P53 Gene Exons Research Articles

Mutations of the p53 gene and microsatellite inestability (MSI) as prognostic factors in metastatic colorectal cancer (CRC)

22088 Background: Several genetic changes have been described associated with CRC, but the prognostic significance of most of them remains controversial. We analysed the distribution and the association with survival of some molecular markers in CCR tissues. Methods: From March-04 to June-05 73 patients were included with recent diagnosis of CRC: 53M/20F with a mean age of 70y (46–88). There were 25 rectal tumors (34%) and stage distribution was I:11, IIA:24, IIB:2, IIIA:3, IIIB:9, IIIC:8 and IV:16. During the anatomopathologic exam of the resected specimens, fresh samples were obtained (tumoral tissue and normal tissue), and they were stored in freezer vials at −86°C. In every sample all the following analysis were performed: LOH of the APC and DCC genes, MSI and Kras mutations using different biological techniques, and mutations of the p53 gene (exons 5 to 9) by sequence analysis. Results: LOH of DCC was found in 62% of the tumors, LOH of APC in 46% and MSI in 22% (MSI-LOW in 12 patients and MSI-HIGH in 4). Fifty one percent of the patients showed p53 mutations, mainly at the exons 5 (32%) and 8 (30%), and 38% carried a mutation in Kras (27 at the codon 12 and 1 at the codon 13). LOH of DCC was seen more frequently in older patients (p=0.045) and it showed associated with the presence of p53 mutations (p=0.005). In loco-regional stages (I-III), Kras was more frequently mutated in patients without node involvement (stages I-II vs III, p=0.012). In advanced disease, point mutations of p53 (p=0.031) and the abscence of MSI (p=0.022) were associated with a significant worse survival at multivariate analysis, even when clinical variables (age, gender, tumor location, palliative chemotherapy) were included in the model (p53: p=0.023; MSI: p=0.015). Conclusions: In our cohort of patients, mutations of the p53 supressor gene and the absence of MSI in the primary tumor are independent prognostic factors in patients with ACRC at the moment of diagnosis. No significant financial relationships to disclose.

Colorectal carcinoma prognosis can be predicted by alterations in gene p53 exons 5 and 8

Gene p53 alteration is a genetic event described in the progression from adenoma to colorectal carcinoma. Most of the p53 mutations occur in exons 5 to 8 in highly preserved regions and in the three main structural domains of the p53 protein. It is possible that mutations affecting different structural regions may present different effects on the p53 protein function and, due to this, they may have different prognostic meaning. The study population consisted of 353 patients diagnosed with sporadic colorectal cancer. Mutations in 5-8 exons of p53 gene were detected by means of single strand conformation polymorphism (SSCP). All samples that showed different migration bands in SSCP were confirmed by sequencing. A total of 69 patients (19.7%) showed alterations of the gene p53. It was observed that mutation in codon 175 in exon 5 was related to tumors located in the colon (p = 0.01) and the mutation in the codon 288 in exon 8 was related to rectal tumors (p = 0.02). In the study of overall survival, mutation in codon 175 of exon 5 conferred a better prognosis and alterations of exon 8 were related to a worse prognosis in different population subgroups: in men, in patients younger than 71 years old, in the tumors located in the proximal colon, the ones moderately differentiated, and those that are mucinous. According to this study, mutations in different exons of p53 are related to different phenotypes in colorectal cancer. These phenotypes could mean differences in the clinical evolution of the patients.

P53 Testing for Li‐Fraumeni and Li‐Fraumeni‐Like Syndromes

Li-Fraumeni Syndrome (LFS; OMIM #151623) is an autosomal dominant cancer predisposition syndrome characterized by early onset tumors including sarcomas, breast cancer, leukemia, brain tumors, and adrenocortical carcinoma. Li-Fraumeni syndrome is primarily attributed to germline mutations in the p53 tumor suppressor gene, which encodes tumor protein 53. In addition to germline p53 mutations, the p53 gene is the most commonly mutated gene in human cancers, with as much as 50% of tumors containing somatic p53 mutations. This unit provides a protocol to perform germline mutation analysis of the p53 gene. The protocol includes steps for amplification and sequencing of the entire coding region of the p53 gene (exons 2 to 11). The protocol was designed for detecting germline alterations from DNA extracted from blood; however, with some additional optimization, it could also be used to detect somatic mutations in DNA extracted from tumors.

Molecular Genetic Analysis of p53 Intratumoral Heterogeneity in Human Astrocytic Brain Tumors

We investigated genetic heterogeneity of astrocytic gliomas using p53 gene mutations as a marker. Different parts of morphologically heterogeneous astrocytic gliomas were microdissected, and direct DNA sequencing of p53 gene exons 5 through 8 was performed. Thirty-five glioma samples and tumor-adjacent normal-appearing brain tissue from 11 patients were analyzed. Sixteen different p53 gene mutations were found in 7 patients. We found that some tumors were devoid of p53 gene mutations, whereas other tumors carried 1 or often several (up to 3) different mutations. The mutations were present in grade II, III, and IV astrocytic glioma areas. Both severe functionally dead mutants and mutants with remaining transcriptional activity could be observed in the same tumor. We observed that morphologically different parts of a glioma could carry different or similar mutations in the p53 gene and could be either associated or not associated with the locus of heterozygosity at the mutant site. Coexistence of p53 gene mutations and the locus of heterozygosity was common, at least in astrocytomas grade III and in glioblastomas, and also occurred in astrocytoma grade II areas. These results support the notion that intratumoral heterogeneity in brain tumors originates from different molecular defects. Our results are of importance for a further understanding of the molecular mechanisms behind failure to treat glioma patients.

The pattern of p53 gene mutations on oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is the result of accumulation genetic lesion and caused by specific mutation in specific key regulation genes. p53 gene is key target specific regulatory genes which function as negative regulators in cell cycle control. The highest mutation rates found in human cancers and the etiology in high risk populations and the pattern of molecular pathogenesis mechanism involved in the OSCC remain unclear. The purpose of this study was to determine the presence of alteration or mutation of p53 gene and to associate these mutations histopathological status of the patients such as well differentiated and poorly differentiated in OSCC in order to elucidate the molecular pathogenesis mechanism of OSCC based on the pattern of p53 gene. Using 40 untreated well and poorly differentiated OSCC biopsy samples and 16 normal patients were analyzed for the presence of mutation in the conserved region of the p53 gene exons 5 and or 7 by PCR-SSCP mutational analysis for p53 gene showed 70% of total samples : exon 5: 27.5% with heterozygous mutation 81.8%, exon 7: 55% with heterozygous mutation 100%. The incidence of p53 mutation was not significantly associated with well and poorly differentiated OSCC with the exception in exon 5 of p53 gene (p = 0.013) using contingency coefficient. This study concludes that mutation of p53 gene especially in exon 7 may not indirectly play in the progressivity of OSCC with the exception of mutation in exon 5 of p53 which indicates the essential role in the progressivity of OSCC.

P53 protein expression and genetic mutation in two primary cell types in pulmonary sclerosing haemangioma

Aims:To investigate the significance of p53 protein expression and genetic mutations in two primary cell types in pulmonary sclerosing haemangioma (PSH).Methods:p53 protein expression in polygonal cells and cuboidal cells in...

Missense mutation with/without nonsense mutation of the p53 gene is associated with large cell morphology in human malignant lymphoma

Mutations in p53 gene exons 5-9 were studied in 44 non-Hodgkin's lymphomas (NHL) consisting of 35 B-NHL and 9 T-NHL. Missense mutations were found in two diffuse large B-cell lymphomas (DLBL) and one peripheral T-cell lymphoma (unspecified). Double transversion missense and nonsense mutations were detected in one DLBL and one adult T-cell leukemia/lymphoma. Silent mutations were found in two DLBL. Detailed histomorphological study showed that cases harboring p53 missense mutation with/without nonsense mutation tended to have larger nuclei with much more prominent nucleoli. Cytomorphometric analysis was therefore conducted by measuring the gross area of 100 lymphoma cell nuclei in 44 cases and the results were compared between lymphomas harboring p53 missense mutation with/without nonsense mutation and lymphomas harboring p53 silent mutation or lacking mutation. It was found that the lymphomas harboring p53 missense mutation with/without nonsense mutation had a highly significantly larger nuclear gross area than lymphomas with silent p53 mutation or lacking mutation (two-sample t-test, P < 0.00001; Exact Wilcoxon rank-sum test, P < 0.00001). This result suggests that p53 mutation might induce enlargement of neoplastic cell nuclei by some molecular mechanism.

Analysis of p16 Gene Mutation, Deletion and Methylation in Patients with Arseniasis Produced by Indoor Unventilated-Stove Coal Usage in Guizhou, China

The aim of this study was to determine p16 gene mutation, deletion, and promoter 5′ CpG island hypermethylation in peripheral blood mononuclear leukocyte of patients with arseniasis as attributed to exposure to indoor unventilated coal stove. The role of the aberrant change of p16 gene in the induction and development of carcinogenesis in endemic arsenisiasis region in China was also examined. Polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP), multiplex PCR (mPCR), methylation-specific PCR (MSP), and sequencing techniques were performed to detect (1) mutation of the p16 gene exon 2, (2) homozygous deletion of the p16 gene exon 1 and exon 2, and (3) hypermethylation of the promoter CpG island in peripheral blood mononuclear leukocyte of patients with arseniasis. Results showed no mutation was found in exon 2 of p16 gene. The homozygous deletion frequency of p16 gene was 5 and 15% in control and arseniasis patients, respectively. The homozygous deletion occurred mainly in exon 2, with significant deletion frequencies of 9, 13, and 20% in mild, intermediate, and severe arseniasis groups. The significant homozygous deletion frequency was 9 and 39% in noncarcinoma and carcinoma individuals. The positive rate of p16 gene promoter CpG island hyermethylation was 42 and 2% in the exposed group and the control group, respectively. The positive rate was 26, 42, and 50% in mild, intermediate, and severe arseniasis. The marked different positive rate was 22 and 56% in noncarcinoma and carcinoma individuals, respectively. In conclusion, homozygous deletion and hypermethylation of p16 gene may play an important role in the initiation and development of manifestations seen in endemic arseniasis including carcinogenesis.

Clinical Significance of the Detection of the Homozygous Deletion of P16 Gene in Malignant Pleural Effusion

To assess the role of the p16 gene exon 2 homozygous deletion in malignant pleural effusions. The homozygous deletion of p16 gene was determined in 34 pleural effusions due to non-small cell lung cancer (NSCLC) and in 21 cases with tuberculous pleuritis by polymerase chain reaction (PCR), compared with the determination of exfoliated cytology in the same specimens. The PCR analysis showed that the homozygous deletion of p16 exon 2 was identified in 15 of 34 malignant pleural effusions (44.11%), including 8 negative cytology and it was not found any tuberculous pleural effusions. The exfoliated cytology of pleural effusion was positive in 19 of 34 malignant cases (55.88%). By combining two methods, the diagnostic sensitivity was enhanced, from 55.88% (19/34) to 79.41% (27/34), whose positive rate was higher than only determination of p16 exon2 homozygous deletion or exfoliated cytology in malignant pleural effusions (p<0.001, p<0.05 respectively). Our data suggested that combining the examination of exfoliated cytology and homozygous deletion of p16 gene exon2 in pleural effusion can recruit and enhance the diagnostic value of pleural effusion cytology. The detection of the homozygous deletion of the p16 gene in pleural effusion may be a useful adjunct to the cytological and histological examinations of pleural effusion. In cases of undiagnosed exudative pleural effusion with a high clinical suspicion for malignancy, it is reasonable to examine the homozygous deletion of pleural fluid p16 gene. With p16 gene homozygous deletion in pleural effusion, it may be strongly highly likely to be malignant and have a higher metastatic potential.

An optimized microchip electrophoresis system for mutation detection by tandem SSCP and heteroduplex analysis for p53 gene exons 5–9

With the complete sequencing of the human genome, there is a growing need for rapid, highly sensitive genetic mutation detection methods suitable for clinical implementation. DNA-based diagnostics such as single-strand conformational polymorphism (SSCP) and heteroduplex analysis (HA) are commonly used in research laboratories to screen for mutations, but the slab gel electrophoresis (SGE) format is ill-suited for routine clinical use. The translation of these assays from SGE to microfluidic chips offers significant speed, cost, and sensitivity advantages; however, numerous parameters must be optimized to provide highly sensitive mutation detection. Here we present a methodical study of system parameters including polymer matrix, wall coating, analysis temperature, and electric field strengths on the effectiveness of mutation detection by tandem SSCP/HA for DNA samples from exons 5-9 of the p53 gene. The effects of polymer matrix concentration and average molar mass were studied for linear polyacrylamide (LPA) solutions. We determined that a matrix of 8% w/v 600 kDa LPA provides the most reliable SSCP/HA mutation detection on chips. The inclusion of a small amount of the dynamic wall-coating polymer poly-N-hydroxyethylacrylamide in the matrix substantially improves the resolution of SSCP conformers and extends the coating lifetime. We investigated electrophoresis temperatures between 17 and 35 degrees C and found that the lowest temperature accessible on our chip electrophoresis system gives the best condition for high sensitivity of the tandem SSCP/HA method, especially for the SSCP conformers. Finally, the use of electrical fields between 350 and 450 V/cm provided rapid separations (<10 min) with well-resolved DNA peaks for both SSCP and HA.

Evaluation of thep53 tumor suppressor gene mutation in normal rat salivary gland tissue after radioiodine application: An experimental study

In this experimental study, investigators explored p53 tumor suppressor gene mutation induced by low and high doses of iodine-131 sodium iodide (I-131) in salivary gland tissue in rats. Group 1 consisted of 10 rats; low and high I-131 doses were applied at a 1-wk interval. First,low doses of I-131 were injected. (The net injected dose was 47.5-/+9.2 microCi.) After 1 wk, high doses of I-131 were also injected. (The net injected dose was 1007.2-/+53 microCi.) Group 2 consisted of 5 rats, and only a low I-131 dose was applied. (The net injected dose was 52.7-/+5.5 microCi.) The Control Group consisted of 5 rats that did not receive I-131. Thyroidal I-131 uptakes were calculated for Groups 1 and 2 with the use of a gamma camera after 24 h of injections. Immediately after uptake was calculated, salivary glands were resected in all groups and DNA was extracted for genotyping. Genomic DNA of the p53 gene exon 5 was examined by polymerase chain reaction single-strand conformational polymorphism. In Group 1, thyroidal I-131 uptakes were calculated as 12.45%-/+4.14% and 9.66%-/+6.73% after low-dose and high-dose I-131 applications, respectively. In Group 2, thyroidal I-131 uptake was calculated as 13.12%-/+3.04%. In Group 1, p53 gene abnormality was seen in the salivary gland of only 1 of the rats. Double- and single-strand gene profiles showed that both alleles of this rat have a mutated single-strand conformational polymorphism profile of point mutation in the p53 gene exon 5. This rat received the highest low dose and the second highest total dose of I-131; its thyroidal uptakes were the second highest. In the other rats in Group 1, and in Group 2 and the Control Group, p53 gene abnormalities were not observed. In Groups 1 and 2, a significant relationship could not be discerned between thyroidal uptake of I-131 and p53 gene mutation in the salivary gland. No significant relationship was observed between thyroidal uptake alterations and p53 gene mutations in salivary glands in Group 1. A point mutation in the p53 gene exon 5 that was seen in only 1 of the rats in Group 1 seems related to the high-dose application of I-131, although coincidental occurrences could not be excluded. We believe that this topic is open to additional in vivo studies.

Sequence-specific p53 gene damage by chloroacetaldehyde and its repair kinetics in Escherichia coli.

Oxidative stress and certain environmental carcinogens, e.g. vinyl chloride and its metabolite chloroacetaldehyde (CAA), introduce promutagenic exocyclic adducts into DNA, among them 1,N(6)-ethenoadenine (epsilonA), 3,N(4)-ethenocytosine (epsilonC) and N(2),3-ethenoguanine (epsilonG). We studied sequence-specific interaction of the vinyl-chloride metabolite CAA with human p53 gene exons 5-8, using DNA Polymerase Fingerprint Analysis (DPFA), and identified sites of the highest sensitivity. CAA-induced DNA damage was more extensive in p53 regions which revealed secondary structure perturbations, and were localized in regions of mutation hot-spots. These perturbations inhibited DNA synthesis on undamaged template. We also studied the repair kinetics of CAA-induced DNA lesions in E. coli at nucleotide resolution level. A plasmid bearing full length cDNA of human p53 gene was modified in vitro with 360 mM CAA and transformed into E. coli DH5alpha strain, in which the adaptive response system had been induced by MMS treatment before the cells were made competent. Following transformation, plasmids were re-isolated from transformed cultures 35, 40, 50 min and 1-24 h after transformation, and further subjected to LM-PCR, using ANPG, MUG and Fpg glycosylases to identify the sites of DNA damage. In adaptive response-induced E. coli cells the majority of DNA lesions recognized by ANPG glycosylase were removed from plasmid DNA within 35 min, while MUG glycosylase excised base modifications only within 50 min, both in a sequence-dependent manner. In non-adapted cells resolution of plasmid topological forms was perturbed, suggesting inhibition of one or more bacterial topoisomerases by unrepaired epsilon-adducts. We also observed delayed consequences of DNA modification with CAA, manifesting as secondary DNA breaks, which appeared 3 h after transformation of damaged DNA into E. coli, and were repaired after 24 h.

The Carcinogenic Role of Oncogenic HPV and p53 Gene Mutation in Cervical Adenocarcinomas

Thirty tumors were collected from our archive of cervical adenocarcinomas. They were examined with respect to the content of oncogenic HPV and presence of mutations in the p53 gene exons 5 through 8. Furthermore, available clinical information on the cases was reviewed. For the detection of p53 gene and presence of oncogenic HPV, PCR followed by direct sequence analysis of the amplified DNA was employed. Seventeen tumors were identified as HPV-positive, comprising both HPV types 18 and 16. Six cases showed a p53 gene mutation, of which five were of the missence and one of the silent type. No statistical correlation between the occurrence of oncogenic HPV and presence of p53 gene mutation (p = 0.67) was recorded. Among the tumors with p53 gene mutation, three were HPV-positive and three were HPV-negative. The determination of p53 gene mutations was not related to clinical findings such as the stage of the tumor or presence of metastases of the lymph nodes. However, p53 gene mutations were somewhat more prevalent in low differentiated tumors (p < 0.02). The results indicate that oncogenic HPV and p53 gene mutations have independent carcinogenic roles in cervical adenocarcinomas.

P53 Gene mutation and expression of MDM2, P53, P16 protein and their relationship in human glioma

To investigate the effect of P53 protein accumulation and p53 gene mutation in the pathogenesis of glioma and to study the role of MDM2, P53 and P16 protein in glioma formation and progression and their relationship with each other, LSAB immunohistochemical staining method and non-isotopic PCR-SSCP techniques were used to detect the expression of MDM2, P53 and P16 protein and p53 gene mutation in 48 cases of gliomas. The results showed that the positive expression rate of MDM2, P53 and the negative rate of P16 was 22.9%, 41.7% and 60.4%, respectively. The latter two in high grade (grade III, IV) gliomas had a significantly higher rate than in the low grade (grade II) gliomas. Moreover, the co-expression of MDM2 and P53 protein was confirmed in only 1 of 48 cases. No significant difference was found in the rate of the expression of MDM2 between high grade and low grade gliomas (P > 0.1). PCR-SSCP results showed that mutation of 5-8 exons of p53 gene was detected in 17 out of 48 cases (35.42%). Mutation was detected in 16 of 20 cases of positive p53 expression, and another one was detected in 28 cases of negative expression cases. The correlation between p53 mutation and p53 immunopositivity was observed in 89.6% of the cases. P53 gene mutation and the level of MDM2, P53 and P16 protein were not related to age, gender of the patients, tumor location and size. It is concluded that the mutation of p53 and deletion of p16 might play important roles in the tumorigenesis of gliomas and it was significantly associated with the grade of tumor differentiation. P53 protein accumulation can indirectly reflect p53 mutation. MDM2 amplification and overexpression might be an early event in the growth of human gliomas.

Who takes the lead in the development of ulcerative colitis–associated colorectal cancers: mutator, suppressor, or methylator pathway?

Although several genetic alterations have been identified in patients with ulcerative colitis (UC), it remains unclear whether these changes indicate an increased risk for malignancy. This paper analyzes the involvement of suppressor, mutator, and methylator pathways in malignant transformation associated with UC. A total of 60 colonic samples (47 affected non-neoplastic mucosa, 7 dysplasia, and 6 carcinoma) from 51 UC patients were analyzed for 22 microsatellite markers. p53 gene exons 5–8 were analyzed by single-strand conformational polymorphism, and APC gene by denaturing gradient gel electrophoresis (exons 1–14) and protein truncation test (exon 15). Methylation studies for MLH1 and CSPG2 genes were also performed. Microsatellite instability was absent in all samples whereas allelic imbalance (AI) and loss of heterozygosity (LOH) were detected mainly in samples with neoplastic transformation ( P < 0.0001). AI and/or LOH at loci located on chromosomes 5, 9, and 18 were significantly more frequent in neoplastic samples ( P < 0.01), as were TP53 gene mutations ( P < 0.007). A single mutation was detected for APC gene in a cancer sample. MLH1 gene methylation was absent in all analyzed samples, whereas CSPG2 gene methylation was detected in a single non-neoplastic sample. Our results suggest that the suppressor pathway plays the main role in UC associated tumorigenic progression. LOH at specific loci located on chromosomes 5, 9, and 18 appears to be specifically associated with malignancy risk.

Effect of administration of caffeine or green tea on the mutation profile in the p53 gene in early mutant p53-positive patches of epidermal cells induced by chronic UVB-irradiation of hairless SKH-1 mice

Irradiation of SKH-1 mice with UVB light for 20 weeks resulted in a large number of patches of epidermal cells, which was visualized with an antibody that recognizes mutated p53 protein. Oral treatment of mice with caffeine (0.4 mg/ml) or green tea (6 mg tea solids/ml) as the drinking fluid during UVB irradiation decreased the number of patches by approximately 40%. Sequencing analysis of the p53 gene (exons 3 to 9) detected 88, 82 or 39 point mutations in 67, 70 or 29 patches from water, caffeine or tea treated mice, respectively. A major hotspot at codon 270 (Arg-->Cys) accounted for 47.7% (water), 70.7% (caffeine) or 46.2% (tea) of all mutations. Patches from caffeine treated mice had fewer types of mutations than patches from mice treated with water or tea. Administration of caffeine or tea during 20 weeks of UVB irradiation eliminated mutations at codons 149 (Pro-->Ser) and 210 (Arg-->Cys) but increased the frequency of mutations at codon 238 (Ser-->Phe). Topical applications of caffeine (1.2 mg in 100 microl acetone) once a day, five times a week for 6 weeks after stopping UVB decreased the number of patches by 63% when compared with mice treated with acetone. DNA sequencing analysis detected 63 and 68 mutations in 48 and 57 patches from acetone or caffeine treated mice, respectively. Although no differences in the frequency, position or types of mutations were observed, the caffeine group harbored less homozygous mutations (12.3% of the total) than the acetone group (31.3% of the total, P = 0.029). In summary, oral treatment of mice with caffeine or green tea during chronic UVB irradiation changed the mutation profile of the p53 gene in early mutant p53 positive epidermal patches, and topical applications of caffeine after discontinuation of chronic UVB irradiation specifically eliminated patches harboring homozygous p53 mutations.

P53 mutation as a determinant of prognosis in GIST patients treated with imatinib mesylate

9018 Background: Mutation of p53 has been demonstrated to be a poor prognostic factor in many types of human cancer. This study was performed to determine prognostic significance of p53 in patients with metastatic or unresecable malignant GIST who were treated with Imatinib mesylate. Methods: Clinical data of 105 GIST patients treated with Imatinib mesylate at 8 institutions in Korea between June 2001 and April 2004 were reviewed. In 68 cases, paraffin-embedded tissues were available for DNA extraction and direct sequencing to detect mutation of p53 gene (exon 4 - 8) and c-kit gene (exon 9, 11, 13, and 17). Results: Of 68 cases analyzed, p53 mutations were found in 12 cases (18%) at exon 5 (n = 3), exon 7 (n = 6), and exon 8 (n = 3). c-kit gene mutations were observed in 62 cases (91%) at exon 11 (n = 58) and exon 9 (n = 4). c-kit gene mutation rate was significantly higher in cases without p53 mutation (95%) than in cases with p53 mutation (75%) (P = 0.029). Response rates (CR + PR) and disease control rates (CR + PR + SD) were not different according to p53 mutation (68% and 86% for p53 mutation negative cases, and 58% and 83% for p53 mutation positive cases) (P > 0.5). With a median follow-up of 18 months (range, 6 to 38 months), 2-yr progression-free survival (PFS) tended to be lower in p53 mutation positive cases (58%) than in p53 mutation positive cases (65%) (P = 0.2322). 2-yr overall survival (OS) was better in p53 mutation negative cases (89%) than p53 mutation positive cases (75%) (P = 0.0156). A multivariate analysis including p53 mutation and c-kit mutation revealed that presence of p53 mutation remained a poor prognostic factor for survival (relative risk, 5.3; 95% confidence interval, 1.1 - 24.9; P = 0.037) Conclusions: These data suggest that p53 mutation could be a poor prognostic factor in GIST patients treated with Imatinib mesylate. No significant financial relationships to disclose.

The clinical significance of p16 protein non-expression and p16 gene inactivation by deletions and hypermethylation in nasopharyngeal carcinoma

To investigate the clinical significance of p16 protein non-expression and p16 gene inactivation by deletions and hypermethylation in nasopharyngeal carcinoma. Immunohistochemical study for p16 protein was carried out in 90 cases of non-keratinizing carcinoma (NKC) of nasopharynx. P16 gene deletions and hypermethylation were also analyzed by polymerase chain reaction (PCR) and methylation-specific PCR in 23 randomly selected NKC cases. Among the 90 NKC cases studied, 42 cases (46.7%) were negative for p16 protein. The non-expression rate of p16 protein also correlated with the 5-year survival rate. The non-expression rate was 60.0% in patients who died within 5 years, in contrast to 20.0% in those alive for over 5 years after diagnosis. The non-expression rate of p16 protein in cases with or without distant metastasis was 81.8% and 41.8% respectively (P < 0.05), while that in cases with or without local invasion into skull base was 41.7% and 48.5% respectively (P > 0.05). As for molecular analysis, deletion of p16 gene exon 2 was found in 10 of the 23 cases (43.4%) studied, while deletion of p16 gene exon 1 was not detected in these samples. Hypermethylation of p16 gene exon 1 was also noted in 2 of the 23 cases (8.7%). The overall mutation rate of these cases was 52.1%. There is a high incidence of p16 protein non-expression, deletion of p16 gene exon 2 and hypermethylation of p16 gene exon 1 in NKC. P16 gene inactivation may thus play an important role in the pathogenesis of NKC, especially in terms of its metastatic potential.

Patches of Mutant p53-Immunoreactive Epidermal Cells Induced by Chronic UVB Irradiation Harbor the Same p53 Mutations as Squamous Cell Carcinomas in the Skin of Hairless SKH-1 Mice

Treatment of SKH-1 hairless mice with UVB (30 mJ/cm(2)) twice a week for 20 weeks results in the formation of cellular patches, long before the appearance of tumors, that are visualized in epidermal sheets with an antibody (PAb240) recognizing mutated p53 protein. Direct sequencing analysis of the whole coding region of the p53 gene (exons 2-11) detected one or two mutations in 64.4% of 104 analyzed patches and no mutations in nonstained adjacent normal controls. Homozygous mutation was detected in 22.4% of the mutant patches. Except for two nonsense mutations, all others were missense (exons 4-9) and mostly (95.5%) at the DNA-binding domain. Primer extension analysis of cloned PCR fragments found three of four double-mutated patches harboring different mutations in separate alleles. All mutation hotspots reported earlier in UVB-induced mouse squamous cell carcinomas (SCC) at codons 270 (Arg --> Cys), 149 (Pro --> Ser), 275 (Pro --> Leu and Pro --> Ser), and 176 (His --> Tyr) with a frequency of 32.1%, 7.1%, 14.7%, and 3.2% were detected in epidermal patches at a frequency 47.7%, 9.1%, 4.5%, and 2.3%, respectively. Mutations at codons 210 and 191 found in patches at respective frequencies of 8.0% and 4.5% were not previously detected in UVB-induced mouse SCC. In summary, (a) the p53 mutation profile of UVB-induced skin patches and SCC was very similar suggesting that patches are precursor lesions for SCC, (b) a small number of patches harbored mutations that were not before observed in SCC from UVB-treated mice, and (c) about 36% of the patches did not harbor a p53 mutation.

The R72P P53 mutation is associated with familial breast cancer in Jewish women

BRCA1/BRCA2 mutations account for a substantial proportion of familial breast cancer, but clearly mutations in additional genes exist, one candidate being the p53 gene. To evaluate its putative involvement in inherited predisposition to breast/ovarian cancer in Jewish high-risk women, mutational analysis of the p53 gene (exons 4–9) was carried out using exon-specific polymerase chain reaction followed by denaturing gradient gel electrophoresis (DGGE) analysis, complemented by DNA sequencing of abnormally migrating fragments. Overall, 132 Jewish breast cancer patient non-BRCA1/2 mutation carriers and 167 average risk controls (Ashkenazi (n=60), non-Ashkenazi (n=107)) were genotyped, and no inactivating p53 germline mutations were detected. Consistent migration abnormalities were noted in 167 fragments, 134 of which were shown to be the Arg72Pro polymorphism, whereas migration abnormalities in fragments containing exons 4 (n=2) and 6 (n=23) and introns 3 (n=4) and 9 (n=4) corresponded to five previously described polymorphisms. Allele distribution of the R72P missense mutation between ethnically diverse Jewish breast cancer cases and average risk controls showed significant differences: among non-Ashkenazi breast cancer cases, 62.5%, 33.3% and 4.2% were homozygous, heterozygous and homozygous for the Arg72, Arg72Pro and the Pro72 polymorphism, respectively, whereas for controls, the distribution was 22.4%, 65.4% and 12.2%, respectively (P=0.00052), and among Ashkenazi breast cancer cases, allele distribution was 68.5%, 29.6% and 1.9%, whereas for controls, the distribution was 50%, 40% and 10%, respectively (P=0.0125). We conclude that arginine homozygosity at codon 72 of the p53 gene is associated with a significant increased breast cancer risk in Jewish high-risk population.