS

Taken together, the data suggest that SIRT1 promotes CC carcinogenesis. SIRT1 inhibition is a potential treatment strategy for CC.

SIRT1/PGC-1α/PPAR-γ Correlate With Hypoxia-Induced Chemoresistance in Non-Small Cell Lung Cancer

Resistance is the major cause of treatment failure and disease progression in non-small cell lung cancer (NSCLC). There is evidence that hypoxia is a key microenvironmental stress associated with resistance to cisplatin, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), and immunotherapy in solid NSCLCs. Numerous studies have contributed to delineating the mechanisms underlying drug resistance in NSCLC; nevertheless, the mechanisms involved in the resistance associated with hypoxia-induced molecular metabolic adaptations in the microenvironment of NSCLC remain unclear. Studies have highlighted the importance of posttranslational regulation of molecular mediators in the control of mitochondrial function in response to hypoxia-induced metabolic adaptations. Hypoxia can upregulate the expression of sirtuin 1 (SIRT1) in a hypoxia-inducible factor (HIF)-dependent manner. SIRT1 is a stress-dependent metabolic sensor that can deacetylate some key transcriptional factors in both metabolism dependent and independent metabolic pathways such as HIF-1α, peroxisome proliferator-activated receptor gamma (PPAR-γ), and PPAR-gamma coactivator 1-alpha (PGC-1α) to affect mitochondrial function and biogenesis, which has a role in hypoxia-induced chemoresistance in NSCLC. Moreover, SIRT1 and HIF-1α can regulate both innate and adaptive immune responses through metabolism-dependent and -independent ways. The objective of this review is to delineate a possible SIRT1/PGC-1α/PPAR-γ signaling-related molecular metabolic mechanism underlying hypoxia-induced chemotherapy resistance in the NSCLC microenvironment. Targeting hypoxia-related metabolic adaptation may be an attractive therapeutic strategy for overcoming chemoresistance in NSCLC.

Proliferation Increasing Genetic Engineering in Human Corneal Endothelial Cells: A Literature Review

The corneal endothelium is the inner layer of the cornea. Despite comprising only a monolayer of cells, dysfunction of this layer renders millions of people visually impaired worldwide. Currently, corneal endothelial transplantation is the only viable means of restoring vision for these patients. However, because the supply of corneal endothelial grafts does not meet the demand, many patients remain on waiting lists, or are not treated at all. Possible alternative treatment strategies include intracameral injection of human corneal endothelial cells (HCEnCs), biomedical engineering of endothelial grafts and increasing the HCEnC density on grafts that would otherwise have been unsuitable for transplantation. Unfortunately, the limited proliferative capacity of HCEnCs proves to be a major bottleneck to make these alternatives beneficial. To tackle this constraint, proliferation enhancing genetic engineering is being investigated. This review presents the diverse array of genes that have been targeted by different genetic engineering strategies to increase the proliferative capacity of HCEnCs and their relevance for clinical and research applications. Together these proliferation-related genes form the basis to obtain a stable and safe supply of HCEnCs that can tackle the corneal endothelial donor shortage.

Sirt1 deacetylates and stabilizes p62 to promote hepato-carcinogenesis

p62/SQSTM1 is frequently up-regulated in many cancers including hepatocellular carcinoma. Highly expressed p62 promotes hepato-carcinogenesis by activating many signaling pathways including Nrf2, mTORC1, and NFκB signaling. However, the underlying mechanism for p62 up-regulation in hepatocellular carcinoma remains largely unclear. Herein, we confirmed that p62 was up-regulated in hepatocellular carcinoma and its higher expression was associated with shorter overall survival in patients. The knockdown of p62 in hepatocellular carcinoma cells decreased cell growth in vitro and in vivo. Intriguingly, p62 protein stability could be reduced by its acetylation at lysine 295, which was regulated by deacetylase Sirt1 and acetyltransferase GCN5. Acetylated p62 increased its association with the E3 ligase Keap1, which facilitated its poly-ubiquitination-dependent proteasomal degradation. Moreover, Sirt1 was up-regulated to deacetylate and stabilize p62 in hepatocellular carcinoma. Additionally, Hepatocyte Sirt1 conditional knockout mice developed much fewer liver tumors after Diethynitrosamine treatment, which could be reversed by the re-introduction of exogenous p62. Taken together, Sirt1 deacetylates p62 at lysine 295 to disturb Keap1-mediated p62 poly-ubiquitination, thus up-regulating p62 expression to promote hepato-carcinogenesis. Therefore, targeting Sirt1 or p62 is a reasonable strategy for the treatment of hepatocellular carcinoma.

Histones on fire: the effect of Dun1 and Mrc1 on origin firing and replication of hyper-acetylated genomes

As cells replicate their DNA, there is a need to synthesize new histones with which to wrap it. Newly synthesized H3 histones that are incorporated into the assembling chromatin behind the replication fork are acetylated at lysine 56. The acetylation is removed by two deacetylases, Hst3 and Hst4. This process is tightly regulated and any perturbation leads to genomic instability and replicative stress. We recently showed that Dun1, a kinase implicated mainly in the regulation of dNTPs, is vital in cells with hyper-acetylation, to counteract Rad53's inhibition on late-firing origins of replication. Our work showed that ∆hst3 ∆hst4 cells depend on late origin firing for survival, and are unable to prevent Rad53's inhibition when Dun1 is inactive. Thus, our work describes a role for Dun1 that is independent on its known function as a regulator of dNTP levels. Here we show that Mrc1 (Claspin in mammals), a protein that moves with the replicating fork and participates in both replication and checkpoint functions, plays also an essential role in the absence of H3K56Ac deacetylation. The sum of the results shown here and in our recent publication suggests that dormant origins are also utilized in these cells, making Mrc1, which regulates firing from these origins, also essential when histone H3 is hyper-acetylated. Thus, cells suffering from hyper-acetylation of H3K56 experience replication stress caused by a combination of prone-to-collapse forks and limited replication tracts. This combination makes both Dun1 and Mrc1, each acting on different targets, essential for viability.

MicroRNA-Regulated Signaling Pathways: Potential Biomarkers for Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most aggressive and invasive type of pancreatic cancer (PCa) and is expected to be the second most common cause of cancer-associated deaths. The high mortality rate is due to the asymptomatic progression of the clinical features until the advanced stages of the disease and the limited effectiveness of the current therapeutics. Aberrant expression of several microRNAs (miRs/miRNAs) has been related to PDAC progression and thus they could be potential early diagnostic, prognostic, and/or therapeutic predictors for PDAC. miRs are small (18 to 24 nucleotides long) non-coding RNAs, which regulate the expression of key genes by targeting their 3′-untranslated mRNA region. Increased evidence has also suggested that the chemoresistance of PDAC cells is associated with metabolic alterations. Metabolic stress and the dysfunctionality of systems to compensate for the altered metabolic status of PDAC cells is the foundation for cellular damage. Current data have implicated multiple systems as hallmarks of PDAC development, such as glutamine redox imbalance, oxidative stress, and mitochondrial dysfunction. Hence, both the aberrant expression of miRs and dysregulation in metabolism can have unfavorable effects in several biological processes, such as apoptosis, cell proliferation, growth, survival, stress response, angiogenesis, chemoresistance, invasion, and migration. Therefore, due to these dismal statistics, it is crucial to develop beneficial therapeutic strategies based on an improved understanding of the biology of both miRs and metabolic mediators. This review focuses on miR-mediated pathways and therapeutic resistance mechanisms in PDAC and evaluates the impact of metabolic alterations in the progression of PDAC.

The Amazing Acrobat: Yeast's Histone H3K56 Juggles Several Important Roles While Maintaining Perfect Balance

Acetylation on lysine 56 of histone H3 of the yeast Saccharomyces cerevisiae has been implicated in many cellular processes that affect genome stability. Despite being the object of much research, the complete scope of the roles played by K56 acetylation is not fully understood even today. The acetylation is put in place at the S-phase of the cell cycle, in order to flag newly synthesized histones that are incorporated during DNA replication. The signal is removed by two redundant deacetylases, Hst3 and Hst4, at the entry to G2/M phase. Its crucial location, at the entry and exit points of the DNA into and out of the nucleosome, makes this a central modification, and dictates that if acetylation and deacetylation are not well concerted and executed in a timely fashion, severe genomic instability arises. In this review, we explore the wealth of information available on the many roles played by H3K56 acetylation and the deacetylases Hst3 and Hst4 in DNA replication and repair.

Sirtuin 1 and Sirtuin 3 in Granulosa Cell Tumors

Sirtuins (SIRTs) are NAD⁺-dependent deacetylases that regulate proliferation and cell death. In the human ovary, granulosa cells express sirtuin 1 (SIRT1), which has also been detected in human tumors derived from granulosa cells, i.e., granulosa cell tumors (GCTs), and in KGN cells. KGN cells are an established cellular model for the majority of GCTs and were used to explore the role of SIRT1. The SIRT1 activator SRT2104 increased cell proliferation. By contrast, the inhibitor EX527 reduced cell numbers, without inducing apoptosis. These results were supported by the outcome of siRNA-mediated silencing studies. A tissue microarray containing 92 GCTs revealed nuclear and/or cytoplasmic SIRT1 staining in the majority of the samples, and also, SIRT2-7 were detected in most samples. The expression of SIRT1-7 was not correlated with the survival of the patients; however, SIRT3 and SIRT7 expression was significantly correlated with the proliferation marker Ki-67, implying roles in tumor cell proliferation. SIRT3 was identified by a proteomic analysis as the most abundant SIRT in KGN. The results of the siRNA-silencing experiments indicate involvement of SIRT3 in proliferation. Thus, several SIRTs are expressed by GCTs, and SIRT1 and SIRT3 are involved in the growth regulation of KGN. If transferable to GCTs, these SIRTs may represent novel drug targets.

Sirtuins as Important Factors in Pathological States and the Role of Their Molecular Activity Modulators

Sirtuins (SIRTs), enzymes from the family of NAD⁺-dependent histone deacetylases, play an important role in the functioning of the body at the cellular level and participate in many biochemical processes. The multi-directionality of SIRTs encourages scientists to undertake research aimed at understanding the mechanisms of their action and the influence that SIRTs have on the organism. At the same time, new substances are constantly being sought that can modulate the action of SIRTs. Extensive research on the expression of SIRTs in various pathological conditions suggests that regulation of their activity may have positive results in supporting the treatment of certain metabolic, neurodegenerative or cancer diseases or this connected with oxidative stress. Due to such a wide spectrum of activity, SIRTs may also be a prognostic markers of selected pathological conditions and prove helpful in assessing their progression, especially by modulating their activity. The article presents and discusses the activating or inhibiting impact of individual SIRTs modulators. The review also gathered selected currently available information on the expression of SIRTs in individual disease cases as well as the biological role that SIRTs play in the human organism, also in connection with oxidative stress condition, taking into account the progress of knowledge about SIRTs over the years, with particular reference to the latest research results.

Epigenetic crosstalk between hypoxia and tumor driven by HIF regulation

Hypoxia is the major influence factor in physiological and pathological courses which are mainly mediated by hypoxia-inducible factors (HIFs) in response to low oxygen tensions within solid tumors. Under normoxia, HIF signaling pathway is inhibited due to HIF-α subunits degradation. However, in hypoxic conditions, HIF-α is activated and stabilized, and HIF target genes are successively activated, resulting in a series of tumour-specific activities. The activation of HIFs, including HIF-1α, HIF-2α and HIF-3α, subsequently induce downstream target genes which leads to series of responses, the resulting abnormal processes or metabolites in turn affect HIFs stability. Given its functions in tumors progression, HIFs have been regarded as therapeutic targets for improved treatment efficacy. Epigenetics refers to alterations in gene expression that are stable between cell divisions, and sometimes between generations, but do not involve changes in the underlying DNA sequence of the organism. And with the development of research, epigenetic regulation has been found to play an important role in the development of tumors, which providing accumulating basic or clinical evidences for tumor treatments. Here, given how little has been reported about the overall association between hypoxic tumors and epigenetics, we made a more systematic review from epigenetic perspective in hope of helping others better understand hypoxia or HIF pathway, and providing more established and potential therapeutic strategies in tumors to facilitate epigenetic studies of tumors.

Gut Microbiota during Dietary Restrictions: New Insights in Non-Communicable Diseases

In recent decades, there has been a growing interest in dietary restrictions for their promising effects on longevity and health span. Indeed, these strategies are supposed to delay the onset and burden of non-communicable diseases (NCDs) such as obesity, diabetes, cancer and neurological and gastrointestinal inflammatory diseases. At the same time, the gut microbiota has been shown to play a crucial role in NCDs since it is actively involved in maintaining gut homeostasis through its impact on nutrients metabolism, gut barrier, and immune system. There is evidence that dietary restrictions could slow down age-related changes in the types and numbers of gut bacteria, which may counteract gut dysbiosis. The beneficial effects on gut microbiota may positively influence host metabolism, gut barrier permeability, and brain functions, and subsequently, postpone the onset of NCDs prolonging the health span. These new insights could lead to the development of novel strategies for modulating gut microbiota with the end goal of treating/preventing NCDs. This review provides an overview of animal and human studies focusing on gut microbiota variations during different types of dietary restriction, in order to highlight the close relationship between gut microbiota balance and the host's health benefits induced by these nutritional regimens.

Sirtuins and their Biological Relevance in Aging and Age-Related Diseases

Sirtuins, initially described as histone deacetylases and gene silencers in yeast, are now known to have many more functions and to be much more abundant in living organisms. The increasing evidence of sirtuins in the field of ageing and age-related diseases indicates that they may provide novel targets for treating diseases associated with aging and perhaps extend human lifespan. Here, we summarize some of the recent discoveries in sirtuin biology that clearly implicate the functions of sirtuins in the regulation of aging and age-related diseases. Furthermore, human sirtuins are considered promising therapeutic targets for anti-aging and ageing-related diseases and have attracted interest in scientific communities to develop small molecule activators or drugs to ameliorate a wide range of ageing disorders. In this review, we also summarize the discovery and development status of sirtuin-targeted drug and further discuss the potential medical strategies of sirtuins in delaying aging and treating age-related diseases.

Functions of mammalian SIRT4 in cellular metabolism and research progress in human cancer

Sirtuins are mammalian homologs of yeast silent information regulator two (SIRT) and are a highly conserved family of proteins, which act as nicotinamide adenine dinucleotide (NAD⁺)-dependent histone deacetylases. The seven sirtuins (SIRT1-7) share a conserved catalytic core domain; however, they have different enzyme activities, biological functions, and subcellular localizations. Among them, mitochondrial SIRT4 possesses ADP-ribosyltransferase, NAD⁺-dependent deacetylase, lipoamidase, and long-chain deacylase activities and can modulate the function of substrate proteins via ADP-ribosylation, delipoylation, deacetylation and long-chain deacylation. SIRT4 has been shown to play a crucial role in insulin secretion, fatty acid oxidation, amino acid metabolism, ATP homeostasis, apoptosis, neurodegeneration, and cardiovascular diseases. In addition, recent studies have demonstrated that SIRT4 acts as a tumor suppressor. Here, the present review summarizes the enzymatic activities and biological functions of SIRT4, as well as its roles in cellular metabolism and human cancer, which are described in the current literature.

Cytoplasm-localized SIRT1 downregulation attenuates apoptosis and cell cycle arrest in cisplatin-resistant lung cancer A549 cells

Objective: We propose that sirtuin (SIRT) may induce a pro-apoptotic effect by deacetylating transcription factors in A549 cells: depletion of sirtuin-1 (SIRT1) induced cell cycle arrest in cisplatin-resistant A549 (A549/CADD) cells.

Methods: Protein and mRNA levels of SIRT1 were investigated using western blot and RT-PCR. In A549 and A549/CADD cells, the cytotoxicity of cisplatin administration was evaluated by MTT assay, proliferation was measured by ECIS, and the cell cycle distribution was analyzed using FACS. Cells were transfected with pcDNA3.1-Myc-SIRT1 or pcDNA3.1-Myc-Control vectors to analyze the impact of SIRT-1 on cisplatin induced drug resistance. SIRT1 localization was studied using immunofluorescence analysis. In addition, immunoprecipitation and 20S proteasome activity assay were performed to examine the relationship of SIRT1 with the proteasome complex.

Results: A549/CADD cells exhibited a mesenchymal-like cell characteristic. SIRT1 expression was markedly decreased in A549/CADD cells. We observed that cisplatin regulates p53 stability through the depletion of ubiquitination following SIRT1 downregulation. Furthermore, cisplatin treatment increased proteasomal activity and significantly decreased cytoplasmic SIRT1 protein levels in A549/CADD cells.

Conclusion: In this study, we found SIRT1 to be depleted in A549/CADD cells and also determined the underlying resistance mechanism which may act as novel therapeutic targets in overcoming drug resistance.

Modulation of SIRT3 expression through CDK4/6 enhances the anti-cancer effect of sorafenib in hepatocellular carcinoma cells

Background

Hepatocellular carcinoma (HCC) is the leading cause of cancer-related deaths worldwide. The only drug currently approved for clinical use in the treatment of advanced HCC is sorafenib. However, many patients with HCC show reduced sensitivity to sorafenib during treatment. SIRT3, a member of the mammalian sirtuin family, is a tumor suppressor in certain tumor types. However, only few studies have investigated the effects of SIRT3 on tumor prognosis and sorafenib sensitivity in patients with HCC. Here, we aimed to investigate the correlation between SIRT3 expression and glucose metabolism and proliferation in HCC and discover effective compounds that increase endogenous SIRT3 modulation effect of sorafenib.

Methods

To determine the correlation between SIRT3 and glucose related proteins, immunostaining was performed with liver cancer tissue using various antibodies. To investigate whether the expression of SIRT3 in HCC is related to the resistance to sorafenib, we treated sorafenib after the modulation of SIRT3 levels in HCC cell lines (overexpression in Huh7, knockdown in HepG2). We also employed PD0332991 to modulate the SIRT3 expression in HCC cell and conducted functional assays.

Results

SIRT3 expression was downregulated in high glycolytic and proliferative HCC cells of human patients, xenograft model and HCC cell lines. Moreover, SIRT3 expression was downregulated after sorafenib treatment, resulting in reduced drug sensitivity in HCC cell lines. To enhance the anti-tumor effect of sorafenib, we employed PD0332991 (CDK4/6-Rb inhibitor) based on the correlation between SIRT3 and phosphorylated retinoblastoma protein in HCC. Notably, combined treatment with sorafenib and PD0332991 showed an enhancement of the anti-tumor effect in HCC cells.

Conclusions

Our data suggest that the modulation of SIRT3 by CDK4/6 inhibition might be useful for HCC therapy together with sorafenib, which, unfortunately, has limited efficacy and whose use is often associated with drug resistance.

Immunohistochemistry and clinical value of sirtuin 2 in non-metastasized non-small cell lung cancer

Background

This study aimed to define whether sirtuin 2 (SIRT2) expression levels are related to the prognosis of non-small cell lung cancer (NSCLC) patients.

Methods

A survival analysis was carried out using the Kaplan-Meier (KM) plotter database. Immunohistochemical staining was performed and KM's method was used to estimate the survival rates for SIRT2 expression in 72 clinical samples.

Results

A survival analysis of 1,926 NSCLC patients showed that patients with low SIRT2 expression levels had significantly longer overall survival (OS) than those with high SIRT2 expression levels (P=0.0077; HR =1.19). In 72 non-metastasized NSCLC tissues, the positive rate of SIRT2 expression was 90.3% (65/72), among which, the positive expression rates of squamous cell carcinoma (SCC) and adenocarcinoma (ADC) were 96.4% (27/28) and 85.4% (35/41), respectively. Survival analysis showed that patients with low SIRT2 expression levels had significantly longer median survival time (MST) than those with high SIRT2 expression levels (15.0 versus 14.0 months, P=0.029). Furthermore, the results of subgroup analysis demonstrated patients with low SIRT2 expression levels had significantly longer survival time in ADC group (15.0 versus 12.0 months, P=0.022), but there wasn't significant difference in SCC group (15.0 versus 14.0 months, P=0.932). A multivariate Cox proportional hazards model, which included gender, age, TNM stage, differentiation and SIRT2 expression, showed that SIRT2 expression was an independent factor related to prognosis [HR =1.903, 95% confidence interval (95% CI): 1.085-3.339, P=0.025].

Conclusions

SIRT2 expression levels were significantly related to the survival time of patients with lung ADC but not SCC. Our study indicated SIRT2 was perhaps a specific prognostic biomarker for non-metastasized lung ADC.

Comprehensive Analysis of Expression and Prognostic Value of Sirtuins in Ovarian Cancer

Sirtuins (SIRTs) 1–7 are a family of intracellular enzymes, which possess nicotinamide adenine dinucleotide-dependent deacetylase activity. Emerging evidence suggest that SIRTs play vital roles in tumorigenesis by regulating energy metabolism, DNA damage repair, genome stability, and other cancer-associated cellular processes. However, the distinct roles of the seven members in ovarian cancer (OC) remain elusive. The transcriptional expression patterns, prognostic values, and genetic alterations of seven SIRTs in OC patients were investigated in this study using a range of databases: Oncomine and Gene Expression Profiling Interactive Analysis, Kaplan–Meier plotter, the Cancer Genome Atlas, and cBioPortal. The protein–protein interaction networks of SIRTs were assessed in the String database. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway were analyzed in Database for Annotation, Visualization, and Integrated Discovery. The mRNA expression levels of SIRT1–4 and 7 were downregulated, while that of SIRT5 was upregulated and SIRT6 exhibited both expression dysregulation in patients with OC. Dysregulated SIRTs mRNA expression levels were associated with prognosis. Moreover, genetic alterations primarily occurred in SIRT2, 5, and 7. Network analysis indicated that SIRTs and their 20 interactors were associated with tumor-related pathways. This comprehensive bioinformatics analysis revealed that SIRT1–4, 6, and 7 may be new prognostic biomarkers, while SIRT5 is a potential target for accurate therapy for patients with OC, but further studies are needed to confirm this notion. These findings will contribute to a better understanding of the distinct roles of SIRTs in OC.

SIRT1 Modulates the Sensitivity of Prostate Cancer Cells to Vesicular Stomatitis Virus Oncolysis

Oncolytic virotherapy represents a promising experimental anticancer strategy, based on the use of genetically modified viruses to selectively infect and kill cancer cells. Vesicular stomatitis virus (VSV) is a prototypic oncolytic virus (OV) that induces cancer cell death through activation of the apoptotic pathway, although intrinsic resistance to oncolysis is found in some cell lines and many primary tumors, as a consequence of residual innate immunity to the virus. In the effort to improve OV therapeutic efficacy, we previously demonstrated that different agents, including histone deacetylase inhibitors (HDIs), functioned as reversible chemical switches to dampen the innate antiviral response and improve the susceptibility of resistant cancer cells to VSV infection. In the present study, we demonstrated that the NAD⁺-dependent histone deacetylase SIRT1 (silent mating type information regulation 2 homolog 1) plays a key role in the permissivity of prostate cancer PC-3 cells to VSVΔM51 replication and oncolysis. HDI-mediated enhancement of VSVΔM51 infection and cancer cell killing directly correlated with a decrease of SIRT1 expression. Furthermore, pharmacological inhibition as well as silencing of SIRT1 by small interfering RNA (siRNA) was sufficient to sensitize PC-3 cells to VSVΔM51 infection, resulting in augmentation of virus replication and spread. Mechanistically, HDIs such as suberoylanilide hydroxamic acid (SAHA; Vorinostat) and resminostat upregulated the microRNA miR-34a that regulated the level of SIRT1. Taken together, our findings identify SIRT1 as a viral restriction factor that limits VSVΔM51 infection and oncolysis in prostate cancer cells.IMPORTANCE The use of nonpathogenic viruses to target and kill cancer cells is a promising strategy in cancer therapy. However, many types of human cancer are resistant to the oncolytic (cancer-killing) effects of virotherapy. In this study, we identify a host cellular protein, SIRT1, that contributes to the sensitivity of prostate cancer cells to infection by a prototypical oncolytic virus. Knockout of SIRT1 activity increases the sensitivity of prostate cancer cells to virus-mediated killing. At the molecular level, SIRT1 is controlled by a small microRNA termed miR-34a. Altogether, SIRT1 and/or miR-34a levels may serve as predictors of response to oncolytic-virus therapy.

Upregulation of SIRT1 gene in gastric adenocarcinoma

BACKGROUND/AIMS

SIRT1 gene overexpression is reportedly associated with cancer development, via the triggering of DNA repair impairment, and cell proliferation. The study aimed to investigate SIRT1 expression in patients with gastric cancer and its correlations with the clinical and pathological characteristics of the disease.

MATERIALS AND METHODS

All patients (64 patients) who underwent gastric biopsy and were diagnosed with gastric adenocarcinoma and signet ring cell carcinoma between January 2011 and December 2013 were enrolled in the study, and patients with benign gastric biopsy were enrolled in the control group (34 patients). The previously prepared gastric tissues were collected from the pathology department, and SIRT1 gene expressions were evaluated in the gastric tissues of all study patients. Patients were subclassified according to their demographic, clinical, and pathologic features, and the patient and control groups were compared.

RESULTS

Sixty-four patients were included in the study (25 females and 39 males). The mean age of the patients was 66±1 (range: 33-88) years. The SIRT1 gene 2' Average delta cycle threshold (CT) value was 0.102 in the control group, whereas it was 0.292 in the patients with gastric cancer (relative risk: 2.86; p=0.014). The SIRT1 gene was upregulated in all tumor stage subgroups except stage I, female patients, young patients (<45 years), and corpus and cardia tumor subgroups compared to the control group.

CONCLUSION

SIRT1 gene overexpression is associated with gastric adenocarcinoma, and it can be argued that SIRT1 gene upregulation is associated with unfavorable gastric adenocarcinoma prognosis.

Overexpression of SIRT4 inhibits the proliferation of gastric cancer cells through cell cycle arrest

The sirtuins (SIRTs) are a family of nicotinamide-adenine dinucleotide (NAD)⁺-dependent protein deacetylases. SIRT4 is a mitochondrial NAD⁺-dependent adenosine diphsophate-ribosyltransferase. Recent studies demonstrated that SIRT4 can regulate glutamine metabolism and thus act as a tumor suppressor. However, the association of SIRT4 with gastric cancer remains unknown. The present study investigated the potential role of SIRT4 in the proliferation of human gastric cancer cells. Gastric cancer cell lines (SGC-7901 and MNK45) overexpressing SIRT4 were established by lentiviral infection. The effect of overexpression of SIRT4 in gastric cancer was evaluated by determining the cell viability, proliferation activity and colony-forming ability of gastric cancer cells in vitro. Furthermore, the cell cycle profiles of SGC-7901 and MNK45 cells overexpressing SIRT4 were evaluated to provide insights into potential underlying molecular mechanisms. Overexpression of SIRT4 significantly inhibited the proliferation and colony-forming ability of the gastric cancer cells in vitro. Furthermore, overexpression of SIRT4 induced G1 cell cycle arrest via suppression of phosphorylated extracellular signal-regulated kinase, cyclin D and cyclin E. In conclusion, the results of the present study indicated that SIRT4 may function as a tumor suppressor in gastric cancer by regulating cell proliferation, therefore SIRT4 may be a potential therapeutic target against this disease.

[SIRT1 participates in epithelial-mesenchymal transition of EC-9706 and Eca-109 cells in vitro by regulating Snail expression]

OBJECTIVE

To explore the role of SIRT1 in the occurrence of epithelial-mesenchymal transition (EMT) in EC-9706 and Eca-109 cells and the possible mechanism.

METHODS

Three chemically synthesized siRNA targeting SIRT1 were transfected into EC-9706 and Eca-109 cells with the non-transfected cells and cells transfected with the negative siRNAs as controls. Real-time PCR and Western blotting were used to detect the expressions of SIRT1, E-cadherin, vimentin, Snail, Twist1 and ZEB in the cells. Transwell invasion assay and wounding healing assay were used to examine the changes in the invasion and metastasis abilities of the cells after transfection.

RESULTS

EC-9706 and Eca-109 cells transfected with SIRT1 siRNA1 and SIRT1 siRNA3 showed significantly decreased mRNA and protein expressions of SIRT1 (P &lt; 0.05). Transwell invasion assay and wounding healing assay showed that transfection with SIRT1 siRNA1 and SIRT1 siRNA3 caused significantly lowered invasion and metastasis abilities in EC-9706 and Eca-109 cells (P &lt; 0.05). In EC-9706 and Eca-109 cells transfected with SIRT1 siRNA1 and SIRT1 siRNA3, the expression level of E-cadherin was significantly increased while the expressions of vimentin, Snail and Twist were significantly lowered (P &lt; 0.05).

CONCLUSIONS

SIRT1 participates in the invasion and metastasis of EC-9706 and Eca- 109 cells probably by inducing EMT via regulating the expression of Snail.

CPEB1 mediates hepatocellular carcinoma cancer stemness and chemoresistance

Cancer stem cells (CSCs) are a subpopulation of cells within tumors that are believed to possess pluripotent properties and thought to be responsible for tumor initiation, progression, relapse and metastasis. Cytoplasmic polyadenylation element-binding protein 1 (CPEB1), a sequence-specific RNA-binding protein that regulates mRNA polyadenylation and translation, has been linked to cancer progression and metastasis. However, the involvement of CPEB1 in hepatocellular carcinoma (HCC) remains unclear. In this study, we have demonstrated that CPEB1 directly regulates sirtuin 1 (SIRT1) mRNA to mediate cancer stemness in HCC. Cancer stemness was analyzed by self-renewal ability, chemoresistance, metastasis, expression of stemness-related genes and CSC marker-positive cell populations. The results indicate that CPEB1 is downregulated in HCC. Overexpression of CPEB1 dramatically reduced HCC cell stemness, whereas silencing CPEB1 enhances it. Using site-directed mutagenesis, a luciferase reporter assay, and immunoprecipitation, we found that CPEB1 could directly target the 3′-UTR of SIRT1, control poly(A) tail length and suppress its translation to mediate cancer stemness in vitro and in vivo. Overall, our findings suggest that the negative regulation between CPEB1 and SIRT1 contributes to the suppression of cancer stemness in HCC. CPEB1 may have potential as a therapeutic target in HCC.

Associations of sirtuins with clinicopathological parameters and prognosis in non-small cell lung cancer

BACKGROUND

Lung cancer is the leading cause of cancer-related death worldwide and it is critical to discover specific biomarkers to provide better individualized treatment and subsequently better prognosis. The sirtuins (SIRT1-7) have been reported to be involved in cancers including non-small cell lung cancer (NCSLC), however, the results are not consistent and not all the seven sirtuins are explored and compared.

METHODS

TCGA data was downloaded and used to investigate and compare the associations of sirtuins mRNA levels with clinicopathological parameters and prognosis in NSCLC.

RESULTS

Our results suggested SIRT1, SIRT3, SIRT4, and SIRT7 were highly expressed in adeno-carcinoma (ADC) patients and female patients while SIRT5 were highly expressed in squamous cell carcinoma (SCC) patients and male patients. Associations of high SIRT7 with younger onset age, high SIRT1 with distant metastasis and low T stage, and high SIRT4 with high T stage and TNM stage were also found. Kaplan-Meier plot curves and univariate Cox proportional regression analyses indicated that high SIRT2, SIRT4, and SIRT6 expressions were associated with longer overall survival (OS) time. Multivariate analyses indicated that SIRT2 and SIRT6 were still associated with OS. For recurrence-free survival (RFS), high SIRT1 expression was significantly associated with shorter RFS time while high SIRT2-3 and SIRT5-7 expressions were associated with longer RFS time in univariate analyses. After adjusting the confounding factors, significant associations were still found in SIRT1-2 and SIRT5-7 but not in SIRT3. We also stratified the patients by combining SIRT1 and SIRT2 and revealed that the combination of SIRT1 and SIRT2 was a better prediction model for RFS in NSCLC. To preliminarily understand the potential mechanisms of sirtuins in NSCLC carcinogenesis, the genes co-expressed with sirtuins were analyzed and annotated.

CONCLUSION

sirtuins might be the potential therapy targets and prognostic biomarkers in NSCLC.

Sirtuin-4 (SIRT4), a therapeutic target with oncogenic and tumor-suppressive activity in cancer

Several members of the sirtuin (SIRT) family, a highly conserved family of NAD⁺-dependent enzymes, have been shown to play a critical role in both promoting and/or suppressing tumorigenesis. In this study, recent progress in the field concerning SIRT4 and cancer was reviewed, and the relationship between SIRT4 and tumors was investigated. Subsequently, we evaluated the role of SIRT4 with oncogenic or tumor-suppressive activity in cancer, which may provide insight in identifying the underlying mechanism of action of SIRT4 in cancer. Finally, we explored the potential of SIRT4 as a therapeutic target in cancer therapy.

Knockout of SIRT4 decreases chemosensitivity to 5-FU in colorectal cancer cells

Previous studies demonstrated that sirtuin (SIRT) 4 is aberrantly expressed in human malignant tumors and is associated with poor prognosis in patients with colorectal cancer. However, the role of SIRT4 in the progression of human colorectal cancer (CRC) and in chemotherapy remains unclear. In the present study, the expression of SIRT4 in CRC tissues and the effect of SIRT4 on colorectal cancer proliferation, migration and invasion was investigated. Additionally, the effects of SIRT4 on the chemosensitivity in colorectal cancer cells and the underlying molecular mechanisms were also explored. The results demonstrated that SIRT4 expression is significantly downregulated in CRC tissues and cell lines. Downregulation of SIRT4 significantly increased tumor proliferation, migration and invasion. Additionally, downregulation of SIRT4 decreased the chemosensitivity of CRC cells by inhibiting cell apoptosis. Thus, these results suggest that SIRT4 may be a promising therapeutic target in CRC.

SIRT1-mediated downregulation of p27Kip1 is essential for overcoming contact inhibition of Kaposi's sarcoma-associated herpesvirus transformed cells

Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus associated with Kaposi's sarcoma (KS), a malignancy commonly found in AIDS patients. Despite intensive studies in the last two decades, the mechanism of KSHV-induced cellular transformation and tumorigenesis remains unclear. In this study, we found that the expression of SIRT1, a metabolic sensor, was upregulated in a variety of KSHV-infected cells. In a model of KSHV-induced cellular transformation, SIRT1 knockdown with shRNAs or knockout by CRISPR/Cas9 gene editing dramatically suppressed cell proliferation and colony formation in soft agar of KSHV-transformed cells by inducing cell cycle arrest and contact inhibition. SIRT1 knockdown or knockout induced the expression of cyclin-dependent kinase inhibitor 1B (p27^Kip1). Consequently, p27 knockdown rescued the inhibitory effect of SIRT1 knockdown or knockout on cell proliferation and colony formation. Furthermore, treatment of KSHV-transformed cells with a SIRT1 inhibitor, nicotinamide (NAM), had the same effect as SIRT1 knockdown and knockout. NAM significantly inhibited cell proliferation in culture and colony formation in soft agar, and induced cell cycle arrest. Significantly, NAM inhibited the progression of tumors and extended the survival of mice in a KSHV-induced tumor model. Collectively, these results demonstrate that SIRT1 suppression of p27 is required for KSHV-induced tumorigenesis and identify a potential therapeutic target for KS.

MEK1 signaling promotes self-renewal and tumorigenicity of liver cancer stem cells via maintaining SIRT1 protein stabilization

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death. This high mortality has been commonly attributed to the presence of residual cancer stem cells (CSCs). Meanwhile, MEK1 signaling is regarded as a key molecular in HCC maintenance and development. However, nobody has figured out the particular mechanisms that how MEK1 signaling regulates liver CSCs self-renewal. In this study, we show that inhibition or depletion of MEK1 can significantly decrease liver CSCs self-renewal and tumor growth both in vitro and vivo conditions. Furthermore, we demonstrate that MEK1 signaling promotes liver CSCs self-renewal and tumorigenicity by maintaining SIRT1 level. Mechanistically, MEK1 signaling keeps SIRT1 protein stabilization through activating SIRT1 ubiquitination, which inhibits proteasomal degradation. Clinical analysis shows that patients co-expression of MEK1 and SIRT1 are associated with poor survival. Our finding indicates that MEK1-SIRT1 can act as a novel diagnostic biomarker and inhibition of MEK1 may be a viable therapeutic option for targeting liver CSCs treatment.

Dual SIRT1 expression patterns strongly suggests its bivalent role in human breast cancer

Breast cancer is the most common cancer in women, and the leading cause of cancer death in women worldwide. SIRT1 (silent mating type information regulation 2 homolog) 1 is a class-III histone deacetylase involved in apoptosis regulation, DNA repair and tumorigenesis. However, its role in breast carcinoma remains controversial, as both tumor-suppressive and tumor-promoting functions have been reported. Also, there are very few reports available where expression of SIRT1 is comprehensively analyzed in breast tumors classified by molecular subtype. Here, using a cohort of 50 human breast tumors and their matched normal tissues, we investigated SIRT1 expression levels in the 5 molecular subtypes of breast cancer according to the St Gallen classification (2013). Tumors and their corresponding normal tissue samples were collected from all patients, and SIRT1 mRNA and protein expression levels were then examined by real-time quantitative polymerase chain reaction and immunoblotting, respectively. After statistical analysis, the results showed a dual expression profile of SIRT1 in human breast carcinoma, with significant overexpression in luminal and HER2-enriched subtypes and significantly reduced expression in the triple-negative subtype. We also found an inverse correlation between SIRT1 expression and breast cancer aggressivity. These novel findings suggest that SIRT1 plays a dual role in breast tumors depending on its expression rate and the molecular subtype of the cancer. Our data also point to a potential role for SIRT1 as a prognostic biomarker in breast cancer.

SIRT6 delays cellular senescence by promoting p27Kip1 ubiquitin-proteasome degradation

Sirtuin6(SIRT6) has been implicated as a key factor in aging and aging-related diseases. However, the role of SIRT6 in cellular senescence has not been fully understood. Here, we show that SIRT6 repressed the expression of p27^Kip1 (p27) in cellular senescence. The expression of SIRT6 was reduced during cellular senescence, whereas enforced SIRT6 expression promoted cell proliferation and antagonized cellular senescence. In addition, we demonstrated that SIRT6 promoted p27 degradation by proteasome and SIRT6 decreased the acetylation level and protein half-life of p27. p27 acetylation increased its protein stability. Furthermore, SIRT6 directly interacted with p27. Importantly, p27 was strongly acetylated and had a prolonged protein half-life with the reduction of SIRT6 when cells were senescent, compared with those young cells. Finally, SIRT6 markedly rescued senescence induced by p27. Our findings indicate that SIRT6 decreases p27 acetylation, leading to its degradation via ubiquitin-proteasome pathway and then delays cellular senescence.

Tenovin-6 inhibits proliferation and survival of diffuse large B-cell lymphoma cells by blocking autophagy

Diffuse large B-cell lymphoma (DLBCL) is one of the most aggressive non-Hodgkin lymphomas. It is curable but one-third of cases are refractory to therapy or relapse after initial response highlighting the urgent need for developing novel therapeutic approaches. Targeting sirtuins, particularly SIRT1 by genetic approaches or using pharmaceutical inhibitor tenovin-6, has shown promising therapeutic potential in various hematopoietic malignancies. However, it remains unknown whether these approaches are effective for DLBCL. In this study, we have found that tenovin-6 potently inhibits the proliferation and survival of DLBCL cells. Surprisingly, specific knockdown of SIRT1/2/3 has no effect on DLBCL. Mechanistically, tenovin-6 increases the level of microtubule-associated protein 1 light chain 3B (LC3B)-II in a SIRT1/2/3- and p53-independent manner in DLBCL cell lines. Tenovin-6-mediated increase of LC3B-II is through inhibition of classical autophagy pathway. Furthermore, inhibition of the autophagy pathway by using other inhibitors or by knocking down key genes in the pathway impairs cell proliferation and survival of DLBCL cells. These results indicate that targeting the autophagic pathway could be a novel therapeutic strategy for DLBCL and that precaution should be taken to interpret data where tenovin-6 was used as an inhibitor of sirtuins.

Phosphorylated SIRT1 associates with replication origins to prevent excess replication initiation and preserve genomic stability

Chromatin structure affects DNA replication patterns, but the role of specific chromatin modifiers in regulating the replication process is yet unclear. We report that phosphorylation of the human SIRT1 deacetylase on Threonine 530 (T530-pSIRT1) modulates DNA synthesis. T530-pSIRT1 associates with replication origins and inhibits replication from a group of 'dormant' potential replication origins, which initiate replication only when cells are subject to replication stress. Although both active and dormant origins bind T530-pSIRT1, active origins are distinguished from dormant origins by their unique association with an open chromatin mark, histone H3 methylated on lysine 4. SIRT1 phosphorylation also facilitates replication fork elongation. SIRT1 T530 phosphorylation is essential to prevent DNA breakage upon replication stress and cells harboring SIRT1 that cannot be phosphorylated exhibit a high prevalence of extrachromosomal elements, hallmarks of perturbed replication. These observations suggest that SIRT1 phosphorylation modulates the distribution of replication initiation events to insure genomic stability.

SIRT1 Regulates the Chemoresistance and Invasiveness of Ovarian Carcinoma Cells

BACKGROUND

SIRT1 is a longevity gene that forestalls aging and age-related diseases including cancer, and has recently attracted widespread attention due to its overexpression in some cancers. We previously identified the overexpression of SIRT1 in ovarian carcinoma (OvCa) as a poor prognostic factor. However, mechanistic insights into the function of SIRT1 in OvCa have yet to be elucidated.

METHODS

Quantitative real-time reverse PCR (qRT-PCR) and Western blotting were employed to examine the expression of SIRT1 in a panel of human OvCa cell lines. si-RNA or sh-RNA and cDNA technologies were utilized to knockdown or overexpress SIRT1, respectively. The effects of SIRT1 on proliferation and chemoresistance were examined using a WST-1 assay, and the underlying mechanisms were confirmed using an apoptotic assay, and the quantification of glutathione (GSH), and reactive oxygen species (ROS). The aggressiveness of SIRT1 was analyzed using in vitro invasion and migration assays.

RESULTS

SIRT1 was more strongly expressed in OvCa cell lines than in the immortalized ovarian epithelium at the gene and protein levels. Stress up-regulated the expression of SIRT1 in dose- and time-dependent manners. SIRT1 significantly enhanced the proliferation (P<.05), chemoresistance (P<.05), and aggressiveness of OvCa cells by up-regulating multiple antioxidant pathways to inhibit oxidative stress. Further study into the overexpression of SIRT1 demonstrated the up-regulation of several stemness-associated genes and enrichment of CD44v9 via an as-yet-unidentified pathway.

CONCLUSIONS

Our results suggest that SIRT1 plays a role in the acquisition of aggressiveness and chemoresistance by OvCa, and has potential as a therapeutic target for OvCa.

Induction of sirtuin-1 signaling by resveratrol induces human chondrosarcoma cell apoptosis and exhibits antitumor activity

Chondrosarcoma is a malignant primary bone tumor. Sirtuin-1 (SIRT1), which is a member of sirtuin family, plays a dual role either in cancer promotion or suppression. There is no report about the role of SIRT1 in the human chondrosarcoma cells. Resveratrol is a potent activator of SIRT1. However, its effects on chondrosarcoma have not been extensively studied. Here, we investigated the role of SIRT1 induction by resveratrol in human chondrosarcoma cell growth and tumor progression. Resveratrol significantly decreased cell viability and induced cell apoptosis in human chondrosarcoma cells in a dose-dependent manner. The protein expression and activity of SIRT1 were activated after treatment with resveratrol. Resveratrol significantly inhibited NF-κB signaling by deacetylating the p65 subunit of NF-κB complex, which could be reversed by siRNA-SIRT1 transfection or deacetylation inhibitor MS-275. Resveratrol induced-apoptosis involved a caspase-3-mediated mechanism. Both siRNA-SIRT1 transfection and MS-275 significantly inhibited the resveratrol-induced caspase-3 cleavage and activity in human chondrosarcoma cells. Moreover, in vivo chondrosarcoma xenograft study revealed a dramatic reduction in tumor volume and the increased SIRT1 and cleaved caspase-3 expressions in tumors by resveratrol treatment. These results suggest that resveratrol induces chondrosarcoma cell apoptosis via a SIRT1-activated NF-κB deacetylation and exhibits anti-chondrosarcoma activity in vivo.

Expression profile of SIRT2 in human melanoma and implications for sirtuin-based chemotherapy

Melanoma is cancer of melanin-containing melanocyte cells. This neoplasm is one of the most deadly forms of skin cancer, and currently available therapeutic options are insufficient in significantly improve outcomes for many patients. Therefore, novel targets are required to effectively manage this neoplasm. Several sirtuins have previously been found to be upregulated in melanoma, so in this study, the expression profile of SIRT2 was determined. Employing a tissue microarray containing benign nevi, primary melanomas, and lymph node metastases, we have found that the tissue from lymph node metastases appears to have a significant upregulation of SIRT2 relative to primary tumors across the nuclear, cytoplasmic, and whole cell data. Additionally, SIRT2 staining was found to be higher in the nucleus of metastatic melanomas compared to cytoplasmic staining. As SIRT2 is considered to be a predominantly cytoplasmic protein, this is a novel and very interesting finding. This, combined with previous studies that show other sirtuins are increased in melanoma and involved in cellular proliferation and survival, leads to the suggestion that exploring pan-sirtuin inhibitors may be the best target for the next iteration of melanoma chemotherapeutics.

Reversible modulation of SIRT1 activity in a mouse strain

The SIRT1 protein deacetylase is reported to have a remarkably wide spectrum of biological functions affecting such varied processes as aging, cancer, metabolism, neurodegeneration and immunity. However, the SIRT1 literature is also full of contradictions. To help establish the role(s) of SIRT1 in these and other biological processes, we set out to create a mouse in which the SIRT1 activity could be toggled between on and off states by fusing the estrogen receptor ligand-binding domain (ER) to the C terminus of the SIRT1 protein. We found that the catalytic activity of the SIRT1-ER fusion protein increased 4–5 fold in cells treated with its ligand, 4-hydroxy-tamoxifen (4OHT). The 4OHT-induced activation of SIRT1-ER was due in large part to a 2 to 4-fold increase in abundance of the SIRT1-ER protein in cells in culture and in tissues in vivo. This increase is reversible and is a consequence of 4OHT-induced stabilization of the SIRT1-ER protein. Since changes in SIRT1 level or activity of 2–4 fold are frequently reported to be sufficient to affect its biological functions, this mouse should be helpful in establishing the causal relationships between SIRT1 and the diseases and processes it affects.

Tenovin-6 impairs autophagy by inhibiting autophagic flux

Tenovin-6 has attracted significant interest because it activates p53 and inhibits sirtuins. It has anti-neoplastic effects on multiple hematopoietic malignancies and solid tumors in both in vitro and in vivo studies. Tenovin-6 was recently shown to impair the autophagy pathway in chronic lymphocytic leukemia cells and pediatric soft tissue sarcoma cells. However, whether tenovin-6 has a general inhibitory effect on autophagy and whether there is any involvement with SIRT1 and p53, both of which are regulators of the autophagy pathway, remain unclear. In this study, we have demonstrated that tenovin-6 increases microtubule-associated protein 1 light chain 3 (LC3-II) level in diverse cell types in a time- and dose-dependent manner. Mechanistically, the increase of LC3-II by tenovin-6 is caused by inhibition of the classical autophagy pathway via impairing lysosomal function without affecting the fusion between autophagosomes and lysosomes. Furthermore, we have revealed that tenovin-6 activation of p53 is cell type dependent, and tenovin-6 inhibition of autophagy is not dependent on its regulatory functions on p53 and SIRT1. Our results have shown that tenovin-6 is a potent autophagy inhibitor, and raised the precaution in interpreting results where tenovin-6 is used as an inhibitor of SIRT1.

Desynchronization of Circadian Clocks in Cancer: A Metabolic and Epigenetic Connection

Circadian clocks are innate oscillators that drive daily rhythms in metabolism, physiology, and behavior. 24-h rhythms in gene expression, driven by core clock transcription factors, reflect the epigenetic state of the cell, which in turn is dictated by the metabolic environment. Cancer cells alter their metabolic state and gene expression and therefore are likely to tweak circadian clock function in their favor. Over the past decade, we have witnessed an extraordinary increase in systems-level studies that suggest intricate mechanistic links between the cellular metabolome and the circadian epigenome. In parallel, reprogramming of cellular clock function in cancers is increasingly evident and the role of clock genes in the development of hematological tumors, as well as their pathophysiological effects on tissues distal to the tumor, has been described. Furthermore, the interplay between components of the circadian clock, metabolic enzymes, and oncogenes is starting to be better understood, such as the close association between overexpression of the Myc oncogene and perturbation of circadian and metabolic rhythms, thus opening new avenues to treat cancers. This review article explores current knowledge on the circadian metabolome and the molecular pathways they control, with a focus on their involvement in the development of hematopoietic malignancies.

miR-200a controls hepatic stellate cell activation and fibrosis via SIRT1/Notch1 signal pathway

OBJECTIVES

miR-200a has been established as a key regulator of HSC activation processes in liver fibrosis. Epigenetic silencing of miR-200a contributing to SIRT1 over-expression has been discussed in breast cancer; however, whether miR-200a controls SIRT1 gene expression in hepatic fibrosis is still unknown.

METHODS AND MATERIALS

We analyzed miR-200a regulation of SIRT1 expression in CCl₄-induced liver fibrosis and TGF-β1-mediated activation of HSC. miR-200a, SIRT1, α-SMA, Col1A1, Notch1 and NICD expression were estimated by Western blotting, qRT-PCR and Immunohistochemistry. HSCs were transfected with miR-200a mimic, miR-200a inhibitor and SIRT1-RNAi. Luciferase reporter assays further confirmed the interaction between miR-200a and the SIRT1 mRNA 3'-UTR. Cell proliferation ability was assessed by MTT and cell cycle.

RESULTS

We found that treatment activated HSC with miR-200a mimics, restored miR-200a expression and reduced SIRT1 levels. Conversely, treatment activated HSC with miR-200a inhibitors, decreased miR-200a expression and up-regulated SIRT1 levels. Restoration of miR-200a or the knockdown of SIRT1 prevented HSC activation and proliferation. We have established the SIRT1 transcript as subject to regulation by miR-200a, through miR-200a targeting of SIRT1 3'-UTR. Finally, HSC transfected with SIRT1-siRNA increased the levels of Notch1 protein and mRNA expression.

CONCLUSIONS

Our study demonstrated that miR-200a regulates SIRT1/Notch1 expression during HSC activation and fibrosis.