A simple p53 functional assay for screening cell lines, blood, and tumors

Tumor suppressor activity of AP2alpha mediated through a direct interaction with p53

The AP2 transcription factor family is a set of developmentally regulated, retinoic acid inducible genes composed of four related factors, AP2alpha, AP2beta, AP2gamma, and AP2delta. AP2 factors orchestrate a variety of cell processes including apoptosis, cell growth, and tissue differentiation during embryogenesis. In studies of primary malignancies, AP2alpha has been shown to function as a tumor suppressor in breast cancer, colon cancer, and malignant melanoma. In cell culture models, overexpression of AP2alpha inhibits cell division and stable colony formation, whereas, a dominant-negative AP2alpha mutant increases invasiveness and tumorigenicity. Here we show that AP2alpha targets the p53 tumor suppressor protein. Studies with chromatin immunoprecipitation demonstrate that AP2alpha is brought to p53 binding sites in p53-regulated promoters. The interaction between AP2alpha and p53 augments p53-mediated transcriptional activation, which results in up-regulation of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1). AP2alpha is able to induce G(1) and G(2) cell cycle arrest only in the presence of wild-type p53. Thus, we conclude that the tumor suppressor activity of AP2alpha is mediated through a direct interaction with p53. These results also provide a mechanism to explain patterns of gene expression in cancers where AP2alpha is known to function as a tumor suppressor.

Prognostic value of TP53 transcriptional activity on p21 and bax in patients with esophageal squamous cell carcinomas treated by definitive chemoradiotherapy

PURPOSE

The aim of this study was to evaluate biologic factors on survival and clinical response after definitive concomitant chemoradiotherapy (CRT) in patients with esophageal squamous cell carcinoma (ESCC).

METHODS AND MATERIALS

TP53 protein hyperexpression (immunochemistry [IHC]) and functional assay (FA) of TP53, measuring the ability of TP53 to transactivate p21 and bax reporter systems, were performed in patients with ESCC treated by CRT. The impact of parameters studied on survival and clinical response to CRT was assessed.

RESULTS

Thirty-eight patients with ESCC were included. TP53 alterations were detected in 84.2% of cases with FA. All TP53 mutations abolished the transactivation of p21 and bax reporter systems. After CRT, complete response rate was 55.3%. The median survival of the population was 17.5 months. Serum albumin (p = 0.002), weight loss <10% (p = 0.005), and response to treatment (p < 0.001) were significantly linked with survival. TP53 alteration in FA was not significantly predictive of response to CRT (p = 0.132) nor survival (p = 0.154).

CONCLUSIONS

Our results suggest that wild-type TP53 in ESCC could be associated with good response to definitive CRT. However, the small rate of ESCC with wild-type TP53 suggests that systematic determination of TP53 status is not appropriate for the management of the ESCC population.

Increased incidence of ERBB2 overexpression and TP53 mutation in inflammatory breast cancer

Inflammatory breast cancer (IBC) is one of the most aggressive forms of breast cancer. We studied the biological characteristics of these tumours by comparing the overexpression of oncogenes ERBB2, MYC, CCND1 and RHOC and TP53 gene mutation rates in IBC with those found in locally advanced and not otherwise specified breast cancers. The prevalence of the TP53 mutation was much higher in IBC than in the two other types of cancer (57% vs 30). Unexpectedly, however, in IBC tumours, histological grade was independent of TP53 status. In addition, ERBB2 overexpression was twice as frequent in inflammatory as in non-inflammatory tumours, whereas the frequencies of MYC, CCND1 and RHOC overexpression did not vary significantly among the three types of breast cancer. These findings suggest that IBC tumours constitute a distinct subset with a specific pathogenesis. Given the importance of TP53 and ERBB2 in the response to treatments, our observations have important therapeutic implications for the clinical management of IBC patients.

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.

Effect of mutated TP53 on response of advanced breast cancers to high-dose chemotherapy

TP53 activation by genotoxic drugs can induce apoptosis or cell-cycle arrest. Thus, whether the gene is mutated or wild type could affect the response of a tumour to chemotherapy. Clinical data are unclear, possibly as a result of heterogeneity of tumours, drugs, methods of assessing response, or TP53 status. We studied 50 non-inflammatory, locally advanced breast cancers that had been treated with high doses of a combination of epirubicin and cyclophosphamide. We noted eight complete responses, which all occurred in the 14 patients with tumours containing mutated TP53 (p<0.0001). In high-grade, advanced breast cancers, inactivation of the TP53 pathway could greatly improve the response to this chemotherapy regimen.

High sensitivity of detection of TP53 somatic mutations by fluorescence-assisted mismatch analysis

We analyzed exons 5-9 of the TP53 gene in 41 breast cancers using direct sequencing, PCR-SSCP (single-strand conformation polymorphism), and fluorescence-assisted mismatch analysis (FAMA), to test the level of specificity and sensitivity of each method. A major issue for the correct detection of TP53 somatic mutations in primary tumors is often represented by the large amount of normal DNA, which can cause excessive dilution of the mutant allele, with consequent possible false-negative results. High sensitivity upon dilution of the mutant allele has been demonstrated for FAMA, a method based on the chemical cleavage of a mismatch within heteroduplex DNA molecules. Exons 5-9 of the TP53 gene were analyzed by FAMA using only two long bifluorescent fragments. Differences in sensitivity, accuracy, and specificity were observed among the above-mentioned procedures. Thirteen of the 41 samples (31.7%) revealed TP53 genetic alterations by automated sequencing, 19 samples (46.3%) were positive for SSCP, whereas 14 samples (34%) showed variants detectable by FAMA. Seven samples were positive in SSCP, but negative in both FAMA and sequencing assays; however, 2 SSCP-negative samples revealed evident signals by FAMA, indicating the presence of TP53 mutations. One of the latter samples showed the alteration by sequence analysis, whereas the other failed to reveal the mutation signal even by sequencing, as a consequence of the very small amount of the mutant allele resulting from the excess of contaminating normal DNA. Our results show that FAMA may represent a suitable and accurate assay for the routine diagnosis of TP53 somatic mutations in DNAs from solid tumor biopsies.

Bax, Bcl-2, and p53 expression in endometrial cancer

BACKGROUND

It has not been fully clarified whether alteration of Bax and other apoptosis-relating proteins of Bcl-2 and p53 is involved in endometrial carcinogenesis.

METHODS

A total of 56 frozen tissues, which included 14 normal endometria, 13 endometrial hyperplasias (10 without atypia and 3 with atypia), and 29 endometrial carcinomas, were examined for the expression of Bax, Bcl-2, and p53 using immunohistochemistry. For Bax-negative cases, PCR-direct sequencing was performed for the bax gene. For cases with p53 overexpression, mutational analysis was performed for the p53 gene using a yeast functional assay and sequencing.

RESULTS

Both Bax and Bcl-2 were distinctly expressed in the normal proliferative phase endometrium. A decreased Bcl-2/Bax ratio in the secretory phase endometrial gland cells due to suppressed Bcl-2 expression was observed. Bax expression was positive in all 13 endometrial hyperplasias, while it was absent in 6 of 29 endometrial carcinomas (20.7%). Negative Bax expression in endometrial carcinoma was not related to tumor stage, histologic subtype, or other histopathologic prognostic factors. Bax expression showed no relationship to either p53 overexpression or Bcl-2 expression. In the DNA of 6 Bax-negative cases, we found a frameshift insertion mutation at codon 58 (AAG to CAAG) in the BH3 domain despite the absence of mutation in the (G)8 tract, suggesting that this codon may be another preferred target for bax mutation other than the (G)8 tract. Mutational analysis was available for 7 of 10 cases with p53 overexpression, in which 5 cases were found to have a missense mutation and 2 cases had no mutation of the p53 gene. At least 10 of 29 (34.5%) cases of endometrial carcinoma were associated with sequence-verified mutation in the bax gene and/or p53 gene.

CONCLUSIONS

The bax gene frameshift mutation appears to cause a loss of Bax expression in endometrial carcinoma. Codon 58 may be a preferred target of bax gene mutation in endometrial carcinomas. The bax gene mutation seems to occur in the early stage of the genesis of a subset of endometrial carcinomas.

A novel p53 mutational hotspot in skin tumors from UV-irradiated Xpc mutant mice alters transactivation functions

A mutation in codon 122 of the mouse p53 gene resulting in a T to L amino acid substitution (T122-->L) is frequently associated with skin cancer in UV-irradiated mice that are both homozygous mutant for the nucleotide excision repair (NER) gene Xpc (Xpc(-/-)) and hemizygous mutant for the p53 gene. We investigated the functional consequences of the mouse T122-->L mutation when expressed either in mammalian cells or in the yeast Saccharomyces cerevisiae. Similar to a non-functional allele, high expression of the T122-->L allele in p53(-/-) mouse embryo fibroblasts and human Saos-2 cells failed to suppress growth. However, the T122-->L mutant p53 showed wild-type transactivation levels with Bax and MDM2 promoters when expressed in either cell type and retained transactivation of the p21 and the c-Fos promoters in one cell line. Using a recently developed rheostatable p53 induction system in yeast we assessed the T122-->L transactivation capacity at low levels of protein expression using 12 different p53 response elements (REs). Compared to wild-type p53 the T122-->L protein manifested an unusual transactivation pattern comprising reduced and enhanced activity with specific REs. The high incidence of the T122-->L mutant allele in the Xpc(-/-) background suggests that both genetic and epigenetic conditions may facilitate the emergence of particular functional p53 mutations. Furthermore, the approach that we have taken also provides for the dissection of functions that may be retained in many p53 tumor alleles.

Influences of base excision repair defects on the lethality and mutagenicity induced by Me-lex, a sequence-selective N3-adenine methylating agent

Due to its minor groove selectivity, Me-lex preferentially generates N3-methyladenine (3-MeA) adducts in double-stranded DNA. We undertook a genetic approach in yeast to establish the influence of base excision repair (BER) defects on the processing of Me-lex lesions on plasmid DNA that harbors the p53 cDNA as target. We constructed a panel of isogenic strains containing a reporter gene to test p53 function and the following gene deletions: deltamag1, deltaapn1apn2, and deltaapn1apn2mag1. When compared with the wild-type strain, a decrease in survival was observed in deltamag1, deltaapn1apn2, and deltaapn1apn2mag1. The Me-lex-induced mutation frequency increased in the following order: wild type < deltamag1< deltaapn1apn2 = deltaapn1apn2mag1. A total of 77 mutants (23 in wild type, 31 in deltamag1, and 23 in deltaapn1apn2) were sequenced. Eighty-one independent mutations (24 in wild type, 34 in deltamag1, and 23 in deltaapn1apn2) were detected. The majority of base pair substitutions were AT-targeted in all strains (14/23, 61% in wild type; 20/34, 59%, in deltamag1; and 14/23, 61%, in deltaapn1apn2). The Mag1 deletion was associated with a significant decrease of GC > AT transitions when compared with both the wild-type and the AP endonuclease mutants. This is the first time that the impact of Mag1 and/or AP endonuclease defects on the mutational spectra caused by 3-MeA has been determined. The results suggest that 3-MeA is critical for Me-lex cytotoxicity and that its mutagenicity is slightly elevated in the absence of Mag1 glycosylase activity but significantly higher in the absence of AP endonuclease activity.

Targeted expression of oncogenic K-ras in intestinal epithelium causes spontaneous tumorigenesis in mice

BACKGROUND & AIMS

Ras oncoproteins are mutated in about 50% of human colorectal cancers, but their precise role in tumor initiation or progression is still unclear.

METHODS

This study presents transgenic mice that express K-ras(V12G), the most frequent oncogenic mutation in human tumors, under control of the murine villin promoter in epithelial cells of the large and small intestine.

RESULTS

More than 80% of the transgenic animals displayed single or multiple intestinal lesions, ranging from aberrant crypt foci (ACF) to invasive adenocarcinomas. Expression of K-ras(V12G) caused activation of the MAP kinase cascade, and the tumors were frequently characterized by deregulated cellular proliferation. Unexpectedly, we obtained no evidence of inactivating mutations of the tumor suppressor gene Apc, the "gatekeeper" in colonic epithelial proliferation. However, spontaneous mutation of the tumor-suppressor gene p53, a frequent feature in the human disease, was found in 3 of 7 tumors that were tested.

CONCLUSIONS

This animal model recapitulates the stages of tumor progression as well as a part of the genetic alterations found in human colorectal cancer. Furthermore, it indicates that activation of K-ras in concert with mutations in p53 may constitute a route to digestive tumor formation and growth, underlining the fact that the pathway to intestinal cancer is not necessarily a single road.

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).

Investigations on a clinically and functionally unusual and novel germline p53 mutation

This report describes an individual with a rare choroid plexus papilloma in adulthood (age 29) after earlier having an osteosarcoma (age 22). The results from this study, and others, suggest that it may be advisable to consider the possibility of a germline p53 mutation in adults presenting with choroid plexus tumours. In the current study automated DNA sequencing of genomic DNA detected a novel germline 7 base pair insertion in exon 5 of the p53 gene in this patient. The alteration in frame would produce amino acid substitutions beginning with alanine to glycine at position 161 and a stop codon at position 182 in the mutated protein. Surprisingly two assays of p53 function gave apparently wild-type results on peripheral blood lymphocytes from this individual. These results led us to carry out more detailed functional tests on the mutant protein. The mutant allele was expressed either at very low levels or not at all in phytohaemagglutinin stimulated lymphocytes. Further, the mutant protein was completely non-functional in terms of its ability to transactivate a series of p53-responsive genes (p21(WAF1), bax, PIG3), to transrepress a target gene and to inhibit colony growth in transfected Saos-2 cells. However, surprisingly, data from irradiated peripheral blood lymphocytes and transfected Saos-2 cells, suggested that this truncated, mutant protein retains significant ability to induce apoptosis.

Antiviral agent Cidofovir restores p53 function and enhances the radiosensitivity in HPV-associated cancers

High-risk human papillomaviruses (HPVs) have been associated to the development of cervical and some other human cancers. Most of them express E6 and E7 oncoproteins, able to bind to p53 and retinoblastoma (pRb) tumor suppressor proteins respectively and neutralize their function. Restoration of these pathways by blocking E6 and E7 expression would provide a selective therapeutic effect. Here, we show that a clinically approved antiviral agent Cidofovir reduced E6 and E7 expression in cervical carcinoma Me180 and head and neck squamous cell carcinoma HEP2 cells at the transcriptional level. Cidofovir induced the accumulation of active p53 and pRb associated to induction of cyclin dependent kinase inhibitor p21(WAF1/CIP1) in Me180 and HEP2 cells. p53 induction was also shown in Hela HPV-positive cervical carcinoma cell line. In addition, S phase cell cycle accumulation with concomitant decrease of cyclin A expression were associated to the antiproliferative activity of Cidofovir in HPV-treated cells. Combining Cidofovir to irradiation both in vivo and in nude mice xenografts resulted in a marked radiosensitization in HPV-positive cells, which was not observed in virus negative cells. This study provides the basis for a new anticancer strategy to enhance the antitumor effect of ionizing radiation in HPV-related cancers, without increase deleterious effects.

Complex functions of mutant p53 alleles from human prostate cancer

BACKGROUND

Few studies have used multiple assays to examine the functionality of mutant p53 in prostate cancer (CaP). We employed seven functional assays to study 16 representative mutant p53 alleles, six from localized and ten from metastatic CaP.

METHODS

Yeast assays were employed to determine loss of function (LOF), partial function (PF), and dominant-negative status. Assays using p53-null Saos2 cells were used to determine whether mammalian cells transfected with mutant p53 could up-regulate the MDR-1 or PCNA promoters, alter IL-6 expression or confer the ability to grow in soft agar. As a further test of gain of function (GOF), p53-null PC3 cells stably transfected with these mutant p53 alleles were examined for cell cycle distributions.

RESULTS

All 16 mutant p53 alleles demonstrated either total or partial LOF. All but one allele also had at least one gain of function; however, the pattern of GOF was different for each mutant allele. Alleles derived from both localized and metastatic CaP had similar GOF characteristics; however, only alleles from metastatic disease had significantly increased S-phase fractions.

CONCLUSIONS

Different mutant p53 alleles from CaP had different, complex functional profiles. The lack of predictable patterns for these alleles suggest that each mutation may uniquely affect p53 function.

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.

Wild-type p53 induced sensitization of mutant p53 TNF-resistant cells: role of caspase-8 and mitochondria

In the present study, we have investigated the mechanisms by which the restoration of wild-type (wt) p53 functions in p53 mutant cells increases their susceptibility to the cytotoxic action of tumor necrosis factor (TNF). Our data indicate that the resistance of p53-mutated cl.1001 cells to TNF-induced cell death was not due to a defect in the expression of TRADD and FADD, yet correlated with a reduced caspase-8 activation as well as a deficient mitochondrial membrane permeabilization. Moreover, cl.1001 cells failed to translocate the mitochondrial AIF and cytochrome c to the nucleus and to the cytosol, respectively, in response to TNF. Sensitization of these cells, following infection with a recombinant adenovirus encoding wtp53, to TNF-induced cytotoxicity resulted in the restoration of caspase-8 cleavage and the reestablishment of mitochondrial signs of apoptosis. These findings suggest that the cross-talk between p53 and TNF-induced cell death depends on mitochondria and that the combination of TNF and Adwtp53 may be a potential strategy to sensitize mutant p53 TNF-resistant tumors to the cytotoxic action of this cytokine.

Determination of optimal conditions for analysis of p53 status in leukemic cells using functional analysis of separated alleles in yeast

Tumor suppressor p53 is transcription factor that participates in control of many cellular functions. Somatic mutations of the p53 gene are frequently detected in human cancers. Several methods can be used for identification of p53 mutations, including FASAY - functional analysis of separated alleles in yeast. FASAY distinguishes yeast colonies expressing functional p53 protein from colonies producing a dysfunctional p53 protein simply on the basis of color. The validity of the method depends on a low background level. There are several sources of background as PCR-induced point mutations, low quality of RNA and alternative splicing of intron 9 affecting the p53 carboxy-terminus. In the present work we show that FASAY can be successfully used for analysis of mRNA isolated from blood samples that were collected and stored for 24 hours at 0 degrees C without undesired increase of background. We also measured fidelity of several commonly used DNA polymerases and determined the most suitable kinds of Pfu DNA polymerases for FASAY. Reaction conditions described in this report allow routine analysis of p53 status in leukemic cells using FASAY.

The Li-Fraumeni syndrome

Li-Fraumeni syndrome (LFS) has been the most common terminology used for the syndrome. It is a rare familial dominantly inherited cancer syndrome characterized by a wide spectrum of neoplasms occurring in children and young adults. The canonical definition of LFS includes a proband diagnosed with sarcoma before 45 years of age, a first-degree relative with cancer before this same age and another first- or second-degree relative in the lineage with any cancer before this age or sarcoma at any age. Multiple studies have reported p53 germline mutations in LFS families in various parts of the world. As in sporadic tumors, loss of heterozygosity leading to the inactivation of the wild-type allele by deletion or mutation is observed in LFS tumors. Cancer-risk in mutation carriers has been estimated to be 73% in males and nearly 100% in females, the difference almost entirely explained by breast cancer. The identification of germline p53 mutations in rare cancer-prone families has given rise to the medical, counseling, psychological and ethical problems.

p53 functional assays: detecting p53 mutations in both the germline and in sporadic tumours

The tumour suppressor gene p53 is the gene most often reported to be mutated in clinical cancers with something like half of all tumours harbouring mutations. Further, many studies have suggested that p53 mutations have prognostic importance and sometimes are a significant factor in determining the response of tumours to therapy. The value of knowing the p53 status of individual tumours will increase if currently researched strategies aimed at developing p53-based treatment protocols come to fruition. There are quite a number of techniques used to detect p53 defects in both tumours and in the germline of cancer-prone families, although some of these methods are indirect and each has certain drawbacks. In this brief review we will discuss the value of two assays of p53 function as a means of detecting and partly characterizing p53 mutations. The two assays are the apoptotic assay, which measures the response of peripheral blood lymphocytes to radiation-induced DNA damage and the FASAY, a yeast based assay which assesses the ability of a given p53 protein to transactivate p53 target genes. Both of these assays are rapid, yielding results within 5 days. Further, they not only offer the possibility of detecting p53 mutations but also of characterizing a given mutation in terms of two of p53's most important functions, namely the induction of apoptosis and the transactivation of target genes.

Dominant-negative mutation of p53 tumor suppressor gene in endometrial carcinoma

BACKGROUND

It has been suggested that mutation of the TP53 tumor suppressor gene is involved in endometrial carcinogenesis. However, the status of p53 function in endometrial cancers has not yet been investigated in detail.

METHODS

We surveyed inactivating p53 mutations in endometrial carcinomas using the yeast p53 functional assay, which can evaluate the transcriptional activity of p53 in vivo in yeast. To the detected p53 mutants, we also applied a transdominance assay, which assesses the dominant-negative property of mutants.

RESULTS

Of 23 endometrial carcinomas, 9 tumors (39.1%) were found to harbor p53 mutations. Only 1 of the 6 mutants in 18 endometrioid-type tumors showed dominant-negative capacity. In contrast to the endometrioid-type tumor, all 3 mutations in 5 serous-type tumors (R273H, 9-bp deletion in codons 240-243, and R248W) showed dominant-negative capacity and presented in a homozygous state in the tumors, indicating a complete functional inactivation.

CONCLUSIONS

Although this study included a relatively small number of cases and therefore is a preliminary study, these results suggest that the dominant-negative mutation of the TP53 gene is related to serous adenocarcinoma. The role of the dominant-negative status of p53 mutants in endometrial carcinogenesis and progression of this disease should be further investigated.

Loss of MDM2 expression in human head and neck squamous cell carcinomas and clinical significance

The transforming potential of the MDM2 oncogene has been attributed to the overproduction of the protein. In order to investigate regulation of MDM2 expression in head and neck squamous cell carcinomas, we analysed MDM2 gene amplification, and mRNA and protein expression in tumour specimens from 62 patients, in cell lines, and in normal epithelium adjacent to tumours or obtained from healthy patients. Additionally, TP53-induced MDM2-P2 transcription was evaluated and compared with TP53 status. MDM2 gene amplification and mRNA over-expression is infrequent, 7 and 9%, respectively. The predominant transcript codes for full-length MDM2 protein (90kD) and the level of alternatively spliced forms is not significant. We show that only 47% of tumours exhibit MDM2 immunostaining in more than one third of the neoplastic cells, and thus more than half of the tumours display no or low levels of MDM2 protein. In contrast, MDM2 protein is always detectable in basal and parabasal cells of morphologically normal epithelium outside the invasively growing tumour, as well as in a normal uvula sample. Similarly, the total amount of MDM2 transcripts analysed by reverse transcriptase-polymerase chain reaction is reduced in tumour samples compared to normal tissues, essentially due to a decrease in P2 transcript levels. The relationship between mutated p53 status and low levels of MDM2 found in cell lines is also observed to a certain extent in primary tumour samples. Overall, there is a high frequency of TP53 mutation and under-expression of MDM2 in the head and neck tumours. Moreover, a significant association of decreased MDM2 expression is observed with advanced tumour stage and 3 years survival.

Prognostic molecular markers in non-small cell lung cancer

Although TNM stage is the most significant prognostic parameter in lung cancer, additional parameters are required for explaining variability of survival. Hence molecular alterations in lung cancer have been extensively studied. Most prominent among them are alterations in the p53-p21 pathway, controlling the G1/S transition. They are the most commonly observed aberrations in non-small cell lung cancer (NSCLC). The results of p53 mutations on an individual patient's changes for survival are rather controversial. In a recent study however, after analyzing p53 abnormalities both by direct sequencing and immunohistochemistry together with evaluation of bcl-2 protein expression, we have found that p53 alterations were significantly associated with poor overall survival. Recently, a more sensitive yeast functional assay for altered p53 protein has been developed, with about 70% positivity in NSCLC patients and a correlation with shortened survival. The clinical significance of p21WAF1, the protein encoded by the target gene of p53 transcription, is still controversial; however expression has been associated with favorable prognosis in squamous cell carcinoma type. The 'Rb pathway' involving two oncogenes (cyclins D and E) and two tumor suppressor genes (Rb and p16) represents another major source of molecular alterations in lung cancer. Loss of Rb does not seem to significantly influence prognosis, white loss of p16 has been show repeatedly to be a factor for poor survival. Hypermethylation of the promoter region has been proposed as an alternative mechanism for inactivation of the p16 gene. The relation between cyclin D and E expression and prognosis, still is matter of controversy. Ras mutations are reported especially in adenocarcinoma; considered alone they bear no clear relation with prognosis, in opposition when considering them together with other molecular alterations. As a conclusion, a variety of molecular markers have been implicated in the prognosis of NSCLC. However, conflicting results were reported in the literature. Thus further investigations will be required, especially the use of newer molecular assays and the development of appropriate markers or panels of molecular markers.

Differential p53 protein expression in breast cancer fine needle aspirates: the potential for in vivo monitoring

Fine needle aspiration (FNA) biopsy is the least invasive method of sampling breast cancer in vivo and provides material for breast cancer diagnosis. FNA has also been used to examine cellular markers to predict and monitor the effects of therapy. The aim of this study was to assess the accuracy of using FNA material compared with resected cancer for Western blotting studies of the p53 pathway, a key to tumour response to radiotherapy and chemotherapy. Paired samples of breast cancer FNAs collected pre-operatively and post-operatively were compared with tissue samples obtained at the time of surgical resection. Western blots were probed for p53 using the antibodies DO12 and DO1, and for levels of downstream proteins p21/WAF1 and p27. The protein extracted by FNA was sufficient for up to 5 Western blot studies. p53 expression and phosphorylation did not differ significantly pre- and post-operatively, indicating that intra-operative manipulation does not affect p53 expression or downstream activation in breast cancer. However, expression of p53, p21 and p27 varied between individual patients suggesting a range of p53 pathway activation in breast cancer. Immunohistochemistry confirmed that the cancer cells accounted for the protein expression detected on Western blots. FNA yields adequate protein for Western blotting studies and could be used as a method to monitor p53 activity in vivo before and during anti-cancer treatment possibly providing early evidence of tumour response to therapy.

Development of a yeast stop codon assay readily and generally applicable to human genes

We established a yeast-based method to screen chain-terminating mutations that is readily applicable to any gene of interest. Based on the finding that 18- to 24-base-long homologous sequences are sufficient for gap repair in vivo in yeast, we used a strategy to amplify a test-gene fragment with addition of 24-bp sequences homologous to both cut-ends of a yeast expression vector, pMT18. After co-transformation with the amplified fragment and the linearized pMT18, each yeast (Saccharomyces cerevisiae) cell automatically forms a single-copy circular plasmid (because of CEN/ARS), which expresses a test-gene::ADE2 chimera protein. When the reading frame of the test-gene contains a nonsense or frameshift mutation, truncation of the chimera protein results in lack of ADE2 activity, leading to formation of a red colony. By using a nested polymerase chain reaction using proofreading Pfu polymerase to ensure specificity of the product, the assay achieved a low background (false positivity). We applied the assay to BRCA1, APC, hMSH6, and E-cadherin genes, and successfully detected mutations in mRNA and genomic DNA. Because this method--universal stop codon assay--requires only 4 to 5 days to screen a number of samples for any target gene, it may serve as a high-throughput screening system of general utility for chain-terminating mutations that are most prevalent in human genetic diseases.

Induction of apoptosis in melanoma cell lines by p53 and its related proteins

Melanoma cells rarely contain mutant p53 and hardly undergo apoptosis by wild-type p53. By using recombinant adenoviruses that express p53 or p53-related p51A or p73beta, we tested their apoptotic activities in melanoma cells. Yeast functional assay revealed a mutation of p53 at the 258th codon (AAA [K] instead of GAA [E]) in one cell line, 70W, out of six human melanoma cell lines analyzed (SK-mel-23, SK-mel-24, SK-mel-118, TXM18, 70W, and G361). Adenovirus-mediated transfer of p53, p51A, and/or p73beta suppressed growth and induced apoptotic DNA fragmentation of SK-mel-23, SK-mel-118, and 70W cells. Interestingly, p51A induced DNA fragmentation in them more significantly than p53 and p73beta. By Western blotting we analyzed levels of apoptosis-related proteins in cells expressing p53 family members. Apoptotic Bax and antiapoptotic Bcl-2 were not significantly upregulated or downregulated by expression of p53, p51A, or p73beta, except for p53-expressing 70W cells, which contained a larger amount of Bax protein than LacZ-expressing cells. Activation of caspase-3 was demonstrated only in p51A-expressing SK-mel-118 cells. We show here that p51A can mediate apoptosis in both wild-type and mutant p53-expressing melanoma cells more significantly than p53 and p73beta. It is also suggested that in melanoma cells (i) cellular target protein(s) other than Bcl-2 and Bax might be responsible for induction of p51A-mediated apoptosis and (ii) caspase-3 is not always involved in the apoptosis by p53 family members.

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.

Different p16INK4a and p14ARF expression patterns in acute myeloid leukaemia and normal blood leukocytes

The p16INK4a gene is often disrupted or transcriptionally silenced by CpG island methylation in human cancers. However, in acute myeloid leukaemia (AML) alterations of the INK4a-ARF tumour suppressor locus are rarely found despite the noted variable p16INK4a mRNA and protein levels. The p14ARF, an alternative reading frame protein encoded from the same INK4a-ARF locus, is a potent tumour suppressor functionally linked to p53. There is little known regarding the role of p14ARF in primary human tumours. Therefore, we analysed the expression patterns of these two tumour suppressors in 37 cases of AML. The relative expression of p16INK4a and p14ARF mRNA in AML blasts, measured by a specific p16INK4a/p14ARF multiplex RT-PCR, was significantly shifted towards p14ARF whereas relatively lower levels of p16INK4a were detected. Quantitative RT-PCR revealed significantly higher expression of both transcripts in AML blasts when compared to normal differentiated myeloid cells or CD34+ progenitor cells. Furthermore, a good correlation between p16INK4a protein and mRNA was observed, whereas no correlation was found with p14ARF. Our results suggest: a) increased levels of both p16INK4a and p14ARF may participate in the pathogenesis of AML, b) that high p14ARF mRNA expression might influence p16INK4a transcription and c) that post-transcriptional regulatory mechanisms are important for p14ARF expression.

Two metachronous tumors in the radiotherapy fields of a patient with Li-Fraumeni syndrome

A woman with a family history of brain tumors in her daughter and sister presented with a breast cancer. She subsequently developed two metachronous primary tumors: a small-cell lung cancer and a colon carcinoma. These tumors arose within the internal mammary radiotherapy field and within the field irradiated for ovariolysis. The p53 gene was analyzed in whole blood lymphocytes using a functional assay developed in yeast Saccharomyces cerevisiae, which tests the transcriptional competence of p53. DNA from the colon cancer cells was analyzed by polymerase chain reaction and sequencing. The patient had a germline-inactivating p53 mutation, confirming the diagnosis of Li-Fraumeni syndrome (LFS). The colon tumor and the lung tumor both conserved the mutant p53 allele but had lost the wild-type allele. This observation and the experimental data suggest an abnormal sensitivity of LFS patients to radiogenic carcinogenesis. The indications and extent of radiotherapy in patients with a clinical or molecular diagnosis of LFS should be discussed individually and should take into account the risk of secondary neoplasms arising in the radiation fields.

p73 is not mutated in meningiomas as determined with a functional yeast assay but p73 expression increases with tumor grade

The p53 gene is normally wild type in meningiomas. Since all three members of the p53 gene family recognize the same DNA sequence, tumors containing wild type p53 could decrease transactivation of p53 target genes by mutating either p63 or p73. In meningiomas the most likely target is p73, because loss of heterozygosity of the chromosomal band containing p73 is the commonest genetic lesion in these tumors. To screen p73 for mutations we have developed a functional assay which tests the ability of p73 to activate transcription from a p53-responsive promoter in yeast. The assay correctly identified p73 mutants with mutations equivalent to hotspot mutations in p53, demonstrating that the assay can detect transcriptionally inactive p73. No mutations in p73 were identified in meningiomas. p73 RNA level was higher in more advanced tumors, but there was no correlation between the expression level of p73 and p21, a known p53 target gene. The yeast assay was also used to measure the intrinsic sensitivity of the p73 protein to mutagenesis. Like p53, p73 is exceptionally easy to inactivate as a transcription factor by point mutation. Taken together, these results indicate that p53 and p73 serve very different functions in tumors.

p53 mutants can often transactivate promoters containing a p21 but not Bax or PIG3 responsive elements

The human p53 protein acts mainly as a stress inducible transcription factor transactivating several genes involved in cell cycle arrest (e.g. p21) or apoptosis (e.g. Bax, PIG3). Roughly half of all human tumours contains p53 missense mutations. Virtually all tumour-derived p53 mutants are unable to activate Bax transcription but some retain the ability to activate p21 transcription. Identification of these mutants may have valuable clinical implications. We have determined the transactivation ability of 77 p53 mutants using reporter yeast strains containing a p53-regulated ADE2 gene whose promoter is regulated by p53 responsive elements derived from the regulatory region of the p21, Bax and PIG3 genes. We also assessed the influence of temperature on transactivation. Our results indicate that a significant proportion of mutants [16/77 (21%); 10/64 (16%) considering only tumour-derived mutants] are transcriptionally active, especially with the p21 promoter. Discriminant mutants preferentially affect less conserved (P<0.04, Fisher's exact test), more rarely mutated (P<0.006, Fisher's exact test) amino acids. Temperature sensitivity is frequently observed, but is more common among discriminant than non-discriminant mutants (P<0.003, Fisher's exact test). Finally, we extended the analysis to a group of mutants isolated in BRCA-associated tumours that surprisingly were indistinguishable from wild type in standard transcription, growth suppression and apoptosis assays in human cells, but showed gain of function in transformation assays. The incidence of transcriptionally active mutations among this group was significantly higher than in the panel of mutants studied previously (P<0.001, Fisher's exact test). Since it is not possible to predict the behaviour of a mutant from first principles, we propose that the yeast assay be used to compile a functional p53 database and fill the gap between the biophysical, pharmacological and clinical fields.

Amifostine (WR2721) restores transcriptional activity of specific p53 mutant proteins in a yeast functional assay

Many p53 mutants found in human cancer have an altered ability to bind DNA and transactivate gene expression. Re-expression of functional p53 in cells in which the endogenous TP53 gene is inactivated has been demonstrated to restore a non-tumorigenic phenotype. Pharmacological modulation of p53 mutant conformation may therefore represent a mechanism to reactivate p53 function and consequently improve response to radio- and chemotherapy. We have recently reported that the radio- and chemoprotector Amifostine (WR2721, Ethyol) activates wild-type p53 in cultured mammalian cells. In the present study, we have used a yeast functional assay to investigate the effect of WR2721 on the transcriptional activity of p53. WR2721 restored this activity in a temperature-sensitive mutant V272M (valine to methionine at codon 272) expressed at the non-permissive temperature and it also partially restored the transcriptional activity of several other conformationally flexible p53 mutants. The results indicate that the yeast functional assay may be used to identify compounds that modulate p53 activity, with potential therapeutic implications.

Novel human p53 mutations that are toxic to yeast can enhance transactivation of specific promoters and reactivate tumor p53 mutants

Since highly expressed human p53 can inhibit human and yeast cell growth, we predicted that p53 mutants could be generated with increased growth inhibition of the yeast Saccharomyces cerevisiae and that these would be useful for characterizing p53 functions and tumor p53 mutants. A random mutagenesis screen led to the isolation of mutations in the DNA binding domain that result in p53 being lethal even at moderate expression levels in yeast. Three independent mutants had an alanine change at the evolutionary invariant V122 in the L1 loop. The other toxic mutations affected codons 277 (C277R, C277W) and 279 (G279R). This latter amino acid change was also reported in tumors, while all the other mutations are novel. A recently developed rheostatable GALI promoter system that provides graded increases in expression of p53 was used to examine the transactivation function of the toxic mutations when expression was greatly reduced and cells were viable. At low expression levels the toxic mutants lacked transactivation from a 3xRGC responsive element (RE). Surprisingly some exhibited enhanced transactivation with p21 and bax REs. The V122A mutant was able to re-activate transactivation of various p53 tumor mutants and retained growth inhibition when co-expressed with dominant-negative tumor mutations. Upon expression in human Saos-2 cells the V122A p53 mutant caused growth suppression, was capable of transactivation and exhibited higher than wild type activity with the bax promoter in luciferase assays. A non-functional p53 tumor mutant was partially reactivated by V122A for both transactivation and growth suppression. Thus, the screen for toxic p53 mutants in yeast can identify novel p53 variants that may be useful in dissecting p53 regulated cellular responses and in developing p53-based cancer therapies.

Apoptosis-related gene and protein expression in human lymphoma xenografts (Raji) after low dose rate radiation using 67Cu-2IT-BAT-Lym-1 radioimmunotherapy

Despite low radiation dose rates, radioimmunotherapy (RIT) has proven particularly effective in the treatment of malignancies, such as lymphoma. Apoptosis has been suggested to be a major mechanism for cell death from continuous low-dose rate radiation from radioimmunotherapy. The goal of this study was to examine Raji lymphoma xenografts for induction of apoptosis and modulation of apoptosis-related gene and protein expression in response to 67Cu-2IT-BAT-Lym-1 RIT. In preclinical and clinical trials, 67Cu-2IT-BAT-Lym-1 has shown an exceptionally long tumor residence time associated with substantial cumulated radiation doses. The Raji model mirrors human lymphomas that have mutant p53 and increased BCL2 expression. Untreated athymic BALB/c nu/nu mice and mice treated with 400 micrograms Lym-1, or 335-500 microCi 67Cu on less than 400 micrograms Lym-1 antibody, were observed for toxicity and response over 84 days. Subgroups of 4-5 mice were sacrificed at 3, 6 and 24 h after therapy so that tumors could be examined for poly(ADP-ribose) polymerase (PARP) and DNA ladder evidence for apoptosis and for BCL2, p53, p21, GADD45, TGF-beta 1 and c-MYC gene and protein expression. Untreated tumors had little evidence of apoptosis and Lym-1 had no effect on apoptosis or gene expression. 67Cu-2IT-BAT-Lym-1 RIT induced an overall response rate of 50% with tolerable toxicity, and 29% of the tumors were cured at cumulated tumor radiation doses of about 1800 cGy. Apoptosis was greatly increased in the RIT treated Raji xenografts as evidenced by cleavage of PARP to the characteristic 85 kD fragment at 3 and 6 h and by the DNA cleavage pattern. BCL2 gene and protein expression were substantially decreased at 3 and 24 h, respectively, after 67Cu-2IT-BAT-Lym-1 RIT despite only modest cumulated radiation doses (56 cGy at 3 h). Evidence for apoptosis preceded tumor regression by 4-6 days. In these therapy-resistant, human lymphoma tumors treated with 67Cu-2IT-BAT-Lym-1, apoptosis was convincingly demonstrated to be a major mechanism for the effectiveness of RIT and occurred by p53-independent mechanisms.

A p53 dose-response relationship for sensitivity to DNA damage in isogenic teratocarcinoma cells

Teratocarcinomas are tumors that arise from primordial germ cells and are readily curable with DNA-damaging chemotherapeutic drugs. Teratocarcinoma cells ex vivo in tissue culture are also relatively chemosensitive and undergo apoptotic death in response to DNA damage. We have previously hypothesized that the observed sensitivity of this tumor type to DNA damage is related to high basal expression of wild-type p53 protein. We have now addressed this issue by characterizing the DNA damage response of isogenic teratocarcinoma cells that differ only in their level of expression of wild-type p53 protein. We find a clear p53 dose-response relationship in these cells for rapid apoptosis following DNA damage that correlates with diminished colony formation in clonogenic survival assays. These results suggest that strategies to increase basal wild-type p53 protein expression prior to treatment with DNA-damaging drugs may improve curability in other tumor types.

Identification of partial loss of function p53 gene mutations utilizing a yeast-based functional assay

Missense mutations within the central DNA binding region of p53 are the most prevalent mutations found in human cancer. Numerous studies indicate that 'hot-spot' p53 mutants (which comprise approximately 30% of human p53 gene mutations) are largely devoid of transcriptional activity. However, a growing body of evidence indicates that some non-hot-spot p53 mutants retain some degree of transcriptional activity in vivo, particularly against strong p53 binding sites. We have modified a previously described yeast-based p53 functional assay to readily identify such partial loss of function p53 mutants. We demonstrate the utility of this modified p53 functional assay using a diverse panel of p53 mutants.

Translational control of human p53 expression in yeast mediated by 5'-UTR-ORF structural interaction

We have expressed human p53 cDNA in the yeast Saccharomyces cerevisiae and shown that the level of production and the length of the p53 protein depends on the presence of untranslated mRNA regions (UTRs). The expression of the ORF alone leads to a p53 protein of correct size (53 kDa) that accumulates to high levels, concomitantly with the presence of a small amount of a p40 protein (40 kDa). However, when either the entire 5'-UTR and a part of the 3'- or 5'-UTR alone is used, this leads to the production of small amounts of the 40 kDa truncated form only. The p40 protein corresponds to a truncated form of p53 at the C-terminal extremity since it reacts only with a monoclonal antibody recognising the N-terminal epitope. This effect on the amount and length of p53 protein had no correlation at the mRNA level, suggesting that translational control probably occurs through the 5'-UTR. We propose a model of structural interaction between this UTR and a part of the ORF mRNA for the regulation of p53 expression in this heterologous context.

A promoter function of the CCCGGG Sma I recognition sequence and its specific role in determining p53 status and identifying DNA damaging agents

The tumour suppressor p53 protein regulates many genes involved in cellular responses to DNA damage. To date, a common transcriptionally active DNA-binding site for p53 in vivo has not been identified. The pGL3-Basic vector contains a modified fire-fly luciferase cDNA designated luc+ and is designed for studying putative regulatory sequences as it lacks any known eukaryotic promoter sequences. We report here that the CCCGGG sequence, a Sma I site, in the cloning region of the pGL3-Basic vector can promote p53-dependent transcription of the luc+ gene. We have demonstrated, by electrophoretic mobility shift assay (EMSA), that human p53 is able to bind to the CCCGGG sequence in vitro. These data provide the first demonstration that the CCCGGG sequence is a transcriptionally active DNA-binding site for p53. Thus, the pGL3-Basic vector could be used as an indicator of p53 transcriptional activity, to determine the p53 status of cell lines and to identify DNA damaging agents that initiate the activation of p53. The CCCGGG sequence has been found to be present in a number of promoter regions of p53-regulated genes. This and the present study suggest that the CCCGGG sequence may be a consensus sequence recognized by p53 in vivo and may be used to identify genes whose expression may be controlled by p53.

The role of p53 in human cancer

In the two decades since its original discovery, p53 has found a singularly prominent place in our understanding of human cancer. Although the biochemistry of p53 has been worked out in some detail, our knowledge of the biologic consequences of p53 dysfunction is still quite rudimentary. Over the next several years, it will be important to determine how best to harness the complex properties of p53's ability to induce cellular growth arrest and cell death to generate novel, effective approaches to cancer therapy. Furthermore, a clearer appreciation of the direct interaction of epigenetic factors with p53 will lead to development of strategies to inhibit tumour initiation and progression. The next decade promises to offer exciting opportunities to apply our vast knowledge of this intriguing tumor suppressor to clinical advantage.

p53 mutants exhibiting enhanced transcriptional activation and altered promoter selectivity are revealed using a sensitive, yeast-based functional assay

Changes in promoter specificity and binding affinity that may be associated with p53 mutations or post-translational modifications are useful in understanding p53 structure/function relationships and categorizing tumor mutations. We have exploited variable expression of human p53 in yeast to identify mutants with novel phenotypes that would correspond to altered promoter selectivity and affinity. The p53 cDNA regions coding for the DNA binding and tetramerization domains were subjected to random PCR mutagenesis and were cloned directly by recombination in yeast into a vector with a GAL1 promoter whose level of expression could be easily varied. p53 variants exhibiting higher than wild type levels of transactivation (supertrans) for the RGC responsive element were identified at low level of p53 protein expression. All the p53 mutants obtained with this screen were located in the DNA binding domain. Two out of 17 supertrans mutants have been found in tumors. Six mutations were in the L1 loop region between amino acids 115 and 124. The transactivation potential of a panel of supertrans p53 mutants on different promoters was evaluated using the p53 responsive elements, RGC, PIG3, p21 and bax. Although all mutants retained some activity with all promoters, we found different patterns of induction based on strength and promoter specificity. In particular none of the mutants was supertrans for the p21 responsive element. Interestingly, further analysis in yeast showed that the transactivation function could be retained even in the presence of dominant-negative p53 tumor mutations that could inhibit wild type p53. Five mutants were also characterized in human cells in terms of growth suppression and transactivation of various promoters. These novel supertrans p53 mutants may be useful in studies aimed at dissecting p53 downstream pathways, understanding specific interactions between p53 and the DNA, and could replace wild type p53 in cancer gene therapy protocols. The approach may also prove useful in identifying p53 tumor mutations.

Molecular and clinical differences between adenocarcinomas of the esophagus and of the gastric cardia

Adenocarcinoma of the esophagus (ADCE) with Barrett's mucosa and adenocarcinoma of the cardia (ADCC) are often reported as a single pathological entity. In this study we have used strict anatomical-pathological criteria to distinguish between these two lesions and we have investigated their differences in TP53 mutations, MDM2 gene amplification, and cytokeratin expression. DNA was extracted from the tumor areas of formalin-fixed, paraffin-embedded sections in 26 ADCC and 28 ADCE patients. TP53 mutations were detected by temporal temperature gradient electrophoresis and identified by sequencing. MDM2 amplification was assessed by differential polymerase chain reaction. The expression of cytokeratins 4, 7, and 13 was examined by immunohistochemistry. In ADCC, the male to female ratio was 1.8:1, compared to 27:1 in ADCE. Five ADCC patients had a history of other neoplasms, compared to only one ADCE patient. The two types of tumor differed in the prevalence of TP53 mutations (31% in ADCC and 50% in ADCE) and of MDM2 gene amplification (19% in ADCC and 4% in ADCE), and in the pattern of expression of cytokeratin 7 (positive in 100% of ADCE and in 41% of ADCC) and cytokeratin 13 (positive in 81% of ADCE and in 36.5% of ADCC). ADCE and ADCC differ in their clinical characteristics, in the prevalence of TP53 mutations and MDM2 amplifications, and in the patterns of cytokeratin expression. These results support the notion that ADCC and ADCE are distinct pathological entities.

Analysis of stepwise genetic changes in an AIDS-related Burkitt's lymphoma

In this study, immunoglobulin variable (Ig V) region genes, c-myc re-arrangement and sequence and p53 status were analyzed in clones derived from a Burkitt's lymphoma cell line (LAM) in which it was previously demonstrated that Epstein-Barr virus (EBV) infection occurred late during lymphomagenesis. Such evidence was based on the finding that 2 groups of cellular clones, characterized by the same c-myc re-arrangement but different EBV-fused termini, were obtained from the LAM cell line. The Ig V gene sequences were identical for the 2 groups of clones with different EBV-fused termini. The Ig variable heavy (V(H)) gene sequence displayed a substantial accumulation of point mutations (but no intra-clonal diversification), whereas the productive Ig V lambda (V(lambda)) gene sequence was virtually unmutated. Studies on the Ig V kappa (V(kappa)) locus suggested a receptor revision event (with a switch from kappa to lambda chain production) prior to EBV infection. Likewise, it was determined that the mutations observed in both p53 alleles and in the re-arranged c-myc gene occurred before EBV infection. Based on these findings, we present a model for the various steps of lymphomagenesis. It is proposed that stimulation by an antigen or a superantigen initially favored the clonal expansion and accumulation of other cytogenetic changes, including those involved in receptor editing. These events occurred prior to or during the germinal center (GC) phase of B-cell maturation. Thereafter, possibly upon exit of the cells from the GC, EBV infection occurred, further promoting lymphomagenesis.

Detection of PTEN nonsense mutation and psiPTEN expression in central nervous system high-grade astrocytic tumors by a yeast-based stop codon assay

We have developed a new yeast-based assay for the detection of PTEN nonsense mutation, and applied it to a total of 42 astrocytic tumors. The assay utilizes homologous recombination of PCR-amplified PTEN cDNA samples to a yeast vector which expresses an in-frame PTEN::ADE2 chimera protein. An allele of nonsense mutation in the sample PTEN mRNA gives a truncated chimera protein in a yeast cell, resulting in the formation of a red colony. The assay and subsequent sequence analysis demonstrated nonsense mutations as red colonies of more than 10% in one of 10 anaplastic astrocytomas and six of 18 glioblastomas, but none in six pilocytic astrocytomas or in eight astrocytomas. Sequence analysis of white colonies showed one missense mutation in a glioblastoma. Interestingly, four of seven nonsense mutations were frame-shifts due to exon skipping. In addition, pink colonies were found in one of six pilocytic astrocytomas, three of eight astrocytomas, two of 10 anaplastic astrocytomas, and 10 of 18 glioblastomas. Sequence analysis of the pink colonies revealed a sequence similar to those reported as psiPTEN/PTH2. By testing mRNA and genomic DNA, it was found to be a processed pseudogene which was transcribed. The psiPTEN expression was complementary to PTEN mutation, for 14 of 18 glioblastomas showed either PTEN mutation or psiPTEN expression and only one case showed both PTEN mutation and psiPTEN expression (P<0.046), suggesting a pathological role of psiPTEN expression as an alternative to PTEN mutation in glioblastomas.

Application of advances in molecular biology to the treatment of brain tumors

Recent advances in molecular biology have substantially improved our understanding of the molecular genetics of primary brain neoplasms. Soon each histopathologic category of glioma will be further divided into subgroups according to similar genetic background, gene expression profile, and similarity of biologic responses to radiotherapy or chemotherapy. Identification of key molecules that are specifically altered in neoplastic cells will provide candidate molecular targets for tumor treatment. Novel therapeutic tools for targeting tumor cells, such as viral vectors for gene therapy, have been created. In the near future, the accumulation of new knowledge in brain tumor biology and genetics, combined with rational drug design, will revolutionize the treatment of malignant gliomas, which are among the most lethal human cancers.

Novel p53 splice site mutations in three families with Li-Fraumeni syndrome

Germline mutations in the p53 tumor suppressor gene predispose to a variety of cancers in families with Li-Fraumeni syndrome. Most germline p53 mutations observed to date cause amino acid substitutions in the protein's central sequence-specific DNA binding domain. Outside this conserved core region, however, we found novel alterations in sequences that regulate precursor mRNA splicing in three Li-Fraumeni syndrome families. Two splice site mutations affected the consensus sequence at the splice donor sites of introns 1 and 9, and produced unstable variant transcripts in normal cells. A third mutation at the splice acceptor site of intron 9 generated splicing at a cryptic acceptor site in intron 9. These splice site alterations emphasize the need to examine both noncoding and untranslated regions of the p53 gene for germline mutations in Li-Fraumeni syndrome families. Oncogene (2000) 19, 4230 - 4235

Improving the detection of p53 mutations in breast cancer by use of the FASAY, a functional assay

The aim of this investigation was to examine the ability of the yeast-based functional assay, the functional analysis for the separation of alleles in yeast (FASAY), to detect p53 mutations in breast cancers when compared with immunohistochemistry and automated sequencing of the whole p53 gene (exons 1-11). To achieve this, all three methods were carried out on a cohort of aggressive breast tumors. In those tumors, in which the FASAY analysis indicated the presence of a mutation, cDNA was extracted from red yeast colonies and was sequenced to identify the base change in the p53 gene. The FASAY detected all 24 mutations found in the series of 48 tumors, whereas initial automated sequencing of genomic DNA detected 18/24 mutations. A second round of automated sequencing carried out using an independent source of genomic DNA detected mutations in 3 of the 6 tumors that originally appeared to lack a mutation in genomic DNA. All but 1 of the mutations originally missed by sequencing of genomic DNA were point mutations. Five mutations in this series (21%) were outside the commonly investigated exons 5-8, reinforcing the need to extend sequencing beyond this region. Of 24 tumors, 14 had strong immunohistochemical staining, and all 14 had p53 mutations; the majority of mutations missed by immunohistochemistry produced a truncated protein. Strong staining was not seen in tumors lacking a p53 mutation. The FASAY proved to be a rapid, reliable, and effective method for identifying those breast tumors harboring p53 mutations.

P53 germline mutations in childhood cancers and cancer risk for carrier individuals

The family history of cancer in children treated for a solid malignant tumour in the Paediatric Oncology Department at Institute Gustave-Roussy, has been investigated. In order to determine the role of germline p53 mutations in genetic predisposition to childhood cancer, germline p53 mutations were sought in individuals with at least one relative (first- or second-degree relative or first cousin) affected by any cancer before 46 years of age, or affected by multiple cancers. Screening for germline p53 mutation was possible in 268 index cases among individuals fulfilling selection criteria. Seventeen (6.3%) mutations were identified, of which 13 were inherited and four were de novo. Using maximum likelihood methods that incorporate retrospective family data and correct for ascertainment bias, the lifetime risk of cancer for mutation carriers was estimated to be 73% for males and nearly 100% for females with a high risk of breast cancer accounting for the difference. The risk of cancer associated with such mutations is very high and no evidence of low penetrance mutation was found. These mutations are frequently inherited but de novo mutations are not rare.

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.