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 tumour suppressor protein p53 normally functions as a tetramer in a defined conformational state. Mutations within p53 which contribute to cancer development frequently induce a conformational shift in the protein which correlates with loss of wild type growth suppressor functions. Both the cell encoded mdm2 protein and the human papillomavirus oncoprotein E6 can regulate p53 function and we have examined the interaction of these proteins with p53. The E6/p53 association is sensitive to conformational alterations in the p53 protein, although oligomerisation is not necessary for this interaction to occur. Analysis of C-terminal p53 truncations has indicated that the region between residues 327 and 347 may play a role in E6 binding. Since monomeric forms of p53 retain transcriptional and transformation suppressor activities, our results indicate that E6 targets p53 proteins which retain these wild type functions. Conversely, the interaction of p53 with mdm2 is not dependent on the conformation of the p53 protein but is significantly impaired by loss of quaternary structure. It is possible that mdm2 plays a role in mediating activities of p53 which, unlike transcriptional activation, depend on oligomerisation.
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PMID:Oligomerisation of full length p53 contributes to the interaction with mdm2 but not HPV E6. 775 47

Wild-type human p53 protein is able to self-associate and consists predominantly of homotetramers in solution. In earlier work we identified the protein sequence motifs involved in p53 quaternary structure and showed that while monomeric p53 protein retains tumour suppressor function, monomeric tumour mutant p53 lacks dominant transforming activity. In this report we use point mutated and truncated cDNA genes encoding self-association defective human p53 proteins to investigate the relationship between p53 protein quaternary structure and the associated activities of transcription transactivation and target specific DNA binding. We show that p53 binds to a target oligonucleotide as a protein homodimer and that p53 dimerisation is required for detectable DNA binding. We found no evidence for p53 tetramer: DNA complexes and we suggest that the quaternary structure status of p53 may regulate a DNA binding associated activity. Monomeric p53 proteins failed to bind DNA in these assays but exhibited increased transactivating activity. Thus, both transcription transactivation and tumour suppressor functions act independently of p53 protein self-association and DNA binding. We propose that our results validate the p53 dimerisation motif as a target for rational anticancer drug design. We predict that compounds able to block p53 dimer assembly would inhibit the dominant transforming activities of mutant p53 in tumours retaining expression of a mutant allele, while leaving intact the wild-type p53 associated activities of transcription transactivation and transformation suppression in unaffected tissue.
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PMID:Human p53 binds DNA as a protein homodimer but monomeric variants retain full transcription transactivation activity. 841 20

Wild-type p53 (wtp53) is a tumour suppressor gene involved in cell cycle regulation. The mdm2 protein can complex with the p53 protein and influence its function as a regulator of cell growth. To detect and quantify wtp53 and mdm2 mRNA expression, we established the competitive reverse transcription/polymerase chain reaction for these genes and for the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The target RNA differed from the competitor cRNA by having 183 bp, 205 bp and 173 bp deletions for p53, mdm2 and GAPDH, respectively. Target RNA and known concentrations of competitor cRNA were co-reverse transcribed and co-amplified with the same primers. Target cDNA and the corresponding competitor cDNA were amplified at the same efficiency.
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PMID:Competitive reverse transcription/polymerase chain reaction for the quantification of p53 and mdm2 mRNA expression. 902 80

The p53 tumour suppressor gene is a cell cycle regulator, able to induce cell cycle arrest to allow DNA repair or apoptosis. The molecular mechanisms underlying p53 action imply transactivation of p53 dependent genes such as WAF1 (for wild type p53 associated fragment 1) and the murine double minute (MDM2) gene. In some cases, inactivation of the p53 gene results from p53 gene mutations leading to p53 protein accumulation, but in others it may results from mechanisms other than mutation, such as interaction with viral or cellular proteins. The expression of p53 protein and p53 transactivated gene proteins p21/WAF1 and MDM2, combined with in situ detection of apoptosis, was studied in specimens of CMV-infected patients as an in vivo model of p53 alteration not due to point mutation. p53 positivity was found in CMV + cells in different tissues, in cells with typical inclusion bodies, and in in situ hybridization and immunohistochemistry CMV + cells without inclusions (hidden infection). Although this p53 reactivity was accompanied by the expression of MDM2 and p21/WAF1 proteins, the patterns of MDM2 and p21/WAF1 protein expression were mutually exclusive, and were associated with the presence or absence of inclusion bodies. Nuclei bearing inclusion bodies were usually MDM2+, p21/ WAF1-, while hidden infected cells were usually MDM2-, p21/WAF1+. Apoptosis was not detected in any tissue section from CMV-infected patients. Two alternative patterns were found in CMV-infected tissues: p53+, p21/WAF1+, MDM2-, or p53+, p21/WAF1-. MDM2+ protein expression. These may represent examples of p53 dependent alternative effects in the course of CMV infection. Early stages are represented by CMV + cells without inclusion bodies, which display p53 and p21/ WAF1 expression, suggesting that p53 could be acting as a growth suppressor protein. Late CMV infection is represented by cells harbouring inclusion bodies. These cells showed a p53+, p21/WAF1-, MDM2+ profile, consistent with MDM2 mediated p53 inactivation. The absence of p21/WAF1 expression and lack of apoptosis suggest that the p53 protein expressed by MDM2+ cells could be functionally inactivated in CMV-infected cells with inclusion bodies. Previous studies have suggested that p53 inactivation by MDM2 over-expression occurs in sarcomas and lymphomas. Our observations seem to indicate that this mechanism of MDM2 mediated p53 inactivation may play a role in the late phase of CMV infection.
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PMID:p53 expression in CMV-infected cells: association with the alternative expression of the p53 transactivated genes p21/WAF1 and MDM2. 906 34

The mdm2 protein interacts with a number of proteins involved in cell growth control. Such interactions favour cell proliferation and may explain the oncogenic potential of mdm2 when over-expressed in cells. Interaction with the tumour suppressor p53 involves the N-terminus of mdm2 and targets p53 for rapid degradation by the ubiquitin pathway. We now describe a novel, highly conserved exon of mdm2 (exon alpha) which includes an in-frame UGA stop codon. Expression of exon alpha disrupts in vitro translation of the p53 binding domain of mdm2. We propose that exon alpha induces translation re-initiation at an internal AUG codon within the mdm2 alpha mRNA isoform. The putative mdm2 alpha protein lacks the N-terminus of mdm2 and shows little, if any, binding capacity for p53. Mdm2 alpha mRNA is expressed in a tissue-specific manner and is observed predominantly in testis and peripheral blood lymphocytes. We propose that mdm2 alpha expression may provide a mechanism for uncoupling mdm2-p53 interaction in certain cell types and/or under specific conditions of cell growth.
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PMID:A novel exon within the mdm2 gene modulates translation initiation in vitro and disrupts the p53-binding domain of mdm2 protein. 1059 3

Tumorogenesis is associated with several events by which a normal cell transforms itself into a tumour cell with an increased proliferation rate. One of the most important research initiatives in this area is the characterization of the molecular mechanisms involved in tumorogenesis and cancer. Oncogenes and tumour suppressor genes are directly involved in the cell cycle, differentiation, and apoptosis. The cellular oncogene MDM2 seems to be abnormally elevated in several human tumours, specially in sarcomas. The MDM2 gene product, mdm2 protein, pS3 and retinoblastoma (Rb) proteins, play crucial roles in the control of the cell cycle. The molecular interactions between mdm2, pS3 and Rb in cancer, are associated with a loss of control in the G1 phase of the cell cycle leading to uncontrolled cell proliferation. Studies by gene amplification appear to show an incomplete picture of mdm2 protein levels in tumour cells. The simultaneous determination of mdm2 protein and mRNA levels seems to give a more accurate interpretation of the abnormal function of the mdm2 protein. Thus, in addition to gene amplification, different mechanisms by which mdm2 is overexpressed in cancer cells also play an important role in tumorogenesis.
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PMID:[Tumorogenesis and mdm2 protein]. 1100 60

The p300-CBP-associated factor (PCAF) is a histone acetyltransferase (HAT) involved in the reversible acetylation of various transcriptional regulators, including the tumour suppressor p53. It is implicated in many cellular processes, such as transcription, differentiation, proliferation and apoptosis. We observed that knockdown of PCAF expression in HeLa or U2OS cell lines induces stabilization of the oncoprotein Hdm2, a RING finger E3 ligase primarily known for its role in controlling p53 stability. To investigate the molecular basis of this effect, we examined whether PCAF is involved in Hdm2 ubiquitination. Here, we show that PCAF, in addition to its acetyltransferase activity, possesses an intrinsic ubiquitination activity that is critical for controlling Hdm2 expression levels, and thus p53 functions. Our data highlight a regulatory crosstalk between PCAF and Hdm2 activities, which is likely to have a central role in the subtle control of p53 activity after DNA damage.
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PMID:Intrinsic ubiquitination activity of PCAF controls the stability of the oncoprotein Hdm2. 1729 53

USP7 (HAUSP) is a deubiquitinating enzyme, which plays a crucial role in regulating the levels of the p53 tumour suppressor protein, through its ability to prevent the proteasomal degradation of the Ubiquitin ligase for p53, Hdm2. Supporting evidence suggests that an inhibitor of USP7 would act to abrogate the action of Hdm2, and thereby elevate levels of the p53 protein, with associated therapeutic benefits in cancer and potentially other diseases. In this article, we describe the characterisation of differential enzyme activity of both the full length and putative catalytic domain of human USP7 expressed in both bacterial and insect cell expression systems. We also demonstrate the way in which variations in the reducing environment surrounding the enzyme can dramatically affect both the stability of the enzyme and the range of small molecules able to inhibit the catalytic activity of the enzyme. Furthermore, we describe the validation and use of this assay for a high-throughput screening approach, again highlighting the critical nature of the enzyme's environment. Taken together, these findings not only increase our understanding of the enzymatic activity of deubiquitinating enzymes, but also highlight several key considerations of importance in the development of therapeutic agents against this novel class of therapeutic targets.
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PMID:Enzymatic characterisation of USP7 deubiquitinating activity and inhibition. 2146 92

Inactivation of the p53 tumour suppressor, either by mutation or by overexpression of its inhibitors Hdm2 and HdmX is the most frequent event in cancer. Reactivation of p53 by targeting Hdm2 and HdmX is therefore a promising strategy for therapy. However, Hdm2 inhibitors do not prevent inhibition of p53 by HdmX, which impedes p53-mediated apoptosis. Here, we show that p53 reactivation by the small molecule RITA leads to efficient HdmX degradation in tumour cell lines of different origin and in xenograft tumours in vivo. Notably, HdmX degradation occurs selectively in cancer cells, but not in non-transformed cells. We identified the inhibition of the wild-type p53-induced phosphatase 1 (Wip1) as the major mechanism important for full engagement of p53 activity accomplished by restoration of the ataxia telangiectasia mutated (ATM) kinase-signalling cascade, which leads to HdmX degradation. In contrast to previously reported transactivation of Wip1 by p53, we observed p53-dependent repression of Wip1 expression, which disrupts the negative feedback loop conferred by Wip1. Our study reveals that the depletion of both HdmX and Wip1 potentiates cell death due to sustained activation of p53. Thus, RITA is an example of a p53-reactivating drug that not only blocks Hdm2, but also inhibits two important negative regulators of p53 - HdmX and Wip1, leading to efficient elimination of tumour cells.
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PMID:Abrogation of Wip1 expression by RITA-activated p53 potentiates apoptosis induction via activation of ATM and inhibition of HdmX. 2154 7

The tumour suppressor p53 transactivates the expression of its target genes to exert its functions. Here, we identify a pleckstrin homology domain-containing protein (PHLDB3)-encoding gene as a p53 target. PHLDB3 overexpression increases proliferation and restrains apoptosis of wild-type p53-harboring cancer cells by reducing p53 protein levels. PHLDB3 binds to MDM2 (mouse double minute 2 homolog) and facilitates MDM2-mediated ubiquitination and degradation of p53. Knockdown of PHLDB3 more efficiently inhibits the growth of mouse xenograft tumours derived from human colon cancer HCT116 cells that contain wild type p53 compared with p53-deficient HCT116 cells, and also sensitizes tumour cells to doxorubicin and 5-Fluorouracil. Analysis of cancer genomic databases reveals that PHLDB3 is amplified and/or highly expressed in numerous human cancers. Altogether, these results demonstrate that PHLDB3 promotes tumour growth by inactivating p53 in a negative feedback fashion and suggest PHLDB3 as a potential therapeutic target in various human cancers.
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PMID:Pleckstrin homology domain-containing protein PHLDB3 supports cancer growth via a negative feedback loop involving p53. 2800 6


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