Human Sir2-related protein SIRT1 associates with the bHLH repressors HES1 and HEY2 and is involved in HES1- and HEY2-mediated transcriptional repression

RIP140 regulates transcription factor HES1 oscillatory expression and mitogenic activity in colon cancer cells

The transcription factor receptor-interacting protein 140 (RIP140) regulates intestinal homeostasis and tumorigenesis through Wnt signaling. In this study, we investigated its effect on the Notch/HES1 signaling pathway. In colorectal cancer (CRC) cell lines, RIP140 positively regulated HES1 gene expression at the transcriptional level via a recombining binding protein suppressor of hairless (RBPJ)/neurogenic locus notch homolog protein 1 (NICD)-mediated mechanism. In support of these in vitro data, RIP140 and HES1 expression significantly correlated in mouse intestine and in a cohort of CRC samples, thus supporting the positive regulation of HES1 gene expression by RIP140. Interestingly, when the Notch pathway is fully activated, RIP140 exerted a strong inhibition of HES1 gene transcription controlled by the level of HES1 itself. Moreover, RIP140 directly interacts with HES1 and reversed its mitogenic activity in human CRC cells. In line with this observation, HES1 levels were associated with a better patient survival only when tumors expressed high levels of RIP140. Our data identify RIP140 as a key regulator of the Notch/HES1 signaling pathway, with a dual effect on HES1 gene expression at the transcriptional level and a strong impact on colon cancer cell proliferation.

Beta cell dysfunction induced by bone morphogenetic protein (BMP)-2 is associated with histone modifications and decreased NeuroD1 chromatin binding

Insufficient insulin secretion is a hallmark of type 2 diabetes and has been attributed to beta cell identity loss characterized by decreased expression of several key beta cell genes. The pro-inflammatory factor BMP-2 is upregulated in islets of Langerhans from individuals with diabetes and acts as an inhibitor of beta cell function and proliferation. Exposure to BMP-2 induces expression of Id1-4, Hes-1, and Hey-1 which are transcriptional regulators associated with loss of differentiation. The aim of this study was to investigate the mechanism by which BMP-2 induces beta cell dysfunction and loss of cell maturity. Mouse islets exposed to BMP-2 for 10 days showed impaired glucose-stimulated insulin secretion and beta cell proliferation. BMP-2-induced beta cell dysfunction was associated with decreased expression of cell maturity and proliferation markers specific to the beta cell such as Ins1, Ucn3, and Ki67 and increased expression of Id1-4, Hes-1, and Hey-1. The top 30 most regulated proteins significantly correlated with corresponding mRNA expression. BMP-2-induced gene expression changes were associated with a predominant reduction in acetylation of H3K27 and a decrease in NeuroD1 chromatin binding activity. These results show that BMP-2 induces loss of beta cell maturity and suggest that remodeling of H3K27ac and decreased NeuroD1 DNA binding activity participate in the effect of BMP-2 on beta cell dysfunction.

KLF14 regulates the growth of hepatocellular carcinoma cells via its modulation of iron homeostasis through the repression of iron-responsive element-binding protein 2

BACKGROUND

Hepatocellular carcinoma (HCC) is a multifactor-driven malignant tumor with rapid progression, which causes the difficulty to substantially improve the prognosis of HCC. Limited understanding of the mechanisms in HCC impedes the development of efficacious therapies. Despite Krüpple-Like factors (KLFs) were reported to be participated in HCC pathogenesis, the function of KLF14 in HCC remains largely unexplored.

METHODS

We generated KLF14 overexpressed and silenced liver cancer cells, and nude mouse xenograft models for the in vitro and in vivo study. Luciferase reporter assay, ChIP-qPCR, Co-IP, immunofluorescence were performed for mechanism research. The expression of KLF14 in HCC samples was analyzed by quantitative RT-PCR, Western blotting, and immunohistochemistry (IHC) analysis.

RESULTS

KLF14 was significantly downregulated in human HCC tissues, which was highly correlated with poor prognosis. Inhibition of KLF14 promoted liver cancer cells proliferation and overexpression of KLF14 suppressed cells growth. KLF14 exerts its anti-tumor function by inhibiting Iron-responsive element-binding protein 2 (IRP2), which then causes transferrin receptor-1(TfR1) downregulation and ferritin upregulation on the basis of IRP-IREs system. This then leading to cellular iron deficiency and HCC cells growth suppression in vitro and in vivo. Interestingly, KLF14 suppressed the transcription of IRP2 via recruiting SIRT1 to reduce the histone acetylation of the IRP2 promoter, resulting in iron depletion and cell growth suppression. More important, we found fluphenazine is an activator of KLF14, inhibiting HCC cells growth through inducing iron deficiency.

CONCLUSION

KLF14 acts as a tumor suppressor which inhibits the proliferation of HCC cells by modulating cellular iron metabolism via the repression of IRP2. We identified Fluphenazine, as an activator of KLF14, could be a potential compound for HCC therapy. Our findings therefore provide an innovative insight into the pathogenesis of HCC and a promising therapeutic target.

OpenVar: functional annotation of variants in non-canonical open reading frames

Background

Recent technological advances have revealed thousands of functional open reading frames (ORF) that have eluded reference genome annotations. These overlooked ORFs are found throughout the genome, in any reading frame of transcripts, mature or non-coding, and can overlap annotated ORFs in a different reading frame. The exploration of these novel ORFs in genomic datasets and of their role in genetic traits is hindered by a lack of software.

Results

Here, we present OpenVar, a genomic variant annotator that mends that gap and fosters meaningful discoveries. To illustrate the potential of OpenVar, we analysed all variants within SynMicDB, a database of cancer-associated synonymous mutations. By including non-canonical ORFs in the analysis, OpenVar yields a 33.6-fold, 13.8-fold and 8.3-fold increase in high impact variants over Annovar, SnpEff and VEP respectively. We highlighted an overlapping non-canonical ORF in the HEY2 gene where variants significantly clustered.

Conclusions

OpenVar integrates non-canonical ORFs in the analysis of genomic variants, unveiling new research avenues to better understand the genotype–phenotype relationships.

Follicle-stimulating hormone regulates Notch signalling in the seminiferous epithelium of continuously and seasonally breeding rodents

CONTEXT

Juxtacrine (contact-dependent) communication between the cells of seminiferous epithelium mediated by Notch signalling is of importance for the proper course of spermatogenesis in mammals.

AIMS

The present study was designed to evaluate the role of follicle-stimulating hormone (FSH) in the regulation of Notch signalling in rodent seminiferous epithelium.

METHODS

We explored the effects (1) of pharmacological inhibition of the hypothalamus-pituitary-gonadal (HPG) axis and FSH replacement in pubertal rats, and (2) of photoinhibition of HPG axis followed by FSH substitution in seasonally breeding rodents, bank voles, on Notch pathway activity. Experiments on isolated rat Sertoli cells exposed to FSH were also performed. Gene and protein expressions of Notch pathway components were analysed using RT-qPCR, western blot and immunohistochemistry/immunofluorescence.

KEY RESULTS

Distribution patterns of Notch pathway proteins in bank vole and rat seminiferous epithelium were comparable; however, levels of activated Notch1 and Notch3, hairy/enhancer of split 1 (HES1) and hairy/enhancer of split-related with YRPW motif 1 (HEY1) in bank voles were dependent on the length of the photoperiod. In response to FSH similar changes in these proteins were found in both species, indicating that FSH is a negative regulator of Notch pathway activity in seminiferous epithelium.

CONCLUSIONS

Our results support a common mechanism of FSH action on Notch pathway during onset and recrudescence of spermatogenesis in rodents.

IMPLICATIONS

Interaction between FSH signalling and Notch pathway in Sertoli cells may be involved in spermatogenic activity changes of the testes occurring during puberty or photoperiod shift in continuously and seasonally breeding rodents, respectively.

PIF7 controls leaf cell proliferation through an AN3 substitution repression mechanism

Phytochrome photoreceptors can markedly alter leaf blade growth in response to far-red (FR) rich neighbor shade, yet we have a limited understanding of how this is accomplished. This study identifies ANGUSTIFOLIA3 (AN3) as a central component in phytochrome promotion of leaf cell proliferation and PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) as a potent repressor. AN3 and PIF7 impose opposing regulation on a shared suite of genes through common cis-acting promoter elements. In response to FR light, activated PIF7 blocks AN3 action by evicting and substituting for AN3 at target promoters. This molecular switch module provides a mechanism through which changes in external light quality can dynamically manipulate gene expression, cell division, and leaf size.

Plants are agile, plastic organisms able to adapt to everchanging circumstances. Responding to far-red (FR) wavelengths from nearby vegetation, shade-intolerant species elicit the adaptive shade-avoidance syndrome (SAS), characterized by elongated petioles, leaf hyponasty, and smaller leaves. We utilized end-of-day FR (EODFR) treatments to interrogate molecular processes that underlie the SAS leaf response. Genetic analysis established that PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) is required for EODFR-mediated constraint of leaf blade cell division, while EODFR messenger RNA sequencing data identified ANGUSTIFOLIA3 (AN3) as a potential PIF7 target. We show that PIF7 can suppress AN3 transcription by directly interacting with and sequestering AN3. We also establish that PIF7 and AN3 impose antagonistic control of gene expression via common cis-acting promoter motifs in several cell-cycle regulator genes. EODFR triggers the molecular substitution of AN3 to PIF7 at G-box/PBE-box promoter regions and a switch from promotion to repression of gene expression.

Ticagrelor Increases SIRT1 and HES1 mRNA Levels in Peripheral Blood Cells from Patients with Stable Coronary Artery Disease and Chronic Obstructive Pulmonary Disease

Ticagrelor is a powerful P2Y₁₂ inhibitor with pleiotropic effects in the cardiovascular system. Consistently, we have reported that in patients with stable coronary artery disease (CAD) and concomitant chronic obstructive pulmonary disease (COPD) who underwent percutaneous coronary intervention (PCI), 1-month treatment with ticagrelor was superior in improving biological markers of endothelial function, compared with clopidogrel. The objective of this study was to investigate the mechanisms underlying these beneficial effects of ticagrelor by conducting molecular analyses of RNA isolated from peripheral blood cells of these patients. We determined mRNAs levels of markers of inflammation and oxidative stress, such as RORγt (T helper 17 cells marker), FoxP3 (regulatory T cells marker), NLRP3, ICAM1, SIRT1, Notch ligands JAG1 and DLL4, and HES1, a Notch target gene. We found that 1-month treatment with ticagrelor, but not clopidogrel, led to increased levels of SIRT1 and HES1 mRNAs. In patients treated with ticagrelor or clopidogrel, we observed a negative correlation among changes in both SIRT1 and HES1 mRNA and serum levels of Epidermal Growth Factor (EGF), a marker of endothelial dysfunction found to be reduced by ticagrelor treatment in our previous study. In conclusion, we report that in stable CAD/COPD patients ticagrelor positively regulates HES1 and SIRT1, two genes playing a protective role in the context of inflammation and oxidative stress. Our observations confirm and expand previous studies showing that the beneficial effects of ticagrelor in stable CAD/COPD patients may be, at least in part, mediated by its capacity to reduce systemic inflammation and oxidative stress.

Role of Sirtuins in Tumor Angiogenesis

Generally, changes in the metabolic status of cells under conditions like hypoxia and accumulation of lactate can be sensed by various sensing mechanisms, leading to modulation of a number of signal transduction pathways and transcription factors. Several of the proangiogenic cytokines like VEGF, FGF, PDGF, TGF-β, Ang-2, ILs, etc. are secreted by cancer cells, under hypoxic microenvironment. These cytokines bind to their receptors on the endothelial cells and activates a number of signaling pathways including Akt/PIP3, Src, p38/MAPK, Smad2/3, etc., which ultimately results in the proliferation and migration of endothelial cells. Transcription factors that are activated in response to the metabolic status of tumors include HIFs, NF-κb, p53, El-2, and FOXO. Many of these transcription factors has been reported to be regulated by a class of histone deacetylase called sirtuins. Sirtuins are NAD+ dependent histone deacetylases that play pivotal role in the regulation of tumor cell metabolism, proliferation, migration and angiogenesis. The major function of sirtuins include, deacetylation of histones as well as some non-histone proteins like NF-κB, FOXOs, PPAR⋎, PGC1-α, enzymes like acetyl coenzymeA and structural proteins like α tubulin. In the cell, sirtuins are generally considered as the redox sensors and their activities are dependent on the metabolic status of the cell. Understanding the intricate regulatory mechanisms adopted by sirtuins, is crucial in devising effective therapeutic strategies against angiogenesis, metastasis and tumor progression. Keeping this in mind, the present review focuses on the role of sirtuins in the process of tumor angiogenesis and the regulatory mechanisms employed by them.

Notch Signaling-Induced Oscillatory Gene Expression May Drive Neurogenesis in the Developing Retina

After integrating classic and cutting-edge research, we proposed a unified model that attempts to explain the key steps of mammalian retinal neurogenesis. We proposed that the Notch signaling-induced lateral inhibition mechanism promotes oscillatory expression of Hes1. Oscillating Hes1 inhibitory activity as a result leads to oscillatory expression of Notch signaling inhibitors, activators/inhibitors of retinal neuronal phenotypes, and cell cycle-promoting genes all within a retinal progenitor cell (RPC). We provided a mechanism explaining not only how oscillatory expression prevents the progenitor-to-precursor transition, but also how this transition happens. Our proposal of the mechanism posits that the levels of the above factors not only oscillate but also rise (with the exception of Hes1) as the factors accumulate within a progenitor. Depending on which factors accumulate fastest and reach the required supra-threshold levels (cell cycle activators or Notch signaling inhibitors), the progenitor either proliferates or begins to differentiate without any further proliferation when Notch signaling ceases. Thus, oscillatory gene expression may regulate an RPC's decision to proliferate or differentiate. Meanwhile, a post-mitotic precursor's selection of one retinal neuronal phenotype over many others depends on the expression level of key transcription factors (activators) required for each of these retinal neuronal phenotypes. Because the events described above are stochastic due to oscillatory gene expression and gene product inheritance from a mother RPC after its division, an RPC or precursor's decision requires the assignment of probabilities to specific outcomes in the selection process. While low and sustained (non-oscillatory) Notch signaling activity is required to promote the transition of retinal progenitors into various retinal neuronal phenotypes, we propose that the lateral inhibition mechanism, combined with high expression of the BMP signaling-induced Inhibitor of Differentiation (ID) protein family, promotes high and sustained (non-oscillatory) Hes1 and Hes5 expression. These events facilitate the transition of an RPC into the Müller glia (MG) phenotype at the late stage of retinal development.

Phenotypically distinct female castes in honey bees are defined by alternative chromatin states during larval development

The capacity of the honey bee to produce three phenotypically distinct organisms (two female castes; queens and sterile workers, and haploid male drones) from one genotype represents one of the most remarkable examples of developmental plasticity in any phylum. The queen-worker morphological and reproductive divide is environmentally controlled during post-embryonic development by differential feeding. Previous studies implicated metabolic flux acting via epigenetic regulation, in particular DNA methylation and microRNAs, in establishing distinct patterns of gene expression underlying caste-specific developmental trajectories. We produce the first genome-wide maps of chromatin structure in the honey bee at a key larval stage in which developmental canalization into queen or worker is virtually irreversible. We find extensive genome-wide differences in H3K4me3, H3K27ac, and H3K36me3, many of which correlate with caste-specific transcription. Furthermore, we identify H3K27ac as a key chromatin modification, with caste-specific regions of intronic H3K27ac directing the worker caste. These regions may harbor the first examples of caste-specific enhancer elements in the honey bee. Our results demonstrate a key role for chromatin modifications in the establishment and maintenance of caste-specific transcriptional programs in the honey bee. We show that at 96 h of larval growth, the queen-specific chromatin pattern is already established, whereas the worker determination is not, thus providing experimental support for the perceived timing of this critical point in developmental heterochrony in two types of honey bee females. In a broader context, our study provides novel data on environmentally regulated organismal plasticity and the molecular foundation of the evolutionary origins of eusociality.

The circadian clock in adult neural stem cell maintenance

Neural stem cells persist in the adult central nervous system as a continuing source of astrocytes, oligodendrocytes and neurons. Various signalling pathways and transcription factors actively maintain this population by regulating cell cycle entry and exit. Similarly, the circadian clock is interconnected with the cell cycle and actively maintains stem cell populations in various tissues. Here, we discuss emerging evidence for an important role of the circadian clock in neural stem cell maintenance. We propose that the NAD⁺-dependent deacetylase SIRT1 exerts control over the circadian clock in adult neural stem cell function to limit exhaustion of their population. Conversely, disruption of the circadian clock may compromise neural stem cell quiescence resulting in a premature decline of the neural stem cell population. As such, energy metabolism and the circadian clock converge in adult neural stem cell maintenance.

SRT2104 attenuates diabetes-induced aortic endothelial dysfunction via inhibition of P53

Endothelial dysfunction contributes to diabetic macrovascular complications. Sirtuin 1 (SIRT1) protects against diabetic vasculopathy. SRT2104 is a novel SIRT1 activator and was not previously studied for its effects on diabetes-induced aortic endothelial dysfunction. Additionally, whether or to what extent deacetylation of P53, a substrate of SIRT1, is required for the effects of SIRT1 activation was unclear, given the fact that SIRT1 has multiple targets. Moreover, little was known about the pathogenic role of P53 in diabetes-induced aortic injury. To these ends, diabetes was induced by streptozotocin in C57BL/6 mice. The diabetic mice developed enhanced aortic contractility, oxidative stress, inflammation, P53 hyperacetylation and a remarkable decrease in SIRT1 protein, the effects of which were rescued by SRT2104. In HG-treated endothelial cells (ECs), P53 siRNA and SRT2104 produced similar effects on the induction of SIRT1 and the inhibition of P53 acetylation, oxidative stress and inflammation. Interestingly, SRT2104 failed to further enhance these effects in the presence of P53 siRNA. Moreover, P53 activation by nutlin3a completely abolished SRT2104's protection against HG-induced oxidative stress and inflammation. Further, forced activation of P53 by nutlin3a increased aortic contractility in the healthy mice and generated endothelial oxidative stress and inflammation in both the normal glucose-cultured ECs and the aortas of the healthy mice. Collectively, the present study demonstrates that P53 deacetylation predominantly mediates SRT2104's protection against diabetes-induced aortic endothelial dysfunction and highlights the pathogenic role of P53 in aortic endothelial dysfunction.

A Notch-independent mechanism contributes to the induction of Hes1 gene expression in response to hypoxia in P19 cells

Hes1 is a Notch target gene that plays a major role during embryonic development. Previous studies have shown that HIF-1α can interact with the Notch intracellular domain and enhance Notch target gene expression. In this study, we have identified a Notch-independent mechanism that regulates the responsiveness of the Hes1 gene to hypoxia. Using P19 cells we show that silencing the Notch DNA binding partner CSL does not prevent hypoxia-dependent upregulation of Hes1 expression. In contrast to CSL, knockdown of HIF-1α or Arnt expression prevents Hes1 induction in hypoxia. Deletion analysis of the Hes1 promoter identified a minimal region near the transcription start site that is still responsive to hypoxia. In addition, we show that mutating the GA-binding protein (GABP) motif significantly reduced Hes1 promoter-responsiveness to hypoxia or to HIF-1 overexpression whereas mutation of the hypoxia-responsive element (HRE) present in this region had no effect. Chromatin immunoprecipitation assays demonstrated that HIF-1α binds to the proximal region of the Hes1 promoter in a Notch-independent manner. Using the same experimental approach, the presence of GABPα and GABPβ1 was also observed in the same region of the promoter. Loss- and gain-of-function studies demonstrated that Hes1 gene expression is upregulated by hypoxia in a GABP-dependent manner. Finally, co-immunoprecipitation assays demonstrated that HIF-1α but not HIF-2α is able to interact with either GABPα or GABPβ1. These results suggest a Notch-independent mechanism where HIF-1 and GABP contribute to the upregulation of Hes1 gene expression in response to hypoxia.

Fine-Tuning of the Kaposi's Sarcoma-Associated Herpesvirus Life Cycle in Neighboring Cells through the RTA-JAG1-Notch Pathway

Kaposi’s sarcoma (KS)-associated herpesvirus (KSHV) is an oncogenic pathogen that displays latent and lytic life cycles. In KS lesions, infiltrated immune cells, secreted viral and/or cellular cytokines, and hypoxia orchestrate a chronic pro-lytic microenvironment that can promote KSHV reactivation. However, only a small subset of viruses spontaneously undergoes lytic replication in this pro-lytic microenvironment while the majority remains in latency. Here, we show that the expression of the Notch ligand JAG1 is induced by KSHV-encoded replication and transcription activator (RTA) during reactivation. JAG1 up-regulation activates Notch signaling in neighboring cells and prevents viral lytic replication. The suppression of JAG1 and Notch1 with inhibitors or small interfering RNA promotes lytic replication in the presence of RTA induction or under conditions of hypoxia. The underlying mechanism involves the Notch downstream effector hairy and enhancer of split 1 (Hes1), which directly binds lytic gene promoters and attenuates viral lytic gene expression. RTA interacts with lymphoid enhancer-binding factor 1 (LEF1), disrupts LEF1/Groucho/TLE suppressive complexes and releases LEF1 to activate JAG1 expression. Taken together, our results suggest that cells with viral lytic replication can inhibit KSHV reactivation in neighboring cells through an RTA-JAG1-Notch pathway. These data provide insight into the mechanism by which the virus maintains the balance between lytic and latent infection in the pro-lytic tumor microenvironment.

KSHV infected cells display significant heterogeneity in viral lytic replication within the universal pro-lytic inflammatory milieu, suggesting that the balance between latency and reactivation is carefully regulated. This fine-tuned regulatory mechanism is essential for KSHV to persist in the host and drive cells to malignancy. In the present study, we show that KSHV can usurp the Notch signaling pathway to inhibit the viral lytic life cycle in neighboring cells. Notch signaling in surrounding cells can be activated through an RTA-JAG1-Notch pathway initiated by cells in which KSHV is reactivated. Activated Notch inhibits KSHV reactivation through its downstream effector Hes1. These findings suggest that the ability of Notch to determine the fate of adjacent cells is hijacked by KSHV to maintain its life cycle, providing a mechanistic explanation for the phenomenon by which only a small fraction of viruses enters lytic replication in the common pro-lytic microenvironment.

A potent and selective small molecule inhibitor of sirtuin 1 promotes differentiation of pluripotent P19 cells into functional neurons

Sirtuin 1 (SIRT1) is known to suppress differentiation of pluripotent/multipotent cells and neural progenitor cells into neurons by blocking activation of transcription factors critical for neurogenesis. EX-527 is a highly selective and potent inhibitor against SIRT1 and has been used as a chemical probe that modulates SIRT1-associated biological processes. However, the effect of EX-527 on neuronal differentiation in pluripotent cells has not been well elucidated. Here, we report an examination of EX-527 effects on neurogenesis of pluripotent P19 cells. The results showed that EX-527 greatly accelerated differentiation of P19 cells into neurons without generation of cardiac cells and astrocytes. Importantly, neurons derived from P19 cells treated with EX-527 generated voltage-dependent sodium currents and depolarization-induced action potentials. The findings indicate that the differentiated cells have electrophysiological properties. The present study suggests that the selective SIRT1 inhibitor could have the potential of being employed as a chemical inducer to generate functionally active neurons.

Selection of cell fate in the organ of Corti involves the integration of Hes/Hey signaling at the Atoh1 promoter

Determination of cell fate within the prosensory domain of the developing cochlear duct relies on the temporal and spatial regulation of the bHLH transcription factor Atoh1. Auditory hair cells and supporting cells arise in a wave of differentiation that patterns them into discrete rows mediated by Notch-dependent lateral inhibition. However, the mechanism responsible for selecting sensory cells from within the prosensory competence domain remains poorly understood. We show in mice that rather than being upregulated in rows of cells, Atoh1 is subject to transcriptional activation in groups of prosensory cells, and that highly conserved sites for Hes/Hey repressor binding in the Atoh1 promoter are needed to select the hair cell and supporting cell fate. During perinatal supporting cell transdifferentiation, which is a model of hair cell regeneration, we show that derepression is sufficient to induce Atoh1 expression, suggesting a mechanism for priming the 3' Atoh1 autoregulatory enhancer needed for hair cell expression.

Resveratrol: A Potential Hippocampal Plasticity Enhancer

The search for molecules capable of restoring altered hippocampal plasticity in psychiatric and neurological conditions is one of the most important tasks of modern neuroscience. It is well established that neural plasticity, such as the ability of the postnatal hippocampus to continuously generate newly functional neurons throughout life, a process called adult hippocampal neurogenesis (AHN), can be modulated not only by pharmacological agents, physical exercise, and environmental enrichment, but also by “nutraceutical” agents. In this review we focus on resveratrol, a phenol and phytoalexin found in the skin of grapes and red berries, as well as in nuts. Resveratrol has been reported to have antioxidant and antitumor properties, but its effects as a neural plasticity inducer are still debated. The current review examines recent evidence implicating resveratrol in regulating hippocampal neural plasticity and in mitigating the effects of various disorders and diseases on this important brain structure. Overall, findings show that resveratrol can improve cognition and mood and enhance hippocampal plasticity and AHN; however, some studies report opposite effects, with resveratrol inhibiting aspects of AHN. Therefore, further investigation is needed to resolve these controversies before resveratrol can be established as a safe coadjuvant in preventing and treating neuropsychiatric conditions.

HSP25 down-regulation enhanced p53 acetylation by dissociation of SIRT1 from p53 in doxorubicin-induced H9c2 cell apoptosis

Heat shock proteins (HSPs) play important roles in cellular stress resistance. Previous reports had already suggested that HSP27 played multiple roles in preventing doxorubicin-induced cardiotoxicity. Although HSP25 might have biological functions similar to its human homolog HSP27, the mechanism of HSP25 is still unclear in doxorubicin-induced cardiomyocyte apoptosis. To investigate HSP25 biological function on doxorubicin-induced apoptosis, flow cytometry was employed to analyze cell apoptosis in over-expressing HSP25 H9c2 cells in presence of doxorubicin. Unexpectedly, the H9c2 cells of over-expressing HSP25 have no protective effect on doxorubicin-induced apoptosis. Moreover, no detectable interactions were detected by coimmunoprecipitation between HSP25 and cytochrome c, and HSP25 over-expression failed in preventing cytochrome c release induced by doxorubicin. However, down-regulation of endogenous HSP25 by a specific small hairpin RNA aggravates apoptosis in H9c2 cells. Subsequent studies found that HSP25, but not HSP90, HSP70, and HSP20, interacted with SIRT1. Knockdown of HSP25 decreased the interaction between SIRT1 and p53, leading to increased p53 acetylation on K379, up-regulated pro-apoptotic Bax protein expression, induced cytochrome c release, and triggered caspase-3 and caspase-9 activation. These findings indicated a novel mechanism by which HSP25 regulated p53 acetylation through dissociation of SIRT1 from p53 in doxorubicin-induced H9c2 cell apoptosis.

Hes1: a key role in stemness, metastasis and multidrug resistance

Hes1 is one mammalian counterpart of the Hairy and Enhancer of split proteins that play a critical role in many physiological processes including cellular differentiation, cell cycle arrest, apoptosis and self-renewal ability. Recent studies have shown that Hes1 functions in the maintenance of cancer stem cells (CSCs), metastasis and antagonizing drug-induced apoptosis. Pathways that are involved in the up-regulation of Hes1 level canonically or non-canonically, such as the Hedgehog, Wnt and hypoxia pathways are frequently aberrant in cancer cells. Here, we summarize the recent data supporting the idea that Hes1 may have an important function in the maintenance of cancer stem cells self-renewal, cancer metastasis, and epithelial-mesenchymal transition (EMT) process induction, as well as chemotherapy resistance, and conclude with the possible mechanisms by which Hes1 functions have their effect, as well as their crosstalk with other carcinogenic signaling pathways.

Autoregulatory Control of Smooth Muscle Myosin Light Chain Kinase Promoter by Notch Signaling

Smooth muscle myosin light chain kinase (SM-MLCK) is the key enzyme responsible for phosphorylation of regulatory myosin light chain (MLC20), resulting in actin-myosin cross-bridging and force generation in vascular smooth muscle required for physiological vasoreactivity and blood pressure control. In this study, we investigated the combinatorial role of myocardin/serum response factor (SRF) and Notch signaling in the transcriptional regulation of MLCK gene expression. Promoter reporter analyses in rat A10 smooth muscle cells revealed a bimodal pattern of MLCK promoter activity and gene expression upon stimulation with constitutively active Notch1 in presence of myocardin or by Jagged1 ligand stimulation. An initial Notch1-induced increase in MLCK transcription was followed by loss in promoter sensitivity, which could be restored with further Notch1 dose escalation. Real-time PCR analyses revealed that endogenous levels of Hairy Related Transcription (HRT) factor 2 (HRT2) peaked concurrently with inhibitory concentrations of Notch1. Forced expression of HRT2 demonstrated simultaneous repression of both myocardin- and Notch1-induced MLCK promoter activity. HRT2-mediated repression was further confirmed by HRT2 truncations and siHRT2 treatments that rescued MLCK promoter activity and gene expression. Chromatin immunoprecipitation studies revealed both Jagged1 ligand- and Notch1-enhanced myocardin/SRF complex formation at the promoter CArG element. In contrast, heightened levels of HRT2 concomitantly disrupted myocardin/SRF and Notch transcription complex formation at respective CArG and CSL binding elements. Taken together, SM-MLCK promoter activity appears highly sensitive to the relative levels of Notch1 signaling, HRT2, and myocardin. These findings identify a novel Notch-dependent HRT2 autoregulatory circuit coordinating transcriptional regulation of SM-MLCK.

Notch signaling represses GATA4-induced expression of genes involved in steroid biosynthesis

Notch2 and Notch3 and genes of the Notch signaling network are dynamically expressed in developing follicles, where they are essential for granulosa cell proliferation and meiotic maturation. Notch receptors, ligands, and downstream effector genes are also expressed in testicular Leydig cells, predicting a potential role in regulating steroidogenesis. In this study, we sought to determine if Notch signaling in small follicles regulates the proliferation response of granulosa cells to FSH and represses the up-regulation steroidogenic gene expression that occurs in response to FSH as the follicle grows. Inhibition of Notch signaling in small preantral follicles led to the up-regulation of the expression of genes in the steroid biosynthetic pathway. Similarly, progesterone secretion by MA-10 Leydig cells was significantly inhibited by constitutively active Notch. Together, these data indicated that Notch signaling inhibits steroidogenesis. GATA4 has been shown to be a positive regulator of steroidogenic genes, including STAR protein, P450 aromatase, and 3B-hydroxysteroid dehydrogenase. We observed that Notch downstream effectors HEY1, HEY2, and HEYL are able to differentially regulate these GATA4-dependent promoters. These data are supported by the presence of HEY/HES binding sites in these promoters. These studies indicate that Notch signaling has a role in the complex regulation of the steroidogenic pathway.

Overexpression of a dominant-negative mutant of SIRT1 in mouse heart causes cardiomyocyte apoptosis and early-onset heart failure

SIRT1, a mammalian ortholog of yeast silent information regulator 2 (Sir2), is an NAD(+)-dependent protein deacetylase that plays a critical role in the regulation of vascular function. The current study aims to investigate the functional significance of deacetylase activity of SIRT1 in heart. Here we show that the early postnatal hearts expressed the highest level of SIRT1 deacetylase activity compared to adult and aged hearts. We generated transgenic mice with cardiac-specific expression of a dominant-negative form of the human SIRT1 (SIRT1H363Y), which represses endogenous SIRT1 activity. The transgenic mice displayed dilated atrial and ventricular chambers, and died early in the postnatal period. Pathological, echocardiographic and molecular phenotype confirmed the presence of dilated cardiomyopathy. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling analysis revealed a greater abundance of apoptotic nuclei in the hearts of transgenic mice. Furthermore, we show that cardiomyocyte apoptosis caused by suppression of SIRT1 activity is, at least in part, due to increased p53 acetylation and upregulated Bax expression. These results indicate that dominant negative form of SIRT1 (SIRT1H363Y) overexpression in mouse hearts causes cardiomyocyte apoptosis and early-onset heart failure, suggesting a critical role of SIRT1 in preserving normal cardiac development during the early postnatal period.

The involvement of NFAT transcriptional activity suppression in SIRT1-mediated inhibition of COX-2 expression induced by PMA/Ionomycin

SIRT1, a class III histone deacetylase, acts as a negative regulator for many transcription factors, and plays protective roles in inflammation and atherosclerosis. Transcription factor nuclear factor of activated T cells (NFAT) has been previously shown to play pro-inflammatory roles in endothelial cells. Inhibition of NFAT signaling may be an attractive target to regulate inflammation in atherosclerosis. However, whether NFAT transcriptional activity is suppressed by SIRT1 remains unknown. In this study, we found that SIRT1 suppressed NFAT-mediated transcriptional activity. SIRT1 interacted with NFAT, and the NHR and RHR domains of NFAT mediated the interaction with SIRT1. Moreover, we found that SIRT1 primarily deacetylated NFATc3. Adenoviral over-expression of SIRT1 suppressed PMA and calcium ionophore Ionomycin (PMA/Io)-induced COX-2 expression in human umbilical vein endothelial cells (HUVECs), while SIRT1 RNAi reversed the effects in HUVECs. Moreover, inhibition of COX-2 expression by SIRT1 in PMA/Io-treated HUVECs was largely abrogated by inhibiting NFAT activation. Furthermore, SIRT1 inhibited NFAT-induced COX-2 promoter activity, and reduced NFAT binding to the COX-2 promoter in PMA/Io-treated HUVECs. These results suggest that suppression of NFAT transcriptional activity is involved in SIRT1-mediated inhibition of COX-2 expression induced by PMA/Io, and that the negative regulatory mechanisms of NFAT by SIRT1 may contribute to its anti-inflammatory effects in atherosclerosis.

Repression of SIRT1 promotes the differentiation of mouse induced pluripotent stem cells into neural stem cells

The use of transplanting functional neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs) has increased for the treatment of brain diseases. As such, it is important to understand the molecular mechanisms that promote NSCs differentiation of iPSCs for future NSC-based therapies. Sirtuin 1 (SIRT1), a NAD(+)-dependent protein deacetylase, has attracted significant attention over the past decade due to its prominent role in processes including organ development, longevity, and cancer. However, it remains unclear whether SIRT1 plays a role in the differentiation of mouse iPSCs toward NSCs. In this study, we produced NSCs from mouse iPSCs using serum-free medium supplemented with retinoic acid. We then assessed changes in the expression of SIRT1 and microRNA-34a, which regulates SIRT1 expression. Moreover, we used a SIRT1 inhibitor to investigate the role of SIRT1 in NSCs differentiation of iPSCs. Data revealed that the expression of SIRT1 decreased, whereas miRNAs-34a increased, during this process. In addition, the inhibition of SIRT1 enhanced the generation of NSCs and mature neurocytes. This suggests that SIRT1 negatively regulated the differentiation of mouse iPSCs into NSCs, and that this process may be regulated by miRNA-34a.

Transcriptional impact of dietary methionine restriction on systemic inflammation: relevance to biomarkers of metabolic disease during aging

Calorie restriction (CR) without malnutrition increases lifespan and produces significant improvements in biomarkers of metabolic health. The improvements are attributable in part to effects of CR on energy balance, which limit fat accumulation by restricting energy intake. Normal age-associated increases in adiposity and insulin resistance are associated with development of a systemic proinflammatory state, while chronic CR limits fat deposition and expression of inflammatory markers. Dietary methionine restriction (MR) has emerged as an effective CR mimetic because it produces a comparable extension in lifespan. MR also reduces adiposity through a compensatory increase in energy expenditure that effectively limits fat accumulation, but essentially nothing is known about the effects of MR on systemic inflammation. Here, we review the relationships between these two interventions and discuss their transcriptional impact. In addition, using tissues from rats after long-term consumption of CR or MR diets, transcriptional profiling was used to examine retrospectively the systems biology of 59 networks of molecules annotated to inflammation. Transcriptional effects of both diets occurred primarily in white adipose tissue and liver, and the responses to MR were far more robust than those to CR. The primary transcriptional targets of MR in both liver and white adipose tissue were phagocytes and macrophages, where expression of genes associated with immune cell infiltration and quantity was reduced. These findings support the conclusion that anti-inflammatory responses produced by CR and MR are not strictly dependent upon reduced adiposity but are significantly influenced by the metabolic mechanisms through which energy balance is altered.

Hey bHLH transcription factors

Hey bHLH transcription factors are direct targets of canonical Notch signaling. The three mammalian Hey proteins are closely related to Hes proteins and they primarily repress target genes by either directly binding to core promoters or by inhibiting other transcriptional activators. Individual candidate gene approaches and systematic screens identified a number of Hey target genes, which often encode other transcription factors involved in various developmental processes. Here, we review data on interaction partners and target genes and conclude with a model for Hey target gene regulation. Furthermore, we discuss how expression of Hey proteins affects processes like cell fate decisions and differentiation, e.g., in cardiovascular, skeletal, and neural development or oncogenesis and how this relates to the observed developmental defects and phenotypes observed in various knockout mice.

SIRT1 Inhibits p53 but not NF-κB Transcriptional Activity during Differentiation of Mouse Embryonic Stem Cells into Embryoid Bodies

BACKGROUND AND OBJECTIVES

SIRT1, a histone diacetylase, modify transactivation function of various transcription factor including p53 and NF-κB. p53 and NF-κB is involved in in vitro differentiation of mouse embryonic stem cells (mESC) into mouse embryoid body (mEB). These suggest that SIRT1 might affect in vitro differentiation of mESC into mEB by regulation of p53 and NF-κB.

METHODS AND RESULTS

In this study we analyzed the effect of SIRT1 in in vitro differentiation of mESC into mEB using wild and SIRT1 knockout mESC. To examine SIRT1-specific gene in mESC, this study conducted microarray-based differential gene expression analysis between wild and SIRT1 knockout mESC. Comparing their gene expression patterns, this study determined a list of genes regulated by SIRT1. cDNA microarray data-set analysis revealed that genes associated with transcription and signal transduction are significantly modified in SIRT1 knockout mESC. cDNA microarray data-set analysis between mESC and EB in wild and SIRT1 showed that SIRT1 inhibits p53 signaling pathway but not affect NF-κB signaling pathway.

CONCLUSIONS

This study suggests that SIRT1 modify mESC differentiation by regulation of p53 transcriptional activity.

SIRT1 is a Highly Networked Protein That Mediates the Adaptation to Chronic Physiological Stress

SIRT1 is a NAD(+)-dependent protein deacetylase that has a very large number of established protein substrates and an equally impressive list of biological functions thought to be regulated by its activity. Perhaps as notable is the remarkable number of points of conflict concerning the role of SIRT1 in biological processes. For example, evidence exists suggesting that SIRT1 is a tumor suppressor, is an oncogene, or has no effect on oncogenesis. Similarly, SIRT1 is variably reported to induce, inhibit, or have no effect on autophagy. We believe that the resolution of many conflicting results is possible by considering recent reports indicating that SIRT1 is an important hub interacting with a complex network of proteins that collectively regulate a wide variety of biological processes including cancer and autophagy. A number of the interacting proteins are themselves hubs that, like SIRT1, utilize intrinsically disordered regions for their promiscuous interactions. Many studies investigating SIRT1 function have been carried out on cell lines carrying undetermined numbers of alterations to the proteins comprising the SIRT1 network or on inbred mouse strains carrying fixed mutations affecting some of these proteins. Thus, the effects of modulating SIRT1 amount and/or activity are importantly determined by the genetic background of the cell (or the inbred strain of mice), and the effects attributed to SIRT1 are synthetic with the background of mutations and epigenetic differences between cells and organisms. Work on mice carrying alterations to the Sirt1 gene suggests that the network in which SIRT1 functions plays an important role in mediating physiological adaptation to various sources of chronic stress such as calorie restriction and calorie overload. Whether the catalytic activity of SIRT1 and the nuclear concentration of the co-factor, NAD(+), are responsible for modulating this activity remains to be determined. However, the effect of modulating SIRT1 activity must be interpreted in the context of the cell or tissue under investigation. Indeed, for SIRT1, we argue that context is everything.

The role of SIRT1 in ocular aging

The sirtuins are a highly conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylases that helps regulate the lifespan of diverse organisms. The human genome encodes seven different sirtuins (SIRT1-7), which share a common catalytic core domain but possess distinct N- and C-terminal extensions. Dysfunction of some sirtuins have been associated with age-related diseases, such as cancer, type II diabetes, obesity-associated metabolic diseases, neurodegeneration, and cardiac aging, as well as the response to environmental stress. SIRT1 is one of the targets of resveratrol, a polyphenolic SIRT1 activator that has been shown to increase the lifespan and to protect various organs against aging. A number of animal studies have been conducted to examine the role of sirtuins in ocular aging. Here we review current knowledge about SIRT1 and ocular aging. The available data indicate that SIRT1 is localized in the nucleus and cytoplasm of cells forming all normal ocular structures, including the cornea, lens, iris, ciliary body, and retina. Upregulation of SIRT1 has been shown to have an important protective effect against various ocular diseases, such as cataract, retinal degeneration, optic neuritis, and uveitis, in animal models. These results suggest that SIRT1 may provide protection against diseases related to oxidative stress-induced ocular damage, including cataract, age-related macular degeneration, and optic nerve degeneration in glaucoma patients.

SIRT1 regulates the neurogenic potential of neural precursors in the adult subventricular zone and hippocampus

Within the two neurogenic niches of the adult mammalian brain, i.e., the subventricular zone lining the lateral ventricle and the subgranular zone of the hippocampus, there exist distinct populations of proliferating neural precursor cells that differentiate to generate new neurons. Numerous studies have suggested that epigenetic regulation by histone-modifying proteins is important in guiding precursor differentiation during development; however, the role of these proteins in regulating neural precursor activity in the adult neurogenic niches remains poorly understood. Here we examine the role of an NAD(+) -dependent histone deacetylase, SIRT1, in modulating the neurogenic potential of neural precursors in the neurogenic niches of the adult mouse brain. We show that SIRT1 is expressed by proliferating adult subventricular zone and hippocampal neural precursors, although its transcript and protein levels are dramatically reduced during neural precursor differentiation. Utilizing a lentiviral-mediated delivery strategy, we demonstrate that abrogation of SIRT1 signaling by RNAi does not affect neural precursor numbers or their proliferation. However, SIRT1 knock down results in a significant increase in neuronal production in both the subventricular zone and the hippocampus. In contrast, enhancing SIRT1 signaling either through lentiviral-mediated SIRT1 overexpression or through use of the SIRT1 chemical activator Resveratrol prevents adult neural precursors from differentiating into neurons. Importantly, knock down of SIRT1 in hippocampal precursors in vivo, either through RNAi or through genetic ablation, promotes their neurogenic potential. These findings highlight SIRT1 signaling as a negative regulator of neuronal differentiation of adult subventricular zone and hippocampal neural precursors. © 2013 Wiley Periodicals, Inc.

SIRT1 suppresses PMA and ionomycin-induced ICAM-1 expression in endothelial cells

Intercellular adhesion molecule-1 (ICAM-1) plays an important role in the recruitment of leukocytes to the endothelium, which causes inflammation and initiation of atherosclerosis. We have previously shown that endothelium-specific over-expression of class III deacetylase SIRT1 decreases atherosclerosis. We therefore addressed the hypothesis that SIRT1 suppresses ICAM-1 expression in the endothelial cells. Here, we found that expression of SIRT1 and ICAM-1 was significantly induced by PMA and ionomycin (PMA/Io) in human umbilical vein endothelial cells (HUVECs). Adenovirus-mediated over-expression of SIRT1 significantly inhibited PMA/Io-induced ICAM-1 expression in HUVECs. Knockdown of SIRT1 by RNA interference (RNAi) resulted in increased expression of ICAM-1 in HUVECs. Luciferase report assay showed that over-expression of SIRT1 suppressed ICAM-1 promoter activity both in basic and in PMA/Io-induced conditions. We further found that SIRT1 was involved in transcription complex binding on the ICAM-1 promoter by chromatin immunoprecipitation (ChIP) assays. Furthermore, SIRT1 RNAi increased NF-κB p65 binding ability to the ICAM-1 promoter by ChIP assays. Overall, these data suggests that SIRT1 inhibits ICAM-1 expression in endothelial cells, which may contribute to its anti-atherosclerosis effect.

SIRT1 regulates endothelial Notch signaling in lung cancer

Background

Sirtuin 1 (SIRT1) acts as a key regulator of vascular endothelial homeostasis, angiogenesis, and endothelial dysfunction. However, the underlying mechanism for SIRT1-mediated lung carcinoma angiogenesis remains unknown. Herein, we report that the nicotinamide adenine dinucleotide 1 (NAD1)-dependent deacetylase SIRT1 can function as an intrinsic negative modulator of Delta-like ligand 4 (DLL4)/Notch signaling in Lewis lung carcinoma (LLC) xenograft-derived vascular endothelial cells (lung cancer-derived ECs).

Principal Findings

SIRT1 negatively regulates Notch1 intracellular domain (N1IC) and Notch1 target genes HEY1 and HEY2 in response to Delta-like ligand 4 (DLL4) stimulation. Furthermore, SIRT1 deacetylated and repressed N1IC expression. Quantitative chromatin immunoprecipitation (qChIP) analysis and gene reporter assay demonstrated that SIRT1 bound to one highly conserved region, which was located at approximately −500 bp upstream of the transcriptional start site of Notch1,and repressed Notch1 transcription. Inhibition of endothelial cell growth and sprouting angiogenesis by DLL4/Notch signaling was enhanced in SIRT1-silenced lung cancer-derived EC and rescued by Notch inhibitor DAPT. In vivo, an increase in proangiogenic activity was observed in Matrigel plugs from endothelial-specific SIRT1 knock-in mice. SIRT1 also enhanced tumor neovascularization and tumor growth of LLC xenografts.

Conclusions

Our results show that SIRT1 facilitates endothelial cell branching and proliferation to increase vessel density and promote lung tumor growth through down-regulation of DLL4/Notch signaling and deacetylation of N1IC. Thus, targeting SIRT1 activity or/and gene expression may represent a novel mechanism in the treatment of lung cancer.

Glutamine depletion and glucose depletion trigger growth inhibition via distinctive gene expression reprogramming

Glutamine (Gln) and glucose (Glc) represent two important nutrients for proliferating cells, consistent with the observations that oncogenic processes are associated with enhanced glycolysis and glutaminolysis. Gln depletion and Glc depletion have been shown to trigger growth arrest and eventually cell death. Solid tumors often outgrow the blood supply, resulting in ischemia, which is associated with hypoxia and nutrient insufficiency. Whereas oxygen-sensing and adaptive mechanisms to hypoxia have been well-studied, how cells directly sense and respond to Gln and Glc insufficiency remains unclear. Using mRNA profiling techniques, we compared the gene expression profiles of acute Gln-depleted cells, Glc-depleted cells and cells adapted to Gln depletion. Here we report the global changes of the gene expression in those cells cultured under the defined nutrient conditions. Analysis of mRNA profiling data revealed that Gln and Glc depletion triggered dramatic gene expression reprogramming. Either Gln or Glc deletion leads to changes of the expression of cell cycle genes, but these conditions have distinctive effects on transcription regulators and gene expression profiles. Moreover, Gln and Glc depletion triggered distinguishable ER-stress responses. The gene expression patterns support that Gln and Glc have distinctive metabolic roles in supporting cell survival and proliferation, and cells use different mechanisms to sense and respond to Gln and Glc insufficiency. Our mRNA profiling database provides a resource for further investigating the nutrient-sensing mechanisms and potential effects of Glc and Gln abundance on the biological behaviors of cells.

Divergent modulation of neuronal differentiation by caspase-2 and -9

Human Ntera2/cl.D1 (NT2) cells treated with retinoic acid (RA) differentiate towards a well characterized neuronal phenotype sharing many features with human fetal neurons. In view of the emerging role of caspases in murine stem cell/neural precursor differentiation, caspases activity was evaluated during RA differentiation. Caspase-2, -3 and -9 activity was transiently and selectively increased in differentiating and non-apoptotic NT2-cells. SiRNA-mediated selective silencing of either caspase-2 (si-Casp2) or -9 (si-Casp9) was implemented in order to dissect the role of distinct caspases. The RA-induced expression of neuronal markers, i.e. neural cell adhesion molecule (NCAM), microtubule associated protein-2 (MAP2) and tyrosine hydroxylase (TH) mRNAs and proteins, was decreased in si-Casp9, but markedly increased in si-Casp2 cells. During RA-induced NT2 differentiation, the class III histone deacetylase Sirt1, a putative caspase substrate implicated in the regulation of the proneural bHLH MASH1 gene expression, was cleaved to a ∼100 kDa fragment. Sirt1 cleavage was markedly reduced in si-Casp9 cells, even though caspase-3 was normally activated, but was not affected (still cleaved) in si-Casp2 cells, despite a marked reduction of caspase-3 activity. The expression of MASH1 mRNA was higher and occurred earlier in si-Casp2 cells, while was reduced at early time points during differentiation in si-Casp9 cells. Thus, caspase-2 and -9 may perform opposite functions during RA-induced NT2 neuronal differentiation. While caspase-9 activation is relevant for proper neuronal differentiation, likely through the fine tuning of Sirt1 function, caspase-2 activation appears to hinder the RA-induced neuronal differentiation of NT2 cells.

Epigenetic code and self-identity

Epigenetics is a new and expanding science that studies the chromatin-based regulation of gene expression. It is achieving considerable importance, especially with regard to developmental mechanisms that drive cell and organ differentiation, as well as in all those biological processes that involve response and adaptation to environmental stimuli. One of the most interesting biological questions concerning animals, especially human beings, is the ability to distinguish self from nonself. This ability has developed throughout evolution, both as the main function of the immune system, which defends against attack by foreign organisms and at the level of consciousness of oneself as an individual, one of the highest functions of the brain that enables social life. Here we will attempt to dissect the epigenetic mechanisms involved in establishing these higher functions and describe some alterations of the epigenetic machinery responsible for the impairment of correct self-recognition and self-identity.

Novel cis-regulatory modules control expression of the Hairy and Enhancer of Split-1 (HES1) transcription factor in myoblasts

The expression profile of a gene is controlled by DNA sequences called cis-regulatory modules (CRMs). CRMs can function over large genomic distances and can be located many kilobases away from their target promoters. hes1 is a key developmental gene that is overexpressed in certain cancers and is a primary target of NOTCH signaling. Despite this, analysis of hes1 transcriptional control has been limited solely to its promoter. Here, we identify seven conserved DNA sequence blocks, representing the hes1 promoter and six novel CRMs, within 57 kb upstream of the mouse hes1 gene. We identify 12 binding sites for the RBP-Jκ NOTCH effector and a single M-CAT motif within these regions. We validate RBP-Jκ and TEAD family occupancy in cells in culture and test the response of each of these CRMs to active NOTCH. We show that two regions, CRM5 and CRM7, function as enhancers, and four can repress transcription. A pair of RBP-Jκ motifs arranged in a tail-tail configuration in CRM5 and the M-CAT motif in CRM7 are necessary for enhancer function. Furthermore, these enhancers are occupied by transcriptional co-activators and loop onto the hes1 promoter within the endogenous hes1 locus. This work demonstrates the power of combining computational genomics and experimental methodologies to identify novel CRMs and characterize their function.

SRT1720 improves survival and healthspan of obese mice

Sirt1 is an NAD⁺-dependent deacetylase that extends lifespan in lower organisms and improves metabolism and delays the onset of age-related diseases in mammals. Here we show that SRT1720, a synthetic compound that was identified for its ability to activate Sirt1 in vitro, extends both mean and maximum lifespan of adult mice fed a high-fat diet. This lifespan extension is accompanied by health benefits including reduced liver steatosis, increased insulin sensitivity, enhanced locomotor activity and normalization of gene expression profiles and markers of inflammation and apoptosis, all in the absence of any observable toxicity. Using a conditional SIRT1 knockout mouse and specific gene knockdowns we show SRT1720 affects mitochondrial respiration in a Sirt1- and PGC-1α-dependent manner. These findings indicate that SRT1720 has long-term benefits and demonstrate for the first time the feasibility of designing novel molecules that are safe and effective in promoting longevity and preventing multiple age-related diseases in mammals.

Sirt1 deacetylates c-Myc and promotes c-Myc/Max association

The c-Myc oncoprotein plays critical roles in multiple biological processes by controlling cell proliferation, apoptosis, differentiation, and metabolism. Especially, c-Myc is frequently overexpressed in many human cancers and widely involved in tumorigenesis. However, how the post-translational modifications, especially acetylation of c-Myc, contribute to its activity in the leukemia cells remains largely unknown. Sirt1, a NAD-dependent class III histone deacetylase, has a paradoxical role in tumorigenesis by deacetylating several transcription factors, including p53, E2F1 and forkhead proteins. In this study, we show that Sirt1 interacts physically with the C-terminus of c-Myc and deacetylates c-Myc both in vitro and in vivo. Moreover, the deacetylation of c-Myc by Sirt1 promotes its association with Max, a partner essential for its activation, thereby facilitating c-Myc transactivation activity on hTERT promoter. Finally, inhibition of endogenous Sirt1 in K562 cells by either RNAi or its inhibitor NAM causes the overall decrease of c-Myc target genes expression, including hTERT, cyclinD2 and LDHA, which further suppress cell proliferation and arrest cell cycle at G1/S phase. Thus, our results demonstrate the positive effect of Sirt1 on c-Myc activity by efficiently enhancing c-Myc/Max association in human leukemia cell line K562, suggesting a potential role of Sirt1 in tumorigenesis.

Mammalian Sirt1: insights on its biological functions

Sirt1 (member of the sirtuin family) is a nicotinamide adenosine dinucleotide (NAD)-dependent deacetylase that removes acetyl groups from various proteins. Sirt1 performs a wide variety of functions in biological systems. The current review focuses on the biological functions of Sirt1 in obesity-associated metabolic diseases, cancer, adipose tissue, aging, cellular senescence, cardiac aging and stress, prion-mediated neurodegeneration, inflammatory signaling in response to environmental stress, development and placental cell survival.

Modulations of hMOF autoacetylation by SIRT1 regulate hMOF recruitment and activities on the chromatin

A wide variety of nuclear regulators and enzymes are subjected to acetylation of the lysine residue, which regulates different aspects of protein functions. The MYST family histone acetyltransferase, human ortholog of MOF (hMOF), plays critical roles in transcription activation by acetylating nucleosomal H4K16. In this study, we found that hMOF acetylates itself in vitro and in vivo, and the acetylation is restricted to the conserved MYST domain (C2HC zinc finger and HAT), of which the K274 residue is the major autoacetylation site. Furthermore, the class III histone deacetylase SIRT1 was found to interact with the MYST domain of hMOF through the deacetylase catalytic region and deacetylate autoacetylated hMOF. In vitro binding assays showed that non-acetylated hMOF robustly binds to nucleosomes while acetylation decreases the binding ability. In HeLa cells, the recruitment of hMOF to the chromatin increases in response to SIRT1 overexpression and decreases after knockdown of SIRT1. The acetylation mimic mutation K274Q apparently decreases the chromatin recruitment of hMOF as well as the global H4K16Ac level in HeLa cells. Finally, upon SIRT1 knockdown, hMOF recruitment to the gene body region of its target gene HoxA9 decreases, accompanied with decrease of H4K16Ac at the same region and repression of HoxA9 transcription. These results suggest a dynamic interplay between SIRT1 and hMOF in regulating H4K16 acetylation.

Acetylation-dependent regulation of endothelial Notch signalling by the SIRT1 deacetylase

Notch signalling is a key intercellular communication mechanism that is essential for cell specification and tissue patterning, and which coordinates critical steps of blood vessel growth. Although subtle alterations in Notch activity suffice to elicit profound differences in endothelial behaviour and blood vessel formation, little is known about the regulation and adaptation of endothelial Notch responses. Here we report that the NAD(+)-dependent deacetylase SIRT1 acts as an intrinsic negative modulator of Notch signalling in endothelial cells. We show that acetylation of the Notch1 intracellular domain (NICD) on conserved lysines controls the amplitude and duration of Notch responses by altering NICD protein turnover. SIRT1 associates with NICD and functions as a NICD deacetylase, which opposes the acetylation-induced NICD stabilization. Consequently, endothelial cells lacking SIRT1 activity are sensitized to Notch signalling, resulting in impaired growth, sprout elongation and enhanced Notch target gene expression in response to DLL4 stimulation, thereby promoting a non-sprouting, stalk-cell-like phenotype. In vivo, inactivation of Sirt1 in zebrafish and mice causes reduced vascular branching and density as a consequence of enhanced Notch signalling. Our findings identify reversible acetylation of the NICD as a molecular mechanism to adapt the dynamics of Notch signalling, and indicate that SIRT1 acts as rheostat to fine-tune endothelial Notch responses.

Notch- and transducin-like enhancer of split (TLE)-dependent histone deacetylation explain interleukin 12 (IL-12) p70 inhibition by zymosan

The fungal analog zymosan induces IL-23 and low amounts of IL-12 p70. This study addresses the molecular mechanisms underlying this cytokine pattern in human monocyte-derived dendritic cells. The transcriptional regulation of il23a, one of the chains of IL-23, depended on the activation of c-Rel and histone H3 phosphorylation, as judged from the association of c-Rel with the il23a promoter and the correlation between IL-23 production and Ser-10-histone H3 phosphorylation. Consistent with its reduced ability to produce IL-12 p70, zymosan induced a transient occupancy of the il12a promoter by c-Rel, blocked the production of IL-12 p70 and the transcription of il12a induced by other stimuli, and triggered the expression and nuclear translocation of the transcriptional repressors of the Notch family hairy and enhancer of split (Hes)-1, Hes5, hairy/enhancer-of-split related with YRPW motif protein (Hey)-1, and transducin-like enhancer of split (TLE). Zymosan also induced the interaction of Hes1 and TLE with histone H3 phosphorylated on Ser-10 and deacetylated on Lys-14. Inhibition of class III histone deacetylases increased the production of IL-12 p70 and partially blunted the inhibitory effect of zymosan on the production of IL-12 p70 elicited by LPS and IFN-γ. These results indicate that the selective induction of IL-23 by β-glucans is explained by the activation of c-Rel associated with Ser-10-histone H3 phosphorylation in the il23a promoter mediated by mitogen- and stress-activated kinase and/or protein kinase A and inhibition of il12a transcription by a mechanism involving activation of several corepressors with the ability to bind TLE and to promote histone deacetylation.