Leukemic and non-leukemic lymphocytes from patients with Li Fraumeni syndrome demonstrate loss of p53 function, Bcl-2 family dysregulation and intrinsic resistance to conventional chemotherapeutic drugs but not flavopiridol

Li Fraumeni syndrome (LFS) is characterised by a predisposition to the early onset of certain tumors and is associated with germline mutation of the anti-oncogene p53. In this study we analysed the in vitro responses of lymphocytes from two LFS patients to chemotherapeutic drugs in terms of apoptosis induction and the expression of key intracellular proteins that regulate this process. One of the LFS patients also suffered from B-cell chronic lymphocytic leukemia (B-CLL) and hence presented with a light-chain restricted B-cell lymphocytosis while the other patient had entirely normal blood counts. The B-lymphocytes from both LFS patients showed a marked degree of resistance to chlorambucil and fludarabine when compared to age-matched controls but were remarkably sensitive to the novel flavone, flavopiridol. Loss of function of p53 was demonstrated by a failure to induce Bax and p21 protein expression. In addition, altered basal expression patterns of Bcl-2 and Bax, two key regulators of apoptosis, were found in the LFS lymphocytes when compared with controls. These results suggest that LFS lymphocytes carrying a p53 mutation show intrinsic resistance to conventional chemotherapeutic drugs and this is associated with dysregulation of Bcl-2 family proteins. Furthermore, The innate resistance profile was similar in leukemic and non-leukemic lymphocytes and was therefore independent of genetic changes acquired during malignant transformation. Novel agents that induce p53-independent cell killing may be useful not only in the treatment of LFS-associated tumors but also drug resistant tumors in general where p53 and/or Bcl-2 family dysregulation is a feature.

[Description of a new TP53 gene germline mutation in a family with the Li-Fraumeni syndrome. Genetic counselling to healthy mutation carriers]

BACKGROUND

Li-Fraumeni syndrome is a dominantly inherited disorder characterized by early-onset breast cancer, soft-tissue sarcomas and osteosarcomas, acute leukemia, adrenocortical neoplasms and central nervous system tumors. Germline mutations in gene TP53 are identified in a percentage of affected families.

PATIENTS AND METHOD

Eight families with aggregation of childhood sarcomas, brain tumors, breast cancers in pre-menopausal women, and renal tumors were screened for TP53 germ-line mutations. SSCP and posterior direct sequencing were performed for genetic analysis. We also report a previously undescribed family with the Li-Fraumeni syndrome carrying a germline mutation.

RESULTS

Seven families fulfilled so-called Li-Fraumeni like criteria and one fulfilled classical criteria. A new germ-line mutation in codon 238 at exon 7 of the gene TP53 was identified in the family fulfilling classical criteria. This mutation has not been previously reported.

CONCLUSIONS

The clinical heterogeneity as well as the molecular complexity and consequences of mutation analysis and genetic counseling make it necessary to develop protocols in this area. A multidisciplinary approach is needed; this approach should be coordinated by a Familial Cancer Genetic Counseling Unit.

Is there anticipation in the age at onset of cancer in families with Li-Fraumeni syndrome?

Anticipation in the age at onset of cancer in successive generations was described in several familial cancer syndromes. Based on multiple statistical analyses of a database of families with germline TP53 mutations, and using several different approaches and measures to eliminate possible biases, we show that anticipation may be a feature of the Li-Fraumeni syndrome. Definitive proof of anticipation in pedigrees with germline TP53 mutations will require more family data and further analysis, as well as research on the role of the p53 protein in processes like genome stability, which may represent the biological basis of anticipation in these families. This should have important practical implications for genetic testing, counselling, and preventative care for individuals at risk.

Genetics of childhood cancer

In recent years, knowledge of the molecular genetics of childhood cancers has been increasing at an exponential rate. The study of the molecular mechanisms of oncogenesis has led to an understanding of the role that tumor suppressors, oncogenes, and deoxyribonucleic acid (DNA) repair genes play in development of the disease. Chromosomal translocations can lead to the disruption of growth regulatory genes or the formation of growth stimulatory fusion genes in leukemias and solid tumors. These alterations can occur sporadically or can be inherited, which often leads to cancer in children or young adults. Often, the presence of specific genetic alterations can be used to diagnose a cancer that otherwise would be difficult to verify. Genetic mutations also can be prognostic indicators and guide the treatment plan of the physician.

p53 Germline mutation in a patient with Li-Fraumeni Syndrome and three metachronous malignancies

PURPOSE

Germline mutations of the p53 coding region are present in approximately 50-70% of patients with Li-Fraumeni Syndrome (LFS), a rare hereditary disorder of familial and intraindividual clustering of different malignancies such as sarcoma (index tumor), breast cancer, brain tumors, leukemias, and adrenocortical carcinomas, the latter usually in young children. Both onset and spectrum of malignancies in individuals with LFS are thus heterogenous and may, less frequently, also include other epithelial and mesenchymal tumors. A 32-year-old female presented for genetic counseling with a history of leiomyosarcoma at age 22, malignant melanoma (a rare component of LFS) at age 26, and breast cancer at age 30. All three tumors had been treated surgically. Astrocytoma and breast cancer, respectively, had been diagnosed in her brother and mother before age 30. Other malignancies diagnosed early in life in relatives of the mother were: prostate cancer, stomach cancer, and carcinoma of the larynx.

METHODS

Upon written informed consent, DNA was extracted from peripheral blood mononuclear cells of the proband, and p53 exons 4-8 analyzed for mutations by SSCP and DNA sequencing.

RESULTS

A G:C to A:T mutation at codon 175 of p53 resulting in an arginine --> histidine substitution was detected, confirming the clinical diagnosis of LFS.

CONCLUSIONS

The patient and her family are being followed further, but testing of her children for the presence of this mutation is currently being withheld. The difficulties in the management and treatment of patients with this clinically heterogenous disorder are discussed.

Telomerase protects cancer-prone human cells from chromosomal instability and spontaneous immortalization

Studies were conducted to directly test whether the introduction of telomerase protects cancer-prone human mammary epithelial cells from chromosomal instability and spontaneous immortalization. Using a model for Li Fraumeni Syndrome (LFS), infection of human telomerase resulted in maintenance of telomere lengths, extension of in vitro lifespan, and prevention of spontaneous immortalization. In stark contrast to the spontaneously immortalized LFS cells, cells expressing ectopic telomerase displayed a remarkably stable karyotype and even after >150 population doublings, did not express endogenous telomerase. Since the hTERT-infected and spontaneously immortal LFS cells, like the parental cells, exhibit loss of p53 function, our data suggests that telomere shortening is the primary driving force for the genomic instability characteristic of LFS cells, while p53 inactivation is necessary for triggering the spontaneous immortalization event. Collectively, our data indicate that exogenous telomerase prevents chromosomal instability and spontaneous immortalization of LFS cells, suggesting a unique protective role for telomerase in the progression to immortalization.

The IARC TP53 database: new online mutation analysis and recommendations to users

Mutations in the tumor suppressor gene TP53 are frequent in most human cancers. Comparison of the mutation patterns in different cancers may reveal clues on the natural history of the disease. Over the past 10 years, several databases of TP53 mutations have been developed. The most extensive of these databases is maintained and developed at the International Agency for Research on Cancer. The database compiles all mutations (somatic and inherited), as well as polymorphisms, that have been reported in the published literature since 1989. The IARC TP53 mutation dataset is the largest dataset available on the variations of any human gene. The database is available at www.iarc.fr/P53/. In this paper, we describe recent developments of the database. These developments include restructuring of the database, which is now patient-centered, with more detailed annotations on the patient (carcinogen exposure, virus infection, genetic background). In addition, a new on-line application to retrieve somatic mutation data and analyze mutation patterns is now available. We also discuss limitations on the use of the database and provide recommendations to users.

Identification of a rare polymorphism in the human TP53 promoter

The majority of families with classic Li-Fraumeni Syndrome (LFS) and a significant proportion of Li-Fraumeni-like (LFL) families have a germline mutation in the TP53 tumor suppressor gene. However around 20% of LFS and 60% of LFL families have no identifiable genetic defect in the coding region or splice junctions of TP53, and the genetic basis for cancer susceptibility in these families remains largely uncharacterized. To determine whether promoter mutations could be responsible for the Li-Fraumeni phenotype, we sequenced the TP53 promoter in index cases from members of classic LFS and LFL families without detectable TP53 mutations. We identified an identical single nucleotide deletion within the C/EBP- like site of the promoter in two out of eighteen such families (11%), compared to only one of a total of 366 control samples (0.3%). Although this result is highly significant (P=0.006, Fischer's exact test), the mutation did not affect the expression of TP53 in our hands. We provide evidence that this site is not utilized in the wild type TP53 promoter and further, that mutation of this site in LFS/LFL does not have a functional effect. We conclude that the sequence variant is a rare polymorphism arising within the TP53 promoter. However, the significantly increased frequency of this variant in LFS/LFL remains intriguing.

A novel, de novo germline TP53 mutation in a rare presentation of the Li-Fraumeni syndrome in the maxilla

We undertook the genetic analysis of a classic Li-Fraumeni syndrome (LFS) family with clustering of primary tumours including two maxillary sarcomas, a rare LFS site of tumour occurrence. Our aim was to investigate the presence of a specific type of TP53 mutation that could be associated with this unusual predilection of site for cancer occurrence. Mutational screening of the coding region of TP53 revealed an A>T transversion in codon 144 of exon 5 (CAG>CTG, Gln>Leu) in the germline of one of the three affected members, with loss of heterozygosity (LOH) in the tumour tissue. All other affected members were negative for germline or somatic TP53 mutations. TP53 immunohistochemistry was uninformative. The mutation we report is a de novo constitutional TP53 mutation that has not been previously described in the literature. It could explain the more burdened phenotype of the affected patient (died at 21 months). Alternative mechanisms to explain the overall family phenotype are discussed.

RNA polymerase III transcription can be derepressed by oncogenes or mutations that compromise p53 function in tumours and Li-Fraumeni syndrome

RNA polymerase (pol) III synthesizes essential small RNAs, including tRNA and 5S rRNA. Wild-type p53 can repress pol III transcription both in vitro and in vivo. Many tumours carry substitutions in p53 which have selective effects on its functions. We identify tumour-derived mutations that compromise the ability of p53 to regulate pol III transcription. Furthermore, substitution R175H, the most common mutation in cancers, converts p53 from a repressor to an activator of pol III. Oncoproteins neutralize p53 in some tumours; we show that human papillomavirus E6 and cellular hdm2 can both release pol III from repression by p53. These data suggest that the restraining influence of p53 on pol III will be lost in many tumours. In addition to these features of sporadic cancers, some individuals inherit mutant forms of p53 and consequently suffer from Li-Fraumeni syndrome, showing genetic predisposition to certain malignancies. We find that pol III transcriptional activity is often highly elevated in primary fibroblasts from Li-Fraumeni patients, especially if the germline p53 mutation is followed by loss of the remaining allele. Our data suggest that p53 status can have a profound effect upon pol III transcription and hence on the biosynthetic capacity of cells.

[Specialized genetic counseling in pediatric and adult oncology patients]

Five to ten percent of oncological diseases exhibit monogenic mode of inheritance. They occur as a consequence of the germline mutations of tumor suppressor genes and of the genes engaged in reparative processes. Most common monogenically determined oncological diseases are: AD form of breast and ovarian cancer, hereditary nonpolyposis colorectal cancer (HNPCC, Lynch sy.) and familiar adenomatous polyposis (FAP). The aim of the genetic investigation is to evaluate whether the index family deals with the hereditary form of tumor predisposition, than, if possible, to perform DNA analysis in the family and to propose preventive screening program (methods) for the probands in risk.

Genes other than BRCA1 and BRCA2 involved in breast cancer susceptibility

This review focuses on genes other than the high penetrance genes BRCA1 and BRCA2 that are involved in breast cancer susceptibility. The goal of this review is the discovery of polymorphisms that are either associated with breast cancer or that are in strong linkage disequilibrium with breast cancer causing variants. An association with breast cancer at a 5% significance level was found for 13 polymorphisms in 10 genes described in more than one breast cancer study. Our data will help focus on the further analysis of genetic polymorphisms in populations of appropriate size, and especially on the combinations of such polymorphisms. This will facilitate determination of population attributable risks, understanding of gene-gene interactions, and improving estimates of genetic cancer risks.

Analysis of TP53 germline mutations in pediatric tumor patients using DNA microarray-based sequencing technology

BACKGROUND

Whereas in sporadic human malignancies mutations of the TP53 tumor-suppressor gene occur in cancers of almost every organ and histologic subtype, patients with an inborn TP53 defect are at high risk to develop, in particular, soft tissue and bone sarcomas, brain tumors, leukaemias, adrenocortical tumors, and breast cancer. To demonstrate the usefulness of microarray technology applied to TP53 sequencing in pediatric tumors, we investigated young patients suffering from tumors typical of the Li-Fraumeni context who were, therefore, candidates for harboring inborn defects in tumor-suppressor genes.

PROCEDURE

Six individuals were studied, including typical Li-Fraumeni patients as well as patients without any family history of cancer. DNA samples were independently analyzed for TP53 mutations by GeneChip and standard automated laser fluorescence (ALF) sequencing technology.

RESULTS

The tumor and corresponding constitutional DNA samples clearly showed identical mutations which were confirmed by ALF sequencing. All coding exons (exons 2-11) of TP53 were analyzed simultaneously. The entire sequencing procedure and data analysis was carried out within 24 hr.

CONCLUSIONS

The GeneChip TP53-sequencing assay may be feasible for routine molecular genetic diagnostics in determining the TP53 status of childhood-tumor patients and in enabling a disease management based on the genetic background of the individual.

Individual-specific liability groups in genetic linkage, with applications to kindreds with Li-Fraumeni syndrome

In this report, we present a simple and powerful way to incorporate individual-specific liability classes into linkage analysis. The proposed method is applicable to both quantitative and qualitative traits. In linkage studies, we may have information about different covariates. Incorporation of these covariates along with the estimates of residual familial effects, age-at-onset effects, and susceptibility in the definition of liability classes can increase the power to detect genetic linkage. In this study, we show how one can form individual-specific liability classes and use these classes in standard linkage-analysis programs, such as the widely used LINKAGE package, to perform more powerful genetic linkage analysis. Our simulation study shows that this approach yields higher LOD scores and more-accurate estimates of the recombination fraction in the families showing linkage. The proposed method is also applied to kindreds collected, at the M. D. Anderson Cancer Center, through probands with childhood soft-tissue sarcoma. Confirmed germ-line mutations in the p53 tumor-suppressor gene have been identified in these families. Application of our method to these families yielded significantly higher LOD scores and more-accurate recombination fractions than did analysis that did not account for individual-specific covariate information.

Delayed chromosome changes in gamma-irradiated normal and Li-Fraumeni fibroblasts

Knockout mice with only one Trp53 allele (+/- genotype) are highly susceptible to radiation-induced cancers, possibly through numerical chromosome changes. Patients with the Li-Fraumeni syndrome, having heterozygous TP53 germline mutations (+/mut genotype), are also susceptible to spontaneous and radiogenic cancers. We have investigated the susceptibility of six Li-Fraumeni syndrome +/mut and six normal fibroblast strains to induced numerical and unstable structural aberrations at six population doublings after exposure to 3 or 6 Gy gamma rays. Four of the irradiated Li-Fraumeni syndrome strains showed small increases in both aberration types, similar to those seen in the normal strains. In two irradiated Li-Fraumeni syndrome strains, there were high levels of induced structural changes, and one of these showed a modest increase in hyperploidy. We suggest that enhanced sensitivity to delayed radiation-induced chromosome changes in Li-Fraumeni syndrome cells requires other genetic alterations in addition to TP53 heterozygosity, apparently in contrast to the situation in Trp53 heterozygous null mice. If such additional alterations occur in vivo in Li-Fraumeni syndrome patients, they may predispose them to radiogenic cancers, mainly through enhanced structural rather than numerical chromosome changes. Our findings raise questions about the validity of quantitative extrapolation of cytogenetic data from Trp53-defective mice to radiogenic cancer risk in humans.

Microsatellite instability, PTEN and p53 germline mutations in glioma families

Rare inherited syndromes that to some extent explain familial glioma include Turcot's syndrome, Li-Fraumeni syndrome and neurofibromatosis types I and II. The majority of families with glioma do not meet the clinical criteria for any of these syndromes. In order to study the genetic origin of familial glioma, tumour DNA (n = 35) or blood samples (n = 8) were collected from 25 families. The glioma tumours were tested for microsatellite instability (MSI) with two markers, BAT25 and BAT26, since glioma is associated with hereditary non-polyposis colon cancer (HNPCC) in Turcot's syndrome. Furthermore, p53 was screened from blood DNA (exons 2-11) with temporal temperature gradient electrophoresis (TTGE) since germline mutations in p53 are seen in Li-Fraumeni syndrome. In gliomas, there is a wide variety of somatic mutations, such as, for instance, in p53, the epidermal growth factor receptor (EGFR) and p16. The tumour suppressor gene PTEN is also often somatically mutated in glioma, therefore it is attractive as a candidate gene for germline mutations in familial glioma. Blood DNA was directly sequenced for mutations in PTEN exons 1-9. The analysis showed that no mutations were found in either of the studied tumour suppressor genes, and no MSI-positive tumours were found. A common polymorphism in p53 at codon 72 (arginine/proline) was found in 6/8 of the patients. Apparently, mutation in the tested tumour suppressor genes or DNA mismatch repair genes does not explain the familial glioma observed in these families.

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.

Assessing TP53 status in human tumours to evaluate clinical outcome

TP53 is probably the most extensively studied tumour-suppressor gene, and patients with TP53 mutations are known to have a poor outcome. However, inconsistencies in the analysis of TP53 status, and failure to realize that different mutations behave in different ways, prevent us from effectively applying our vast knowledge of this protein in clinical practice. What simple steps can be taken to ensure that patients benefit from our understanding of TP53?

Analysis of p53 tumor suppressor gene in families with multiple glioma patients

The high incidence of gliomas in Li-Fraumeni families and the high frequency of somatic p53 mutations in sporadic glial tumors have raised the possibility that germline p53 mutations could play an important role in familial aggregation of gliomas. In the present study, 18 families with two or more gliomas were screened for germline p53 mutation. The families were identified through questionnaires sent to 369 consecutive glioma patients operated at Tampere University Hospital during 1983-1994. In these families, a family history of cancer was verified through the Finnish Cancer Registry. Interestingly, the questionnaires reveled only 15 of 57 cancers (index gliomas excluded) retrieved through the Cancer Registry. None of the 18 families fufilled the criteria for classic Li-Fraumeni syndrome. Immunostaining analysis of p53 protein accumulation suggested that alterations of the p53 gene are as common in familial as in sporadic gliomas. Sequencing analysis of exons 4-10 of the p53 gene revealed no germline mutations in any of the 18 families. Thus, although occasional glioma families carrying germline p53 mutations have been identified in earlier studies, systematic evaluation of familial glioma patients suggests that the p53 gene is not a common susceptibility gene in case of familial gliomas. The p53 tumor suppressor gene seems to have a similar role in the tumorigenesis of most familial and sporadic gliomas.