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)

p53 stimulates the transcription of a number of genes, such as MDM2, Waf1, and GADD45. We and others have shown previously that this activity of p53 can be inhibited by adenovirus type 2 or 12 large E1B proteins. Here we show that the adenovirus E1A proteins also can repress the stimulation of transcription by p53, both in transient transfections and in stably transfected cell lines. The inhibition by E1A occurs without a significant effect on the DNA-binding capacity of p53. Furthermore, the activity of a fusion protein containing the N-terminal part of p53 linked to the GAL4 DNA-binding domain can be suppressed by E1A. This indicates that E1A affects the transcription activation domain of p53, although tryptic phosphopeptide mapping revealed that the level of phosphorylation of this domain does not change significantly in E1A-expressing cell lines. Gel filtration studies, however, showed p53 to be present in complexes of increased molecular weight as a result of E1A expression. Apparently, E1A can cause increased homo- or hetero-oligomerization of p53, which might result in the inactivation of the transcription activation domain of p53. Additionally, we found that transfectants stably expressing E1A have lost the ability to arrest in G1 after DNA damage, indicating that E1A can abolish the normal biological function of p53.
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PMID:Adenovirus E1A proteins inhibit activation of transcription by p53. 862 76

DNA-damaging agents such as ionizing radiation (IR) activate the tumor suppressor p53, and, in turn, p53 transactivates a number of downstream effector genes such as GADD45, CIP1/WAF1, and MDM2. The induction of these downstream genes following IR appears to be strictly dependent upon the presence of wild-type functional p53 known to evoke G1 arrest. In this study, we characterized 56 cell lines from 9 different tumor types with predetermined p53 genotype by measuring the induction of GADD45, CIP1/WAF1, and MDM2 relative mRNA levels after IR. A higher fraction of melanoma lines had wild-type (wt) p53 (5/8, or 63%) compared to the nonmelanoma lines (11/48, or 23%). Most wt p53 (nonmelanoma) cell lines (11/12, or 92%) showed clear induction of both GADD45 and CIP1/WAF1. On the other hand, many wt p53 melanoma lines (4/5, or 80%) showed normal induction of CIP1/WAF1, but little or no induction of GADD45. Despite this defect in GADD45 induction, we found that all wt p53 melanoma lines exhibited strong G1 arrest and increased levels of p53 protein after IR. The results demonstrated that radiation-induced G1 arrest could occur by the p53-CIP1/WAF1 pathway without appreciable induction of GADD45 in melanoma lines. Time course experiments demonstrated prolonged induced expression of CIP1/WAF1 mRNA transcripts in melanoma lines in which GADD45 induction was lacking, suggesting some sort of compensatory mechanism involving CIP1/WAF1, in cell lines with defective GADD45 induction. We could reproduce this compensatory effect in RKO colon carcinoma cells in which GADD45 expression was blocked by constitutive antisense vectors. These findings reveal that defective induction of GADD45 following IR is common in human melanoma cell lines.
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PMID:An abnormality in the p53 pathway following gamma-irradiation in many wild-type p53 human melanoma lines. 863 Oct 22

We have previously reported that WI-L2-NS, a human lymphoblastoid cell line, has very high basal levels of GADD45 mRNA and protein in spite of a p53 mutation at amino acid 237. Regardless of the amount of Gadd45 in this cell line, no growth suppression activity was detected. We report here that in WI-L2-NS, the mutated p53 protein adopts predominantly a wild type (wt) conformation and binds to the p53 binding site in the GADD45 third intron. In this cell line, the already high levels of mutated p53 protein can be induced further by ionizing radiation (IR) but the response of the p53 downstream effector genes is altered. Induction of GADD45 and CIP1/WAF1 is reduced compared to p53 wt cell lines but is still substantially higher than the average fold induction obtained from 39 p53 mutant cell lines. Induction of the MDM2 gene was not detected in WI-L2-NS following IR. The induction pattern of the three p53 effector genes by the alkylating agent methylmethane sulfonate (MMS) was also attenuated in WI-L2-NS cells. In TK6 cells, a WI-L2-NS sister cell line having a p53 wt genotype, the induction of the p53 downstream effectors is normal, i.e. induced, both at the protein and the mRNA levels. These results indicate that the DNA binding activity of the mutated p53 protein in WI-L2-NS might be responsible, at least in part, for the high basal levels of GADD45 but can not mediate the full induction of the p53 downstream effector genes. The reason(s) for the inability of Gadd45 to suppress growth in this cell line remains however unknown.
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PMID:Characterization of the GADD45 response to ionizing radiation in WI-L2-NS cells, a p53 mutant cell line. 867 20

The p53 gene product is part of a pathway regulating growth arrest at the G1 checkpoint of the cell cycle. Mutation of other components of this pathway, including the products of the ataxia telangiectasia (AT), GADD45, mdm2, and p21WAF1/CIP1 genes may have effects comparable to mutations in the p53 gene. The GADD45 gene is induced by ionizing radiation and several DNA-damaging xenobiotics. Induction requires the binding of wild-type p53 to an evoulutionarily highly conserved putative intronic p53 binding site in intron 3 of GADD45. We recently analyzed the entire coding region of the p53 gene in primary breast cancers of Midwestern white women and found 21 mutations among 53 tumors (39.6%). We now have shown by direct sequencing that there are no mutations in the intronic p53 binding site of the GADD45 gene in any of the 53 primary breast cancers and no mutations in the entire coding region of the GADD45 gene in a subset of 26 consecutive tumors (12 with p53 mutation and 14 without p53 mutation). The only sequence variation detected was a common polymorphism in intron 3. The absence of mutations in the GADD45 gene, including the putative p53-binding intronic site, suggests that this gene is not a frequent target of mutations in breast cancer. Although mutations of the p53 gene have been studied in a wide spectrum of human cancers, GADD45 has not been examined in any tumor or cell line to the best of our knowledge. Our results raise the possibility that mutation of the GADD45 gene alone is not functionally equivalent to loss of wild-type p53 activity.
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PMID:A polymorphism but no mutations in the GADD45 gene in breast cancers. 883 60

The tumor suppressor p53 is required for induction of its downstream effector genes such as GADD45 and CIP1/WAF1 by ionizing radiation (IR). This response is probably mediated through defined p53 binding sites located in the promoter of CIP1/WAF1 and in the third intron of GADD45. In contrast, the gadd gene stress response to base-damaging agents, such as methylmethane sulfonate (MMS) or UV radiation, or medium depletion (starvation) occurs in all mammalian cells examined to date regardless of p53 status for both GADD45 and also GADD153, which is not IR-responsive in many lines with functional p53. These agents strongly induce the p53 protein and raise the possibility that, although p53 is not required for the typical "gadd" response to these agents, p53 may contribute to these non-IR stress responses. This possibility was confirmed by the finding that disruption of p53 function by transfection with dominant-negative vectors expressing HPV E6, mutant p53, or SV40 T Ag reduced the induction of GADD45 and GADD153 as measured by increases in mRNA and protein levels in human lines with wild-type p53. Similarly, induction of these genes by MMS or UV radiation was consistently stronger in the parental mouse embryo fibroblasts compared to cells derived from mice where both p53 alleles had been deleted. Similar qualitative responses were also seen for CIP1/WAF1. In agreement with reduced induction of p53-regulated genes, the G1 checkpoint activated by MMS or UV radiation was markedly abrogated in p53-wt human MCF-7 breast carcinoma cells by E6 expression. Interestingly, induction of reporter constructs driven by the GADD45 or GADD153 promoters was substantially reduced in human cells transfected with mutant p53 or E6 expression vectors or in cells lacking p53 following treatment with MMS, UV radiation, or starvation. Because neither promoter is inducible by IR, and neither contains a strong p53 binding site, these results indicate that p53 has a synergistic or cooperative role in these non-IR stress responses for both GADD45 and GADD153, and that this role is not mediated through identifiable p53-binding sites.
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PMID:Abrogation of p53 function affects gadd gene responses to DNA base-damaging agents and starvation. 889 53

Camptothecin (CPT) traps covalent DNA topoisomerase I-linked DNA single-strand breaks (cleavable complexes). To determine the differences in DNA damage signalling leading to differential sensitivity to CPT, two human colon cancer cell lines, SW620 and KM12, with nonfunctional p53 and the same level of topoisomerase I cleavable complex formation but differential sensitivity to CPT (Cancer Res. 56:4430-7; 1996) were studied. The levels of mRNA expression of DNA damage-inducible or death-related genes were measured at different times after CPT treatment. KM12 cells exhibited 3-fold higher basal levels of BCL-2 mRNA. Consistently, secondary DNA fragmentation, quantitated using a filter elution assay, was detected 24 h later and was 2-4-fold lower in KM12 cells than in SW620 cells. No induction of BAX was detected in either cell line. Consistent with the absence of functional p53, p21CIP1/WAF1 and GADD45 genes were not induced within the first 24 h. However, in SW620 cells, both mRNA levels were increased more than 10-fold at 48 h. The BCL-2-related gene MCL-1 and topoisomerase II mRNA were induced at 24 h, and topoisomerase I mRNA levels increased 3-fold at 48 h, only in SW620 cells. We conclude that cellular response to CPT-induced DNA damage can involve p53-independent pathways leading to the induction of p53-effector genes. Induction of these genes at the onset of apoptosis is associated with CPT sensitivity.
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PMID:Differential GADD45, p21CIP1/WAF1, MCL-1 and topoisomerase II gene induction and secondary DNA fragmentation after camptothecin-induced DNA damage in two mutant p53 human colon cancer cell lines. 893 95

Long-term unilateral ureteral obstruction (UUO) initiates a series of renal events leading to proliferation of interstitial fibroblasts and proliferation/repair of tubular cells. This is evidenced by significant increases in proliferating cell nuclear antigen (PCNA) positive nuclei during UUO. Several pathologic settings requiring DNA replication and/or DNA repair are dependent upon the expression of p53 and at least one of two p53-dependent proteins, termed p21 (also called WAF1) and GADD45. We therefore sought to determine if p53, p21 (WAF1) or GADD45 mRNA levels were changed in obstruction. There was a progressive increase in the amount of p53 mRNA and p21 (WAF1) mRNA at 1, 3, 5 and 8 days of continuous UUO. The amount of GADD45 mRNA was found not to change. Treatment of the experimental animals with an ACE inhibitor on day 4 through day 8 of UUO significantly blunted the increase in p53 and p21 (WAF1) expression. ACE inhibitor treatment also significantly decreased the number of PCNA-positive renal cell nuclei during UUO. These results suggest that during ureteral obstruction the p53 and p21 (WAF1) genes are activated. ACE inhibitor treatment reduces p53 and p21 (WAF1) expression. This reduction is at least in part due to an inhibition of interstitial cell proliferation.
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PMID:Control of p53 and p21 (WAF1) expression during unilateral ureteral obstruction. 894 27

Loss of p53 function in cancer cells commonly results in a condition of genomic instability. This is believed to emanate from a loss of the G1 checkpoint response to DNA damage. While the role of p53 in the induction of a G1 arrest is well-accepted, additional p53 functions are being discovered. Cell cycle checkpoints presumably function to allow additional time for DNA repair after damage is incurred, however, genetic studies in yeast suggest that components of the checkpoint pathway may also be involved in DNA lesion processing (Lydall and Weinert, 1995). Recent evidence suggests that this may also be the case for p53, as suggested by numerous reports linking p53 function to DNA repair. Thus, loss of p53 function might contribute to genomic instability independent of G1-arrest. In the present study, we explored the effect of p53 disruption and consequences of antisense GADD45 expression on the DNA repair capacity of human colon carcinoma RKO cells. DNA repair was assayed using host-cell reactivation of u.v.-damaged reporter plasmids and unscheduled DNA synthesis experiments in transiently-transfected cells. We show that a number of transfected genes that suppress p53 function reduce the ability of cells to repair u.v.-induced DNA damage. Moreover, cells in which expression of the p53-regulated gene GADD45 was blocked by antisense vectors, also showed altered levels of DNA repair. Blocking Gadd45 expression by constitutive antisense expression sensitized cells to killing by u.v.-radiation or by cis-platinum (II) diamine-dichloride (CDDP, or cisplatin), a cancer chemotherapy drug which produces DNA cross-links. These findings suggest the involvement of downstream effectors of the p53 pathway in the coordination of cell cycle arrest and DNA repair.
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PMID:Antisense GADD45 expression results in decreased DNA repair and sensitizes cells to u.v.-irradiation or cisplatin. 895 Sep 93

A camptothecin (CPT)-resistant cell line (MCF-7/C4) was established from MCF-7 cells by mutagenic treatment with methylmethanesulfonate and selection with CPT. MCF-7/C4 is 30-fold resistant to CPT and is cross-resistant to UV and cis-dichlorodiammineplatinum(II) but not to VP-16 or ionizing radiation. Topoisomerase I (top1)-mediated cleavable complexes in the presence of CPT, measured by oligonucleotide assay and by alkaline elution, were similar in both cell lines. Other top1 parameters such as top1 protein, RNA levels, and DNA relaxation were also similar in both cell lines. Thus, CPT resistance is not due to alterations in top1 activity but is caused by changes in the downstream pathways from the top1-induced damage. Both cell lines had similar doubling time (22 hr), but MCF-7/C4 cells showed reduced S-phase fraction in the absence of CPT and reduced G2 delay after CPT treatment. p53, GADD45, and p21WAF1/CIP1 were induced similarly by CPT in both cell lines. The overall repair capacity estimated by the ability of cells to reactivate UV-damaged pSV-CAT plasmid was increased in MCF-7/C4 cells. These observations suggest that enhanced DNA repair is one of the factors involved in CPT resistance.
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PMID:Acquired camptothecin resistance of human breast cancer MCF-7/C4 cells with normal topoisomerase I and elevated DNA repair. 896 67

Among the p53-regulated genes that have been identified thus far, cyclin G is a relatively recent one. We conducted a series of experiments aimed at elucidating cyclin G function. Ectopic overexpression of cyclin G in human RKO colon carcinoma cells accelerated cell growth. Transfection of normal human fibroblasts with the cyclin G expression vector promoted clonal expansion. Cyclin G immune complexes isolated from the transfected cells exhibited appreciable levels of cyclin-dependent kinase activity, as evidenced using histone H1 as a substrate. The retinoblastoma protein, pRb, was detectable in cyclin G immune complexes, raising the possibility that Rb may be one mediator of cyclin G action. Cyclin G-overexpressing cells were more sensitive to cisplatin cytotoxicity than the parent cells, probably because cyclin G overexpression overrides cell cycle checkpoint(s). Overexpression of another p53-regulated gene, GADD45, by contrast, protected cells from cisplatin killing. These findings suggest that different downstream effectors of the p53 pathway may exert different effects on cellular survival after treatment with cancer chemotherapy drugs such as cisplatin.
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PMID:The p53-regulated cyclin G gene promotes cell growth: p53 downstream effectors cyclin G and Gadd45 exert different effects on cisplatin chemosensitivity. 901 7


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