The MspI polymorphism in intron 6 of p53 (TP53) detected by digestion of PCR products

Functional consequence of the p53 codon 72 polymorphism in colorectal cancer

Background

The codon 72 polymorphism in p53 has been implicated in colorectal cancer (CRC) risk, prognosis and CRC health disparities. We examined the functional consequence of this polymorphism in CRC.

Experimental Design

Plasmids (pCMV6) that express different phenotypes of p53 [p53 wild type (wt) at codon 72 (R72^wt), R72^wt with mutation at codon 273 cysteine (R72^273Cys), p53 mutation at codon 72 (P72^wt) and P72^wt with mutation at codon 273 (P72^273Cys)] were constructed. The CRC cell line Caco2, which does not express p53 for in vitro studies, was used as host. CRC xenografts were established in severe combined immunodeficient (SCID) mice using established cell lines. CRC surgical specimens, corresponding normal colon, and tumor xenografts were sequenced for codon 72 polymorphism of p53. Proteins signaling mechanisms were evaluated to assess the functional consequence of P72 phenotype of p53.

Results

This study demonstrated a significantly increased survival of cells expressing P72^wt, mutant phenotype, versus R72^wt phenotype. WB analyses revealed that P72^wt induced activation of p38 and RAF/MEK/ extracellular signal-regulated kinase (ERK) MAP kinases. Activation of CREB was found to be higher in tumors that exhibit P72 phenotype. Metastatic lesions of CRC expressed more phospho-CREB than non-metastatic lesions. The expression of P72^wt promoted CRC metastasis.

Conclusions

P72 contributes to the aggressiveness of CRC. Because P72 is over-expressed in CRC, specifically in African-American patients, this suggests a role for P72 in cancer health disparities. This work was supported by NIH/NCI Workforce Diversity Grant R21-CA171251 & U54CA118948.

Molecular heterogeneity in malignant peripheral nerve sheath tumors associated with neurofibromatosis type 1

Neurofibromatosis type-1 (NF1), resulting from NF1 gene loss of function, is characterized by an increased risk of developing benign and malignant peripheral nerve sheath tumors (MPNSTs). Whereas the cellular heterogeneity of NF1-associated tumors has been well studied, the molecular heterogeneity of MPNSTs is still poorly understood. Mutational heterogeneity within these malignant tumors greatly complicates the study of the underlying mechanisms of tumorigenesis. We have explored this molecular heterogeneity by performing loss of heterozygosity (LOH) analysis of the NF1, TP53, RB1, PTEN, and CDKN2A genes on sections of 10 MPNSTs derived from 10 unrelated NF1 patients. LOH data for the TP53 gene was found to correlate with the results of p53 immunohistochemical analysis in the same tumor sections. Further, approximately 70% of MPNSTs were found to display intra-tumoral molecular heterogeneity as evidenced by differences in the level of LOH between different sections of the same tumor samples. This study constitutes the first systematic analysis of molecular heterogeneity within MPNSTs derived from NF1 patients. Appreciation of the existence of molecular heterogeneity in NF1-associated tumors is important not only for optimizing somatic mutation detection, but also for understanding the mechanisms of NF1 tumorigenesis, a prerequisite for the development of specifically targeted cancer therapeutics.

ras and p53 in the prediction of survival in Dukes' stage B colorectal carcinoma

Aims-To determine possible associations between p53 allelic deletion, c-Ki-ras mutational activation, immunohistochemical detection of p53 and ras proteins, various clinicopathological variables, and patient outcome in 168 Dukes' stage B colorectal carcinomas.Methods-Allelic deletion at the p53 tumour suppressor gene locus was detected using polymerase chain reaction (PCR) based loss of heterozygosity (LOH) assays. Overexpressed proteins were detected using the CM1 polyclonal antibody. A PCR based assay was used to detect the presence of activating mutations at codon 12 of c-Ki-ras. Immunostaining was carried out using a monoclonal antibody to p21(ras).Results-p53 LOH, CM1 immunostaining, c-Ki-ras mutational activation, and p21(ras) immunostaining were not predictive of survival by logrank analysis. Multivariate analysis using Cox regression did not predict survival in this group of tumours.Conclusions-Aberrations in ras and p53 are unlikely to play an important role in the subdivision of patients with Dukes' stage B colorectal carcinoma into more accurate prognostic strata. It is possible that later genetic events are more important in conferring a specific phenotype on the resultant Dukes' stage B tumour.

Analysis of NF1 somatic mutations in cutaneous neurofibromas from patients with high tumor burden

Neurofibromatosis type 1, (NF1) is a complex, autosomal dominant disorder characterized by benign and malignant tumors which result from NF1 gene mutations. The molecular mechanisms that underlie NF1 tumorigenesis are still poorly understood although inactivation of other modifying loci in conjunction with NF1 mutations is postulated to be involved. These modifying loci may include deficiencies in mismatch repair genes and elements involved in cell cycle regulation (TP53, RB1, and CDKN2A). We have analyzed the somatic mutations in 89 cutaneous neurofibromas derived from three unrelated NF1 patients with high tumor burden, by loss of heterozygosity (LOH) analysis of the NF1, TP53, RB1, and CDKN2A genes, by assessing microsatellite instability (MSI), by direct sequencing of the NF1, TP53, and several mismatch repair (MMR) genes and by multiplex ligation-dependent probe amplification of the NF1 and TP53 genes. The aim was both to assess the possible clonality of these tumors and also to assess the involvement of other potential genetic loci in the development of these neurofibromas. Somatic NF1 mutations were identified in 57 (64%) of neurofibroma samples. Each mutation was distinct demonstrating the independent origin of each tumor. While somatic LOH of the TP53 gene was identified in four tumors, no specific deletions or sequence variations were identified. LOH of markers flanking the RB1 gene was also found in one tumor but no CDKN2A mutations were detected. Although evidence of MSI was seen in 21 tumors, no MMR gene alterations were identified. The identification of LOH involving TP53 and RB1 loci is a novel finding in benign cutaneous neurofibromas possibly demonstrating an alternative underlying molecular mechanism associated with the development of these benign tumors from this cohort of patients.

Development and progression of colorectal neoplasia

A variety of genetic and molecular alterations underlie the development and progression of colorectal neoplasia (CRN). Most of these cancers arise sporadically due to multiple somatic mutations and genetic instability. Genetic instability includes chromosomal instability (CIN) and microsatellite instability (MSI), which is observed in most hereditary non-polyposis colon cancers (HNPCCs) and accounts for a small proportion of sporadic CRN. Although many biomarkers have been used in the diagnosis and prediction of the clinical outcomes of CRNs, no single marker has established value. New markers and genes associated with the development and progression of CRNs are being discovered at an accelerated rate. CRN is a heterogeneous disease, especially with respect to the anatomic location of the tumor, race/ethnicity differences, and genetic and dietary interactions that influence its development and progression and act as confounders. Hence, efforts related to biomarker discovery should focus on identification of individual differences based on tumor stage, tumor anatomic location, and race/ethnicity; on the discovery of molecules (genes, mRNA transcripts, and proteins) relevant to these differences; and on development of therapeutic approaches to target these molecules in developing personalized medicine. Such strategies have the potential of reducing the personal and socio-economic burden of CRNs. Here, we systematically review molecular and other pathologic features as they relate to the development, early detection, diagnosis, prognosis, progression, and prevention of CRNs, especially colorectal cancers (CRCs).

Prognostic significance of p53 codon 72 polymorphism differs with race in colorectal adenocarcinoma

PURPOSE

Several studies have examined the prognostic value of the codon 72 polymorphism of the p53 gene in colorectal adenocarcinoma, but none have addressed patient race/ethnicity. Therefore, this study assessed the prognostic value of this polymorphism in African American and Caucasian colorectal adenocarcinoma patients separately.

EXPERIMENTAL DESIGN

Colorectal adenocarcinomas from 137 African Americans and 236 non-Hispanic Caucasians were assessed for p53 mutations and genotyped for the codon 72 polymorphism. The phenotypes were correlated with p53 mutational status, clinicopathologic features, and patient survival using the chi(2) test and Kaplan-Meier and Cox regression models.

RESULTS

The incidence of p53 mutations was similar in African American and Caucasian patients (50% versus 54%, respectively); however, the homozygous Pro72 allele frequency was higher in African Americans (17%) as compared with Caucasians (7%). In contrast, the homozygous Arg72 allele frequency was higher in Caucasians (36%) than in African Americans (19%). In African Americans but not Caucasians, the Pro/Pro phenotype significantly correlated with a higher incidence of missense p53 mutations and with nodal metastasis. African Americans, but not Caucasians, with the Pro/Pro phenotype had significantly higher mortality (log-rank P = 0.005 versus. P = 0.886) and risk of death due to colorectal adenocarcinoma (hazard ratio, 2.15; 95% confidence interval, 1.02-4.53 versus hazard ratio, 1.60; 95% confidence interval, 0.69-3.18) than those with the phenotype Arg/Arg or Arg/Pro.

CONCLUSIONS

The higher frequency of the Pro/Pro phenotype of p53 in African American patients with colorectal adenocarcinoma is associated with an increased incidence of p53 mutations, with advanced tumor stage, and with short survival.

Polymorphisms in p53 and the p53 pathway: roles in cancer susceptibility and response to treatment

The p53 tumour suppressor protein lies at the crossroads of multiple cellular response pathways that control the fate of the cell in response to endogenous or exogenous stresses and inactivation of the p53 tumour suppressor signalling pathway is seen in most human cancers. Such aberrant p53 activity may be caused by mutations in the TP53 gene sequence producing truncated or inactive mutant proteins, or by aberrant production of other proteins that regulate p53 activity, such as gene amplification and overexpression of MDM2 or viral proteins that inhibit or degrade p53. Recent studies have also suggested that inherited genetic polymorphisms in the p53 pathway influence tumour formation, progression and/or response to therapy. In some cases, these variants are clearly associated with clinico-pathological variables or prognosis of cancer, whereas in other cases the evidence is less conclusive. Here, we review the evidence that common polymorphisms in various aspects of p53 biology have important consequences for overall tumour susceptibility, clinico-pathology and prognosis. We also suggest reasons for some of the reported discrepancies in the effects of common polymorphisms on tumourigenesis, which relate to the complexity of effects on tumour formation in combination with other oncogenic changes and other polymorphisms. It is likely that future studies of combinations of polymorphisms in the p53 pathway will be useful for predicting tumour susceptibility in the human population and may serve as predictive biomarkers of tumour response to standard therapies.

Polymorphisms in TP53 and MDM2 combined are associated with high grade endometrial cancer

OBJECTIVES

Determinants of endometrial cancer grade have not been precisely defined, however, cell cycle control is considered to be integrally involved in endometrial cancer development. TP53 and MDM2 are essential components for cell cycle arrest and apoptosis. Polymorphisms in these genes cause TP53 inactivation and MDM2 over-expression, leading to accumulation of genetic errors.

METHODS

One polymorphism in MDM2, rs2279744 (SNP309) and three polymorphisms in TP53 rs1042522 (R72P), rs17878362 and rs1625895 were genotyped in 191 endometrial cancer cases and 291 controls using PCR-based fragment analysis, RFLP analysis and real-time PCR.

RESULTS

The results showed no associations of the three TP53 polymorphisms and MDM2 SNP309 alone or in combination with endometrial cancer risk. However, the combination of MDM2 SNP309 and the three TP53 polymorphisms was significantly associated with a higher grade of endometrial cancer (wild-type genotypes versus variant genotypes: OR 4.15, 95% CI 1.82-9.46, p=0.0003). Analysis of family history of breast cancer revealed that the variant genotypes of the three TP53 polymorphisms were significantly related to a higher frequency of family members with breast cancer in comparison to endometrial cancer cases without a family history of breast cancer (wild-type genotypes versus variant genotypes: OR 2.78, 95% CI 1.36-5.67, p=0.004).

CONCLUSIONS

The combination of the MDM2 SNP309 and the three TP53 polymorphisms appear to be related to a higher grade of endometrial cancer. The association of the endometrial cancer cases with family history of breast cancer and the three TP53 polymorphisms suggests that this constellation of malignancies may represent a low-risk familial cancer grouping.

Metabolic gene polymorphisms andp53mutations in healthy centenarians and younger controls

To obtain insights into the genetic mechanisms of ageing, we studied the frequency of the simultaneous presence of polymorphisms in phase I and phase II genes and of several p53 germline mutations in a group of 66 nonagenarians and centenarians in good health, selected from a larger sample of a multicentre Italian study in Northern Italy, and in a sample of 150 young healthy volunteers of the same ethnic group. We found a statistically significant difference in the frequency of 1the GSTT1 deletion and the p53 genotypes: the absence of any p53 polymorphisms and of GSTT1 deletion, and the simultaneous presence of the three p53 polymorphisms and of GSTT1 deletion, were much more frequent in young subjects than in centenarians (41.5% versus 26.9% and 8.8% versus 3.8%, respectively). One hypothesis to explain this difference is that subjects with both GSTT1 deletion and p53 polymorphisms may accumulate carcinogens and may have reduced DNA repair ability, and thus are more at risk for cancer. Another possible explanation is that both metabolic genes and p53 act on pathways related to cell ageing and death, and therefore certain composite genetic patterns could represent a generic mechanism of protection against ageing, not just against the development of chronic diseases. It is likely that longevity is related to a complex genetic trait as well as to certain environmental exposures.

Allelic loss at TP53 is not related to p53 protein overexpression in primary human endometrial carcinomas

We examined loss of heterozygosity (LOH) at the TP53 gene in primary human endometrial carcinomas (EC), and investigated the relationship between allelic loss, p53 protein overexpression, pRb-1 pathway alterations and MIB-1 proliferative activity. Applying the non-isotopic PCR-RFLP/VNTR-silver staining techniques, we investigated TP53 LOH in 46 tumors at four polymorphic loci. Out of 42 informative carcinomas, LOH was found in 19% of the cases studied. In general, there was no significant relationship between LOH and the clinical and pathological variables of cancer, including patient age, clinical stage, histological grade or depth of myometrial invasion. Interestingly, none of 7 tumors associated with hyperplasia revealed allelic imbalance, whereas 8 of 27 (30%) tumors without hyperplasia exhibited LOH (p=0.312; Fisher's exact test). Overexpression of nuclear p53 was not correlated with allelic loss at TP53 (p=0.336, Fisher's exact test). It is worth pointing out that p53 immunoreactivity was significantly related to proliferative activity of cancer (R=0.42, p=0.0037; Spearman's rank correlation test). A tendency towards a poorer outcome was reported in EC patients displaying TP53 LOH during short-time follow-up (p=0.093; log-rank test). None of the tumors simultaneously showed LOH at TP53 and RB1 genes (R=-0.211, p=0.16; Spearman's rank correlation test). p16INK4A alterations (LOH and gene deletion) occurred concomitantly, with 3 tumors showing the TP53 allelic loss, whereas the cyclin D1/cdk4 complex was overexpressed in a case with TP53 LOH. Altogether, losses at TP53 were not associated with p53 nuclear overexpression, but may affect a subset of EC patients characterized by an unfavorable prognosis at short-time follow-up. Allelic loss at TP53 seems to arise independently of LOH at the RB1 gene in carcinomas of the uterine corpus in humans. Disruptions at p16INK4A and/or cdk4/cyclin D1 concomitantly occurring with TP53 LOH may participate in the development of a subset of endometrioid-type ECs.

p53 status and response to radiotherapy in rectal cancer: a prospective multilevel analysis

The aim of this study was to evaluate, in a prospective study, the predictive role of p53 status analysed at four different levels in identifying the response to preoperative radiotherapy in rectal adenocarcinoma. Before treatment, 70 patients were staged and endoscopic forceps biopsies from the tumour area were taken. p53 status was assessed by total cDNA sequencing, allelic loss analysis, immunohistochemistry, and p53 antibodies. Neoadjuvant treatment was based on preoperative radiotherapy or radiochemotherapy. Response to therapy was evaluated after surgery by both pathologic downstaging and histologic tumour regression grade. In all, 35 patients (50.0%) had p53 gene mutations; 44.4% of patients had an allelic loss; nuclear p53 overexpression was observed in 39 patients (55.7%); and p53 antibodies were detected in 11 patients (16.7%). In the multilevel analysis of p53 status, gene mutations correlated with both nuclear protein overexpression (P<0.0001) and loss of heterozygosity (P=0.013). In all, 29 patients (41.4%) were downstaged by pathologic analysis, and 19 patients (29.2%) were classified as tumour regression grade 1. Whatever the method of evaluation of treatment response, no correlation between p53 alterations and response to radiotherapy was observed. Our results do not support the use of p53 alterations alone as a predictive marker for response to radiotherapy in rectal carcinoma.

Intronic TP53 Germline Sequence Variants Modify the Risk in German Breast/Ovarian Cancer Families

To establish the contribution of TP53 germline mutations to familial breast/ovarian cancer in Germany we screened the complete coding region of the TP53 gene in a series of German breast/ovarian cancer families negative for mutations in the BRCA1 and BRCA2 genes.Two different intronic TP53 sequence variants were identified in 6/48 (12.5%) breast/ovarian cancer families. A novel A to T nucleotide change at position 17708 in intron 10 segregating with the disease was detected in three breast cancer families (6.2%). One 17708 A>T-associated breast tumour showed loss of the wild-type allele. This variant was also found in 5/112 (4.5%) healthy controls indicating that it is a polymorphism. A second sequence variant changing a G to C at position 13964 in intron 6 not segregating with the disease was found in two breast cancer families and one breast-ovarian cancer family (6.2%). This variant has previously been shown to occur at an elevated frequency in hereditary breast cancer patients from North America and to be of functional importance leading to inhibition of apoptosis and prolongation of cell survival after DNA-damage. Screening of 185 consecutive unselected German breast cancer patients revealed the 13964 G>C variant in four patients (2.2%). Immunohistochemical analysis of the TP53 protein showed negative immunoreactivity in normal and tumour tissues of one 17708 A>T and six 13964 G>C carriers. TP53 overexpression was detected in the tumour tissue of one sporadic breast cancer patient carrying the 13964 G>C variant. Our results show that intronic changes of the TP53 gene may act as or be associated with risk modifiers in familial breast cancer.

TP53 haplotype-based analysis and incidence of post-angioplasty restenosis

The tumor suppressor gene product, in particular tumor suppressor protein p53 (TP53), has been suggested to play a role in post-angioplasty restenosis. However, no genetic-epidemiological studies relating to TP53 gene polymorphism(s) and the incidence of post-angioplasty restenosis are available. TP53 11951_11966dup16bp, R72P, and 13494G>A polymorphisms were characterized in a cohort of 779 patients, of whom 342 cases had developed restenosis (as defined by >50% loss of lumen compared with immediate post-procedure results) at repeat quantitative coronary angiography at six months post angioplasty. The haplotype-frequency distribution was marginally different between cases and controls with restenosis risk (chi(2)(7df)=13.08, P=0.070). Multivariable haplotype-based logistic regression indicated that haplotypes 16bp(-) -P72-G13494 [corrected], and 16bp(+) -P72-A13494 [corrected] exhibit protective effects on restenosis risk (odds ratio=0.58, 95%CI=0.40-0.83, P=0.0033; odds ratio=0.69, 95%CI=0.48-0.99, P=0.049, respectively). Multivariable haplotype-based linear regression again showed similar, significant association with degree of lumen loss. The present findings indicate protective effects of TP53 16bp(-) -P72-G13494 [corrected], and 16bp(+) -P72-A13494 [corrected] haplotypes in the incidence of restenosis after angioplasty. Furthermore, our study demonstrates that a haplotype-based approach can be more informative than a single-marker or marker-by-marker analysis.

Restriction enzymes in the analysis of genetic alterations responsible for cancer progression

BACKGROUND

Molecular approaches are increasingly being employed to dissect the genetic changes accompanying tumour formation. These methods can often be confusing to the non-specialist as they include complex molecular steps. This can reduce the usefulness of such molecular data to clinicians. The authors aim to aid interpretation of molecular studies in general by presenting a comprehensive review of one molecular approach, i.e. the use of restriction enzymes in molecular studies of tumour development.

METHOD

A review was made of the molecular studies that have employed restriction enzymes in gastrointestinal cancer research. These studies have used restriction enzymes to analyse point mutation induction, gene methylation status and the deletion of chromosomal loci. In addition, emphasis is placed on some of the important considerations for the molecular analysis of tumours that can affect the molecular data obtained.

RESULTS

Restriction enzyme digestion has played, and continues to play, a major role in analysing the genetic changes in cancer. Many adaptations of basic restriction enzyme methodologies have enhanced the application of this approach in cancer genetics.

CONCLUSION

The availability of 200 different restriction enzymes, each recognizing different sequences in DNA, has been invaluable in studying cancer genetics. It is hoped that current advances in protein engineering will facilitate the creation of novel restriction enzymes with tailor-made sequence specificities. This will further improve the applicability of restriction enzymes in cancer genetics.

Significance of intron 6 sequence variations in the TP53 gene in Li-Fraumeni syndrome

Many polymorphisms have been reported in the TP53 gene. Some of these are within the coding region, and may affect the function of the p53 protein, others are within introns or non-coding regions, and their significance is unclear. Recently, a number of publications have claimed that polymorphisms within intron 6 are responsible for inherited predisposition to childhood malignancies, familial breast cancer, and Li-Fraumeni syndrome (LFS). We find no evidence for intron 6 sequence variants predisposing to LFS in our cohort of families and, furthermore, we show that some of the conclusions of other groups cannot be supported by data from our analysis.

TP53 polymorphisms and haplotypes in South Amerindians and neo-Brazilians

To evaluate the genetic diversity of Brazilian populations and contribute to the knowledge of their evolutionary history this study investigated three TP53 polymorphisms (BstUI and MspI RFLPs in exon 4 and intron 6, respectively, and a 16 bp duplication in intron 3). The populations studied were: 114 Amerindians from five Brazilian Indian tribes (Gavião, Surui, Zoró, Wai-Wai and Xavante), 95 Euro-Brazilians and 70 Afro-Brazilians. The polymorphisms were all analysed using PCR amplifications. Gene frequencies and haplotype prevalences were calculated using the ARLEQUIN software. The genetic affinities of these groups with other world populations were estimated by the D(A) distance and neighbour joining method, using the NJBAFD computer program. Neo-Brazilians (immigrants from Europe and Africa) generally presented more variability than Amerindians, Afro-Brazilians being the most variable population. Among Amerindians, Gavião is the only group polymorphic for the three markers. Wai-Wai showed variability in BstUI and MspI RFLPs, while the other tribes were monomorphic for the 16 bp A1 and MspI A2 alleles. A rare haplotype (1-2-1) was verified among the Wai-Wai. This haplotype was previously described in a Chinese sample only, but with low frequency. Therefore, either this combination was lost in the other tribes by genetic drift, recombination, or other factor, or it occurs in the Wai-Wai and Chinese by independent events. The Gavião also presented a haplotype (2-1-1) not observed in the other Amerindians; but since it is present in Euro- and Afro-Brazilians. its occurrence there is probably due to interethnic admixture. The relationships of several world populations obtained using TP53 indicates that this marker is very efficient in clustering populations of the same ethnic group.

Immunohistochemical expression of p53 in breast carcinoma is associated with the intron 1 BglII polymorphism of the p53 gene

Breast carcinoma is a public health problem worldwide. It is known that both genetic and environmental factors are important for breast carcinogenesis and that structural and/or functional alterations at p53 gene are commonly observed in breast tumors. In addition, polymorphisms of several genes in either their coding or non-coding sequences have been found related to cancer risk and/or clinicopathological characteristics of tumors. In this study we have evaluated the intron 1 BglII polymorphism of the p53 gene with a PCR-based approach in 117 cases of breast cancer and 102 healthy women and its association with the immunohistochemical expression of p53 in the tumors. The results showed that the presence of the polymorphism (allele 2) is highly associated with the tumor expression of p53 (p<0.0001) and that there is a trend for increased frequency of allele 2 in cases than in controls (p=0.2376). These data suggest that the germ-line variation in the intron 1 of the p53 gene could produce functional or structural changes of the protein that is reflected by its abnormal expression.

p53 and WAF1 polymorphisms in Jewish-Israeli women with epithelial ovarian cancer and its association with BRCA mutations

OBJECTIVE

To investigate whether polymorphic p53 and WAF1 alleles are associated with clinical, demographic and histopathological features and BRCA mutation in women with ovarian cancer.

DESIGN

A cross-sectional study.

POPULATION

Two hundred and twenty-one nonselected Israeli women with epithelial ovarian cancer.

METHODS

DNA was analysed for known polymorphisms in intron 3 (a 16 nucleotide single repeat) and intron 6 (a G to A change at nucleotide 13,494) of the p53 gene, the S31R polymorphism in the WAF1 gene, and for three predominant Jewish mutations in the BRCA genes (185delAG and 5382insC in BRCA1, and 6174delT in BRCA2).

MAIN OUTCOME MEASURE

The rate of polymorphic p53 and WAF1 alleles and their association with BRCA mutation, ethnic origin, age and stage at diagnosis, and family history of cancer.

RESULTS

Of the tested women, 72 (32.6%) were either BRCA1 (n = 57) or BRCA2 (n = 15) mutation carriers. Sixty-eight of 213 (31.9%) were heterozygous for intron 3 polymorphism, 67/193 (34.7%) for intron 6 polymorphism, and 22/154 (14.3%) for S31R of the WAF1 gene. The p53 and WAF1 polymorphism rate did not differ between BRCA mutation carriers and noncarriers. No significant association between specific p53 or WAF1 genotypes, and clinical, histopathological or demographic variables was observed.

CONCLUSION

In Jewish-Israeli women with sporadic and familial ovarian cancer, p53 or WAF1 polymorphisms do not seem to affect the phenotype.

Well-differentiated villoglandular adenocarcinoma of the uterine cervix: oncogene/tumor suppressor gene alterations and human papillomavirus genotyping

Twelve well-differentiated villoglandular adenocarcinomas (WDVAs) of the uterine cervix were retrospectively analyzed for the presence and specific genotype of human papillomavirus (HPV), tumor suppressor loss (p53, MCC, APC, BRCA1), cancer gene mutation (K-ras-2, exons 1 and 2, p53 exons 5 to 8), and oncogene amplification (c-erbB-2/HER-2/neu, int-2). Tissue for genetic evaluation was obtained by microdissection, using 4-micron-thick histology sections of archival, formalin-fixed, paraffin-embedded specimens. Genotyping involved nucleic acid amplification and DNA sequencing with gene-specific oligonucleotides and L1 region consensus primers for common strains of HPV. Point mutation and HPV strain determination were accomplished by DNA sequence analysis. Tumor suppressor gene loss and oncogene amplification were performed by allelic imbalance analysis in informative subjects based on DNA sequence and microsatellite-length polymorphisms. HPV was present in all tumors and consisted of type 16 (n = 5, 42%) and type 18 (n = 7, 58%) strains, which have been closely associated with cervical neoplasia. K-ras-2 and p53 genes did not manifest point mutational damage. There was no evidence of oncogene amplification or tumor suppressor gene loss. The presence of HPV in all 12 tumors supports the role of HPV infection in the molecular pathogenesis of this uncommon neoplasm. The absence of associated oncogene or tumor suppressor gene damage is consistent with indolent biological behavior and the favorable prognosis of this unusual tumor.

Cumulative prognostic value of p53 mutations and bcl-2 protein expression in head-and-neck cancer treated by radiotherapy

We investigated the prognostic significance of p53-gene mutation (exon 5-9) and bcl-2-protein expression in primary squamous-cell carcinoma of the head and neck (HNSCC) treated by curative radiotherapy (RT). Primary squamous-cell carcinomas for analysis were obtained from 85 consecutive head-and-neck-cancer patients, with complete follow-up data. We detected bcl-2 protein in 24% (20/85) of HNSCC studied; 38 (45%) of the 85 tumours had cells bearing p53 mutations. A strong association was observed between tobacco exposure and bcl-2-protein expression (p = 0.003), an association also evident in those patients who had a p53-mutated carcinoma (p = 0.049). Moreover, we found that most of the bcl-2-positive cancers (70%) were also mutated in the p53 gene (p = 0.010). In univariate and in multivariate analyses, the simultaneous detection of bcl-2 expression and a p53-gene mutation in a tumour biopsy specimen was associated with greater risk of locoregional failure (p = 0.002 and 0.001 respectively) and worse survival (p = 0. 045 and 0.033) within 5 years in HNSCC patients treated by RT. The present study shows a cumulative prognostic value of simultaneous detection of bcl-2 over-expression and p53-gene aberration in some primary HNSCC treated with conventional RT, and provides further evidence for cross-talk between p53 and bcl-2, suggesting that these genes are important determinants of radiation-induced apoptosis, thereby modulating resistance to RT. Int. J. Cancer (Pred. Oncol.) 84:573-579, 1999.

TP53 mutation and haplotype analysis of two large African American families

Two large apparently unrelated African American families with a high incidence of breast cancer and other tumors characteristic of Li-Fraumeni breast sarcoma cancer family syndrome were studied. Mutation screening revealed that in both families the affected members carried a germline mutation of the TP53 gene at codon 133 (ATG--> ACG, M133T). In order to determine whether an ancestral haplotype was shared by these two families, polymorphic markers within and flanking the TP53 gene were studied. Haplotype analysis using five markers revealed an identical haplotype shared by the two families. Loss of heterozygosity at the TP53 locus in the probands' tumor tissues from each family was observed; in each case, the retained allele carried the common haplotype. The frequency of this haplotype in the general African American population is <0.003. This unique haplotype, combined with the rare TP53 mutation, suggests that these African American families share a common ancestry. This finding suggests that other African Americans may be carriers of this mutation and thus may be at risk of early-onset breast cancer or other cancers characteristic of the Li-Fraumeni breast sarcoma cancer family syndrome. The finding of recurring mutations in African Americans may facilitate carrier screening and identification in this population.

Infrequent p53 gene alterations in ulcerative colitis

The purpose of this study was to determine whether point mutations and loss of the p53 gene take place in ulcerative colitis which is histologically negative for dysplasia. DNA was extracted from 13 frozen rectal or colon biopsies and blood samples. Ulcerative colitis was classified histologically as active (10 cases) and inactive (3 cases). Exons 5-8 were amplified by PCR, treated with exonuclease and shrimp alkaline phosphatase and sequenced by the dideoxy chain termination method with the Sequenase Version 2.0 DNA sequencing kit. PCR products of intron 6 and exon 4 were digested with MspI and AccII, respectively, for RFLP analysis. No p53 gene mutation was detected in these cases. The number of informative patients for loss of heterozygosity (LOH) at the p53 intron 6 was high, 11 out of 12 (92%), whereas no LOH was observed. LOH affecting p53 exon 4 was not detected in lesions from 5 of 12 patients (42%). In ulcerative colitis, tumor progression is similar to that in sporadic colon cancer, and other oncogenes and tumor suppressor genes are likely to be mutated before the p53 gene.

Hereditary TP53 codon 292 and somatic P16INK4A codon 94 mutations in a Li-Fraumeni syndrome family

Li-Fraumeni syndrome is an autosomal dominant disorder that is characterized by various types of cancer in childhood and adult cases. Although hereditary TP53 mutation is very rare in different human cancers, it has been frequently reported in Li-Fraumeni syndrome. On the other hand, hereditary mutations of TP57KIP2, P15INK4B, and P16INK4A, which affect the cell cycle similar to TP53, were observed in some types of cancer. In a Turkish family with the diagnosis of Li-Fraumeni syndrome, we analyzed the mutation pattern of TP53, P57KIP2, P15INK4B, and P16INK4A in the peripheral blood, and loss of heterozygosity (homo/hemizygous deletion) pattern of TP53 and P15INK4B/P16INK4A in two tumor tissues. The propositus had a seminoma, his daughter a medulloblastoma, and one of his healthy cousins, a TP53 codon 292 missense point mutation (AAA-->ATA; Lys-->Ile) in the peripheral blood cells. Tumor tissue obtained from the propositus with the seminoma revealed loss of heterozygosity in the TP53 gene. In the analyses of tumor tissues from the propositus and his daughter, a P16INK4A codon 94 missense point mutation (GCG-->GAG; Ala-->Glu) was observed with the hereditary TP53 mutation. P16INK4A codon 94 mutation observed in our family is a novel mutation in Li-Fraumeni syndrome. No other gene alteration in TP53, P57KIP2, P15INK4B, and P16INK4A was observed. Existence of the P16INK4A mutation and the hereditary TP53 mutation with or without loss of heterozygosity in the TP53 gene (seminoma/medulloblastoma) may be evidence for a common mechanism involved in tumorogenesis. The gene alterations in TP53 and P16INK4A genes may be used as tumor markers in our family.

Highly sensitive mutation screening by REF with low concentrations of urea: A blinded analysis of a 2-kb region of the p53 gene reveals two common haplotypes

Restriction endonuclease fingerprinting (REF), a hybrid modification of single-strand conformation polymorphism (SSCP) and restriction endonuclease digestion, has been used previously to detect mutations in 1- to 2-kb segments of DNA. This paper demonstrates that fragment resolution, and thus sensitivity of REF, can be markedly improved by electrophoresis under partially denaturing, rather than nondenaturing, conditions, for genes with a high G+C content. A 2. 1-kb segment of the p53 tumor suppressor gene (54.5% G+C) containing exons 5-9, including the intervening introns, was screened in a blinded analysis of 48 samples from human breast tumors containing known wild-type or mutant p53 genes. In gels containing 0.5 M urea, 97% of the mutant samples were detected correctly, and more than 80% of the mutations were localized within a 200-bp region. In the process of this methodological analysis, it was discovered that: (1) there are two common and four uncommon haplotypes; (2) the two common haplotypes occurred in the three races examined, suggesting an ancient origin; and (3) haplotype II is of substantially higher frequency in the Chinese relative to Japanese (P = 0.023) and Caucasians (P = 0.005). Two other improvements in the REF procedure included (1) the selection of an optimal set of restriction endonucleases by new software (REF Select) developed recently in our laboratory; and (2) the addition of an oligonucleotide "tail," containing two recognition sequences for restriction endonucleases, to the PCR primers to prevent coterminal fragments at the end of amplified products. These modifications facilitate the use of REF for efficient and sensitive mutation screening in p53 and other genes with a high G+C content.

Loss of heterozygosity of p53 gene of oral cancer detected by exfoliative cytology

The p53 tumor suppressor gene is a 16-20-kb section of cellular DNA located on the short arm of human chromosome 17 at position 17 P 13.1. Allelic deletions and/or point mutations in p53 gene are now known to be associated with the development of carcinogenesis. A hallmark of p53 is that both alleles are generally altered during transformation, which usually represents a loss of heterozygosity (LOH). In this study 30 normal dental students and 22 oral cancer patients were collected from the affiliated hospital of Chung Shan Medical and Dental College, Taichung, Taiwan. Extractions of DNA from the buccal mucosa or cancer surface were sampled by cytology brush. The two polymorphic restriction sites exon 4 and intron 6 within the p53 gene were amplified with polymerase chain reactions followed by restriction fragment length polymorphism assay. In heterozygous individuals, 66% of oral cancers demonstrated loss of p53 gene heterozygosity at the exon 4 site, and 50% showed LOH at the intron 6 site. These results indicate that inactivation of p53 gene is associated with development and/or progression of oral cancer. The essential advantages of oral exfoliative cytology are the non-invasiveness, painlessness, rapidity, ease and cost-effectiveness of cell sampling and DNA extraction. Furthermore, this experimental assay might be useful for preliminary screening of carcinogenesis in human beings.

p53 and p16INK4A mutations during the progression of glomus tumor

Glomus tumors are significantly rare tumors of carotid body. The great majority of these tumors are benign in character. Here we present two brothers with hereditary glomus jugulare tumor who had consanguineous parents. Radiotherapy was applied approximately 8 and 10 years ago for treatment in both cases. Eight years later, one of these cases came to our notice due to relapse. The mutation pattern of p53, p57KIP2, p16INK4A and p15NK4B genes which have roles in the cell cycle, was analyzed in tumor samples obtained from the two affected cases in the initial phase and from one of these cases at relapse. The DNA sample obtained from the case in initial diagnosis phase revealed no p53, p57KIP2, p16INK4A or p15INK4B mutation. He is still in remission phase. Despite the lack of p53, p57KIP2, p16INK4A and p15INK4B mutation at initial diagnosis the tumor DNA of the other case in relapse revealed p53 codon 243 (ATG-->ATC; met-->ile) and p16 codon 97 (GAC-->AAC; asp-->asn) missense point mutations. No loss of heterozygosity in p53 and p16INK4A was observed by microsatellite analysis of tumoral tissues in these cases. P53 and p16INK4A mutations observed in relapse phase were in conserved regions of both genes. No previous reports have been published with these mutations in glomus tumor during progression. The mutation observed in this case may due to radiotherapy. In spite of this possibility, the missense point mutations in conserved region of p53 and p16INK4A genes may indicate the role of p53 and p16INK4A in tumor progression of glomus tumors.

A novel germ-line mutation in the noncoding region of the p53 gene in a Li-Fraumeni family

We identified a novel germ-line p53 mutation in the noncoding, nonsplicing regions of a Li-Fraumeni family. Patients belonging to this family included pediatric medulloblastoma and rhabdomyosarcoma patients and a breast carcinoma patient. Three positions in the p53 gene were analyzed for loss of heterozygosity (LOH). One of the three loci retained heterozygosity, whereas the other two exhibited LOH. Sequence analysis of the third locus identified a change of 5'-CCGGGTGA-3' to 5'-CCAGGTTGGA-3', 63 bp downstream of exon 6. The mutation was identified in the germ line of the two pediatric patients and in each of the related parents. We excluded any additional mutation in the entire coding region of the p53 gene, including splice-site intronic sequences. Strong positive nuclear staining of the p53 protein was detected in both normal and tumor paraffin-embedded tissues. Eighty-five normal persons were negative for this alteration, which thus supports it as a mutation. These results may indicate that genetic changes within the noncoding region of the p53 gene may serve as an alternative mechanism of activating this gene. Mutations in the noncoding region of this gene should be further studied.

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

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

Polymorphisms in the p53 gene in thyroid tumours and blood samples of children from areas in Belarus

We present changes in the p53 gene in a group of 70 thyroid tumours and 40 blood samples obtained from children from Belarus. Three thyroid tumours show a polymorphism in exon 6 (codon 213) and 5 tumours show a polymorphism in intron 6, 37 bp upstream to the 5'-end of exon 7. Only one patient has a mutation in exon 7 (codon 258) resulting in an amino acid substitution in the protein p53. The distribution of polymorphisms in the 40 blood samples was as follows: three patients had a polymorphism in exon 6 and two persons had a polymorphism in intron 6. One polymorphism in intron 6 was also found in the group of 30 healthy children from Belarus. The fact that the differences in the sequence in p53 found in the tumours was also seen in the blood of these patients demonstrates that they are polymorphisms not induced by radiation exposure. It is difficult to conclude, if the polymorphisms found by us could be associated with the predisposition to radiation-induced cancer.

p53 mutation as the second event in juvenile chronic myelogenous leukemia in a patient with neurofibromatosis type 1

BACKGROUND

Young patients with neurofibromatosis type 1 (NF1) are at increased risk of developing various malignancies, most of which are myeloid disorders. The observed loss of NF1 allele in the myeloid malignancies of NF1 patients suggests a role of NF1 as a tumor suppressor gene. Loss of 17p was found to be quite frequent in neural crest tumors from patients with NF1, raising the possibility of p53 tumor suppressor gene involvement in other NF1-related tumors.

METHODS

The authors studied mutations in the NF1 and p53 genes, using loss of heterozygosity, single strand conformation polymorphism, heteroduplex and sequencing analyses.

RESULTS

An NF1 germline mutation was identified in exon 31 of a child who developed juvenile chronic myelogenous leukemia (JCML). The mutation was segregated within the proband's family. A 14bp deletion at exon 6 of the p53 gene was observed when JCML was diagnosed, and the wild-type p53 allele was lost during progression of the disease. No loss of the normal NF1 allele could be detected.

CONCLUSIONS

A germline mutation in the NF1 gene and sequential inactivation of p53 alleles in the malignant clone of JCML raise the possibility of a correlation between NF1 and p53 genes in the tumorigenesis of JCML.

Loss of heterozygosity of the retinoblastoma and p53 genes in primary cervical carcinomas with human papillomavirus infection

OBJECTIVE

Paired DNA samples from 55 primary uterine cervical carcinomas and normal bloods were studied for chromosomal allelic loss (loss of heterozygosity; LOH) of the retinoblastoma (Rb) and p53 gene loci by polymerase chain reaction (PCR) or PCR-restriction fragment length polymorphism analysis. All the study samples contained at least one of the oncogenic human papillomavirus (HPV) type 16 and/or 18 sequences. And the relationships between allelic losses of these genes and conventional clinicopathological parameters were evaluated.

METHODS

In order to detect LOH of the Rb gene in cervical cancers, we analyzed four polymorphic intronic sites (intron 1, 17, 20, and 25) of the Rb gene and one additional microsatellite near the Rb locus (D13S118). For detection of the LOH in p53, three intragenic polymorphisms (exon 1, exon 4, intron 6) and one microsatellite distal to the p53 gene (D17S5) were examined.

RESULTS

By analyzing this system, we could increase the heterozygosity of the Rb and p53 loci up to 0.91 and 1, respectively. The observed allelic loss rates of the Rb and p53 loci in informative cases were 14% (7/50) and 5.5% (3/55), respectively. The patients with LOH at the D13S118 locus also had the allelic loss of the Rb gene, whereas only one of the four patients with LOH at the D17S5 locus showed a concomittant allelic loss of the p53 gene. The frequency of cervical cancer with one LOH at the Rb or p53 loci was 20% (11/55). No shifted bands were observed in the PCR-single-strand conformation polymorphism analysis of the p53 gene. The LOH of the Rb or p53 gene was not significantly associated with other parameters including clinical stage, histological type, degree of differentiation, status of HPV infection, and p53 gene mutation.

CONCLUSION

Concerning the results above, we conclude that the allelic imbalance of the Rb or p53 gene itself is not implicated as a major contributing factor in the malignant transformation or the tumor progression in HPV-positive uterine cervical cancers.

Exon 5 mutations in the p53 gene in relapsed childhood acute lymphoblastic leukemia

Thirty seven children with relapsed acute lymphoblastic leukemia (ALL), 25 B-lineage and 12 T-lineage, were analyzed for p53 alterations at different stages of the disease. Loss of heterozygosity (LOH) was detected in the relapse phase in three patients. p53 mutations were identified by single strand conformation polymorphism (SSCP) and sequencing analyzes in seven of the 37 ALL patients (19%); three B-lineage (12%) and four T-lineage (33%). Most of the mutations were identified in the relapse phase. In two exceptional cases, one of the mutations was indicated as a germ line and the other was already present at diagnosis. No p53 mutation was identified in any of the other 20 available bone marrow samples obtained at diagnosis. No correlation between the p53 status and clinical outcome could be determined. The majority of the mutations (four out of seven, 57%) were clustered at exon 5. Our data implicate that p53 exon 5 is a frequent site of mutations in relapsed childhood ALL.

Polymorphisms of H-ras-1 and p53 in breast cancer and lung cancer: a meta-analysis

Certain polymorphic variants of H-ras-1 and p53 have been investigated for an association between inheritance and cancer risk. The results of a metaanalysis, which reviews studies of H-ras-1 rare alleles and p53 codon 72 allelic variants in breast and lung cancer, are presented. The data constituted evidence for elevated risk of both breast and lung cancer with inheritance of rare H-ras-1 alleles. Calculated population attributable risks are 0.092 and 0.037 for breast and lung cancer, respectively. The frequency of the rare H-ras-1 alleles was observed to be greater in African Americans than in Caucasians, and a specific allele (A3.5) that is common in African Americans was found only at low frequency in Caucasians. For p53 a consensus has yet to be reached. Lung cancer studies conducted in Caucasian and African-American populations have found no evidence of risk associated with the proline variant of codon 72. Two similar studies conducted in Japanese populations suggested an association between p53 genotype distribution and lung cancer risk. However, one implicates the proline allele but the other implicates the arginine allele. The frequency of the proline variant is significantly dependent on race. Frequencies have been reported for control populations of Japanese (0.347 and 0.401), Caucasian (0.295, 0.284, and 0.214), African American (0.628 and 0.527), and Mexican American (0.263).

Loss of heterozygosity in normal tissue adjacent to breast carcinomas

Loss of heterozygosity (LOH) was detected in morphologically normal lobules adjacent to breast cancers. The most frequent aberration was at chromosome 3p22-25; of ten cases with this LOH in the carcinoma, six displayed the same LOH in adjacent normal lobules. This suggests that in a subset of sporadic breast cancers, a tumor suppresser gene at 3p22-25 may be important in initiation or early progression of tumorigenesis. Among sixteen breast cancers with LOH at 17p13.1 and five breast cancers with LOH at 11p15.5, one case each displayed the same LOH in adjacent normal lobules. Thus the molecular heterogeneity that characterizes invasive breast cancers may occur at the earliest detectable stages of progression.

Feasibility of using decades-old archival tissues in molecular oncology/epidemiology

Archival tissues are a bountiful resource for various studies. Polymerase chain reaction permits the use of such tissues for molecular biological analyses of disease causation. However, a comprehensive study using a large number of decades-old samples (20 or more years) for molecular oncology/epidemiology has never been shown to be feasible. We have relied upon the unique tumor registry of atomic bomb survivors to show that such studies are possible using 275 hepatocellular carcinoma and 41 skin cancer cases. We used 23 relatively recent thyroid papillary carcinoma cases from persons living in the vicinity of the Chernobyl nuclear reactor accident for comparison. Degradation of DNA is severe in autopsy hepatocellular carcinoma samples but can be compensated for by decreasing the polymerase chain reaction product size. Increasing the amount of DNA that is used by a factor of 8 improved amplification efficiency from approximately 60 to 80%. Age of the samples was not as great a problem as was the source of procurement. The extracted DNA can be used for all types of assays that require polymerase chain reaction amplification, such as restriction fragment length polymorphism, single-strand conformation polymorphism, and direct sequencing.

Spontaneous immortalization of cultured skin fibroblasts obtained from a high-dose atomic bomb survivor

Two immortal fibroblastic cell strains (substrains) were established by culturing healthy skin cells obtained from a high-dose atomic bomb survivor (female, age 76 years, 5.14 Gy) for more than 4 years. Designated FM-U and FM-M, the two substrains share the same marker chromosome, t(5q-;6p+), but are karyotypically different, possessing hypodiploid chromosome numbers (39-43) in the former and hypertriploid (69-76) in the latter. Thus far, the two strains have passed through 117 and 156 subcultures or more than 230 and 310 cumulative population doublings, respectively, each passage requiring 4-6 days in the former and 3-4 days in the latter. In the process of immortalization, sequential rearrangement among various chromosomes presumably due to telomeric and interstitial telomeric fusions took place following the telomere shortening, particularly in the senescence and postsenescence phase cells. Of particular interest is the fact that loss of heterozygosity (LOH) of the p53 gene was demonstrated in these immortalized cell populations. In addition, the allelic patterns of the LOH of p53 differed. Further evidence indicative of infinite proliferation was demonstrated in both strains, such as the telomere elongation and the significantly low frequency of cells possessing dicentric chromosomes.

N-ras mutations in radiation-induced murine leukemic cells

N-ras mutations were examined in DNA samples extracted from the spleen of CBA/Ca mice that developed myeloid leukemia (ML) following exposure to radiations of different qualities. A total of 17 ML cases, i.e. 5 cases of neutron-induced and 12 cases of photon- (3 gamma-ray and 9 x-ray) induced ML were included in the study along with 12 DNA samples from the bone marrow cells of control mice. Polymerase chain reaction-single strand conformational polymorphisms (PCR-SSCP) and the direct sequencing of PCR products were used to analyze three regions of the N-ras gene: (i) a 120 base-pair (bp) long portion of exon I (codons 2-37); (ii) a 103 bp long portion of exon II (codons 48-82); and (iii) a 107 bp long portion of exon III (codons 118-150). PCR-SSCP mobility shifts indicated mutations within only exon II of the N-ras gene. Such mutations were more prevalent in samples from mice exposed to fast neutrons. The exact type and location of these mutations were then determined by direct DNA sequencing. Silent point mutations, i.e. base transitions at the third base of codons 57 (GAC-->GAT), 62 (CAA-->CAC), or 70 (CAG-->CAA) were present only in mice that developed ML after exposure to fast neutrons. A base transversion at the third base of codon 61 (CAA-->CAC) was also observed in some ML cases. DNA sequencing demonstrated that ML samples contained normal as well as mutated DNA sequences. The higher frequency of N-ras mutations in neutron-induced ML suggested that fast neutrons are more effective in inducing genomic instability at the N-ras region of the genome. More importantly, N-ras mutations are not the initiating event in radiation leukemogenesis. This conclusion was supported by the finding that N-ras mutations were detected only in mice with an overt leukemic phenotype but not in mice with minimal tissue infiltration of leukemic cells, suggesting that the disease may be present prior to the presence of N-ras mutations. Alternatively, N-ras may be present in these mice but a large number of normal spleen cells in these mice interferes with the detection of mutation in a small population of leukemic cells.

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

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

Benign neurofibromas in type 1 neurofibromatosis (NF1) show somatic deletions of the NF1 gene

Neurofibromatosis type 1 (NF1) is one of the most common human autosomal dominant diseases. NF1 is characterized by café-au-lait spots (CLS), axillary freckles and Lisch nodules of the iris. Another hallmark of NF1 is the development of neurofibromas, benign tumours that arise from peripheral nerve sheaths. NF1 patients also have an increased incidence of certain malignant tumours. Malignancies in NF1 are believed to follow the 'two-hit' hypothesis, in which one allele is constitutionally inactivated while the other allele is subsequently inactivated ('second hit') at the somatic level. This hypothesis has not, however, been fully tested in the aetiology of benign neurofibromas. This is a crucial issue since it addresses not only the basic mechanism behind the genesis of neurofibromas, but may also indicate a mechanism common to many or all NF1 features. Using both NF1 intragenic polymorphisms as well as markers from flanking and more distal regions of chromosome 17, we have investigated loss of heterozygosity (LOH) in 22 neurofibromas from five unrelated NF1 patients. Eight of these tumours revealed somatic deletions involving NF1, indicating that inactivation of NF1 is associated with at least some neurofibromas.

Detection of loss of heterozygosity in the p53 tumor suppressor gene using a PCR-based assay

Inactivation of the p53 tumor suppressor gene has been reported to be a prognostic factor in several human cancer types. Normal function of the gene is affected by deletion in one allele; dysfunction of the other allele is often caused by a mutation. In tumors of heterozygous individuals, deletion of one allele can be detected as loss of heterozygosity (LOH). A recently found variable number of tandem repeats (VNTR) segment in intron 1 of the p53 gene seems to be highly polymorphic and, therefore, a very useful marker in detecting LOH in various types of tumor samples. We in vitro amplified the VNTR segment from genomic DNA samples of 101 lung cancer patients and run conventional agarose gel electrophoreses in order to detect the alleles of various length, differing by the number of repeats. The usefulness of the method was studied using DNA from white blood cell samples and from fresh and formalin-fixed, paraffin-embedded tumor samples. Of the patients, 56% were found to have two different alleles, i.e. were informative in this assay. In 18% of the lung tumors from the informative cases, LOH in the p53 suppressor gene was detected.

Detection of P53 tumor-suppressor-gene protein in bladder tumors and prostate cancer: possible clinical implications

For a variety of human malignancies such as breast cancer and cancer of the prostate, p53 oncoprotein overexpression indicating an alteration of the p53 tumor-suppressor gene has been described as a prognostic factor for a poor clinical outcome. To investigate the overexpression of p53 oncoprotein in transitional-cell carcinoma of the bladder, 58 bladder cancer specimens of different clinical stages and histological grades were investigated using an immunohistochemical approach. A correlation between p53 positivity and tumor stage was observed, with an increase from 38.5% of superficial (Ta) tumors to 83.3% of muscle-invasive (T3/T4) tumors staining positively for p53 oncoprotein. Furthermore, an increase from 46.7% of G1 tumors to 75% of G3 tumors was observed. In 22 of 25 (87%) informative patients the results of the immunohistochemical staining could be verified by the determination of p53 mutations as detected by polymerase chain reaction (PCR)-directed analysis of restriction-fragment-length polymorphisms (RFLP). To determine the prognostic value of p53 immunohistochemistry for the clinical course of superficial bladder cancer, the overexpression of p53 oncoprotein was investigated in 41 patients with superficial bladder tumors (T1) undergoing complete transurethral tumor resection. The detection of p53 protein was correlated with further clinically important variables such as sex, age, histological grading, former instillation therapy, and immunohistochemical determination of the proliferation rate by staining for PCNA (proliferating-cell nuclear antigen; monoclonal antibody PC10).(ABSTRACT TRUNCATED AT 250 WORDS)

Overexpression of the p53 oncoprotein in carcinoma in situ of the testis

Carcinoma in situ (CIS) is regarded as the precursor lesion of testicular germ cell tumors. In adults CIS cells have also been described within the normal testicular tissue adjacent to mature teratomas with a frequency of 52-88%. These CIS-cells can be identified by immunohistochemical staining for "placental like alkaline phosphatase" (PLAP). In four of eight patients with mature teratomas CIS was identified by immunohistochemistry for "PLAP" in atrophic testicular tubules adjacent to the tumors. In three of these patients cells of CIS were positive for the p53 oncoprotein, indicating a mutational inactivation of the p53 tumor suppressor gene. The malignant potential of mature teratomas, which do occur without histological signs of malignancy, may therefore be associated with the occurrence of CIS within the histologically normal appearing testicular tissue adjacent to the mature tumor. Immunohistochemical positivity for the p53 protein in CIS cells of some patients may indicate that the mutational inactivation of the p53 tumor suppressor gene could be involved early in the development of testicular germ cell tumors.

p53 mutations and overexpression in locally advanced breast cancers

Alterations in the p53 gene were analysed in 39 patients with locally advanced breast cancers (LABCs) (stage III-IV) with inflammatory signs in most cases (UICC stage T4d = 32 patients) by molecular and immunohistochemical (IHC) approaches. All patients were included in the same therapy protocol. Using polymerase chain reaction (PCR) and a single-strand conformational polymorphism migration technique (SSCP), the presence of mutations in exons 2-11, covering the entire coding sequence of the p53 gene, was evaluated. Using the mouse specific anti-human p53 monoclonal antibody (PAb 1801), we also looked for overexpression of the p53 protein in tissue sections. In 16 cases shifted bands were reproducibly identified by PCR-SSCP, and all but one (localised to exon 10) were in exons 5-8, the usual mutational hotspots. Fifteen of these 16 samples were sequenced and 14 of the suspected mutations (36%) were confirmed. Most of them (12) were single nucleotide substitutions, and transitions were more frequent (eight cases) than transversions (four cases). Fourteen of the tumour samples were positively stained with the monoclonal antibody PAb 1801, 11 with nuclear staining only, two with mixed cytoplasmic and nuclear staining and one with cytoplasmic staining only. Staining patterns were very heterogeneous in terms of the percentage of positive cells (10-75%) and their distribution in the tissue section (isolated foci or dispersed cells). In 11 of the 14 mutated cases a positive immunostaining was observed. The presence of a p53 mutation was significantly associated with larger tumour diameter (chi 2 = 7.490, P = 0.0062) and the presence of clinical metastases (stage IV) (chi 2 = 10.113, P = 0.0015). A non-statistically significant trend of association was observed between p53 mutation, negative oestrogen receptors and lower response rate to therapy. Our results in this group of patients and the heterogeneity of the staining of tumour cells in tissue sections suggest that p53 mutations could be a late event in this non-familial form of breast cancer.

Rapid detection of loss of heterozygosity of chromosome 17p by polymerase chain reaction-based variable number of tandem repeat analysis and detection of single-strand conformation polymorphism of intragenic p53 polymorphisms

Intragenic restriction site polymorphisms in amino acid residue 72 in exon 4 and a Mspl polymorphism in intron 6 of the p53 tumour suppressor gene can both serve as polymorphic markers. Probe YNZ22 (D17S5) is a highly polymorphic, variable number of tandem repeat (VNTR) marker which maps to chromosome 17p13.1 where the p53 gene is located. Locus specific amplification by polymerase chain reaction (PCR) technique and subsequent non-isotopic single-strand conformation polymorphism analysis of the PCR fragments was used for the detection of loss heterozygosity (LOH) of 17p including the p53 gene locus. In combination with a PCR-based method for the analysis of the VNTR locus D17S5 using unique sequences flanking the polymorphic region of YNZ22 we investigated tumour DNA and corresponding constitutional DNA from 69 patients, including 39 patients with gastric cancer, 21 patients with osteosarcomas and 9 patients with Ewing's sarcomas. Using all three methods, 49/69 (71%) patients were informative for LOH, which revealed allelic loss in 5/39 (12.8%) gastric cancers, 1/9 (11.1%) Ewing's sarcoma, and 4/20 (20%) osteosarcomas.

TP53 allele loss, mutations and expression in malignant melanoma

p53 alterations at the DNA, mRNA and protein levels were studied in tumour metastases sampled from 30 patients with malignant melanoma. Paraffin-embedded sections from these and an additional 12 patients were examined for the presence of p53 protein. TP53 gene aberrations were found in 7 of 30 (23%) of the patients, six of which showed loss of heterozygosity (LOH). Point mutations were detected in only two cases, one of which had LOH whereas the other was non-informative. Increased levels of p53 mRNA were present in only one tumour with, but in six cases without, detectable DNA abnormalities. Four of the latter and six tumours with normal transcript levels had immunohistochemically detectable levels of p53 protein. In 25 cases in which corresponding primary and metastatic lesions could be compared, closely similar immunoreactivity patterns were observed. Increased expression of the MDM2 gene was found in only one tumour in parallel with overexpression of p53. Altogether, the data indicate that inactivation of the p53 regulatory pathway is not of major significance in the tumorigenesis of malignant melanoma. However, a significant association was found between p53 immunoreactivity and the relapse-free period in patients with superficial spreading melanoma. That increased protein expression was predominantly found in tumours without DNA alterations might suggest a role for the wild-type p53 protein in restricting malignant cell proliferation in these cases.

Genetic alterations of the TP53 gene, p53 protein expression and HPV infection in primary cervical carcinomas

Primary cervical carcinomas from 92 patients were investigated for genetic alterations in the tumour suppressor gene TP53. Studies of allelic imbalance (AI) were performed by Southern blot analysis and by using two PCR (polymerase chain reaction) polymorphisms within the TP53 gene. AI in the tumour was observed in 22 per cent (11 of 52 informative patients) and was significantly associated with recurrence both in a univariate (P = 0.013) and in a multivariate (P = 0.045) analysis. The DNA samples were subjected to mutation analysis of four of the conserved domains in the TP53 gene, using PCR followed by constant denaturant gel electrophoresis (CDGE). Mutations were observed in 2 of 92 tumours (2 per cent), of which one was a silent mutation and the other a frameshift. Overexpression of the p53 protein was found by immunostaining of sections from formalin-fixed, paraffin-embedded material in 55 per cent (51/92) of the tumours. In 88 per cent (45/51) of these, overexpression was present in less than 5 per cent of the tumour cells. Overexpression was significantly associated with relapse-free survival only in a univariate analysis (P = 0.045). AI of the TP53 locus did not correlate with p53 expression or mutation. The important gene on 17p, responsible for the shorter disease-free survival for patients with AI of TP53, may therefore be another gene closely linked to TP53. In addition, the 92 tumour samples were tested for the presence of human papillomavirus (HPV) types 16 and 18. Fifty-four per cent (50/92) of the samples were positive for HPV 16 using in situ hybridization, and 93 per cent (86/92) using the PCR technique. The numbers for HPV 18 were 15 per cent (14/92) and 23 per cent (21/92), respectively. Twenty-one per cent (19/92) were positive for both HPV 16 and HPV 18, while 4 per cent (4/92) were negative for both HPV 16 and 18. The tumour with the frameshift TP53 mutation was HPV 16-positive, and the four samples negative for HPV 16 and 18 did not contain TP53 mutations within the conserved domains but had elevated p53 protein expression.