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PubMed1987

Radiation-induced forward and reverse specific locus mutations and dominant cataract mutations in treated strain BALB/c and DBA/2 male mice.

Strain BALB/c and DBA/2 mice were chosen to investigate the effects of genetic background on the radiation-induced mutation rate since they exhibit differences in their radiation sensitivity. Males were exposed to 3 + 3-Gy X-irradiation and mated to untreated specific locus Test-stock females. Offspring resulting from treated spermatogonia were screened for induced specific locus forward and reverse mutations and dominant cataract mutations. Since BALB/c mice are homozygous brown and albino, specific locus forward mutations could be screened at 5 of the 7 specific loci (a, d, se, p, s), while reverse mutations could be screened at the b and c loci. Strain DBA/2 is homozygous non-agouti, brown and dilute. Therefore, specific locus forward mutations could be screened at 4 loci (c, se, p, s) and reverse mutations were screened at the a, b and d loci. Results indicate no effect of genetic background on the sensitivity to mutation induction of specific locus forward mutations, while for the dominant cataract alleles strain DBA/2 exhibited a higher mutation rate than either strain BALB/c or similarly treated (101/El X C3H/El)F1 mice. If, by confirmation, these differences should be demonstrated to be real, it is interesting that strain DBA/2 should exhibit a greater sensitivity to radiation-induced dominant mutations. First, strain DBA/2 was chosen as radiation resistant or repair competent. The observation that DBA/2 exhibited a higher sensitivity to radiation-induced mutation may indicate a role for repair, albeit misrepair, in the mutation process. Second, that the effect of genotype was only observed for the mutation rate to dominant cataract alleles may reflect a difference in the spectrum of DNA alterations which result in dominant or recessive alleles. A dominant allele is more likely misinformation, such that as heterozygote it interferes with the wild-type allele. By comparison, a recessive allele may result from any DNA alteration leading to the loss of a functional gene product. One reverse mutation at each of the a and d loci was recovered in the present experiments. The similarities of the present results for radiation-induced reverse mutations with the extensive data on the spontaneous reverse mutation rates are interesting. Reverse mutations were recovered only at the a and d loci. Further, the reverse mutations recovered at the a locus were to alternate alleles (at, Aw or Asy) while true reverse mutations were apparently recovered at the d locus.

Abnormalities, Radiation-Induced↗
PubMed1994

X-ray-induced specific-locus mutations in the ad-3 region of two-component heterokaryons of Neurospora crassa. XII. Analysis of multiple-locus ad-3 mutations reveals a nonrandom distribution of the separate sites of recessive lethal damage throughout the genome.

Previous studies on X-ray-induced adenine-3 mutations induced in heterokaryon 12 of Neurospora crassa showed that they consisted of gene/point mutations, multilocus deletion mutations, and 3 different genotypic classes of multiple-locus mutations (designated [-3]IR + RLCL, ad-3R + RLCL, and ad-3R + RL). In the present paper, multiple-locus mutations consisting of gene/point mutations at the ad-3A or the ad-3B locus with sites of recessive lethal damage closely linked to the ad-3 region (designated ad-3R + RLCL) or with sites of recessive lethal damage elsewhere in the genome (designated ad-3R + RL) were analyzed to determine whether they resulted from mutations at the same sites or different sites throughout the genome. It was assumed that if the recessive lethal mutations in individual multiple-locus mutations showed complementation on adenine-supplemented medium, they resulted from mutations at different sites. Multiple-locus mutations from both major genotypic classes were combined, as forced heterokaryons, in all possible pairwise combinations and then were plated out on adenine-supplemented medium. These studies indicated that 89.3% (50/56) of the recessive lethal mutations in these 2 classes of multiple-locus mutations complement one another. Thus, they are presumed to have resulted predominantly from genetic damage at different sites throughout the genome. Within the group of 20 multiple-locus mutations that did not complement in various pairwise combinations, 90% (18/20) appear to map in a region, distal to the ad-3 region, defined by a series of overlapping multilocus deletion mutations in 6 mutations of genotype ad-3R + RLCL. The other 10% (2/20) are located elsewhere on Linkage Group I or elsewhere in the genome. The present data base on multiple-locus mutations is unique; such events either can not be detected, or can only be detected with difficulty, in other eukaryotic specific-locus assay systems such as mammalian cells in culture, Drosophila or mice. Our data on X-ray-induced ad-3 specific-locus mutations from the present and previous studies demonstrate the presence of additional sites of genetic damage, both closely linked with the ad-3 region or elsewhere in the genome, in ad-3 specific-locus mutations. Because the frequencies of each class of multiple-locus mutations is dose-dependent, they must be taken into account in genetic risk assessment exercises. Failure to acknowledge the presence of such additional sites of genetic damage in the utilization of specific-locus data could result in underestimation of the risk of human exposure to environmental mutagens.

Adenine↗
PubMed2000

Ionizing radiation and genetic risks. XI. The doubling dose estimates from the mid-1950s to the present and the conceptual change to the use of human data on spontaneous mutation rates and mouse data on induced mutation rates for doubling dose calculations.

This paper provides an overview of the concept of doubling dose, changes in the database employed for calculating it over the past 30 years and recent advances in this area. The doubling dose is estimated as a ratio of the average rates of spontaneous and induced mutations in a defined set of genes. The reciprocal of the doubling dose is the relative mutation risk per unit dose and is one of the quantities used in estimating genetic risks of radiation exposures. Most of the doubling dose estimates used thus far have been based on mouse data on spontaneous and induced rates of mutations. Initially restricted to mutations in defined genes (with particular focus on the seven genes at which induced recessive mutations were studied in different laboratories), the doubling dose concept was subsequently expanded to include other endpoints of genetic damage. At least during the past 20 years, the magnitude of the doubling dose has remained unchanged at approximately 1 Gy for chronic low LET radiation exposures. One of the assumptions underlying the use of the doubling dose based on mouse data for predicting genetic risks in humans, namely, that the spontaneous rates of mutations in mouse and human genes are similar, is incorrect; this is because of the fact that, unlike in the mouse, the mutation rate in humans differs between the two sexes (being higher in males than in females) and increases with paternal age. Further, an additional source of uncertainty in spontaneous mutation rate estimates in mice has been uncovered. This is related to the non-inclusion of mutations which arise as germinal mosaics and which result in clusters of identical mutations in the following generation. In view of these reasons, it is suggested that a prudent way forward is to revert to the use of human data on spontaneous mutation rates and mouse data on induced mutation rates for doubling dose calculations as was first done in the 1972 BEIR report of the US National Academy of Sciences. The advantages of this procedure are the following: (i) estimates of spontaneous mutation rates in humans, which are usually presented as sex-averaged rates, automatically include sex differences and paternal age-effects; (ii) since human geneticists count all mutations that arise anew irrespective of whether they are part of a cluster or not, had clusters occurred, they would have been included in mutation rate calculations and (iii) one stays close to the aim of risk estimation, namely, estimation of the risk of genetic diseases in humans. On the basis of detailed analyses of the pertinent data, it is now estimated that the average spontaneous mutation rate of human genes (n=135 genes) is: (2.95+/-0.64)x10(-6) per gene and the average induced mutation rate of mouse genes (n=34) is: (0.36+/-0.10)x10(-5) per gene per Gy for chronic low LET radiation. The resultant doubling dose is (0.82+/-0.29) Gy. The standard error of the doubling dose estimate incorporates sampling variability across loci for estimates of spontaneous and induced mutation rates as well as variability in induced mutation rates in individual mouse experiments on radiation-induced mutations. We suggest the use of a rounded doubling dose value of 1 Gy for estimating genetic risks of radiation. Although this value is the same as that used previously, its conceptual basis is different and the present estimate is based on more extensive data than has so far been the case.

Animals↗
PubMed1996

Characterization of the factor VIII defect in 147 patients with sporadic hemophilia A: family studies indicate a mutation type-dependent sex ratio of mutation frequencies.

The clinical manifestation of hemophilia A is caused by a wide range of different mutations. In this study the factor VIII genes of 147 severe hemophilia A patients--all exclusively from sporadic families--were screened for mutations by use of the complete panel of modern DNA techniques. The pathogenous defect could be characterized in 126 patients (85.7 percent). Fifty-five patients (37.4 percent) showed a F8A-gene inversion, 47 (32.0 percent) a point mutation, 14 (9.5 percent) a small deletion, 8 (5.4 percent) a large deletion, and 2 (1.4 percent) a small insertion. Further, four (2.7 percent) mutations were localized but could not be sequenced yet. No mutation could be identified in 17 patients (11.6 percent). Sixteen (10.9 percent) of the identified mutations occurred in the B domain. Four of these were located in an adenosine nucleotide stretch at codon 1192, indicating a mutation hotspot. Somatic mosaicisms were detected in 3 (3.9 percent) of 76 patients, mothers, comprising 3 of 16 de novo mutations in the patients mothers. Investigation of family relatives allowed detection of a de novo mutation in 16 of 76 two-generation and 28 of 34 three-generation families. On the basis of these data, the male:female ratio of mutation frequencies (k) was estimated as k = 3.6. By use of the quotients of mutation origin in maternal grandfather to patients mother or to maternal grandmother, k was directly estimated as k = 15 and k = 7.5, respectively. Considering each mutation type separately, we revealed a mutation type-specific sex ratio of mutation frequencies. Point mutations showed a 5-to-10-fold-higher and inversions a >10-fold-higher mutation rate in male germ cells, whereas deletions showed a >5-fold-higher mutation rate in female germ cells. Consequently, and in accordance with the data of other diseases like Duchenne muscular dystrophy, our results indicate that at least for X-chromosomal disorders the male:female mutation rate of a disease is determined by its proportion of the different mutation types.

Base Sequence↗
PubMed1979

Is there a proportionality between the spontaneous and the X-ray-induction rates of mutations? Experiments with mutations at 13 X-chromosome loci in Drosophila melanogaster.

The X-ray induction of recessive visible specific locus mutations at 14 X-chromsome loci was studied in Drosophila melanogaster using the "Maxy" technique. The X-ray exposure was 3000 R to 5-day-old males and the sampling of germ cells was restricted to mature spermatozoa. Presumptive mutant females recovered in the F1 generation were tested for transmission, allelism, fertility and viability in males. A total of 128 mutations (115 completes and 13 mosaics including those that were male viable as well as male-lethal) recovered among 38 898 female progeny were found to be transmitted. On the basis of the above frequency, the average mutation rate can be estimated as 7.8 X 10(-8)/locus/R; for mutations that were viable and fertile in males, the rate is 3.0 X 10(-5)/locus/R (49 mutations among 38 898 progeny). The frequency of mutations at the different loci encompassed a wide range: while no mutations were recovered at the raspberry and carnation loci, at others, the numbers ranged from 1 at echinus to 31 at garnet; in addition, the proportion of mutations that was male-viable was also different, depending on the locus. Schalet's extensive data on spontaneous mutations at 13 (of the 14 loci employed in the present study) loci permit an estimate of the spontaneous rate which is 6.1 X 10(-6)/locus (a total of39 mutations among 490 000 progeny); for mutations that were viable and fertile in males, the rate is 3.0 X 10(-6)/locus (19 mutations among 490 000 progeny). The mutability of the different loci varied over a 9-fold range. When the different loci are ranked depending on their relative mutability (for spontaneous and induced mutations) it is found that in general, loci that mutate spontaneously relatively more frequently are also those at which more mutations have been recovered in the radiation experiments and likewise, those that are less mutable spontaneously are also those that mutate less after irradiation. Since the data are limited, it is concluded that the above finding is not inconsistent with the assumption of proportionality between spontaneous and induction rates of mutations. On the basis of the above results, a doubling dose of 100 R can be calculated for the X-ray induction of specific-locus mutations in Drosophila spermatozoa.

Animals↗
PubMed2005

The coupon collector and the suppressor mutation: estimating the number of compensatory mutations by maximum likelihood.

Compensatory mutation occurs when a loss of fitness caused by a deleterious mutation is restored by its epistatic interaction with a second mutation at a different site in the genome. How many different compensatory mutations can act on a given deleterious mutation? Although this quantity is fundamentally important to understanding the evolutionary consequence of mutation and the genetic complexity of adaptation, it remains poorly understood. To determine the shape of the statistical distribution for the number of compensatory mutations per deleterious mutation, we have performed a maximum-likelihood analysis of experimental data collected from the suppressor mutation literature. Suppressor mutations are used widely to assess protein interactions and are under certain conditions equivalent to compensatory mutations. By comparing the maximum likelihood of a variety of candidate distribution functions, we established that an L-shaped gamma distribution (alpha=0.564, theta=21.01) is the most successful at explaining the collected data. This distribution predicts an average of 11.8 compensatory mutations per deleterious mutation. Furthermore, the success of the L-shaped gamma distribution is robust to variation in mutation rates among sites. We have detected significant differences among viral, prokaryotic, and eukaryotic data subsets in the number of compensatory mutations and also in the proportion of compensatory mutations that are intragenic. This is the first attempt to characterize the overall diversity of compensatory mutations, identifying a consistent and accurate prior distribution of compensatory mutation diversity for theoretical evolutionary models.

Epistasis, Genetic↗
PubMed1995

Mutations of K-ras oncogene and absence of H-ras mutations in squamous cell carcinomas of the lung.

Mutations of the K-ras gene have been implicated in the pathogenesis of human lung adenocarcinomas. In most studies published so far, squamous cell lung cancers harbored ras mutations only exceptionally or no mutations were detected at all. We have examined 141 lung tumor DNA samples for mutations in codons 12, 13, and 61 of K-ras and H-ras oncogenes. A large panel of 118 squamous cell carcinomas was included in the study. For K-ras codon 12, we used a sensitive two-step PCR-restriction fragment length polymorphism method which detects <1% of mutated DNA in the sample. K-ras mutations were found in 17 tumors (12%; 14 in codon 12 and 3 in codon 13). Among 19 adenocarcinomas, mutation was revealed in 7 samples (37%). Of these, one sample harbored two point mutations in codon 12. Nine mutational events were found in squamous cell carcinomas (8%, one adenosquamous carcinoma included, all in codon 12). Of four large cell carcinomas, one contained a mutation. Mutant-enriched PCR products harboring mutations were directly sequenced. Fifteen mutational events were G-->T transversions or G-->A transitions, one was a G-->C transition, and one sample revealed a frameshift deletion of one G from codon 12. Similar mutational spectrum was found in both squamous cell carcinomas and adenocarcinomas, suggesting similar carcinogenic pathways in both histological types of the tumor. The presence of mutations did not correlate with the stage of the disease. Moreover, we analyzed all samples for mutations in codons 12, 13, and 61 of the H-ras gene. We found only one mutation in codon 12. Thus, H-ras mutations apparently play an inferior role in lung carcinogenesis. We conclude that mutations of the K-ras oncogene can play a role in the development of not only lung adenocarcinomas but also of a subset (about 8%) of squamous cell carcinomas.

Adenocarcinoma↗
PubMed2006

Ploidy controls the success of mutators and nature of mutations during budding yeast evolution.

BACKGROUND: We used the budding yeast Saccharomyces cerevisiae to ask how elevated mutation rates affect the evolution of asexual eukaryotic populations. Mismatch repair defective and nonmutator strains were competed during adaptation to four laboratory environments (rich medium, low glucose, high salt, and a nonfermentable carbon source). RESULTS: In diploids, mutators have an advantage over nonmutators in all conditions, and mutators that win competitions are on average fitter than nonmutator winners. In contrast, haploid mutators have no advantage when competed against haploid nonmutators, and haploid mutator winners are less fit than nonmutator winners. The diploid mutator winners were all superior to their ancestors both in the condition they had adapted to, and in two of the other conditions. This phenotype was due to a mutation or class of mutations that confers a large growth advantage during the respiratory phase of yeast cultures that precedes stationary phase. This generalist mutation(s) was not selected in diploid nonmutator strains or in haploid strains, which adapt primarily by fixing specialist (condition-specific) mutations. In diploid mutators, such mutations also occur, and the majority accumulates after the fixation of the generalist mutation. CONCLUSIONS: We conclude that the advantage of mutators depends on ploidy and that diploid mutators can give rise to beneficial mutations that are inaccessible to nonmutators and haploid mutators.

Adaptation, Physiological↗
PubMed2005

iMARS--mutation analysis reporting software: an analysis of spontaneous cII mutation spectra.

The sensitivity of any mutational assay is determined by the level at which spontaneous mutations occur in the corresponding untreated controls. Establishing the type and frequency at which mutations occur naturally within a test system is essential if one is to draw scientifically sound conclusions regarding chemically induced mutations. Currently, mutation-spectra analysis is laborious and time-consuming. Thus, we have developed iMARS, a comprehensive mutation-spectrum analysis package that utilises routinely used methodologies and visualisation tools. To demonstrate the use and capabilities of iMARS, we have analysed the distribution, types and sequence context of spontaneous base substitutions derived from the cII gene mutation assay in transgenic animals. Analysis of spontaneous mutation spectra revealed variation both within and between the transgenic rodent test systems Big Blue Mouse, MutaMouse and Big Blue Rat. The most common spontaneous base substitutions were G:C-->A:T transitions and G:C-->T:A transversions. All Big Blue Mouse spectra were significantly different from each other by distribution and nearly all by mutation type, whereas the converse was true for the other test systems. Twenty-eight mutation hotspots were observed across all spectra generally occurring in CG, GA/TC, GG and GC dinucleotides. A mutation hotspot at nucleotide 212 occurred at a higher frequency in MutaMouse and Big Blue Rat. In addition, CG dinucleotides were the most mutable in all spectra except two Big Blue Mouse spectra. Thus, spontaneous base-substitution spectra showed more variation in distribution, type and sequence context in Big Blue Mouse relative to spectra derived from MutaMouse and Big Blue Rat. The results of our analysis provide a baseline reference for mutation studies utilising the cII gene in transgenic rodent models. The potential differences in spontaneous base-substitution spectra should be considered when making comparisons between these test systems. The ease at which iMARS has allowed us to carry out an exhaustive investigation to assess mutation distribution, mutation type, strand bias, target sequences and motifs, as well as predict mutation hotspots provides us with a valuable tool in helping to distinguish true chemically induced hotspots from background mutations and gives a true reflection of mutation frequency.

Animals↗
PubMed2005

Consistent absence of BRAF mutations in cervical and endometrial cancer despite KRAS mutation status.

BACKGROUND: Mutational activation of KRAS and BRAF proto-oncogenes contributes to the development of many human cancers. Current research on gynecological cancer and specifically in cervical and endometrial cancer is focused on the mechanisms of their mutational activation. OBJECTIVES: In view of the paucity of data on their mutation frequency and the status of BRAF in these two types of gynecological cancer, we performed a systematic molecular study in 114 clinically and histologically well-defined malignant tumors of uterine cervix and endometrium and correlated the mutation status of KRAS and BRAF with the age at diagnosis and with tumor grade, stage or histological type. METHODS: Direct sequence analysis of the PCR products of KRAS and BRAF genes was used to screen for known activating mutations. RESULTS: In 67 cases of endometrial cancer, six KRAS mutations (8.9%) were found, four at codon 12 (5.9%) and two at codon 13 (2.9%), while no mutation was detected at codon 61. Most of the mutations occurred in surgical stage I and in the endometrioid adenocarcinoma subtype. We also detected three KRAS point mutations (6.3%) in the 47 cervical cancer samples, two at codon 12 (4.2%) and one at codon 13 (2.1%), while there was no mutation at codon 61. On the contrary, no mutation was identified in BRAF exon 15 for either endometrial or cervical cancer samples at position V600, which represents the most frequently mutated site of BRAF in human cancer. There was no association between KRAS mutations with either histological type, tumor grade or stage. Interestingly, however, KRAS mutation status in endometrial cancer was strongly associated with increased age at diagnosis (P < 0.001). CONCLUSIONS: Our data document (a) the absence of BRAF mutations in cervical and endometrial cancer, despite the mutation status of KRAS, (b) suggest that KRAS mutations reflect an early event in endometrial carcinogenesis and (c) imply that BRAF activation is involving alternative pathways in these two types of cancer.

Adult↗
PubMed1997

Development of a rapid assay for detecting gyrA mutations in Escherichia coli and determination of incidence of gyrA mutations in clinical strains isolated from patients with complicated urinary tract infections.

The MICs of ofloxacin for 743 strains of Escherichia coli isolated from 1988 to 1994 were determined by testing. The strains were from patients with urinary tract infections complicated by functional or anatomical disorders of the urinary tract. Those determined to be ofloxacin resistant (MIC, > or =12.5 microg/ml) comprised 3 of 395 strains (1.3%) from the 1988 to 1990 group, 2 of 166 strains (1.2%) from the 1991 to 1992 group, and 7 of 182 strains (3.8%) from the 1993 to 1994 group. The incidence of resistant strains increased significantly during this period. The percentage of isolates with moderately decreased susceptibilities to ofloxacin (MIC, 0.39 to 3.13 microg/ml) also rose during the same period. To determine the incidence of gyrA mutations in urinary-tract-derived strains of E. coli, we developed a simple and rapid assay based on PCR amplification of the region of the gyrA gene containing the mutation sites followed by digestion of the PCR product with a restriction enzyme. Using this assay, we examined all 182 strains isolated in 1993 and 1994 for the presence of mutations at Ser-83 and Asp-87 in the gyrA gene. Of these strains, 33 (18.1%) had mutations in the gyrA gene. The incidences of mutations at Ser-83, at Asp-87, and at both codons were 10.4 (19 strains), 4.4 (8 strains), and 3.3% (6 strains), respectively. To determine the correlation of the mutations in the gyrA gene with susceptibilities to quinolones (nalidixic acid, ofloxacin, norfloxacin, and ciprofloxacin), we further examined 116 strains for which the MICs of ofloxacin were > or =0.2 microg/ml that were chosen from the isolates in the 1988 to 1992 group. The MICs of nalidixic acid for the strains without mutations at either Ser-83 or Asp-87 were < or =25 microg/ml, whereas those for the strains with single mutations or double mutations were from 50 to >800 microg/ml. For the fluoroquinolones, significant differences in the distributions of the MICs were observed among the strains without mutations, with single mutations, and with double mutations. The accumulation of mutations in the gyrA gene was associated with an increase in fluoroquinolone resistance. Ofloxacin MICs for the majority of the strains with single and double mutations were 0.39 to 3.13 and 6.25 to 100 microg/ml, respectively. This study demonstrates a chronological increase in the percentage of not only highly fluoroquinolone-resistant strains, corresponding to those with double mutations in the gyrA gene, but also strains with moderately decreased susceptibilities to fluoroquinolones, corresponding to those with single mutations. This increase in the incidence of strains with a single mutation in the gyrA gene portends a further increase in the incidence of strains with clinically significant resistance to fluoroquinolones.

Anti-Infective Agents↗
PubMed2005

RB1 gene mutation up-date, a meta-analysis based on 932 reported mutations available in a searchable database.

BACKGROUND: Retinoblastoma, a prototype of hereditary cancer, is the most common intraocular tumour in children and potential cause of blindness from therapeutic eye ablation, second tumours in germ line carrier's survivors, and even death when left untreated. The molecular scanning of RB1 in search of germ line mutations lead to the publication of more than 900 mutations whose knowledge is important for genetic counselling and the characterization of phenotypic-genotypic relationships. RESULTS: A searchable database (RBGMdb) has been constructed with 932 published RB1 mutations. The spectrum of these mutations has been analyzed with the following results: 1) the retinoblastoma protein is frequently inactivated by deletions and nonsense mutations while missense mutations are the main inactivating event in most genetic diseases. 2) Near 40% of RB1 gene mutations are recurrent and gather in sixteen hot points, including twelve nonsense, two missense and three splicing mutations. The remainder mutations are scattered along RB1, being most frequent in exons 9, 10, 14, 17, 18, 20, and 23. 3) The analysis of RB1 mutations by country of origin of the patients identifies two groups in which the incidence of nonsense and splicing mutations show differences extremely significant, and suggest the involvement of predisposing ethnic backgrounds. 4) A significant association between late age at diagnosis and splicing mutations in bilateral retinoblastoma patients suggests the occurrence of a delayed-onset genotype. 5) Most of the reported mutations in low-penetrance families fall in three groups: a) Mutations in regulatory sequences at the promoter resulting in low expression of a normal Rb; b) Missense and in-frame deletions affecting non-essential sequence motifs which result in a partial inactivation of Rb functions; c) Splicing mutations leading to the reduction of normal mRNA splicing or to alternative splicing involving either true oncogenic or defective (weak) alleles. CONCLUSION: The analysis of RB1 gene mutations logged in the RBGMdb has shown relevant phenotype-genotype relationships and provided working hypothesis to ascertain mechanisms linking certain mutations to ethnicity, delayed onset of the disease and low-penetrance. Gene profiling of tumors will help to clarify the genetic background linked to ethnicity and variable expressivity or delayed onset phenotypes.

Codon, Nonsense↗
PubMed1997

TP53 mutational pattern in Spanish and Polish non-small cell lung cancer patients: null mutations are associated with poor prognosis.

Inactivation of TP53 tumor suppressor gene is the most frequent molecular alteration in NSCLC, involving up to 60% of cases. Furthermore, TP53 mutational spectrum is related to the type of mutagen exposure, as well as racial and/or diet differences. Nearly 95% of TP53 perturbations affect codons included within exons 5-8 which encode for almost the entire DNA-binding domain. In this study we addressed the possible prognostic value of the molecular alterations identified in exons 5-8 of the TP53 gene in DNAs from 151 paraffin-embedded NSCLC sections corresponding to 59 Spanish and 92 Polish stage I-IIIA resected patients. PCR/single-strand conformation polymorphism (SSCP) analysis revealed that the occurrence of TP53 exon 5-8 mutations was 17/59 (29%) in the Spanish cohort and 17/92 (18%) in the Polish group. However, when DNA sequencing analysis was performed, these frequencies were reduced because of the presence of SSCP-false positive, intronic and silent mutations and polymorphisms. Fifteen of the 59 Spanish NSCLC tumors (25%) harbored TP53 mutations affecting exons 5-8 coding sequences, whereas only 12 of 92 Polish neoplasms (13%) contained alterations in the central hydrophobic region of p53. Our results indicate that the occurrence of TP53 mutations affecting exon 5-8 coding sequences in some European NSCLC populations may be lower than previously reported, and that the TP53 mutational patterns of these cohorts differ somewhat. The Spanish NSCLC patients contained missense mutations (9/59, 15%) and a relatively high percentage of null mutations (5/59, 8%) while the Polish patients mostly harbored missense mutations (9/92, 10%) and only one tumor contained a null type (1/92, 1%). Moreover, most TP53 missense mutations in the Spanish group were located outside the conserved regions, whereas the same mutations in the Polish group affected conserved amino acids. Furthermore, the Polish patients harbored a high percentage of G-->A transitions (most of them at non-CpG sites), while G-->T transversions were predominant in the Spanish group. Our findings suggest that there may be different racial or exogenous factors in these two populations which may help to explain both the distinct TP53 mutational pattern and the lower frequency obtained in the Polish group. The presence of missense mutations did not confer a worse clinical outcome in these subsets of NSCLC patients. However, patients whose tumors contained null TP53 gene mutations had a 5 month median disease-free survival time in contrast with 42 months in those patients without mutations (P=0.008). These findings suggest that loss of p53 function may enhance tumor progression in NSCLC patients independently of whether dominant negative TP53 missense mutations are present.

Aged↗
PubMed2001

The application of the restriction site mutation assay to compare 1-ethyl-1-nitrosourea-induced mutations between the endogenous p53 gene and the transgenic LacZ gene in MutaMouse testes.

Transgenic mouse modelling has provided a new approach to study the various steps involved in spontaneous and induced mutagenesis in rodent somatic and germline tissues in vivo. However, the important question arises as to whether mutations occur at the same rate in transgenes as in endogenous genes. Here, the restriction site mutation (RSM) assay was used to study mutations induced in the endogenous p53 gene and LacZ transgene of MutaMouse testes treated with 1-ethyl-1-nitrosourea (ENU). The aim of these experiments was to compare mutation susceptibility between the endogenous p53 gene and the integrated LacZ gene in the transgenic mouse. ENU-treated and control testes were analysed 102 days after treatment; a total of 297 RSM analyses were performed on ENU-treated and untreated testis DNA. Ten mutational events were detected in the p53 gene (exon 5 and intron 8), two of which occurred in untreated animals and probably represent spontaneous events. Only a single mutation was detected in the LacZ gene of an ENU-treated animal by the RSM assay. Thus the RSM assay can readily detect ENU-induced mutations in the p53 gene, but not in the LacZ transgene. Comparison of the LacZ RSM mutation data with results from a previous study of identically dosed MutaMice in the transgenic selection assay [Ashby, J., Gorelick,N.J. and Shelby,M.D. (1997) Mutat. Res., 388, 111-122] showed that LacZ mutations were far more readily recovered with the MutaMouse transgenic selection assay than by RSM analysis. The reason for the relative inability of the RSM assay to detect LacZ mutations may be the smaller target size of the RSM analysis compared with the transgenic selection assay (16 bases compared with 3000 bases). Taking into account the different target sizes by calculating the mutation frequency per base allowed the RSM data regarding p53 and LacZ to be compared with previously published data from transgenic selection assays. These studies demonstrated that the p53 mutations were present at mutation frequencies (per base) 5- to 70-fold higher than the LacZ gene mutations. In addition, the LacZ mutation frequency per base found in the RSM was an order of magnitude higher than that found in the transgenic selection assay. The transgenic selection assay is more sensitive per locus (due to the larger target of the LacZ gene), as evidenced by ability to detect ENU-induced testes mutations readily.

Alkylating Agents↗
PubMed2003

Relationship between E-cadherin gene mutation and p53 gene mutation, p53 accumulation, Bcl-2 expression and Ki-67 staining in diffuse-type gastric carcinoma.

E-cadherin mutations are found in 50% of diffuse-type gastric carcinoma, but not in intestinal gastric carcinoma. Because cell-cell adhesion mediated by E-cadherin plays an important role in epithelial cell survival, E-cadherin mutations could alter the apoptotic behavior of tumor cells. p53 and Bcl-2 family members are also important regulators of cellular apoptosis. This is the first study that investigates the relationship between E-cadherin gene mutation and p53 gene mutation, p53 accumulation, Bcl-2 expression, and Ki-67 expression in diffuse-type gastric carcinoma (24 cases, E-cadherin mutation status: wild-type in 8 patients and mutant in 16 patients). The mutation status of exons 5-8 of p53 was analyzed by denaturing high pressure liquid chromatography (DHPLC) in formalin-fixed, paraffin-embedded tumor sections, followed by direct sequencing of cases with aberrant chromatographic patterns. p53 mutations were found in 1 of 8 tumors without E-cadherin mutation (12.5%) and in 1 of 16 tumors with E-cadherin mutation (6.3%), a difference that was not statistically significant (p = 1.00). p53 accumulation was found in 8 of 24 tumors (33.3%) by immunohistochemical staining. p53 accumulation was significantly more frequent in tumors without E-cadherin mutations (5 of 8 tumors, 62.5%) than in gastric carcinoma tissues with E-cadherin mutations (3 of 16 tumors, 18.8%, p = 0.03). Bcl-2 staining was not observed in gastric carcinoma cells without E-cadherin mutations, but was detectable in 5 of 16 tumors with E-cadherin mutations (31.3%), a difference that was not statistically significant (p = 0.13). No relationship was observed between Ki-67 staining and the E-cadherin mutation status (p = 1.00). These data suggest that the presence of E-cadherin mutations can significantly alter the accumulation of the apoptosis-regulating p53 protein, whereas no correlation with the p53 mutation status or with Ki-67 staining was observed.

Adenocarcinoma↗
PubMed2005

Autoimmune regulator-1 messenger ribonucleic acid analysis in a novel intronic mutation and two additional novel AIRE gene mutations in a cohort of autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy patients.

CONTEXT: Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare autosomal recessive disease associated with mutations in the AIRE gene. OBJECTIVE: Our objective was to investigate clinical and mutational characteristics of 12 Slovenian patients from 10 families with APECED. METHODS: Direct sequencing, restriction fragment length polymorphism, and amplification refractory mutation system analyses were used to identify AIRE gene mutations. Autoimmune regulator (AIRE)-1 mRNA analysis was used to confirm pathogenicity of the intronic mutation. RESULTS: The prevalence of APECED in Slovenian population was estimated to be 1 in 43,000, which is significantly higher compared with the neighboring populations. Three novel mutations were identified among six different mutations detected in the AIRE gene. The first novel mutation was an intronic mutation (653-7_-5delCTC) affecting proper splicing by using a nearby new acceptor splice site as demonstrated by AIRE-1 mRNA analyses. The second and third novel mutations were frame-shift mutations located in exon 5 (540delG) and exon 9 (1064-1068dupCCCGG), both leading to premature truncation of the AIRE protein. The Finnish R257X mutation was the most frequent AIRE gene mutation in Slovenian patients with APECED (16 of 24 alleles). CONCLUSIONS: Three novel AIRE gene mutations were identified. For the first time, a novel intronic mutation was investigated on the mRNA level in APECED. This could be particularly important for APECED patients where no or only heterozygous mutation on the genomic DNA level is detected.

Adolescent↗
PubMed2000

Exhaustive mutation analysis of the NF1 gene allows identification of 95% of mutations and reveals a high frequency of unusual splicing defects.

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant disorders and is caused by mutations in the NF1 gene. Mutation detection is complex due to the large size of the NF1 gene, the presence of pseudogenes and the great variety of possible lesions. Although there is no evidence for locus heterogeneity in NF1, mutation detection rates rarely exceed 50%. We studied 67 unrelated NF1 patients fulfilling the NIH diagnostic criteria, 29 familial and 38 sporadic cases, using a cascade of complementary techniques. We performed a protein truncation test starting from puromycin-treated EBV cell lines and, if no mutation was found, continued with heteroduplex, FISH, Southern blot and cytogenetic analysis. We identified the germline mutation in 64 of 67 patients and 32 of the mutations are novel. This is the highest mutation detection rate reported in a study of typical NF1 patients. All mutations were studied at the genomic and RNA level. The mutational spectrum consisted of 25 nonsense, 12 frameshift, 19 splice mutations, six missense and/or small in-frame deletions, one deletion of the entire NF1 gene, and a translocation t(14;17)(q32;q11.2). Our data suggest that exons 10a-10c and 37 are mutation-rich regions and that together with some recurrent mutations they may account for almost 30% of the mutations in classical NF1 patients. We found a high frequency of unusual splice mutations outside of the AG/GT 5 cent and 3 cent splice sites. As some of these mutations form stable transcripts, it remains possible that a truncated neurofibromin is formed.

Alternative Splicing↗
PubMed2004

Differences in recurrent COL7A1 mutations in dystrophic epidermolysis bullosa: ethnic-specific and worldwide recurrent mutations.

Dystrophic epidermolysis bullosa (DEB) is caused by mutations in the gene encoding type VII collagen (COL7A1). Although most COL7A1 mutations are unique to individual families, small numbers of mutations are recurrent. The recurrent mutations R578X, 7786delG, and R2814X seem to be exclusive to a specific ethnic group, the British population. The mutations 5818delC, 6573+1G-->C, and E2857X are present only in individuals of Japanese ethnic origin. On the other hand, the mutations 425A-->G and G2043R have been found in several different ethnic groups. The purpose of this study was to clarify whether these recurrent mutations are also found in patients of other ethnic groups with DEB, mainly Asian patients. We demonstrated the absence of the recurrent mutations R578X, 7786delG, and R2814X in 42 non-British patients with DEB and detected the mutations 425A-->G in a French patient and G2043R in Japanese and Chinese patients with DEB. The mutations 5818delC, 6573+1G-->C, and E2857X were detected in 11 Japanese patients (13 alleles) with DEB. Our results confirm that R578X, 7786delG, and R2814X mutations are specifically limited to British patients, and the mutations 5818delC, 6573+1G-->C, and E2857X are frequent in Japanese patients. On the other hand, the mutations 425A-->G and G2043R can be found in different ethnic groups. In conclusion, our results further support the notion that recurrent mutations can be classified into two types, ethnic-specific mutation and worldwide mutation.

Alanine↗