Clonality and stability of the p53 gene in human astrocytic tumor cells: quantitative analysis of p53 gene mutations by yeast functional assay

Programmed cell death detection methods: a systematic review and a categorical comparison

Programmed cell death is considered a key player in a variety of cellular processes that helps to regulate tissue growth, embryogenesis, cell turnover, immune response, and other biological processes. Among different types of cell death, apoptosis has been studied widely, especially in the field of cancer research to understand and analyse cellular mechanisms, and signaling pathways that control cell cycle arrest. Hallmarks of different types of cell death have been identified by following the patterns and events through microscopy. Identified biomarkers have also supported drug development to induce cell death in cancerous cells. There are various serological and microscopic techniques with advantages and limitations, that are available and are being utilized to detect and study the mechanism of cell death. The complexity of the mechanism and difficulties in distinguishing among different types of programmed cell death make it challenging to carry out the interventions and delay its progression. In this review, mechanisms of different forms of programmed cell death along with their conventional and unconventional methods of detection of have been critically reviewed systematically and categorized on the basis of morphological hallmarks and biomarkers to understand the principle, mechanism, application, advantages and disadvantages of each method. Furthermore, a very comprehensive comparative analysis has been drawn to highlight the most efficient and effective methods of detection of programmed cell death, helping researchers to make a reliable and prudent selection among the available methods of cell death assay. Conclusively, how programmed cell death detection methods can be improved and can provide information about distinctive stages of cell death detection have been discussed.

Analysis of TP53 mutation status in human cancer cell lines: a reassessment

Tumor-derived cell lines play an important role in the investigation of tumor biology and genetics. Across a wide array of studies, they have been tools of choice for the discovery of important genes involved in cancer and for the analysis of the cellular pathways that are impaired by diverse oncogenic events. They are also invaluable for screening novel anticancer drugs. The TP53 protein is a major component of multiple pathways that regulate cellular response to various types of stress. Therefore, TP53 status affects the phenotype of tumor cell lines profoundly and must be carefully ascertained for any experimental project. In the present review, we use the 2014 release of the UMD TP53 database to show that TP53 status is still controversial for numerous cell lines, including some widely used lines from the NCI-60 panel. Our analysis clearly confirms that, despite numerous warnings, the misidentification of cell lines is still present as a silent and neglected issue, and that extreme care must be taken when determining the status of p53, because errors may lead to disastrous experimental interpretations. A novel compendium gathering the TP53 status of 2,500 cell lines has been made available (http://p53.fr). A stand-alone application can be used to browse the database and extract pertinent information on cell lines and associated TP53 mutations. It will be updated regularly to minimize any scientific issues associated with the use of misidentified cell lines (http://p53.fr).

Clonal analysis in recurrent astrocytic, oligoastrocytic and oligodendroglial tumors implicates IDH1- mutation as common tumor initiating event

Background

To investigate the dynamics of inter- and intratumoral molecular alterations during tumor progression in recurrent gliomas.

Methodology/Principal Findings

To address intertumoral heterogeneity we investigated non- microdissected tumor tissue of 106 gliomas representing 51 recurrent tumors. To address intratumoral heterogeneity a set of 16 gliomas representing 7 tumor pairs with at least one recurrence, and 4 single mixed gliomas were investigated by microdissection of distinct oligodendroglial and astrocytic tumor components. All tumors and tumor components were analyzed for allelic loss of 1p/19q (LOH 1p/19q), for TP53- mutations and for R132 mutations in the IDH1 gene. The investigation of non- microdissected tumor tissue revealed clonality in 75% (38/51). Aberrant molecular alterations upon recurrence were detected in 25% (13/51). 64% (9/14) of these were novel and associated with tumor progression. Loss of previously detected alterations was observed in 36% (5/14). One tumor pair (1/14; 7%) was significant for both. Intratumoral clonality was detected in 57% (4/7) of the microdissected tumor pairs and in 75% (3/4) of single microdissected tumors. 43% (3/7) of tumor pairs and one single tumor (25%) revealed intratumoral heterogeneity. While intratumoral heterogeneity affected both the TP53- mutational status and the LOH1p/19q status, all tumors with intratumoral heterogeneity shared the R132 IDH1- mutation as a common feature in both their microdissected components.

Conclusions/Significance

The majority of recurrent gliomas are of monoclonal origin. However, the detection of divertive tumor cell clones in morphological distinct tumor components sharing IDH1- mutations as early event may provide insight into the tumorigenesis of true mixed gliomas.

Mobile phone use and glioma risk: comparison of epidemiological study results with incidence trends in the United States

OBJECTIVE

In view of mobile phone exposure being classified as a possible human carcinogen by the International Agency for Research on Cancer (IARC), we determined the compatibility of two recent reports of glioma risk (forming the basis of the IARC's classification) with observed incidence trends in the United States.

DESIGN

Comparison of observed rates with projected rates of glioma incidence for 1997-2008. We estimated projected rates by combining relative risks reported in the 2010 Interphone study and a 2011 Swedish study by Hardell and colleagues with rates adjusted for age, registry, and sex; data for mobile phone use; and various latency periods.

SETTING

US population based data for glioma incidence in 1992-2008, from 12 registries in the Surveillance, Epidemiology, and End Results (SEER) programme (Atlanta, Detroit, Los Angeles, San Francisco, San Jose-Monterey, Seattle, rural Georgia, Connecticut, Hawaii, Iowa, New Mexico, and Utah).

PARTICIPANTS

Data for 24,813 non-Hispanic white people diagnosed with glioma at age 18 years or older.

RESULTS

Age specific incidence rates of glioma remained generally constant in 1992-2008 (-0.02% change per year, 95% confidence interval -0.28% to 0.25%), a period coinciding with a substantial increase in mobile phone use from close to 0% to almost 100% of the US population. If phone use was associated with glioma risk, we expected glioma incidence rates to be higher than those observed, even with a latency period of 10 years and low relative risks (1.5). Based on relative risks of glioma by tumour latency and cumulative hours of phone use in the Swedish study, predicted rates should have been at least 40% higher than observed rates in 2008. However, predicted glioma rates based on the small proportion of highly exposed people in the Interphone study could be consistent with the observed data. Results remained valid if we used either non-regular users or low users of mobile phones as the baseline category, and if we constrained relative risks to be more than 1.

CONCLUSIONS

Raised risks of glioma with mobile phone use, as reported by one (Swedish) study forming the basis of the IARC's re-evaluation of mobile phone exposure, are not consistent with observed incidence trends in US population data, although the US data could be consistent with the modest excess risks in the Interphone study.

Mutant p53 R248Q but not R248W enhances in vitro invasiveness of human lung cancer NCI-H1299 cells

More than half of all human cancers are associated with mutations of the TP53 gene. In regard to the functional interaction with the remaining wild-type (WT) p53 allele, p53 mutations are classified into two types, recessive and dominant-negative (DN) mutations. The latter mutant protein has a DN activity over the remaining WT allele. We previously showed that the DN p53 mutant was useful as a predictor of poor outcome or a risk factor for metastatic recurrence in patients with some types of cancers, regardless of the presence or absence of loss of heterozygosity (LOH) of WT p53, suggesting that the DN p53 had 'gain-of-function (GOF)' activity besides the transdominance function. In this study, we investigated GOF activity of two DN p53 mutants which had a point mutation at codon 248 (R248Q and R248W), one of the hot spots, by transfecting them respectively into H1299 cells which originally expressed no p53 protein. Growth activity of the transfectants with the two mutants was not different from that of parent or Mock transfectants. Meanwhile, in vitro invasions of Matrigel and type I collagen gel by R248Q-transfectants were significantly higher than those by R248W-transfectants or the control cells. However, there were no differences in cell motile activities, expressions of extracellular matrix-degradative enzymes such as matrix metalloproteinases, urokinase-type plasminogen activator and heparanase, and their inhibitors, between R248Q- and R248W-transfectants. These findings indicate that the p53 mutants have a different quality in GOF activities even if the mutations occurred at the same codon. And detailed information of the status of p53, including transdominancy and GOF activity, is expected to be useful for diagnosis and therapeutic strategy fitting the individual patients.

p53 and chemosensitivity in bladder cancer

Urothelial carcinoma is the second most common genitourinary malignancy. Although the majority of patients present with superficial bladder tumors, there are several clinical problems, such as progression to invasive tumors, poor prognosis of invasive tumors, and chemosensitivity. Alterations in p53 represent one of the most common genetic events in patients with invasive urothelial carcinoma and are suggested to be linked to tumor progression, prognosis, and chemosensitivity. p53 possesses various functions, including induction of cell-cycle arrest, apoptosis, DNA repair, and antioxidants; it acts as a killer and a healer. In this article, we review the roles of p53 pathways in bladder carcinogenesis and findings from recent studies of ours and other groups, and we discuss the clinical significance of the abrogation of p53 pathways in the treatment of urothelial carcinoma.

Establishment and characterization of human urothelial cancer xenografts in severe combined immunodeficient mice

AIM

To establish and characterize a murine xenograft model of human urothelial cancer in severe combined immunodeficient (SCID) mice for therapeutic simulation.

METHODS

Pieces of 30 freshly resected urothelial tumors (24 obtained from bladder and 6 from ureter or pelvis) were implanted subcutaneously into SCID mice, and xenograft tumors were passed in tumorigenic cases. At each passage, histopathology, TP53 mutational status assessed by yeast p53 functional assay, and the Ki-67 labeling index (LI) were examined to evaluate the preservation of original features. A growth delay assay after single-dose irradiation was performed in four representative xenografts.

RESULTS

Tumor growth was observed in 18 mice (60%, 18/30). Histologically, 15 of the 18 were epithelial carcinomas similar to the original tumors, whereas the other 3 were Epstein-Barr virus-associated lymphoproliferative disease, resulting in a 50% (15/30) take rate. No correlation was found between the tumor take rate and the clinicopathologic features, TP53 mutational status, or Ki-67 LI of the patients' tumors. Of these 15 xenografts, 11 xenografts were passed from 3 to 10 generations. TP53 mutational status remained stable during the passages, and the Ki-67 LI of eight xenografts was within a range of 50% of the LI of the original tumors, although the other three xenografts increased by over 50%. Specific growth delay after irradiation, independent of the original tumor growth speed and Ki-67 LI, was observed in four xenografts.

CONCLUSIONS

SCID mice are useful recipients for investigations of human urothelial cancer with a wide biological range. This easy-to-handle xenograft system can help to develop a better in vivo preclinical evaluation system for therapeutic agents as well as the investigation of tumor pathophysiology.

Intratumoral DNA stem-line heterogeneity in superficial spreading melanoma

BACKGROUND

In primary melanomas, data on the degree of intratumoral heterogeneity to date have been lacking.

OBJECTIVE

Our purpose was to investigate intratumoral DNA stem-line heterogeneity in superficial spreading melanoma (SSM).

METHODS

Multiple measuring fields of 54 SSMs (tumor thickness median 1.60 mm) were studied by DNA image cytometry to obtain data on the number of DNA stem lines per tumor, their ploidy characteristics, and intratumoral distribution. Results were compared with standard histopathological criteria.

RESULTS

Twenty-three of 54 SSMs were found to have two or three distinct proliferating tumor cell stem lines (1.46 +/- 0.57 per tumor). Stem lines appeared spatially separated in 22 of 23 SMMs. At least 3 measuring fields per tumor were necessary to identify all stem lines with a likelihood of 95%. DNA heterogeneity correlated with tumor thickness, but occurred in 5 of 19 cases of pT1 melanoma.

CONCLUSIONS

Primary SSMs can be regarded as potentially clonally unstable with a tendency for spatial separation of tumor cell stem lines.

Frequent co-alterations of TP53, p16/CDKN2A, p14ARF, PTEN tumor suppressor genes in human glioma cell lines

In this study we established the simultaneous status of TP53, p16, p14ARF and PTEN tumor suppressor genes in 34 randomly chosen human glioma cell lines. Nine cell lines (26.4%) harbored mutations or deletions in all four tumor suppressor genes and 22 cell lines (64%) had alterations in at least three. Mutations/deletions were found at the following frequencies: TP53 (76.5%), p14ARF (64.7%), p16 (64.7%), PTEN (73.5%). Thus, there was a high incidence of alterations in the cellular pathways involving the p53 transcription factor (94.1%), the retinoblastoma protein (64.7%) and the PTEN phosphatase (73.5%) and 91% of cell lines carried mutations in two or more pathways. This provides the first clear genetic evidence that these tumor suppressors participate in biological pathways which are functioning separately/independently in glioma cells. The status of the gene alterations did not correlate with tumorigenicity in immunocompromized mice or any clinical parameters. Although the mutation rate was higher in glioma cell lines than that reported for glioma tissues, the alterations were molecularly representative of those found in adult de novo glioblastoma. This study highlights the importance of developing therapeutic approaches applicable to tumors with a broad range of genetic alterations and also provides an invaluable panel of glioma cell lines to make this possible.

p53 and brain tumors: from gene mutations to gene therapy

The p53 tumor suppressor gene (TP53) is the most frequently altered gene in human cancer and is also found mutated in several types of brain tumors. Loss of p53 function plays a central role in the development of cancer. The characterization of the biochemical pathways by which p53 alteration triggers tumorigenesis is the foundation for the design of novel therapeutic approaches. Investigations of the intracellular mechanisms at the origin of p53 tumor suppressive functions have shown that p53 is a transcription factor able to sense a variety of cellular insults and induce a dual response: cell growth arrest/senescence or apoptosis. Less well studied are p53's influences on extracellular events such as tumor angiogenesis, immunology and invasion. Here, we review these findings and specifically discuss their implications for brain tumor genesis, molecular diagnosis and prognosis. Of clinical importance are the findings that brain tumors with wild type (wt) or mutant p53 status may respond differently to radiation therapy and that novel therapeutic strategies using TP53 gene transfer or specifically targeting tumor cells with mutated p53 are being evaluated in clinical trials.

Clinical evaluation of p53 mutations in urothelial carcinoma by IHC and FASAY

OBJECTIVES

To assess the clinical benefit of the methods of detection of p53 mutations in human urothelial carcinoma.

METHODS

A total of 75 surgical specimens of urothelial carcinoma were analyzed using a yeast functional assay (FASAY) and immunohistochemistry (IHC), in combination with sequencing analysis.

RESULTS

Of the 75 specimens, 24 (32.0%) were positive (mutant) by FASAY and 23 (30.7%) were positive by IHC. The sequencing analysis confirmed that all 24 FASAY-positive tumors harbored mutations, and no mutations were detected in any FASAY-negative tumors. In contrast, nuclear accumulation of p53 protein was detected in 9 (17.6%) of 51 tumors with no mutation, and 10 (41.7%) of 24 tumors with mutation showed no positive staining on IHC. The mutations detected by FASAY and IHC were both associated with stage and grade, but null mutations of p53 were not associated with stage. Concerning chemosensitivity, 6 (85.7%) of 7 responders harbored p53 missense mutations in at least one allele (P = 0.01), and only 4 (57.1%) were judged positive by IHC (P = 0.13).

CONCLUSIONS

FASAY is more accurate than IHC in detecting the various types of p53 mutations, suggesting that a comprehensive approach for the detection of p53 mutations may be essential to elucidate their clinical significance.

Loss of p53 transcriptional activity in hepatocellular carcinoma evaluated by yeast-based functional assay: comparison with p53 immunohistochemistry

We studied the transcriptional activity of p53 protein in 50 tissues of hepatocellular carcinoma (HCC) using a yeast functional assay. In this assay, red yeast colonies indicate that p53 protein cannot bind to its specific domain and has lost its transcriptional activity. We also clarified whether mutant p53 protein could inactivate wild-type p53 protein in a transdominant manner using a modified yeast assay. In addition, we examined whether immunohistochemically detectable p53 protein was functionally inactive. The incidence of p53 inactivation was significantly higher in tumors with capsular invasion. Out of 21 tumors diagnosed with p53 mutations, 11 exhibited >75% red colonies, and all contained missense mutations. In these tumors, p53 function was lost because there was supposedly no intact p53 gene on either allele. One missense mutant produced <60% red colonies, but it was also considered inactive as a p53 protein heterotetramer because of its transdominant activity. In 7 of the remaining 9 tumors, p53 was considered to be mutated on one allele and intact on the other. All of these 7 tumors contained nonsense or frameshift mutations and had no transdominant activity, which suggested that p53 function remained intact. Alternately, immunohistochemical analysis demonstrated that all of the tumors with missense mutations were positively immunostained, whereas those that contained nonsense or frameshift mutations were negatively stained. Consequently, positively immunostaining tumors mostly coincided with p53-inactive tumors. These yeast-based assays suggested that p53 function was retained in some mutant cases. Immunohistochemistry was helpful in screening functionally inactive p53 protein in HCCs.

Detection of TP53 mutation in ameloblastoma by the use of a yeast functional assay

BACKGROUND

Mutations in TP53 have been observed in a variety of tumors including oral lesions, though there are no reports in ameloblastomas. The purpose of the study was to examine the TP53 status of ameloblastomas using newly developed yeast functional assay whose accuracy and sensitivity has been proven to be higher than those of the previous DNA structure-based methods such as single strand conformation polymorphism (SSCP) analysis.

METHODS

TP53 status was analyzed by yeast functional assay and DNA sequencing in 12 cases of ameloblastoma which were diagnosed histologically and represented the clinical features of a benign tumor. After the extraction of RNA from the frozen tissue samples without microdissection, reverse transcription (RT)-PCR was carried out and these samples were used. The assay can detect mutations of p53 mRNA between codons 67 and 347 by the DNA-binding activity of the protein and reveal them as red colonies.

RESULTS

One case of 47-year-old male gave 17% red colonies of yeast and the other 11 cases gave 5.4% (mean; range, 3-8%). To confirm this result, we obtained other nine samples from the case of 17% red colonies, which contained or did not contain tumor tissues, and analyzed them by the assay. Seven samples that were histologically negative for tumor cells gave 4.7% red colonies (mean; range, 1-7%). Two samples that were histologically positive for tumor cells gave 20 or 46% of red colonies. The p53 plasmids were recovered from the red colonies of these three samples showing high red colony ratios and were subjected to sequencing analysis after purification. In all these samples, the same clonal mutation of TGT (Cys) 238 TAT (Tyr) was demonstrated.

CONCLUSIONS

These results suggest that TP53 mutation may be involved in molecular pathogenesis in a subset of ameloblastomas, though it is infrequent.

Influence of p53 mutations on prognosis of patients with glioblastoma

BACKGROUND

The influence of p53 mutations on the biology of astrocytic tumors is controversial. p53 is thought to be inactivated in the early stage of gliomagenesis; however, what role its inactivation plays in the malignancy of gliomas remains unknown. To understand the significance of p53 inactivation, the authors identified the locus of p53 gene mutation in glioma samples at different stages of progression and studied the correlation between the mutation and clinical behavior.

METHODS

Samples from newly diagnosed gliomas, including pure and mixed astrocytomas, were analyzed for p53 mutations using a yeast functional assay. To determine the locus of the gene mutations, DNA sequencing was performed.

RESULTS

The incidence of p53 mutations was higher in anaplastic astrocytomas (AA, 48%) than glioblastomas (GBM, 31%). There was no significant difference in the average ages of GBM patients with and without p53 mutations (54.9 years +/- 2.3 and 53.2 years +/- 4.6, respectively). In GBM patients, the mutation did not affect progression free survival or overall survival. Astrocytomas and GBM differed in the distribution of p53 mutation loci.

CONCLUSIONS

The p53 gene mutation does not markedly affect the survival of GBM patients. The difference in the location of p53 mutations between AA and GBM suggests that in gliomas, the p53 mutation may contribute not only to tumorigenesis (as an early event) but also to progression to malignancy (as a late event).

p53 as a potential predictive factor of response to chemotherapy: feasibility of p53 assessment using a functional test in yeast from trucut biopsies in breast cancer patients

Assessment of the predictive value of p53 requires the testing of large numbers of samples from patients enrolled in prospective phase III clinical trials. The goal of this study was to determine whether p53 status can be determined by p53 yeast functional assay using the limiting amounts of material that can typically be obtained in prospective phase III trials (particularly when chemotherapy is given before surgery). All patients presenting with a clinically palpable tumour which could be considered large enough to perform a trucut biopsy (> or =2 cm breast tumour) were eligible for this study. Two trucut biopsies and one incisional biopsy were performed on the surgical specimens (mastectomy or tumourectomy). Samples were snap frozen and cryostat sections were taken for histology and p53 testing. Thirty patients were included. Three samples out of 90 failed to give any p53 PCR products, probably because these samples contained almost entirely fibrous tissue. Of the 87 samples that could be tested, the incisional and trucut biopsies results were fully concordant in every case. p53 could be defined in 97% of patients by double trucut biopsy. Eight out of 30 tumours tested were mutant for p53 (27%). p53 status can be reliably determined by yeast assay from single frozen sections of trucut biopsies. Histological examination before p53 testing is essential to exclude cases where the p53 result may reflect only the status of the normal cells in the biopsy.

Restoration of endogenous wild-type p53 activity in a glioblastoma cell line with intrinsic temperature-sensitive p53 induces growth arrest but not apoptosis

p53 protein is a transcription factor involved in multiple tumor-suppressor activities including cell cycle control and apoptosis. TP53 gene is frequently mutated in glioblastoma, suggesting the importance of inactivation of this gene product in gliomagenesis. Restoration of p53 function in glioblastoma cell lines deficient for p53 has shown that p53 induces growth arrest or apoptosis depending on the cell line and vector used to transduce wild-type TP53 alleles. Considering that astrocytes grow and express p53, it is not clear whether these results reflect physiologic responses or the result of p53 overexpression in combination with cellular responses to viral vector infection. Here, we reassessed this issue using a glioblastoma cell line (LN382) that expresses an endogenous temperature-sensitive mutant p53. This cell line expresses TP53 alleles (100% as determined by a p53 transcriptional assay in yeast) mutated at codon 197 GTG (Val) > CTG (Leu). We found that the p53 protein in these cells acted as an inactive mutant at 37 degrees C and as a functional wild-type p53 below 34 degrees C as demonstrated by several lines of evidence, including (i) restoration of transactivating ability in yeast, (ii) induction of p53-modulated genes such as CDKN1(p21) and transforming growth factor-alpha, (iii) disappearance of accumulated p53 protein in the nucleus and (iv) decrease in steady state p53 protein levels. This temperature switch allowed p53 levels, which were close to physiological levels to dramatically reduce LN382 cell proliferation by inducing a G(1)/S cell cycle block, but not to induce apoptosis. The lack of apoptosis was considered to be a result of the low level p53 expression, because increasing wild-type p53 levels by adenoviral-mediated gene transfer caused apoptosis in these cells. The LN382 cell line will be extremely useful for investigations into the roles of p53 in cellular responses to a variety of stimuli or damages.

Dependence of efficient adenoviral gene delivery in malignant glioma cells on the expression levels of the Coxsackievirus and adenovirus receptor

OBJECT

Recombinant adenovirus is used as a competent vector in a wide spectrum of cancer gene therapies because of its high efficiency in gene delivery. To study the feasibility of gene therapy in malignant gliomas, the authors examined the antiproliferative effect of the adenovirally transduced wild-type p53 tumor suppressor gene by using 15 different high-grade glioma cell lines.

METHODS

Although growth suppression in association with a high adenoviral p53 transduction efficiency was seen in five of 15 cell lines, it was not observed in the remaining 10 cell lines. To clarify the underlying mechanism, we examined the expression levels of the Coxsackievirus and adenovirus receptor (CAR), which is the primary receptor for adenovirus, and of the integrins alpha vbeta3 and alpha vbeta5, which promote adenoviral internalization. The expression level of the CAR gene showed a close correlation to adenoviral gene transduction efficiency in the tested cell lines, whereas the expression levels of the integrins did not. The CAR expression was decreased by wild-type p53 transduction in U251MG cells harboring mutant p53 and increased by antisense inhibition of p53 in LN443 cells with endogenous wild-type p53.

CONCLUSIONS

The results of this study indicate that CAR expression is a critical determinant of transduction efficiencies in adenovirus-based gene therapy for human malignant gliomas.

The clonal origin and clonal evolution of epithelial tumours

While the origin of tumours, whether from one cell or many, has been a source of fascination for experimental oncologists for some time, in recent years there has been a veritable explosion of information about the clonal architecture of tumours and their antecedents, stimulated, in the main, by the ready accessibility of new molecular techniques. While most of these new results have apparently confirmed the monoclonal origin of human epithelial (and other) tumours, there are a significant number of studies in which this conclusion just cannot be made. Moreover, analysis of many articles show that the potential impact of such considerations as patch size and clonal evolution on determinations of clonality have largely been ignored, with the result that a number of these studies are confounded. However, the clonal architecture of preneoplastic lesions provide some interesting insights --many lesions which might have been hitherto regarded as hyperplasias are apparently clonal in derivation. If this is indeed true, it calls into some question our hopeful corollary that a monoclonal origin presages a neoplastic habitus. Finally, it is clear, for many reasons, that methods of analysis which involve the disaggregation of tissues, albeit microdissected, are far from ideal and we should be putting more effort into techniques where the clonal architecture of normal tissues, preneoplastic and preinvasive lesions and their derivative tumours can be directly visualized in situ.

p53 status in multiple human urothelial cancers: assessment for clonality by the yeast p53 functional assay in combination with p53 immunohistochemistry

Multifocal synchronous or metachronous tumor development is a common observation in human urothelial cancer cases. However, the underlying mechanism has remained obscure. We have employed a new tool to investigate the p53 gene status, the yeast p53 functional assay, in combination with immunohistochemistry in a total of 50 tumor samples from 32 cases with urothelial cancers, including 8 with multiple synchronous tumor development and 2 demonstrating metachronous tumors. p53 mutations were found in 13 cases (9 with missense mutations, 3 with deletion, 1 with splicing mutation) by the yeast p53 functional assay. p53 protein overexpression was seen in all 9 cases with missense mutations, but in only one of the 4 cases with nonsense mutations. Two tumors without p53 mutation also showed positive p53 immunoreactivity. Overall, p53 abnormalities including mutations and/or protein overexpression were found in 15 (47%) cases. p53 abnormalities were significantly more frequent in non-papillary and in high grade tumors. Loss of the wild type allele in addition to a p53 mutation was suggested in 8 of the 15 (53%) cases. All 4 cases with mutations in multiple synchronous tumors had identical p53 mutations in the separate urothelial cancers, strongly suggestive of monoclonality. The one case with multiple metachronous tumors, in contrast, was characterized by variation in the p53 status, indicative of different clonal origins. In conclusion, combined assessment for p53 status as used here (yeast p53 functional assay plus immunohistochemistry) may provide insights into the molecular mechanisms of urothelial carcinogenesis.

Adenovirus type 5 E1A immortalizes primary rat cells expressing wild-type p53

Adenovirus (Ad) E1A induces apoptosis in cells expressing wild-type p53, and stable transformation by Ad E1A requires the co-introduction of an anti-apoptotic gene such as Ad E1B 19K. Thus, cells immortalized by Ad E1A alone might have lost functional p53. In order to analyze the p53 in rat cells expressing Ad E1A, we established rat cell lines by transfecting primary rat embryo fibroblast (REF) and baby rat kidney (BRK) cells with cloned Ad5 E1A. By using a yeast functional assay, we analyzed p53 in six primary REF and three BRK cell lines immortalized by Ad5 E1A as well as five spontaneously immortalized rat cell lines (REF52, NRK, WFB, Rat-1 and 3Y1). The yeast functional assay revealed that all of the spontaneously and Ad5 ElA-immortalized rat cell lines except for 3Y1 expressed wild-type p53. All of the Ad5 E1A-immortalized rat cell lines contained p53 detectable by immunoprecipitation. Recombinant adenovirus expressing rat p53 cloned from a REF cell line immortalized by Ad5 E1A, as well as that expressing murine wild-type p53, induced apoptosis in p53-null cells in collaboration with E1A. Thus, it is suggested that the mutation of p53 appears to be not frequent in the spontaneous immortalization of primary rat cells, and that the functional loss of wild-type p53 is not a prerequisite of E1A-mediated immortalization.

A point mutation of human p53, which was not detected as a mutation by a yeast functional assay, led to apoptosis but not p21Waf1/Cip1/Sdi1 expression in response to ionizing radiation in a human osteosarcoma cell line, Saos-2

PURPOSE

The 123A point mutation of p53 showed increased radiosensitivity, whereas other mutations (143A, 175H, and 273H) were not affected. To determine the reason for increased radiosensitivity of the 123A mutation, the response of the transformant of 123A mutation to ionizing radiation (IR) was examined and compared to those of transformants with the wild type p53 or other point mutations (143A, 175H, and 273H).

METHODS AND MATERIALS

Stable transformants with a mutant or wild type p53 made by introducing cDNA into the human osteosarcoma cell line, Saos-2, which lacks an endogenous p53 were used. The transcriptional activity of mutant p53 was examined using a yeast functional assay. The transformants were examined for the accumulation of p53, the induction of p21Waf1/Cip1/Sdi1 (hereafter referred to as p21), and the other response of p53-responsive genes (MDM2, Bax, and Bcl-2) by Western blotting. Apoptosis was analyzed by detection of DNA fragmentation.

RESULTS

The 123A point mutation of p53 was detected as a wild type in the yeast functional assay. The 123A mutant accumulated p53 in response to IR. The 123A mutant did not induce p21, but normally responded to MDM2, Bax, and Bcl-2. The 123A mutant entered apoptosis earlier than the wild type p53 transformant, and induced Fas at earlier in response to IR.

CONCLUSION

The 123A mutant led to apoptosis, but not p21 expression in response to IR. The occurrence of apoptosis, but not induction of p21, corresponded to the radiosensitivity in the transformant. The early occurrence of apoptosis in 123A transformants may depend on the early induction of Fas.

Use of a yeast assay to detect functional alterations in p53 in prostate cancer: review and future directions

BACKGROUND

While many studies have suggested that p53 mutations are common in human cancers, the functional activity of these mutant alleles has not yet been fully addressed. We believe that information about the functional status of individual p53 mutants will prove to be important for a better understanding of the role of p53 in tumor development and progression. Ultimately, this information could also influence treatment decisions for individual cancer patients.

METHODS

A recently developed yeast functional assay can be used to assess the transactivational activity of p53 mutants. Furthermore, this assay is more sensitive than single strand conformational polymorphism (SSCP) for detection of p53 mutations. In this review, we summarize the mechanism of this new technique and describe its applications in cancer research, with an emphasis on prostate cancer.

RESULTS

The use of the yeast functional assay provides a simple, sensitive, and reproducible method for detecting p53 mutations and for determining the transactivational activity and dominant-negative role of individual p53 mutants.

CONCLUSIONS

This method may be adapted to analyze other transcriptional factors, including the human androgen receptor.

p53 inactivating mutations in Chinese nasopharyngeal carcinomas

Previously a low frequency of p53 mutations was detected in nasopharyngeal carcinoma (NPC) using molecular techniques to screen for mutations, yet immunohistochemical staining revealed a high frequency of p53 aberrant proteins. These findings might be attributed to the occurrence of p53 mutations outside the common hot spots and/or the inactivation of the protein through interactions with cellular or viral proteins. Using a previously established simple and sensitive p53 yeast functional assay, we blindly screened 25 nasopharyngeal biopsies for p53 mutations from exons 4 to 11. p53 was mutated in 27.3% of NPC specimens and in 0% of the nasopharyngeal biopsies from patients with non-malignant diseases. Two p53 mutations were detected in exon 7 and two were detected in exon 8. Interestingly, the exon 8 mutations observed in NPC lie in codons which appear to be hot spots for mutations in other head and neck cancers.

Significant correlation of nitric oxide synthase activity and p53 gene mutation in stage I lung adenocarcinoma

Nitric oxide (NO) and its derivatives can directly cause DNA damage and mutation in vitro and may play a role in the multistage carcinogenic process. It has been reported that NO induces mutation in the p53 tumor suppressor gene; we therefore analyzed the relationship between NO synthase (NOS) activity and p53 gene status in early-stage lung adenocarcinoma. Surgical samples were classified into two categories: 14 lung adenocarcinomas with high NOS activity (>25 pmol/min/g tissue, category A), and 16 with low NOS activity (<25 pmol/min/g tissue, category B). A yeast functional assay for p53 mutations disclosed a red colony that corresponded to a mutation in the p53 gene in 8 cases (57.1%) in category A and 3 cases (18.8%) in category B, the frequency being significantly higher in the former (P<0.05). A p53 DNA sequence analysis revealed that 5 of the 8 p53 mutation-positive samples in category A had a G:C-to-T:A transversion, which is reported to be a major target of NO. The mechanism of carcinogenesis of adenocarcinoma is not fully understood, but these results suggest that an excess of endogenously formed NO may induce a p53 gene mutation containing mainly G:C-to-T:A transversion in the early stage of lung adenocarcinoma. Our results suggest that NO has potential mutagenic and carcinogenic activity, and may play important roles in human lung adenocarcinoma.

Absence of p53 gene mutations in a tumor panel representative of pilocytic astrocytoma diversity using a p53 functional assay

Although p53-gene mutations occur with significant frequency in diffuse low-grade and high-grade astrocytomas, and are postulated to play an important role in tumorigenesis in these cases, the role of the p53 gene in pilocytic astrocytomas remains unclear. Published data using DNA-based assays for p53-gene analysis in these tumors have shown contradictory results in mutation frequency (0-14%). It is not known whether these heterogeneous results stem from the biological diversity of this tumor group or from technical problems. To re-evaluate p53-gene status in pilocytic tumors, we analyzed 18 tumors chosen to represent the clinical and biological heterogeneity of this tumor type with respect to anatomical location, patient age, gender, ethnic origin (Caucasian or Japanese) and the concomitant occurrence of neurofibromatosis type 1 (NF1). All primary tumors were histologically diagnosed as pilocytic astrocytoma (WHO grade I), except for one anaplastic pilocytic astrocytoma (WHO grade III) which developed in an NF1 patient and recurred as glioblastoma multiforme (WHO grade IV). p53 mutations were detected using an assay in yeast which tests the transcriptional activity of p53 proteins synthesized from tumor mRNA-derived p53-cDNA templates. None of 18 tumors, including 3 NF1-related tumors, showed p53-gene mutations between and including exons 4 and 11. We conclude that p53-gene mutations are extremely rare findings in pilocytic astrocytomas, and are absent even in those exceptional cases in which malignant progression of such tumors has occurred.

Nitric oxide as a carcinogen: analysis by yeast functional assay of inactivating p53 mutations induced by nitric oxide

We have used a yeast p53 functional assay to study induction of mutations in the p53 tumor suppressor gene by nitric oxide and cytosine methylation. The yeast assay identifies only biologically important p53 mutations. p53 cDNA was treated with the nitric oxide donor sydnonimine, PCR-amplified and transfected into yeast. Sydnonimine produced a significant, dose-dependent increase in C:G-->A:T transversions. Many important p53 mutational hotspots are postulated to arise by deamination of methylCpG in tumors. We therefore examined nitric oxide induction of mutations in p53 cDNA methylated by PCR-mediated substitution of 5-methylcytosine for cytosine or by treatment with the SssI CpG methylase. Both methylation procedures increased the baseline mutation rate, and nitric oxide treatment produced a further increase in mutation yield. Sequence analysis showed that methylation alone led to C:G-->T:A transitions, whereas nitric oxide treatment simply produced more C:G-->A:T transversions. Thus the most important factor in C:G-->T:A transition at CpG sites identified in this experimental system is cytosine methylation, consistent with spontaneous conversion of 5-methylcytosine to thymine by deamination.

Homozygous p53 gene mutation in a radiation-induced glioblastoma 10 years after treatment for an intracranial germ cell tumor: case report

OBJECTIVE

Radiation-induced glioma is a rare but serious complication of radiotherapy. Underlying radiation-induced mutations in oncogenes or tumor suppressor genes have not previously been described.

CLINICAL PRESENTATION

A 16-year-old female patient developed a glioblastoma in the right frontal lobe 10 years after treatment of a suprasellar germ cell tumor with 50 Gy ionizing radiation. The glioblastoma was undetectable on a high-resolution magnetic resonance image obtained 3 months before diagnosis.

METHODS AND RESULTS

A p53 functional assay was used to examine the transcriptional competence of the p53 tumor suppressor gene. This assay scores the content of mutant p53 alleles in tumor and blood samples quantitatively as a percentage of red yeast colonies. The glioblastoma contained 95% mutant p53 alleles, whereas blood from the patient and her parents contained only normal background levels of red colonies. Sequencing revealed that the mutation in the tumor was a 3-base pair deletion affecting codons 238 and 239. Intragenic deletion within the p53 deoxyribonucleic acid binding domain is uncommon in sporadic tumors but would be entirely consistent with misrepair of a radiation-induced double-strand deoxyribonucleic acid break in this case.

CONCLUSION

This is the first case in which a causative underlying genetic event has been identified in a radiation-induced glioblastoma. We infer that mutation of one p53 allele occurred at the time of radiotherapy, and the sudden appearance of the tumor 10 years later occurred after loss of the remaining wild-type allele and/or other genetic alterations, such as chromosome 10 loss and epidermal growth factor receptor gene amplification.