Cancer risks from germline p53 mutations

Association between TP53 gene Arg72Pro polymorphism and Wilms' tumor risk in a Chinese population

Wilms' tumor is one of the most prevalent pediatric malignancies, ranking fourth in childhood cancer worldwide. TP53 is a critical tumor suppressor gene, which encodes a 53 kDa protein, p53. The p53 functions to protect against cancer by regulating cell cycle and apoptosis and maintaining DNA integrity. TP53 gene is highly polymorphic. Several TP53 gene polymorphisms have been considered to be associated with cancer risk. Of them, a nonsynonymous polymorphism, Arg72Pro (rs1042522 C>G), has been most extensively studied for the association with cancer risk; however, few studies have investigated its effect on Wilms' tumor. Because of the central role of p53 in cell cycle control, the TP53 gene Arg72Pro polymorphism is also a good potential candidate predisposition locus for this pediatric cancer. We genotyped this polymorphism in 145 patients and 531 cancer-free controls recruited from Chinese children by Taqman methodology. Overall, our result suggested a lack of association between the TP53 gene Arg72Pro polymorphism and Wilms' tumor. In the stratified analysis, we found that carriers of CG/GG genotypes had a significantly increased Wilms' tumor risk in children not older than 18 months (adjusted odds ratio =2.04, 95% confidence interval =1.003-4.13, P=0.049) compared with CC genotype carriers. Our study indicated that the TP53 gene Arg72Pro polymorphism may have a weak, age-related effect on Wilms' tumor risk in Chinese children. These findings need further validations in other populations with larger sample size.

Targeting ATM-deficient CLL through interference with DNA repair pathways

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in the Western world and accounts for approximately 30% of adult leukemias and 25% of non-Hodgkin lymphomas. The median age at diagnosis is 72 years. During recent years numerous genetic aberrations have been identified that are associated with an aggressive course of the disease and resistance against genotoxic chemotherapies. The DNA damage-responsive proapoptotic ATM-CHK2-p53 signaling pathway is frequently mutationally inactivated in CLL either through large deletions on chromosome 11q (ATM) or 17p (TP53), or through protein-damaging mutations. Here, we focus on the role of ATM signaling for the immediate DNA damage response, DNA repair and leukemogenesis. We further discuss novel therapeutic concepts for the targeted treatment of ATM-defective CLLs. We specifically highlight the potential use of PARP1 and DNA-PKcs inhibitors for the treatment of ATM-mutant CLL clones. Lastly, we briefly discuss the current state of genetically engineered mouse models of the disease and emphasize the use of these preclinical tools as a common platform for the development and validation of novel therapeutic agents.

Mutations and polymorphisms in TP53 gene--an overview on the role in colorectal cancer

A functionally normal TP53 is essential to protect organisms from developing cancer. Somatic mutations in the gene represent one of the highest recurring perturbations in human tumours, including colorectal cancer (CRC). However, the variegated phenotype of wide spectrum of somatic mutations in TP53 and the complexity of the disease prevent a straight interpretation of the mutational analysis in tumours. In addition to the presence of somatic mutations, polymorphic features of the gene may also contribute to alteration of the normal TP53 functioning and variants, mainly in the form of single nucleotide polymorphisms, can be expected to impact susceptibility to sporadic CRC. In the present study, we reviewed the potential role of alterations in the TP53 gene, both somatic mutations and inherited sequence variations, in predisposition to CRC and in the prognosis and response to therapy. The available data from association studies have mostly shown contradictory outcomes. The majority of the studies were based on limited sample sizes and focussed on a limited number of polymorphisms, with main being the rs1042522 (Arg72Pro). Thus far, there is no possible generalisation of the role of TP53 as also a predictor of therapeutic response and prognosis. The effects of TP53, and its abnormalities, on the response of tumours to cytotoxic drugs, radiation and chemoradiation are complex. However, from studies it is emerging that the inherited genetics of TP53 pathway components could be utilised to further define patient populations in their abilities to induce p53 activity in response to either DNA damaging or p53-targeted therapies.

Exploiting synthetic lethal interactions between DNA damage signaling, checkpoint control, and p53 for targeted cancer therapy

DNA damage signaling and checkpoint control pathways are among the most commonly mutated networks in human tumors. Emerging data suggest that synthetic lethal interactions between mutated oncogenes or tumor suppressor genes with molecules involved in the DNA damage response and DNA repair pathways can be therapeutically exploited to preferentially kill cancer cells. In this review, we discuss the concept of synthetic lethality with a focus on p53, a commonly lost tumor suppressor gene, in the context of DNA damage signaling. We describe several recent examples in which this concept was successfully applied to target tumor cells in culture or in mouse models, as well as in human cancer patients.

Modeling human osteosarcoma in the mouse: From bedside to bench

Osteosarcoma (OS) is the most common primary tumour of bone, occurring predominantly in the second decade of life. High-dose cytotoxic chemotherapy and surgical resection have improved prognosis, with long-term survival for patients with localized (non-metastatic) disease approaching 70%. At presentation approximately 20% of patients have metastases and almost all patients with recurrent OS have metastatic disease and cure rates for patients with metastatic or recurrent disease remain poor (<20% survival). Over the past 20 years, considerable progress has been made in the understanding of OS pathogenesis, yet these insights have not translated into substantial therapeutic advances and clinical outcomes. Further progress is essential in order to develop molecularly based therapies that target both primary lesions as well as metastatic disease. The increasing sophistication with which gene expression can be modulated in the mouse, both positively and negatively in addition to temporally, has allowed for the recent generation of more faithful OS models than have previously been available. These murine OS models can recapitulate all aspects of the disease process, from initiation and establishment to invasion and dissemination to distant sites. The development and utilisation of murine models that faithfully recapitulate human osteosarcoma, complementing existing approaches using human and canine disease, holds significant promise in furthering our understanding of the genetic basis of the disease and, more critically, in advancing pre-clinical studies aimed at the rational development and trialing of new therapeutic approaches.

TP53 Arg72Pro polymorphism and colorectal cancer risk: a systematic review and meta-analysis

BACKGROUND

The TP53 rs1042522 polymorphism (c.215C>G, Arg72Pro) has been extensively investigated as a potential risk factor for colorectal cancer, but the results have thus far been inconclusive.

METHODS

We searched multiple electronic databases to identify studies investigating the association between the Arg72Pro polymorphism and colorectal cancer. Individual study odds ratios (OR) and their confidence intervals were estimated using allele-frequency, recessive, and dominant genetic models. Summary ORs where estimated using random effects models.

RESULTS

We identified 23 eligible case-control studies, investigating 6,514 cases and 9,334 controls. There was significant between-study heterogeneity for all genetic models. The control group in one of the studies was not in Hardy-Weinberg equilibrium; only three studies reported that genotyping was blinded to case/control status and five studies used tumor tissue for case genotyping. Overall, we did not identify any association between rs1042522 and colorectal cancer risk under an allele-frequency comparison (OR, 0.99; 95% confidence interval, 0.89-1.09). Likewise, no association was evident under dominant or recessive models. Studies using tumor tissue for case genotyping found a protective effect for the Pro allele, compared with studies using somatic DNA (P(interaction) = 0.03). Results were also inconsistent between different genotyping methods (P(interaction) = 0.03).

CONCLUSION

We did not identify an association between TP53 rs1042522 and colorectal cancer. Published results seem to be driven by technical artifacts rather than true biological effects.

IMPACT

Future genetic association studies should use more rigorous genotyping methods and avoid the use of tumor tissue as a source of DNA to prevent genotype misclassification due to loss of heterozygosity.

Exploiting synthetic lethal interactions for targeted cancer therapy

Emerging data suggests that synthetic lethal interactions between mutated oncogenes/tumor suppressor genes and molecules involved in DNA damage signaling and repair can be therapeutically exploited to preferentially kill tumor cells. In this review, we discuss the concept of synthetic lethality, and describe several recent examples in which this concept was successfully implemented to target tumor cells in culture, in mouse models, and in human cancer patients.

DNA repair gene polymorphisms affect cytotoxicity in the National Cancer Institute Human Tumour Cell Line Screening Panel

Polymorphisms in DNA repair genes have been suggested to increase the risk of cancer and other diseases, but the epidemiological studies are often not consistent, and the results confusing. We have examined the effect of polymorphisms in base and nucleotide excision-repair genes, as well as regulatory and signalling genes, on cytotoxic sensitivity of tumour cell lines used for screening anticancer drugs by the National Cancer Institute. It was found that for the TP53 P72R and ERCC2 D312N polymorphisms, the heterozygous genotype was most sensitive, while for the OGG1 S326C and NOS3 g.-786T>C polymorphisms the homozygous-variant genotype was most sensitive. The biggest increase in sensitization was found with the XRCC1 R399Q homozygous dominant genotype. The sensitization was found across a broad range of drugs, indicating the importance of DNA repair responses. It was also found that while the other gene polymorphisms were in Hardy-Weinberg equilibrium, the TP53 P72R heterozygous genotype was relatively depleted. For the OGG1 polymorphism, the repair of 8-oxo-guainine from DNA was measured in three panel cell lines that differed in their OGG1 genotype. The cell line with the homozygous-variant genotype had a much poorer repair than the other genotypes, as predicted. The correlation of polymorphisms with cytotoxicity may be an approach to understanding their effects which may be difficult to reveal in epidemiological studies.

Comparative study in the expression of p53, EGFR, TGF-alpha, and cyclin D1 in verrucous carcinoma, verrucous hyperplasia, and squamous cell carcinoma of head and neck region

Verrucous carcinoma (VC) is a locally invasive, nonmetastasizing variant of squamous cell carcinoma (SCC) with distinct clinical and histologic features. Molecular alterations detectable by immunohistochemical analyses in VC have not been extensively studied. This study investigates the expression of p53, epidermal growth factor receptor (EGFR), transforming growth factor-alpha (TGF-alpha), and cyclin D1 in VC, verrucous hyperplasia (VH), and classic SCC of the head and neck. Twenty-six cases of VC, 12 cases of SCC of various differentiations, and 4 cases of VH were studied. Formalin-fixed, paraffin-embedded archival material was used for immunohistochemistry (avidin-biotin immunoperoxidase technique) to study the expression of oncogenes and their tumor markers. Identification of p53 protein was found in 100% of VH, 88% of VC, and 100% of SCC. EGFR expression was noted in 25% of VH, 54% of VC, 40% of well-differentiated SCC (WDSCC), and 100% of moderately and poorly differentiated SCC (MDSCC/PDSCC). TGF-alpha was detected in 25% of VH, 88% of VC, 80% WDSCC, and 100% of MDSCC/PDSCC. Cyclin-D1 expression was seen in 75% of VH, 35% of VC, 100% of WDSCC, 67% of MDSCC, and 50% of PDSCC. Correlation between the level of expression of all markers and the grade of this group of squamous lesions revealed statistically significant correlation coefficients for p53 and EGFR but not for TGF-alpha and cyclin D1.

Segregation analysis of cancer in families of glioma patients

A small proportion of brain tumors are attributed to a genetic predisposition; however, the hereditary proportion is undetermined. This study evaluates the degree of familial aggregation of cancer in a large series of brain tumor patients. Our study included 5,088 relatives of 639 probands (3,810 first- and 1,278 second-degree), diagnosed with a glioma between June 1992 and June 1995 at The University of Texas M. D. Anderson Cancer Center, Houston, Texas, with diagnosis under age 65 years, and residents of the United States or Canada. We conducted an in-person or telephone interview with patients and/or their next-of-kin, and obtained family histories for the probands' first-degree (parents, siblings, offspring) and selected second-degree relatives (aunts, uncles, grandparents) using a sequential sampling strategy. Reported cancers were documented by medical records and/or death certificates (if the relative was deceased and medical records were unavailable). We conducted segregation analysis using the Pedigree Analysis Program (PAP). The analyses were divided into two categories: (1) all 639 families, and (2) a subset of families whose gliomas stained positive on p53 immunohistochemistry analysis. We demonstrated that a multifactorial Mendelian model was favored, while a model postulating a purely environmental cause of brain cancer was rejected. This study indicates that familial cancer in relatives of glioma patients are probably a result of multigenic action, and familial clustering of cancer among relatives of glioma patients may involve unknown environmental exposures.

Release from apoptosis correlates with tumor progression in the AKR lymphoma

Disturbance of apoptosis is an established factor in tumorigenesis. The role of apoptosis in tumor progression is not yet clear. In the present study we compared the tendency to spontaneous apoptosis (and the proliferative capacity) of tumor cells derived from primary (PT) and metastatic tumor (MT) cells of several AKR lymphoma variants. Apoptosis-related gene expression was also compared. Our results indicate that release from apoptosis has a role in the tumor progression of this T cell lymphoma. At the cellular level, a markedly lower apoptotic tendency was observed in MT than in PT cells. The existence of macrophages only in PT also supports the presence of apoptotic cells in local but not in MTs. By contrast, proliferative capacity does not determine tumor aggressiveness in this system. At the molecular level, we found a higher staining intensity for bcl-2 in MT than in PT cells, suggesting that bcl-2 might be responsible for the reduced apoptosis in MT compared to PT cells. Evidence for p53 overexpression was found in the MT cells of one of the variants but in none of the PT. Comparison of Fas receptor, unexpectedly showed an increased expression in MT versus PT cells, possibly indicating resistance to Fas-induced apoptosis in the MT cells.

Poor clinical significance of p53 gene polymorphism in acute myeloid leukemia

The cancer susceptibility according to the p53 polymorphism at codon 72 has been in controversy. In this study, the clinical significance of p53 polymorphism in de novo acute myeloid leukemia (AML) was examined. Although the allelic frequency of Arg in 200 patients with AML (64.3%) tended to be greater than that in normal controls (56. 6%), these frequencies were within the normal range according to the previous data in Japan (from 59.9 to 65.3%). p53 mutations, found in nine (4.5%) of the 200 patients, were not related to the polymorphism. Six of 93 patients showing heterozygosity at codon 72 had allelic imbalance according to the polymerase chain reaction assay, which occurred in either allele and was associated with p53 mutation and poor prognosis (P=0.01). However, the p53 polymorphism was not associated with clinical features, complete remission rates or prognosis of AML. These results indicate that the p53 genotype at codon 72 is useful to detect loss of heterozygosity but not associated with risk, pathophysiology or therapeutic response of AML.

The p53 tumor suppressor protein reduces point mutation frequency of a shuttle vector modified by the chemical mutagens (+/-)7, 8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, aflatoxin B1 and meta-chloroperoxybenzoic acid

p53 has been postulated to be the guardian of the genome. However, results supporting the prediction that point mutation frequencies are elevated in p53-deficient cells either have not been forthcoming or have been equivocal. To analyse the effect of p53 on point mutation frequency, we used the supF gene of the pYZ289 shuttle vector as a mutagenic target. pYZ289 was treated in vitro by ultraviolet irradiation, aflatoxin B1, (+/-)7,8-dihydroxy-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and meta-chloroperoxybenzoic acid and then transfected into p53-deficient cells with or without a p53 expression vector. p53 reduced the mutant frequency up to fivefold when pYZ289 was treated with aflatoxin B1, (+/-)7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene or meta-chloroperoxybenzoic acid but not when it was ultraviolet-irradiated. The p53-dependent mutation frequency reduction was higher at a higher level of premutational lesions for aflatoxin B1 and (+/-)7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and at a lower level of lesions for meta-chloroperoxybenzoic acid. This suggests that the chemical mutagens produce, in a dose-dependent fashion, two kinds of DNA damage, one subject to p53-dependent mutation frequency reduction and the other not. These results indicate that p53 can reduce the point mutation frequency in a shuttle vector treated by chemical mutagens and suggest that p53 can act as guardian of the genome for at least some kinds of point mutations.

A novel TP53 germ-line mutation identified in a girl with a primitive neuroectodermal tumor and her father

A search of TP53 mutations was undertaken in a series of 51 pediatric brain tumors. The only germ-line mutation was detected in a 9-year-old girl with a PNET. Her family history was unremarkable for neoplastic disease, except for the paternal grandfather, who died of a gallbladder carcinoma at an advanced age. The mutation was a thymine deletion at the first base of codon 241, leading to termination codon at position 246 that has not previously been reported. This mutation was found to be inherited from the proband's father, who was healthy at age 40. In the tumoral sample, loss of heterozygosity in several 17p markers was found, the only TP53 allele preserved in the tumor was the mutated one. The presence of two short tandem repeats and two different palindromic sequences spanning the deletion lead us to propose the predisposition of this region to forming a complex secondary structure during replication. Consequently, it could have facilitated the present deletion. Furthermore, six other short deletions affecting--partially or totally--the region implicated in the folding model that we propose have been described in the literature. These findings confirm that this sequence represents a hotspot of deletion in the TP53 gene.

Li-Fraumeni syndrome and the role of the p53 tumor suppressor gene in cancer susceptibility

Mutation of the tumor suppressor gene p53 is a molecular genetic event frequently observed in human cancer, and inactivating missense mutations usually are accompanied by the resultant overexpression of mutant p53 protein. In gynecologic cancers, p53 is also often altered; the frequency varies depending on types of cancers and where they develop. Further, human papillomavirus oncoproteins that inactivate p53 and Rb proteins play important roles in the development of several gynecologic cancers. Individuals who are heterozygous for germline mutations of the p53 gene are strongly predisposed to a variety of cancers. The identification of these individuals may have profound value in the future when therapies or chemopreventive agents specific for the p53 alteration are available. The role of p53 tumor suppressor gene in gynecologic cancers and heritable cancer susceptibility syndromes including Li-Fraumeni and Lynch II syndromes is an active and important area of study.

Genetics of pediatric central nervous system tumors

PURPOSE

Pediatric central nervous system (CNS) tumors comprise a wide variety of histologic subtypes ranging from the benign juvenile pilocytic astrocytoma to the highly aggressive atypical teratoid/rhabdoid tumor. Although some brain tumors are seen in association with inherited genetic disorders which predispose to malignancies, most are sporadic. Current knowledge regarding the cytogenetic and molecular genetic events which have been implicated in the development or progression of common brain tumors in children in the subject of this review.

METHODS

Combined cytogenetic and molecular genetic approaches, including fluorescence in situ hybridization, have been used to identify genomic alterations in different histologic types of pediatric brain tumors.

RESULTS

The most frequent abnormality in primitive neuroectodermal tumor/medulloblastoma is an i(17q), present in approximately 50% of cases. This finding implicates the presence of a tumor suppressor gene on 17p, which is important in tumor development. A number of genes on 17p have been eliminated as candidates for this locus, including TP53. A tumor suppressor gene in chromosome band 22q11.2 has been hypothesized to play a role in atypical teratoid/rhabdoid tumors, and positional cloning strategies are in progress to identify a rhabdoid tumor gene. Chromosome 22 deletions are also seen in meningiomas and a small percentage of ependymomas, but it is not yet known whether the same gene is responsible for more than one malignancy. With regard to childhood astrocytomas, tumor-associated genetic changes have not yet been identified for the common juvenile pilocytic or low grade diffuse astrocytoma. In contrast, malignant anaplastic astrocytomas and glioblastoma multiforme have abnormalities similar to those seen in adults, including loss of alleles on 17p13 and TP53 mutations, trisomy 7, EGFR rearrangements, and loss of chromosomes 10 and 22.

CONCLUSIONS

The presence of tumor-associated genetic abnormalities has clinical utility in a differential diagnostic setting, and has lead to the identification of genes which contribute to tumorigenesis.

The oncology nurse's role in cancer risk assessment and counseling

OBJECTIVE

To provide a comprehensive overview of the role of the oncology nurse in cancer risk assessment and counseling.

DATA SOURCES

Review articles, research studies, and book chapters.

CONCLUSION

New genetic discoveries are changing how risk for some cancers is being determined and managed. Cancer risk counseling and genetic testing are emerging components of clinical care.

IMPLICATIONS FOR NURSING PRACTICE

Oncology nurses will have an increasingly important role in casefinding, risk assessment, education, counseling, psychosocial support, health advocacy, and the coordination of services and referrals for cancer risk management. In addition, nurses can conduct research on the effects of these new genetic applications on individuals and families, and educate others about the implications of this evolving field.

Clinical applications of tumor suppressor genes and oncogenes in cancer

In the search for new ways to better diagnose and monitor cancer, scientists have turned to oncogenes and tumor suppressor genes. These genes are involved in cell differentiation, communication and proliferation and their alteration is frequently associated with cancer. Such alterations include mutations, translocations, amplifications and deletions. In this review, I give examples of using the detection of such alterations for patient diagnosis and monitoring. The practical examples are restricted to a few cancer types, but the identification of new tumor suppressor genes, like BRCA-1 and BRCA-2, is creating new possibilities for determining cancer risk of individual family members. There is no doubt that the cloning of new genes which predispose to sporadic cancer will lead to the introduction of widespread testing to assess risk and to the application of preventive measures.

Molecular pathogenesis of astrocytoma and glioblastoma multiforme

Our understanding of the complexity of genetic abnormalities involved in the tumourigenesis of malignant gliomas is as yet rudimentary. However, we can discern distinctive patterns of loss of genetic material and amplification of chromosomal regions that characterize both the different types of gliomas as well as the different malignancy grades. In this review, we discuss through specific examples of recent work on astrocytomas and glioblastoma multiforme, the importance of several tumour suppressor genes and oncogenes in the development of these glial tumours. In conclusion it would seem that distinct genetic changes in different genes, the protein products of which interact in particular growth control mechanism may lead to the same cellular abnormality. It seems likely that many further genetic abnormalities affecting genes coding for proteins, either involved in the cellular mechanisms yet identified or in new growth control mechanisms. Will be found in the near future.

Prognostic significance of p53 nuclear and cytoplasmic overexpression in right and left colorectal adenocarcinomas

The prognostic significance of nuclear and cytoplasmic p53 protein, detected immunocytochemically using CM1 and PAb 1801 antibodies, was evaluated in right-sided and left-sided colorectal adenocarcinomas from 293 patients. CM1 nuclear and cytoplasmic p53 accumulation occurred in 38 and 25% of cases, respectively. PAb 1801 nuclear staining occurred in 18%, with no cytoplasmic staining. CM1 expression either in the nucleus or in the cytoplasm was positively related to PAb 1801 expression (P < 0.001 and P = 0.009, respectively). The incidence of CM1 nuclear and cytoplasmic expression was more frequent in right-sided tumours (P = 0.023 and P = 0.034, respectively), while PAb 1801 nuclear staining was more common in left-sided tumours (P = 0.011). In survival analyses, CM1 nuclear overexpression in the right-sided tumours (P = 0.016) and CM1 cytoplasmic overexpression in left-sided tumours (P = 0.04) were prognostic indicators, independent of Dukes' stage, DNA ploidy, PAb 1801 expression and each other. Further analysis showed that the prognostic value of CM1 nuclear expression was greater in right-sided tumours than in left-sided tumours (P = 0.018). The nuclear and cytoplasmic p53 protein detected with CM1 and PAb 1801 may play different roles in tumour progression and provide prognostic indicators for right- and left-sided colorectal tumours.

Dominant-negative p53 mutations selected in yeast hit cancer hot spots

Clinically important mutant p53 proteins may be tumorigenic through a dominant-negative mechanism or due to a gain-of-function. Examples for both hypotheses have been described; however, it remains unclear to what extent they apply to TP53 mutations in general. Here it is shown that the mutational spectrum of dominant-negative p53 mutants selected in a novel yeast assay correlates tightly with p53 mutations in cancer. Two classes of dominant-negative mutations are described; the more dominant one affects codons that are essential for the stabilization of the DNA-binding surface of the p53 core domain and for the direct interaction of p53 with its DNA binding sites. These results predict that the vast majority of TP53 mutations leading to cancer do so in a dominant-negative fashion.

Rothmund-Thomson syndrome in siblings: evidence for acquired in vivo mosaicism

Rothmund-Thomson syndrome (RTS) is an autosomal recessive disorder characterized by skin abnormalities that appear in infancy, skeletal abnormalities, juvenile cataracts and other manifestations of premature aging, and a predisposition to malignancy. The diagnosis is made on clinical grounds as no consistent laboratory test has been identified. Chromosome studies have been reported for only three patients with RTS and in two of these three, trisomy 8 mosaicism was found. We performed a variety of cytogenetic and molecular genetic studies on two siblings with RTS and on their phenotypically normal parents. Two chromosomally abnormal clones involving either trisomy 8 or i(8q) were found in both patients with RTS. These clones were present in vivo, as they were seen in interphase buccal smears and lymphocytes from unstimulated preparations using both conventional cytogenetic studies and fluorescence in situ hybridization (FISH) with a centromere probe for chromosome 8. These results suggest that RTS is associated with in vivo clonal chromosomal rearrangements causing an acquired somatic mosaicism.

A novel polymorphism in intron 6 of the human p53 gene: a possible association with cancer predisposition and susceptibility

We present a novel polymorphic 8-bp sequence in intron 6 of the p53 gene that maps between bp 55 and 62 of the 3' end of exon 6. Of normal blood samples, 32% were heterozygotic for this polymorphism and display a NN' genotype, whereas 68% of the population is homozygotic for the N genotype. The rare homozygotic genotype N' was detected only in four blood samples of cancer patients. Peripheral blood of gastrointestinal (GI) and breast tumor patients demonstrated a higher incidence of heterozygosity (50%) than that of normal individuals. Analysis of the distribution of this polymorphism in tumor samples showed loss of heterozygosity (LOH). This LOH during tumor progression could exhibit preference to each one of the polymorphic alleles. The rare presentation of one allele and the increased incidence of heterozygosity in carcinoma patients may suggest an association between this polymorphism with cancer predisposition and susceptibility. The fact that genetic alterations occurring in noncoding regions may play a role in tumor development only further increases the extent of involvement of p53 in carcinogenesis.

Alteration of the tumor suppressor gene p53 in a high fraction of hormone refractory prostate cancer

PURPOSE

We studied the role of p53 tumor suppressor gene alteration in prostate cancer progression by demonstrating a difference in abnormal p53 findings between early and hormone refractory disease.

MATERIALS AND METHODS

The study included p53 immunohistochemistry of 26 archival transurethral resection specimens from patients with radiation recurrent and hormone refractory disease, 27 untreated primary tumors and 8 untreated metastatic lesions. p53 mutation analysis of tumor deoxyribonucleic acid (DNA) from microdissected specimens was done by cold single strand conformational polymorphism and DNA sequencing.

RESULTS

Elevated p53 protein was present in 16 of 17 hormone refractory specimens (94%), 4 of 8 untreated metastatic tumors (50%) and 6 of 27 primary untreated tumors (22%). DNA analysis of representative specimens with elevated p53 confirmed p53 gene alterations in 9 of 11 cases (82%).

CONCLUSIONS

Our study revealed a clear progression of increased p53 alteration from untreated primary to hormone refractory disease (p < 0.00005).

p53 mutations in matched primary and metastatic human tumors

Mutations in the p53 tumor suppressor gene have been found to be the most frequent genetic alterations in human malignancies. To further examine the idea that neoplastic progression is associated with mutations in the p53 gene, we analyzed matched primary and metastatic tumor samples. The samples included 15 pairs of breast cancer and metastases to lymph nodes, four pairs of gastrointestinal adenocarcinomas and metastases to liver, one colon adenocarcinoma and metastasis to a lymph node, and one lung carcinoma and metastasis in the pleura. Genomic DNA or cDNA from each tumor sample was amplified by the polymerase chain reaction and labeled by using one biotinylated primer. The DNA strands were separated with magnetic streptavidin beads and sequenced directly. p53 mutations were detected in 11 of 21 patients (52%) in either primary tumors, metastases, or both. In six of these patients the primary tumor and matched metastasis shared the same single mutation. In the other patients an additional mutation in the primary tumor only or a mutation in the metastasis only was observed. Our data suggest that tumor development and progression toward metastasis involves structural alterations in the p53 gene that occur early in carcinogenesis. In some cases, genetic changes in metastatic spreading may also include the appearance of a mutation in a metastasis derived from a primary tumor expressing wild-type p53, a selection of metastatic cells with a single mutation from a primary tumor expressing two different mutations, or loss of heterozygosity.

Clinical applications of the p53 tumor suppressor gene

The interest on the p53 gene has grown enormously in the last 4 years. It is now known that p53 is directly involved in important cellular functions including regulation of the cell cycle, and that its alteration may be one of the important steps in the initiation of cancer. In this review I will cover briefly basic and clinical aspects related to the p53 gene and protein and explore ways of using the accumulated knowledge for patient diagnosis and monitoring. The literature suggests that it is now appropriate to start assessing the p53 gene status of breast tumors for prognosis. Therapeutic options are at an infancy stage. A new diagnostic approach based on the immune response of cancer patients against mutant proteins is discussed, by using the p53 mutant protein as a model. Although the cancer patient has not as yet benefited directly from the enormous number of investigations on the p53 gene and protein, there is hope that in the long-term these studies will promote the understanding of cancer initiation and progression at the molecular level with a practical return at a later phase.

Apoptosis and nuclear levels of p53 protein and proliferating cell nuclear antigen in human hepatoma cells cultured with tumor promoters

Anticancer drugs etoposide and mitomycin C increased nuclear p53 protein and decreased proliferating cell nuclear antigen (PCNA) of PLC/PRF/5 human hepatoma cells. These changes were followed by DNA fragmentation and apoptosis. Teleocidin antagonized both apoptosis and alterations of nuclear p53 protein and PCNA induced by these anticancer drugs. In contrast, thapsigargin antagonized only drug-induced nuclear accumulation of p53 protein. Therefore, the inhibition of apoptosis appears not to be the common mechanism of tumor promotion. Both tumor promoters suppressed the increase in nuclear p53 protein, suggesting that an inadequate DNA repair due to the reduced nuclear accumulation of p53 protein might be playing important role in enhancing carcinogenesis.

Towards understanding the molecular basis of thyroid cancer

Cancer is a multistep phenomenon and multiple genetic lesions are involved in the emergence of the cancerous lesion. This has best been demonstrated in colonic cancer. The authors review their work and that of others highlighting what is known about thyroid cancer. They implicate ras mutations predominantly in follicular carcinoma, rearrangement of the ret proto-oncogene in papillary carcinoma and the tumor suppressor genes p53 and retinoblastoma gene product in all stages of thyroid carcinoma. They find a low rate of ret proto-oncogene rearrangement in the Saudi population (>5%) as compared to elsewhere in the world (20%). They find TSH receptor message abundance to be predictive of prognosis in thyroid cancer patients. Lastly, they examine whether the abundance of the anti-metastatic gene nm23 message abundance negatively correlated with the tendency of thyroid tumors to metastasize and find that not to be the case in thyroid carcinoma. The study of oncogenes and tumor suppressor genes in the pathogenesis of thyroid cancer is in its infancy; however, rapid progress is being made in identifying genes participating in malignant thyroid cell transformation.

Germline p53 mutations are frequently detected in young children with rhabdomyosarcoma

We investigated the possibility that a proportion of children with sporadic rhabdomyosarcoma (RMS) carry constitutional mutations of the p53 tumor suppressor gene. 33 patients with sporadic RMS at two large outpatient pediatric oncology clinics submitted blood samples. Genomic DNA was extracted from peripheral blood leukocytes and PCR was used to amplify exons 2-11 of the p53 gene. Amplified genomic DNA was screened for the presence of germline p53 mutations using single-strand conformation polymorphism (SSCP) analysis. The DNA sequence of those samples that showed aberrant migration of bands on SSCP analysis was determined to identify the precise nature of the gene mutations. Patient records were reviewed to assess clinical correlates of the mutant p53 carrier state. Heterozygous constitutional mutations were detected in 3/33 patient samples screened. Two of these missense mutations are located in exon 7 and one in exon 8 of the p53 gene. The presence of mutations was not correlated with tumor histology, stage, or site. However, an association between young age at diagnosis and presence of a constitutional p53 mutation was noted: 3/13 children under the age of 3 yr at diagnosis carried mutations, whereas none of 20 children over 3 yr of age at diagnosis harbored a detectable constitutional mutation. These results in children with RMS corroborates previous findings in other clinical settings suggesting that the mutant p53 carrier state may predispose individuals to malignancy at an early age. Although this study did not assess whether the mutations were preexisting or new germline alterations, assessment of close relatives of RMS patients for cancer risk and predictive genetic testing may be indicated.

Germ-line p53 mutations in 15 families with Li-Fraumeni syndrome

Germ-line mutations of the tumor-suppressor gene p53 have been observed in some families with the Li-Fraumeni syndrome (LFS), a familial cancer syndrome in which affected relatives develop a diverse set of early-onset malignancies including breast carcinoma, sarcomas, and brain tumors. The analysis of the p53 gene in LFS families has been limited, in most studies to date, to the region between exon 5 and exon 9. In order to determine the frequency and distribution of germ-line p53 mutations in LFS, we sequenced the 10 coding exons of the p53 gene in lymphocytes and fibroblast cell lines derived from 15 families with the syndrome. Germ-line mutations were observed in eight families. Six mutations were missense mutations located between exons 5 and 8. One mutation was a nonsense mutation in exon 6, and one mutation was a splicing mutation in intron 4, generating aberrant shorter p53 RNA(s). In three families, a mutation of the p53 gene was observed in the fibroblast cell line derived from the proband. However, the mutation was not found in affected relatives in two families and in the blood from the one individual, indicating that the mutation probably occurred during cell culture in vitro. In four families, no mutation was observed. This study indicates that germ-line p53 mutations in LFS are mostly located between exons 5 and 8 and that approximately 50% of patients with LFS have no germ-line mutations in the coding region of the p53 gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Familial brain tumour syndrome associated with a p53 germline deletion of codon 236

This report describes clinical, neuropathological and molecular genetic findings in a Swiss family with four brain tumours in only two generations. The neoplasms observed covered a wide range of biologic behaviour, from a slowly growing lesion already apparent at birth, to anaplastic astrocytoma in a young adult and glioblastomas at the age of less than 10 years. The only non-neural neoplasms in this family were a case of leukemia and an adrenocortical carcinoma. A germline deletion of codon 236 of the p53 tumour suppressor gene was identified as an underlying cause and detected in all affected family members. This mutation has not previously been reported as germline transmission or in sporadic tumours. The unusual accumulation of CNS tumours may be due to a certain organ-specific effect of this particular p53 mutation or it may reflect the specific genetic back-ground of this family.

Genetically modified skin to treat disease: potential and limitations

Molecular definition of disease at the level of the gene and advances in recombinant DNA technology suggest that many diseases are amenable to correction by genes not bearing the defective elements that result in disease. Many questions must be answered before this therapy can be used to correct chronic diseases. These questions fall into safety and efficacy categories. Experience with transplanting cellular elements of skin or skin substitutes (defined as skin that possess the cell types and a dermal structure to develop into a functioning skin) to athymic rodents is considerable and is seen as a system where these questions can be answered. This paper reviews these questions and presents our early analysis of genetically modified cells in skin substitutes in vivo and in vitro. Experimental data demonstrate that both a matrix of woven nylon, housing a fibroblast generated collage, and dead dermis can be utilized to shuttle genetically modified human fibroblasts from the laboratory to an in vivo setting. Genetically modified fibroblasts do not migrate from the shuttle to the surrounding tissue. The survival of significant numbers, approximately 70%, of genetically modified fibroblasts for at least 6 weeks in these shuttles, supports this general approach as having clinical utility. It is also concluded that skin substitute systems can be used to generate a genetically modified skin in vitro that has the capacity to develop into functional skin in vivo. Further, as genetically modified keratinocytes differentiate there is increased production by the transgene, supporting the concept that keratinocytes have true potential as shuttles for therapeutic genes. This work demonstrates that transplantation of systems containing genetically modified cells of the skin can be used to experimentally define many aspects of gene therapy using skin before this technology is taken to the clinic. Examples include determining the effect of gene transduction and expression on structure and function of the genetically modified skin as well as on distant skin and an assessment of the translational capacity of the transgene as function of time and cell number.

Uterine papillary serous adenocarcinoma. A 10-case study of p53 and c-erbB-2 expression and DNA content

BACKGROUND

Uterine papillary serous adenocarcinoma (UPSA) is a highly aggressive neoplasm with a great tendency for dissemination. p53 and c-erbB-2 immunoreactivity and DNA ploidy are considered to be indicators of prognosis for endometrial carcinomas.

METHODS

Ten cases of patients with UPSA are reported. An attempt to relate pathologic findings with immunohistochemical stains for p53- and c-erbB-2-associated proteins, ploidy, and survival was made.

RESULTS

Three patients were classified as having Stage I; three, Stage II; two, Stage III; and two, Stage IV. Myometrial invasion was present with nine tumors and involved over 50% of the myometrial thickness in five. Uterine lymph vessel invasion was detected in seven cases. Peritoneal spread occurred in six patients. Overexpression of p53 was observed in six tumors, immunoreactivity for c-erbB-2 in four, and aneuploidy in seven. However, only peritoneal spread correlated significantly with survival (P < 0.005).

CONCLUSIONS

UPSA is a tumor with a high metastatic potential that exhibits immunoreactivity for p53 and c-erbB-2 and aneuploidy more often than that reported for conventional endometrioid adenocarcinomas.

Frequent mutations of p53 gene in oesophageal squamous cell carcinomas with and without human papillomavirus (HPV) involvement suggest the dominant role of environmental carcinogens in oesophageal carcinogenesis

Epidemiological evidence suggests that alcohol intake, use of tobacco, ingestion of mycotoxins and nitrosamines and nutritional deficiencies are high-risk factors for the development of oesophageal cancer. Similarly, viral infections have been postulated to play a role in some tumours. However, the molecular events underlying the development of oesophageal carcinoma are poorly understood as yet. Loss of p53 tumour-suppressor gene function has been found in different human malignancies, and it can occur in a variety of ways, including gene mutation and interaction with the E6 protein of oncogenic human papillomaviruses (HPVs). Because the oesophageal mucosa is potentially exposed to mutagens and HPVs, we studied DNA samples derived from nine HPV-positive squamous cell carcinomas and 12 HPV-negative tumours. Exons 5-9 of the p53 gene containing phylogenetically conserved domains were examined using the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) technique. HPV detection was done using DNA in situ hybridisation with biotin-labelled HPV DNA probes. Mutations were detected in eight (38%) out of the 21 cases. Three mutations were found in exons 5/6, three in exon 7 and two in exon 8/9. Six (50%) of the 12 HPV-negative carcinomas showed p53 mutations. Two (22.2%) of the nine HPV-positive carcinomas were found to contain p53 mutations as well; one contained HPV 16 DNA sequences and showed p53 mutation in exon 8/9, and the other was HPV 6/11 positive with the mutation in exon 5/6. Although mutations were more common in HPV-negative tumours (50.0% vs 22.2%), the difference in p53 mutations in HPV-positive and -negative tumours did not reach statistical significance (P = 0.1946). These data indicate that inactivation of the p53 gene is a frequent event in oesophageal squamous cell carcinomas and such an inactivation might be an important molecular pathway for the development of oesophageal cancer. The findings of p53 mutations in HPV-positive oesophageal carcinomas suggest that HPV and p53 mutation were not mutually exclusive events. The presence of frequent mutations of p53 gene in both HPV-positive and -negative oesophageal carcinomas suggests a dominant role of environmental carcinogens in oesophageal carcinogenesis.

p53, a potential target for tumor-directed T cells

Cell lineage-specific cellular proteins, oncogenes from viral or cellular origin and tumor suppressor genes encode tumor-specific/associated antigens. Such antigens can elicit an major compatibility complex (MHC) class I-restricted cytotoxic T lymphocyte (CTL) response, either naturally in cancer patients or following appropriate immunostimulation (in vitro or in vivo). The reported immune responses in humans to the melanoma-associated MAGE gene products, GP100 and tyrosinase, all self-proteins, support the idea to use wild-type p53 products as targets for T cells. An important step towards this goal is identification of potential p53 CTL epitopes. We identified the wild-type p53 peptides with the highest affinity to the HLA-A*0201 molecule using two assays: the previously described MHC peptide-binding assay and the peptide competition assay. We obtained CTL against four p53 peptides with a high affinity for the HLA-A*0201 molecule. These findings are discussed next to a short review concerning the p53 literature.

Screening patients for heterozygous p53 mutations using a functional assay in yeast

Inherited mutations of the p53 gene significantly increase the risk of developing diverse malignancies, and germline p53 mutations can be detected by assaying the transcriptional activity of the p53 protein in mammalian cells. Here we describe a method starting with lymphocytes that allows detection of germline p53 mutations by 'functional' analysis of p53 protein expressed in Saccharomyces cerevisiae. The p53 PCR products are directly cloned into yeast expression vectors in vivo and subsequently tested for transcriptional activity in a simple growth assay. This technique, functional analysis of separated alleles in yeast (FASAY), requires only a few steps, can be automated readily and should permit screening for germline or somatic heterozygous mutations in any gene whose function can be monitored in yeast.

Tumourigenesis associated with the p53 tumour suppressor gene

The p53 gene is contained within 16-20 kb of cellular DNA located on the short arm of human chromosome 17 at position 17p13.1. This gene encodes a 393-amino-acid nuclear phosphoprotein involved in the regulation of cell proliferation. Current evidence suggests that loss of normal p53 function is associated with cell transformation in vitro and development of neoplasms in vivo. More than 50% of human malignancies of epithelial, mesenchymal, haematopoietic, lymphoid, and central nervous system origin analysed thus far, were shown to contain an altered p53 gene. The oncoproteins derived from several tumour viruses, including the SV40 large T antigen, the adenovirus E1B protein and papillomavirus E6 protein, as well as specific cellular gene products, e.g. murine double minute-2 (MDM2), were found to bind to the wild-type p53 protein and presumably lead to inactivation of this gene product. Therefore, the inactivation of p53 tumour suppressor gene is currently regarded as an almost universal step in the development of human cancers. The current data on p53-associated tumourigenesis are briefly discussed in this minireview.