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)

p53-mediated increase in cyclin-dependent kinase inhibitor p21(WAF1) protein is thought to be the major mediator of cell cycle arrest after DNA damage. Previously p21 protein levels have been reported to increase or to decrease after UV irradiation. We show that p21 protein is degraded after irradiation of a variety of cell types with low but not high doses of UV. Cell cycle arrest occurs despite p21 degradation via Tyr(15) inhibitory phosphorylation of cdk2 and differs from the classical p21-dependent checkpoint elicited by ionizing radiation. In contrast to the basal turnover of p21, degradation of p21 switches to ubiquitin/Skp2-dependent proteasome pathway following UV irradiation. ATR activation after UV irradiation is essential for signaling p21 degradation. Finally, UV-induced p21 degradation is essential for optimal DNA repair. These results provide novel insight into regulation of p21 protein and its role in the cellular response to DNA damage.
 ...
PMID:UV irradiation triggers ubiquitin-dependent degradation of p21(WAF1) to promote DNA repair. 1367 83

NFBD1/MDC1 (mediator of DNA damage checkpoint 1) is a nuclear factor with an amino-terminal FHA (forkhead-associated) domain and a tandem repeat of BRCT (breast cancer susceptibility gene-1 carboxyl terminus) domains. We have previously shown that NFBD1 is an early participant in DNA damage signaling pathways and that ionizing radiation-induced nuclear foci (IRIF) of NFBD1 colocalize with several DNA checkpoint signaling and repair factors. We report here that NFBD1 physically associates with ATM, p53, components of the MRE11-RAD50-NBS1 (MRN) complex, and gamma-H2AX. An overexpressed FHA domain-containing fragment of NFBD1 binds to endogenous NFBD1 and components of the MRN complex, but not to gamma-H2AX. This fragment interferes with IRIF formation by endogenous NFBD1, MRE11, or NBS1. A BRCT domain-containing fragment of NFBD1 binds to gamma-H2AX and 53BP1, but not to components of the MRN complex, and abolishes IRIF formation by NFBD1, MRE11, NBS1, 53BP1, CHK2 phospho-T68, gamma-H2AX, and possible ATM/ATR substrates recognized by anti-phospho-SQ/TQ antibody. These results suggest that NFBD1 is an ATM/ATR-dependent organizer that recruits DNA checkpoint signaling and repair proteins to the sites of DNA damage.
 ...
PMID:NFBD1/MDC1 regulates ionizing radiation-induced focus formation by DNA checkpoint signaling and repair factors. 1451 63

Cisplatin is one of the most potent antitumor agents known, displaying clinical activity against a wide variety of solid tumors. Its cytotoxic mode of action is mediated by its interaction with DNA to form DNA adducts, primarily intrastrand crosslink adducts, which activate several signal transduction pathways, including those involving ATR, p53, p73, and MAPK, and culminate in the activation of apoptosis. DNA damage-mediated apoptotic signals, however, can be attenuated, and the resistance that ensues is a major limitation of cisplatin-based chemotherapy. The mechanisms responsible for cisplatin resistance are several, and contribute to the multifactorial nature of the problem. Resistance mechanisms that limit the extent of DNA damage include reduced drug uptake, increased drug inactivation, and increased DNA adduct repair. Origins of these pharmacologic-based mechanisms, however, are at the molecular level. Mechanisms that inhibit propagation of the DNA damage signal to the apoptotic machinery include loss of damage recognition, overexpression of HER-2/neu, activation of the PI3-K/Akt (also known as PI3-K/PKB) pathway, loss of p53 function, overexpression of antiapoptotic bcl-2, and interference in caspase activation. The molecular signature defining the resistant phenotype varies between tumors, and the number of resistance mechanisms activated in response to selection pressures dictates the overall extent of cisplatin resistance.
 ...
PMID:Cisplatin: mode of cytotoxic action and molecular basis of resistance. 1457 37

The ATM-dependent accumulation of p53 and induction of p21waf1 are key events for G1 cell-cycle checkpoint arrest following DNA damage. In ATM-null AT cells, even though the p53 and p21waf1 responses are kinetically delayed and quantitatively reduced, the G1 checkpoint is virtually disrupted, suggesting that these proteins arrive too late in G1 to enforce the arrest. As the precise mechanism remains unclear, we examined the response to DNA double-strand breaks generated by gamma-radiation (IR), to determine if ATM deficiency affects the cell-cycle phase regulation of these molecules. We find that, after irradiation, whereas normal LCL-N cells markedly increase their levels of p53 in all phases of the cell cycle, AT cells fail to show any p53 increase in the G1 phase. In addition, whereas in LCL-N p21waf1 is induced in G1 and G2-M, in AT cells this induction is partly seen in G2-M, but not in G1, indicating a different cell-cycle phase regulation of p53 and p21waf1 as a result of ATM deficiency. The levels and catalytic activity of the p53-targeting kinases ATR and DNA-PK in LCL-N and AT cells are very similar throughout the cell cycle, both before and after IR, thus excluding a phase-specific activity for these kinases. Collectively, our findings demonstrate that, in ATM-deficient cells, the p53-dependent p21waf1 response to DNA damage is not only quantitatively reduced, but also specifically suppressed in the G1 phase, thus providing a mechanistic explanation for the severe disruption of the G1 checkpoint in AT cells.
 ...
PMID:DNA damage-induced cell-cycle phase regulation of p53 and p21waf1 in normal and ATM-defective cells. 1458 14

The methylxanthine drug Pentoxifylline is reviewed for new properties which have emerged only relatively recently and for which clinical applications can be expected. After a summary on the established systemic effects of Pentoxifylline on the microcirculation and reduction of tumour anoxia, the role of the drug in the treatment of vasoocclusive disorders, cerebral ischemia, infectious diseases, septic shock and acute respiratory distress, the review focuses on another level of drug action which is based on in vitro observations in a variety of cell lines. Pentoxifylline and the related drug Caffeine are known radiosensitizers especially in p53 mutant cells. The explanation that the drug abrogates the G2 block and shortens repair in G2 by promoting early entry into mitosis is not anymore tenable because enhancement of radiotoxicity requires presence of the drug during irradiation and fails when the drug is added after irradiation at the G2 maximum. Repair assays by measurement of recovery ratios and by delayed plating experiments indeed strongly suggested a role in repair which is now confirmed for Pentoxifylline by constant field gel electrophoresis (CFGE) measurements and for Pentoxifylline and for Caffeine by use of a variety of repair mutants. The picture now emerging shows that Caffeine and Pentoxifylline inhibit homologous recombination by targeting members of the PIK kinase family (ATM and ATR) which facilitate repair in G2. Pentoxifylline induced repair inhibition between irradiation dose fractions to counter interfraction repair has been successfully applied in a model for stereotactic surgery. Another realistic avenue of application of Pentoxifylline in tumour therapy comes from experiments which show that repair events in G2 can be targeted directly by addition of cytotoxic drugs and Pentoxifylline at the G2 maximum. Under these conditions massive dose enhancement factors of up to 80 have been observed suggesting that it may be possible to realise dramatic improvements to tumour growth control in the clinic.
 ...
PMID:Inhibition of DNA repair by Pentoxifylline and related methylxanthine derivatives. 1459 74

Flavonoids (FVs) are an important class of plant compounds postulated to be one of the constituents responsible for the beneficial effects of fruits and vegetables on health, including heart disease and cancer. At pharmacological levels, various naturally-occurring flavonoids have been shown to be cancer-protective in a variety of animal models and flavonoid derivatives, such as flavopyridol, are being assessed as chemotherapy drugs in clinical trials. This report has investigated the effects of the most common dietary FVs on several major signalling pathways in biopsies of human epithelial cells using primary cultures freshly isolated from biopsies and has obtained evidence for the previously unrecognised importance of stress kinase responses induced by kaempferol (KF), apigenin (AP) and luteolin (LU). KF, AP and LU all activated ATM/ATR (mutated in ataxia-telangiectasia and related) kinases and the p38 stress kinase and this was associated with induction of GADD45 and cell cycle arrest in G2, but not induction of apoptosis. These effects were not due to general toxicity since they were reversible on removal of FV. The inductions of ATM/ATR and p38 were functionally important since caffeine, an inhibitor of ATM/ATR, and the p38-specific inhibitor, SB203580, prevented induction of GADD45 and growth arrest by these three flavonoids. In contrast, although quercetin (QU) activated ATM (but not ATR), it did not activate p38 kinase, GADD45 or p53. QU may interfere with one of the lipoxygenase (LOX) pathways since the growth inhibitory effects of QU (but not the other three flavonoids) could be reversed by addition of LOX metabolites, particularly 12- and 15-hydroxyeicostetraenic acids.
 ...
PMID:Effects of dietary flavonoids on major signal transduction pathways in human epithelial cells. 1460 32

The DNA replication checkpoint is an inhibitory pathway ensuring that mitosis occurs only after completion of DNA synthesis. Its function may be relevant to the stability of the genome. The essential elements of this checkpoint are ATM/ATR kinases that indirectly lead to the phosphorylation and inhibition of the mitosis-promoting factor (Cdc2/cyclin B1). The function of this checkpoint was analysed in diverse nontransformed and tumour-derived cell lines. All cell lines tested arrested mitosis entry when DNA synthesis was inhibited by hydroxyurea (HU) treatment. But, unlike what has been described in yeast and Xenopus, in normal rat kidney (NRK) cells and NIH 3T3 fibroblasts, the arrest induced by HU treatment was not abrogated by caffeine, an ATM and ATR inhibitor. This indicated the presence of an ATM/ATR-independent response to DNA synthesis inhibition in these nontransformed mammalian cell lines. Interestingly, the behaviour of different tumour cell lines after caffeine treatment varied. While SW480, NP29, NP18 and HeLa cells did not enter mitosis in the presence of caffeine after HU treatment, in CaCo2, DLD1, HCT116 and HT29 caffeine abrogated the checkpoint response. In nontransformed cell lines, lack of cyclin B1 accumulation was observed when DNA synthesis was inhibited. This response was not abrogated by caffeine. In the tumour cell lines, a good correlation between the ability to arrest cell cycle when DNA synthesis was inhibited in the presence of caffeine and the lack of cyclin B1 accumulation was observed. Thus, there is an ATM/ATR-independent checkpoint response that leads to a decrease in cyclin B1 accumulation. However, this response is not functional in some tumour cell lines. Using inhibitors of p38alpha and beta, Mek1, 2 and p53-/- knocked-out fibroblasts, we showed that these proteins were also not involved in this particular checkpoint response. Lack of cyclin B1 accumulation after DNA synthesis inhibition in NRK cells was not due to increased degradation of the protein, but correlated with a decrease in mRNA accumulation.
 ...
PMID:ATM/ATR-independent inhibition of cyclin B accumulation in response to hydroxyurea in nontransformed cell lines is altered in tumour cell lines. 1461 52

Cdc7 kinase plays an essential role in firing of replication origins by phosphorylating components of the replication complexes. Cdc7 kinase has also been implicated in S phase checkpoint signaling downstream of the ATR and Chk1 kinases. Inactivation of Cdc7 in yeast results in arrest of cell growth with 1C DNA content after completion of the ongoing DNA replication. In contrast, conditional inactivation of Cdc7 in undifferentiated mouse embryonic stem (ES) cells leads to growth arrest with rapid cessation of DNA synthesis, suggesting requirement of Cdc7 functions for continuation of ongoing DNA synthesis. Furthermore, loss of Cdc7 function induces recombinational repair (nuclear Rad51 foci) and G2/M checkpoint responses (inhibition of Cdc2 kinase). Eventually, p53 becomes highly activated and the cells undergo massive p53-dependent apoptosis. Thus, defective origin activation in mammalian cells can generate DNA replication checkpoint signals. Efficient removal of those cells in which replication has been perturbed, through cell death, may be beneficial to maintain the highest level of genetic integrity in totipotent stem cells. Partial, rather than total, loss of Cdc7 kinase expression results in retarded growth at both cellular and whole body levels, with especially profound impairment of germ cell development.
 ...
PMID:Functions of mammalian Cdc7 kinase in initiation/monitoring of DNA replication and development. 1464 27

The ability of caffeine to reverse cell cycle checkpoint function and enhance genotoxicity after DNA damage was examined in telomerase-expressing human fibroblasts. Caffeine reversed the ATM-dependent S and G2 checkpoint responses to DNA damage induced by ionizing radiation (IR), as well as the ATR- and Chk1-dependent S checkpoint response to ultraviolet radiation (UVC). Remarkably, under conditions in which IR-induced G2 delay was reversed by caffeine, IR-induced G1 arrest was not. Incubation in caffeine did not increase the percentage of cells entering the S phase 6-8h after irradiation; ATM-dependent phosphorylation of p53 and transactivation of p21(Cip1/Waf1) post-IR were resistant to caffeine. Caffeine alone induced a concentration- and time-dependent inhibition of DNA synthesis. It inhibited the entry of human fibroblasts into S phase by 70-80% regardless of the presence or absence of wildtype ATM or p53. Caffeine also enhanced the inhibition of cell proliferation induced by UVC in XP variant fibroblasts. This effect was reversed by expression of DNA polymerase eta, indicating that translesion synthesis of UVC-induced pyrimidine dimers by DNA pol eta protects human fibroblasts against UVC genotoxic effects even when other DNA repair functions are compromised by caffeine.
 ...
PMID:Caffeine and human DNA metabolism: the magic and the mystery. 1464 31

Severe levels of hypoxia (oxygen concentrations of less that 0.02%) have been shown to induce a rapid S-phase arrest. The mechanism behind hypoxia-induced S-phase arrest is unclear, we show here that it was not mediated by a shortage of nucleosides and was not dependent on p53, p21 or Hif 1alpha status. The drugs aphidicolin and hydroxyurea both induce rapid replication arrest and have been used throughout the literature to study the ATR-mediated response to stalled replication. We have shown previously that hypoxia induces ATR-dependent phosphorylation of p53, Chk1 and histone H2AX. Using comet-assays to detect DNA-damage we found that both aphidicolin and hydroxyurea induced significant levels of DNA-damage while hypoxia did not. Here we show that like aphidicolin and hydroxyurea, hypoxia induces phosphorylation of Nbs1 at serine 343 and Rad17 serine 645. Hypoxia-dependent phosphorylation of Nbs1 and Rad17 was ATM-independent and therefore likely to be a result of the ATR kinase activity. In contrast, p53 was phosphorylated differentially in response to the three treatments considered here. p53 was phosphorylated at serine 15 in response to all three treatments but was only phosphorylated at serine 20 in response to the drug treatments. We propose that treatment with either aphidicolin or hydroxyurea leads to not only replication arrest but also DNA-damage and therefore both ATM and ATR-mediated signaling. In contrast replication arrest induced by severe hypoxia is sensed exclusively through ATR, with ATM only having a role to play after re-oxygenation.
 ...
PMID:Comparison of hypoxia-induced replication arrest with hydroxyurea and aphidicolin-induced arrest. 1464 37


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>