Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P43146 (tumour suppressor)
 5,935 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The p53 protein is a multifunctional transcription factor which orchestrates cellular responses to DNA damage, so helping to conserve genomic stability. It may also regulate genes involved in intercellular signalling, such as thrombospondin, a negative regulator of angiogenesis and metastatic spread. Activation of p53 target genes requires sequence-specific DNA binding, a function which maps to the central core of the protein. Missense point mutations within this domain inactivate p53 tumour suppressor function and involve either (i) DNA contact residues, or (ii) residues important for conformational structure. Using in vitro techniques we have analysed seven DNA contact mutants and 17 structural mutants known to occur in cancer. We show that DNA contact mutants can be carried into specific DNA interaction when co-expressed with wild type protein. For structural mutants, 9/17 retained DNA binding capacity and, with one exception, DNA binding correlated with conformational flexibility of the mutant protein. The exception was Asp281, which appeared essential for DNA interaction, probably due to its ability to form salt bridges with DNA contact residues Arg273 and Arg280. We suggest that different classes of p53 mutant may prove amenable to different strategies for restoration of wild type tumour suppressor function as means of anti-cancer therapy.
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PMID:Specific DNA binding by different classes of human p53 mutants. 765 40

Mutation of the p53 gene is one of the most common genetic lesions observed in human cancer. The p53 protein functions as a transcription factor, however it is still unresolved to what extend this property is related to its tumour suppressor activity. Since there is evidence that protein modifications as well as protein-protein interactions may regulate p53 function, we have studied p53 protein-DNA complex formation in nuclear extracts prepared from human tumour cell lines. In 13 different cell lines PAb421-induced DNA binding activity was compared to the level and conformation of the endogenous p53 protein. Surprisingly, sequence-specific p53 DNA binding activity was detected not only in cell lines that express wild-type p53, but also in seven cell lines which contain only mutant protein. Oligonucleotide competition analyses with various p53 target sequences and methylation interference experiments establish that wild-type and mutant p53 differ significantly in their sequence-specific interactions. Our analysis also provides evidence that the PAb1620 conformation is neither sufficient nor essential for DNA binding of endogenous p53 and that the cellular environment in addition to the specific point mutation may influence p53 DNA binding activity.
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PMID:p53 derived from human tumour cell lines and containing distinct point mutations can be activated to bind its consensus target sequence. 789 29

p73 (ref. 1) has high homology with the tumour suppressor p53 (refs 2-4), as well as with p63, a gene implicated in the maintenance of epithelial stem cells. Despite the localization of the p73 gene to chromosome 1p36.3, a region of frequent aberration in a wide range of human cancers, and the ability of p73 to transactivate p53 target genes, it is unclear whether p73 functions as a tumour suppressor. Here we show that mice functionally deficient for all p73 isoforms exhibit profound defects, including hippocampal dysgenesis, hydrocephalus, chronic infections and inflammation, as well as abnormalities in pheromone sensory pathways. In contrast to p53-deficient mice, however, those lacking p73 show no increased susceptibility to spontaneous tumorigenesis. We report the mechanistic basis of the hippocampal dysgenesis and the loss of pheromone responses, and show that new, potentially dominant-negative, p73 variants are the predominant expression products of this gene in developing and adult tissues. Our data suggest that there is a marked divergence in the physiological functions of the p53 family members, and reveal unique roles for p73 in neurogenesis, sensory pathways and homeostatic control.
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PMID:p73-deficient mice have neurological, pheromonal and inflammatory defects but lack spontaneous tumours. 1071 51

The p53 tumour suppressor is a transcriptional factor whose activity is modulated by protein stability and post-translational modifications including acetylation. The mechanism by which acetylated p53 is maintained in vivo remains unclear. Here we show that the deacetylation of p53 is mediated by an histone deacetylase-1 (HDAC1)-containing complex. We have also purified a p53 target protein in the deacetylase complexes (designated PID; but identical to metastasis-associated protein 2 (MTA2)), which has been identified as a component of the NuRD complex. PID specifically interacts with p53 both in vitro and in vivo, and its expression reduces significantly the steady-state levels of acetylated p53. PID expression strongly represses p53-dependent transcriptional activation, and, notably, it modulates p53-mediated cell growth arrest and apoptosis. These results show that deacetylation and functional interactions by the PID/MTA2-associated NuRD complex may represent an important pathway to regulate p53 function.
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PMID:Deacetylation of p53 modulates its effect on cell growth and apoptosis. 1109 47

The tumour suppressor gene p53 is the gene most often reported to be mutated in clinical cancers with something like half of all tumours harbouring mutations. Further, many studies have suggested that p53 mutations have prognostic importance and sometimes are a significant factor in determining the response of tumours to therapy. The value of knowing the p53 status of individual tumours will increase if currently researched strategies aimed at developing p53-based treatment protocols come to fruition. There are quite a number of techniques used to detect p53 defects in both tumours and in the germline of cancer-prone families, although some of these methods are indirect and each has certain drawbacks. In this brief review we will discuss the value of two assays of p53 function as a means of detecting and partly characterizing p53 mutations. The two assays are the apoptotic assay, which measures the response of peripheral blood lymphocytes to radiation-induced DNA damage and the FASAY, a yeast based assay which assesses the ability of a given p53 protein to transactivate p53 target genes. Both of these assays are rapid, yielding results within 5 days. Further, they not only offer the possibility of detecting p53 mutations but also of characterizing a given mutation in terms of two of p53's most important functions, namely the induction of apoptosis and the transactivation of target genes.
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PMID:p53 functional assays: detecting p53 mutations in both the germline and in sporadic tumours. 1128 15

The tumour suppressor gene p53 is frequently mutated in human cancer. Tumour derived p53 mutants are usually transcriptionally inactive, but some mutants retain the ability to transactivate a subset of p53 target genes. In addition to simple loss of function, some p53 mutants may be carcinogenic through a dominant negative mechanism. Aiming at a more general classification of p53 mutants into predictive functional categories it is important to determine (i) which p53 mutants are dominant, (ii) what features characterize dominant mutants and (iii) whether dominance is target gene specific. The ability of 71 p53 mutants to inhibit wild type p53 was determined using a simple yeast transcriptional assay. Approximately 30% of the mutants were dominant. They preferentially affect highly conserved amino acids (P<0.005), which are frequently mutated in tumours (P<0.005), and usually located near the DNA binding surface of the protein (P<0.001). Different tumour-derived amino acid substitutions at the same codon usually have the same dominance phenotype. To determine whether the ability of p53 mutants to inhibit wild type p53 is target gene specific, the dominance towards p21, bax, and PIG3 binding sites was examined. Approximately 40% of the 45 mutants examined were dominant for the p21 (17/45) or PIG3 (20/45) responsive elements and 71% (32/45) were dominant for the bax responsive element. These differences are statistically significant (p21 vs bax, P<0.003; bax vs PIG3, P<0.02, Fisher's exact test) and defined a hierarchy of dominance. Finally, we extended the analysis to a group of mutants isolated in BRCA-associated tumours, some of which retained wild type level of transcription in yeast as well as in human cells, but show gain of function in transformation assays. Since transformation assays require transdominant inhibition of the endogenous wild type allele, one possible explanation for the behaviour of the BRCA-associated mutants is that they adopt conformations able to bind DNA alone but not in mixed tetramers with wild type p53. The yeast data do not support this explanation, because all BRCA-associated mutants that behaved as wild type in transcription assay were recessive in dominance assays.
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PMID:Tumour p53 mutations exhibit promoter selective dominance over wild type p53. 1189 95

The E1 region of adenovirus (Ad) type 5 is capable of transforming cells. According to current concepts, the Ad E1B 55 kDa (E1B 55K) protein enables transformed cells to grow by constantly binding and inactivating the p53 tumour suppressor protein. To test this model, the transcriptional activity of p53 was determined in Ad E1-transformed cells. Surprisingly, it was found that a p53-responsive promoter is highly active in Ad E1-transformed cells and further activated only 3- to 4-fold (compared to 200-fold in p53(-/-) cells) by exogenously expressed p53 or p53mt24-28, a p53 mutant that is transcriptionally active but unable to bind the E1B 55K. On the other hand, the transient overexpression of E1B 55K led to a strong downregulation of a p53-responsive promoter relative to its baseline activity in Ad E1-transformed cells but not in p53(-/-) cells. COS-7 cells, transformed by simian virus 40 (SV40), also showed constitutive p53 activity, whereas HeLa cells, transformed with oncogenic human papillomavirus, did not. Upon stable transfection, Ad E1-transformed cells but not p53(-/-) cells gave rise to colonies that expressed exogenous p53 or p53mt24-28 but, nonetheless, grew at near-wild-type rates. It is proposed that E1B 55K or the SV40 tumour antigen are saturated by the p53 protein, which accumulates in virus-transformed cells, leaving a proportion of active p53 molecules. The transformation of cells by the Ad E1 genes confers permissiveness for active p53, conceivably by inactivating the relevant products of p53 target genes that would otherwise prevent cell growth. Thus, Ad-transformed cells contain and tolerate active p53.
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PMID:Adenovirus E1-transformed cells grow despite the continuous presence of transcriptionally active p53. 1212 69

The tumour suppressor gene p53 is the most commonly mutated gene in solid tumours. Although less common in haematological malignancies, 10-15% of B-cell chronic lymphocytic leukaemia (B-CLL) cases carry a p53 mutation. Recently, the compound P53-dependent reactivation and induction of massive apoptosis (PRIMA-1) has been shown to induce cytotoxic effects and apoptosis in human tumour cells by restoration of the transcriptional activity of mutated p53. This is believed to be mediated by a change in the conformation of mutated p53 protein, restoring DNA binding and activation of p53 target genes. We studied the effects of PRIMA-1 and commonly used anti-leukaemic drugs on B-CLL cells from 14 patients with and without hemizygous p53 deletion. Cells obtained from peripheral blood or bone marrow were exposed to PRIMA-1 and fludarabine alone or in combination. PRIMA-1 showed cytotoxic effects on B-CLL cells from samples with and without hemizygous p53 deletion. Furthermore, conventional B-CLL drugs were less effective in cell samples with hemizygous p53 deletion and the response depended on the size of the p53 deleted clone. Finally, we found evidence for synergistic and additive effects of PRIMA-1 in combination with fludarabine.
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PMID:Effects of PRIMA-1 on chronic lymphocytic leukaemia cells with and without hemizygous p53 deletion. 1549 Dec 87

p53 is a tumour suppressor that regulates the cellular response to genotoxic stresses. p53 is a short-lived protein and its activity is regulated mostly by stabilization via different post-translational modifications. Here we report a novel mechanism of p53 regulation through lysine methylation by Set9 methyltransferase. Set9 specifically methylates p53 at one residue within the carboxyl-terminus regulatory region. Methylated p53 is restricted to the nucleus and the modification positively affects its stability. Set9 regulates the expression of p53 target genes in a manner dependent on the p53-methylation site. The crystal structure of a ternary complex of Set9 with a p53 peptide and the cofactor product S-adenosyl-l-homocysteine (AdoHcy) provides the molecular basis for recognition of p53 by this lysine methyltransferase.
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PMID:Regulation of p53 activity through lysine methylation. 1552 38

The p53 tumour suppressor functions as a transcriptional activator, and several p53-inducible genes that play a critical proapoptotic role have been described. Moreover, p53 regulates the expression of various proteins participating in autoregulatory feedback loops, including proteins that negatively control p53 stability (Mdm2 and Pirh2) or modulate stress-induced phosphorylation of p53 on Ser-46 (p53DINP1 or Wip1), a key event for p53-induced apoptosis. Here, we describe a new systematic analysis of p53 targets using oligonucleotide chips, and report the identification of dapk1 as a novel p53 target. We demonstrate that dapk1 mRNA levels increase in a p53-dependent manner in various cellular settings. Both human and mouse dapk1 genomic loci contain DNA sequences that bind p53 in vitro and in vivo. Since dapk1 encodes a serine/threonine kinase previously shown to suppress oncogene-induced transformation by activating a p19ARF/p53-dependent apoptotic checkpoint, our results suggest that Dapk1 participates in a new positive feedback loop controlling p53 activation and apoptosis.
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PMID:dapk1, encoding an activator of a p19ARF-p53-mediated apoptotic checkpoint, is a transcription target of p53. 1560 85


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