Tumor suppressor HIC1 directly regulates SIRT1 to modulate p53-dependent DNA-damage responses

Galangin Induces Autophagy via Deacetylation of LC3 by SIRT1 in HepG2 Cells

Galangin suppresses proliferation and induces apoptosis and autophagy in hepatocellular carcinoma (HCC) cells, but the precise mechanism is not clear. In this study, we demonstrated that galangin induced autophagy, enhanced the binding of SIRT1-LC3 and reduced the acetylation of endogenous LC3 in HepG2 cells. But this autophagy was inhibited by inactivation of SIRT1 meanwhile, galangin failed to reduce the acetylation of endogenous LC3 after SIRT1 was knocked-down. Collectively, these findings demonstrate a new mechanism by which galangin induces autophagy via the deacetylation of endogenous LC3 by SIRT1.

Expression of the significance of silent information regulator type-1 in Angioimmunoblastic T-cell lymphoma is greater association with tumorigenesis and has strong implications for adverse prognosis

Silent information regulator type-1 (SIRT1) is the best-studied member of the Sirtuin (Sir2) family of nicotinamide dinucleotide (NAD)-dependent class III histone deacetylases (HDACs). Rrecently, it is suggested that SIRT1 may be involved in the development of malignant tumors including mouse lymphoma, but has not yet been explored in Angioimmunoblastic T-cell lymphoma (AITL). Therefore, we investigated the prevalence and the prognostic impact of SIRT1 expression in AITL. Immunohistochemical expression of SIRT1, p53 were evaluated by using a 2 mm core from 45 AITL patients. Positive expression of SIRT1 was seen in 71.11% (32 of 45) of patients and p53 expression were seen in 53.33% (24 of 45). SIRT1 and p53 expression were significantly associated with shorter PFS by univariate analysis (P=0.009 and P < 0.001, respectively), multivariate analysis also shows that SIRT1 expression relate to worse prognosis. We also suggest inferior survival in AITL with the combined expression of SIRT1 and clinical characteristics of high IPI scores, high clinical stage, increased serum LDH, decreased HGB and increased γ-Globulin. In conclusion, our results indicate that SIRT1 is strongly expressed in AITL and it act as a clinically significant prognostic indicator for AITL patients, may also serve as a therapeutic target in AITL.

Mitochondrial function in hypoxic ischemic injury and influence of aging

Mitochondria are a major target in hypoxic/ischemic injury. Mitochondrial impairment increases with age leading to dysregulation of molecular pathways linked to mitochondria. The perturbation of mitochondrial homeostasis and cellular energetics worsens outcome following hypoxic-ischemic insults in elderly individuals. In response to acute injury conditions, cellular machinery relies on rapid adaptations by modulating posttranslational modifications. Therefore, post-translational regulation of molecular mediators such as hypoxia-inducible factor 1α (HIF-1α), peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), c-MYC, SIRT1 and AMPK play a critical role in the control of the glycolytic-mitochondrial energy axis in response to hypoxic-ischemic conditions. The deficiency of oxygen and nutrients leads to decreased energetic reliance on mitochondria, promoting glycolysis. The combination of pseudohypoxia, declining autophagy, and dysregulation of stress responses with aging adds to impaired host response to hypoxic-ischemic injury. Furthermore, intermitochondrial signal propagation and tissue wide oscillations in mitochondrial metabolism in response to oxidative stress are emerging as vital to cellular energetics. Recently reported intercellular transport of mitochondria through tunneling nanotubes also play a role in the response to and treatments for ischemic injury. In this review we attempt to provide an overview of some of the molecular mechanisms and potential therapies involved in the alteration of cellular energetics with aging and injury with a neurobiological perspective.

Understanding Genetic Heterogeneity in Type 2 Diabetes by Delineating Physiological Phenotypes: SIRT1 and its Gene Network in Impaired Insulin Secretion

Type 2 diabetes (T2D) is a chronic metabolic disease which shows an exponential increase in all parts of the world. However, the disease is controllable by early detection and modified lifestyle. A series of factors have been associated with the pathogenesis of diabetes, and genes are considered to play a critical role. The individual risk of developing T2D is determined by an altered genetic background of the en-zymes involved in several metabolism-related biological mechanisms, including glucose homeostasis, insulin metab-olism, the glucose and ion transporters involved in glucose uptake, transcription factors, signaling intermediates of insulin signaling pathways, insulin production and secretion, pancreatic tissue development, and apoptosis. However, many candidate genes have shown heterogeneity of associations with the disease in different populations. A possible approach to resolving this complexity and under-standing genetic heterogeneity is to delineate the physiological phenotypes one by one as studying them in combination may cause discrepancies in association studies. A systems biology approach involving regulatory proteins, transcription factors, and microRNAs is one way to understand and identify key factors in complex diseases such as T2D. Our earlier studies have screened more than 100 single nucleotide polymorphisms (SNPs) belonging to more than 60 globally known T2D candidate genes in the Indian population. We observed that genes invariably involved in the activity of pancreatic β-cells provide susceptibility to type 2 diabetes (T2D). Encouraged by these results, we attempted to delineate in this review one of the commonest physiological phenotypes in T2D, namely impaired insulin secretion, as the cause of hyperglycemia. This review is also intended to explain the genetic basis of the pathophysiology of insulin secretion in the context of variations in the SIRT1 gene, a major switch that modulates insulin secretion, and a set of other genes such as HHEX, PGC-α, TCF7L2, UCP2, and ND3 which were found to be in association with T2D. The review aims to look at the genotypic and transcriptional regulatory relationships with the disease phenotype.

DNA methylation patterns as noninvasive biomarkers and targets of epigenetic therapies in colorectal cancer

Aberrant DNA methylation is frequently detected in gastrointestinal tumors, and can therefore potentially be used to screen, diagnose, prognosticate, and predict colorectal cancers (CRCs). Although colonoscopic screening remains the gold standard for CRC screening, this procedure is invasive, expensive, and suffers from poor patient compliance. Methylated DNA is an attractive choice for a biomarker substrate because CRCs harbor hundreds of aberrantly methylated genes. Furthermore, abundance in extracellular environments and resistance to degradation and enrichment in serum, stool, and other noninvasive bodily fluids, allows quantitative measurements of methylated DNA biomarkers. This article describes the most important studies that investigated the efficacy of serum- or stool-derived methylated DNA as population-based screening biomarkers in CRC, details several mechanisms and factors that control DNA methylation, describes a better use of prevailing technologies that discover novel DNA methylation biomarkers, and illustrates the diversity of demethylating agents and their applicability toward clinical impact.

Multiple functions of p21 in cell cycle, apoptosis and transcriptional regulation after DNA damage

An appropriate control over cell cycle progression depends on many factors. Cyclin-dependent kinase (CDK) inhibitor p21 (also known as p21(WAF1/Cip1)) is one of these factors that promote cell cycle arrest in response to a variety of stimuli. The inhibitory effect of P21 on cell cycle progression correlates with its nuclear localization. P21 can be induced by both p53-dependent and p53-independent mechanisms. Some other important functions attributed to p21 include transcriptional regulation, modulation or inhibition of apoptosis. These functions are largely dependent on direct p21/protein interactions and also on p21 subcellular localizations. In addition, p21 can play a role in DNA repair by interacting with proliferating cell nuclear antigen (PCNA). In this review, we will focus on the multiple functions of p21 in cell cycle regulation, apoptosis and gene transcription after DNA damage and briefly discuss the pathways and factors that have critical roles in p21 expression and activity.

High-throughput screening of Sirtuin family of genes in breast cancer

Mammalian Sirtuins have been shown to perform distinct cellular functions and deregulated expression of these genes was reported to be involved in the development of various malignancies including breast cancer. An increasing number of evidence indicates that Sirtuins have both tumor promoter and tumor suppressor functions. However, the roles of Sirtuins have not been well-reported in breast cancer. In the present study, quantitative expression levels of Sirtuins (SIRT1-7) in breast cancer patients and breast cancer cell lines (MCF-7 and SKBR3) and control cell line (CRL-4010) were assessed by using a high-throughput real-time PCR method. As a result, Sirtuins were found to be differentially expressed in breast cancer tissues and cancer cell lines. Particularly, expressions of SIRT1 and SIRT4 were found to be significantly down-regulated in breast cancer tissues and SKBR3 breast cancer cells. In contrast, SIRT2, SIRT3, and SIRT5 genes were shown to be up-regulated in our study. Although SIRT6 and SIRT7 were also up-regulated in breast cancer tissues, these expression changes were statistically insignificant. Additionally, SIRT2, SIRT3, SIRT5, SIRT6 and SIRT7 were found to be differentially expressed in breast cancer cell lines. Yet, these changes were not well-correlated with tissue expression levels. In conclusion, Sirtuin family of genes shows differential expressions in breast cancer tissues and cells and SIRT1 and SIRT4 seem to play key tumor suppressor roles in breast cancer development. Herein, we report expression levels of Sirtuin family of genes in both breast cancer tissues and cancer cell lines simultaneously.

NAMPT protects against 6-hydroxydopamine-induced neurotoxicity in PC12 cells through modulating SIRT1 activity

Parkinson's disease (PD) is the second most common progressive neurodegenerative movement disorder. Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the first rate‑limiting step in the nicotinamide adenine dinucleotide (NAD+) biosynthetic pathway in mammals, is a substrate for NAD+‑dependent enzymes, such as sirtuin 1 (SIRT1), and contributes to cell fate decisions. However, the role of NAMPT in PD has remained to be fully elucidated. In the present study, PC12 cells were treated with the neurotoxin 6-hydroxydopamine (6‑OHDA) to establish an in vitro model of PD, following which an obvious inhibitory effect on the levels of NAMPT and NAD+ as well as the NAD+/NADH ratio was detected. In addition, pre‑incubation with FK866, a highly specific NAMPT inhibitor, enhanced the inhibitory effects of 6‑OHDA on the viability of PC12, while pre‑incubation with nicotinamide mononucleotide (NMN), am enzymatic product of NAMPT, had the opposite effect. Furthermore, it was revealed that NMN markedly attenuated 6‑OHDA‑induced decreases in superoxide dismutase activity and glutathione levels, as well as 6‑OHDA‑induced increases in malondialdehyde and lactate dehydrogenase in PC12 cells. Furthermore, 6‑OHDA significantly reduced SIRT1 activity in PC12 cells, which was inhibited by NMN. The pharmacological activator resveratrol also significantly inhibited 6‑OHDA‑mediated decreases in PC12 cell viability while reversing 6‑OHDA‑induced decreases in SIRT1 levels. The results of the present study suggested that NMT protected against 6‑OHDA‑induced decreases in PC12 cell viability, and that SIRT1 activation had a role in this process. Treatment with NMN to activate SIRT1 may represent a novel therapeutic strategy for treating PD.

Association between SIRT1 Gene Polymorphisms and Breast Cancer in Egyptians

Background

Breast cancer is reported to cause the highest mortality among female cancer patients. Previous studies have explored the association of silent mating-type information regulator 2 homolog 1 (SIRT1) gene expression with prognosis in breast cancer. However, no studies exist, so far, on the role of SIRT1 gene polymorphism in breast cancer risk or prognosis. The present study aimed to assess the association between SIRT1 gene polymorphisms and breast cancer in Egyptians.

Methods

The study comprised 980 Egyptian females divided into a breast cancer group (541 patients) and a healthy control group (439 subjects). SIRT1 gene single nucleotide polymorphisms (SNPs) rs3758391, rs3740051 and rs12778366 were genotyped using real-time polymerase chain reaction (RT-PCR). Allelic and genotypic frequencies were determined in both groups and association with breast cancer and clinicopathological characteristics was assessed.

Results

Breast cancer patients exhibited elevated serum SIRT1 levels which varied among different tumor grades. SIRT1 rs3758391 and rs12778366 TT genotypes were more frequent, exhibited higher SIRT1 levels than CC and CT genotypes and were associated with histologic grade and lymph node status. SIRT1 rs12778366 TT genotype also correlated with negative estrogen receptor (ER) and progesterone receptor (PR) statuses. The T allele frequency for both SNPs was higher in breast cancer patients than in normal subjects. Combined GG and AG genotypes of rs3740051 were more frequent, showed higher serum SIRT1 levels than the AA genotype, and were associated with ER and PR expression. Furthermore, inheritance of the G allele was associated with breast cancer.

Conclusions

Our findings reveal that rs3758391 and rs12778366 polymorphisms of SIRT1 gene are associated with breast cancer risk and prognosis in the Egyptian population.

Sirt1 Is Required for Resveratrol-Mediated Chemopreventive Effects in Colorectal Cancer Cells

Sirt1 is a NAD⁺-dependent protein-modifying enzyme involved in regulating gene expression, DNA damage repair, metabolism and survival, as well as acts as an important subcellular target of resveratrol. The complex mechanisms underlying Sirt1 signaling during carcinogenesis remain controversial, as it can serve both as a tumor promoter and suppressor. Whether resveratrol-mediated chemopreventive effects are mediated via Sirt1 in CRC growth and metastasis remains unclear; which was the subject of this study. We found that resveratrol suppressed proliferation and invasion of two different human CRC cells in a dose-dependent manner, and interestingly, this was accompanied with a significant decrease in Ki-67 expression. By transient transfection of CRC cells with Sirt1-ASO, we demonstrated that the anti-tumor effects of resveratrol on cells was abolished, suggesting the essential role of this enzyme in the resveratrol signaling pathway. Moreover, resveratrol downregulated nuclear localization of NF-κB, NF-κB phosphorylation and its acetylation, causing attenuation of NF-κB-regulated gene products (MMP-9, CXCR4) involved in tumor-invasion and metastasis. Finally, Sirt1 was found to interact directly with NF-κB, and resveratrol did not suppress Sirt1-ASO-induced NF-κB phosphorylation, acetylation and NF-κB-regulated gene products. Overall, our results demonstrate that resveratrol can suppress tumorigenesis, at least in part by targeting Sirt1 and suppression of NF-κB activation.

HIC1 Expression Distinguishes Intestinal Carcinomas Sensitive to Chemotherapy

Neoplastic growth is frequently associated with genomic DNA methylation that causes transcriptional silencing of tumor suppressor genes. We used a collection of colorectal polyps and carcinomas in combination with bioinformatics analysis of large datasets to study the expression and methylation of Hypermethylated in cancer 1 (HIC1), a tumor suppressor gene inactivated in many neoplasms. In premalignant stages, HIC1 expression was decreased, and the decrease was linked to methylation of a specific region in the HIC1 locus. However, in carcinomas, the HIC1 expression was variable and, in some specimens, comparable to healthy tissue. Importantly, high HIC1 production distinguished a specific type of chemotherapy-responsive tumors.

Regain control of p53: Targeting leukemia stem cells by isoform-specific HDAC inhibition

Leukemia stem cells (LSCs) are self-renewable, leukemia-initiating populations that are often resistant to traditional chemotherapy and tyrosine kinase inhibitors currently used for treatment of acute or chronic myeloid leukemia. The persistence and continued acquisition of mutations in resistant LSCs represent a major cause of refractory disease and/or relapse after remission. Understanding the mechanisms regulating LSC growth and survival is critical in devising effective therapies that will improve treatment response and outcome. Several recent studies indicate that the p53 tumor suppressor pathway is often inactivated in de novo myeloid leukemia through oncogenic-specific mechanisms, which converge on aberrant p53 protein deacetylation. Here, we summarize our current understanding of the various mechanisms underlying deregulation of histone deacetylases (HDACs), which could be exploited to restore p53 activity and enhance targeting of LSCs in molecularly defined patient subsets.

Cellular localization of NRF2 determines the self-renewal and osteogenic differentiation potential of human MSCs via the P53-SIRT1 axis

NRF2 (nuclear factor erythroid-derived 2-like 2) plays an important role in defense against oxidative stress at the cellular level. Recently, the roles of NRF2 in embryonic and adult stem cells have been reported, but its role in maintaining self-renewal and differentiation potential remains unknown. We studied the mechanisms of NRF2 action in mesenchymal stem cells (MSCs) derived from human bone marrow. We found that the cellular localization of NRF2 changed during prolonged cell passage and osteogenic differentiation. Blocking the nuclear import of NRF2 using ochratoxin A (OTA) induced the loss of the self-renewal and osteogenic potential of early-passage (EP) MSCs. Conversely, reinforcing the nuclear import of NRF2 using tert-butylhydroquinone (t-BHQ) improved the self-renewal capacity and maintained the differentiation potential in the osteogenic lineage of EP MSCs. Real-time quantitative PCR and western blot analysis showed that NRF2 positively regulates sirtuin 1 (SIRT1) at the mRNA and protein levels via the negative regulation of p53. The self-renewal and osteogenic potential suppressed in OTA-treated or NRF2-targeting small hairpin RNA (shRNA)-infected EP MSCs were rescued by introducing small interfering RNA (siRNA) targeting p53. t-BHQ treatment in late-passage (LP) MSCs, which lost their self-renewal and osteogenic potential, reversed these effects. In LP MSCs treated with t-BHQ for ∼7 days, the phosphorylation and nuclear localization of NRF2 improved and SIRT1 protein level increased, whereas p53 protein levels decreased. Therefore, our results suggest that NRF2 plays an important role in regulating p53 and SIRT1 to maintain MSC stemness. This study is the first to establish a functional link between NRF2 and SIRT1 expression in the maintenance of MSC self-renewal and differentiation potential.

DNA damage and the balance between survival and death in cancer biology

DNA is vulnerable to damage resulting from endogenous metabolites, environmental and dietary carcinogens, some anti-inflammatory drugs, and genotoxic cancer therapeutics. Cells respond to DNA damage by activating complex signalling networks that decide cell fate, promoting not only DNA repair and survival but also cell death. The decision between cell survival and death following DNA damage rests on factors that are involved in DNA damage recognition, and DNA repair and damage tolerance, as well as on factors involved in the activation of apoptosis, necrosis, autophagy and senescence. The pathways that dictate cell fate are entwined and have key roles in cancer initiation and progression. Furthermore, they determine the outcome of cancer therapy with genotoxic drugs. Understanding the molecular basis of these pathways is important not only for gaining insight into carcinogenesis, but also in promoting successful cancer therapy. In this Review, we describe key decision-making nodes in the complex interplay between cell survival and death following DNA damage.

Oncogenic role of SIRT1 associated with tumor invasion, lymph node metastasis, and poor disease-free survival in triple negative breast cancer

The aim of this study is to evaluate the biological role and clinical implications of silent mating type information regulation 2 homolog 1 (SIRT1) as a novel candidate for target therapy in triple negative breast cancer (TNBC) for which there is no specific agent. 344 patients who received surgical resection for TNBC from January 2003 to December 2006 at Seoul National University Hospital were enrolled, and the role of SIRT1 protein was evaluated via immunohistochemistry on tissue samples. In vivo experiments to evaluate tumor invasiveness were carried out with three human TNBC cell lines following SIRT1-siRNA transfection. Expression of SIRT1 significantly correlated with lymph node metastasis (p = 0.008). In multivariate analysis, SIRT1 expression (p = 0.011), T stage (p = 0.014), and lymphatic invasion (p < 0.001) were revealed to be independent predictive factors for lymph node metastasis. Combination of these three parameters revealed predictive performance for lymph node metastasis with an area under the curve (AUC) of 0.689 on receiver operating characteristics (ROC) curves analysis. SIRT1 expression correlated with shorter disease-free survival (P = 0.003) but not with overall survival. Inhibition of SIRT1 with small interfering RNA (siRNA) conspicuously suppressed the invasiveness of TNBC cell lines. This study reveals the role of SIRT1 on tumor invasiveness and unfavorable clinical outcomes, and we suggest its potential role as a prognostic indicator as well as a novel therapeutic target in TNBC.

Association of SIRT1 and HMGA1 expression in non-small cell lung cancer

The roles of Silent mating type information regulation 2 homolog 1 (SIRT1) and High mobility group A1 (HMGA1) in human diseases have been extensively studied separately; however, to the best of our knowledge, the current study is the first to report on their interrelationship in lung cancer. The association of SIRT1 and HMGA1 in non-small cell lung cancer (NSCLC) was investigated by evaluating their expression and prognostic significance in 260 patients with NSCLC using immunohistochemistry. SIRT1 and HMGA1 expression were found to be significantly correlated with each other (P<0.001), and both were significantly associated with clinicopathological parameters, including histological type and degree of differentiation. In squamous cell carcinoma (SCC), SIRT1⁺ specimens were significantly associated with shorter overall survival (OS) time (P=0.019). However, in patients with adenocarcinoma (AD), no association was identified between SIRT1 and OS. In addition, HMGA1⁺ specimens were significantly associated with poor differentiation (P=0.028), and were more frequent in SCC than AD (P=0.015). However, HMGA1 was not associated with OS on univariate Cox regression analysis or Kaplan-Meier analysis (both P>0.05). SIRT1/HMGA1 coexpression was significantly associated with male gender (P=0.016), and moderately and poorly differentiated histological grade (P=0.025). The findings indicate that SIRT1 and HMGA1 may have significant effects during tumor progression in NSCLC, particularly in patients with SCC, and are potentially useful as prognostic indicators for patients with NSCLC.

The multifaceted functions of sirtuins in cancer

The sirtuins (SIRTs; of which there are seven in mammals) are NAD(+)-dependent enzymes that regulate a large number of cellular pathways and forestall the progression of ageing and age-associated diseases. In recent years, the role of sirtuins in cancer biology has become increasingly apparent, and growing evidence demonstrates that sirtuins regulate many processes that go awry in cancer cells, such as cellular metabolism, the regulation of chromatin structure and the maintenance of genomic stability. In this article, we review recent advances in our understanding of how sirtuins affect cancer metabolism, DNA repair and the tumour microenvironment and how activating or inhibiting sirtuins may be important in preventing or treating cancer.

Extremely low frequency electromagnetic field sensitizes cisplatin-resistant human ovarian adenocarcinoma cells via P53 activation

In the following study, extremely low frequency electromagnetic fields (EL-EMF) radiation was used to restore sensitivity in the cisplatin-resistant A2780 ovarian cancer cells. For this purpose A2780 cells were treated with different doses of cisplatin and EL-EMF (50 Hz, 200 gauss, and 2 h) alone. Cytotoxicity was the measurement using MTT assay. After calculating IC50 for cisplatin (90 µg/ml) a lower concentration from IC50 (30 and 60 µg/ml) was used to be combined with EL-EMF. We compare the effects of each cisplatin, EL-EMF and combination groups using acridine orange-propidium iodide (AO/PI) and DAPI staining, caspase 3/9 activation assay and Annexin/PI assay. We also assessed changes in P53 and Matrix metalloproteinases 2 (MMPs) gene expression with semi-quantitative RT-PCR. Results indicated an EL-EMF-dependent proliferative decrease which was found <10 %, and occurred independently of cisplatin. The decreased proliferation rate for 30 and 60 µg/ml cisplatin was about 20 and 40 %, respectively, while for synergistic groups 30 and 60 µg/ml cisplatin with 2 h EL-EMF exposer, showed 47 and 71 % decrease in viability in rats. DAPI staining indicated that chromatin break down significantly increased in synergistic groups. Acridine orange staining also confirmed MTT assay results. Caspase activity significantly increased in the combined groups. Semi-quantitative RT-PCR showed that in synergistic groups of cisplatin and EL-EMF, expression of P53 was increased but the expression level of MPP-2 gene decreased. Results from this study showed that changes generated by the non-invasive EL-EMF can make resistant cells sensitive to cisplatin.

SIRT1 contributes to aldose reductase expression through modulating NFAT5 under osmotic stress: In vitro and in silico insights

So far, a myriad of molecules were characterized to modulate NFAT5 and its downstream targets. Among these NFAT5 modifiers, SIRT1 was proposed to have a promising role in NFAT5 dependent events, yet the exact underlying mechanism still remains obscure. Hence, the link between SIRT1 and NFAT5-aldose reductase (AR) axis under osmotic stress, was aimed to be delineated in this study. A unique osmotic stress model was generated and its mechanistic components were deciphered in U937 monocytes. In this model, AR expression and nuclear NFAT5 stabilization were revealed to be positively regulated by SIRT1 through utilization of pharmacological modulators. Overexpression and co-transfection studies of NFAT5 and SIRT1 further validated the contribution of SIRT1 to AR and NFAT5. The involvement of SIRT1 activity in these events was mediated via modification of DNA binding of NFAT5 to AR ORE region. Besides, NFAT5 and SIRT1 were also shown to co-immunoprecipitate under isosmotic conditions and this interaction was disrupted by osmotic stress. Further in silico experiments were conducted to investigate if SIRT1 directly targets NFAT5. In this regard, certain lysine residues of NFAT5, when kept deacetylated, were found to contribute to its DNA binding and SIRT1 was shown to directly bind K282 of NFAT5. Based on these in vitro and in silico findings, SIRT1 was identified, for the first time, as a novel positive regulator of NFAT5 dependent AR expression under osmotic stress in U937 monocytes.

The role of sirtuins in cardiac disease

Modification of histones is one of the important mechanisms of epigenetics, in which genetic control is determined by factors other than an individual's DNA sequence. Sirtuin family proteins, which are class III histone deacetylases, were originally identified as gene silencers that affect the mating type of yeast, leading to the name "silent mating-type information regulation 2" (SIR2). They are characterized by their requirement of nicotinamide adenine dinucleotide for their enzyme activity, unlike other classes of histone deacetylases. Sirtuins have been traditionally linked to longevity and the beneficial effects of calorie restriction and DNA damage repair. Recently, sirtuins have been shown to be involved in a wide range of physiological and pathological processes, including aging, energy responses to low calorie availability, and stress resistance, as well as apoptosis and inflammation. Sirtuins can also regulate mitochondrial biogenesis and circadian clocks. Seven sirtuin family proteins (Sirt1-7) have been identified as mammalian SIR2 orthologs, localized in different subcellular compartments, namely, the cytoplasm (Sirt1, 2), the mitochondria (Sirt3, 4, 5), and the nucleus (Sirt1, 2, 6, 7). Sirt1 is evolutionarily close to yeast SIR2 and has been the most intensively investigated in the cardiovascular system. Endogenous Sirt1 plays a pivotal role in mediating the cell death/survival process and has been implicated in the pathogenesis of cardiovascular disease. Downregulation of Sirt2 is protective against ischemic-reperfusion injury. Increased Sirt3 expression has been shown to correlate with longevity in humans. In addition, Sirt3 protects cardiomyocytes from aging and oxidative stress and suppresses cardiac hypertrophy. Sirt6 has also recently been demonstrated to attenuate cardiac hypertrophy, and Sirt7 is known to regulate apoptosis and stress responses in the heart. On the other hand, the roles of Sirt4 and Sirt5 in the heart remain largely uncharacterized.

SIRT1 is involved in oncogenic signaling mediated by GPER in breast cancer

A number of tumors exhibit an altered expression of sirtuins, including NAD⁺-dependent histone deacetylase silent information regulator 1 (SIRT1) that may act as a tumor suppressor or tumor promoter mainly depending on the tumor types. For instance, in breast cancer cells SIRT1 was shown to exert an essential role toward the oncogenic signaling mediated by the estrogen receptor-α (ERα). In accordance with these findings, the suppression of SIRT1 led to the inhibition of the transduction pathway triggered by ERα. As the regulation of SIRT1 has not been investigated in cancer cells lacking ER, in the present study we ascertained the expression and function of SIRT1 by estrogens in ER-negative breast cancer cells and cancer-associated fibroblasts obtained from breast cancer patients. Our results show that 17β-estradiol (E2) and the selective ligand of GPER, namely G-1, induce the expression of SIRT1 through GPER and the subsequent activation of the EGFR/ERK/c-fos/AP-1 transduction pathway. Moreover, we demonstrate that SIRT1 is involved in the pro-survival effects elicited by E2 through GPER, like the prevention of cell cycle arrest and cell death induced by the DNA damaging agent etoposide. Interestingly, the aforementioned actions of estrogens were abolished silencing GPER or SIRT1, as well as using the SIRT1 inhibitor Sirtinol. In addition, we provide evidence regarding the involvement of SIRT1 in tumor growth stimulated by GPER ligands in breast cancer cells and xenograft models. Altogether, our data suggest that SIRT1 may be included in the transduction network activated by estrogens through GPER toward the breast cancer progression.

De Novo Assembly of the Donkey White Blood Cell Transcriptome and a Comparative Analysis of Phenotype-Associated Genes between Donkeys and Horses

Prior to the mechanization of agriculture and labor-intensive tasks, humans used donkeys (Equus africanus asinus) for farm work and packing. However, as mechanization increased, donkeys have been increasingly raised for meat, milk, and fur in China. To maintain the development of the donkey industry, breeding programs should focus on traits related to these new uses. Compared to conventional marker-assisted breeding plans, genome- and transcriptome-based selection methods are more efficient and effective. To analyze the coding genes of the donkey genome, we assembled the transcriptome of donkey white blood cells de novo. Using transcriptomic deep-sequencing data, we identified 264,714 distinct donkey unigenes and predicted 38,949 protein fragments. We annotated the donkey unigenes by BLAST searches against the non-redundant (NR) protein database. We also compared the donkey protein sequences with those of the horse (E. caballus) and wild horse (E. przewalskii), and linked the donkey protein fragments with mammalian phenotypes. As the outer ear size of donkeys and horses are obviously different, we compared the outer ear size-associated proteins in donkeys and horses. We identified three ear size-associated proteins, HIC1, PRKRA, and KMT2A, with sequence differences among the donkey, horse, and wild horse loci. Since the donkey genome sequence has not been released, the de novo assembled donkey transcriptome is helpful for preliminary investigations of donkey cultivars and for genetic improvement.

Role of DNA methylation in renal cell carcinoma

Alterations in DNA methylation are seen in cancers and have also been examined in clear cell renal cell carcinoma (ccRCC). Numerous tumor suppressor genes have been reported to be partially or completely silenced due to hypermethylation of their promoters in single-locus studies, and the use of hypomethylating agents has been shown to restore the expression of many of these genes in vitro. In particular, members of the Wnt and TGF-beta pathways, pro-apoptotic genes such as APAF-1 and negative cell-cycle regulators such as KILLIN have been shown to be epigenetically silenced in numerous studies in ccRCC. Recently, TCGA analysis of a large cohort of ccRCC samples demonstrated that aberrant hypermethylation correlated with the stage and grade in kidney cancer. Our genome-wide studies also revealed aberrant widespread hypermethylation that affected regulatory regions of the kidney genome in ccRCC. We also observed that aberrant enhancer hypermethylation was predictive of adverse prognosis in ccRCC. Recent discovery of mutations affecting epigenetic regulators reinforces the importance of these changes in the pathophysiology of ccRCC and points to the potential of epigenetic modulators in the treatment of this malignancy.

HIC1 Tumor Suppressor Loss Potentiates TLR2/NF-κB Signaling and Promotes Tissue Damage-Associated Tumorigenesis

Hypermethylated in cancer 1 (HIC1) represents a prototypic tumor suppressor gene frequently inactivated by DNA methylation in many types of solid tumors. The gene encodes a sequence-specific transcriptional repressor controlling expression of several genes involved in cell cycle or stress control. In this study, a Hic1 allele was conditionally deleted, using a Cre/loxP system, to identify genes influenced by the loss of Hic1. One of the transcripts upregulated upon Hic1 ablation is the toll-like receptor 2 (TLR2). Tlr2 expression levels increased in Hic1-deficient mouse embryonic fibroblasts (MEF) and cultured intestinal organoids or in human cells upon HIC1 knockdown. In addition, HIC1 associated with the TLR2 gene regulatory elements, as detected by chromatin immunoprecipitation, indicating that Tlr2 indeed represents a direct Hic1 target. The Tlr2 receptor senses "danger" signals of microbial or endogenous origin to trigger multiple signaling pathways, including NF-κB signaling. Interestingly, Hic1 deficiency promoted NF-κB pathway activity not only in cells stimulated with Tlr2 ligand, but also in cells treated with NF-κB activators that stimulate different surface receptors. In the intestine, Hic1 is mainly expressed in differentiated epithelial cells and its ablation leads to increased Tlr2 production. Finally, in a chemical-induced mouse model of carcinogenesis, Hic1 absence resulted in larger Tlr2-positive colonic tumors that showed increased proportion of proliferating cells.

IMPLICATIONS

The tumor-suppressive function of Hic1 in colon is related to its inhibitory action on proproliferative signaling mediated by the Tlr2 receptor present on tumor cells.

Resveratrol Induced Premature Senescence Is Associated with DNA Damage Mediated SIRT1 and SIRT2 Down-Regulation

The natural polyphenolic compound resveratrol (3,4,5-trihydroxy-trans-stilbene) has broad spectrum health beneficial activities including antioxidant, anti-inflammatory, anti-aging, anti-cancer, cardioprotective, and neuroprotective effects. Remarkably, resveratrol also induces apoptosis and cellular senescence in primary and cancer cells. Resveratrol's anti-aging effects both in vitro and in vivo attributed to activation of a (NAD)-dependent histone deacetylase family member sirtuin-1 (SIRT1) protein. In mammals seven members (SIRT1-7) of sirtuin family have been identified. Among those, SIRT1 is the most extensively studied with perceptive effects on mammalian physiology and suppression of the diseases of aging. Yet no data has specified the role of sirtuins, under conditions where resveratrol treatment induces senescence. Current study was undertaken to investigate the effects of resveratrol in human primary dermal fibroblasts (BJ) and to clarify the role of sirtuin family members in particular SIRT1 and SIRT2 that are known to be involved in cellular stress responses and cell cycle, respectively. Here, we show that resveratrol decreases proliferation of BJ cells in a time and dose dependent manner. In addition the increase in senescence associated β-galactosidase (SA-β-gal) activity and methylated H3K9-me indicate the induction of premature senescence. A significant increase in phosphorylation of γ-H2AX, a surrogate of DNA double strand breaks, as well as in levels of p53, p21CIP1 and p16INK4A is also detected. Interestingly, at concentrations where resveratrol induced premature senescence we show a significant decrease in SIRT1 and SIRT2 levels by Western Blot and quantitative RT-PCR analysis. Conversely inhibition of SIRT1 and SIRT2 via siRNA or sirtinol treatment also induced senescence in BJ fibroblasts associated with increased SA-β-gal activity, γ-H2AX phosphorylation and p53, p21CIP1 and p16INK4A levels. Interestingly DNA damaging agent doxorubicin also induced senescence in BJ fibroblasts associated with decreased SIRT1/2 levels. In conclusion our data reveal that resveratrol induced premature senescence is associated with SIRT1 and SIRT2 down regulation in human dermal fibroblasts. Here we suggest that the concomitant decline in SIRT1/2 expression in response to resveratrol treatment may be a cause for induction of senescence, which is most likely mediated by a regulatory mechanism activated by DNA damage response.

Sirtuin 3 inhibits hepatocellular carcinoma growth through the glycogen synthase kinase-3β/BCL2-associated X protein-dependent apoptotic pathway

SIRT3 is a class III histone deacetylase that has been implicated in a variety of cancers. The role of SIRT3 in hepatocellular carcinoma (HCC) remains elusive. In this study, we found that SIRT3 expression was frequently repressed in HCC and its downregulation was closely associated with tumor grade and size. Ectopic expression of SIRT3 inhibited cell growth and induced apoptosis in HCC cells, whereas depletion of SIRT3 in immortalized hepatocyte promoted cell growth and decreased epirubicin-induced apoptosis. Mechanistic studies revealed that SIRT3 deacetylated and activated glycogen synthase kinase-3β (GSK-3β), which subsequently induced expression and mitochondrial translocation of the pro-apoptotic protein BCL2-associated X protein (Bax) to promote apoptosis. GSK-3β inhibitor or gene silencing of BAX reversed SIRT3-induced growth inhibition and apoptosis. Furthermore, SIRT3 overexpression also suppressed tumor growth in vivo. Together, this study reveals a role of SIRT3/GSK-3β/Bax signaling pathway in the suppression of HCC growth, and also suggests that targeting this pathway may represent a potential therapeutic approach for HCC treatment.

Sirtuin-4 (SIRT4) is downregulated and associated with some clinicopathological features in gastric adenocarcinoma

BACKGROUND

Several members of the SIRT family (SIRT1-7), which are a highly conserved family of NAD(+)-dependent enzymes, play an important role in tumor formation. Recently, several studies have suggested that SIRT4 can regulate glutamine metabolism yet have tumor suppressor function too. However, our understanding of SIRT4 expression and its association with the clinicopathological parameters remains poor.

METHOD

We evaluated SIRT4 protein expression levels in gastric adenocarcinoma and corresponding normal gastric tissue by immunohistochemical staining on a tissue microarray that included 75 gastric adenocarcinoma patients. We also determined the association between SIRT4 expression levels and selected clinicopathological parameters in gastric adenocarcinoma.

RESULTS

We found that the expression level of SIRT4 in gastric adenocarcinoma was significantly lower than the corresponding normal tissue levels (P=0.003). Besides, lower SIRT4 levels were observed in pathological grade (P=0.002), depth of tumor invasion (P=0.034), positive lymph node numbers (P=0.005) and UICC stage (P=0.002).

CONCLUSIONS

Our results support the notion that SIRT4 behaves as a tumor suppressor at the human tissue protein level. In addition, our data indicate that SIRT4 might be closely involved in the process of gastric adenocarcinoma development and it might potentially serve as a diagnostic biomarker and therapeutic target in gastric adenocarcinoma.

SIRT1 inhibition in pancreatic cancer models: contrasting effects in vitro and in vivo

Gemcitabine remains the standard treatment for pancreatic cancer, although most patients acquire resistance to the therapy. Up-regulated in pancreatic cancer, SIRT1 is involved in tumorigenesis and drug resistance. However the mechanism through which SIRT1 regulates drug sensitivity in cancer cells is mainly unknown. We hypothesise that inhibiting SIRT1 activity may increase sensitivity of pancreatic cancer cells to gemcitabine treatment through the regulation of apototic cell death, cell cycle, epithelial-mesenschymal-transition (EMT) and senescence. We demonstrate that gemcitabine or 6-Chloro-2,3,4,9-tetrahydro-1 H-Carbazole-1-carboxamide (EX527) SIRT1 inhibitor reduces PANC-1 cell proliferation in vitro. EX527 enhanced sensitivity of PANC-1 cells to gemcitabine treatment through increased apoptosis. However, EX527 displayed no beneficial effect either as a monotreatment or in combination with gemcitabine in the modulation of cell cycle progression. Combination treatment did not reverse the two phenomena known to affect drug sensitivity, namely EMT and senescence, which are both induced by gemcitabine. Unexpectedly, EX527 promoted PANC-1 xenograft tumour growth in SCID mice compared to control group. Dual tX527 and gemcitabine displayed no synergistic effect compared to gemcitabine alone. The study reveals that SIRT1 is involved in chemoresistance and that inhibiting SIRT1 activity with EX527 sensitised PANC-1 cells to gemcitabine treatment in vitro. Sensitisation of cells is shown to be mainly through induction of micronuclei formation as a result of DNA damage and apoptosis in vitro. However, the absence of positive combinatorial effects in vivo indicates possible effects on cells of the tumor microenvironment and suggests caution regarding the clinical relevance of tissue culture findings with EX527.

Pemetrexed induces apoptosis in malignant mesothelioma and lung cancer cells through activation of reactive oxygen species and inhibition of sirtuin 1

Pemetrexed is a multitargeted antifolate used for the treatment of malignant mesothelioma and non-small cell lung cancer (NSCLC). However, the mechanism by which pemetrexed induces apoptosis remains unclear. In the present study, we investigated the involvement of reactive oxygen species (ROS) and sirtuin 1 (SIRT1) in pemetrexed-induced apoptosis in MSTO-211 malignant mesothelioma cells and A549 NSCLC cells. Pemetrexed enhanced caspase-dependent apoptosis, induced intracellular ROS generation, and downregulated SIRT1 in the MSTO-211 and A549 cells. Pemetrexed-induced apoptosis, which was prevented by pretreatment with N-acetyl-cysteine (NAC), was mediated by effects on the mitochondria, including mitochondrial membrane potential transition (MPT) and cytosolic release of cytochrome c, and also involved regulation of SIRT1 expression. Interference with SIRT1 expression using siRNA enhanced pemetrexed-induced apoptosis through mitochondrial dysfunction and ROS generation, whereas resveratrol, an activator of SIRT1, protected against pemetrexed-induced apoptosis. These results show that pemetrexed induces apoptosis in MSTO-211 mesothelioma cells and A549 NSCLC cells through mitochondrial dysfunction mediated by ROS accumulation and SIRT1 downregulation.

Expression of the tumor suppressor gene hypermethylated in cancer 1 in laryngeal carcinoma

Hypermethylated in cancer 1 (HIC1) is a putative suppressor gene, cooperating with TP53 in the regulation of apoptosis. The promoter site of this gene contains CpG islands susceptible to methylation. Altered methylation leads to the silencing of HIC1. Persistent loss of HIC1 function reflects the attenuation of proapoptotic characteristics of TP53 and may constitute the background for carcinogenesis. Altered methylation profiles along with diminished expression of HIC1 were documented in a number of solid neoplasms. The aim of this study was to evaluate the expression of the HIC1 gene in laryngeal carcinoma. RNA was extracted from samples of laryngeal cancer and corresponding healthy tissues of 21 patients with advanced laryngeal cancer (T3-T4). The amount of RNA (cDNA) was evaluated using reverse transcription-quantitative polymerase chain reaction with GADPH as the reference gene. Data demonstrated that HIC1 expression was significantly reduced in laryngeal cancer tissues. The relative expression of HIC1 was found to be ~40% lower in tumor samples compared to that in healthy controls. The median tumor/normal tissue ratio for HIC1 was 0.615. These results suggest that low HIC1 expression may be associated with neoplastic transformation in the larynx.

Sirtuin inhibitors as anticancer agents

Sirtuins are a class of enzymes with nicotinamide adenine dinucleotide (NAD)-dependent protein lysine deacylase function. By deacylating various substrate proteins, including histones, transcription factors, and metabolic enzymes, sirtuins regulate various biological processes, such as transcription, cell survival, DNA damage and repair, and longevity. Small molecules that can inhibit sirtuins have been developed and many of them have shown anticancer activity. Here, we summarize the major biological findings that connect sirtuins to cancer and the different types of sirtuin inhibitors developed. Interestingly, biological data suggest that sirtuins have both tumor-suppressing and tumor-promoting roles. However, most pharmacological studies with small-molecule inhibitors suggest that inhibiting sirtuins has anticancer effects. We discuss possible explanations for this discrepancy and suggest possible future directions to further establish sirtuin inhibitors as anticancer agents.

Acrylamide Induces Senescence in Macrophages through a Process Involving ATF3, ROS, p38/JNK, and a Telomerase-Independent Pathway

Senescence, which is irreversible cell cycle arrest, is induced by various types of DNA damage, including genotoxic stress. Senescent cells show dysregulation of tumor suppressor genes and other regulators of cellular proliferation. Activating transcription factor 3 (ATF3) plays a pleiotropic role in biological processes through genotoxic stress. In this study, we examined the effects of acrylamide (ACR), a genotoxic carcinogen, on cellular senescence and the molecular mechanisms of ATF3 function in macrophages. Treatment of macrophages with ACR at low concentrations (<1.0 mM) resulted in senescence-like morphology and an increase in senescence-associated β-galactosidase (SA-β-gal) activity. Exposure of macrophages to ACR led to stress-induced, telomerase-independent senescence. In addition, ACR treatment for 1, 3, or 5 days showed a concentration-dependent increase in ATF3 expression and G0/G1 phase arrest. To better understand the role of ATF3 in controlling the senescence response to ACR, SA-β-gal activity was examined using ATF3 knockdown and overexpression. ACR-mediated senescence was significantly decreased by knockdown of ATF3, whereas it was increased with ATF3 overexpression. We found that ATF3 regulated p53 and p21 levels. ATF3 also played an important role in regulating intracellular reactive oxygen species (ROS) production in response to ACR treatment. Moreover, phosphorylation of p38 and JNK kinases, which were activated during ATF3-mediated senescence, was observed in ACR-treated macrophages. Taken together, these results suggest that ATF3 contributes to ACR-induced senescence by enhancing ROS production, activating p38 and JNK kinases, and promoting the ATF3-dependent expression of p53, resulting in regulation of cellular senescence in macrophages.

SIRT1 regulates oncogenesis via a mutant p53-dependent pathway in hepatocellular carcinoma

BACKGROUND & AIMS

SIRT1 is a class III histone deacetylase that plays diverse roles in various cancers. However, the clinical significance of SIRT1 in hepatocellular carcinoma (HCC) remains unknown.

METHODS

We analysed p53 mutations and the activation of SIRT1 in 252 hepatitis B virus-positive HCC cases. None of the patients had been subjected to pre-operative treatment.

RESULTS

We examined 57 p53 mutations from 248 HCC tissues. Activated SIRT1 (phosphorylated form of Ser47), in the context of mutant p53, predicted a longer relapse-free survival (RFS) but not a longer overall survival (OS) (RFS: p = 0.007, OS: p = 0.280) in HCC tissues harbouring mutant p53. In multivariate analysis, activated SIRT1 remained a significant predictor of longer RFS (OR = 0.307, CI: 0.143-0.660, p=0.002). Analysis of 248 paired specimens revealed a significant correlation between activated SIRT1 (Ser47) and activated AMPK (Thr172) in HCC tissues harbouring mutant p53 (p = 0.003, n = 57). The combination of these 2 parameters was a powerful predictor for a good prognosis in these patients. In vitro, SIRT1 inactivation stimulated the growth of HCC cells, bearing mutated p53, by suppressing AMPK activity and subsequently enhancing mammalian target of rapamycin (mTOR) activity, resulting in induction of p70S6K1 activation in HCC cells. Metformin, an AMPK activator, more strongly suppressed cell growth in p53-mutant cell lines with inactive SIRT1 than in p53-mutant cell lines with active SIRT1.

CONCLUSIONS

SIRT1 exerted anti-carcinogenic effects via the AMPK-mTOR pathway in HCC in the context of mutant p53. Metformin could be a therapeutic drug for HCC in patients with mutated p53, inactivated SIRT1, and AMPK expression.

Simple sugar intake and hepatocellular carcinoma: epidemiological and mechanistic insight

Sugar intake has dramatically increased during the last few decades. Specifically, there has been a clear trend towards higher consumption of fructose and high fructose corn syrup, which are the most common added sugars in processed food, soft drinks and other sweetened beverages. Although still controversial, this rising trend in simple sugar consumption has been positively associated with weight gain and obesity, insulin resistance and type 2 diabetes mellitus and non-alcoholic fatty liver disease. Interestingly, all of these metabolic alterations have also been related to the development of hepatocellular carcinoma. The purpose of this review is to discuss the evidence coming from epidemiological studies and data from animal models relating the consumption of simple sugars, and specifically fructose, with an increased risk of hepatocellular carcinoma and to gain insight into the putative molecular mechanisms involved.

High levels of SIRT1 expression enhance tumorigenesis and associate with a poor prognosis of colorectal carcinoma patients

SIRT1, a NAD⁺ dependent class III deacetylase, takes part in many important biological processes. Previous studies show that SIRT1 is overexpressed in some cancers and plays an essential role in tumorigenesis. However, the association between SIRT1 and colorectal cancer (CRC) is still unclear. We found that many CRC specimens had strong SIRT1 expression, which had an obvious correlation with poor prognosis of CRC patients. Meanwhile, SIRT1 expression had a co-localization with CD133, a current universal marker to characterize colorectal cancer stem cells (CSCs). In vitro studies also revealed that SIRT1 was overexpressed in colorectal CSC-like cells. Moreover, SIRT1 deficiency decreased percentage of CD133⁺ cells, attenuated the abilities of colony and sphere formation, and inhibited tumorigenicity in vivo in CRC cells. Further study demonstrated that the expressions of several stemness-associated genes, including Oct4, Nanog, Cripto, Tert and Lin28, were reduced by SIRT1 knockdown in CRC cells. Taken together, our findings suggest that SIRT1 plays a crucial role in keeping the characteristics of CSCs cells. SIRT1 is a potential independent prognostic factor of CRC patients after tumor resection with curative intent, and will contribute to providing a promising new approach to target at CSCs in CRC treatment.

Anticancer agents targeted to sirtuins

Sirtuins are nicotinamide adenine dinucleotide⁺-dependent deacetylases of which there are seven isoforms (SIRT1–7). Sirtuin activity is linked to gene expression, lifespan extension, neurodegeneration, and age-related disorders. Numerous studies have suggested that sirtuins could be of great significance with regard to both antiaging and tumorigenesis, depending on its targets in specific signaling pathways or in specific cancers. Recent studies have identified small chemical compounds that modulate sirtuins, and these modulators have enabled a greater understanding of the biological function and molecular mechanisms of sirtuins. This review highlights the possibility of sirtuins, especially SIRT1 and SIRT2, for cancer therapy targets, and focuses on the therapeutic potential of sirtuin modulators both in cancer prevention and treatment.

Correlation and prognostic value of SIRT1 and Notch1 signaling in breast cancer

BACKGROUND

SIRT1 expression and Notch1 signaling have been implicated in tumorigenesis in many cancers, but their association with survival in breast cancer has not been determined. The purpose of this study was to assess the possible prognostic value of SIRT1, N1IC, and Snail expression in breast cancer patients.

METHODS

Immunohistochemistry was performed to examine the expression of SIRT1, N1IC, and Snail, and the combined expression of SIRT1 and N1IC, using tissue microarrays containing breast cancer tissue and matched adjacent normal breast tissue from 150 breast cancer patients. Survival analysis was carried out using the Kaplan-Meier method. Univariate and multivariate analysis were used to evaluate the prognostic value of SIRT1, N1IC, Snail and combined SIRT1/N1IC expression, in addition to other clinicopathological factors, including grade, lymph node status, disease stage, and estrogen, progesterone, and human epidermal growth factor receptor 2 receptor status in breast carcinoma patients.

RESULTS

SIRT1, N1IC, and Snail were all found to be highly expressed and an inverse correlation between SIRT1 and N1IC in breast cancer tissue. The three markers significantly correlated with lymph node status. Patients with low SIRT1 expression exhibited shorter overall survival (OS) and disease-free survival (DFS), and patients with combined low expression of SIRT1 and high expression of N1IC had the worse OS and DFS. Univariate and multivariate survival analysis revealed that low expression of SIRT1 and SIRT1-low/N1IC-high expression were independent prognostic factors for poor survival.

CONCLUSIONS

These results suggest that low expression of SIRT1 or the combined low expression of SIRT1 and high expression of N1IC could be used as indicators of poor prognosis, and may represent novel therapeutic targets in breast cancer.

Sirtuin1 Maintains Actin Cytoskeleton by Deacetylation of Cortactin in Injured Podocytes

Recent studies have highlighted the renoprotective effect of sirtuin1 (SIRT1), a deacetylase that contributes to cellular regulation. However, the pathophysiologic role of SIRT1 in podocytes remains unclear. Here, we investigated the function of SIRT1 in podocytes. We first established podocyte-specific Sirt1 knockout (SIRT1(pod-/-)) mice. We then induced glomerular disease by nephrotoxic serum injection. The increase in urinary albumin excretion and BUN and the severity of glomerular injury were all significantly greater in SIRT1(pod-/-) mice than in wild-type mice. Western blot analysis and immunofluorescence showed a significant decrease in podocyte-specific proteins in SIRT1(pod-/-) mice, and electron microscopy showed marked exacerbation of podocyte injury, including actin cytoskeleton derangement in SIRT1(pod-/-) mice compared with wild-type mice. Protamine sulfate-induced podocyte injury was also exacerbated by podocyte-specific SIRT1 deficiency. In vitro, actin cytoskeleton derangement in H2O2-treated podocytes became prominent when the cells were pretreated with SIRT1 inhibitors. Conversely, this H2O2-induced derangement was ameliorated by SIRT1 activation. Furthermore, SIRT1 activation deacetylated the actin-binding and -polymerizing protein cortactin in the nucleus and facilitated deacetylated cortactin localization in the cytoplasm. Cortactin knockdown or inhibition of the nuclear export of cortactin induced actin cytoskeleton derangement and dissociation of cortactin from F-actin, suggesting the necessity of cytoplasmic cortactin for maintenance of the actin cytoskeleton. Taken together, these findings indicate that SIRT1 protects podocytes and prevents glomerular injury by deacetylating cortactin and thereby, maintaining actin cytoskeleton integrity.

The role of SIRT1 in cancer: the saga continues

This Commentary highlights the article by Di Sante et al, which presents data supporting the status of SIRT1 as a tumor suppressor in prostate cancer.

Suppression of deacetylase SIRT1 mediates tumor-suppressive NOTCH response and offers a novel treatment option in metastatic Ewing sarcoma

The developmental receptor NOTCH plays an important role in various human cancers as a consequence of oncogenic mutations. Here we describe a novel mechanism of NOTCH-induced tumor suppression involving modulation of the deacetylase SIRT1, providing a rationale for the use of SIRT1 inhibitors to treat cancers where this mechanism is inactivated because of SIRT1 overexpression. In Ewing sarcoma cells, NOTCH signaling is abrogated by the driver oncogene EWS-FLI1. Restoration of NOTCH signaling caused growth arrest due to activation of the NOTCH effector HEY1, directly suppressing SIRT1 and thereby activating p53. This mechanism of tumor suppression was validated in Ewing sarcoma cells, B-cell tumors, and human keratinocytes where NOTCH dysregulation has been implicated pathogenically. Notably, the SIRT1/2 inhibitor Tenovin-6 killed Ewing sarcoma cells in vitro and prohibited tumor growth and spread in an established xenograft model in zebrafish. Using immunohistochemistry to analyze primary tissue specimens, we found that high SIRT1 expression was associated with Ewing sarcoma metastasis and poor prognosis. Our findings suggest a mechanistic rationale for the use of SIRT1 inhibitors being developed to treat metastatic disease in patients with Ewing sarcoma.

A critical role for interferon regulatory factor 9 in cerebral ischemic stroke

The failure of past efforts to develop effective stroke treatments is at least partially because these treatments often interfered with essential physiological functions, even though they are targeted toward pathophysiological events, such as inflammation, excitotoxicity, and oxidative stress. Thus, the direct targeting of endogenous neuroprotective or destructive elements holds promise as a potential new approach to treating this devastating condition. Interferon regulatory factor 9 (IRF9), a transcription factor that regulates innate immune responses, has been implicated in neurological pathology. Here, we provide new evidence that IRF9 directly mediates neuronal death in male mice. In response to ischemia/reperfusion (I/R), IRF9 accumulated in neurons. IRF9 deficiency markedly mitigated both poststroke neuronal death and neurological deficits, whereas the neuron-specific overexpression of IRF9 sensitized neurons to death. The histone deacetylase Sirt1 was identified as a novel negative transcriptional target of IRF9 both in vivo and in vitro. IRF9 inhibits Sirt1 deacetylase activity, culminating in the acetylation and activation of p53-mediated cell death signaling. Importantly, both the genetic and pharmacological manipulation of Sirt1 effectively counteracted the pathophysiological effects of IRF9 on stroke outcome. These findings indicate that, rather than activating a delayed innate immune response, IRF9 directly activates neuronal death signaling pathways through the downregulation of Sirt1 deacetylase in response to acute I/R stress.