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

Cell cycle checkpoints that monitor DNA damage and spindle assembly are essential for the maintenance of genetic integrity, and drugs that target these checkpoints are important chemotherapeutic agents. We have examined how cells respond to DNA damage while the spindle-assembly checkpoint is activated. Single cell electrophoresis and phosphorylation of histone H2AX indicated that several chemotherapeutic agents could induce DNA damage during mitotic block. DNA damage during mitotic block triggered CDC2 inactivation, histone H3 dephosphorylation, and chromosome decondensation. Cells did not progress into G1 but seemed to retract to a G2-like state containing 4N DNA content, with stabilized cyclin A and cyclin B1 binding to Thr14/Tyr15-phosphorylated CDC2. The loss of mitotic cells was not due to cell death because there was no discernible effect on caspase-3 activation, DNA fragmentation, or viability. Extensive DNA damage during mitotic block inactivated cyclin B1-CDC2 and prevented G1 entry when the block was removed. The mitotic DNA damage responses were independent of p53 and pRb, but they were dependent on ATM. CDC25A that accumulated during mitosis was rapidly destroyed after DNA damage in an ATM-dependent manner. Ectopic expression of CDC25A or nonphosphorylatable CDC2 effectively inhibited the dephosphorylation of histone H3 after DNA damage. Hence, although spindle disruption and DNA damage provide conflicting signals to regulate CDC2, the negative regulation by the DNA damage checkpoint could overcome the positive regulation by the spindle-assembly checkpoint.
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PMID:DNA damage during the spindle-assembly checkpoint degrades CDC25A, inhibits cyclin-CDC2 complexes, and reverses cells to interphase. 1451 13

Histone modification enables the ordered regulation of DNA-related processes. Here, we ask if p53, which interacts with histone modifying complexes in vivo, influences histone H3 modification. For this purpose, we compared isogenic clones of human p53+/+ and p53-/- cells in which it is reasonable to attribute any observed differences in histone modification to p53-related effects. Cell growth and cell cycle analyses indicated equivalent proliferation rates for the p53+/+ and p53-/- cell clones. Modification of histone H3 was determined under normal cell growth conditions and also after UV irradiation and/or treatment with trichostatin A (TSA) or nicotinamide (two inhibitors of histone deacetylation). Site-specific histone H3 modifications were determined by immunoblotting. We provide evidence that p53 influences histone H3 acetylation at lysine 9 (K9) and K14, whereas acetylation of K18 appears to be p53 independent. The most striking p53-related effects are at K9, which is underacetylated in p53-/- cells under normal conditions of growth but which shows a dramatic increase in acetylation after combined treatment with UV plus TSA. Conversely, phosphorylation of serine 10 (S10P) is elevated in p53-/- cells and reduced after UV plus TSA treatment. Similar reciprocity between K9Ac and S10P was not evident in p53+/+ cells. Abnormal S10P in p53-/- cells was also observed under completely different experimental conditions where cells were treated with nocodazole to induce G(2)-M arrest and elevation of S10P (which is linked with G(2)-M of the cell cycle). On removal of nocodazole, the p53+/+ cells exhibited rapid reduction in S10P levels and cell cycle recovery. In contrast, the p53-/- cells retained elevated S10P levels and failed to show normal cell cycle recovery. Phosphorylation of S10 is known to be linked with the initiation of chromosome condensation in G(2) and is also important for proper chromosome segregation at mitosis. Our results indicate that loss of p53, directly or indirectly, perturbs the normal regulation of S10 phosphorylation. We suggest that this effect may contribute toward the development of abnormal chromosomes and aneuploidy in p53-deficient cancers.
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PMID:Loss of p53 has site-specific effects on histone H3 modification, including serine 10 phosphorylation important for maintenance of ploidy. 1458 61

Histone acetyltransferase (HAT) proteins often exhibit a high degree of specificity for lysine-bearing protein substrates. We have previously reported on the structure of the Tetrahymena Gcn5 HAT protein (tGcn5) bound to its preferred histone H3 substrate, revealing the mode of substrate binding by the Gcn5/PCAF family of HAT proteins. Interestingly, the Gcn5/PCAF HAT family has a remarkable ability to acetylate lysine residues within diverse cognate sites such as those found around lysines 14, 8, and 320 of histones H3, H4, and p53, respectively. To investigate the molecular basis for this, we now report on the crystal structures of tGcn5 bound to 19-residue histone H4 and p53 peptides. A comparison of these structures with tGcn5 bound to histone H3 reveals that the Gcn5/PCAF HATs can accommodate divergent substrates by utilizing analogous interactions with the lysine target and two C-terminal residues with a related chemical nature, suggesting that these interactions play a general role in Gcn5/PCAF substrate binding selectivity. In contrast, while the histone H3 complex shows extensive interactions with tGcn5 and peptide residues N-terminal to the target lysine, the corresponding residues in histone H4 and p53 are disordered, suggesting that the N-terminal substrate region plays an important role in the enhanced affinity of the Gcn5/PCAF HAT proteins for histone H3. Together, these studies provide a framework for understanding the substrate selectivity of HAT proteins.
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PMID:Molecular basis for Gcn5/PCAF histone acetyltransferase selectivity for histone and nonhistone substrates. 1466 47

Ceramide, a compound derived from sphingomyelin, a sphingolipid precursor, affects cell functions such as growth, differentiation, cell division and apoptosis. We have shown that the phytosphingosine derivative, tetra-acetyl phytosphingosine (TAPS), inhibits the growth of HaCaT cells mainly by inducing apoptosis. In this study, we investigated its effect on the cell cycle and on cell cycle regulatory proteins. We showed by flow cytometry and staining for BrdU and phosphorylated histone H3 that the cells accumulated in S phase and arrested in G2 phase and did not divide before undergoing apoptosis. The level of the pro-apoptotic regulator Bax peaked after 6 h and then returned to normal, whereas the level of the anti-apoptotic regulator Bcl-xL, which is presumably induced in order to inhibit apoptosis, started to increase at 6 h, and remained high for 24 h. Phosphorylation of Cdc2 on Tyr-15 greatly increased while p21 rose to a plateau at 8 h. Levels of p53 and Mad2 proteins were unchanged. Our observations suggest that TAPS induces apoptosis of the HaCaT cells at least in part via transient G2 arrest.
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PMID:Induction of apoptosis and expression of cell cycle regulatory proteins in response to a phytosphingosine derivative in HaCaT human keratinocyte cells. 1474 23

Camptothecin and Adriamycin are clinically important inhibitors for topoisomerase (Topo) I and Topo II, respectively. The ataxia-telangiectasia mutated (ATM) product is essential for ionizing radiation-induced DNA damage responses, but the role of ATM in Topo poisons-induced checkpoints remains unresolved. We found that distinct mechanisms are involved in the activation of different cell cycle checkpoints at different concentrations of Adriamycin and camptothecin. Adriamycin promotes the G(1) checkpoint through activation of the p53-p21(CIP1/WAF1) pathway and decrease of pRb phosphorylation. Phosphorylation of p53(Ser20) after Adriamycin treatment is ATM dependent, but is not required for the full activation of p53. The G(1) checkpoint is dependent on ATM at low doses but not at high doses of Adriamycin. In contrast, the Adriamycin-induced G(2) checkpoint is independent on ATM but sensitive to caffeine. Adriamycin inhibits histone H3(Ser10) phosphorylation through inhibitory phosphorylation of CDC2 at low doses and down-regulation of cyclin B1 at high doses. The camptothecin-induced intra-S checkpoint is partially dependent on ATM, and is associated with inhibitory phosphorylation of cyclin-dependent kinase 2 and reduction of BrdUrd incorporation after mid-S phase. Finally, apoptosis associated with high doses of Adriamycin or camptothecin is not influenced by the absence of ATM. These data indicate that the involvement of ATM following treatment with Topo poisons differs extensively with dosage and for different cell cycle checkpoints.
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PMID:Topoisomerase poisons differentially activate DNA damage checkpoints through ataxia-telangiectasia mutated-dependent and -independent mechanisms. 1514 Oct 20

Regulation of chromatin through histone acetylation is an important step in gene expression. The Gcn5 histone acetyltransferase is part of protein complexes, e.g., the SAGA complex, that interact with transcriptional activators, targeting the enzyme to specific promoters and assisting in recruitment of the basal RNA polymerase transcription machinery. The Ada2 protein directly binds to Gcn5 and stimulates its catalytic activity. Drosophila contains two Ada2 proteins, Drosophila Ada2a (dAda2a) and dAda2b. We have generated flies that lack dAda2b, which is part of a Drosophila SAGA-like complex. dAda2b is required for viability in Drosophila, and its deletion causes a reduction in histone H3 acetylation. A global hypoacetylation of chromatin was detected on polytene chromosomes in dAda2b mutants. This indicates that the dGcn5-dAda2b complex could have functions in addition to assisting in transcriptional activation through gene-specific acetylation. Although the Drosophila p53 protein was previously shown to interact with the SAGA-like complex in vitro, we find that p53 induction of reaper gene expression occurs normally in dAda2b mutants. Moreover, dAda2b mutant animals show excessive p53-dependent apoptosis in response to gamma radiation. Based on this result, we speculate that dAda2b may be necessary for efficient DNA repair or generation of a DNA damage signal. This could be an evolutionarily conserved function, since a yeast ada2 mutant is also sensitive to a genotoxic agent.
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PMID:Drosophila Ada2b is required for viability and normal histone H3 acetylation. 1534 70

Histone acetylation appears to play an important role in transcriptional regulation. Inactivation of chromatin by histone deacetylation is involved in the transcriptional repression of several tumour suppressor genes, including p21(WAF1/CIP1). However, the in vivo status of histone acetylation in human cancers, including gastric carcinoma, is not well understood. This study shows that histone H3 in the p21(WAF1/CIP1) promoter region is hypoacetylated and that this hypoacetylation is associated with reduced p21(WAF1/CIP1) expression in gastric carcinoma specimens. Chromatin immunoprecipitation assays revealed that histone H3 was hypoacetylated in the p21(WAF1/CIP1) promoter and coding regions in 10 (34.5%) and 10 (34.5%) of 29 gastric carcinoma specimens, respectively. Hypoacetylation of histone H4 in the p21(WAF1/CIP1) promoter and coding regions was observed in 6 (20.7%) and 16 (55.2%) of 29 gastric carcinoma specimens, respectively. p21(WAF1/CIP1) mRNA levels were associated with histone H3 acetylation status in the p21(WAF1/CIP1) promoter region (p = 0.047) but not p53 mutation status (p = 0.460). In gastric carcinoma cell lines, expression of p21(WAF1/CIP1) protein was induced by trichostatin A, a histone deacetylase inhibitor. This induction was associated with hyperacetylation of histone H3 in the p21(WAF1/CIP1) promoter region. Hyperacetylation of histone H4 in the p21(WAF1/CIP1) promoter region did not appear to be associated with increased expression. Induction of p21(WAF1/CIP1) protein expression was associated with hyperacetylation of histones H3 and H4 in the p21(WAF1/CIP1) coding region. Expression of a dominant-negative mutant of p53 reduced expression of p21(WAF1/CIP1) protein. Histone H4 acetylation in both the promoter and coding regions of the p21(WAF1/CIP1) gene in cells expressing dominant-negative p53 was less than half of that in cells expressing wild-type p53, whereas histone H3 acetylation in both the promoter and coding regions was slightly reduced (by approximately 20%) in cells expressing the dominant-negative p53. These findings provide evidence that alteration of histone acetylation occurs in human cancer tissue specimens such as those from gastric carcinoma.
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PMID:Histone H3 acetylation is associated with reduced p21(WAF1/CIP1) expression by gastric carcinoma. 1558 62

As combinations of genetic and/or epigenetic alterations occurring during salivary gland carcinogenesis are largely unknown, we here analyzed 36 salivary gland carcinomas (SGCs) for changes in INK4a/ARF, RB1, p21, p27, PTEN, p53, MDM2 and O6-MGMT genes using methylation specific PCR (MSP), loss of heterozygosity (LOH) assays and mutational analysis with immunohistochemistry (IHC), as well as histone H3 and H4 acetylation status. The RB1 gene was found to be the most frequently methylated (41.7% of cases), while methylation of p27(Kip1) and O6-MGMT were less frequent 8.3% and 5.6%, respectively). Two other genes, p21(Waf1) and PTEN, were unmethylated in the SGCs examined. RB1 methylation significantly correlated with loss of expression as determined by IHC (P=0.03), and also a poor prognosis (P=0.02). p53 mutations were found in 8 cases (22.2%), coupled with p14ARF hypermethylation in two cases. LOH in INK4a/ARF and the RB1 locus was observed in 33.3% and 28.6% of the lesions, respectively. There was no correlation between 9p21 LOH and methylation of the INK4a/ARF gene. Promoter hypermethylation of RB1 coupled with LOH was evident in three samples immuno-negative for RB1. Acetylation of histone H3 and H4 was detected in 6 and 5 cases, respectively. These findings indicate that epigenetic silencing of tumour suppressor genes via promoter hypermethylation might be crucial for salivary gland carcinogenesis, particularly in the RB1 gene. Thus epigenetic events including methylation and acetylation as well as genetic alterations may have important contributions.
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PMID:Genetic and epigenetic alteration profiles for multiple genes in salivary gland carcinomas. 1569 18

Rabdosia rubescens is a herbal medicine used to treat esophageal cancer in China. In this study, the sesquiterpene oridonin, an isoprenoid, was isolated from Rabdosia rubescens. Mass spectroscopy and carbon 13 NMR spectroscopy were used to identify the structure of the purified compound. It was then evaluated for biological activity against human cell lines derived from prostate (DU-145, LNCaP), breast (MCF-7), and ovarian (A2780 and PTX10) cancers. Oridonin exhibited anti-proliferative activity toward all cancer cell lines tested, with an IC50 estimated by the MTT cell viability assay ranging from 5.8+/-2.3 to 11.72+/-4.8 microM. Flow cytometric analysis demonstrated that oridonin induced a G1 phase arrest in androgen receptor-positive LNCaP cells containing wt p53, while it blocked the cell cycle at G2 and M phases in androgen receptor-negative DU-145 cells with mutated p53; the arrest in M was verified by examination of cell morphology and by the increased frequency of cells with Ser-10 phosphorylated histone H3. The increased incidence of apoptosis, identified by characteristic changes in cell morphology, was seen in tumor lines treated with oridonin. Notably, at concentrations that induced apoptosis among tumor cells, oridonin failed to induce apoptosis in cultures of normal human fibroblasts. Western blot analysis was used to determine the protein expression of cancer suppressor genes, p53 (wt) and Bax, and the proto-oncogene, Bcl-2 in LNCaP cells following treatment with oridonin. Oridonin up-regulated p53 and Bax and down-regulated Bcl-2 expression in a dose-dependent manner. To further explore the possible interaction between oridonin and DNA, its absorption spectrum was measured in the presence and absence of double stranded (ds) DNA. Spectral shifts and an increase in absorption band intensity were observed indicating interaction of oridonin with DNA bases. The nature of the binding is not clear at present though no evidence of histone H2AX phosphorylation on Ser-139 was apparent in DU-145 cells treated with oridonin that would indicate the induction of ds DNA breaks. In conclusion, oridonin inhibits cancer cell growth in a cell cycle specific manner and shifts the balance between pro- and anti-apoptotic proteins in favor of apoptosis. The present data suggest that further studies are warranted to assess the potential of oridonin in cancer prevention and/or treatment.
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PMID:The cytostatic and cytotoxic effects of oridonin (Rubescenin), a diterpenoid from Rabdosia rubescens, on tumor cells of different lineage. 1570 11

8-Chloro-adenosine (8-Cl-Ado) is a potent chemotherapeutic agent whose cytotoxicity in a variety of tumor cell lines has been widely investigated. However, the molecular mechanisms are uncertain. In this study, we found that exposure of human lung cancer cell lines A549 (p53-wt) and H1299 (p53-depleted) to 8-Cl-Ado induced cell arrest in the G2/M phase, which was accompanied by accumulation of binucleated and polymorphonucleated cells resulting from aberrant mitosis and failed cytokinesis. Western blotting showed the loss of phosphorylated forms of Cdc2 and Cdc25C that allowed progression into mitosis. Furthermore, the increase in Ser10-phosphorylated histone H3-positive cells revealed by fluorescence-activated cell sorting suggested that the agent-targeted cells were able to exit the G2 phase and enter the M phase. Immunocytochemistry showed that microtubule and microfilament arrays were changed in exposed cells, indicating that the dynamic instability of microtubules and microfilaments was lost, which may correlate with mitotic dividing failure. Aberrant mitosis resulted in mitotic catastrophe followed by varying degrees of apoptosis, depending on the cell lines. Thus, 8-Cl-Ado appears to exert its cytotoxicity toward cells in culture by inducing mitotic catastrophe.
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PMID:Exposure of human lung cancer cells to 8-chloro-adenosine induces G2/M arrest and mitotic catastrophe. 1572 Aug 7


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