UNIPROT:P04637 - FACTA Search

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Query: UNIPROT:P04637 (p53)
77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The development of resistance to radiation and chemotherapeutic agents that cause DNA damage is a major problem for the treatment of breast and other cancers. The p53 tumor suppressor gene plays a direct role in the signaling of cell cycle arrest and apoptosis in response to DNA damage, and p53 gene mutations have been correlated with increased resistance to DNA-damaging agents. Herpes simplex virus thymidine kinase (HSV-tk) gene transfer followed by ganciclovir (GCV) treatment is a novel tumor ablation strategy that has shown good success in a variety of experimental tumor models. However, GCV cytotoxicity is believed to be mediated by DNA damage-induced apoptosis, and the relationship between p53 gene status, p53-mediated apoptosis, and the sensitivity of human tumors to HSV-tk/GCV treatment has not been firmly established. To address this issue, we compared the therapeutic efficacy of adenovirus-mediated HSV-tk gene transfer and GCV treatment in two human breast cancer cell lines: MCF-7 cells, which express wild-type p53, and MDA-MB-468 cells, which express high levels of a mutant p53 (273 Arg-His). Treating MCF-7 cells with AdHSV-tk/GCV led to the predicted increase in endogenous p53 and p21WAF1/CIP1 protein levels, and apoptosis was observed in a significant proportion of the target cell population. However, treating MDA-MB-468 cells under the same conditions resulted in a much stronger apoptotic response in the absence of induction in p21WAF1/CIP1 protein levels. This latter result suggested that HSV-tk/GCV treatment can activate a strong p53-independent apoptotic response in tumor cells that lack functional p53. To confirm this observation, four additional human breast cancer cell lines expressing mutant p53 were examined. Although a significant degree of variability in GCV chemosensitivity was observed in these cell lines, all displayed a greater reduction in cell viability than MCF-7 or normal mammary cells treated under the same conditions. These results suggest that endogenous p53 status does not correlate with chemosensitivity to HSV-tk/GCV treatment. Furthermore, evidence for a p53-independent apoptotic response serves to extend the potential of this therapeutic strategy to tumors that express mutant p53 and that may have developed resistance to conventional genotoxic agents.
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PMID:Differential chemosensitivity of breast cancer cells to ganciclovir treatment following adenovirus-mediated herpes simplex virus thymidine kinase gene transfer. 1019 85

The genotoxic risks from exposure to polycyclic aromatic hydrocarbons (PAHs) have long been recognized. Less well understood are the potential genotoxic risks of the atmospheric reaction products of this class of compounds. In this investigation, we have utilized several human cell assays to evaluate the genotoxicity of naphthalene, phenanthrene, and their atmospheric reaction products 1-nitronaphthalene, 2-nitronaphthalene (2NN), 1-hydroxy-2NN, 2-hydroxy-1-nitronaphthalene, 1,4-naphthoquinone, and 2-nitrodibenzopyranone (2NDBP). In addition, simulated atmospheric reaction products of naphthalene were generated in a 6,700 liter (L) Teflon environmental chamber, collected on a solid adsorbent, extracted, and fractionated by normal-phase high-performance liquid chromatography (HPLC). Individual fractions were then analyzed using gas chromatography/mass spectrometry (GC/MS), and tested for genotoxic effects. Genotoxicity was primarily determined using the human B-lymphoblastoid cell line, MCL-5, which expresses several transfected P450 and epoxide hydrolase genes. Mutagenicity was evaluated at both the heterozygous thymidine kinase (tk) locus and the hemizygous hypoxanthine phosphoribosyl transferase (hprt) locus, permitting detection of both intragenic and chromosomal scale mutational events. Test compounds were also screened using the CREST modified micronucleus assay. The results indicate that 2NN and 2NDBP possess greater mutagenic potency than their parent compounds, and, interestingly, both compounds induced significant increases in mutation frequency at the tk but not the hprt locus. These findings suggest a mechanistic difference in human cell response to 2NN and 2NDBP as compared to bacteria, where both compounds were previously shown to induce point mutations in the Salmonella typhimurium reversion assay. The genotoxicity of 2NN and 2NDBP in human cells, together with their high concentrations in ambient air relative to nitro-PAHs directly emitted from combustion sources, emphasizes the need to consider atmospheric reaction products of PAHs in assessments of the genotoxicity of air pollutants. We also investigated whether transfected cytochrome P450 monooxygenase activities were required to activate 2NN and 2NDBP to genotoxic species, and whether a single enzyme could be sufficient for metabolic activation. Three directly related cell lines with multiple (MCL-5), single (AHH-1 1A1), or no (L3) transfected cytochrome P450 genes were used. AHH-1 is additionally distinguished by elevated mutagenic response at the tk locus, a heterozygous mutation in p53, and apoptosis capacity. The effect of these metabolic and genetic differences on genotoxicity of 2NN, 2NDBP, and beta-naphthylamine (beta NA) was also investigated. The results indicated that 2NN and 2NDBP were not activated to genotoxic species through nitroreduction pathways. Mutagenicity induced at the tk locus was dependent on oxidative metabolism, provided by transfected cytochrome P450 enzymes in MCL-5 and AHH-1 1A1. Mutagenicity was not observed in the L3 cell line, which does not carry transfected cytochrome P450 activities. The negative response of beta NA in all cell lines indicates that, contrary to previous hypotheses, 2NN and beta NA are not activated by similar metabolic pathways in these human cell lines. Taken as a whole, these results suggest that the genotoxicity of nitro-PAHs in human cells requires oxidative metabolism.
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PMID:Evaluation of the potential health effects of the atmospheric reaction products of polycyclic aromatic hydrocarbons. 1031 78

Retinoic acid (RA), which was injected within 4 h after partial hepatectomy (PH), inhibited DNA synthesis in regenerating liver. The inhibition was accompanied by apoptosis, evidenced by in situ end labeling and gel electrophoresis of DNA fragmentation. Characteristic DNA fragmentation was obvious at 4 h and reached a maximum at 8 h after injection. Northern blot analysis revealed that RA repressed the expression of c-fos and c-jun at 15 and 30 min with the up-regulation of retinoic acid receptor gamma (RARgamma) and RARbeta at 2 h after PH. The transglutaminase II mRNA level and activity were increased by RA injection at 4 h and 8 h after PH, respectively. The mRNA levels of thymidylate synthase and thymidine kinase, which are rate determining enzymes of DNA synthesis, decreased in RA injected rats. No change was seen in the expression of p53 and p21WAF1/CIP1 which have been suggested to participate in the apoptosis process. These results suggest that RA exerts the antiproliferative activity only on the early stage of liver regeneration accompanied by the repression of c-fos and c-jun expression and induction of apoptosis.
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PMID:Retinoic acid repressed the expression of c-fos and c-jun and induced apoptosis in regenerating rat liver after partial hepatectomy. 1039 42

To explore further the possibility that some forms of mutated p53 may increase mutagenesis in a positive manner, a double p53 knockout cell line was created, using a promoterless gene targeting approach. The identity of these p53-null cells was confirmed by Southern blot and Western blot analyses. Radiation-induced toxicity and mutagenicity was then compared among p53-null cells, TK6 cells with wild-type p53, and WTK1 cells with a p53 point mutation in codon 237. At the autosomal, heterozygous thymidine kinase locus, p53-null cells had equivalent background mutation frequencies and were approximately equally mutable as TK6, whereas WTK1 was much more sensitive to spontaneously arising and X-ray-induced mutation. Thus, these results indicate that the lack of wild-type p53 did not lead to increased mutagenesis.
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PMID:Radiation-induced mutations at the autosomal thymidine kinase locus are not elevated in p53-null cells. 1039 47

Suicide gene therapy systems such as the herpes simplex thymidine kinase/ganciclovir system (TK/GCV) may kill cancer cells by apoptosis through as yet undefined mechanisms. Here we show that TK/GCV treatment induces p53 accumulation and increases cell surface expression of CD95 and tumor necrosis factor receptor, which is likely to involve p53-mediated translocation of CD95 to the cell surface. TK/GCV-induced apoptosis involves CD95-L-independent CD95 aggregation leading to the formation of a Fas-associated death domain protein (FADD) and caspase-8-containing, death-inducing signaling complex. Dominant negative FADD, the caspase-8 inhibitor zIETD-fmk [Z-Ile-Glu(OMe)-Thr-Asp(OMe)-fluoromethylketone], and zVAD-fmk (Z-Val-Ala-Asp-fluoromethylketone) partially abrogate TK/GCV-induced apoptosis. In addition to apoptosis induction, TK/GCV treatment strongly sensitizes for CD95-L-, TNF-, and TNF-related, apoptosis-inducing, ligand (TRAIL)-induced cell death in constitutively resistant cells. These findings may be used to increase the efficacy of TK/GCV and other suicide gene therapy systems for the treatment of cancer.
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PMID:Herpes simplex virus thymidine kinase/ganciclovir-induced apoptosis involves ligand-independent death receptor aggregation and activation of caspases. 1041 38

Because many tumors have mutated p53, one potential strategy proposed for cancer gene therapy is the introduction of the wild-type p53 gene into tumor cells. One puzzling aspect of this approach is that currently available gene transfer protocols result in a small percentage of tumor cells being transduced in vivo, thus implicating a "bystander effect" to achieve therapeutic efficacy. Because bystander effects in the context of p53-mediated gene therapy have not been well characterized, we evaluated the role of in vitro and in vivo bystander effects of adenovirally delivered p53 (AdWTp53). Using human tumor cell lines that did not express p53 protein but were infectible with adenovirus and showed sensitivity to p53-mediated apoptosis, we were unable to demonstrate an AdWTp53-mediated in vitro bystander effect, despite seeing strong bystander effects when cells were infected with an adenovirus containing the suicide gene herpes simplex virus thymidine kinase and treated with ganciclovir. In contrast, in vivo flank mixing studies using one of these cell lines showed a weak but significant p53-mediated bystander effect (a 40% inhibition of tumor growth). This bystander effect translated into a small survival advantage in an established intraperitoneal tumor model when tumor burden was low at the time of viral instillation. The survival advantage was lost, however, when tumor burden was increased. This study indicates that treatment of human tumors using AdWTp53 may be possible; however, because of the weak bystander effect in vivo, effective treatment will likely require a large percentage of tumor cells to be transduced.
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PMID:The evaluation of adenoviral p53-mediated bystander effect in gene therapy of cancer. 1041 47

Transduction of cancer cells with herpes simplex virus thymidine kinase gene (HSVtk) followed by prodrug ganciclovir (GCV) treatment has been shown to induce apoptosis. In this study, four murine tumors including B16F10 melanoma, NG4TL4 sarcoma, H6 hepatoma and 1MEA 7R.1 hepatoma were found to vary in sensitivity to this gene therapy strategy in vitro but, at effective doses of GCV, the HSVtk-transduced cells of all four tumors showed similar kinetics of early rise in p53 protein levels, then cell cycle S-/G2-phase arrest and finally signs of apoptosis. Immunoblot analyses revealed that Fas (CD95/APO-1), Fas ligand (FasL) and two downstream mediators, RIP and caspase-3, (CPP32, YAMA, Apopain) were increased in GCV-treated HSVtk-transduced tumor cells the cell cycle arrest and before apoptosis. Increased expression of FasL could also be observed in vivo in HSVtk-transduced tumors induced to regress by GCV treatment. Enzyme measurements using specific substrate showed that the caspase-3 activation followed kinetically the FasL expression. More than half of the HSVtk/GCV-induced cell death could be abrogated by addition to the cell culture medium of a specific antisense oligonucleotide to block FasL synthesis, a recombinant Fas/Fc chimeric protein to compete with Fas receptor for FasL binding, or cell-permeable specific tetrapeptide inhibitors of caspase-3 or caspase-8.
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PMID:Involvement of Fas (CD95/APO-1) and Fas ligand in apoptosis induced by ganciclovir treatment of tumor cells transduced with herpes simplex virus thymidine kinase. 1043 92

We examined the effect of herpes simplex virus-thymidine kinase gene (HSV-TK)-mediated suicide gene therapy on human esophageal cancer. Two human lines, T.Tn cells which bears truncated p53 and TE2 cells with wild-type p53, were transduced with the HSV-TK gene and tested for their sensitivities to a prodrug, ganciclovir (GCV). The transduced cells, T.Tn/TK and TE2/TK, increased in vitro sensitivity to GCV compared with that of respective wild-type cells. However, the growth suppression of T.Tn/TK tumors induced by GCV was marginal in nude mice and the tumors regrew thereafter. In contrast, the growth of TE2/TK tumors was significantly inhibited by GCV and all the tumors disappeared. The status of the p53 gene of tumor cells thereby may influence the efficacy of the HSV-TK/GCV system.
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PMID:Differential efficacy of suicide gene therapy by herpes simplex virus-thymidine kinase gene reflects the status of p53 gene in human esophageal cancer cells. 1062 68

Recent evidence has suggested that tumor cells having a wild-type p53 status are more sensitive to chemotherapeutic agents and radiation than cells that lack functional p53. The heightened sensitivity of wild-type p53 cells is thought to be attributable to their propensity to undergo p53-mediated apoptosis after insult. Given that suicide gene therapy is essentially tumor-targeted chemotherapy, we examined the hypothesis that coexpression of wild-type p53 could enhance the efficacy of adenovirus-mediated suicide gene therapy. Human Hep3B and SK-OV-3 cells, which are null for p53, were infected with a pair of replication-deficient adenoviruses that expressed a cytosine deaminase/herpes simplex virus thymidine kinase (CD/HSV-1 TK) fusion gene without (fusion gene nonreplicative adenovirus, FGNR) or with (FGNRp53) the wild-type human p53 gene. The sensitivity of cells to the CD/5-fluorocytosine (CD/5-FC) and HSV-1 TK/ ganciclovir (GCV) enzyme/prodrug systems was determined in vitro and in vivo. Coexpression of p53 did not enhance the cytotoxicity of either the CD/5-FC or HSV-1 TK/GCV system in vitro. The failure to observe an effect of p53 could not be explained on the basis of insufficient or transient p53 expression, because FGNRp53-infected cells growth arrested in G1, induced Bax, and underwent apoptosis at an increased rate after prodrug treatment, particularly when the adenovirus E1A protein was present. Intratumoral injection of FGNRp53 concomitant with single or double pro-drug therapy resulted in a tumor growth delay that was equal to or less than that observed with the FGNR virus. Our results indicate that coexpression of p53 may not necessarily improve the efficacy of adenovirus-mediated CD/ 5-FC and HSV-1 TK/GCV suicide gene therapies in vivo.
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PMID:Efficacy of adenovirus-mediated CD/5-FC and HSV-1 thymidine kinase/ganciclovir suicide gene therapies concomitant with p53 gene therapy. 1063 64

Gene therapy of oral cancer will require expression of genes by promoters that are both powerful and relatively tumor specific. We compared the level of expression of a reporter gene from promoters of human cytomegalovirus (CMV), SV40 virus, mouse mammary tumor virus (MMTV), human papillomaviruses (HPV) types 16 and 18, and the human multi-drug-resistance gene (mdr1), in several lines of oral cancer cells. In the oral cancer cell line 686LN the rank order of expression levels was: CMV > SV40 > HPV > mdr1 > MMTV. Unlike in previous reports the mdr1 promoter was no more active in two cancer cell lines with mutations in the p53 gene than in two other lines with wild-type p53, and its expression level could not be increased by either doxorubicin or taxol. On the other hand, expression from the MMTV promoter was increased over 10-fold by the presence of 1 microM dexamethasone. Thus, by an appropriate choice of promoter and inducer a wide variety of expression levels, over a 3-log range, could be attained in 686LN cells. The oral cancer-specificity of each promoter was judged by comparing expression in the neuroblastoma line IMR32. The most specific promoters were those from papillomaviruses, which were up to 45 times more active in the oral cancer cells, and the least specific was the CMV promoter. In order to find if an HPV-derived promoter was sufficient to produce expression of a suicide phenotype the 686 promoter was cloned adjacent to the thymidine kinase gene of herpes simplex and the construct was expressed from an adenovirus vector. The vector reduced the growth of 686LN cells over a 5-day period by up to 32% when optimal concentrations of virus and ganciclovir were used. These data will be valuable in the design of new constructs for gene therapy of oral cancer.
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PMID:Strength and specificity of different gene promoters in oral cancer cells. 1074 75

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