Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has been reported that p53 acetylation, which promotes cellular senescence, can be regulated by the NAD(+)-dependent deacetylase SIRT1, the human homolog of yeast Sir2, a protein that modulates lifespan. To clarify the role of SIRT1 in cellular senescence induced by oxidative stress, we treated normal human diploid fibroblast TIG-3 cells with H(2)O(2) and examined DNA cleavage, depletion of intracellular NAD(+), expression of p21, SIRT1, and acetylated p53, cell cycle arrest, and senescence-associated beta-galactosidase (SA-beta-gal) activity. DNA cleavage was observed immediately in TIG-3 cells treated with H(2)O(2), though no cell death was observed. NAD(+) levels in TIG-3 cells treated with H(2)O(2) were also decreased significantly. Pre-incubation with the poly (ADP-ribose) polymerase (PARP) inhibitor resulted in preservation of intracellular NAD(+) levels. The amount of acetylated p53 was increased in TIG-3 cells at 4h after H(2)O(2) treatment, while there was little to no decrease in SIRT1 protein expression. The expression level of p21 was increased at 12h and continued to increase for up to 24h. Additionally, exposure of TIG-3 cells to H(2)O(2) induced cell cycle arrest at 24h and increased SA-beta-gal activity at 48h. This pathway likely plays an important role in the acceleration of cellular senescence by oxidative stress.
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PMID:H2O2 accelerates cellular senescence by accumulation of acetylated p53 via decrease in the function of SIRT1 by NAD+ depletion. 1759 14

The activity of Rb (retinoblastoma protein) is regulated by phosphorylation and acetylation events. Active Rb is hypophosphorylated and acetylated on multiple residues. Inactivation of Rb involves concerted hyper-phosphorylation by cyclin-CDK (cyclin-dependent kinase) complexes combined with deacetylation of appropriate lysine residues within Rb. In the present study, using in vivo co-immunoprecipitation experiments, we identified mammalian SIRT1 (sirtuin 1) as a binding partner for Rb and its family members p107 and p130. Formation of Rb-SIRT1 complexes required the pocket domain of Rb. p300 catalysed the acetylation of Rb, and SIRT1 was a potent deacetylase for Rb. The ability of SIRT1 to catalyse the deacetylation of Rb was dependent on NAD and was inhibited by the SIRT1 inhibitor nicotinamide. Deacetylated lysine residues within Rb formed a domain similar to the SIRT1-targeted domain of the p53 tumour suppressor protein. Cultures of arrested cells, via contact inhibition or DNA damage, exhibited decreased Rb phosphorylation and increased Rb acetylation. Overexpression of SIRT1 in either confluent or etoposide-treated cells resulted in a significant reduction in Rb acetylation, which was restored with nicotinamide. Gene knockdown of SIRT1 by siRNA (short interfering RNA) produced an accumulation of acetylated Rb. This increase was augmented further when siRNA against SIRT1 was used in conjunction with nicotinamide. In conclusion, our results demonstrate that SIRT1 is an in vitro and in vivo deacetylase for the Rb tumour suppressor protein.
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PMID:Deacetylation of the retinoblastoma tumour suppressor protein by SIRT1. 1762 57

Sirt1, a conserved nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase, has been implicated in modulating transcriptional silencing and cell survival, and seems to play a key role in carcinogenesis through deacetylation of important regulatory proteins. This makes it a potential target in cancer therapy. The purpose of this study was to determine whether inhibition of Sirt1 by using antisense oligonucleotides (ASODN) induces apoptosis and enhances radiation sensitization in A549 lung cancer cells. Initially, transient transfection of A549 lung cancer cells with ASODN against Sirt1 specifically reduced Sirt1 expression in a dose-dependent and sequence-specific manner, at both mRNA and proteins levels. The inhibition of Sirt1 obviously decreased A549 cells survival, induced G1 arrest as well as apoptosis. Furthermore, the inhibition of Sirt1 by ASODN greatly increased radiation-induced antiproliferation effects involving in increasing acetylation of tumour suppressor p53 and Bax expression in A549 lung cancer cells. In summary, our results indicate that downregulation of Sirt1 by ASODN decreases survival and increases radiation-induced antiproliferation effects of human lung cancer cells and suggest that inhibition of Sirt1 by ASODN may be a potential gene therapy approach to the treatment of lung cancer.
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PMID:Downregulation of Sirt1 by antisense oligonucleotides induces apoptosis and enhances radiation sensitization in A549 lung cancer cells. 1762 72

Mechanisms underlying the role of reactive oxygen species (ROS) generated by flavin-containing oxidases in regulating cell cycle progression were examined in human and rodent fibroblasts. Incubation of confluent cell cultures with nontoxic/nonclastogenic concentrations of the flavoprotein inhibitor, diphenyleneiodonium (DPI), reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase activity and basal ROS levels, but increased proteolysis of cyclin D1, p21(Waf1) and phospho-p38(MAPK). When these cells were allowed to proliferate by subculture in DPI-free medium, an extensive G(1) delay was observed with concomitant activation of p53/p21(Waf1) signaling and reduced phosphorylation of mitogen-activated kinases. Compensation for decreased oxidant generation by simultaneous exposure to DPI and nontoxic doses of the ROS generators, gamma-radiation or t-butyl-hydroperoxide, attenuated the G(1) delay. Whereas the DPI-induced G(1) checkpoint was completely dependent on PHOX91, ATM and WAF1, it was only partially dependent on P53. Interestingly, G(1) to S progression was not affected when another flavin-containing enzyme, nitric oxide synthase, was inhibited nor was it associated with changes in mitochondrial membrane potential. Proliferating cells treated with DPI also experienced a significant but attenuated delay in G(2). We propose that ATM performs a critical function in mediating normal cellular proliferation that is regulated by nonphagocytic NAD(P)H oxidase enzymes activity, which may serve as a novel target for arresting cancer cells in G(1).
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PMID:Regulation of normal cell cycle progression by flavin-containing oxidases. 1763 56

We found that beta-lapachone (beta-lap), a novel bioreductive drug, caused rapid apoptosis and clonogenic cell death in A549 human lung epithelial cancer cells in vitro in a dose-dependent manner. The clonogenic cell death caused by beta-lap could be significantly inhibited by dicoumarol, an inhibitor of NAD(P)H:quinone oxido-reductase (NQO1), and also by siRNA for NQO1, demonstrating that NQO1-induced bioreduction of beta-lap is an essential step in beta-lap-induced cell death. Irradiation of A549 cells with 4 Gy caused a long-lasting upregulation of NQO1, thereby increasing NQO1-mediated beta-lap-induced cell deaths. Although the direct cause of beta-lap-induced apoptosis is not yet clear, beta-lap treatment reduced the expression of p53 and NF-kappaB, whereas it increased cytochrome C release, caspase-3 activity, and gammaH2AX foci formation. Importantly, beta-lap treatment immediately after irradiation enhanced radiation-induced cell death, indicating that beta-lap sensitizes cancer cells to radiation, in addition to directly killing some of the cells. The growth of A549 tumors induced in immunocompromised mice could be markedly suppressed by local radiation therapy when followed by beta-lap treatment. This is the first study to demonstrate that combined radiotherapy and beta-lap treatment can have a significant effect on human tumor xenografts.
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PMID:Upregulation of NAD(P)H:quinone oxidoreductase by radiation potentiates the effect of bioreductive beta-lapachone on cancer cells. 1778 82

The NAD(+)-dependent protein deacetylase SIRT1 is linked to cellular survival pathways by virtue of keeping the tumor suppressor gene p53 and members of the forkhead transcription factor family deacetylated. To validate SIRT1 as a therapeutic anti-cancer target, we performed immunohistochemistry experiments to study the in vivo expression of SIRT1 in cancer specimens. We show that human SIRT1 is highly expressed in cancer cell lines as well as in tissue samples from colon carcinoma patients. Interestingly, there is a strong cytosolic component in the SIRT1 expression pattern. We further characterized SIRT1 in p53-wild-type and -mutant cell lines and show that SIRT1 mRNA-knockdown leads to a p53-independent decrease of cell proliferation and induction of apoptosis. In addition, SIRT1 expression has been found to be inducible upon DNA damage. A previously discovered small molecule SIRT1 inhibitor with nanomolar in vitro activity has been tested in cancer relevant assays. The SIRT1 inhibitory compound showed no potent anti-proliferative activity despite hitting its molecular target within tumor cells. From these studies we conclude that it may not be sufficient to block the catalytic function of SIRT1, and that its survival effects may be mainly brought about by means other then the deacetylase function. The increased cytosolic expression of SIRT1 in cancer cells could be an indicator of such novel functions.
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PMID:Function of the SIRT1 protein deacetylase in cancer. 1780 2

Yeast Sir2 plays critical roles in gene silencing, stress resistance and longevity. Mammalian Sirt1 NAD(+)-dependent protein deacetylase, the closest homolog of Sir2, regulates cell cycle, cellular senescence, apoptosis and metabolism, by functional interactions with a number of biological molecules such as p53. To investigate a role of Sirt1 in endothelial dysfunction and premature senescence, we examined the effects of Sirt1 inhibition in human umbilical vein endothelial cells (HUVEC). Sirt1 inhibition by sirtinol, which is a 2-hydroxy-1-napthaldehyde derivative, or siRNA for Sirt1-induced premature senescence-like phenotype, as judged by increased senescence-associated beta-galactosidase (SA-beta-gal) activity, sustained growth arrest and enlarged and flattened cell morphology at 10 days after the treatment. Sixty-four percent of sirtinol (60 mumol/L)-treated HUVEC was SA-beta-gal-positive, whereas only 17% of vehicle-treated cells were positive. Sirt1 inhibition by sirtinol or Sirt1 siRNA increased PAI-1 expression and decreased both protein expression and activity of eNOS. Treatment with sirtinol or Sirt1 siRNA increased acetylation of p53, while p53 expression was unaltered. Impaired epidermal growth factor-induced activation of mitogen-activated protein kinases was associated with Sirt1 inhibition-induced senescence-like growth arrest. Conversely, overexpression of Sirt1 prevented hydrogen peroxide-induced SA-beta-gal activity, morphological changes and deranged expression of PAI-1 and eNOS. These results showed that Sirt1 inhibition increased p53 acetylation and induced premature senescence-like phenotype in parallel with increased PAI-1 and decreased eNOS expression. Our data suggest that Sirt1 may exert protective effects against endothelial dysfunction by preventing stress-induced premature senescence and deranged expression of PAI-1 and eNOS.
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PMID:Sirt1 modulates premature senescence-like phenotype in human endothelial cells. 1791 62

Quinones are abundant cyclic organic compounds present in the environment as well as in pro- and eukaryotic cells. Several species have been shown to possess enzymes that afford the two-electron reduction to the hydroquinone form in an attempt to avoid the generation of one-electron reduced semiquinone known to cause oxidative stress. These enzymes utilize a flavin cofactor, either FMN or FAD, to transfer a hydride from an electron donor, such as NAD(P)H, to a quinone substrate. This family of flavin-dependent quinone reductases shares a flavodoxin-like structure and reaction mechanism pointing towards a common evolutionary origin. Recent studies of their physiological functions in eukaryotes suggest a role beyond detoxication of quinones and involvement in the oxygen stress response. Accordingly, mammalian quinone reductases emerge as central molecular switches that control the lifespan of transcription factors, such as p53, and hence participate in the development of apoptosis and cell transformation.
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PMID:Flavin-dependent quinone reductases. 1793 60

Werner syndrome is an autosomal recessive disorder associated with premature aging and cancer predisposition caused by mutations of the WRN gene. WRN is a member of the RecQ DNA helicase family with functions in maintaining genome stability. Sir2, an NAD-dependent histone deacetylase, has been proven to extend life span in yeast and Caenorhabditis elegans. Mammalian Sir2 (SIRT1) has also been found to regulate premature cellular senescence induced by the tumor suppressors PML and p53. SIRT1 plays an important role in cell survival promoted by calorie restriction. Here we show that SIRT1 interacts with WRN both in vitro and in vivo; this interaction is enhanced after DNA damage. WRN can be acetylated by acetyltransferase CBP/p300, and SIRT1 can deacetylate WRN both in vitro and in vivo. WRN acetylation decreases its helicase and exonuclease activities, and SIRT1 can reverse this effect. WRN acetylation alters its nuclear distribution. Down-regulation of SIRT1 reduces WRN translocation from nucleoplasm to nucleoli after DNA damage. These results suggest that SIRT1 regulates WRN-mediated cellular responses to DNA damage through deacetylation of WRN.
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PMID:Regulation of WRN protein cellular localization and enzymatic activities by SIRT1-mediated deacetylation. 1820 16

Poly(ADP-ribosyl)ation is a post-translational modification catalyzed mostly by the 116-kDa enzyme poly(ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme that transfers an ADP-ribose moiety onto a limited number of nuclear proteins, including itself. When cells are exposed to environmental stresses such as alkylating agents or free radicals, there is up to a 500-fold increase in net poly(ADP-ribose) synthesis in response to DNA strand breaks. The enzyme responsible for 80% to 90% of this stimulated poly(ADP-ribose) synthesis is PARP-1, while other PARPs are responsible for the remaining 10% to 20%. The physiological meaning of these phenomena is not clear; however, it can be interpreted as a way of translating an event occurring on DNA to the nucleus by protein modification and finally to the cytoplasm via NAD(+) depletion. It has also been proposed that the presence of negatively charged poly(ADP-ribose) at the site of DNA damage may play several roles in regulation of base excision repair, p53 functions, and apoptosis. This unit describes protocols for measuring the levels of poly(ADP-ribose) in cells using nonisotopic reagents and for identifying the poly(ADP-ribose) polymerase enzymes present in cells.
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PMID:Nonisotopic methods for determination of poly(ADP-ribose) levels and detection of poly(ADP-ribose) polymerase. 1822 47


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