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)

The Discs Large (DLG) tumour suppressor protein is targeted for ubiquitin mediated degradation by the high risk human papillomavirus (HPV) E6 proteins. In this study we have used a mutational analysis of E6 in order to investigate the mechanism by which this occurs. We first show that the differences in the affinities of HPV-16 and of HPV-18 E6 proteins for binding DLG is reflected in their respective abilities to target DLG for degradation. A mutational analysis of HPV-18 E6 has enabled us to define regions within the carboxy terminal half of the protein which are essential for the ability of E6 to direct the degradation of DLG. Mutants within the amino terminal portion of E6 which have lost the ability to bind the E6-AP ubiquitin ligase, as measured by their ability to degrade p53, nonetheless retain the ability to degrade DLG. Significant levels of DLG degradation are also obtained using wheat germ extracts which lack E6-AP. Finally, we show that the transfer of the DLG binding domain onto the low risk HPV-6 E6 confers DLG binding activity to that protein and, most significantly, allows HPV-6 E6 to target DLG for degradation. These results indicate that E6 mediated degradation of DLG does not involve the E6-AP ubiquitin ligase and, in addition, shows that the high and low risk HPV E6 proteins most likely share a common cellular intermediary in the ubiquitin pathway.
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PMID:HPV E6 targeted degradation of the discs large protein: evidence for the involvement of a novel ubiquitin ligase. 1069 89

We previously showed that oncoprotein MDM2 has ubiquitin ligase activity toward tumor suppressor p53. In that paper, we showed very weak homology in the carboxyl terminal portion between MDM2 and E6AP (HECT domain). We mutated the cysteine residue (C464) corresponding to the residue essential for the ubiquitin ligase activity of E6AP and this mutation diminished the ligase activity of MDM2. The cysteine residue described above is also one of the cysteine residues that form the RING finger domain of MDM2. We tried to find out whether the diminishing of the activity by the mutation is attributable to the disruption of the RING finger domain or not. When the ring finger domain of MDM2 was deleted, the truncation mutant did not have the ubiquitin ligase activity. When we mutated the seven cysteine residues of RING finger domain of MDM2 in the carboxyl terminus, the disruption of each residue in the RING finger completely diminished the ubiquitin ligase activity of MDM2 toward MDM2 itself and toward tumor suppressor p53. These data indicate that the RING finger domain in MDM2 is essential for its ubiquitin ligase activity toward p53 and itself.
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PMID:Activity of MDM2, a ubiquitin ligase, toward p53 or itself is dependent on the RING finger domain of the ligase. 1072 39

The p53 tumor suppressor is regulated by the MDM2 oncoprotein through a negative feedback mechanism. MDM2 promotes the ubiquitination and proteasome-dependent degradation of p53, possibly by acting as a ubiquitin ligase. In cervical cancer cells containing high-risk human papillomaviruses (HPV), p53 is also targeted for degradation by the HPV E6 oncoprotein in combination with the cellular E6-AP ubiquitin ligase. In this report, we describe the identification of efficient antisense oligonucleotides against human E6-AP. The roles of MDM2 and E6-AP in p53 regulation were investigated using a novel E6-AP antisense oligonucleotide and a previously characterized MDM2 antisense oligonucleotide. In HPV16-positive and HPV-18 positive cervical cancer cells, inhibition of E6-AP, but not MDM2, expression results in significant induction of p53. In HPV-negative tumor cells, p53 is activated by inhibition of MDM2 but not E6-AP. Furthermore, treatment with both E6-AP and MDM2 antisense oligonucleotides in HPV-positive cells does not lead to further induction of p53 over inhibition of E6-AP alone. Therefore, E6-AP-mediated degradation is dominant over MDM2 in cervical cancer cells but does not have a significant role in HPV-negative cells.
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PMID:The roles of E6-AP and MDM2 in p53 regulation in human papillomavirus-positive cervical cancer cells. 1072 57

The p53 tumor suppressor is activated by many diverse stress signals through mechanisms that result in stabilization and accumulation of the p53 protein. p53 is normally degraded through the proteasome following interaction with MDM2, which both functions as a ubiquitin ligase for p53 and shuttles to the cytoplasm, where p53 degradation occurs. Stabilization of p53 in response to stress is associated with inhibition of MDM2-mediated degradation, which has been associated with phosphorylation of p53 in response to DNA damage or activation of ARF. In this study we show distinct responses, as measured by phosphorylation, transcriptional activity, and subcellular localization, of p53 stabilized by different activating signals. Although normal cells and wild-type p53-expressing tumor cells showed similar responses to actinomycin D and camptothecin treatment, the transcriptional activity of stabilized p53 induced by deferoxamine mesylate, which mimics hypoxia, in normal cells was lost in all three tumor cell lines tested. Our results show that multiple pathways exist to stabilize p53 in response to different forms of stress, and they may involve down-regulation of MDM2 expression or regulation of the subcellular localization of p53 or MDM2. Loss of any one of these pathways may predispose cells to malignant transformation, although reactivation of p53 might be achieved through alternative pathways that remain functional in these tumor cells.
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PMID:Stress signals utilize multiple pathways to stabilize p53. 1075 6

The Mdm2 protein is a key regulator of p53 activity and stability. Upon binding, Mdm2 inhibits the transcription regulatory activity of p53 and promotes its rapid degradation. In this study we investigated the effect of the human Mdm2 homologue Hdmx on p53 stability. We found that Hdmx does not target p53 for degradation, although, like Mdm2, it inhibits p53-mediated transcription activation. On the contrary, Hdmx was found to counteract the degradation of p53 by Mdm2, and to stabilize both p53 and Mdm2. The RING finger of Hdmx was found to be necessary and sufficient for this stabilization, and it probably involves hetero-oligomerization with the RING finger of Mdm2, which may lead to inhibition of Mdm2's ubiquitin ligase activity. However, Hdmx does not relieve the inhibition by Mdm2 of transcription activation by p53, probably due to the formation of a trimeric complex consisting of Hdmx, Mdm2, and p53. We propose a model in which Hdmx secures a pool of largely inactive p53, which, upon the induction of stress, can be quickly activated.
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PMID:Hdmx stabilizes Mdm2 and p53. 1082 96

Mdm2 is an E3 ubiquitin ligase for the p53 tumor suppressor protein. We demonstrate that Mdm2 is conjugated with SUMO-1 (sumoylated) at Lys-446, which is located within the RING finger domain and plays a critical role in Mdm2 self-ubiquitination. Whereas mutant Mdm2(K446R) is stabilized, it elicits increased degradation of p53 and concomitant inhibition of p53-mediated apoptosis. In vitro sumoylation of Mdm2 abrogates its self-ubiquitination and increases its ubiquitin ligase activity toward p53. Radiation caused a dose- and time-dependent decrease in the degree of Mdm2 SUMO-1 modification, which is inversely correlated with the levels of p53. Our results suggest that the maintenance of the intrinsic activity of a RING finger E3 ubiquitin ligase is sumoylation dependent and that reduced Mdm2 sumoylation in response to DNA damage contributes to p53 stability.
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PMID:SUMO-1 modification of Mdm2 prevents its self-ubiquitination and increases Mdm2 ability to ubiquitinate p53. 1220 42

E6 is an oncoprotein implicated in cervical cancers produced by " high risk " human papillomaviruses. E6 binds specifically to several cellular proteins, including the tumour suppressor p53 and the ubiquitin ligase E6-AP. However, E6 is also a DNA-binding protein which recognizes a structural motive present in four-way junctions. Here, we demonstrate that the C-terminal zinc-binding domain of E6, expressed separately from the rest of the protein, fully retains the selective four-way junction recognition activity. The domain can bind to two identical and independent sites on a single junction, whereas full-length E6 can only bind to one site. The junction bound to either one or two domains adopts an extended square conformation. These results allow us to assign the structure-dependent DNA recognition activity of E6 to its C-terminal domain, which therefore represents a new class of zinc-stabilized DNA-binding module. Comparison with the binding characteristics of other junction-specific proteins enlightens the rules which govern protein-induced deformation of four-way DNA junctions.
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PMID:Specific recognition of four-way DNA junctions by the C-terminal zinc-binding domain of HPV oncoprotein E6. 1116 88

The wild type p53 tumor suppressor protein is rapidly degraded in normal cells by MDM2, the ubiquitin ligase that serves as the key regulator of p53 function by modulating protein stability. Cellular exposure to genotoxic stress triggers the stabilization of p53 by multiple pathways that converge upon interference with MDM2 function. In this study, we first investigated the ability of HDM2 (MDM2 human homologue) to degrade endogenous p53 in neuroblastoma (NB). Although the p53 protein in NB has been reported to be constitutively stabilized, we find that HDM2 in NB is functional and facilitates the rapid turnover of p53 in nonstressed cells via the proteasome pathway. Second, we examined the relationship between p53 and HDM2 in the adriamycin-mediated stabilization of p53 in NB. We demonstrate that while p53 stabilization depends neither upon the phosphorylation of specific N-terminal sites nor upon dissociation from HDM2, it requires inactivation of functional HDM2. In support of this notion, p53 stabilization following adriamycin resulted in an inhibition of both p53 ubiquitination and HDM2 ligase activity. Taken together, these data implicate a requirement for enzymatic inactivation of HDM2 as a novel mechanism for p53 stabilization in the DNA damage response pathway.
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PMID:Requirement for HDM2 activity in the rapid degradation of p53 in neuroblastoma. 1127 10

Genotoxic stress activation of the tumor suppressor transcription factor p53 involves post-translational C-terminal modifications that increase both protein stability and DNA binding activity. We compared the requirement for p53 protein activation of p53 target sequences in two major p53-regulated genes, p21/WAF1 (encoding a cell cycle inhibitory protein) and Mdm2 (encoding a ubiquitin ligase that targets p53 for proteolytic degradation). The p53 binding site in the proximal p21/WAF1 promoter contains a single p53 binding consensus sequence, while the p53 binding site in the Mdm2 promoter contains two consensus sequences linked by a 17 bp spacer. Binding of recombinant p53 protein to the p21/WAF1 binding site required monoclonal antibody PAb421, which can mimic activating phosphorylation and/or acetylation events at the C-terminus. In contrast, recombinant p53 bound strongly to the Mdm2 binding site in the absence of PAb421 antibody. Separate binding to each consensus sequence of the Mdm2 binding site still required PAb421, indicating that p53 binding was not simply due to greater affinity to the Mdm2 consensus sequences. Linking two p21/WAF1 binding sites with the 17 bp spacer region from the Mdm2 gene eliminated the PAb421 requirement for p53 binding to the p21/WAF1 site. These results suggest a mechanism for regulation of Mdm2 gene transcription that differs from that other p53-induced genes by its lack of a requirement for C-terminal activation of p53 protein. A steady induction of Mdm2 protein would maintain p53 protein at low levels until post-translational modifications following DNA damage increased p53 activity towards other genes, mediating p53 growth inhibitory and apoptotic activities.
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PMID:Binding to the naturally occurring double p53 binding site of the Mdm2 promoter alleviates the requirement for p53 C-terminal activation. 1132 84

Previously, we found that the protein kinase C (PKC) inhibitor H7 stimulates p53 to accumulate in a form incapable of inducing transcription from p53-dependent promoters. We concluded that H7 inhibits constitutive C-terminal phosphorylation of p53, which regulates its turnover in unstressed cells. We now show that p53 and its inhibitor MDM2 (HDM2 in human cells) are together in the nuclei of H7-treated cells and can be co-immunoprecipitated. Despite this association of p53 with the ubiquitin ligase MDM2, ubiquitinated p53 was not detected in H7-treated cells. Furthermore, co-treatment with H7 and the proteosome inhibitor LLnL prevented the accumulation of ubiquitinated p53 that was observed in cells treated solely with LLnL. In addition, treatment of cells with the PKC activator phorbol ester stimulated the ubiquitination of p53 and reduced its ability to accumulate after stress. H7 did not induce the phosphorylation of human p53 on Ser-15 (Ser-18 in mouse protein), a modification that occurs in response to DNA damage and leads to the release of MDM2 and to transactivation by p53. We conclude that phosphorylation of the C-terminal domain of p53 by PKC increases its ubiquitination and degradation in unstressed cells.
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PMID:Regulation of ubiquitination and degradation of p53 in unstressed cells through C-terminal phosphorylation. 1143 70


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