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)

Suicide gene therapy systems such as the herpes simplex thymidine kinase/ganciclovir system (TK/GCV) may kill cancer cells by apoptosis through as yet undefined mechanisms. Here we show that TK/GCV treatment induces p53 accumulation and increases cell surface expression of CD95 and tumor necrosis factor receptor, which is likely to involve p53-mediated translocation of CD95 to the cell surface. TK/GCV-induced apoptosis involves CD95-L-independent CD95 aggregation leading to the formation of a Fas-associated death domain protein (FADD) and caspase-8-containing, death-inducing signaling complex. Dominant negative FADD, the caspase-8 inhibitor zIETD-fmk [Z-Ile-Glu(OMe)-Thr-Asp(OMe)-fluoromethylketone], and zVAD-fmk (Z-Val-Ala-Asp-fluoromethylketone) partially abrogate TK/GCV-induced apoptosis. In addition to apoptosis induction, TK/GCV treatment strongly sensitizes for CD95-L-, TNF-, and TNF-related, apoptosis-inducing, ligand (TRAIL)-induced cell death in constitutively resistant cells. These findings may be used to increase the efficacy of TK/GCV and other suicide gene therapy systems for the treatment of cancer.
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PMID:Herpes simplex virus thymidine kinase/ganciclovir-induced apoptosis involves ligand-independent death receptor aggregation and activation of caspases. 1041 38

Ligand-induced glucocorticoid receptor (GR) activation has recently been linked to the inhibition of cell proliferation via the transcriptional induction of p21(WAF1/Cip1), which functions as a universal inhibitor of cyclin-dependent protein kinases. Herein, we identify a Ser/Thr protein phosphatase (PP5) that promotes cellular proliferation by inhibiting both glucocorticoid and p53-mediated signaling pathways leading to p21(WAF1/Cip1)-mediated growth arrest. The suppression of PP5 expression (1) markedly increases the association of GR with its cognate DNA-binding sequence, (2) induces GR transcriptional activity without the addition of hormone, and (3) increases dexamethasone-mediated induction of GR reporter activity to a level that is approximately 10 times greater than the maximal response obtainable in the presence of PP5. PP5 has no apparent effect on the binding of hormone to the GR, and dexamethasone-mediated growth arrest correlates with an increase in p53 phosphorylation. Comparative studies in p53-wild-type, p53-defective, and p53-deficient cell lines indicate that either (1) p53 participates in GR-mediated induction of p21(WAF1/Cip1), with the hyperphosphorylation of basal p53 induced by glucocorticoids sufficient for the propagation of an antiproliferative response when PP5 expression is inhibited, or (2) PP5 acts where p53-mediated and GR-induced signaling networks converge to regulate the transcriptional induction of p21(WAF1/Cip1). Thus, aberrant PP5 expression may have an additive effect on the development of human cancers by promoting cell proliferation via the inhibition of a GR-induced antiproliferative signaling cascade, and facilitating neoplastic transformation via the inhibition of a growth-arresting p53-mediated response that guards against genomic instability.
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PMID:Ser/Thr protein phosphatase type 5 (PP5) is a negative regulator of glucocorticoid receptor-mediated growth arrest. 1041 57

The ability to separate the isoforms of human tumour suppressor protein p53 expressed in insect cells using heparin-Sepharose correlates with differences in the isoelectric point of p53, demonstrating that p53 can be heterogeneously modified and providing support for the use of insect cells as a model system for identifying novel signalling pathways that target p53. One p53 isoform that was reduced in its binding to the monoclonal antibody DO-1 could be stimulated in its binding to DO-1 by prior incubation with protein phosphatases, suggesting the presence of a previously unidentified N-terminal phosphorylation site capable of masking the DO-1 epitope. A synthetic peptide from the N-terminal domain of p53 containing phosphate at Ser(20) inhibited DO-1 binding, thus identifying the phosphorylation site responsible for DO-1 epitope masking. Monoclonal antibodies overlapping the DO-1 epitope were developed that are specific for phospho-Thr(18) (adjacent to the DO-1 epitope) and phospho-Ser(20) (within the DO-1 epitope) to determine whether direct evidence could be obtained for novel phosphorylation sites in human p53. A monoclonal antibody highly specific for phospho-Ser(20) detected significant phosphorylation of human p53 expressed in insect cells, whereas the relative proportion of p53 modified at Thr(18) was substantially lower. The relevance of these two novel phosphorylation sites to p53 regulation in human cells was made evident by the extensive phosphorylation of human p53 at Thr(18) and Ser(20) in a panel of human breast cancers with a wild-type p53 status. Phospho-Ser(20) or phospho-Thr(18) containing p53 peptides are as effective as the phospho-Ser(15) peptide at reducing mdm2 (mouse double minute 2) protein binding, indicating that the functional effects of these phosphorylation events might be to regulate the binding of heterologous proteins to p53. These results provide evidence in vivo for two novel phosphorylation sites within p53 at Ser(20) and Thr(18) that can affect p53 protein-protein interactions and indicate that some human cancers might have amplified one or more Ser(20) and Thr(18) kinase signalling cascades to modulate p53 activity.
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PMID:Novel phosphorylation sites of human tumour suppressor protein p53 at Ser20 and Thr18 that disrupt the binding of mdm2 (mouse double minute 2) protein are modified in human cancers. 1043 10

Okadaic acid (OA), a toxin from the black sponge Halicondria okadai, is a specific inhibitor of serine/threonine protein phosphatases 1 (PP1) and 2A (PP2A). OA is a tumor promoter but also induces apoptosis in some tumor cell lines. In this study, we determined whether ras mutation and/or p53 status are characteristics associated with the cell's sensitivity to the induction of apoptosis by OA. Several cell lines that differed in ras and p53 mutations were treated with OA (10-100 nM). At 24 to 48 h after treatment, the percentage of cells undergoing apoptosis was quantitated. The cell lines with mutations in either H-ras (human bladder carcinoma cell line T24 and mouse keratinocyte cell line 308), or K-ras (human colon carcinoma cell lines DLD-1 and HCT116; human prostate cancer cell lines LNCaP and PC-3; human lung cancer cell lines Calu-6 and SKLU-1; and human pancreatic cancer cell line MIAPaCa2) were more sensitive to OA-induced apoptosis (3- to 10-fold) than the cell lines that lacked the ras mutation (mouse epidermal cell lines C50 and JB6; murine fibroblast cell line NIH3T3; human colon cancer cell line HT29; human kidney epithelial cell line Hs715.K; and human pancreatic cancer cell line Bx-PC3). Similarly, using isogenic cell lines we found that overexpression of mutated H-ras in NIH3T3 and in SV40 immortalized human uroepithelial cells (SVHUC) enhanced their sensitivity to undergo apoptosis in response to OA treatment. The T24, DLD-1, SKLU-1, Calu-6, and MIAPaCa2 cell lines express mutated p53. The SVHUC as well as their ras-transfected counterparts have inactive p53 due to complex formation between large "T" antigen and p53. Taken together, these results imply that OA-induced apoptosis may involve a p53-independent pathway. The transfectants (NIH3T3-ras and SVHUC-ras), which express mutated H-ras, have up-regulated PP2A activity. OA treatment inhibited in vivo the levels of PP1 and PP2A activity, and induced apoptosis in SVHUC-ras and other cell lines. We conclude that OA-induced cell death pathway in ras-activated cell lines may involve a cross talk between PP1 and PP2A and ras signaling pathways. In light of the present results, the current theory that OA promotes mouse skin tumor formation by selective expansion of initiated cells that harbor ras mutations needs reevaluation.
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PMID:Ras mutation, irrespective of cell type and p53 status, determines a cell's destiny to undergo apoptosis by okadaic acid, an inhibitor of protein phosphatase 1 and 2A. 1046 39

The hormonally active form of vitamin D3, 1,25-dihydroxyvitamin D3, and its two analogues, EB 1089 and CB 1093, are novel putative anticancer agents with an interesting profile of induction of growth inhibition, differentiation, and apoptosis in tumor cells. To study the signaling pathways mediating these events, we used two human breast cancer cell lines: MCF-7 cells, expressing a wild-type p53 tumor suppressor protein, and T47D cells, lacking a functional p53. Vitamin D compounds induced a growth arrest followed by apoptosis in both cell lines at concentrations ranging from 1 to 100 nM, indicating that p53 is not necessary for growth-inhibitory effects induced by vitamin D compounds. Surprisingly, apoptosis induced by these compounds occurred also independently of known caspases. Inhibition of caspase activation by overexpression of a cowpox-derived caspase inhibitor CrmA or by addition of inhibitory peptides acetyl-Asp-Glu-Val-Asp-aldehyde (200 microM), acetyl-Ile-Glu-Thr-Asp-aldehyde (50 microM), and Z-Val-Ala-D,L-Asp-fluoromethylketone (1 microM) showed no effect on the induction of growth arrest or apoptosis by vitamin D compounds under assay conditions in which apoptosis induced by TNF or staurosporine was effectively inhibited. Moreover, overexpression of caspase-3 in MCF-7 cells had no sensitizing effect to vitamin D compounds, and neither caspase-3-like protease activity nor cleavage of a caspase substrate poly(ADP)ribose polymerase was detected in lysates from apoptotic cells following the treatment with these compounds. Contrary to CrmA, overexpression of an antiapoptotic protein Bcl-2 in MCF-7 cells conferred a nearly complete protection from apoptosis induced by vitamin D compounds. Taken together, these data indicate that vitamin D compounds induce apoptosis via a novel caspase- and p53-independent pathway that can be inhibited by Bcl-2. This may prove useful in the treatment of tumors that are resistant to therapeutic agents that are dependent on the activation of p53 and/or caspases.
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PMID:Apoptosis induced by vitamin D compounds in breast cancer cells is inhibited by Bcl-2 but does not involve known caspases or p53. 1051 95

Overexpression of p53 causes G2 arrest, attributable in part to the loss of CDC2 activity. Transcription of cdc2 and cyclin B1, determined using reporter constructs driven by the two promoters, was suppressed in response to the induction of p53. Suppression requires the regions -287 to -123 of the cyclin B1 promoter and -104 to -74 of the cdc2 promoter. p53 did not affect the inhibitory phosphorylations of CDC2 at threonine 14 or tyrosine 15 or the activity of the cyclin-dependent kinase that activates CDC2 by phosphorylating it at threonine 161. Overexpression of p53 may also interfere with the accumulation of CDC2/cyclin B1 in the nucleus, required for cells to enter mitosis. Constitutive expression of cyclin B1, alone or in combination with the constitutively active CDC2 protein T14A Y15F, did not reverse p53-dependent G2 arrest. However, targeting cyclin B1 to the nucleus in cells also expressing CDC2 T14A Y15F did overcome this arrest. It is likely that several distinct pathways contribute to p53-dependent G2 arrest.
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PMID:Mechanisms of G2 arrest in response to overexpression of p53. 1056 59

Cell cycle arrest after different types of DNA damage can occur in either G1 phase or G2 phase of the cell cycle, involving the distinct mechanisms of p53/p21(Cip1/Waf1) induction, and phosphorylation of Cdc2, respectively. Treatment of asynchronously growing Swiss3T3 cells with the chemotherapeutic drug adriamycin induced a predominantly G2 cell cycle arrest. Here we investigate why Swiss3T3 cells were arrested in G2 phase and not in G1 phase after adriamycin-induced damage. We show that adriamycin was capable of inducing a G1 cell cycle arrest, both during the G0-G1 transition and during the G1 phase of the normal cell cycle. In G0 cells, adriamycin induced a prolonged cell cycle arrest. However, adriamycin caused only a transient cell cycle delay when added to cells at later time points during G0-G1 transition or at the G1 phase of normal cell cycle. The G1 arrest correlated with the induction of p53 and p21(Cip1/Waf1), and the exit from the arrest correlated with the decline of their expression. In contrast to the G1 arrest, adriamycin-induced G2 arrest was relatively tight and correlated with the Thr-14/Tyr-15 phosphorylation of cyclin B-Cdc2 complexes. The relative stringency of the G1 versus G2 cell cycle arrest may explain the predominance of G2 arrest after adriamycin treatment in mammalian cells.
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PMID:G1 versus G2 cell cycle arrest after adriamycin-induced damage in mouse Swiss3T3 cells. 1056 15

The Sp1 transcription factor plays an important role in mediating the p53-independent activation of the p21(WAF1) (WAF1) promoter by phorbol 12-myristate13-acetate (PMA) in hematopoietic cells. Using GAL4-Sp1 fusion proteins and a luciferase reporter, PMA is shown to activate the transcriptional activity of Sp1 independent of the WAF1 promoter. This activation does not require the Ser/Thr-rich region of Sp1 and can be mediated by 41 amino acids (152-193) of Sp1 that are important for the interaction with human TAF130. Because transforming growth factor-beta enhances WAF1 promoter activity through both Sp1 and Smad proteins, the role of Smads in PMA transcriptional activation was examined. PMA addition to hematopoietic cells was found to activate a GAL4/Smad-dependent promoter and the transforming growth factor-beta-responsive promoter, p3TP-lux. Immunofluorescence data demonstrate that PMA addition to hematopoietic cells induces the translocation of Smad3 to the nucleus. However, Smad3 does not stimulate the WAF1 promoter, but rather slightly inhibits the PMA-mediated induction of transcription from this upstream region. Additionally, transfection of Smad3 did not enhance the activation of GAL4/Sp1 by PMA. These results demonstrate that, while PMA can activate Smad-mediated transcription, Smad proteins do not appear to play a major role in the PMA induction of the WAF1 promoter.
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PMID:The role of the Smad3 protein in phorbol ester-induced promoter expression. 1060 Dec 54

p53 is a potent transcription factor which is regulated by sequential multisite phosphorylation and acetylation. In this paper, we identify threonine 18 of p53, a key site in regulating the interaction between p53 and its regulatory partner MDM2, as a novel site phosphorylated in vitro by purified recombinant casein kinase 1 (CK1) delta. Strikingly, phosphorylation of threonine 18 is dependent upon prior phosphorylation of serine 15. These data highlight an additional and physiologically important target residue for CK1 in p53 and suggest a potential mechanism by which sequential modification of a pivotal N-terminal residue in p53 may occur following stress-activated modification of serine 15.
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PMID:Protein kinase CK1 is a p53-threonine 18 kinase which requires prior phosphorylation of serine 15. 1060 44

Ataxia telangiectasia mutated (ATM) phosphorylates p53 protein in response to ionizing radiation, but the complex phenotype of AT cells suggests that it must have other cellular substrates as well. To identify substrates for ATM and the related kinases ATR and DNA-PK, we optimized in vitro kinase assays and developed a rapid peptide screening method to determine general phosphorylation consensus sequences. ATM and ATR require Mn(2+), but not DNA ends or Ku proteins, for optimal in vitro activity while DNA-PKCs requires Mg(2+), DNA ends, and Ku proteins. From p53 peptide mutagenesis analysis, we found that the sequence S/TQ is a minimal essential requirement for all three kinases. In addition, hydrophobic amino acids and negatively charged amino acids immediately NH(2)-terminal to serine or threonine are positive determinants and positively charged amino acids in the region are negative determinants for substrate phosphorylation. We determined a general phosphorylation consensus sequence for ATM and identified putative in vitro targets by using glutathione S-transferase peptides as substrates. Putative ATM in vitro targets include p95/nibrin, Mre11, Brca1, Rad17, PTS, WRN, and ATM (S440) itself. Brca2, phosphatidylinositol 3-kinase, and DNA-5B peptides were phosphorylated specifically by ATR, and DNA Ligase IV is a specific in vitro substrate of DNA-PK.
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PMID:Substrate specificities and identification of putative substrates of ATM kinase family members. 1060 6


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