Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:B6E4X6 (mutant p53)
 3,342 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Highly purified p53 protein from different sources was able to degrade DNA with a 3'-to-5' polarity, yielding deoxynucleoside monophosphates as reaction products. This exonuclease activity was dependent on Mg2+ and inhibited by addition of 5 mM nucleoside monophosphates. This exonuclease activity is intrinsic to the wild-type p53 protein: it copurified with p53 during p53 preparation; only purified wild-type p53, but not identically purified mutant p53 proteins displayed exonuclease activity; the exonuclease activity could be reconstituted from SDS gel-purified and urea-renatured p53 protein and mapped to the core domain of the p53 molecule; and finally, purified p53 protein could be UV-cross-linked to GMP. A p53-intrinsic exonuclease activity should substantially extend our view on the role of p53 as a "guardian of the genome."
 ...
PMID:p53 Protein exhibits 3'-to-5' exonuclease activity. 867 15

Restriction endonuclease fingerprinting (REF), a hybrid modification of single-strand conformation polymorphism (SSCP) and restriction endonuclease digestion, has been used previously to detect mutations in 1- to 2-kb segments of DNA. This paper demonstrates that fragment resolution, and thus sensitivity of REF, can be markedly improved by electrophoresis under partially denaturing, rather than nondenaturing, conditions, for genes with a high G+C content. A 2. 1-kb segment of the p53 tumor suppressor gene (54.5% G+C) containing exons 5-9, including the intervening introns, was screened in a blinded analysis of 48 samples from human breast tumors containing known wild-type or mutant p53 genes. In gels containing 0.5 M urea, 97% of the mutant samples were detected correctly, and more than 80% of the mutations were localized within a 200-bp region. In the process of this methodological analysis, it was discovered that: (1) there are two common and four uncommon haplotypes; (2) the two common haplotypes occurred in the three races examined, suggesting an ancient origin; and (3) haplotype II is of substantially higher frequency in the Chinese relative to Japanese (P = 0.023) and Caucasians (P = 0.005). Two other improvements in the REF procedure included (1) the selection of an optimal set of restriction endonucleases by new software (REF Select) developed recently in our laboratory; and (2) the addition of an oligonucleotide "tail," containing two recognition sequences for restriction endonucleases, to the PCR primers to prevent coterminal fragments at the end of amplified products. These modifications facilitate the use of REF for efficient and sensitive mutation screening in p53 and other genes with a high G+C content.
 ...
PMID:Highly sensitive mutation screening by REF with low concentrations of urea: A blinded analysis of a 2-kb region of the p53 gene reveals two common haplotypes. 1042 40

Homozygous chromosome 9p deletions in gliomas commonly include the CDKN2A and CDKN2B genes, which code for the structurally highly homologous cdk inhibitors/tumor suppressors p16 and p15, respectively. Alternative splicing of the CDKN2A gene results in the expression of p14(ARF). Interestingly, not only p16 and p15, but also the structurally unrelated p14(ARF) appear to function as negative cell cycle regulators. Concerted inactivation of p16, p15 and p14(ARF) could be demonstrated in seven of nine glioblastoma cell lines. Strong suppression of tumorigenicity after transfection with p16 and p15 alone or in combination was seen in cell lines containing neither endogenous p16 nor p15 but functional pRB. Significantly weaker growth suppression was observed in tumors either retaining expression of both p16 and p15 or p15 only. p14(ARF) proved to be a potent tumor suppressor in the presence of wild-type p53, while mutant p53 substantially reduced growth inhibition by p14(ARF). No differences between p16 and p15 effects could be observed, suggesting a largely overlapping function of p16 and p15. To facilitate further research into p16/p15 effects, three cell lines with conditional, tetracycline-controlled p16 expression were established. Reversible growth suppression mediated by p16 was observed in these models. Combined inactivation of CDKN2A and CDKN2B, i.e., loss of both p16 and p15 as well as p14(ARF), results in disruption of two major growth control pathways involving pRB and p53 in malignant gliomas. Therefore, homozygous co-deletions of CDKN2A and CDKN2B rather than mutations targeting individual transcripts are frequently selected for in these tumors.
 ...
PMID:Functional evidence for a role of combined CDKN2A (p16-p14(ARF))/CDKN2B (p15) gene inactivation in malignant gliomas. 1054 65

Identification of Mdm2 and JNK as proteins that target degradation of wt p53 prompted us to examine their effect on mutant p53, which exhibits a prolonged half-life. Of five mutant p53 forms studied for association with the targeting molecules, two no longer bound to Mdm2 and JNK. Three mutant forms, which exhibit high expression levels, showed lower affinity for association with Mdm2 and JNK in concordance with greater affinity to p14(ARF), which is among the stabilizing p53 molecules. Monitoring mutant p53 stability in vitro confirmed that, while certain forms of mutant p53 are no longer affected by either JNK or Mdm2, others are targeted for degradation by JNK/Mdm2, albeit at lower efficiency when compared with wt p53. Expression of wt p53 in tumor cells revealed a short half-life, suggesting that the targeting molecules are functional. Forced expression of mutant p53 in p53 null cells confirmed pattern of association with JNK/Mdm2 and prolonged half-life, as found in the tumor cells. Over-expression of Mdm2 in either tumor (which do express endogenous functional Mdm2) or in p53 null cells decreased the stability of mutant p53 suggesting that, despite its expression, Mdm2/JNK are insufficient (amount/affinity) for targeting mutant p53 degradation. Based on both in vitro and in vivo analyses, we conclude that the prolonged half-life of mutant p53 depends on the nature of the mutation, which either alters association with targeting molecules, ratio between p53 and targeting/stabilizing molecules or targeting efficiency.
 ...
PMID:Analysis of JNK, Mdm2 and p14(ARF) contribution to the regulation of mutant p53 stability. 1065 7

Inactivation of both the pRb (pRb-cyclin D1/cyclin-dependent kinase 4/6-p16) and p53 (p53-p21(WAF1)-p14(ARF)) pathways is thought to be essential for immortalization in vitro and malignant transformation in vivo. We identified different combinations of pRb and p53 pathway alterations in 12 invasive transitional cell carcinomas (TCCs) and addressed the functional significance of the different combinations observed. Results showed four combinations of alterations including -pRb/-p53 (ie., pRb inactivated in the pRb pathway and p53 inactivated in the p53 pathway; four TCCs), -p16/-p53 (four TCCs), -p16/-p21(WAF1) (one TCC), and -p16/ -p14(ARF) (two TCCs). These groups include two new combinations (ie., -p16/-p53 and -p16/-p21(WAF1)) not reported previously for TCCs. An alteration in the key components of the p53 pathway was not detected in one invasive TCC that had inactivated p16. Note that all four TCCs with inactivated pRb had mutant p53; thus, the combinations of -pRb/ -p21(WAF1) and -pRb/-p14(ARF) were not observed. Only two of eight TCCs with altered p16 had concomitant p14(ARF) loss, demonstrating that simultaneous inactivation of these two 9p21INK4a tumor suppressor genes is not obligatory. To determine the biological phenotypes of TCCs with different combinations of pRb and p53 pathway alterations, their downstream responses to gamma radiation were studied in vitro. As expected, none of eight TCCs with mutant p53 responded to gamma radiation by elevation of p53, p21(WAF1), or mdm2 or by cell cycle arrest. Only two of four TCCs with wild-type p53 and wild-type pRb (the combination of -p16/-p14(ARF)) showed normal downstream responses to gamma radiation and underwent cell cycle arrest. Two TCCs with wild-type pRb and wild-type p53 (the combination of -pl6/-p21(WAF1) and one TCC with -p16) failed to show cell cycle arrest in response to radiation. This was attributed to the absence of p21(WAF1) in one TCC. In summary, these data support a model of invasive bladder cancer pathogenesis in which both the pRb and p53 pathways are usually inactivated and the biology of the tumor is impacted by the mechanism of their inactivations.
 ...
PMID:Different combinations of genetic/epigenetic alterations inactivate the p53 and pRb pathways in invasive human bladder cancers. 1091 61

The hallmark of Burkitt lymphoma (BL) is a constitutively activated c-myc gene that drives tumor cell growth. A majority of BL-derived cell lines also carry mutant p53. In addition, the p16INK4a promoter is hypermethylated in most BL biopsies and BL cell lines, leading to silencing of this gene. Activation of c-myc and/or cell cycle dysregulation can induce ARF expression and p53-dependent apoptosis. We therefore investigated the p14ARF-MDM2-p53 pathway in BL cell lines. p14ARF was expressed and localized to nucleoli in all BL carrying mutant p53. Three out of seven BL carrying wt p53 had a homozygous deletion of the CDKN2A locus that encodes both p14ARF and p16INK4a. Three BL carrying wild type p53 retained the CDKN2A locus and overexpressed MDM2. DNA sequencing revealed a point mutation in CDKN2A exon 2 in one of these BL, Seraphine. However, this point mutation did not affect p14ARF's nucleolar localization or ability to induce p53. The Bmi-1 protein that negatively regulates the p14ARF promoter and co-operates with c-myc in tumorigenesis was expressed at low to moderate levels in all BL analysed. Our results indicate that inactivation of the ARF-MDM2-p53 pathway is an essential step during the development of Burkitt lymphoma, presumably as a mechanism to escape c-myc induced apoptosis.
 ...
PMID:p14ARF homozygous deletion or MDM2 overexpression in Burkitt lymphoma lines carrying wild type p53. 1136 Feb 1

We are investigating cooperating genetic events in the genesis of breast cancer, using the mouse as a model system. We have shown cooperativity between a mutant allele of p53 (p53-172H) and overexpressed ErbB2 in mammary tumorigenesis in transgenic mice. We are now performing additional crosses to further examine oncogene cooperativity with ErbB2 and p53-172H. We attempted to test the dominant oncogenic potential of p53-172H in an in vivo setting by crossing the p53-172H transgene together with ErbB2 onto either a p53(-/-) or a p53(+/-) background. We show that the p53-172H allele and the heterozygous p53 genotype have an identical impact on the latency of ErbB2-induced mammary tumors; there was no evidence of additivity or synergy between p53-172H and the p53(+/-) genotype. On the p53(-/-) background, we obtained no mammary tumors due to the early onset of lymphomas and sarcomas, thus precluding assessment of the effect of the p53-172H transgene on mammary tumorigenesis in a p53-null background. Thus, in this in vivo model for breast cancer, we failed to find evidence that p53-172H can function as a dominant oncogenic allele, but rather found support for its being essentially equivalent to a null allele in its impact on ErbB2-induced mammary tumorigenesis. By comparative genome analysis, we showed that a common feature of tumors arising in ErbB2/mutant p53 mice (p53-null allele with or without p53-172H) is a loss of chromosome 4, a feature of many epithelial tumors in mice and one that is consistent with a role for loss of INK4a/ARF in such tumors. We also attempted to accelerate ErbB2-induced mammary tumorigenesis with mouse mammary tumor virus (MMTV) proviral tagging mutagenesis, but we were surprised to find that mice with MMTV alone had the same latency as mice with both MMTV and ErbB2, indicating no cooperativity between ErbB2 and MMTV. This may have been due to the mixed C3H/HeN x FVB strain background used in this cross.
 ...
PMID:Cooperating oncogenic events in murine mammary tumorigenesis: assessment of ErbB2, mutant p53, and mouse mammary tumor virus. 1141 97

Malignant transformation occurs in cells that overexpress c-Myc or that inappropriately activate E2F-1. Transformation occurs after the selection of cells that have acquired resistance to apoptosis that is triggered by these oncogenes, and a key mediator of this cell death process is the p53 tumor suppressor. In IL-3-dependent immortal 32D.3 myeloid cells the ARF/p53 apoptotic pathway is inactivated, as these cells fail to express ARF. Nonetheless, both c-Myc and E2F-1 overexpression accelerated apoptosis when these cells were deprived of IL-3. Here we report that c-Myc or E2F-1 overexpression suppresses Bcl-2 protein and RNA levels, and that restoration of Bcl-2 protein effectively blocks the accelerated apoptosis that occurs when c-Myc- or E2F-1-overexpressing cells are deprived of IL-3. Blocking p53 activity with mutant p53 did not abrogate E2F-1-induced suppression of Bcl-2. Analysis of immortal myeloid cells engineered to overexpress c-Myc and E2F-1 DNA binding mutants revealed that DNA binding activity of these oncoproteins is required to suppress Bcl-2 expression. These results suggest that the targeting of Bcl-2 family members is an important mechanism of oncogene-induced apoptosis, and that this occurs independent of the ARF/p53 pathway.
 ...
PMID:Bcl-2 is an apoptotic target suppressed by both c-Myc and E2F-1. 1170 23

The tumor suppressor p53 is a labile protein whose level is known to be regulated by the Mdm-2-ubiquitin-proteasome degradation pathway. We have found another pathway for p53 proteasomal degradation regulated by NAD(P)H quinone oxidoreductase 1 (NQO1). Inhibition of NQO1 activity by dicoumarol induces p53 and p73 proteasomal degradation. A mutant p53 (p53([22,23])), which is resistant to Mdm-2-mediated degradation, was susceptible to dicoumarol-induced degradation. This finding indicates that the NQO1-regulated proteasomal p53 degradation is Mdm-2-independent. The tumor suppressor p14(ARF) and the viral oncogenes SV40 LT and adenovirus E1A that are known to stabilize p53 inhibited dicoumarol-induced p53 degradation. Unlike Mdm-2-mediated degradation, the NQO1-regulated p53 degradation pathway was not associated with accumulation of ubiquitin-conjugated p53. In vitro studies indicate that dicoumarol-induced p53 degradation was ubiquitin-independent and ATP-dependent. Inhibition of NQO1 activity in cells with a temperature-sensitive E1 ubiquitin-activating enzyme induced p53 degradation and inhibited apoptosis at the restrictive temperature without ubiquitination. Mdm-2 failed to induce p53 degradation under these conditions. Our results establish a Mdm-2- and ubiquitin-independent mechanism for proteasomal degradation of p53 that is regulated by NQO1. The lack of NQO1 activity that stabilizes a tumor suppressor such as p53 can explain why humans carrying a polymorphic inactive NQO1 are more susceptible to tumor development.
 ...
PMID:Mdm-2 and ubiquitin-independent p53 proteasomal degradation regulated by NQO1. 1223 53

CP-31398, a styrylquinazoline, emerged from a high throughput screen for therapeutic agents that restore a wild-type-associated epitope (monoclonal antibody 1620) on the DNA-binding domain of the p53 protein. We found that CP-31398 can not only restore p53 function in mutant p53-expressing cells but also significantly increase the protein level and promote the activity of wild-type p53 in multiple human cell lines, including ATM-null cells. Cells treated with CP-31398 undergo either cell cycle arrest or apoptosis. Further investigation showed that CP-31398 blocks the ubiquitination and degradation of p53 but not in human papillomavirus E6-expressing cells. Of note, CP-31398 does not block the physical association between p53 and MDM2 in vivo. Moreover, unlike the DNA-damaging agent adriamycin, which induces strong phosphorylation of p53 on serines 15 and 20, CP-31398 exposure leads to no measurable phosphorylation on these sites. We found that CP-31398 could also stabilize exogenous p53 in p53 mutant, wild-type, and p53-null human cells, even in MDM2-null p53(-/-) mouse embryonic fibroblasts. Our results suggest a model wherein CP-31398-mediated stabilization of p53 may result from reduced ubiquitination, leading to high levels of transcriptionally active p53. Further understanding of this mechanism may lead to novel strategies for p53 stabilization and tumor suppression in cancers, even those with absent ARF or high MDM2 expression.
 ...
PMID:Stabilization of p53 by CP-31398 inhibits ubiquitination without altering phosphorylation at serine 15 or 20 or MDM2 binding. 1261 87


1 2 3 Next >>