Role of NAD-dependent deacetylases SIRT1 and SIRT2 in radiation and cisplatin-induced cell death in vertebrate cells

MHY2245, a Sirtuin Inhibitor, Induces Cell Cycle Arrest and Apoptosis in HCT116 Human Colorectal Cancer Cells

Sirtuins (SIRTs), which are nicotinamide adenine dinucleotide-dependent class III histone deacetylases, regulate cell division, survival, and senescence. Although sirtinol, a synthetic SIRT inhibitor, is known to exhibit antitumor effects, its mechanism of action is not well understood. Therefore, we aimed to assess the anticancer effects and underlying mechanism of MHY2245, a derivative of sirtinol, in HCT116 human colorectal cancer cells in vitro. Treatment with MHY2245 decreased SIRT1 activity and caused DNA damage, leading to the upregulation of p53 acetylation, and increased levels of p53, phosphorylation of H2A histone family member X, ataxia telangiectasia and Rad3-related kinase, checkpoint kinase 1 (Chk1), and Chk2. The level of the breast cancer type 1 susceptibility protein was also found to decrease. MHY2245 induced G2/M phase cell cycle arrest via the downregulation of cyclin B1, cell division cycle protein 2 (Cdc2), and Cdc25c. Further, MHY2245 induced HCT116 cell death via apoptosis, which was accompanied by internucleosomal DNA fragmentation, decreased B-cell lymphoma 2 (Bcl-2) levels, increased Bcl-2-asscociated X protein levels, cleavage of poly(ADP-ribose) polymerase, and activation of caspases -3, -8, and -9. Overall, MHY2245 induces cell cycle arrest, triggers apoptosis through caspase activation, and exhibits DNA damage response-associated anticancer effects.

Protective Effect of Sirt1 against Radiation-Induced Damage

Radiotherapy is an important method for the treatment of malignant tumors. It can directly or indirectly lead to the formation of free radicals and DNA damage, resulting in a series of biological effects, including tumor cell death and normal tissue damage. These radiation effects are typically accompanied by the abnormal expression of sirtuin 1 (Sirt1), which deacetylates histones and non-histones. These Sirt1 substrates, including transcription factors and some catalytic enzymes, play a crucial role in anti-oxidative stress, DNA damage repair, autophagy regulation, anti-senescence, and apoptosis, which are closely related to triggering cell defense and survival in radiation-induced damage. In this article, we review the mechanisms underlying cellular responses to ionizing radiation and the role of Sirt1 in the process, with the aim of providing a theoretical basis for protection against radiation by Sirt1 as well as novel targets for developing radioprotective agents.

Renoprotective effects of estrogen on acute kidney injury: the role of SIRT1

Acute kidney injury (AKI) is a common syndrome associated with high morbidity and mortality, despite progress in medical care. Many studies have shown that there are sex differences and different role of sex hormones particularly estrogens in kidney injury. In this regard, the incidence and rate of progression of kidney diseases are higher in men compared with women. These observations suggest that female sex hormone may be renoprotective. Silent information regulator 2 homolog 1 (SIRT1) is a histone deacetylase, which is implicated in multiple biologic processes in several organisms. In the kidneys, SIRT1 inhibits renal cell apoptosis, inflammation, and fibrosis. Studies have reported a link between SIRT1 and estrogen. In addition, SIRT1 regulates ERα expression and inhibition of SIRT1 activity suppresses ERα expression. This effect leads to inhibition of estrogen-responsive gene expression. In this text, we review the role of SIRT1 in mediating the protective effects of estrogen in the onset and progression of AKI.

SIRT2 is involved in cisplatin-induced acute kidney injury through regulation of mitogen-activated protein kinase phosphatase-1

BACKGROUND

Activation of mitogen-activated protein kinase phosphatase-1 (MKP-1), a dual-specificity protein phosphatase, regulates mitogen-activated protein kinase signaling. C-Jun N-terminal kinase (JNK) and p38 are activated in cisplatin-induced renal injury. However, the change of MKP-1 expression in cisplatin-induced renal injury and the regulatory effect of sirtuin 2 (SIRT2), a nicotinamide adenine dinucleotide-dependent deacetylase, on MKP-1 remains unknown.

METHODS

To address these issues, we used constitutional Sirt2 knockout (KO) mice, transgenic (TG) mice with increased expression of SIRT2 specifically in proximal tubular epithelial cellsand wild-type (WT) mice. Cisplatin nephrotoxicity was induced by intraperitoneal injection of cisplatin.

RESULTS

MKP-1 expression in the kidney was decreased after cisplatin treatment. Cisplatin-induced downregulation of MKP-1 was reversed in Sirt2 KO mice kidney and further decreased in Sirt2 TG mice kidney. We observed similar phenomenon with SIRT2-knockdown or SIRT2-overexpressed tubular epithelial cells. Phosphorylation of p38 and JNK, a downstream signal pathway of MKP-1, increased in WT mice kidney following treatment with cisplatin. A decrease in SIRT2 suppressed cisplatin-induced phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Overexpression of SIRT2 further increased phosphorylation of p38 and JNK in kidney and tubular epithelial cells. Acetylation of MKP-1 was significantly increased in SIRT2-knockdown cells and decreased in SIRT2-overexpressed cells after cisplatin stimulation. Sirt2 KO mice and Sirt2 TG mice showed amelioration and aggravation of renal injury, apoptosis, necroptosis and inflammation induced by cisplatin.

CONCLUSION

Our data show that SIRT2 is associated with cisplatin-induced renal injury through regulation of MKP-1 expression.

Intrathecal Injection of SIRT1-modified Human Mesenchymal Stem Cells Alleviates Neuropathic Pain in Rat

Accumulating evidence has elucidated that human mesenchymal stem cells (hMSCs) exert profound analgesic effects on numerous animal models of neuropathic pain, including drug-induced peripheral nerves, diabetes-induced neuropathy, and chronic constriction injury. We aimed to address whether forcing expression of sirtuin 1 (SIRT1) can enhance the efficacy of hMSCs on alleviation of pain sensation. A rat model of chronic constriction injury (CCI) mimicking peripheral nerve injury was incorporated in the study. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) testing were used to measure pain-related behavior. Our results demonstrated that SIRT1 was decreased post-CCI surgery. Compared to hMSCs-control implantation, the hMSCs-SIRT1 (hMSCs overexpressing SIRT1) implantation exhibited superior effects on reducing pro-inflammatory cytokine levels in serum and spinal dorsal horn, while ameliorating neuropathic pain in CCI rat. Engineering hMSCs such as overexpressing SIRT1 may serve as a promising strategy for the treatment of patients with neuropathic pain.

SIRT2 inhibition activates hypoxia-inducible factor 1α signaling and mediates neuronal survival

Sirtuins are deacetylases dependent on nicotine adenine dinucleotide (NAD) and take an important role in metabolism and aging. In mammals, there are seven sirtuins (SlRTl-7), and only SIRT2 is predominantly localized in cytoplasm. Under hypoxic environments, metazoan organisms must maintain oxygen homeostasis to survive. Hypoxia conditions induce reduction the ratio of NAD⁺/NADH, and aberrant increases or decreases in cellular O₂ concentration induced excessive reactive oxygen species generation. Here, we report that inhibition of SIRT2 stabilizes hypoxia-inducible factor 1α (HIF-1α) protein levels and enhances hypoxia-responsive element-containing gene expression. We also show that the SIRT2 inhibitor AGK2 induces VEGF and HO-1 gene expression and protects neuronal viability from oxidative stress. Our findings suggest that SIRT2 negatively regulates HIF-1α signaling, indicating that SIRT2 inhibition may be a useful treatment strategy following ischemic injury.

The Antiangiogenesis Role of Histone Deacetylase Inhibitors: Their Potential Application to Tumor Therapy and Tissue Repair

Angiogenesis, a process of new blood vessel formation from existing blood vessels, plays an important role in tumor growth and the tissue repair process. It is generally acknowledged that angiogenesis might contribute two both processes. In tumor growth, angiogenesis often increases oncogenic signaling, and in tissue repair, it decreases the stiffness of wound tissue and potentially exacerbates scar formation, resulting in pain and poor function. These poor outcomes are due to an increase in the expression of important genes involved in angiogenesis, such as hypoxia-inducible factor-1 alpha (HIF-1α) and its transcriptional target vascular endothelial growth factor (VEGF). Therefore, this adverse effect of angiogenesis should be taken into consideration. Limiting vessel growth instead of boosting growth may be beneficial for favorable long-term healing outcomes. Posttranslational modifications, including acetylation, which is mediated by histone acetyltransferases, and deacetylation, which is mediated by histone deacetylases (HDACs), are critical to HIF-1α function. Most studies have indicated that HDAC inhibitors (HDACIs) show great promise as antiangiogenic agents in the early phase of clinical trials. In this review, we discuss the role of the HDACs HIF-1α and VEGF in angiogenesis. Furthermore, we also discuss the molecular and cellular underpinnings of the effects of HDACIs on antiangiogenesis, which creates new avenues for anticancer therapeutics and the repair of wounded tissue.

Lapatinib sensitivity in nasopharyngeal carcinoma is modulated by SIRT2-mediated FOXO3 deacetylation

Background

Chemoresistance is an obstacle to the successful treatment of nasopharyngeal carcinoma (NPC). Lapatinib is a targeted tyrosine kinase inhibitor therapeutic drug also used to treat NPC, but high doses are often required to achieve a result. To investigate the mechanism for the development of Lapatinib resistance, we characterised a number of NPC cell lines to determine the role of FOXO3 and sirtuins in regulating NPC resistance.

Methods

Sulforhodamine B (SRB) assays, Clonogenic assays, Protein extraction, quantification and western blotting, RT qPCR, Co-immunoprecipitation assay.

Results

To explore novel treatment strategies, we first characterized the Lapatinib-sensitivity of a panel of NPC cell lines by SRB and clonogenic cytotoxic assays and found that the metastatic NPC (C666–1 and 5-8F) cells are highly resistant whereas the poorly metastatic lines (6-10B, TW01 and HK-1) are sensitive to Lapatinib. Western blot analysis of the Lapatinib-sensitive 6-10B and resistant 5-8F NPC cells showed that the expression of phosphorylated/inactive FOXO3 (P-FOXO3;T32), its target FOXM1 and its regulator SIRT2 correlate negatively with Lapatinib response and sensitivity, suggesting that SIRT2 mediates FOXO3 deacetylation to promote Lapatinib resistance. In agreement, clonogenic cytotoxic assays using wild-type and foxo1/3/4^−/− mouse embryonic fibroblasts (MEFs) showed that FOXO1/3/4-deletion significantly attenuates Lapatinib-induced cytotoxicity, confirming that FOXO proteins are essential for mediating Lapatinib response. SRB cell viability assays using chemical SIRT inhibitors (i.e. sirtinol, Ex527, AGK2 and AK1) revealed that all SIRT inhibitors can reduce NPC cell viability, but only the SIRT2-specific inhibitors AK1 and AGK2 further enhance the Lapatinib cytotoxicity. Consistently, clonogenic assays demonstrated that the SIRT2 inhibitors AK1 and AGK2 as well as SIRT2-knockdown increase Lapatinib cytotoxicity further in both the sensitive and resistant NPC cells. Co-immunoprecipitation studies showed that besides Lapatinib treatment, SIRT2-pharmaceutical inhibition and silencing also led to an increase in FOXO3 acetylation. Importantly, SIRT2 inhibition and depletion further enhanced Lapatinib-mediated FOXO3-acetylation in NPC cells.

Conclusion

Collectively, our results suggest the involvement of SIRT2-mediated FOXO3 deacetylation in Lapatinib response and sensitivity, and that SIRT2 can specifically antagonise the cytotoxicity of Lapatinib through mediating FOXO3 deacetylation in both sensitive and resistant NPC cells. The present findings also propose that SIRT2 can be an important biomarker for metastatic and Lapatinib resistant NPC and that targeting the SIRT2-FOXO3 axis may provide novel strategies for treating NPC and for overcoming chemoresistance.

Ovarian Follicle Depletion Induced by Chemotherapy and the Investigational Stages of Potential Fertility-Protective Treatments-A Review

Ovarian follicle pool depletion, infertility, and premature menopause are all known sequelae of cancer treatment that negatively impact the quality of life of young cancer survivors. The mechanisms involved in this undesired iatrogenic ovarian damage have been intensively studied, but many of them remain unclear. Several chemotherapeutic drugs have been shown to induce direct and indirect DNA-damage and/or cellular stress, which are often followed by apoptosis and/or autophagy. Damage to the ovarian micro-vessel network induced by chemotherapeutic agents also seems to contribute to ovarian dysfunction. Another proposed mechanism behind ovarian follicle pool depletion is the overactivation of primordial follicles from the quiescent pool; however, current experimental data are inconsistent regarding these effects. There is great interest in characterizing the mechanisms involved in ovarian damage because this might lead to the identification of potentially protective substances as possible future therapeutics. Research in this field is still at an experimental stage, and further investigations are needed to develop effective and individualized treatments for clinical application. This review provides an overview of the current knowledge and the proposed hypothesis behind chemotherapy-induced ovarian damage, as well as current knowledge on possible co-treatments that might protect the ovary and the follicles from such damages.

Stabilization of P/CAF, as a ubiquitin ligase toward MDM2, suppresses mitotic cell death through p53-p21 activation in HCT116 cells with SIRT2 suppression

We previously reported that the suppression of SIRT2, an NAD + -dependent protein deacetylases, induces p53 accumulation via degradation of p300 and the subsequent MDM2 degradation, eventually leading to apoptosis in HeLa cells. The present study identified a novel pathway of p53 accumulation by SIRT2 suppression in HCT116(p53+/+) cells in which SIRT2 suppression led to escape from mitotic cell death caused by spindle assembly checkpoint activation induced by microtubule inhibitors such as nocodazole but not apoptosis or G1 or G2 arrest. We found that SIRT2 interacts with P/CAF, a histone acetyltransferase, which also acts as a ubiquitin ligase against MDM2. SIRT2 suppression led to an increase of P/CAF acetylation and its stabilization followed by a decrease in MDM2 and activation of the p53-p21 pathway. Depression of mitotic cell death in HCT116(p53+/+) cells with SIRT2 suppression was released by suppression of P/CAF or p21. Thus, the P/CAF-MDM2-p53-p21 axis enables the escape from mitotic cell death and confers resistance to nocodazole in HCT116(p53+/+) cells with SIRT2 suppression. As SIRT2 has attracted attention as a potential target for cancer therapeutics for p53 regulation, the present study provides a molecular basis for the efficacy of SIRT2 for future cancer therapy based on p53 regulation. These findings also suggest an undesirable function of the SIRT2 suppression associated with activation of the p53-p21 pathway in the suppression of mitotic cell death caused by spindle assembly checkpoint activation.

Novel small molecule SIRT2 inhibitors induce cell death in leukemic cell lines

BACKGROUND

Sirtuin 2 (SIRT2) is a member of the sirtuin family, nicotinamide adenine dinucleotide⁺-dependent deacylases, which participates in modulation of cell cycle control, neurodegeneration, and tumorigenesis. SIRT2 expression increases in acute myeloid leukemia blasts. Downregulation of SIRT2 using siRNA causes apoptosis of HeLa cells. Therefore, selective inhibitors of SIRT2 are candidate therapeutic agents for cancer. Adult T-cell leukemia/lymphoma (ATL) is a T-cell malignancy that has a poor prognosis and develops after long-term infection with human T-cell leukemia virus (HTLV)-1. Sirtuin 1 inhibition has been shown to induce apoptosis and autophagy in HTLV-1-infected cell lines, whereas the effects of SIRT2 inhibition alone have not been elucidated.

METHODS

We assessed the efficacy of our small molecule selective SIRT2 inhibitors NCO-90/141 to induce leukemic cell death. Cell viability was examined using the cell proliferation reagent Cell Count Reagent SF. Apoptotic cells were detected by annexin V-FITC and terminal deoxynucleotidyl transferase dUTP nick end labeling assays by flow cytometry. Caspase activity was detected using an APOPCYTO Intracellular Caspase Activity Detection Kit. The presence of autophagic vacuoles was assessed using a Cyto-ID Autophagy Detection Kit.

RESULTS

Our novel small molecule SIRT2-specific inhibitors NCO-90/141 inhibited cell growth of leukemic cell lines including HTLV-1-transformed T-cells. NCO-90/141 induced apoptosis via caspase activation and mitochondrial superoxide generation in leukemic cell lines. However, a caspase inhibitor did not prevent this caspase-associated cell death. Interestingly, NCO-90/141 increased the LC3-II level together with autophagosome accumulation, indicating autophagic cell death. Thus, NCO-90/141 simultaneously caused apoptosis and autophagy.

CONCLUSIONS

These results suggest that NCO-90/141 are highly effective against leukemic cells in caspase-dependent or -independent manners via autophagy, and they may have a novel therapeutic potential for treatment of leukemias including ATL.

Dichloroacetic acid (DCA) synergizes with the SIRT2 inhibitor Sirtinol and AGK2 to enhance anti-tumor efficacy in non-small cell lung cancer

Combination chemotherapy is a potentially promising approach to enhance anticancer activity, overcome drug resistance, and improve disease-free and overall survival. The current study investigates the antitumor activity of sodium dichloroacetic acid (DCA) in combination with SIRT2 inhibitor Sirtinol and AGK2. We found that combining DCA with Sirtinol produced a synergistic therapeutic benefit in A549 and H1299 NSCLC cells in vitro and in a mouse A549 xenograft model. Synergistic potentiation of oxidative phosphorylation (OXPHOS) was observed, including decreased glucose consumption, decreased lactate production, increased OCR and increased ROS generation, possibly via co-targeting pyruvate dehydrogenase alpha 1(PDHA1). Mechanically, AGK2 and Sirtinol were found to increase the lysine-acetylation and decrease the serine-phosphorylation of PDHA1, which enabled the two inhibitors to synergize with DCA to further activate PDHA1. Besides, a AMPKα-ROS feed-forward loop was notably activated after the combined treatments compared with mono-therapy. Our results indicate that the combination of DCA and SIRT2 inhibitor may provide a promising therapeutic strategy to effectively kill cancer cells.

The clinicopathological significance of SIRT1 expression in colon cancer: An immunohistochemical study and meta-analysis

OBJECTIVE

The aim of this study was to determine the clinicopathological significance and potential prognostic role of SIRT1 expression in colorectal cancer (CRC) using immunohistochemistry and meta-analysis.

METHODS

Immunohistochemistry was performed on 265 archival paraffin-embedded human CRC specimens to investigate the correlation between SIRT1 expression and clinicopathological characteristics, including patient survival. To elucidate the potential prognostic value of SIRT1 expression, a meta-analysis was performed using data on 2132 patients from eight eligible studies.

RESULTS

SIRT1 was highly expressed in 24.5% of the 265 CRC specimens analyzed. High SIRT1 expression correlated with vascular invasion (P =  0.041). High SIRT1 expression also significantly correlated with expression of SNAI (P =  0.001), but not E-cadherin (P =  0.958). However, there was no significant correlation between SIRT1 expression and other clinicopathological parameters. High SIRT1 expression in the CRC specimens significantly correlated with a worse overall survival rate, independent of SNAI expression. However, based on the meta-analysis, high SIRT1 expression was not significantly correlated with overall survival rates [hazard ratio (HR) 1.111, 95% confidential interval (CI) 0.799-1.544].

CONCLUSION

In our retrospective study, high SIRT1 expression significantly correlated with vascular invasion and a worse prognosis. However, because the results from the meta-analysis differed the retrospective arm of our study, additional cumulative studies are needed to determine the prognostic value of SIRT1 in CRC.

Sirtuin 2 mutations in human cancers impair its function in genome maintenance

mutations in genome maintenance and tumor suppression.

The expression of SIRT1 regulates the metastaticplasticity of chondrosarcoma cells by inducing epithelial-mesenchymal transition

SIRT1 belongs to the mammalian sirtuin family and plays an important role in deacetylating histone and nonhistone proteins. It is reported that SIRT1 is associated with tumor metastasis in several kinds of tumors. However, the effect of SIRT1 on the metastasis of chondrosarcoma cells is still unknown. In this study, we demonstrated that up and down-regulation of SIRT1 expression could significantly change the invasive and metastatic potential in chondrosarcoma cell line. Besides that, the result from the nude mice confirmed the effect of SIRT1 on metastasis of chondrosarcoma cells. Furthermore, we also found that SIRT1 effectively enhanced the metastasis by inducing epithelial-mesenchymal transition (EMT) in chondrosarcoma cells. Inhibition the expression of SIRT1 could block the incidence of metastasis and EMT in chondrosarcoma cells. In addition, we also observed that SIRT1 could enhance the expression of Twist which is a key transcriptional factor of EMT. A clinicopathological analysis showed that SIRT1 expression was significantly correlated with the poor prognosis of pelvis chondrosarcoma. Kaplan-Meier survival curves revealed that positive SIRT1 expression was associated with poor prognosis in patients with pelvis chondrosarcoma. Taken together, these results indicate that SIRT1 may promote the metastasis of chondrosarcoma by inducing EMT and can be a potential molecular target for chondrosarcoma therapy.

Sirt1 expression is associated with CD31 expression in blood cells from patients with chronic obstructive pulmonary disease

Background

Cigarette smoke induced oxidative stress has been shown to reduce silent information regulator 1 (Sirt1) levels in lung tissue from smokers and patients with COPD patients. Sirt1 is known to inhibit endothelial senescence and may play a protective role in vascular cells. Endothelial progenitor cells (EPCs) are mobilized into circulation under various pathophysiological conditions, and are thought to play an important role in tissue repair in chronic obstructive lung disease (COPD). Therefore, Sirt1 and EPC-associated mRNAs were measured in blood samples from patients with COPD and from cultured CD34⁺ progenitor cells to examine whether these genes are associated with COPD development.

Methods

This study included 358 patients with a smoking history of more than 10 pack-years. RNA was extracted from blood samples and from CD34⁺ progenitor cells treated with cigarette smoke extract (CSE), followed by assessment of CD31, CD34, Sirt1 mRNA, miR-34a, and miR-126-3p expression by real-time RT-PCR.

Results

The expression of CD31, CD34, Sirt1 mRNAs, and miR-126-3p decreased and that of miR-34a increased in moderate COPD compared with that in control smokers. However, no significant differences in these genes were observed in blood cells from patients with severe COPD compared with those in control smokers. CSE significantly decreased Sirt1 and increased miR-34a expression in cultured progenitor cells.

Conclusion

Sirt1 expression in blood cells from patients with COPD could be a biomarker for disease stability in patients with moderate COPD. MiR-34a may participate in apoptosis and/or senescence of EPCs in smokers. Decreased expression of CD31, CD34, and miR-126-3p potentially represents decreased numbers of EPCs in blood cell from patients with COPD.

Regulation of B cell differentiation by the ubiquitin-binding protein TAX1BP1

Tax1-binding protein 1 (TAX1BP1) is a ubiquitin-binding protein that restricts nuclear factor-κB (NF-κB) activation and facilitates the termination of aberrant inflammation. However, its roles in B-cell activation and differentiation are poorly understood. To evaluate the function of TAX1BP1 in B cells, we established TAX1BP1-deficient DT40 B cells that are hyper-responsive to CD40-induced extracellular signal-regulated kinase (ERK) activation signaling, exhibit prolonged and exaggerated ERK phosphorylation and show enhanced B lymphocyte-induced maturation protein 1 (Blimp-1; a transcription factor inducing plasma cell differentiation) expression that is ERK-dependent. Furthermore, TAX1BP1-deficient cells exhibit significantly decreased surface IgM expression and increased IgM secretion. Moreover, TAX1BP1-deficient mice display reduced germinal center formation and antigen-specific antibody production. These findings show that TAX1BP1 restricts ERK activation and Blimp-1 expression and regulates germinal center formation.

Nicotinamide Phosphoribosyltransferase Upregulation by Phenylephrine Reduces Radiation Injury in Submandibular Gland

PURPOSE

Radiation therapy for head and neck cancer commonly leads to radiation sialadenitis. Emerging evidence has indicated that phenylephrine pretreatment reduces radiosensitivity in the salivary gland; however, the underlying cytoprotective mechanism remains unclear. Nicotinamide phosphoribosyltransferase (NAMPT) is not only a key enzyme for the nicotinamide adenine dinucleotide salvage pathway, but also a cytokine participating in cell survival, metabolism, and longevity, with a broad effect on cellular functions in physiology and pathology. However, the regulatory events of NAMPT in response to the irradiated salivary gland are unknown.

METHODS AND MATERIALS

The cell viability of primary cultured submandibular gland cells was determined using the PrestoBlue assay. NAMPT expression was measured using reverse transcriptase polymerase chain reaction and Western blotting in vitro and in vivo. Silent information regulator 1 (SIRT1) and phosphorylated Akt protein levels were examined by Western blotting. The cellular locations of NAMPT and SIRT1 were detected by immunohistochemistry. NAMPT promoter activity was assessed using the luciferase reporter gene assay.

RESULTS

NAMPT was mainly distributed in the cytoplasm of granular convoluted tubule cells and ductal cells in normal submandibular glands. mRNA and protein expression of NAMPT was downregulated after radiation but upregulated with phenylephrine pretreatment both in vivo and in vitro. Moreover, the protein expression of phosphorylated Akt and SIRT1 was decreased in irradiated glands, and phenylephrine pretreatment restored the expression of both. SIRT1 was mainly located in the cell nucleus and cytoplasm in the normal submandibular gland. Phenylephrine dramatically enhanced the expression of SIRT1, which was significantly reduced by radiation. Furthermore, phenylephrine induced a marked increase of NAMPT promoter activity.

CONCLUSIONS

These findings reveal the regulatory mechanisms of NAMPT expression, which help to understand the mechanism of the cytoprotective role of phenylephrine on irradiated tissues.

SIRT2 mediates multidrug resistance in acute myelogenous leukemia cells via ERK1/2 signaling pathway

SIRT2, one of nicotinamide adenine dinucleotide (NAD+)-dependent class Ⅲ histone deacetylase family proteins, has been found to be involved in the proliferation and survival of acute myeloid leukemia (AML) cells. However, its effect on drug resistance on chemoresistant AML cells is unclear. In the present study, we first found that SIRT2 was expressed at higher level in the relapsed AML patients than the newly diagnosed patients. Consistent with this observation, the expression level of SIRT2 was higher in HL60/A cells than that in HL60 cells. Depletion of SIRT2 by shRNAs in HL60/A cells resulted in decreased MRP1 level, enhanced drug accumulation and triggered more apoptosis. By contrast, overexpression of SIRT2 in HL60 cells led to increased MRP1 level, drug efflux and attenuated drug sensitivity. Moreover, the decreased expression of phosphorylated ERK1/2 was detected in SIRT2-depleted HL60/A cells and increased expression of phosphorylated ERK1/2 was observed in SIRT2 overexpressed HL60 cells. Furthermore, blockage of ERK1/2 signaling pathway with the chemical inhibitor PD98059, further induced apoptosis of HL60/A cells conferred by SIRT2 depletion. Importantly, ERK1/2 inhibition was able to reverse the drug resistance of HL60 conferred by SIRT2 overexpression. Thus, our findings collectively suggested that the expression level of SIRT2 has a positive relationship with DNR/Ara-C resistance and activity of ERK1/2 signaling pathway. SIRT2 might regulate DNR/Ara-C sensitivity in AML cells at least partially through the ERK1/2 pathway.

Deletion of NAD(P)H:quinone oxidoreductase 1 represses Mre11-Rad50-Nbs1 complex protein expression in cisplatin-induced nephrotoxicity

The Mre11, Rad50, and Nbs1 (MRN) complex is a DNA double-strand break sensor involved in DNA damage repair. Herein, we explored whether deletion of

NAD(P)H

quinone oxidoreductase 1 (NQO1), a cytoprotective gene, affected MRN complex expression in the kidney after cisplatin-induced acute kidney injury (AKI). In vitro, cisplatin increased the expression of MRN complex proteins and NQO1 in NQO1-expressing ACHN cells in a time- and concentration-dependent manner. The expression of MRN complex proteins was relatively inhibited in NQO1-knockdown cells. In vivo, increased expression of renal MRN complex proteins was accompanied by upregulation of γ-H2A histone member X, a DNA damage marker, in cisplatin-treated wild-type mice. Although the NQO1-knockout (NQO1(-/-)) mice showed more severe cisplatin-induced renal damage, the renal expression of MRN complex proteins was lower than in NQO1-expressing mice; expression of poly[ADP-ribose] polymerase 1, which promotes MRN complex accumulation, was also lower in these animals. In addition, cisplatin-induced expression of DNA damage repair-related proteins, ataxia telangiectasia mutated and sirtuin1, markedly decreased in the NQO1(-/-) group, relative to the NQO1-expressing mice. These findings suggest that NQO1 deletion might be associated with decreased MRN complex expression, which might be partially responsible for the exacerbation of cisplatin-induced AKI in the absence of NQO1.

Group IVA Cytosolic Phospholipase A2 Regulates the G2-to-M Transition by Modulating the Activity of Tumor Suppressor SIRT2

The G2-to-M transition (or prophase) checkpoint of the cell cycle is a critical regulator of mitotic entry. SIRT2, a tumor suppressor gene, contributes to the control of this checkpoint by blocking mitotic entry under cellular stress. However, the mechanism underlying both SIRT2 activation and regulation of the G2-to-M transition remains largely unknown. Here, we report the formation of a multiprotein complex at the G2-to-M transition in vitro and in vivo. Group IVA cytosolic phospholipase A2 (cPLA2α) acts as a bridge in this complex to promote binding of SIRT2 to cyclin A-Cdk2. Cyclin A-Cdk2 then phosphorylates SIRT2 at Ser331. This phosphorylation reduces SIRT2 catalytic activity and its binding affinity to centrosomes and mitotic spindles, promoting G2-to-M transition. We show that the inhibitory effect of cPLA2α on SIRT2 activity impacts various cellular processes, including cellular levels of histone H4 acetylated at K16 (Ac-H4K16) and Ac-α-tubulin. This regulatory effect of cPLA2α on SIRT2 defines a novel function of cPLA2α independent of its phospholipase activity and may have implications for the impact of SIRT2-related effects on tumorigenesis and age-related diseases.

MicroRNA‑34a induces apoptosis in PC12 cells by reducing B‑cell lymphoma 2 and sirtuin‑1 expression

MicroRNA-34a (miR-34a) is a direct target of p53 and was reported to induce cell cycle arrest, apoptosis and senescence. Inhibition of the NAD-dependent deacetylase sirtuin-1 (SIRT1) by miR-34a leads to an increase in acetylated p53, which promotes cell apoptosis. B-cell lymphoma 2 (Bcl-2) is also involved in apoptosis, and was originally characterized with respect to its role in controlling outer mitochondrial membrane integrity. The effect of miR-34a in PC12 cells has not yet been reported. In the present study, it was hypothesized that Bcl-2 and SIRT1 may be critical downstream targets of miR-34a that participate in apoptosis induction. miR-34a mimics and inhibitors were transfected into PC12 cells, and the apoptosis and proliferation rates were compared between groups. It was demonstrated that induction of miR-34a promotes apoptosis and senescence, inhibits proliferation, and leads to marked alterations in SIRT1, Bcl-12 and acetyl (ac)-p53 expression. These data indicate that miR-34a may be important in neuropathy.

Overexpression of SIRT1 promotes metastasis through epithelial-mesenchymal transition in hepatocellular carcinoma

BACKGROUND

SIRT1 is a member of the mammalian sirtuin family with the ability to deacetylate histone and nonhistone proteins. The correlation between SIRT1 expression and tumor metastasis in several types of cancer has aroused widespread concern. This study investigated SIRT1 expression and its prognostic value in hepatocellular carcinoma (HCC). The function of SIRT1 in hepatocarcinogenesis was further investigated in cell culture and mouse models.

METHODS

Western blotting and immunohistochemistry were used to explore SIRT1 expression in HCC cell lines and primary HCC clinical specimens. The functions of SIRT1 in the migration and invasion in the HCC cell line were analyzed by infecting cells with adenovirus containing full-length SIRT1 or sh-RNA. The effect of SIRT1 on tumorigenicity in nude mice was also investigated.

RESULTS

SIRT1 expression was significantly overexpressed in the tumor tissues and HCC cell lines. SIRT1 significantly promoted the ability of migration and invasion in HCC cells. In addition, experiments with a mouse model revealed that SIRT1 overexpression enhanced HCC tumor metastasis in vivo. Furthermore, we demonstrated that SIRT1 significantly enhanced the invasive and metastatic potential by inducing epithelial-mesenchymal transition in HCC cells. A clinicopathological analysis showed that SIRT1 expression was significantly correlated with tumor size, tumor number, and TNM staging. Kaplan-Meier survival curves revealed that positive SIRT1 expression was associated with poor prognosis in patients with HCC.

CONCLUSIONS

Our data suggest that SIRT1 may play an important role in HCC progression and could be a potential molecular therapy target for HCC.

Anticancer agents targeted to sirtuins

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

SIRT2 interacts with β-catenin to inhibit Wnt signaling output in response to radiation-induced stress

Wnt signaling is critical to maintaining cellular homeostasis via regulation of cell division, mitigation of cell stress, and degradation. Aberrations in Wnt signaling contribute to carcinogenesis and metastasis, whereas sirtuins have purported roles in carcinogenesis, aging, and neurodegeneration. Therefore, the hypothesis that sirtuin 2 (SIRT2) directly interacts with β-catenin and whether this interaction alters the expression of Wnt target genes to produce an altered cellular phenotype was tested. Coimmunoprecipitation studies, using mouse embryonic fibroblasts (MEF) from Sirt2 wild-type and genomic knockout mice, demonstrate that β-catenin directly binds SIRT2. Moreover, this interaction increases in response to oxidative stress induced by ionizing radiation. In addition, this association inhibits the expression of important Wnt target genes such as survivin (BIRC5), cyclin D1 (CCND1), and c-myc (MYC). In Sirt2 null MEFs, an upregulation of matrix metalloproteinase 9 (MMP9) and decreased E-cadherin (CDH1) expression is observed that produces increased cellular migration and invasion. Together, these data demonstrate that SIRT2, a tumor suppressor lost in multiple cancers, inhibits the Wnt signaling pathway in nonmalignant cells by binding to β-catenin and that SIRT2 plays a critical role in the response to oxidative stress from radiation.

IMPLICATIONS

Disruption of the SIRT2-β-catenin interaction represents an endogenous therapeutic target to prevent transformation and preserve the integrity of aging cells against exogenous stressors such as reactive oxygen species.

Prevention of chemotherapy-induced ovarian damage: possible roles for hormonal and non-hormonal attenuating agents

BACKGROUND

Current options for female fertility preservation in the face of cytotoxic treatments include embryo, oocyte and ovarian tissue cryopreservation. However these methods are limited by the patient age, status or available timeframe before treatment and they necessitate invasive procedures. Agents which can prevent or attenuate the ovotoxic effects of treatment would provide significant advantages over the existing fertility preservation techniques, and would allow patients to retain their natural fertility without the necessity for costly, invasive and risky procedures. Recent studies have contributed to our understanding of the mechanisms involved in cytotoxicity-induced ovarian follicle loss and highlight a number of agents that may be able to prevent or reduce this loss.

METHODS

This paper reviews the relevant literature (research articles published in English up to December 2013) on the mechanisms of cytotoxic-induced ovarian damage and the implications for fertility preservation. We present a comprehensive discussion of the potential agents that have been shown to preserve the ovarian follicle reserve in the face of cytotoxic treatments, including an analysis of their respective advantages and risks, and mechanisms of action.

RESULTS

Multiple molecular pathways are involved in the cellular response to cytotoxic treatments, and specific cellular reactions depend on variables including the drug class and dose, cell type, and cell stage. A number of agents acting on different elements of these pathways have demonstrated potential for preventing or reducing ovarian follicle loss, although in most cases, the studies are still very preliminary.

CONCLUSIONS

Advances in our understanding of the mechanisms and pathways involved in both cytotoxic ovarian damage and follicle growth and development have opened up new directions for fertility preservation. In order to bring these agents from the lab to the clinic, it will be vital to accurately evaluate the efficacy of each agent and additionally to demonstrate that co-treatment with these agents will not interfere with the anti-cancer activity of the chemotherapy drugs, or produce genetically comprised embryos.

SIRT1/PARP1 crosstalk: connecting DNA damage and metabolism

An intricate network regulates the activities of SIRT1 and PARP1 proteins and continues to be uncovered. Both SIRT1 and PARP1 share a common co-factor nicotinamide adenine dinucleotide (NAD+) and several common substrates, including regulators of DNA damage response and circadian rhythms. We review this complex network using an interactive Molecular Interaction Map (MIM) to explore the interplay between these two proteins. Here we discuss how NAD + competition and post-transcriptional/translational feedback mechanisms create a regulatory network sensitive to environmental cues, such as genotoxic stress and metabolic states, and examine the role of those interactions in DNA repair and ultimately, cell fate decisions.

E. coli endotoxin modulates the expression of Sirtuin proteins in PBMC in humans

Background. Sirtuin (SIRT) proteins are class I histone deacetylases displaying gene regulatory functions in inflammatory, cancer, and metabolic diseases. These SIRT actions involve the nuclear factor κB and its inhibitor IκB pathway. However, the regulation of SIRT in vivo is still unclear. Material and Methods. In a human endotoxemia model, 20 healthy male subjects received an intravenous bolus of 2 ng/kg body weight Escherichia coli endotoxin (LPS). SIRT expression was investigated in peripheral blood mononuclear cells (PBMC) with qPCR and Western blot before and 3 hours, 6 hours, and 24 hours after LPS challenge. Additionally, SIRT regulation was studied in vitro in cultivated PBMC after incubation with 20 ng/mL LPS. Results. A downregulation by >40% of SIRT1 mRNA was detectable 3 hours after LPS and of SIRT3 mRNA 6 hours after LPS. SIRT3, IκBα, and IκB-β protein expressions were decreased 3 and 6 hours after LPS. SIRT2 mRNA or protein expression did not change following LPS. These findings were consistent in vitro and associated with augmented phosphorylation of IκB-β. Discussion. In this E. coli endotoxemia model, SIRT1 and SIRT3 mRNA expressions in PBMC in humans were reduced after LPS challenge. This suggests that SIRT may represent an inflammatory target protein in vivo.

SIRT1 expression is associated with the chemotherapy response and prognosis of patients with advanced NSCLC

Aim

The role of Sirtuin 1 (SIRT 1) in carcinogenesis is controversial. This study was to explore the association between the SIRT1 expression and the clinical characteristics, the responsiveness to chemotherapy and prognosis in Non-small cell lung cancer (NSCLC).

Methods

We enrolled 295 patients with inoperable advanced stage of NSCLC, namely, stage III (A+B) and IV NSCLC. All patients had received platinum-based chemotherapy after diagnosis and the chemotherapy response were evaluated. All patients were followed up for overall survival (OS) and progression free survival (PFS). Invitro, H292 cells were tranfected with SIRT1 small interfering RNA (siRNA). The cell biological behaviors and chemosensitivity to cisplatin treatment were studied. The invivo tumorgenesis and metastasis assays were performed in nude mice.

Results

We found that the SIRT1 expressions were significantly associated with the tumor stage, tumor size and differentiation status. Patients with high SIRT 1 expressions had a significantly higher chance to be resistant to chemotherapy than those with low SIRT 1 expression. Patients with high expression of SIRT1 had significantly shorter OS and DFS than those with low expression. Cox analyses confirmed that the SIRT 1 expression was a strong predictor for a poor OS and PFS in NSCLC patients underwent Platinum-based chemotherapy. Invitro studies revealed that the reduced expression SIRT 1 by siRNA technique significantly inhibited cell proliferation, migration and invasion. More importantly, SIRT1 si-RNA significantly enhanced the chemosensitivity of H292 cells to cisplatin treatment. The invivo tumorgenesis and metastasis assays showed that SIRT1 knockdown dramatically reduced the tumor volume and the metastatic ability in nude mice.

Conclusion

Collectively, our data suggest that the SIRT1 expression may be a molecular marker associated with the NSLCLC clinical features, treatment responsiveness and prognosis of advanced NSCLC.

SIRT2 directs the replication stress response through CDK9 deacetylation

Sirtuin 2 (SIRT2) is a sirtuin family deacetylase that directs acetylome signaling, protects genome integrity, and is a murine tumor suppressor. We show that SIRT2 directs replication stress responses by regulating the activity of cyclin-dependent kinase 9 (CDK9), a protein required for recovery from replication arrest. SIRT2 deficiency results in replication stress sensitivity, impairment in recovery from replication arrest, spontaneous accumulation of replication protein A to foci and chromatin, and a G2/M checkpoint deficit. SIRT2 interacts with and deacetylates CDK9 at lysine 48 in response to replication stress in a manner that is partially dependent on ataxia telangiectasia and Rad3 related (ATR) but not cyclin T or K, thereby stimulating CDK9 kinase activity and promoting recovery from replication arrest. Moreover, wild-type, but not acetylated CDK9, alleviates the replication stress response impairment of SIRT2 deficiency. Collectively, our results define a function for SIRT2 in regulating checkpoint pathways that respond to replication stress through deacetylation of CDK9, providing insight into how SIRT2 maintains genome integrity and a unique mechanism by which SIRT2 may function, at least in part, as a tumor suppressor protein.

Inhibition of the NAD-dependent protein deacetylase SIRT2 induces granulocytic differentiation in human leukemia cells

Sirtuins, NAD-dependent protein deacetylases, play important roles in cellular functions such as metabolism and differentiation. Whether sirtuins function in tumorigenesis is still controversial, but sirtuins are aberrantly expressed in tumors, which may keep cancerous cells undifferentiated. Therefore, we investigated whether the inhibition of sirtuin family proteins induces cellular differentiation in leukemic cells. The sirtuin inhibitors tenovin-6 and BML-266 induce granulocytic differentiation in the acute promyelocytic leukemia (APL) cell line NB4. This differentiation is likely caused by an inhibition of SIRT2 deacetylase activity, judging from the accumulation of acetylated α-tubulin, a major SIRT2 substrate. Unlike the clinically used differentiation inducer all-trans retinoic acid, tenovin-6 shows limited effects on promyelocytic leukemia-retinoic acid receptor α (PML-RAR-α) stability and promyelocytic leukemia nuclear body formation in NB4 cells, suggesting that tenovin-6 does not directly target PML-RAR-α activity. In agreement with this, tenovin-6 induces cellular differentiation in the non-APL cell line HL-60, where PML-RAR-α does not exist. Knocking down SIRT2 by shRNA induces granulocytic differentiation in NB4 cells, which demonstrates that the inhibition of SIRT2 activity is sufficient to induce cell differentiation in NB4 cells. The overexpression of SIRT2 in NB4 cells decreases the level of granulocytic differentiation induced by tenovin-6, which indicates that tenovin-6 induces granulocytic differentiation by inhibiting SIRT2 activity. Taken together, our data suggest that targeting SIRT2 is a viable strategy to induce leukemic cell differentiation.

The histone deacetylase SIRT2 stabilizes Myc oncoproteins

Myc oncoproteins are commonly upregulated in human cancers of different organ origins, stabilized by Aurora A, degraded through ubiquitin-proteasome pathway-mediated proteolysis, and exert oncogenic effects by modulating gene and protein expression. Histone deacetylases are emerging as targets for cancer therapy. Here we demonstrated that the class III histone deacetylase SIRT2 was upregulated by N-Myc in neuroblastoma cells and by c-Myc in pancreatic cancer cells, and that SIRT2 enhanced N-Myc and c-Myc protein stability and promoted cancer cell proliferation. Affymetrix gene array studies revealed that the gene most significantly repressed by SIRT2 was the ubiquitin-protein ligase NEDD4. Consistent with this finding, SIRT2 repressed NEDD4 gene expression by directly binding to the NEDD4 gene core promoter and deacetylating histone H4 lysine 16. Importantly, NEDD4 directly bound to Myc oncoproteins and targeted Myc oncoproteins for ubiquitination and degradation, and small-molecule SIRT2 inhibitors reactivated NEDD4 gene expression, reduced N-Myc and c-Myc protein expression, and suppressed neuroblastoma and pancreatic cancer cell proliferation. Additionally, SIRT2 upregulated and small-molecule SIRT2 inhibitors decreased Aurora A expression. Our data reveal a novel pathway critical for Myc oncoprotein stability, and provide important evidences for potential application of SIRT2 inhibitors for the prevention and therapy of Myc-induced malignancies.

Molecular docking and dynamics simulation, receptor-based hypothesis: application to identify novel sirtuin 2 inhibitors

Sirtuin, NAD(+)-dependent histone deacetylase enzyme, emerged as a potential therapeutic target, and modulations by small molecules could be effective drugs for various diseases. Owing to the absence of complex structure of sirtuin 2 (SIRT2), sirtinol was docked in the NAD(+) binding site and subjected to 5-nseconds molecular dynamics (MD) simulation. LigandScout was used to develop hypotheses based on 3-representative SIRT2 complex structures from MD. Three structure-based hypotheses are generated and merged to form dynamics hypothesis. The dynamics hypothesis was validated using test and decoy sets. The results showed that dynamic hypothesis represents the complementary features of SIRT2 active site. Dynamic hypothesis was used to screen ChemDiv database, and hits were filtered through ADMET, rule of five, and two different molecular docking studies. Finally, 21 molecules were selected as potent leads based on consensus score from LigandFit, Gold fitness score, binding affinity from VINA as well as based on the important interactions with critical residues in SIRT2 active site. Hence, we suggest that the dynamic hypothesis will be reliable in the identification of SIRT2 new lead as well as to reduce time and cost in the drug discovery process.

Sirt-1 is required for the inhibition of apoptosis and inflammatory responses in human tenocytes

Tendon overuse injuries and tendinitis are accompanied by catabolic processes and apoptosis of tenocytes. However, the precise molecular mechanisms of the destructive processes in tendon are not fully understood. Sirt-1, a nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase, has been linked to transcriptional silencing and appears to play a key role in inflammation. The purpose of this study was to examine whether down-regulation of Sirt-1 using antisense oligonucleotides (ASO) affects inflammatory and apoptotic signaling in tenocytes. Transient transfection of tenocytes with ASO against Sirt-1 induced expression of Bax and other proteins involved in apoptosis (cleaved caspase-3 and poly(ADP-ribose)polymerase), acetylation of tumor suppressor p53, and mitochondrial degradation. Interestingly, Sirt-1 was found to interact directly with p53. In contrast, Sirt-1 activator resveratrol inhibited interleukin-1β (IL-1β)- and nicotinamide-induced NF-κB activation and p65 acetylation and suppressed the activation of IκB-α kinase. Resveratrol also reversed the IL-1β- or nicotinamide-induced up-regulation of various gene products that mediate inflammation (cyclooxygenase-2) and matrix degradation (matrix metalloproteinase-9) that are known to be regulated by NF-κB. Knockdown of Sirt-1 by using ASO abolished the inhibitory effects of resveratrol on inflammatory and apoptotic signaling including Akt activation and SCAX suppression. Down-regulation of histone deacetylase Sirt-1 by mRNA interference abrogated the effect of resveratrol on NF-κB suppression, thus highlighting the crucial homeostatic role of this enzyme. Overall, these results suggest for the first time that Sirt-1 can regulate p53 and NF-κB signaling via deacetylation, demonstrating a novel role for resveratrol in the treatment of tendinitis/tendinopathy.

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.

SirT1 regulates radiosensitivity of hepatoma cells differently under normoxic and hypoxic conditions

Intratumoral hypoxic cells are more resistant to radiotherapy due to a reduction in lifespan of DNA-damaging free radicals and augmentation of post-irradiation molecular restoration. SirT1, a member of the mammalian sirtuin family, deacetylates various transcription factors to trigger cell defense and survival in response to stresses and DNA damage. In this study, we provide new evidence indicating that overexpression of SirT1 in hepatoma HepG2 cells allowed the cells to become much more resistant to irradiation under hypoxia than under normoxia. When SirT1 was knocked down in both HepG2 and SK-Hep-1 cells, the radiosensitivity was increased, especially under hypoxia. But this enhanced radiosensitivity in SirT1-deficient cells was extensively decreased by infecting cells with c-Myc siRNA. Furthermore, the expression of c-Myc protein and its acetylation were increased in the SirT1 knockdown cells and these increments under hypoxic conditions were much more notable than under normoxia. In addition, c-Myc interference significantly suppressed phosphorylated p53 protein expression after irradiation, especially under hypoxic conditions. The current findings indicate that SirT1 confers a higher radioresistance in hypoxic cells than in normoxic cells due to the decreased levels of c-Myc protein and its acetylation, and that a c-Myc-dependent radiation-induced phosphorylated p53 may be involved. SirT1 could serve as a novel target of radiation damage and thus as a potential strategy to advance the efficiency of radiotherapy in hepatoma entities.

Effects of gambogic acid on the activation of caspase-3 and downregulation of SIRT1 in RPMI-8226 multiple myeloma cells via the accumulation of ROS

Multiple myeloma (MM) is the second most commonly diagnosed hematologic malignancy. Although new drugs, including bortezomib and lenalidomide, have improved the treatment landscape for MM patients, MM remains incurable. Therefore, screening for novel anti-myeloma drugs is necessary. Gambogic acid (GA), the main active ingredient of gamboges secreted from the Garcinia hanburryi tree, has been reported to exhibit potent anticancer activity in certain solid tumors and hematological malignancies, while there are few studies that are available concerning its effects on MM cells. In the present study, we investigated the anticancer activity of GA on the MM RPMI-8226 cells and further studied the underlying mechanisms by which GA affected the cells. RPMI-8226 cells were cultured and the effect of GA on cell proliferation was analyzed using MTT assay. Hoechst 33258 staining was used to visualize nuclear fragmentation, and reactive oxygen species (ROS) levels were detected. GA was found to have a significant, dose-dependent effect on growth inhibition and apoptosis induction in RPMI-8226 cells. This activity is associated with the accumulation of ROS, which contributes to the activation of caspase-3 and the cleavage of poly (ADP-ribose) polymerase (PARP), accompanied with apoptosis in RPMI-8226 cells treated with GA. Mammalian SIRT1, as the closest homolog of the yeast Sir2, was extensively involved in regulating cell processes, including cell senescence, aging and neuronal protection, as well as having anti-apoptotic properties. Moreover, SIRT1 overexpression has been shown to protect cancer cells from chemotherapy and ionizing radiation. In the present study, we demonstrated that GA has the potential to downregulate the expression of SIRT1 via ROS accumulation. In conclusion, our study found that GA is able to induce apoptosis in RPMI-8226 cells via ROS accumulation followed by caspase-3 activation, PARP cleavage and SIRT1 downregulation. These results suggest that GA may have the potential to not only induce apoptosis in MM cells, but also to decrease the relapse rate of MM.

Activating transcription factor 4 confers a multidrug resistance phenotype to gastric cancer cells through transactivation of SIRT1 expression

BACKGROUND

Multidrug resistance (MDR) in gastric cancer remains a major challenge to clinical treatment. Activating transcription factor 4 (ATF4) is a stress response gene involved in homeostasis and cellular protection. However, the expression and function of ATF4 in gastric cancer MDR remains unknown. In this study, we investigate whether ATF4 play a role in gastric cancer MDR and its potential mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrated that ATF4 overexpression confered the MDR phenotype to gastric cancer cells, while knockdown of ATF4 in the MDR variants induced re-sensitization. In this study we also showed that the NAD(+)-dependent histone deacetylase SIRT1 was required for ATF4-induced MDR effect in gastric cancer cells. We demonstrated that ATF4 facilitated MDR in gastric cancer cells through direct binding to the SIRT1 promoter, resulting in SIRT1 up-regulation. Significantly, inhibition of SIRT1 by small interfering RNA (siRNA) or a specific inhibitor (EX-527) reintroduced therapeutic sensitivity. Also, an increased Bcl-2/Bax ratio and MDR1 expression level were found in ATF4-overexpressing cells.

CONCLUSIONS/SIGNIFICANCE

We showed that ATF4 had a key role in the regulation of MDR in gastric cancer cells in response to chemotherapy and these findings suggest that targeting ATF4 could relieve therapeutic resistance in gastric cancer.

SIRT1 overexpression decreases cisplatin-induced acetylation of NF-κB p65 subunit and cytotoxicity in renal proximal tubule cells

As the increased acetylation of p65 is linked to nuclear factor-κB (NF-κB) activation, the regulation of p65 acetylation can be a potential target for the treatment of inflammatory injury. Cisplatin-induced nephrotoxicity is an important issue in chemotherapy of cancer patients. SIRT1, nicotinamide adenine dinucleotide (NAD(+))-dependent protein deacetylase, has been implicated in a variety of cellular processes such as inflammatory injury and the control of multidrug resistance in cancer. However, there is no report on the effect of SIRT1 overexpression on cisplatin-induced acetylation of p65 subunit of NF-κB and cell injury. To investigate the effect of SIRT1 in on cisplatin-induced acetylation of p65 subunit of NF-κB and cell injury, HK2 cells were exposed with SIRT1 overexpression, LacZ adenovirus or dominant negative adenovirus after treatment with cisplatin. While protein expression of SIRT1 was decreased by cisplatin treatment compared with control buffer treatment, acetylation of NF-κB p65 subunit was significantly increased after treatment with cisplatin. Overexpression of SIRT1 ameliorated the increased acetylation of p65 of NF-κB during cisplatin treatment and cisplatin-induced cytotoxicity. Further, treatment of cisplatin-treated HK2 cells with resveratrol, a SIRT1 activator, also decreased acetylation of NF-κB p65 subunit and cisplatin-induced increase of the cell viability in HK2 cells. Our findings suggests that the regulation of acetylation of p65 of NF-κB through SIRT1 can be a possible target to attenuate cisplatin-induced renal cell damage.

Calorie restriction increases primordial follicle reserve in mature female chemotherapy-treated rats

We assessed the effects of calorie restriction (CR)-mediated protection against chemotherapy damage on ovarian reserve. Forty-eight female Sprague-Dawley rats were randomly divided into four groups: the normal control group (NC group, fed ad libitum), the CR group (fed with 65% food intake of the NC group), the CTX group (injected with cyclophosphamide (CTX) and fed ad libitum), and the CR+CTX group (injected with CTX and fed with 65% food intake of the NC group). Ovarian reserve was examined by vaginal smears and follicle counting. SIRT1 is a deacetylase that is activated by a variety of stressors and targets transcriptional regulators including p53, NF-κB, FOXO1, 3, and 4, and the transcriptional regulator PGC-1α. The expression level of SIRT1, p53 and FOXO3a in the ovary was measured by western blot. CR did not interfere with estrous cycling but maintained estrous cycling in CTX-treated CR rats. The number of primordial follicles in the CR rats was comparable to the NC group, and CR+CTX group rats had more primordial follicles and primary follicles than the CTX group. SIRT1 expression in the ovary was higher in the CR group compared to the control group, and p53 level was lower in the CR group than that in the NC group. There is no significant difference in the expression level of FOXO3a between the CR group and the NC group.

CONCLUSIONS

These results indicate that CR can increase the ovarian follicular reserve and reduce the CTX-induced ovarian damage, and CR positive effects may be due to its intervention in the transition from primordial to primary follicle, and its reduction of oxidative stress.

Testosterone deficiency accelerates neuronal and vascular aging of SAMP8 mice: protective role of eNOS and SIRT1

Oxidative stress and atherosclerosis-related vascular disorders are risk factors for cognitive decline with aging. In a small clinical study in men, testosterone improved cognitive function; however, it is unknown how testosterone ameliorates the pathogenesis of cognitive decline with aging. Here, we investigated whether the cognitive decline in senescence-accelerated mouse prone 8 (SAMP8), which exhibits cognitive impairment and hypogonadism, could be reversed by testosterone, and the mechanism by which testosterone inhibits cognitive decline. We found that treatment with testosterone ameliorated cognitive function and inhibited senescence of hippocampal vascular endothelial cells of SAMP8. Notably, SAMP8 showed enhancement of oxidative stress in the hippocampus. We observed that an NAD⁺-dependent deacetylase, SIRT1, played an important role in the protective effect of testosterone against oxidative stress-induced endothelial senescence. Testosterone increased eNOS activity and subsequently induced SIRT1 expression. SIRT1 inhibited endothelial senescence via up-regulation of eNOS. Finally, we showed, using co-culture system, that senescent endothelial cells promoted neuronal senescence through humoral factors. Our results suggest a critical role of testosterone and SIRT1 in the prevention of vascular and neuronal aging.

The role of sirtuin 2 activation by nicotinamide phosphoribosyltransferase in the aberrant proliferation and survival of myeloid leukemia cells

BACKGROUND

Inhibitors of nicotinamide phosphoribosyltransferase have recently been validated as therapeutic targets in leukemia, but the mechanism of leukemogenic transformation downstream of this enzyme is unclear.

DESIGN AND METHODS

Here, we evaluated whether nicotinamide phosphoribosyltransferase's effects on aberrant proliferation and survival of myeloid leukemic cells are dependent on sirtuin and delineated the downstream signaling pathways operating during this process.

RESULTS

We identified significant upregulation of sirtuin 2 and nicotinamide phosphoribosyltransferase levels in primary acute myeloid leukemia blasts compared to in hematopoietic progenitor cells from healthy individuals. Importantly, specific inhibition of nicotinamide phosphoribosyltransferase or sirtuin 2 significantly reduced proliferation and induced apoptosis in human acute myeloid leukemia cell lines and primary blasts. Intriguingly, we found that protein kinase B/AKT could be deacetylated by nicotinamide phosphoribosyltransferase and sirtuin 2. The anti-leukemic effects of the inhibition of nicotinamide phosphoribosyltransferase or sirtuin 2 were accompanied by acetylation of protein kinase B/AKT with subsequent inhibition by dephosphorylation. This leads to activation of glycogen synthase kinase-3 β via diminished phosphorylation and, ultimately, inactivation of β-catenin by phosphorylation.

CONCLUSIONS

Our results provide strong evidence that nicotinamide phosphoribosyltransferase and sirtuin 2 participate in the aberrant proliferation and survival of leukemic cells, and suggest that the protein kinase B/AKT/ glycogen synthase kinase-3 β/β-catenin pathway is a target for inhibition of nicotinamide phosphoribosyltransferase or sirtuin 2 and, thereby, leukemia cell proliferation.

The dual role of sirtuins in cancer

Among the greatest challenges facing organisms is that of detecting and effectively responding to life-threatening environmental changes that are intimately associated with metabolic fluctuations and certain forms of stress. These conditions have been linked to the onset of many human pathologies, including cancer. Over the past decade, members of the Sir2 family, or sirtuins, have been described as major players in sensing and coordinating stress response. Evidence has imputed mammalian sirtuins in carcinogenesis, although the mechanisms involved seem to be more diverse and complex than previously anticipated. Some sirtuins, such as SirT2 and SirT6, seem to work as tumor suppressors, but others, such as SirT1, are apparently bifunctional: operating as both tumor suppressors and oncogenic factors depending on the context and the study conditions. The mechanisms underlying these apparently contradictory activities are not well understood, although recent findings suggest that they might actually be two sides of the same coin. In this review, the authors summarize current knowledge on the functional implications of sirtuins in cancer and discuss possible explanations for their functional duality.

The novel phloroglucinol PMT7 kills glycolytic cancer cells by blocking autophagy and sensitizing to nutrient stress

The switch from oxidative phosphorylation to glycolytic metabolism results in cells that generate fewer reactive oxygen species (ROS) and are resistant to the intrinsic induction of apoptosis. As a consequence, glycolytic cancer cells are resistant to radiation and chemotherapeutic agents that rely on production of ROS or intrinsic apoptosis. Further, the level of glycolysis correlates with tumor invasion, making glycolytic cancer cells an important target for new therapy development. We have synthesized a novel redox-active quinone phloroglucinol derivative, PMT7. Toxicity of PMT7 was in part due to loss of mitochondrial membrane potential in treated cells with subsequent loss of mitochondrial metabolic activity. Mitochondrial gene knockout ρ0 cells, a model of highly glycolytic cancers, were only half as sensitive as the corresponding wild-type cells and metabolic pathways downstream of MET were unaffected in ρ0 cells. However, PMT7 toxicity was also due to a block in autophagy. Both wild-type and ρ0 cells were susceptible to autophagy blockade, and the resistance of ρ0 cells to PMT7 could be overcome by serum deprivation, a situation where autophagy becomes necessary for survival. The stress response class III deacetylase SIRT1 was not significantly involved in PMT7 toxicity, suggesting that unlike other chemotherapeutic drugs, SIRT1-mediated stress and survival responses were not induced by PMT7. The dependence on autophagy or other scavenging pathways makes glycolytic cancer cells vulnerable. This can be exploited by induction of energetic stress to specifically sensitize glycolytic cells to other stresses such as nutrient deprivation or potentially chemotherapy.