Role of sirtuin histone deacetylase SIRT1 in prostate cancer. A target for prostate cancer management via its inhibition?

Forkhead Box Transcription Factors: Double-Edged Swords in Cancer

A plethora of treatment options exist for cancer therapeutics, but many are limited by side effects and either intrinsic or acquired resistance. The need for more effective targeted cancer treatment has led to the focus on forkhead box (FOX) transcription factors as possible drug targets. Forkhead factors such as FOXA1 and FOXM1 are involved in hormone regulation, immune system modulation, and disease progression through their regulation of the epithelial-mesenchymal transition. Forkhead factors can influence cancer development, progression, metastasis, and drug resistance. In this review, we discuss the various roles of forkhead factors in biological processes that support cancer as well as their function as pioneering factors and their potential as targetable transcription factors in the fight against cancer.

The regulation of long non-coding RNA 00958 (LINC00958) for oral squamous cell carcinoma (OSCC) cells death through absent in melanoma 2 (AIM2) depending on microRNA-4306 and Sirtuin1 (SIRT1) in vitro

Long non-coding RNAs (lncRNAs) have been proposed as potential targets in OSCC gene therapy. Thus, the study aims to analyze how they exert functions in OSCC. LINC00958, AIM2, Gasdermin D (GSDMD) and tumor protein p53 (TP53) expression levels are analyzed by Quantitative Real-time PCR (qPCR) or Western blotting (WB) in OSCC cells lines. The roles of LINC00958 in cell proliferation, cell death, and GSDMD expression respectively were analyzed by Cell Counting Kit-8 (CCK8) assay, flow cytometry and Immunofluorescence (IF) assay. In addition, expressions of pyroptosis- and autophagy-related proteins are evaluated by WB detection. The targeted binding of LINC00958 and miR-4306 or AIM2 mRNA is predicted by bioinformatics analysis and detected by biodual luciferase system. RIP and qPCR assays analyze whether LINC00958 interacts with SIRT1. We found that LINC00958 showed upregulation in OSCC cells compared to normal oral epithelial cells. LINC00958 silencing significantly suppressed OSCC cell proliferation, induced cell death and reduced autophagy. LINC00958 regulated the levels of miR-4306 which binds to the 3'UTR of AIM2, and interacts with and modulates SIRT1 protein expression. LINC00958 regulated GSDMD and AIM2 levels, as well as p53 and SIRT1 levels. SIRT1 overexpression markedly reversed aforementioned effects of LINC00958. LINC00958 not only downregulated miR-4306 levels to activate the pyroptosis pathway mediated by AIM2 and promoted cancer cell survival but also induced a decrease in SIRT protein expression to further reduce p53 levels.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

New insights into antimetastatic signaling pathways of melatonin in skeletomuscular sarcoma of childhood and adolescence

Melatonin is an indole produced by the pineal gland at night under normal light or dark conditions, and its levels, which are higher in children than in adults, begin to decrease prior to the onset of puberty and continue to decline thereafter. Apart from circadian regulatory actions, melatonin has significant apoptotic, angiogenic, oncostatic, and antiproliferative effects on various cancer cells. Particularly, the ability of melatonin to inhibit skeletomuscular sarcoma, which most commonly affects children, teenagers, and young adults, is substantial. In the past few decades, the vast majority of references have focused on the concept of epithelial-mesenchymal transition involvement in invasion and migration to allow carcinoma cells to dissociate from each other and to degrade the extracellular matrix. Recently, researchers have applied this idea to sarcoma cells of mesenchymal origin, e.g., osteosarcoma and Ewing sarcoma, with their ability to initiate the invasion-metastasis cascade. Similarly, interest of the effects of melatonin has shifted from carcinomas to sarcomas. Herein, in this state-of-the-art review, we compiled the knowledge related to the molecular mechanism of antimetastatic actions of melatonin on skeletomuscular sarcoma as in childhood and during adolescence. Utilization of melatonin as an adjuvant with chemotherapeutic drugs for synergy and fortification of the antimetastatic effects for the reinforcement of therapeutic actions are considered.

A meta-analysis of microRNA networks regulated by melatonin in cancer: Portrait of potential candidates for breast cancer treatment

Melatonin is a ubiquitous molecule with a broad spectrum of functions including widespread anti-cancer activities. Identifying how melatonin intervenes in complex molecular signaling at the gene level is essential to guide proper therapies. Using meta-analysis approach, herein we examined the role of melatonin in regulating the expression of 46 microRNAs (miRNAs) and their target genes in breast, oral, gastric, colorectal, and prostate cancers, and glioblastoma. The deregulated miRNA-associated target genes revealed their involvement in the regulation of cellular proliferation, differentiation, apoptosis, senescence, and autophagy. Melatonin changes the expression of miRNA-associated genes in breast, gastric, and oral cancers. These genes are associated with cellular senescence, the hedgehog signaling pathway, cell proliferation, p53 signaling, and the hippo signaling pathway. Conversely, colorectal and prostate cancers as well as glioblastoma and oral carcinoma present a clear pattern of less pronounced changes in the expression of miRNA-associated genes. Most notably, colorectal cancer displayed a unique molecular change in response to melatonin. Considering breast cancer network complexity, we compared the genes found during the meta-analysis with RNA-Seq data from breast cancer-bearing mice treated with melatonin. Mechanistically, melatonin upregulated genes associated with immune responses and apoptotic processes, whereas it downregulated genes involved in cellular aggressiveness/metastasis (eg, mitosis, telomerase activity, and angiogenesis). We further characterized the expression profile of our gene subsets with human breast cancer and found eight upregulated genes and 16 downregulated genes that were appositively correlated with melatonin. Our results pose a multi-dimension network of tumor-associated genes regulated by miRNAs potentially targeted by melatonin.

Molecular and Cellular Mechanisms of Melatonin in Osteosarcoma

Osteosarcoma, the most common primary bone malignancy, occurs most frequently in adolescents with a peak of incidence at 11-15 years. Melatonin, an indole amine hormone, shows a wide range of anticancer activities. The decrease in melatonin levels simultaneously concurs with the increase in bone growth and the peak age distribution of osteosarcoma during puberty, so melatonin has been utilized as an adjunct to chemotherapy to improve the quality of life and clinical outcomes. While a large amount of research has been conducted to understand the complex pleiotropic functions and the molecular and cellular actions elicited by melatonin in various types of cancers, a few review reports have focused on osteosarcoma. Herein, we summarized the anti-osteosarcoma effects of melatonin and its underlying molecular mechanisms to illustrate the known significance of melatonin in osteosarcoma and to address cellular signaling pathways of melatonin in vitro and in animal models. Even in the same kind of osteosarcoma, melatonin has been sparingly investigated to counteract tumor growth, apoptosis, and metastasis through different mechanisms, depending on different cell lines. We highlighted the underlying mechanism of anti-osteosarcoma properties evoked by melatonin, including antioxidant activity, anti-proliferation, induction of apoptosis, and the inhibition of invasion and metastasis. Moreover, we discussed the drug synergy effects of the role of melatonin involved and the method to fortify the anti-cancer effects on osteosarcoma. As a potential therapeutic agent, melatonin is safe for children and adolescents and is a promising candidate for an adjuvant by reinforcing the therapeutic effects and abolishing the unwanted consequences of chemotherapies.

Epigenetic Regulation of Chromatin in Prostate Cancer

Epigenetics refers to mitotically/meiotically heritable mechanisms that regulate gene transcription without a need for changes in the DNA code. Covalent modifications of DNA, in the form of methylation, and histone post-translational modifications, in the form of acetylation and methylation, constitute the epigenetic code of a cell. Both DNA and histone modifications are highly dynamic and often work in unison to define the epigenetic state of a cell. Most epigenetic mechanisms regulate gene transcription by affecting localized/genome-wide transitions between heterochromatin and euchromatin states, thereby altering the accessibility of the transcriptional machinery and in turn, reduce/increase transcriptional output. Altered chromatin structure is associated with cancer progression, and epigenetic plasticity primarily governs the resistance of cancer cells to therapeutic agents. In this chapter, we specifically focus on regulators of histone methylation and acetylation, the two well-studied chromatin post-translational modifications, in the context of prostate cancer.

Nicotinamide N-methyltransferase enhances the progression of prostate cancer by stabilizing sirtuin 1

A previous study demonstrated that nicotinamide N-methyltransferase (NNMT) is upregulated in the tissues of patients with prostate cancer (PCa); however, the specific underlying mechanism of this remains unclear. To begin with, the expression of NNMT was investigated in the peripheral blood of patients with PCa and of healthy control subjects. The results indicated that the expression level of NNMT was elevated in the peripheral blood and tissues of patients with PCa. Furthermore, the overexpression of NNMT enhanced PC-3 cell viability, invasion and migration capacity. Additionally, the overexpression of NNMT significantly increased the mRNA level of sirtuin 1 (SIRT1) in PC-3 cells. In addition, nicotinamide treatment significantly suppressed the expression of SIRT1 even in PC-3 cells transfected with adeno-associated virus-NNMT. Furthermore, the PC-3 cell invasion capacity was notably decreased by the nicotinamide treatment; however, such effects were largely abolished by the overexpression of NNMT in PC-3 cells. These data indicated that NNMT enhanced PC-3 cell migration and invasion mainly by regulating SIRT1 expression. In summary, the present study indicated that NNMT is an important regulator of SIRT1 expression in PC-3 cells and may be a potential therapeutic target for PCa.

MDM2 and P53 polymorphisms contribute together to the risk and survival of prostate cancer

The p53 gene and MDM2 gene play critical roles in cell cycle arrest and apoptosis together. Here, we evaluated the associations of prostate cancer risk and survival with the joint effects of mdm2 and p53 polymorphisms. Totally 1,193 cases and 1,310 age frequency-matched controls were included in the study. Prostate cancer patients were followed to determine the intervals of overall survival and disease-free survival. The Pro⁷²Arg Pro allele (homozygous and heterozygous) were significantly associated with prostate cancer risk with an odds ratio (OR) of 0.77 [95% confidence interval(CI), 0.64-0.93]. SNP309 T alleles were associated with a significantly decreased prostate cancer risk among Pro⁷²Arg Pro alleles carriers (OR=0.79, 95% CI, 0.64-0.98). In addition, comparedwith the Pro⁷²Arg Pro alleles and SNP309 G homozygous, patients carrying both SNP309 T alleles and Pro⁷²Arg Arg homozygous had more favorable disease-free survival (hazard ratio [HR] = 0.59, 95% CI, 0.38-0.93). Our results indicated that SNP309 and Pro⁷²Arg polymorphisms may jointly contributeto the etiology and prognosis of prostate cancer.

Melatonin and sirtuins: A "not-so unexpected" relationship

Epigenetic modifications, including methylation or acetylation as well as post-transcriptional modifications, are mechanisms used by eukaryotic cells to increase the genome diversity in terms of differential gene expression and protein diversity. Among these modifying enzymes, sirtuins, a class III histone deacetylase (HDAC) enzymes, are of particular importance. Sirtuins regulate the cell cycle, DNA repair, cell survival, and apoptosis, thus having important roles in normal and cancer cells. Sirtuins can also regulate metabolic pathways by changing preference for glycolysis under aerobic conditions as well as glutaminolysis. These actions make sirtuins a major target in numerous physiological processes as well as in other contexts such as calorie restriction-induced anti-aging, cancer, or neurodegenerative disease. Interestingly, melatonin, a nighttime-produced indole synthesized by pineal gland and many other organs, has important cytoprotective effects in many tissues including aging, neurodegenerative diseases, immunomodulation, and cancer. The pleiotropic actions of melatonin in different physiological and pathological conditions indicate that may be basic cellular targeted for the indole. Thus, much research has focused attention on the potential mechanisms of the indole in modulating expression and/or activity of sirtuins. Numerous findings report a rise in activity, especially on SIRT1, in a diversity of cells and animal models after melatonin treatment. This contrasts, however, with data reporting an inhibitory effect of melatonin on this sirtuin in some tumor cells. This review tabulates and discusses the recent findings relating melatonin with sirtuins, particularly SIRT1 and mitochondrial SIRT3, showing the apparent dichotomy with the differential actions documented in normal and in cancer cells.

SIRT1 controls cell proliferation by regulating contact inhibition

Contact inhibition keeps cell proliferation in check and serves as a built-in protection against cancer development by arresting cell division upon cell-cell contact. Yet the complete mechanism behind this anti-cancer process remains largely unclear. Here we present SIRT1 as a novel regulator of contact inhibition. SIRT1 performs a wide variety of functions in biological processes, but its involvement in contact inhibition has not been explored to date. We used NIH3T3 cells, which are sensitive to contact inhibition, and H460 and DU145 cancer cells, which lack contact inhibition, to investigate the relationship between SIRT1 and contact inhibition. We show that SIRT1 overexpression in NIH3T3 cells overcomes contact inhibition while SIRT1 knockdown in cancer cells restores their lost contact inhibition. Moreover, we demonstrate that p27 protein expression is controlled by SIRT1 in contact inhibition. Overall, our findings underline the critical role of SIRT1 in contact inhibition and suggest SIRT1 inhibition as a potential strategy to suppress cancer cell growth by restoring contact inhibition.

Brachyury promotes tamoxifen resistance in breast cancer by targeting SIRT1

Tamoxifen is effective for treating estrogen receptor-alpha (ERα)-positive breast cancers. However, few molecular mediators of tamoxifen resistance have been elucidated. In the present study, we determine the underlying roles of Brachyury in tamoxifen resistance. Loss- and gain-of-function assay are utilized to confirm the oncogenic roles of Brachyury in breast cancer. Compared with the normal MCF10A cells, Brachyury is commonly overexpressed in breast cancer cell lines. Knockdown of Brachyury inhibits tamoxifen resistance, whereas overexpression of Brachyury enhances tamoxifen resistance as demonstrated increased cell viability and reduced cell apoptosis. Mechanistically, we demonstrate for the first time that Brachyury mediates tamoxifen resistance by regulating Sirtuin-1 (SIRT1). Collectively, our data, as a proof of principle, indicate that Brachyury is a candidate marker for predicting the clinical efficacy of tamoxifen and targeting SIRT1 could overcome resistance to tamoxifen in breast cancer cells.

MicroRNA-212 negatively regulates starvation induced autophagy in prostate cancer cells by inhibiting SIRT1 and is a modulator of angiogenesis and cellular senescence

Among a number of non-coding RNAs, role of microRNAs (miRNAs) in cancer cell proliferation, cancer initiation, development and metastasis have been extensively studied and miRNA based therapeutic approaches are being pursued. Prostate cancer (PCa) is a major health concern and several deregulated miRNAs have been described in PCa. miR-212 is differentially modulated in multiple cancers however its function remains elusive. In this study, we found that miR-212 is downregulated in PCa tissues when compared with benign adjacent regions (n = 40). Also, we observed reduced levels of circulatory miR-212 in serum from PCa patients (n = 40) when compared with healthy controls (n = 32). Elucidating the functional role of miR-212, we demonstrate that miR-212 negatively modulates starvation induced autophagy in PCa cells by targeting sirtuin 1 (SIRT1). Overexpression of miR-212 also leads to inhibition of angiogenesis and cellular senescence. In conclusion, our study indicates a functional role of miR-212 in PCa and suggests the development of miR-212 based therapies.

Inhibitory effects of SRT1720 on the apoptosis of rabbit chondrocytes by activating SIRT1 via p53/bax and NF-κB/PGC-1α pathways

SRT1720, a new discovered drug, was reported to activate silent information regulator 1 (SIRT1) and inhibit the chondrocyte apoptosis. However, the underlying mechanism remains elusive. In the present study, the chondrocytes were extracted from the cartilage tissues of New Zealand white rabbits, cultured in the presence of sodium nitroprusside (SNP) (2.5 mmol/L) and divided into five groups: 1, 5, 10, and 20 μmol/L SRT1720 groups and blank control group (0 μmol/L SRT1720). MTT assay was used to detect the chondrocyte viability and proliferation, and DAPI staining and flow cytometry to measure the chondrocyte apoptosis. The expression levels of SIRT1, p53, NF-κB/p65, Bax, and peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) were detected by Western blotting and the expression levels of SIRT1, type II collagen, and aggrecan mRNA by RT-PCR. The results showed that in the SRT1720-treated groups, the nuclei of chondrocytes were morphologically intact and had uniform chromatin. In the blank control group, nuclear rupture into debris was observed in chondrocytes. With the SRT1720 concentration increasing, the chondrocyte viability increased, the apoptosis rate decreased, the protein expression levels of SIRT1 and PGC-1α and the mRNA expression levels of type II collagen and aggrecan increased ({ptP}<0.05), and the expression levels of p53, NF-κB and bax decreased (P<0.05). It was suggested that SRT1720 inhibits chondrocyte apoptosis by activating the expression of SIRT1 via p53/bax and NF-κB/PGC-1α pathways.

Effect of SIRT1 Gene on Epithelial-Mesenchymal Transition of Human Prostate Cancer PC-3 Cells

Background

The epithelial-mesenchymal transition (EMT) has been shown to be involved in the process of invasion and metastasis of prostate cancer. SIRT1 is the mammalian homologue of the silent information regulator 2 (Sir2) gene, and is abnormally expressed in prostate cancer cells. Therefore, it is hypothesized that SIRT1 mediates the invasion/metastatic ability of prostate cancer via EMT regulation. This study thus investigated the effect of SIRT1 gene on the invasion and migration of prostate cancer cell line PC-3 via the small interference RNA (siRNA) against SIRT1.

Material/Methods

SiRNA construct was transfected into PC-3 cells, which were tested for the cell migration and invasion ability by scratch assay and Transwell migration assay, respectively. Expression levels of vimentin, E-cadherin, and N-cadherin were further quantified by Western blotting and RT-PCR.

Results

Both mRNA and protein levels of SIRT1 were depressed after siRNA transfection, along with weakened migration and invasion ability of PC-3 cells. Elevated E-cadherin and suppressed N-cadherin and vimentin were observed in those transfected cells.

Conclusions

The silencing of SIRT1 gene in PC-3 cells can suppress the movement, migration, and invasion functions of prostate cancer cells, possibly via the down-regulation of mesenchymal markers vimentin and N-cadherin accompanied with up-regulation of epithelial marker N-cadherin, thus reversing the EMT process.

Aspirin Targets SIRT1 and AMPK to Induce Senescence of Colorectal Carcinoma Cells

Cancer therapies attempt to destroy the entire tumor, but this tends to require toxic compounds and high doses of radiation. Recently, considerable attention has focused on therapy-induced senescence (TIS), which can be induced in cancer cells by low doses of therapeutic drugs or radiation and provides a barrier to tumor development. However, the molecular mechanisms governing TIS remain elusive. Special attention has been paid to the potential chemopreventive effect of aspirin against human colorectal cancer. In this study, we investigated the effects of aspirin on TIS of human colorectal carcinoma (CRC) cells and show that it occurs via sirtuin 1 (SIRT1) and AMP-activated protein kinase (AMPK), two key regulators of cellular metabolism. Aspirin increased the senescence of CRC cells, increased the protein levels of SIRT1, phospho-AMPK (T172), and phospho-acetyl CoA carboxylase (S79), and reduced the cellular level of ATP. Small-interfering RNA-mediated downregulation or pharmacological inhibition of SIRT1 or AMPK significantly attenuated the aspirin-induced cellular senescence in CRC cells. In contrast, treatment with a SIRT1 agonist or an AMP analog induced cellular senescence. Remarkably, SIRT1 knockdown abrogated the aspirin-induced activation of AMPK, and vice versa. During the progression of aspirin-induced cellular senescence in CRC cells, SIRT1 showed increased deacetylase activity at a relatively early time point but was characterized by decreased activity with increased cytoplasmic localization at a later time point. Collectively, these novel findings suggest that aspirin could provide anticancer effects by inducing senescence in human CRC cells through the reciprocal regulation of SIRT1-AMPK pathways.

Expression of sirtuin 1 and 2 is associated with poor prognosis in non-small cell lung cancer patients

Background

Sirtuin 1 (SIRT1) and sirtuin 2 (SIRT2) are NAD+-dependent protein deacetylases involved in the regulation of key cancer-associated genes. In this study we evaluated the relevance of these deacetylases in lung cancer biology.

Material and Methods

Protein levels of SIRT1 and SIRT2 were determined in non-small cell lung cancer (NSCLC) cell lines and primary tumors from 105 patients. Changes in proliferation were assessed after SIRT1 and SIRT2 downregulation in lung cancer cell lines using siRNA-mediated technology or tenovin-1, a SIRT1 and SIRT2 inhibitor.

Results

High SIRT1 and SIRT2 protein levels were found in NSCLC cell lines compared with non-tumor lung epithelial cells. The expression of SIRT1 and SIRT2 proteins was also significantly higher in lung primary tumors than in normal tissue (P<0.001 for both sirtuins). Stronger nuclear SIRT1 staining was observed in adenocarcinomas than in squamous cell carcinomas (P=0.033). Interestingly, in NSCLC patients, high SIRT1 and SIRT2 expression levels were associated with shorter recurrence-free survival (P=0.04 and P=0.007, respectively). Moreover, the combination of high SIRT1 and SIRT2 expression was an independent prognostic factor for shorter recurrence-free survival (P=0.002) and overall survival (P=0.022). In vitro studies showed that SIRT1 and/or SIRT2 downregulation significantly decreased proliferation of NSCLC.

Conclusions

Our results support the hypothesis that SIRT1 and SIRT2 have a protumorigenic role in lung cancer, promoting cell proliferation. Moreover, the expression of these proteins is associated with poor prognosis in NSCLC patients and may help to identify those NSCLC patients with high risk of recurrence that could benefit from adjuvant therapy after resection.

The effect of resveratrol on the recurrent attacks of gouty arthritis

Gouty arthritis is characterized by inflammation induced by monosodium urate crystal (MSU) deposition, which is resulted by increase of serum urate concentration. The management of gout, especially the recurrent attacks of chronic gouty arthritis, is still a problem to be resolved. In this study, we aimed to develop the preventive and therapeutic effects of resveratrol on gouty arthritis. Monosodium urate crystal (MSU) was used to induce gouty arthritis in foot pad of C57BL/6 mice. Yeast polysaccharide and potassium oxonate were used to induce hyperuricemia in Kunming mice. Resveratrol was intraperitoneally injected to the mice in the treatment group. Article inflammation and serum uric acid level were investigated to estimate the effect of resveratrol in gout. Yeast polysaccharide and potassium oxonate were used to induce hyperuricemia in mice, and MSU to induce gouty arthritis. We identified that resveratrol inhibited foot swelling and inflammation-associated 99mTc uptake in gouty mice. Moreover, serum uric acid level was also decreased by resveratrol in hyperuricemia mice. This study highlighted that resveratrol might be applied to prevent the recurrent attack of gouty arthritis because of its inhibition of articular inflammation and down-regulation of serum uric acid.

SIRT1 inactivation evokes antitumor activities in NSCLC through the tumor suppressor p27

P27(Kip1) (CDKN1B) regulates cellular proliferation and senescence, and p27(Kip1) deficiency in cancer is strongly correlated with poor prognosis of multiple cancer types. Understanding the mechanism of p27(Kip1) loss in cancer and the consequences of restoring p27(Kip1) levels is therefore critical for effective management during therapy. Here, SIRT1, a class III histone deacetylase (HDAC), is identified as an important regulator of p27(Kip1) expression. Mechanistically, SIRT1 reduces p27(Kip1) expression by decreasing p27(Kip1) protein stability through the ubiquitin-proteasome pathway. In addition, SIRT1 silencing suppresses non-small cell lung cancer (NSCLC) proliferation and induces senescence in a p27(Kip1)-dependent manner. Furthermore, SIRT1 silencing dramatically suppresses tumor formation and proliferation in two distinct NSCLC xenograft mouse models. Collectively, these data demonstrate that not only SIRT1 is an important regulator of p27(Kip1) but also SIRT inhibition induces senescence and antigrowth potential in lung cancer in vivo.

IMPLICATIONS

SIRT1 is a key regulator of p27 protein levels and SIRT1 inhibition is a viable strategy for NSCLC therapy by means of p27 reactivation.

Down-regulation of mir-221 and mir-222 restrain prostate cancer cell proliferation and migration that is partly mediated by activation of SIRT1

Studies have shown that miR-221 and miR-222 are deregulated in many cancers, including prostate cancer. Nevertheless, the biological role and the underlying mechanisms of miR-221 and miR-222 in the pathogenesis of androgen-independent prostate cancer are still not clear. The proliferation, apoptosis, cell cycle distinction, and migration capacity of prostate cells were determined following transfection of miR-221 or miR-222 inhibitor. The biological impact and regulation of SIRT1 on prostate cancer cells were investigated. MiR-221 and miR-222 were highly expressed in PC-3 cells compared with in LNCap cells. After miR-221 or miR-222 expression was inhibited, the proliferation and migration rates of PC-3 cells decreased and the apoptosis rate increased. Moreover, SIRT1 protein was up-regulated in cells after they were transfected with miR-221 or miR-222 inhibitor. Cells transfected with siSIRT1 showed increased migration and a decreased apoptosis rate, but there was no significant effect on cell proliferation compared with the controls. There was a negative correlation between miR-221 or miR-222 and SIRT1, but no direct target relationship was identified. These data demonstrate that miR-221 and miR-222 are highly expressed in PC-3 cells. Their inhibition leads to reduced cell proliferation and migration and increased apoptosis in prostate cancer cells. These effects are potentially mediated by up-regulation of SIRT1.

Sirt1 is a tumor promoter in lung adenocarcinoma

Sirtuin 1 (Sirt1) is a nicotinamide adenine dinucleotide-dependent class III histone deacetylase. It reportedly can repress cellular apoptosis and senescence to affect DNA repair, stress response and aging. Notably, previous data have indicated that Sirt1 is both a tumor promoter and a tumor suppressor in tumorigenesis. However, Sirt1 expression in primary lung adenocarcinoma remains unknown. Immunohistochemical staining was performed to investigate Sirt1 expression in cancer cells in 125 consecutive resected cases of primary lung adenocarcinoma. Sirt1 expression was found to be increased in 26 (20.8%) of the 125 cases, which correlated significantly with five clinicopathological factors: Ki67 index, hypoxia-inducible factor 1 (HIF1) molecule expression, tumor-node-metastasis (TNM) classification, pulmonary vein invasion and lymphatic duct invasion. In the Sirt1-positive expression group, Sirt1 expression correlated with a higher Ki67 index and higher TNM classification, particularly for lymph node invasion and metastasis, and with a higher number of pulmonary vein invasion and lymphatic duct invasion. Additionally, a negative correlation was identified between HIF1-positive expression and Sirt1-negative expression. These results indicate that Sirt1 overexpression plays a promotional role in tumorigenesis and is closely associated with invasion and metastasis and, thus, it may be associated with prognosis.

Rapamycin induces pluripotent genes associated with avoidance of replicative senescence

Primary rodent cells undergo replicative senescence, independent from telomere shortening. We have recently shown that treatment with rapamycin during passages 3-7 suppressed replicative senescence in rat embryonic fibroblasts (REFs), which otherwise occurred by 10-14 passages. Here, we further investigated rapamycin-primed cells for an extended number of passages. Rapamycin-primed cells continued to proliferate without accumulation of senescent markers. Importantly, these cells retained the ability to undergo serum starvation- and etoposide-induced cell cycle arrest. The p53/p21 pathway was functional. This indicates that rapamycin did not cause either transformation or loss of cell cycle checkpoints. We found that rapamycin activated transcription of pluripotent genes, oct-4, sox-2, nanog, as well as further upregulated telomerase (tert) gene. The rapamycin-derived cells have mostly non-rearranged, near-normal karyotype. Still, when cultivated for a higher number of passages, these cells acquired a chromosomal marker within the chromosome 3. We conclude that suppression mTORC1 activity may prevent replicative senescence without transformation of rodent cells.

Circadian rhythm connections to oxidative stress: implications for human health

SIGNIFICANCE

Oxygen and circadian rhythmicity are essential in a myriad of physiological processes to maintain homeostasis, from blood pressure and sleep/wake cycles, down to cellular signaling pathways that play critical roles in health and disease. If the human body or cells experience significant stress, their ability to regulate internal systems, including redox levels and circadian rhythms, may become impaired. At cellular as well as organismal levels, impairment in redox regulation and circadian rhythms may lead to a number of adverse effects, including the manifestation of a variety of diseases such as heart diseases, neurodegenerative conditions, and cancer.

RECENT ADVANCES

Researchers have come to an understanding as to the basics of the circadian rhythm mechanism, as well as the importance of the numerous species of oxidative stress components. The effects of oxidative stress and dysregulated circadian rhythms have been a subject of intense investigations since they were first discovered, and recent investigations into the molecular mechanisms linking the two have started to elucidate the bases of their connection.

CRITICAL ISSUES

While much is known about the mechanics and importance of oxidative stress systems and circadian rhythms, the front where they interact has had very little research focused on it. This review discusses the idea that these two systems are together intricately involved in the healthy body, as well as in disease.

FUTURE DIRECTIONS

We believe that for a more efficacious management of diseases that have both circadian rhythm and oxidative stress components in their pathogenesis, targeting both systems in tandem would be far more successful.

Relationship between SIRT1 and tumors

Tumorigenesis is closely related to overexpression of oncogenes and/or down-expression of tumor suppressor genes. Gene expression and deacetylase activity of SIRT1, a class Ⅲhistone deacetylase, are up-regulated in tumor cells, which suggests that SIRT1 may be involved in tumorigenesis. SIRT1 may induce deacetylation of tumor suppressor proteins to promote tumorgenesis. SIRT1 promotes tumor occurrence, development, and maintenance of various characteristics possibly by promoting cell proliferation, inhibiting apoptosis, and preventing senescence. On the other hand, SIRT1 can also deacetylase tumor inducers to inhibit tumorigenesis. Therefore, further investigation of the role of SIRT1 in tumorigenesis is of great importance, and SIRT1 may be used as a therapeutic target for tumors.

Methods to investigate the role of SIRT1 in endothelial senescence

Sirtuins are a family of proteins with NAD(+)-dependent deacetylase or mono-ADP-ribosyltransferase activity. SIRT1, the mammalian ortholog most closely related to Sir2 (the first gene of this family discovered in yeast), exhibits anti-senescence activity in a wide range of mammalian cells. Here, we describe the use of an ex vivo senescence model to study SIRT1 function in primary endothelial cells isolated from the porcine aorta. The methods can be applied to the investigation of the role of SIRT1 in the development of endothelial senescence and atherosclerosis.

Lentivirus-mediated siRNA targeting VEGF inhibits gastric cancer growth in vivo

Vascular endothelial growth factor (VEGF), a crucial promoter of blood vessel growth, not only stimulates endothelial cell proliferation, migration and survival, but also increases vascular permeability. The promotion of angiogenesis is a well-known prerequisite for tumor growth, invasion and metastasis. Evidence has shown that VEGF is overexpressed in many types of tumor tissues. Small interfering RNA (siRNA) targeting VEGF may effectively suppress cell proliferation and induce apoptosis in tumor cells. In this study, we aimed to evaluate whether lentivirus-mediated siRNA targeting VEGF inhibits gastric cancer growth in vivo. The transfection of VEGF siRNA into SGC7901 human gastric cancer cells downregulated the expression of VEGF and Bcl-2, but upregulated the expression of p21. In a nude mouse model of subcutaneous xenografts, 24 days after VEGF siRNA treatment, the tumor volume and weight were significantly smaller in the VEGF siRNA group compared to the control scrambled siRNA group. Furthermore, the expression of VEGF, sirtuin 1 (SIRT1), survivin and Bcl-2 was downregulated, whereas the expression of p53 and p21 was upregulated in the tumor cells, indicating that VEGF siRNA induced apoptosis in gastric cancer cells by inhibiting SIRT1 expression, leading to p53 transcriptional upregulation and the activation of downstream p21, while suppressing Bcl-2 and survivin expression. Our results demonstrate that lentivirus-mediated siRNA targeting VEGF offers a potential strategy to prevent the growth of gastric cancer.

Caloric restriction: is mammalian life extension linked to p53?

Caloric restriction, that is limiting food intake, is recognized in mammals as the best characterized and most reproducible strategy for extending lifespan, retarding physiological aging and delaying the onset of age-associated diseases. The aim of this mini review is to argue that p53 is the connection in the abilities of both the Sirt-1 pathway and the TOR pathway to impact on longevity of cells and organisms. This novel, lifespan regulating function of p53 may be evolutionarily more ancient than its relatively recent role in apoptosis and tumour suppression, and is likely to provide many new insights into lifespan modulation.

Expression patterns and potential roles of SIRT1 in human medulloblastoma cells in vivo and in vitro

Medulloblastoma is a primitive neuroectodermal tumor, which originates in the cerebellum, presumably due to the alterations of some neurogenetic elements. Sirtuin 1 (SIRT1), a class III histone deacetylase (HDAC), regulates differentiation of neuronal stem cells but its status in medulloblastomas remains largely unknown. The current study aimed to address this issue by checking SIRT1 expression in noncancerous cerebellar tissues, medulloblastoma tissues and established cell lines. The roles of SIRT1 in proliferation and survival of UW228-3 medulloblastoma cells were analyzed by SIRT1 small interfering RNA (siRNA) transfection and SIRT1 inhibitor nicotinamide treatment. The results revealed that the frequency of SIRT1 expression in medulloblastoma tissues was 64.17% (77/120), while only one out of seven tumor-surrounding noncancerous cerebellar tissues showed restricted SIRT1 expression in the cells within the granule layer. Of the three morphological subtypes, the rates of SIRT1 detection in the large cell/anaplastic cell (79.07%; 34/43) and the classic medulloblastomas (60.29%; 41/68) are higher than that (22.22%; 2/9) in nodular/desmoplastic medulloblastomas (P<0.01 and P<0.05, respectively). Heterogeneous SIRT1 expression was commonly observed in classic medulloblastoma. Inhibition of SIRT1 expression by siRNA arrested 64.96% of UW228-3 medulloblastoma cells in the gap 1 (G1) phase and induced 14.53% of cells to apoptosis at the 48-h time point. Similarly, inhibition of SIRT1 enzymatic activity with nicotinamide brought about G1 arrest and apoptosis in a dose-related fashion. Our data thus indicate: (i) that SIRT1 may act as a G1-phase promoter and a survival factor in medulloblastoma cells; and (ii) that SIRT1 expression is correlated with the formation and prognosis of human medulloblastomas. In this context, SIRT1 would be a potential therapeutic target of medulloblastomas.

Sirtuin inhibition attenuates the production of inflammatory cytokines in lipopolysaccharide-stimulated macrophages

In several inflammatory conditions such as rheumatoid arthritis or sepsis, the regulatory mechanisms of inflammation are inefficient and the excessive inflammatory response leads to damage to the host. Sirtuins are class III histone deacetylases that modulate the activity of several transcription factors that are implicated in immune responses. In this study, we evaluated the impact of sirtuin inhibition on the activation of lipopolysaccharide (LPS)-stimulated J774 macrophages by assessing the production of inflammatory cytokines. The pharmacologic inhibition of sirtuins decreased the production of tumour necrosis factor-alpha (TNF-α) interleukin 6 (IL-6) and Rantes. The reduction of cytokine production was associated with decreased nuclear factor kappa B (NF-κB) activity and inhibitor kappa B alpha (IκBα) phosphorylation while no impact was observed on the phosphorylation status of p38 mitogen-activated kinase (p38 MAPK). This work shows that sirtuin pharmacologic inhibitors are a promising tool for the treatment of inflammatory conditions.

A small molecule Inauhzin inhibits SIRT1 activity and suppresses tumour growth through activation of p53

Although ∼50% of all types of human cancers harbour wild-type TP53, this p53 tumour suppressor is often deactivated through a concerted action by its abnormally elevated suppressors, MDM2, MDMX or SIRT1. Here, we report a novel small molecule Inauhzin (INZ) that effectively reactivates p53 by inhibiting SIRT1 activity, promotes p53-dependent apoptosis of human cancer cells without causing apparently genotoxic stress. Moreover, INZ stabilizes p53 by increasing p53 acetylation and preventing MDM2-mediated ubiquitylation of p53 in cells, though not directly in vitro. Remarkably, INZ inhibits cell proliferation, induces senescence and tumour-specific apoptosis, and represses the growth of xenograft tumours derived from p53-harbouring H460 and HCT116 cells without causing apparent toxicity to normal tissues and the tumour-bearing SCID mice. Hence, our study unearths INZ as a novel anti-cancer therapeutic candidate that inhibits SIRT1 activity and activates p53.

Cooperative effects of Akt-1 and Raf-1 on the induction of cellular senescence in doxorubicin or tamoxifen treated breast cancer cells

Escape from cellular senescence induction is a potent mechanism for chemoresistance. Cellular senescence can be induced in breast cancer cell lines by the removal of estrogen signaling with tamoxifen or by the accumulation of DNA damage induced by the chemotherapeutic drug doxorubicin. Long term culturing of the hormone-sensitive breast cancer cell line MCF-7 in doxorubicin (MCF-7/DoxR) reduced the ability of doxorubicin, but not tamoxifen, to induce senescence. Two pathways that are often upregulated in chemo- and hormonal-resistance are the PI3K/PTEN/Akt/mTOR and Ras/Raf/MEK/ERK pathways. To determine if active Akt-1 and Raf-1 can influence drug-induced senescence, we stably introduced activated ΔAkt-1(CA) and ΔRaf-1(CA) into drug-sensitive and doxorubicin-resistant cells. Expression of a constitutively-active Raf-1 construct resulted in higher baseline senescence, indicating these cells possessed the ability to undergo oncogene-induced-senescence. Constitutive activation of the Akt pathway significantly decreased drug-induced senescence in response to doxorubicin but not tamoxifen in MCF-7 cells. However, constitutive Akt-1 activation in drug-resistant cells containing high levels of active ERK completely escaped cellular senescence induced by doxorubicin and tamoxifen. These results indicate that up regulation of the Ras/PI3K/PTEN/Akt/mTOR pathway in the presence of elevated Ras/Raf/MEK/ERK signaling together can contribute to drug-resistance by diminishing cell senescence in response to chemotherapy. Understanding how breast cancers containing certain oncogenic mutations escape cell senescence in response to chemotherapy and hormonal based therapies may provide insights into the design of more effective drug combinations for the treatment of breast cancer.

Acetylation is indispensable for p53 antiviral activity

Tumor suppressor p53 is known to be a direct transcriptional target of type I interferons (IFNs), contributing to virus-induced apoptosis, and in turn activating itself the interferon pathway. Acetylation, among many other post-translational modifications of p53, is thought to exert a crucial role regulating p53 activity. Here, we examined the contribution of this modification on the antiviral activity mediated by p53. Our results show that virus infection induces p53 acetylation at lysine 379, and that this modification is absolutely required for p53-dependent transcriptional transactivation of both, pro-apoptotic and IFN-stimulated genes induced by virus infection, and for p53-mediated control of virus replication. Thus, our study identifies p53 acetylation as an indispensable event that enables the p53-mediated antiviral response.

Activation of Sirt1 by resveratrol inhibits TNF-α induced inflammation in fibroblasts

Inflammation is one of main mechanisms of autoimmune disorders and a common feature of most diseases. Appropriate suppression of inflammation is a key resolution to treat the diseases. Sirtuin1 (Sirt1) has been shown to play a role in regulation of inflammation. Resveratrol, a potent Sirt1 activator, has anti-inflammation property. However, the detailed mechanism is not fully understood. In this study, we investigated the anti-inflammation role of Sirt1 in NIH/3T3 fibroblast cell line. Upregulation of matrix metalloproteinases 9 (MMP-9), interleukin-1beta (IL-1β), IL-6 and inducible nitric oxide synthase (iNOS) were induced by tumor necrosis factor alpha (TNF-α) in 3T3 cells and resveratrol suppressed overexpression of these pro-inflammatory molecules in a dose-dependent manner. Knockdown of Sirt1 by RNA interference caused 3T3 cells susceptible to TNF-α stimulation and diminished anti-inflammatory effect of resveratrol. We also explored potential anti-inflammatory mechanisms of resveratrol. Resveratrol reduced NF-κB subunit RelA/p65 acetylation, which is notably Sirt1 dependent. Resveratrol also attenuated phosphorylation of mammalian target of rapamycin (mTOR) and S6 ribosomal protein (S6RP) while ameliorating inflammation. Our data demonstrate that resveratrol inhibits TNF-α-induced inflammation via Sirt1. It suggests that Sirt1 is an efficient target for regulation of inflammation. This study provides insight on treatment of inflammation-related diseases.

Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR inhibitors: rationale and importance to inhibiting these pathways in human health

The Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR cascades are often activated by genetic alterations in upstream signaling molecules such as receptor tyrosine kinases (RTK). Integral components of these pathways, Ras, B-Raf, PI3K, and PTEN are also activated/inactivated by mutations. These pathways have profound effects on proliferative, apoptotic and differentiation pathways. Dysregulation of these pathways can contribute to chemotherapeutic drug resistance, proliferation of cancer initiating cells (CICs) and premature aging. This review will evaluate more recently described potential uses of MEK, PI3K, Akt and mTOR inhibitors in the proliferation of malignant cells, suppression of CICs, cellular senescence and prevention of aging. Ras/Raf/MEK/ERK and Ras/PI3K/PTEN/Akt/mTOR pathways play key roles in the regulation of normal and malignant cell growth. Inhibitors targeting these pathways have many potential uses from suppression of cancer, proliferative diseases as well as aging.

Roles of the Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways in controlling growth and sensitivity to therapy-implications for cancer and aging

Dysregulated signaling through the Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways is often the result of genetic alterations in critical components in these pathways or upstream activators. Unrestricted cellular proliferation and decreased sensitivity to apoptotic-inducing agents are typically associated with activation of these pro-survival pathways. This review discusses the functions these pathways have in normal and neoplastic tissue growth and how they contribute to resistance to apoptotic stimuli. Crosstalk and commonly identified mutations that occur within these pathways that contribute to abnormal activation and cancer growth will also be addressed. Finally the recently described roles of these pathways in cancer stem cells, cellular senescence and aging will be evaluated. Controlling the expression of these pathways could ameliorate human health.

SIRT1 RNAi knockdown induces apoptosis and senescence, inhibits invasion and enhances chemosensitivity in pancreatic cancer cells

The NAD(+)-dependent deacetylase, sirtuin 1 (SIRT1), has been recently been suspected to have a role in tumorigenesis. We investigated the expression of SIRT1 in pancreatic cancer and the effect of SIRT1-targeted RNA interference (RNAi) on cell proliferation and tumor formation in a pancreatic cancer cell line, PANC1. The expression of SIRT1 was investigated in 49 specimens of pancreatic cancer and adjacent normal pancreatic tissues. SIRT1 was overexpressed in pancreatic cancer tissues at both the mRNA and protein levels, with increased SIRT1 positivity associated with tumors from patients over 60 years old, tumors larger than 4 cm, higher TNM (extent of tumor (T), the extent of spread to lymph nodes (N), and presence of distant metastasis (M)) stage or the presence of lymph node or hepatic metastases. The PANC-1 was stably transfected with a SIRT1 small hairpin RNA (shRNA) expression plasmid and compared with untransfected and PANC-1-negative RNAi cells. Proliferation of PANC-1-SIRT1-RNAi cells was significantly reduced, accompanied by increased rates of apoptosis, G1 arrest and senescence. Furthermore, FOXO3a expression was markedly upregulated in PANC-1-SIRT1-RNAi cells, but no significant difference in p53 expression was observed. The invasive ability of PANC-1-SIRT1-RNAi cells was markedly reduced in vitro, which was linked to increased E-cadherin and reduced-MMP expression. Additionally, PANC-1-SIRT1-RNAi cells had a significantly reduced capacity to form tumors in vivo compared with untransfected and PANC-1-negative RNAi cells. These results suggest that SIRT1 may promote cell proliferation and tumor formation in pancreatic cancer, and downregulation of SIRT1 using shRNA could provide a novel therapeutic treatment.

Human mitochondrial transcription factor A functions in both nuclei and mitochondria and regulates cancer cell growth

Mitochondrial transcription factor A (mtTFA) is one of the high mobility group protein family and is required for both transcription from and maintenance of mitochondrial genomes. However, the roles of mtTFA have not been extensively studied in cancer cells. Here, we firstly reported the nuclear localization of mtTFA. The proportion of nuclear-localized mtTFA varied among different cancer cells. Some mtTFA binds tightly to the nuclear chromatin. DNA microarray and chromatin immunoprecipitation assays showed that mtTFA can regulate the expression of nuclear genes. Overexpression of mtTFA enhanced the growth of cancer cell lines, whereas downregulation of mtTFA inhibited their growth by regulating mtTFA target genes, such as baculoviral IAP repeat-containing 5 (BIRC5; also known as survivin). Knockdown of mtTFA expression induced p21-dependent G1 cell cycle arrest. These results imply that mtTFA functions in both nuclei and mitochondria to promote cell growth.

Nicotinamide enhances apoptosis of G(M)-CSF-treated neutrophils and attenuates endotoxin-induced airway inflammation in mice

Neutrophils constitute the first line of host defense against invading microorganisms. Yet their removal from the inflammatory environment is fundamental for injury restraint and resolution of inflammation. Nicotinamide, a component of vitamin B3, is known to modulate cell survival. In this study, we assessed the influence of nicotinamide on neutrophil apoptosis, both in vitro and in vivo in a mouse model of endotoxin-induced lung inflammation. In vitro, nicotinamide promoted apoptosis of human blood neutrophils in a dose-dependent manner in the presence of the apoptosis inhibitors granulocyte colony-stimulating factor and granulocyte/macrophage colony-stimulating factor. The highest concentration of nicotinamide completely neutralized the pro-survival effect of granulocyte (macrophage) colony-stimulating factor. Nicotinamide proapoptotic effect was associated with enhanced caspase-3 activity. In addition, nicotinamide slightly reduced neutrophil chemotaxis in vitro. In vivo, pulmonary nicotinamide delivery decreased the levels of cellular and biochemical inflammation markers and increased the percentage of apoptotic neutrophils in bronchoalveolar lavages. Our findings suggest that nicotinamide is an apoptotic stimulus for neutrophils, thereby contributing to the resolution of neutrophilic inflammation in the lungs.

Melatonin, a novel Sirt1 inhibitor, imparts antiproliferative effects against prostate cancer in vitro in culture and in vivo in TRAMP model

We recently demonstrated that Sirt1, a NAD(+) -dependent histone deacetylase, was overexpressed in prostate cancer (PCa) and its inhibition resulted in a significant antiproliferative response in human PCa cells. Studies have suggested a link between Sirt1 and circadian rhythms, the disruption of which has been linked to cancer. Interestingly, a decreased production of the pineal melatonin has been shown to deregulate the circadian rhythm machinery and increase cancer risk. Furthermore, disruption in melatonin production and circadian rhythmicity has been associated with aging. Here, we challenged our hypothesis that melatonin will impart antiproliferative response against PCa via inhibiting Sirt1. We demonstrated that melatonin significantly inhibited Sirt1 protein and activity in vitro in multiple human PCa cell lines, and melatonin-mediated Sirt1 inhibition was accompanied with a significant decrease in the proliferative potential of PCa cells, but not of normal cells. Forced overexpression of Sirt1 partially rescued the PCa cells from melatonin's antiproliferative effects, suggesting that Sirt1 is a direct target of melatonin. Employing transgenic adenocarcinoma of mouse prostate (TRAMP) mice, we also demonstrated that oral administration of melatonin, at human-achievable doses, significantly inhibited PCa tumorigenesis as shown by decreases in (i) prostate and genitourinary weight, (ii) serum insulin-like growth factor-1 (IGF-1)/IGF-binding protein-3 (IGFBP3) ratio, (iii) mRNA and protein levels of the proliferation markers (PCNA, Ki-67). This anti-PCa response was accompanied with a significant decrease in Sirt1 in TRAMP prostate. Our data identified melatonin as a novel inhibitor of Sirt1 and suggest that melatonin can inhibit PCa growth via Sirt1 inhibition.

SIRT1 and AMPK in regulating mammalian senescence: a critical review and a working model

Ageing in mammals remains an unsolved mystery. Anti-ageing is a recurring topic in the history of scientific research. Lifespan extension evoked by Sir2 protein in lower organisms has attracted a large amount of interests in the last decade. This review summarizes recent evidence supporting the role of a Sir2 mammalian homologue, SIRT1 (Silent information regulator T1), in regulating ageing and cellular senescence. The various signaling networks responsible for the anti-ageing and anti-senescence activity of SIRT1 have been discussed. In particular, a counter-balancing model involving the cross-talks between SIRT1 and AMP-activated protein kinase (AMPK), another stress and energy sensor, is suggested for controlling the senescence program in mammalian cells.

Measurement of the cellular deacetylase activity of SIRT1 on p53 via LanthaScreen® technology

Upon genomic insult, the tumor suppressor p53 is phosphorylated and acetylated at specific serine and lysine residues, increasing its stability and transactivation function. Deacetylases, including the type III histone deacetylase SIRT1, remove acetyl groups from p53 and counterbalance acetyltransferase activity during a DNA damage response. This report describes a series of high-throughput LanthaScreen® time-resolved Förster resonance energy transfer (TR-FRET) immunoassays for detection of intracellular p53 phosphorylation of Ser15 and acetylation of Lys382 upon treatment with DNA damage agents, such as etoposide. These assays were used to measure the deacetylase activity of SIRT1 and/or Type I/II Histone deacetylases (HDACs). First, BacMam-mediated overexpression of SIRT1 resulted in dose-dependent deacetylation of GFP-p53 following etoposide treatment of U-2 OS cells, confirming that GFP-p53 serves as a SIRT1 substrate in this assay format. Further, overexpression of the acetyltransferase p300 via BacMam increased the acetylation of GFP-p53 at Lys382. Next, siRNA-mediated knockdown of SIRT1 resulted in increased GFP-p53 acetylation, indicating that endogenous SIRT1 activity can also be measured in U-2 OS cells. Consistent with these results, GFP-p53 acetylation was also increased upon treatment of cells with a small-molecule inhibitor of SIRT1, EX-527. The effect of this compound was dramatically increased when used in combination with chemotherapeutic drug and/or the HDAC inhibitor Trichostatin A, confirming a proposed synergistic mechanism of p53 deacetylation by SIRT1 and Type I/II HDACs. Taken together, the cellular assays described here can be used as high-throughput alternatives to traditional immunoassays such as western blotting for identifying pharmacological modulators of specific p53-modifying enzymes.

SIRT1 variants are associated with aging in a healthy Han Chinese population

BACKGROUND

Aging is influenced by diverse environmental and genetic risk factors. The SIRT1 (silent information regulator 1) gene has been shown to regulate lifespan and aging in previous studies. We determined whether variation in the SIRT1 gene is associated with aging in healthy Chinese population.

METHODS

The study population comprised 482 healthy, unrelated Chinese subjects, of which 246 were aging individuals from 60 to 91years old, and 236 younger individuals from 35 and 59years old. All subjects were from Shenyang, China. Two single-nucleotide polymorphisms (SNP) were analyzed: rs3758391 near the 5' end of the SIRT1 gene; and rs4746720, in the 3' untranslated region.

RESULTS

Differences in allele and genotype frequency were seen between the groups, with rs3758391/C more common than rs3758391/T in the aging subjects (odds ratio=1.453, p=0.026), and with rs3758391/CC more common than rs3758391/CT and rs3758391/TT in the aging subjects (odds ratio=3.042, p=0.027). For the 3' SNP, rs4746720/C was more common than rs4746720/T in the aging subjects (odds ratio=1.347, p=0.022), and rs4746720/CC was more common than rs4746720/CT and rs4746720/CT in the aging subjects (odds ratio=1.461, p=0.049). The haplotype frequency distribution was also different, with haplotype CC more common in the older group (odds ratio=1.63, p=0.01).

CONCLUSION

These results suggest that SIRT1 gene polymorphisms may add a new factor on the multifactorial genetic contributions to aging.

The function of microRNAs, small but potent molecules, in human prostate cancer

Prostate cancer is one of the most significant cancers of men all over the world. The microRNAs (miRNAs) possess crucial functions in pathogenesis of the disease and its gain of androgen independency. The miRNAs are small, approximately 18-24 nucleotides, non-coding, endogenously synthesized RNAs that regulate gene expression post-transcriptionally. They are found in viruses, plants, and animal cells. The miRNAs have critical functions in gene expression and their dysregulation may cause tumor formation and progression of several diseases. Here, we have reviewed the most current literature to elucidate the function of miRNAs in human prostate cancer. We believe that this will help investigators not only working in prostate cancer, but also studying the miRNAs in other diseases to delineate the functions of miRNAs implicated in human prostate cancer development and progression.