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 DNA repair enzyme O6-alkylguanine DNA-alkyltransferase (OGAT) and a deficient mismatch repair system play a critical role in the resistance to chemotherapeutic agents that generate adducts at the O6-position of guanine. However, DNA adducts different from O6-methylguanine might be also involved in cytotoxicity induced by methylating agents. Because the loss of p53 function is generally associated with tumor cell resistance to anticancer chemotherapy, we have investigated whether wild-type p53 might affect chemosensitivity of leukemia cells endowed with high OGAT levels to the methylating agent temozolomide (TZM). The effect of poly(ADP-ribose) polymerase (PADPRP) inhibition, which potentiates the cytotoxic effects of N7-methylguanine and N3-methylguanine, was also assessed in OGAT-proficient cells, either susceptible or tolerant to O6-methylguanine. OGAT-proficient and p53 null HL60 cells were transfected with the human p53 cDNA (p53+ cells). Treatment with TZM concentrations not toxic for the cells transduced with the control vector (p53-cells), induced apoptosis in p53+ cells. These cells were characterized by a lower level of bcl-2 protein than p53- cells, whereas bax and OGAT expression was comparable in both lines. Inhibition of PADPRP potentiated the cytotoxic and apoptotic effects of TZM in either p53- or p53+ HL60 cells. Furthermore, PADPRP inhibitors potentiated apoptosis induced by TZM in Jurkat cells, which possess a mutated p53 gene and are tolerant to O6-methylguanine adducts. The analysis of cell cycle indicated that the drug combination of TZM and PADPRP inhibitors provoked G1 arrest only in p53+ cells. Conversely, G1 arrest was not observed in p53+ cells exposed to TZM alone. It is possible to speculate that PADPRP inhibitors might affect the repair of DNA adducts that are processed differently from O6 methylguanine and induce a different pattern of cell cycle distribution. In conclusion, the results show that p53 increases apoptosis by TZM in OGAT-proficient cells and suggest the potential role of PADPRP inhibitors in enhancing TZM activity against leukemias independently of DNA repair systems.
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PMID:Role of wild-type p53 on the antineoplastic activity of temozolomide alone or combined with inhibitors of poly(ADP-ribose) polymerase. 958 Jun 40

In situ hybridization was used to characterize the expression pattern of the T:G mismatch-specific thymidine-DNA glycosylase (TDG) gene, encoding a DNA repair enzyme which corrects G:T mismatches that result from the hydrolytic deamination of 5-methyl cytosines. TDG transcripts were uniformly and ubiquitously expressed from 7.5-13.5 days post-coitum, but were then markedly enriched in specific tissues of the developing fetus. At 14.5 gestational days, TDG was strongly expressed in the developing nervous system, thymus, lung, liver, kidney and intestine. At later stages, high levels of expression were detected in the thymus, brain, nasal epithelium and within proliferating regions of the intestine, skin, kidney, teeth and bone. This pattern of expression strongly correlated with those of the methyl transferase (MTase) gene, coding for the enzyme which specifically methylates CpG dinucleotides, and the p53 tumour suppressor gene. However, TDG and MTase were differentially expressed during maturation of the male and female germline. We also report that tumors occuring in mice which overexpress MMTV-v-Ha-ras or MMTV-c-myc transgenes or mice heterozygous for p53 gene disruption, all show elevated TDG and MTase expression specific to the transformed tissue.
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PMID:Expression of T:G mismatch-specific thymidine-DNA glycosylase and DNA methyl transferase genes during development and tumorigenesis. 979 35

Caspases play a pivotal role in neuronal cell death during development and after trophic factor withdrawal. However, the mechanisms regulating caspase activity and the role played by caspase activation in response to neuronal injury is poorly understood. The tumor suppressor gene p53 has been implicated in the loss of neuronal viability caused by excitotoxic and DNA damaging agents. In the present study we determined if p53-mediated neuronal cell death required caspase activation. DNA damage increased caspase activity in both cultured embryonic telencephalic and postnatal cortical neurons in a p53-dependent manner. Caspase inhibitors protected embryonic telencephalic neurons, but not postnatal cortical neurons, from DNA damage-induced cell death as measured by direct cell counting and annexin V staining. In marked contrast to the caspase inhibitors, an inhibitor of the DNA repair enzyme, poly(ADP-ribose) polymerase, conferred significant protection from genotoxic and excitotoxic cell death on postnatal cortical neurons but had no effect on embryonic neurons. Glutamate-mediated excitotoxicity in postnatal neurons was not associated with measurable changes in caspase activity, consistent with the failure of caspase inhibitors to prevent cell death under these conditions. Moreover, adenovirus-mediated overexpression of p53 killed embryonic and postnatal neurons without activating caspases. Thus, p53-mediated neuronal cell death may occur via both caspase-dependent and caspase-independent pathways. These results demonstrate that p53 is required for caspase activation in response to some forms of neuronal injury. However, the relative importance of caspase activation in neurons depends on the developmental status of the cell and the specific nature of the death stimulus.
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PMID:Contribution of p53-dependent caspase activation to neuronal cell death declines with neuronal maturation. 1019 17

Many studies have indicated that cancer cells expressing mutant (mt) p53 are resistant to genotoxic stress such as chemotherapy and radiation therapy. Inasmuch as most human oral cancer cells either express mt p53 or are infected with <high risk> human papillomavirus (HPV), we determined the sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a genotoxic chemical carcinogen, the activity of a DNA repair enzyme O6-methylguanine methyl transferase (MGMT) and the status of p53 in 11 human oral cancer cell lines, 2 HPV-immortalized human oral keratinocytes and 3 normal human oral keratinocyte (NHOK) cultures. Ten cancer cell lines demonstrated significantly higher level of MGMT activities compared to normal or immortalized non-tumorigenic cells, while one cancer cell line showed negligible MGMT activity. All immortalized cells and NHOK showed very low MGMT activity. Interestingly, all cancer cells with high MGMT activity expressed either mt p53 or harbored <high risk> HPV DNA. However, infection of one cancer cell line (that does not demonstrate the MGMT activity) with retrovirus expressing an mt p53 protein did not alter the sensitivity of cells to MNNG and the enzyme activity. These data indicate that most human oral cancer cells contain moderately high DNA repair enzyme activity, and in doing so may be resistant to genotoxic stress, but the association of p53 with MGMT activities should further be investigated.
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PMID:High O6-methylguanine methyl transferase activity is frequently found in human oral cancer cells with p53 inactivation. 1049 67

The temporospatial expression pattern of the nuclear DNA repair enzyme redox factor-1 (ref-1), the p53-activated gene (pag) 608 and the effector caspase-3 was examined by in situ hybridization histochemistry in gerbils subjected to two 10-min episodes of unilateral common carotid artery occlusion, separated by 5h. Gene responses were correlated with the metabolic state, as revealed by regional adenosine 5'-triphosphate bioluminescent imaging, and with the degree of histological damage, as assessed by haematoxylin-eosin staining and terminal deoxynucleotidyl transferase-mediated-dUTP nick end labeling (TUNEL), in order to evaluate the role of these genes in the maturation of injury. Focal infarcts developed in the dorsolateral cerebral cortex at the bregma level and the nucleus caudate-putamen within four days after repeated unilateral ischemia, as indicated by a secondary adenosine 5'-triphosphate loss after initial adenosine 5'-triphosphate recovery and by histomorphological signs of pannecrosis. The more caudal cortex at hippocampal levels and the hippocampus (CA1>CA3 area), however, exhibited selective neuronal injury without adenosine 5'-triphosphate depletion. TUNEL+ cells appeared starting 5h after repeated unilateral ischemia. TUNEL+ cells reached maximum levels in the caudate-putamen at 12-24h, but much later in the cortex and hippocampus at two days after ischemia. Remarkably few TUNEL+ cells were noticed in the thalamus, where adenosine 5'-triphosphate state did not recover after reperfusion. Following repeated unilateral ischemia, a transient elevation of ref-1 mRNA was detected after 5h in the cerebral cortex and hippocampal CA1 area. Ref-1 mRNA levels decreased within 12-24h, before the onset of tissue damage. Subsequently, pag608 and caspase-3 mRNA levels increased, closely in parallel with the appearance of DNA fragmented cells, but slightly prior to the deterioration of adenosine 5'-triphosphate state. In the caudate-putamen, pag608 and caspase-3 mRNAs reached maximum levels already 12-24h after repeated common carotid artery occlusion, when DNA fragmentation was most prominent, and declined thereafter. In the cortex and hippocampal CA1-3 areas, where DNA damage appeared more slowly, pag608 and caspase-3 mRNAs were induced starting 24h after ischemia, and remained elevated even after two to four days. The levels of pag608 and caspase-3 mRNAs were similar at rostral and caudal levels of the cortex, as well as in the hippocampal CA1 and CA3 area, although the degree of injury differed considerably between these structures. Notably, pag608 and caspase-3 mRNAs were not elevated in the thalamus after repeated unilateral ischemia. The present report shows a close temporal association between the induction of ref-1, pag608 and caspase-3 mRNAs, the manifestation of cell injury and the secondary adenosine 5'-triphosphate depletion in infarcting brain areas, suggesting (i) that de novo responses of these genes may be involved in the maturation of cell injury and (ii) that apoptotic programs and the secondary deterioration of cerebral energy state may interfere with each other after ischemia.
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PMID:Expression of redox factor-1, p53-activated gene 608 and caspase-3 messenger RNAs following repeated unilateral common carotid artery occlusion in gerbils--relationship to delayed cell injury and secondary failure of energy state. 1118 42

Defects in DNA repair may be responsible for the genesis of mutations in key genes in cancer cells. The tumor suppressor gene p53 is commonly mutated in human cancer by missense point mutations, most of them G:C to A:T transitions. A recognized cause for this type of change is spontaneous deamination of the methylcytosine. However, the persistence of a premutagenic O(6)-methylguanine can also be invoked. This last lesion is removed in the normal cell by the DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT). In many tumor types, epigenetic silencing of MGMT by promoter hypermethylation has been demonstrated and linked to the appearance of G to A mutations in the K-ras oncogene in colorectal tumors. To study the relevance of defective MGMT function by aberrant methylation in relation to the presence of p53 mutations, we studied 314 colorectal tumors for MGMT promoter hypermethylation and p53 mutational spectrum. Inactivation of MGMT by aberrant methylation was associated with the appearance of G:C to A:T transition mutations at p53 (Fischer's exact test, two-tailed; P = 0.01). Overall, MGMT methylated tumors displayed p53 transition mutations in 43 of 126 (34%) cases, whereas MGMT unmethylated tumors only showed G:C to A:T changes in 37 of 188 (19%) tumors. A more striking association was found in G:C to A:T transitions in non-CpG dinucleotides; 71% (12 of 17) of the total non-CpG transition mutations in p53 were observed in MGMT aberrantly methylated tumors (Fischer's exact test, two-tailed; P = 0.008). Our data suggest that epigenetic silencing of MGMT by promoter hypermethylation may lead to G:C to A:T transition mutations in p53.
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PMID:Promoter hypermethylation of the DNA repair gene O(6)-methylguanine-DNA methyltransferase is associated with the presence of G:C to A:T transition mutations in p53 in human colorectal tumorigenesis. 1140 38

The second enzyme in the DNA base excision repair (BER) pathway, apurinic/apyrimidinic (AP) endonuclease or Ape1, hydrolyzes the phosphodiester backbone immediately 5' to an AP site generating a normal 3'-hydroxyl group and an abasic deoxyribose-5-phosphate, which is processed by subsequent enzymes of the BER pathway. AP sites are the most common form of DNA damage, and the persistence of AP sites in DNA results in a block to DNA replication, cytotoxic mutations, and genetic instability. Interestingly, Ape1/ref-1 is a multifunctional protein that not only is a DNA repair enzyme, but also functions as a redox factor maintaining transcription factors, such as Fos, Jun, nuclear factor-kappaB, PAX (paired box-containing family of genes), hypoxia inducible factor-lalpha (HIF-1alpha), HIF-1-like factor, and p53, in an active reduced state. Apel/ref-1 has also been implicated in a number of other activities, one of which is the activation of bioreductive drugs requiring reduction for activity. In this report, we present data supporting our findings that another level of posttranslational modification of Apel/ref-1 that clearly affects the AP endonuclease activity is the reduction or oxidation of this protein. Furthermore, we show data demonstrating that at least one of the sites involved in this redox regulation is the cysteine amino acid found at position 310, immediately adjacent to the crucial histidine residue at position 309 in the DNA repair active site. These findings suggest that the Apel/ref-1 protein may be much more intimately regulated at the posttranslational level than initially imagined.
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PMID:Redox regulation of the DNA repair function of the human AP endonuclease Ape1/ref-1. 1155 53

Mutations in the mismatch DNA repair gene human MutS homologen 2 (hMSH2) are causative for microsatellite instability and carcinogenesis in various human tumours, including hereditary nonpolyposis colorectal cancer. Because microsatellite instability has been detected in malignant melanoma, we have investigated hMSH2 in melanocytic tumours. We found strong nuclear immunoreactivity for hMSH2 that was elevated in malignant melanoma and melanoma metastases as compared to acquired nevi. These findings suggest that increased genomic instability in malignant melanoma is associated with elevated protein levels of this DNA repair enzyme. hMSH2 is not exclusively regulated by proliferative activity in melanocytes, because there was no correlation between staining patterns of hMSH2 and the proliferation marker Ki-67. In contrast, immunoreactivity scores for hMSH2 and p53 were both upregulated in malignant melanocytic tumours. These findings support the concept that hMSH2 gene expression may be regulated in melanocytes by the p53 protein, as has been reported previously in other tissues. Using the reverse transcription-polymerase chain reaction, we detected strong hMSH2 mRNA expression in each of 8 melanoma cell lines analysed (highest amounts in SK-MEL-25 cells, lowest amounts in MML-I cells). In conclusion, our findings indicate that hMSH-2 may be of importance for genetic stability, tumorigenesis and progression of malignant melanoma.
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PMID:DNA mismatch repair enzyme hMSH2 in malignant melanoma: increased immunoreactivity as compared to acquired melanocytic nevi and strong mRNA expression in melanoma cell lines. 1193 86

The mutagenicity of a prominent tobacco carcinogen, benzo[a]pyrene (B[a]P), is believed to result from chemical reactions between its diol epoxide metabolite, (+)-anti-7r,8t-dihydroxy-c9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), and DNA, producing promutagenic lesions, e.g., (+)-trans-anti-7R,8S,9S-trihydroxy-10S-(N(2)-deoxyguanosyl)-7,8,9,10-tetrahydrobenzo[a]pyrene (N(2)-BPDE-dG). Previous studies used the DNA repair enzyme UvrABC endonuclease in combination with ligation-mediated PCR (LMPCR) to demonstrate an increased reactivity of BPDE toward guanine nucleobases within codons 157, 248, and 273 of the p53 tumor suppressor gene (Denissenko, M. F., Pao, A., Tang, M., and Pfeifer, G. P. Science 274, 430-432). These sites are also "hot spots" for mutations observed in lung tumors of smokers, suggesting an involvement of B[a]P in the initiation of lung cancer. However, the LMPCR approach relies on the ability of the repair enzyme to excise BPDE-induced lesions, and thus the slowly repaired lesions may escape detection. Furthermore, BPDE-DNA adduct structure and stereochemistry cannot be determined. In the present work, we performed a direct quantitative analysis of N(2)-BPDE-dG originating from specific guanine nucleobases within p53- and K-ras-derived DNA sequences by using a stable isotope labeling-mass spectrometry approach recently developed in our laboratory. (15)N-labeled dG was placed at defined positions within DNA sequences derived from the K-ras proto-oncogene and p53 tumor suppressor gene, the two genes most frequently mutated in smoking-induced lung cancer. (15)N-labeled DNA was annealed to the complementary strands, followed by BPDE treatment and liquid chromatography-electrospray ionization tandem mass spectrometry analysis (HPLC-ESI-MS/MS) of N(2)-BPDE-dG lesions. The extent of adduct formation at (15)N-labeled guanine was determined directly from the HPLC-ESI-MS/MS peak area ratios of (15)N-N(2)-BPDE-dG and N(2)-BPDE-dG. BPDE-induced guanine adducts were produced nonrandomly along K-ras and p53 gene-derived DNA sequences, with over 5-fold differences in adduct formation depending on sequence context. N(2)-BPDE-dG yield was enhanced by the presence of 5-Me substituent at the cytosine base-paired with the target guanine nucleobase, an endogenous DNA modification characteristic for CpG dinucleotides within the p53 gene. In the K-ras-derived DNA sequence, the majority of N(2)-BPDE-dG adducts originated from the first position of the codon 12 (GGT), consistent with the large number of G --> T transversions observed at this nucleotide in smoking-induced lung cancer. On the contrary, the pattern of N(2)-BPDE-dG formation within the p53 exon 5 sequences did not correlate with the mutational spectrum in lung cancer, suggesting that factors other than N(2)-BPDE-dG formation are responsible for these mutations. The stable isotope labeling HPLC-ESI-MS/MS approach described in this work is universally applicable to studies of modifications to isolated DNA by other carcinogens and alkylating drugs.
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PMID:Formation of benzo[a]pyrene diol epoxide-DNA adducts at specific guanines within K-ras and p53 gene sequences: stable isotope-labeling mass spectrometry approach. 1213 76

The DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT) removes alkylating adducts from the O(6) position of guanine and protects cells from cytotoxic and mutagenic effects. Expression of MGMT is decreased in some cancers, which may be the result of methylation of CpG islands of both the promoter and coding regions of the gene. We studied the methylation status of the MGMT promoter in a very large collection of brain tumors (85) using methylation-specific polymerase chain reaction (PCR). Aberrant methylation occurred in 48% of 85 human brain tumor samples. Quantitative real-time PCR showed that expression of MGMT mRNA levels was significantly decreased (P < 0.001) in those brain tumors that had methylation of the promoter region of their MGMT gene. MGMT can prevent G to A mutations by removing alkyl groups from the O(6) position of guanine. We found a significantly increased frequency of G:C to A:T mutations of the p53 gene in brain tumors having a methylated MGMT promoter compared with those having an unmethylated MGMT promoter (P < 0.05), and all the non-CpG dinucleotide G:C to A:T mutations of p53 were in samples with a methylated MGMT promoter.
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PMID:DNA repair gene O6-methylguanine-DNA methyltransferase: promoter hypermethylation associated with decreased expression and G:C to A:T mutations of p53 in brain tumors. 1250 76


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