Deacetylation Of P53 Research Articles

Resveratrol Upregulates Cardiac SDF-1 in Mice with Acute Myocardial Infarction through the Deacetylation of Cardiac p53.

AimsWe previously demonstrated that resveratrol (RSV) administration causes cardiac stromal cell-derived factor (SDF)-1 upregulation and can enhance the mobilization of stem cells in mice with acute myocardial infarction (AMI). However, the upstream signal transduction involved in SDF-1 regulation in the setting of AMI and RSV administration remains unclear. Because RSV is a sirtuin 1 (SIRT1) activator and SIRT proteins act as deacetylases, we investigated the role of SIRT1 in SDF-1 upregulation and its subsequent effects.Methods and Results In vitro experiments with H9C2 cardiomyocytes under hypoxia and serum-deprivation conditions showed that p53 acted upstream of SDF-1. RSV could not regulate SDF-1 effectively after SIRT1 silencing, indicating that it is dependent on SIRT1. Subsequently, male C57BL/6 mice were divided into four groups: 1) sham, 2) MI, 3) MI+RSV, and 4) MI+RSV plus nicotinamide, an inhibitor of the deacetylase activity of SIRT (MI+RSV+NAM). Compared with the sham mice, AMI caused a slight increase in the cardiac p53 level and resulted in significant SIRT1 downregulation and p53 acetylation or activation. Compared with the MI mice, MI+RSV administration improved the cardiac SDF-1 level and reversed the reduction of SIRT1 and the activation of p53. Furthermore, we observed less cardiac dysfunction in MI+RSV mice and determined that NAM abolished the effects of RSV.ConclusionsRSV enhances cardiac SDF-1 excretion after AMI partially through a SIRT1 normalization/p53 inactivation pathway.

Hepatic NAD salvage pathway is enhanced in mice on a high-fat diet

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme for NAD salvage and the abundance of Nampt has been shown to be altered in non-alcoholic fatty liver disease. It is, however, unknown how hepatic Nampt is regulated in response to accumulation of lipids in the liver of mice fed a high-fat diet (HFD). HFD mice gained more weight, stored more hepatic lipids and had an impaired glucose tolerance compared with control mice. NAD levels as well as Nampt mRNA expression, protein abundance and activity were significantly increased in HFD mice. Enhanced NAD levels were associated with deacetylation of p53 and Nfκb indicating increased activation of Sirt1. Despite impaired glucose tolerance and increased hepatic lipid levels in HFD mice, NAD metabolism was significantly enhanced. Thus, improved NAD metabolism may be a compensatory mechanism to protect against negative impact of hepatic lipid accumulation.

Acetylation of HDAC1 and degradation of SIRT1 form a positive feedback loop to regulate p53 acetylation during heat-shock stress.

The tumor suppressor p53 is an essential transcription factor that sensitively regulates cellular responses to various stresses. Acetylation, a critically important posttranslational modification of p53, is induced in response to cellular stresses. P53 acetylation level strongly correlates with protein stability and activity. The steady-state level of p53 acetylation is balanced by dynamic acetylation and deacetylation. Despite the function of p53 acetylation being well studied, how the steady state of p53 acetylation level is regulated in response to cellular stresses remains unclear. In particular, the dynamic regulation of the deacetylase activities responsible for p53 deacetylation during cellular stress is unknown. In the current study, we investigated the dynamic regulation of HDAC1 (histone deacetylase 1) and SIRT1 (sirtuin 1), two major enzymes for p53 deacetylation, during cell stress. We found that various cell stress events induce HDAC1 acetylation. The increased level of HDAC1 acetylation correlates with the level of p53 acetylation. Acetylated HDAC1 loses the ability to deacetylate p53. Cellular stresses also promote the decline of the SIRT1 protein in a proteasome-dependent pathway, which also results in the increase of p53 acetylation. Importantly, the decreased level of SIRT1 also contributes to the accumulation of HDAC1 acetylation as SIRT1 deacetylates HDAC1. Therefore, the increase of HDAC1 acetylation and reduced level of SIRT1 protein during cellular stress directly link to the induction of p53 acetylation. These results unveil the mechanism underlying the dynamic regulation of p53 acetylation during cell stress.

The regulation of radiosensitivity by p53 and its acetylation

The p53 signaling pathway plays critical roles in determining the radio-sensitivity of normal tissues but is frequently inactivated in cancer. In various cancer cells, p53 has different effects on radio-sensitivity through complex mechanisms. Acetylation of p53 is an important means of post-translational modifications and is indispensable for its activation that is a reversible enzymatic process. Both acetylation and deacetylation of p53 are involved in the fine regulation of cellular responses to DNA damage and genotoxic stress, such as radiation. Targeting the acetylation of p53 may enable the modulation of radio-sensitivity of cancer cells.

Independent role of PP2A and mTORc1 in palmitate induced podocyte death.

Molecular mechanism behind palmitate associated insulin resistance (IR) and podocyte death is not yet fully understood. The present study shows that palmitate treatment induces IR, in human urine derived podocyte-like epithelial cells (HUPECs), which is characterised by decrease in insulin-induced p-AKT, p-GSK3 β and p-ERK1/2. This impairment in insulin signalling prevents insulin induced SIRT 1 expression and deacetylation of p53. Further, palmitate treatment prevents insulin induced phosphorylation of PP2A and FOXO1 but it potentiates the phosphorylation of mTOR at Ser 2448. Interestingly, selective inhibition of PP2A, by Okadaic acid at 5nM, restored insulin induced phosphorylation of AKT, FOXO1, SIRT1 activity and p53 degradation. However, PP2A inhibition had no effect on mTOR phosphorylation at Ser 2448. On the other hand, partial inhibition of mTORc1, by low dose of Rapamycin (1nM) also restored phosphorylation of AKT and SIRT1 activity, whereas no significant changes were observed in insulin induced phosphorylation of PP2A after mTORc1 inhibition. To the best of our knowledge this is the first report suggesting independent role of PP2A and mTORc1 in palmitate induced IR and associated podocyte death. Therefore, the best therapeutic approach for treatment of diabetic kidney disease should involve manipulating phosphorylation of both PP2A and mTORc1.

Pseudokinase tribbles 1 (TRB1) negatively regulates tumor-suppressor activity of p53 through p53 deacetylation.

Tribbles 1 (TRB1) is one of the mammalian orthologs of Drosophila Tribbles, which regulates development and cell proliferation. TRB1 is suggested to act as a scaffold protein in signaling pathways for important cellular processes. TRB1 has also been identified as a myeloid oncogenic driver and mediates leukemogenesis through the mitogen-activated protein extracellular kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway and CCAAT/enhancer binding protein (C/EBP) transcriptional factors. However, the physiological roles of TRB1 in solid tumors have not been clarified. Here, we show that TRB1 interacts with p53 and suppresses its tumor suppressor activity. TRB1 knockdown enhances transcriptional activity of p53 and decreases cell viability. Interestingly, TRB1 enhances histone deacety lase 1 (HDAC1)-mediated p53 deacetylation and decreases DNA binding of p53. These results suggest that TRB1 is involved in the proliferation of tumor cells by inhibiting the activities of tumor suppressor p53 in solid tumors.

Inhibition of HDAC8 Reactivates p53 and Abrogates Leukemia Stem Cell Activity in CBFβ-SMMHC Associated Acute Myeloid Leukemia

The inv(16)-created CBFβ-SMMHC fusion protein inhibits differentiation of hematopoietic stem and progenitor cells (HSPCs) and creates pre-leukemic populations predisposed to acute myeloid leukemia (AML) transformation. However, the molecular mechanism underlying the leukemogenic function of CBFβ-SMMHC has been elusive. Given the low TP53 mutation rate in AML, alternative mechanisms disrupting p53 function are expected. We showed thatCBFβ-SMMHC impairs p53 acetylation and p53 target gene activation through formation of an aberrant protein complex with p53 and HDAC8 (Blood, 120: A772; 122(21): 224). We now show that CBFβ-SMMHC binds to p53 and HDAC8 independently through distinct regions and that HDAC8 mediates the deacetylation of p53 associated with CBFβ-SMMHC. In addition, we generated mice carrying a floxed Hdac8 (Hdac8f) allele and crossed with Cbfb56M/+/Mx1-Cre (Kuo YH et al, Cancer Cell 2006). Deletion of Hdac8 signifiacntly (p<0.0001) reduced the incidence of AML and prolonged disease-free survival. Pharmacologic inhibition of HDAC8 activity with HDAC8-selective inhibitors (HDAC8i) reactivates p53 and selectively induces apoptosis of inv(16)+ AML CD34+ cells while sparing normal HSPCs. To test the effect of HDAC8i on LSC engraftment and leukemia-initiating capacity, we generated Cbfb56M/+/Mx1-Cre mice with a Cre-reporter line expressing tdTomato fluorescence protein following Cre-mediated recombination. AML cells (dTomato+/cKit+) treated with HDAC8i (22d) ex vivo showed reduced engraftment (p=0.025) and enhanced survival (p=0.025) in transplanted mice. To examine whether HDAC8i 22d treatment affects the engraftment capacity on surviving cells, we transplanted equal number (2 x 106) of AML cells treated with either 22d or vehicle in another cohort of mice (n=4). We show that HDAC8i 22d treatment reduced the engraftment of dTomato+/cKit+ AML cells and enhanced survival, suggesting that the engraftment capacity is altered in addition to reducing AML cell survival. We next performed preclinical studies to determine the efficacy of in vivo administration of HDAC8i 22d. AML transplanted mice were randomized into two groups, one group treated with vehicle and the other treated with HDAC8i 22d for 2 weeks. Flow cytometry analysis revealed significantly reduced frequency (p=0.0097) and number (p=0.0101) of dTomato+/cKit+ AML cells in the bone marrow and spleen of 22d treated mice compared to vehicle treated group. To further assess the impact on LSC activity, we transplanted bone marrow cells from these treated mice into secondary recipients and analyzed for AML engraftment. Significant reduction in the frequency (p<0.0001) and the number (p=0.0006) of dTomato+/cKit+ AML cells was observed in the bone marrow and spleen. Furthermore, HDAC8i 22d treated transplants showed no signs of leukemia while vehicle treated transplants are moribund with aggressive AML. These results indicate that HDAC8 inhibition by 22d treatment effectively eliminates engraftment and leukemia-initiating capacity of AML LSCs.In conclusion, our studies identify a novel post-translational p53-inactivating mechanism and demonstrate selective HDAC8 inhibition as a promising approach to target inv(16)+ AML LSCs. DisclosuresNo relevant conflicts of interest to declare.

The Multifunctional Sorting Protein PACS-2 Regulates SIRT1-Mediated Deacetylation of p53 to Modulate p21-Dependent Cell-Cycle Arrest

SIRT1 regulates the DNA damage response by deacetylating p53, thereby repressing p53 transcriptional output. Here, we demonstrate that the sorting protein PACS-2 regulates SIRT1-mediated deacetylation of p53 to modulate the DNA damage response. PACS-2 knockdown cells failed to efficiently undergo p53-induced cell-cycle arrest in response to DNA damage. Accordingly, p53 acetylation was reduced both in PACS-2 knockdown cells and thymocytes from Pacs-2(-/-) mice, thereby blunting induction of the cyclin-dependent kinase inhibitor p21 (CDKN1A). The SIRT1 inhibitor EX-527 or SIRT1 knockdown restored p53 acetylation and p21 induction as well as p21-dependent cell-cycle arrest in PACS-2 knockdown cells. Trafficking studies revealed that cytoplasmic PACS-2 shuttled to the nucleus, where it interacted with SIRT1 and repressed SIRT1-mediated p53 deacetylation. Correspondingly, in vitro assays demonstrated that PACS-2 directly inhibited SIRT1-catalyzed p53 deacetylation. Together, these findings identify PACS-2 as an in vivo mediator of the SIRT1-p53-p21 axis that modulates the DNA damage response.

Salvianolic acid B protects against acute ethanol-induced liver injury through SIRT1-mediated deacetylation of p53 in rats

Salvianolic acid B (SalB) is isolated from the traditional Chinese medical herb salvia miltiorrhiza. It has many biological and pharmaceutical activities. This study aimed to investigate the effect of SalB on acute ethanol-induced hepatic injury in rats and to explore the role of SIRT1 in this process. The results showed that pretreatment with SalB significantly reduced ethanol-induced elevation in aminotransferase activities, decreased hepatotoxic cytokine levels such as Interleukin-6 (IL-6), and increased the antioxidant enzyme activity. Moreover, SalB pretreatment reversed the increase in NF-κB, cleaved caspase-3 and decrease in B-cell lymphoma-extra large (Bcl-xL) caused by ethanol exposure. Importantly, SalB pretreatment significantly increased the expression of SIRT1, a NAD+-dependent deacetylase, whereas the increase in SIRT1 was accompanied by decreased acetyl-p53 expression. In HepG2 cells, SalB pretreatment increased SIRT1 expression in a time and dose-dependent manner and such an increase was abrogated by siRNA knockdown of SIRT1. Additionally, inhibition of SIRT1 significantly increased the acetylation of p53, and blocked SalB-induced acetylation of p53 down-regulation. Collectively, this study indicated that SalB can alleviate acute ethanol-induced hepatocyte apoptosis through SIRT1-mediated deacetylation of p53 pathway.

A Novel Sirtuin 2 (SIRT2) Inhibitor with p53-dependent Pro-apoptotic Activity in Non-small Cell Lung Cancer

Sirtuin 2 (SIRT2) is an NAD(+)-dependent protein deacetylase whose targets include histone H4 lysine 16, p53, and α-tubulin. Because deacetylation of p53 regulates its effect on apoptosis, pharmacological inhibition of SIRT2-dependent p53 deacetylation is of great therapeutic interest for the treatment of cancer. Here, we have identified two structurally related compounds, AEM1 and AEM2, which are selective inhibitors of SIRT2 (IC50 values of 18.5 and 3.8 μM, respectively), but show only weak effects on other sirtuins such as SIRT1, SIRT3, and yeast Sir2. Interestingly, both compounds sensitized non-small cell lung cancer cell lines toward the induction of apoptosis by the DNA-damaging agent etoposide. Importantly, this sensitization was dependent on the presence of functional p53, thus establishing a link between SIRT2 inhibition by these compounds and p53 activation. Further, treatment with AEM1 and AEM2 led to elevated levels of p53 acetylation and to increased expression of CDKN1A, which encodes the cell cycle regulator p21(WAF1), as well as the pro-apoptotic genes PUMA and NOXA, three transcriptional targets of p53. Altogether, our data suggest that inhibition of SIRT2 by these compounds causes increased activation of p53 by decreasing SIRT2-dependent p53 deacetylation. These compounds thus provide a good opportunity for lead optimization and drug development to target p53-proficient cancers.

Effect of SIRT1 on high glucose-induced NF-κB p65 subunit acetylation and MCP-1 expression in rat mesangial cells

Objective To explore the effect of silent information regulator 1(SIRT1)on high glucose-induced nuclear factor-κB(NF-κB)p65 subunit acetylation and monocyte chemoattractant protein 1(MCP-1)expression in rat mesangial cells(RMCs).Methods The lentiviral shRNA plasmid pTRC-shSIRT1was constructed for interference of SIRT1 gene and was identified.The RMCs were divided into high glucose group(treated with high glucose culture medium),resveratrol(SIRT1 activator)+high glucose group(treated with low glucose culture medium containing 1μmol/L resveratrol for 24h,and then with high glucose culture medium),SIRT1 RNAi group(4h after viral pTRC-shSIRT1 infection,and then treated with low-glucose culture medium),SIRT1 RNAi+ high glucose group(4h after viral pTRC-shSIRT1 infection,and then treated with high glucose culture medium);we also established normal control group and hypertonic mannitol control group.The mRNA expression of SIRT1 and MCP-1gene was analyzed by real-time quantitative PCR;the protein expression of SIRT1 and the acetylation of NF-κB p65 subunit were observed by Western blotting analysis.The protein level of MCP-1 in the supernatants was detected by ELISA.Results DNA sequencing confirmed the successful construction of the plasmid pTRC-shSIRT1,which could knocked down SIRT1 mRNA expression(P0.01).High glucose decreased SIRT1 expression and promoted acetylation of NF-κB p65 subunit,and increased MCP-1 mRNA and protein expression.Resveratrol,an activatorof SIRT1,could reverse the above changes induced by high glucose.Conversely,silencing SIRT1 gene significantly accelerated the high glucose-induced acetylation of NF-κB p65 subunit and MCP-1 expression at both mRNA and protein levels(P0.01or P0.05).Conclusion SIRT1 can inhibit high glucose-induced MCP-1 mRNA and protein expression in RMCs,which may involve NF-κB p65 deacetylation.

Aberrant G-CSFR Signaling in Congenital Neutropenia

Clinical observations revealed that congenital neutropenia (CN) patients harboring either ELANE or HAX mutations have similar bone marrow morphology, responses to G-CSF therapy, requirements of G-CSF dosages, and the risk of developing leukemia. Therefore, we suggested a common pathomechanism of defective G-CSFR-triggered granulopoiesis downstream of both mutated genes in these patients. We identified severely diminished expression and functions of the transcription factors lymphoid enhancer binding factor-1 (LEF-1) and C/EBPa in myeloid cells of CN patients, in comparison to healthy individuals and patients with cyclic neutropenia (CyN). LEF-1 expression was abrogated in patients harboring either ELANE or HAX1 mutations, which suggested LEF-1 as a possible common candidate factor for defective G-CSFR signaling. We further identified a mechanism of the diminished LEF-1 expression downstream of HAX1 or ELANE mutations. HAX1 is HCLS1-Associated protein X1. HCLS1 is Hematopoietic Cell-Specific Lyn Substrate 1. We found that HCLS1 protein is expressed at high levels in human myeloid cells and is phosphorylated upon stimulation with G-CSF. HCLS1 interacted with LEF-1 protein, inducing nuclear translocation of LEF-1, LEF-1 autoregulation, C/EBPa activation, and granulocytic differentiation. In CN patients with HAX1 mutations, we found profound defects in the G-CSF-triggered phosphorylation of HCLS1, subsequently leading to abrogated nuclear transport and autoregulation of LEF-1. In CN patients with ELANE mutations we detected severely reduced levels of the natural inhibitor of neutrophil elastase (NE), and secretory leukocyte protease inhibitor (SLPI). We demonstrated the important role of SLPI in myeloid differentiation by activation of Erk1/2 phosphorylation and subsequent phErk1/2-triggered tyrosine phosphorylation and activation of the LEF-1 protein. Therefore, the direct link between ELANE mutations and diminished LEF-1 expression was established: in these patients LEF-1 protein expression is diminished due to the reduced levels of SLPI. We further evaluated how G-CSF treatment overcomes maturation arrest of granulopoiesis in CN patients despite the absence of LEF-1 and C/EBPa in myeloid cells. We identified nicotinamide phosphoribosyltransferase (NAMPT) as an essential enzyme mediating G-CSF-triggered granulopoiesis in healthy individuals and in CN patients. Treatment of healthy individuals with G-CSF resulted in upregulation of NAMPT levels in myeloid cells and in plasma. NAMPT and NAD+ amounts were even more dramatically elevated by G-CSF treatment of CN individuals. The molecular events triggered by NAMPT included elevation of NAD+, NAD+-dependent activation of protein deacetylase sirtuin-1 (SIRT1), binding of SIRT1 to the myeloid specific transcription factors C/EBPα and C/EBPβ, and activation of these transcription factors. In CN patients, C/EBPα expression is severely diminished; therefore “steady-state” granulopoiesis could not be activated. G-CSF treatment induces expression of C/EBPβ in these patients via NAMPT and SIRT1 and operated via the “emergency” pathway. We also investigated the patterns of acquisition of leukemia-associated-mutations in 31 CN patients developing leukemia using next-generation DNA deep sequencing. Intriguingly, 20 of the 31 patients (64.5%) demonstrated mutations within RUNX1. The majority of patients with RUNX1 mutations (85%) had acquired CSF3R mutations. Other leukemia-associated mutations in the patients with RUNX1 mutations were found infrequently. Cytogenetics of the leukemic cells revealed that 10 patients with RUNX1 mutations developed monosomy 7, and six patients had trisomy 21. Single cell analysis in two patients revealed that RUNX1 and CSF3R mutations were segregated in the same malignant clone. Functional studies demonstrated proliferative advantage of CD34+ cells transduced with mutated RUNX1 and CSF3R. By analysis of the leukemogenic role of the defective G-CSFR signaling in CN patients we identified a significant and sustained elevation in the levels of phospho-STAT5 in hematopoietic CD34+ cells of CN patients which were even higher in CN/ acute myeloid leukemia patients. The other possible reason for the leukemogenic transformation could be elevated NAMPT/SIRT-triggered deacetylation of tumor supressor protein p53, proto-oncogene FOXO3a and Akt proteins. Disclosures:No relevant conflicts of interest to declare.

Active regulator of SIRT1 is required for cancer cell survival but not for SIRT1 activity.

The NAD+-dependent deacetylase SIRT1 is involved in diverse cellular processes, and has also been linked with multiple disease states. Among these, SIRT1 expression negatively correlates with cancer survival in both laboratory and clinical studies. Active regulator of SIRT1 (AROS) was the first reported post-transcriptional regulator of SIRT1 activity, enhancing SIRT1-mediated deacetylation and downregulation of the SIRT1 target p53. However, little is known regarding the role of AROS in regulation of SIRT1 during disease. Here, we report the cellular and molecular effects of RNAi-mediated AROS suppression, comparing this with the role of SIRT1 in a panel of human cell lines of both cancerous and non-cancerous origins. Unexpectedly, AROS is found to vary in its modulation of p53 acetylation according to cell context. AROS suppresses p53 acetylation only following the application of cell damaging stress, whereas SIRT1 suppresses p53 under all conditions analysed. This supplements the original characterization of AROS but indicates that SIRT1 activity can persist following suppression of AROS. We also demonstrate that knockdown of AROS induces apoptosis in three cancer cell lines, independent of p53 activation. Importantly, AROS is not required for the viability of three non-cancer cell lines indicating a putative role for AROS in specifically promoting cancer cell survival.

Regulation of FOXOs and p53 by SIRT1 Modulators under Oxidative Stress

Excessive reactive oxygen species (ROS) induce apoptosis and are associated with various diseases and with aging. SIRT1 (sirtuin-1), an NAD+-dependent protein deacetylase, decreases ROS levels and participates in cell survival under oxidative stress conditions. SIRT1 modulates the transcription factors p53, a tumor suppressor and inducer of apoptosis, and the forkhead O (FOXO) family, both of which play roles for cell survival and cell death. In this study, we aimed to know which is working greatly among p53 and FOXOs transcription factors in SIRT1’s cell protective functions under oxidative stress conditions. The antimycin A-induced increase in ROS levels and apoptosis was enhanced by SIRT1 inhibitors nicotinamide and splitomicin, whereas it was suppressed by a SIRT1 activator, resveratrol, and a SIRT1 cofactor, NAD+. SIRT1-siRNA abolished the effects of splitomicin and resveratrol. p53-knockdown experiment in C2C12 cells and experiment using p53-deficient HCT116 cells showed that splitomicin and resveratrol modulated apoptosis by p53-dependent and p53-independent pathways. In p53-independent cell protective pathway, we found that FOXO1, FOXO3a, and FOXO4 were involved in SOD2’s upregulation by resveratrol. The knockdown of these three FOXOs by siRNAs completely abolished the SOD2 induction, ROS reduction, and anti-apoptotic function of resveratrol. Our results indicate that FOXO1, FOXO3a and FOXO4, are indispensable for SIRT1-dependent cell survival against oxidative stress, although deacetylation of p53 has also some role for cell protective function of SIRT1.

Berberine and S allyl cysteine mediated amelioration of DEN + CCl4 induced hepatocarcinoma

BackgroundDiethylnitrosamine (DEN) and carbon tetrachloride (CCl4) have been used as initiator and promoter respectively to establish an animal model for investigating molecular events appear to be involved in development of liver cancer. Use of herbal medicine in therapeutics to avoid the recurrence of hepatocarcinoma has already generated considerable interest among oncologists. In this context studies involving S-allyl-cysteine (SAC) and berberine have come up with promising results. Here we have determined the individual effect of SAC and berberine on the biomolecules associated with DEN+CCl4 induced hepatocarcinoma. Effective therapeutic value of combined treatment has also been estimated. MethodsROS accumulation was analyzed by FACS following DCFDA incubation. Bcl2-Bax and HDAC1‐pMdm2 interaction were demonstrated by co-immunoprecipitation. Immunosorbent assay was performed to analyze PP2A and caspase3 activities. MMP was determined cytofluorimetrically by investigating JC-1 fluorescence. AnnexinV binding was demonstrated by labeling the cells with AnV-FITC followed by flow cytometry. ResultsCytochromeP4502E1 mediated bioactivation of DEN+CCl4 induced Akt dependent pMdm2‐HDAC1 interaction that led to p53 deacetylation, probable cause of its degradation. In parallel, oxidative stress dependent Nrf2‐HO1 activation increased Bcl2 expression which in turn stimulated cell proliferation. SAC in combination with berberine inhibited Akt mediated cell proliferation. Activation of PP2A as well as inhibition of JNK resulted in induction of apoptosis after 30days of treatment. Extension of combined treatment reverted tissue physiology towards control. Co-treated group displayed normal tissue structure. Conclusion and general significanceSAC and berberine mediated HDAC1/Akt inhibition implicates the efficacy of combined treatment in the amelioration of DEN+CCl4 induced hepatocarcinoma.

Protective effect of SIRT1 on toxicity of microglial-derived factors induced by LPS to PC12 cells via the p53-caspase-3-dependent apoptotic pathway

Sirtuin1 (SIRT1) has protective effects in some neurodegenerative disease models, but it is not clear whether SIRT1 play the same role on inflammation-mediated Parkinson's disease (PD) models. In this study, we firstly established an inflammation environment by stimulating microglial BV-2 cells with the inflammatory agent lipopolysaccharides (LPS), which demonstrated by increasing of the levels of TNF-a, and IL-6 in cultured medium. Then we exposed PC12 cells (a model of catecholaminergic neuronal cells) with the supernant from LPS stimulated BV-2 cells (activated BV-2). PC12 cell apoptosis and SIRT1 involved protection were investigated. The results indicated that treatment with LPS caused significant decrease in SIRT1 expression in activated BV-2 cells, and increased the levels of TNF-a and IL-6, as measured by ELISA, whereas resveratrol (a known SIRT1 activator) suppressed this effect, which was conversely strengthened by sirtinol (a SIRT1 inhibitor), suggesting that SIRT1 may be involved in regulating proinflammatory cytokines from microglial activation. Further, we found that factors derived from activated microglia significantly decreased the level of deacetylation of p53 by reducing the expression of SIRT1, an effect that increased the apoptosis of PC12 and reduced cell viability. The addition of resveratrol could protect PC12 cells from inflammation-mediated damage above-mentioned, while nicotinamide (another SIRT1 inhibitor) treatment had the opposite effect of resveratrol. Together, these data suggests that: SIRT1 inhibits LPS-mediated proinflammatory cytokines release in microglia, and circumvents dopaminergic neurons injury induced by activated microglial-derived factors via p53-caspase-3-dependent mechanism of apoptosis. Thus, upregulation of SIRT1 provides a promising research field for therapeutic intervention in neuroinflammation diseases.

Sirtuin 1 inhibition delays cyst formation in autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is caused by mutations in either PKD1 or PKD2 and is characterized by the development of multiple bilateral renal cysts that replace normal kidney tissue. Here, we used Pkd1 mutant mouse models to demonstrate that the nicotinamide adenine dinucleotide-dependent (NAD-dependent) protein deacetylase sirtuin 1 (SIRT1) is involved in the pathophysiology of ADPKD. SIRT1 was upregulated through c-MYC in embryonic and postnatal Pkd1-mutant mouse renal epithelial cells and tissues and could be induced by TNF-α, which is present in cyst fluid during cyst development. Double conditional knockouts of Pkd1 and Sirt1 demonstrated delayed renal cyst formation in postnatal mouse kidneys compared with mice with single conditional knockout of Pkd1. Furthermore, treatment with a pan-sirtuin inhibitor (nicotinamide) or a SIRT1-specific inhibitor (EX-527) delayed cyst growth in Pkd1 knockout mouse embryonic kidneys, Pkd1 conditional knockout postnatal kidneys, and Pkd1 hypomorphic kidneys. Increased SIRT1 expression in Pkd1 mutant renal epithelial cells regulated cystic epithelial cell proliferation through deacetylation and phosphorylation of Rb and regulated cystic epithelial cell death through deacetylation of p53. This newly identified role of SIRT1 signaling in cystic renal epithelial cells provides the opportunity to develop unique therapeutic strategies for ADPKD.

Overexpression of SIRT1 Promotes High Glucose–Attenuated Corneal Epithelial Wound Healing via p53 Regulation of the IGFBP3/IGF-1R/AKT Pathway

To investigate how Sirtuin (silent mating type information regulation 2 homolog) 1 (SIRT1) promotes high glucose-attenuated corneal epithelial wound healing. The effects of high glucose on SIRT1 expression were assessed in primary human corneal epithelial cells (CECs) in treatment of 5 mM d-glucose (normal glucose [NG]) and 25 mM D-glucose (high glucose [HG]) and corneas from Ins2(Akita/+) mice by Western blotting. The osmotic pressure of the NG medium was adjusted to that of the HG medium by adding 20 mM mannitol. Pifithrin-α (PFT-α) was used to inhibit the expression of p53 and an adenovirus was used for overexpression of SIRT1 in vivo and in vitro. How overexpression of SIRT1 promotes HG-attenuated corneal epithelial wound healing via p53 regulation of the IGFBP3 (insulin-like growth factor binding protein-3)/IGF-1 (insulin-like growth factor-1)/AKT pathway was investigated in CECs and Ins2(Akita/+) mice. HG induced the downregulation of SIRT1 and the upregulation of p53 acetylation in primary human CECs and corneas from Ins2(Akita/+) mice. The results of cell migration assay and corneal wound healing from Ins2(Akita/+) mice demonstrated that SIRT1 overexpression strongly promoted wound healing in the presence of HG levels via the downregulation of the IGFBP3 protein. The levels of total p53 expression and acetylated p53 decreased dramatically in the presence of PFT-α, whereas the IGF-1R/AKT pathway was activated in CECs. The results of cell migration assay suggested this posttranslational modification of p53 was involved in the response to cell injury under HG conditions in CECs. The molecular mechanism by which SIRT1 promotes corneal epithelial wound healing was involved in an enhancement of the IGFBP3/IGF-1/AKT pathway through the deacetylation of p53. This study also suggests that SIRT1 has a protective role in the pathogenesis of diabetic keratopathy.

Deacetylation of p53 induces autophagy by suppressing Bmf expression

Interferon γ (IFN-γ)-induced cell death is mediated by the BH3-only domain protein, Bik, in a p53-independent manner. However, the effect of IFN-γ on p53 and how this affects autophagy have not been reported. The present study demonstrates that IFN-γ down-regulated expression of the BH3 domain-only protein, Bmf, in human and mouse airway epithelial cells in a p53-dependent manner. p53 also suppressed Bmf expression in response to other cell death-stimulating agents, including ultraviolet radiation and histone deacetylase inhibitors. IFN-γ did not affect Bmf messenger RNA half-life but increased nuclear p53 levels and the interaction of p53 with the Bmf promoter. IFN-γ-induced interaction of HDAC1 and p53 resulted in the deacetylation of p53 and suppression of Bmf expression independent of p53's proline-rich domain. Suppression of Bmf facilitated IFN-γ-induced autophagy by reducing the interaction of Beclin-1 and Bcl-2. Furthermore, autophagy was prominent in cultured bmf(-/-) but not in bmf(+/+) cells. Collectively, these observations show that deacetylation of p53 suppresses Bmf expression and facilitates autophagy.

Abstract 845: Sirtuin1, a longevity gene, is over-expressed and enhances proliferation and survival of endometrial carcinoma cells via deacetylation of p53.

Abstract Background: Sirtuin1 (SIRT1) is one of the NAD-dependent histone deacetylases, known as a longevity gene induced by caloric restriction or various stresses. SIRT1 also contributes to cell survival under stress conditions through deacetylation of apoptosis or cell cycle-related proteins. The overexpression of SIRT1 in several cancers was reported, however, the expression and function of SIRT1 in endometrial cancer remained undetermined. In this study, we examined the role of SIRT1 on the carcinogenesis and survival of endometrial carcinoma cells. Methods: The expressions of SIRT1 protein was examined by immunostaining using formalin-fixed tissue specimens of 110 endometrial carcinomas, 72 normal endometria and 24 endometrial hyperplasias. Immunoreactivity was evaluated according to the ratio of positive cells in 500 cells and described as a positivity index (PI, full score 100). All of surgical specimens were used after obtaining the consents. The mRNA and protein levels of SIRT1 in endometrial carcinoma cell lines, Ishikawa and HEC1B, were examined using real-time RT-PCR and Western blotting under stresses such as ultraviolet, hypoxia and cisplatin (CDDP) treatment. The viability of those cells under CDDP treatment was examined using WST-1 assay with/without suppression of SIRT1 by SIRT1 inhibitor (EX527) or siRNA. The effect of SIRT1 inhibition on the acetylation of p53 and the p53-related protein expression was in Ishikawa and HEC1B cells were examined using Western blotting under CDDP treatment. Results: Imunoreactivity of SIRT1 protein of carcinoma (PI=37.0±25.6) was significantly higher than that of normal endometrium (PI=25.3±26.5, P= 0.006). The expression of SIRT1 was significantly higher in grade 3 tumors (P= 0.006) and those with lympho-vascular space invasion (P= 0.044). There is a weak correlation between the expression of SIRT1 and growth potential indicated by Ki67 (P=0.051). The expression of SIRT1 protein was inversely correlated with that of p53 in carcinoma tissues and cell lines. In addition, the suppression of SIRT1 significantly reduced cell proliferation activity (P=0.01) and resistance against CDDP (P=0.004) in Ishikawa and HEC1B cells. The suppression of SIRT1 enhanced the acetylation of p53 protein and its downstream proteins. Conclusions: SIRT1 is over-expressed in endometrial carcinoma and may be involved in the carcinogenesis and development. SIRT1 may enhance the survival of endometrial carcinoma cells against various stresses, especially CDDP exposure, via inhibition of p53 by deacetylation. These findings suggest that SIRT1 can be a potent therapeutic target of endometrial carcinoma. Citation Format: Ryoichi Asaka, Tsutomu Miyamoto, Kaori Ishikawa, Yasushi Yamada, Hisanori Kobara, Akihisa Suzuki, Shun'ichiro Taniguchi, Tanri Shiozawa. Sirtuin1, a longevity gene, is over-expressed and enhances proliferation and survival of endometrial carcinoma cells via deacetylation of p53. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 845. doi:10.1158/1538-7445.AM2013-845