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1.
Molecular analysis of spontaneous hypoxanthine phosphoribosyltransferase mutations in thioguanine-resistant HL-60 human leukemia cells 总被引:5,自引:0,他引:5
R J Monnat 《Cancer research》1989,49(1):81-87
We have measured the forward mutation rate at the hypoxanthine phosphoribosyltransferase (HPRT) gene of the human promyelocytic leukemia cell line HL-60 and have determined the molecular spectrum of spontaneous HPRT mutations in 45 independent 6-thioguanine-resistant HL-60 sublines. Four fluctuation tests using a total of 132 replicate HL-60 cultures revealed a mean forward mutation rate of HL-60 cells to thioguanine resistance of 1.7-6 x 10(-7)/cell/generation. Blot hybridization analysis of the X-linked HPRT gene using a human HPRT complementary DNA probe revealed abnormalities in HPRT gene structure and/or HPRT mRNA expression in 24 of 45 (53%) independent thioguanine-resistant HL-60 sublines. Six different classes of mutation were identified. The most prevalent (47%; 21 of 45 mutations) consists of mutations that are not detected by blot hybridization analyses and that do not disrupt HPRT mRNA production. These results suggest that a comparatively low forward mutation rate may be found in malignant human cells that exhibit both karyotypic and molecular evidence of genomic instability and that several different molecular classes of mutation may contribute to thioguanine resistance in HL-60, and perhaps in other, malignant human cells. The forward mutation assay system we have developed using the X-linked HPRT gene of HL-60 cells may be useful for analyses of the mutagenic potential and molecular spectrum of mutations produced by chemotherapeutic agents, suspected human mutagens and carcinogens, and phagocyte respiratory burst oxidants in human cells. 相似文献
2.
Lise Lotte Christensen Reetta Kariola Mari K. Korhonen Friedrik P. Wikman Lone Sunde Anne-Marie Gerdes Henrik Okkels Carsten A. Brandt Inge Bernstein Thomas V. O. Hansen Rikke Hagemann-Madsen Claus L. Andersen Minna Nyström Torben F. Ørntoft 《Familial cancer》2009,8(4):489-500
Recently, we have performed a population based study to analyse the frequency of colorectal cancer related MLH1 and MSH2 missense mutations in the Danish population. Half of the analyzed mutations were rare and most likely only present in the families where they were identified originally. Some of the missense mutations were located in conserved regions in the MLH1 and MSH2 proteins indicating a relation to disease development. In the present study, we functionally characterized 10 rare missense mutations in MLH1 and MSH2 identified in 13 Danish CRC families. To elucidate the pathogenicity of the missense mutations, we carried out in vitro functional analyses. The missense mutations were analyzed for their effect on protein expression and repair efficiency. The results of the functional analysis were correlated with clinical data on the families carrying these mutations. Eight missense mutations resulted in proteins with expression and repair efficiency similar to the wild type. One missense mutation (MSH2 p.Met688Val) caused reduced protein expression and one (MSH2 p.Leu187Arg) caused both reduced protein expression and repair deficiency. The MSH2 p.Leu187Arg mutation was found in an Amsterdam II family presenting with high microsatellite instability and loss of MSH2 and MSH6 proteins in tumours. In conclusion, only 1/10 missense mutations displayed repair deficiency and could be classified as pathogenic. No final conclusion can be drawn on the MSH2 p.Met688Val mutation, which caused reduced protein expression. Although, no deficiencies have been identified in the proteins harbouring the other missense mutations, pathogenicity of these variants cannot be unambiguously excluded. 相似文献
3.
Miyakura Y Sugano K Nomizu T Lefor A Yasuda Y 《Japanese journal of clinical oncology》2012,42(1):78-82
Lynch syndrome is caused by germline mutations of the DNA mismatch repair genes. Missense mutations are often difficult to evaluate as pathogenic. Previously, we reported a missense mutation in exon 12 at codon 600 of the MSH2 gene, causing a substitution of GTT (Val) for GCT (Ala) in a 35-year-old-man with rectal cancer, while the pathogenicity of this mutation is still unclear. In this report, we confirm the same mutation in his 66-year-old mother who had cecal cancer. PCR/direct sequencing analysis of peripheral blood lymphocytes revealed the same missense mutation in exon 12 at codon 600 of the MSH2 gene. The wave height of the capillary sequencer from the wild-type allele was decreased in tumor tissue, indicating loss of heterozygosity in the wild-type allele. Analysis of the tumor showed microsatellite instability high and loss of MSH2 protein expression. This sequence variant has not been reported in another family. This mutation is considered to play a significant and causative role in Lynch syndrome. 相似文献
4.
Vermeulen SJ Nollet F Teugels E Vennekens KM Malfait F Philippé J Speleman F Bracke ME van Roy FM Mareel MM 《Oncogene》1999,18(4):905-915
The acquisition of invasiveness is a crucial step in the malignant progression of cancer. In cancers of the colon and of other organs the E-cadherin/catenin complex, which is implicated in homotypic cell-cell adhesion as well as in signal transduction, serves as a powerful inhibitor of invasion. We show here that one allele of the alphaE-catenin (CTNNA1) gene is mutated in the human colon cancer cell family HCT-8, which is identical to HCT-15, DLD-1 and HRT-18. Genetic instability, due to mutations in the HMSH6 (also called GTBP) mismatch repair gene, results in the spontaneous occurrence of invasive variants, all carrying either a mutation or exon skipping in the second alphaE-catenin allele. The alphaE-catenin gene is therefore, an invasion-suppressor gene in accordance with the two-hit model of Knudsen for tumour-suppressor genes. 相似文献
5.
Mutations in mismatch repair (MMR) genes predispose to hereditary nonpolyposis colon cancer. Those leading to truncated proteins bring about a MMR defect, but phenotypes of missense mutations are harder to predict especially if they do not affect conserved residues. Several systems capable of predicting the phenotypes of MMR missense mutations were described. We deployed one of these to study the MMR defect in MT1 cells, which carry mutations in both alleles of the hMSH6 gene. In one, an A-->T transversion brings about an Asp(1213)Val amino acid change in the highly conserved ATP binding site, whereas the other carries a G-->A transition, which brings about a Val(1260)Ile change at a nonconserved site. The hMSH2/hMSH6 (hMutS alpha) heterodimers carrying these mutations were expressed in the baculovirus system and tested in in vitro MMR assays. As anticipated, the Asp(1213)Val mutation inactivated MMR by disabling the variant hMutS alpha from translocating along the DNA. In contrast, the recombinant Val(1260)Ile variant displayed wild-type activity. Interestingly, partial proteolytic analysis showed that this heterodimer was absent from MT1 extracts, although both hMSH6 alleles in MT1 cells could be shown to be transcribed with an efficiency similar to each other and to that seen in control cells. The MMR defect in MT1 cells is thus the compound result of one mutation that inactivates the ATPase function of hMutS alpha and a second mutation that apparently destabilizes the Val(1260)Ile hMSH6 protein in human cells in vivo. 相似文献
6.
Kim CJ Cho YG Park CH Jeong SW Nam SW Kim SY Lee SH Yoo NJ Lee JY Park WS 《Oncogene》2004,23(53):8591-8596
SIAH-1: is the mammalian homolog of Drosophila seven in absentia (sina) and has been identified as a p53-inducible gene. Siah-1 can induce cell cycle arrests, tumor suppression, and apoptosis through a novel beta-catenin degradation pathway. To determine whether genetic alterations of Siah-1 gene are involved in the development and/or progression of gastric cancer, we searched for mutation of the Siah-1 gene in 95 gastric cancers by single-strand conformational polymorphism and sequencing. The effect of Siah-1 on beta-catenin degradation was further examined in wild- and mutant-type Siah-1-transfected HEK 293T cells. We found two missense mutations of the Siah-1 gene. The cases with Siah-1 mutation showed nuclear translocation and cytoplasmic staining of beta-catenin. Interestingly, two mutants of Siah-1 stabilized cytoplasmic levels of beta-catenin, even after treatment of adriamycin. Furthermore, both mutants failed to suppress cyclin D1 expression and to induce apoptosis. These data suggest that inactivating mutations of the Siah-1 may contribute to the development of gastric cancer through beta-catenin stabilization and apoptosis block. 相似文献
7.
8.
Chronic perturbations of intracellular deoxyribonucleoside triphosphate (dNTP) pools have been associated with a mutator phenotype and increased mutation rates at several genetic loci. We have examined the specific effects of transient pharmacological purine dNTP pool perturbations on mutations induced at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in a cultured human T-lymphoblast cell line. Incubation of CEM cells with 50 microM 2'-deoxyguanosine for 6 h increased intracellular dGTP levels 43-fold and induced a 40-fold increase in mutation frequency at the HPRT locus. Six-h incubations with 5, 10, and 20 microM 2'-deoxyadenosine increased dATP pools 4.8-, 8-, and 14.5-fold, respectively, with 59-, 34-, and 43-fold increases in HPRT mutant fractions. In contrast, 24-h incubations with hydroxyurea at concentrations which inhibited cell growth to similar extents did not induce HPRT mutations. Sequencing of HPRT complementary DNA derived from mutant cell lines revealed that the mutations induced by transient purine dNTP pool perturbations exhibited no significant misincorporation of the nucleotide in excess or next-nucleotide effect, and were similar in nature and location to spontaneous HPRT mutations. We conclude that mutations caused by transient purine dNTP pool elevations in these dividing cells are most likely induced by inhibition of DNA repair processes. 相似文献
9.
Lettieri T Marra G Aquilina G Bignami M Crompton NE Palombo F Jiricny J 《Carcinogenesis》1999,20(3):373-382
Mismatch recognition in human cells is mediated primarily by a heterodimer of hMSH2 and hMSH6. Cells mutated in both alleles of the hMSH6 gene are deficient in the correction of base/base mispairs and insertion/deletion loops of one nucleotide and thus exhibit a strong mutator phenotype, evidenced by elevated mutation rates and microsatellite instability, as well as by tolerance to methylating agents. The decrease in replication fidelity associated with a loss of mismatch correction implies that with each division, these cells are likely to acquire new mutations throughout their genomes. Should such secondary mutations occur in genes linked to replication fidelity or involved in the maintenance of genomic stability, they might contribute to the observed mutator phenotype. The human colon tumour line HCT15 represents one such case. Although it carries inactivating mutations in both hMSH6 alleles, it has also been shown to contain a missense mutation in the coding sequence of the proofreading domain of the polymerase-delta gene. In an attempt to find out whether the phenotype of HCT15 cells was indeed brought about solely by the lack of hMSH6, we stably transfected them with a vector carrying the wild-type hMSH6 cDNA. Our results show that although the levels of transgenic hMSH6 were low, expression of the wild-type protein resulted in a substantial restoration of mismatch binding, mismatch repair capacity and the stability of mononucleotide repeats, as well as in the reduction of mutation rates. Although methylation tolerance of the hMSH6-expressing cells was not markedly affected, the G2 cell cycle checkpoint, absent in N-methyl-N'-nitro-N-nitrosoguanidine-treated control cells, was restored. 相似文献
10.
Shu-Jing Zhang Sumio Endo Tomio Ichikawa Junichi Yoshimura Kiyoshi Onda Ryuichi Tanaka Kazuo Washiyama Toshiro Kumanishi 《Cancer science》1999,90(9):934-941
A total of 10 glioma cell lines were examined to evaluate the status of the MMAC1 gene, a candidate tumor suppressor gene. Six cell lines showed mutations with presumed loss of heterozygosity and 1 cell line showed no mRNA expression. The 6 mutations consisted of 3 3-bp deletions (codons 17, 101 or 199), 1 missense mutation (codon 252) and 2 truncation mutations (1 nonsense mutation at codon 233 and 1 2-bp insertion at codon 241). Among them, the 3-bp deletions, which are a rare type of mutation in MMAC1 gene, were located in the N-terminal half (codons 1–212) of the coding region, which is considered important in MMAC1 function. The missense mutation was located unusually in the C-terminal half (codons 212–403), but it was in a small region in which some other reported missense mutations are clustered. Thus, these 4 mutations were suggested to have functional effects on the MMAC1 activity, like the other 2 mutations with predicted protein truncations. By sequence analysis of cDNA clones, we confirmed that all the mutations including these 4 rare ones were in the MMAC1 gene, not in the PTH2 pseudogene. In 2 cases, we also examined the primary glioma tissues from which the cell lines had been derived and found the same mutations as in the cell lines in both cases. This suggested that the mutations in these cell lines were derived from the primary glioma tissues, but not from artifacts arising during long-term in vitro cultivation. 相似文献
11.
Rare-type mutations of MMAC1 tumor suppressor gene in human glioma cell lines and their tumors of origin. 总被引:1,自引:0,他引:1
S J Zhang S Endo T Ichikawa J Yoshimura K Onda R Tanaka K Washiyama T Kumanishi 《Japanese journal of cancer research》1999,90(9):934-941
A total of 10 glioma cell lines were examined to evaluate the status of the MMAC1 gene, a candidate tumor suppressor gene. Six cell lines showed mutations with presumed loss of heterozygosity and 1 cell line showed no mRNA expression. The 6 mutations consisted of 3 3-bp deletions (codons 17, 101 or 199), 1 missense mutation (codon 252) and 2 truncation mutations (1 nonsense mutation at codon 233 and 12-bp insertion at codon 241). Among them, the 3-bp deletions, which are a rare type of mutation in MMAC1 gene, were located in the N-terminal half (codons 1-212) of the coding region, which is considered important in MMAC1 function. The missense mutation was located unusually in the C-terminal half (codons 212-403), but it was in a small region in which some other reported missense mutations are clustered. Thus, these 4 mutations were suggested to have functional effects on the MMAC1 activity, like the other 2 mutations with predicted protein truncations. By sequence analysis of cDNA clones, we confirmed that all the mutations including these 4 rare ones were in the MMAC1 gene, not in the PTH2 pseudogene. In 2 cases, we also examined the primary glioma tissues from which the cell lines had been derived and found the same mutations as in the cell lines in both cases. This suggested that the mutations in these cell lines were derived from the primary glioma tissues, but not from artifacts arising during long-term in vitro cultivation. 相似文献
12.
Detection of mutations in the DNA polymerase delta gene of human sporadic colorectal cancers and colon cancer cell lines 总被引:4,自引:0,他引:4
Flohr T Dai JC Büttner J Popanda O Hagmüller E Thielmann HW 《International journal of cancer. Journal international du cancer》1999,80(6):919-929
To test the hypothesis whether DNA polymerases acquire mutator properties during tumor development (mutator hypothesis), we examined DNA polymerase delta mRNA in 6 colon cancer cell lines (DLD-1, HCT116, SW48, HT29, SW480 and SW620) and 7 sporadic human colorectal cancers. For analysis we used amplification of cDNA by polymerase chain reaction, single-strand conformation polymorphism and sequencing techniques. In 5 of the cell lines, 9 mutations leading to changes of the amino acid sequence of DNA polymerase delta were detected. Most mutations were found in the cell lines DLD-1, HCT116 and SW48 for which defects in mismatch repair genes had been identified previously. In the majority of cases, wild type and mutated sequences were present. In 2 cell lines (HCT116 and SW48), a single-nucleotide deletion occurred at the same position. This resulted in a premature termination codon by which the DNA interaction domain of the enzyme was eliminated. Furthermore, sequence deviations were found in the tumor tissues of 4 colon cancer patients. Wild-type and altered sequences were present simultaneously. The deviations included missense mutations (2 cases) and silent mutations (2 cases). The missense mutations and one of the silent mutations were found in normal mucosa as well. In addition, the mutation clustered region of a tumor suppressor gene, often found to be defective in colon cancer, the adenomatous polyposis coli (APC) gene, was investigated in surgical specimens and cell lines. One carcinoma and 2 cell lines exhibited amino acid changes in both the DNA polymerase delta gene and in the mutation clustered region of the APC gene. Since most of the mutations detected in the DNA polymerase delta mRNA are likely to alter the structure of the protein, the enzyme is expected to be functionally impaired. In particular, copying fidelity might be decreased, thus contributing to the high mutation rate observed in colorectal cancer. 相似文献
13.
Dominant effects of an Msh6 missense mutation on DNA repair and cancer susceptibility 总被引:5,自引:0,他引:5
Yang G Scherer SJ Shell SS Yang K Kim M Lipkin M Kucherlapati R Kolodner RD Edelmann W 《Cancer cell》2004,6(2):139-150
Mutations in DNA mismatch repair (MMR) genes cause hereditary nonpolyposis colorectal cancer (HNPCC), and MMR defects are associated with a significant proportion of sporadic cancers. MMR maintains genome stability and suppresses tumor formation by preventing the accumulation of mutations and by mediating an apoptotic response to DNA damage. We describe the analysis of a dominant MSH6 missense mutation in yeast and mice that causes loss of DNA repair function while having no effect on the apoptotic response to DNA damaging agents. Our results demonstrate that MSH6 missense mutations can effectively separate the two functions, and that increased mutation rates associated with the loss of DNA repair are sufficient to drive tumorigenesis in MMR-defective tumors. 相似文献
14.
Akira Tachibana Kouichi Tatsumi Toshihiko Masui Takesi Kato 《Molecular carcinogenesis》1996,17(1):41-47
Bloom's syndrome (BS) is an autosomal recessive disorder with a high cancer incidence. BS cells exhibit increased chromosomal instability and sister-chromatid exchange. The rate of spontaneous mutation at the locus encoding hypoxanthine phosphoribosyltransferase (HPRT) in a lymphoblastoid cell line derived from a BS patient, GM3403, was 1.39 × 10−6 mutations/cell/generation, whereas that in TK6, a lymphoblastoid cell line derived from an individual who is not suffering from BS, was 1.75 × 10−8 mutations/cell/generation. Molecular analysis of the HPRT gene in mutant clones by multiplex polymerase chain reaction revealed that 83.3% of the spontaneous mutants from GM3403 cells contained deletions at the HPRT locus, whereas 30.8% of mutants from TK6 cells had deletions. Approximately half of the BS mutants had lost the entire gene. Some mutant clones of GM3403 had also lost markers near the HPRT locus, although no mutant clones from TK6 cells had lost these markers. These results indicate that the mutator phenotype of BS cells is mainly due to an increase in large DNA alterations, reflecting the remarkable genomic instability that could be responsible for cancer proneness in this disease. © 1996 Wiley-Liss, Inc. 相似文献
15.
目的探讨野生型p53基因表达对人肝癌细胞SMMC-7721中POLD1基因的影响。方法设计并构建p53特异性小干扰shRNA绿色荧光真核表达质粒(p53-siRNA)和表达EGFP-p53融合蛋白的p53绿色荧光真核增强表达质粒(pEGFP-p53),通过稳定转染,将表达pEGFP-p53重组质粒、p53-siRNA转染入SMMC-7721细胞;经G418筛选,获得稳定细胞系7721-p53、7721-p53RNAi。通过RT-PCR检测转染后p53、POLD1的mRNA。结果在人肝癌细胞SMMC-7721中,野生型p53高表达组能够抑制POLD1的基因转录(P〈0.001);而低表达组能够促进POLD1的基因转录(P〈0.001)。结论在人肝癌细胞SMMC-7721中,p53能够调控POLD1的基因转录。 相似文献
16.
Ollila S Fitzpatrick R Sarantaus L Kariola R Ambus I Velsher L Hsieh E Andersen MK Raevaara TE Gerdes AM Mangold E Peltomäki P Lynch HT Nyström M 《International journal of oncology》2006,28(1):149-153
A majority of families with hereditary nonpolyposis colorectal cancer (HNPCC) are attributable to germline mutations in three DNA mismatch repair (MMR) genes, MLH1, MSH2 and MSH6. However, the clinical phenotype appears to reflect a complex interplay between the predisposing mutation and putative constitutional and somatic modifiers. Certain MMR gene mutations predispose to combined occurrence of cutaneous sebaceous gland neoplasms and visceral malignancies, which is known as Muir-Torre syndrome (MTS) and regarded as a phenotypic variant of HNPCC. The sebaceous tumors associated with MTS appear in many patients before visceral malignancies providing important predictability of HNPCC-related integral cancers in mutation carriers. Since most sebaceous skin tumors are, however, sporadic, the contribution of non-truncating mutations found in skin cancer patients is difficult to interpret and genetic assessment of MTS requires a functional test. Here, we studied the repair efficiency of the two MSH2 missense mutations, L187P and C697F, found in HNPCC families including a few mutation carriers with sebaceous skin tumors. Both mutations were completely deficient in an MMR assay, which together with tumor findings suggested their predisposing role in both internal and skin malignancies in the families. 相似文献
17.
18.
Peterlongo P Nafa K Lerman GS Glogowski E Shia J Ye TZ Markowitz AJ Guillem JG Kolachana P Boyd JA Offit K Ellis NA 《International journal of cancer. Journal international du cancer》2003,107(4):571-579
Germline mutations in MSH6 can cause HNPCC, which is associated with a tumor phenotype featuring MSI. However, tumors arising in persons with disease-causing mutations of MSH6 may or may not exhibit MSI. We used D-HPLC to screen for germline mutations in the promoter region, the coding region and the 3'-UTR of MSH6. Eighty-four families, enrolled on the basis of Amsterdam I and II criteria (HNPCC families) and less stringent criteria (HNPCC-like families), were tested for MMR gene mutations; 27 families had a disease-causing mutation in MLH1 or MSH2, and the remaining 57 families were tested for mutations in MSH6. Two protein-truncating mutations were identified in each of 2 families fulfilling the Amsterdam I criteria, being present in persons affected with early-onset colorectal cancers exhibiting MSI. Immunohistochemical analysis showed that expression of both MSH2 and MSH6 proteins was lost in the cancer cells of the 2 mutation carriers but only MSH6 protein expression was lost in 2 adenomatous polyps. A third possibly disease-causing mutation was found in a person affected with a tumor that did not exhibit MSI. In addition, we found 4 new polymorphisms and determined that neither of the 2 studied by association analysis conferred susceptibility to colorectal or endometrial cancer. Altogether, our results indicate that disease-causing germline mutations of MSH6 are rare in HNPCC and HNPCC-like families. 相似文献
19.
Fredriksson H Ikonen T Autio V Matikainen MP Helin HJ Tammela TL Koivisto PA Schleutker J 《European journal of cancer (Oxford, England : 1990)》2006,42(16):2802-2806
Several linkage and loss of heterozygosity (LOH) analyses suggest that the region 3p21-p26, which is a chromosomal location of MLH1, could harbour a susceptibility gene for prostate cancer (PRCA). Furthermore, in a recent candidate single nucleotide polymorphism (SNP) analysis the I219V variation of the MLH1 gene was associated with PRCA. Microsatellite instability (MSI) and germ-line MLH1 mutations were originally demonstrated in hereditary non-polyposis colorectal cancer (HNPCC) but MSI and loss of MLH1 function have also been detected in PRCA. To assess the contribution of MLH1 germline mutations to the development of PRCA in Finland different approaches were used. First, the samples from 11 PRCA-colon cancer patients were screened for MLH1, MSH2 and MSH6 protein expression by immunohistochemistry (IHC). IHC revealed one patient with a putative MLH1 aberration and sequencing of this sample revealed five sequence variants including two missense variants P434L and I219V. Second, the samples from Finnish hereditary prostate cancer (HPC) families were used for the screening of MLH1 mutations which produced twelve MLH1 sequence variants including two missense mutations, I219V, as in the PRCA-colon cancer patient, and V647M. P434L and V647 were both novel, rare variants. Carrier frequencies of the I219V mutation were compared between hereditary prostate cancer (HPC) patients, unselected PRCA cases, patients with benign prostate hyperplasia and controls, but no differences between the sample groups were found. P434L was not present in this study population and V647M was a very rare variant found only in one HPC family. According to the present results, MLH1 does not have a major role in PRCA causation in Finland. 相似文献
20.
Gene conversion is a frequent mechanism of inactivation of the wild-type allele in cancers from MLH1/MSH2 deletion carriers 总被引:5,自引:0,他引:5
Zhang J Lindroos A Ollila S Russell A Marra G Mueller H Peltomaki P Plasilova M Heinimann K 《Cancer research》2006,66(2):659-664
Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominantly inherited cancer predisposition syndrome caused by germ line mutations in DNA mismatch repair genes, predominantly MLH1 and MSH2, with large genomic rearrangements accounting for 5% to 20% of all mutations. Although crucial to the understanding of cancer initiation, little is known about the second, somatic hit in HNPCC tumorigenesis, commonly referred to as loss of heterozygosity. Here, we applied a recently developed method, multiplex ligation-dependent probe amplification, to study MLH1/MSH2 copy number changes in 16 unrelated Swiss HNPCC patients, whose cancers displayed microsatellite instability and loss of MLH1 or MSH2 expression, but in whom no germ line mutation could be detected by conventional screening. The aims of the study were (a) to determine the proportion of large genomic rearrangements among Swiss MLH1/MSH2 mutation carriers and (b) to investigate the frequency and nature of loss of heterozygosity as a second, somatic event, in tumors from MLH1/MSH2 germ line deletion carriers. Large genomic deletions were found to account for 4.3% and 10.7% of MLH1 and MSH2 mutations, respectively. Multiplex ligation-dependent probe amplification analysis of 18 cancer specimens from two independent sets of Swiss and Finnish MLH1/MSH2 deletion carriers revealed that somatic mutations identical to the ones in the germ line occur frequently in colorectal cancers (6 of 11; 55%) and are also present in extracolonic HNPCC-associated tumors. Chromosome-specific marker analysis implies that loss of the wild-type allele predominantly occurs through locus-restricted recombinational events, i.e., gene conversion, rather than mitotic recombination or deletion of the respective gene locus. (Cancer Res 2006; (66)2: 659-64). 相似文献