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Matthias Kloor

Publications and source records attributed to Matthias Kloor.

16 recordsLinked to original sources
PubMed2006

Genotype-phenotype comparison of German MLH1 and MSH2 mutation carriers clinically affected with Lynch syndrome: a report by the German HNPCC Consortium.

PURPOSE: Lynch syndrome is linked to germline mutations in mismatch repair genes. We analyzed the genotype-phenotype correlations in the largest cohort so far reported. PATIENTS AND METHODS: Following standard algorithms, we identified 281 of 574 unrelated families with deleterious germline mutations in MLH1 (n = 124) or MSH2 (n = 157). A total of 988 patients with 1,381 cancers were included in this analysis. RESULTS: We identified 181 and 259 individuals with proven or obligatory and 254 and 294 with assumed MLH1 and MSH2 mutations, respectively. Age at diagnosis was younger both in regard to first cancer (40 v 43 years; P < .009) and to first colorectal cancer (CRC; 41 v 44 years; P = .004) in MLH1 (n = 435) versus MSH2 (n = 553) mutation carriers. In both groups, rectal cancers were remarkably frequent, and the time span between first and second CRC was smaller if the first primary occurred left sided. Gastric cancer was the third most frequent malignancy occurring without a similarly affected relative in most cases. All prostate cancers occurred in MSH2 mutation carriers. CONCLUSION: The proportion of rectal cancers and shorter time span to metachronous cancers indicates the need for a defined treatment strategy for primary rectal cancers in hereditary nonpolyposis colorectal cancer patients. Male MLH1 mutation carriers require earlier colonoscopy beginning at age 20 years. We propose regular gastric surveillance starting at age 35 years, regardless of the familial occurrence of this cancer. The association of prostate cancer with MSH2 mutations should be taken into consideration both for clinical and genetic counseling practice.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Prevalence of the mismatch-repair-deficient phenotype in colonic adenomas arising in HNPCC patients: results of a 5-year follow-up study.

In hereditary nonpolyposis colorectal cancer (HNPCC) syndrome, more than 90% of the carcinomas show microsatellite instability (MSI) due to a loss of mismatch repair (MMR) function. Although adenomas are very common in HNPCC and demonstrate an accelerated adenoma-carcinoma sequence, data about the prevalence and development of MSI in these early neoplastic lesions are lacking. To determine whether MSI and loss of MMR-protein expression are already present in early stages of tumorigenesis and could therefore be used as a screening tool to identify HNPCC patients before they develop an invasive carcinoma, we analyzed 71 adenomas of 36 HNPCC patients during a 5-year follow-up study. These 36 patients were part of a cohort of 122 HNPCC patients who were investigated at the Institute of Pathology, Klinikum Kassel, as part of the multicentric German HNPCC Consortium, which currently serves more than 2,880 registered families. The diagnosis of HNPCC was based either on the detection of a pathogenic germline mutation in the MSH2, MLH1, or MSH6 genes or in cases where a pathogenic mutation was not found; diagnosis of HNPCC was made, because all patients fulfilled the Amsterdam or Bethesda criteria and revealed a high degree of MSI (MSI-H) as well as loss of one of the MMR proteins by IHC in the cancer tissue. We found that most adenomas (58/71) were MSI-H and had loss of MMR-protein expression. Of the 71 adenomas, 3 were MSI-H with expression of all MMR proteins, and 3 out of 71 displayed loss of a MMR protein with the microsatellites being classified as microsatellite stable (MSS). However, 7 of the 31 adenomas that were located more than 5 cm away from the carcinoma revealed an MSS status (n=6) or low in MSI (n=1) and expressed all MMR proteins. In summary, a significant percentage of HNPCC-associated adenomas (7/31, 22.6%) developing at a distance of more than 5 cm from the corresponding carcinoma did not show the MSI-H MMR-deficient phenotype and expressed all MMR genes. To our knowledge, this is the first study that shows that in most HNPCC patients, the mutator pathway is already detectable in adenomas, but MMR-proficient adenomas can also be found. Therefore, screening for MMR deficiency should not be applied routinely in adenomas with the goal to identify HNPCC patients.

Adenoma↗
PubMed2006

Tetranucleotide repeats in coding regions: no evidence for involvement in EMAST carcinogenesis.

Genetic instability is a hallmark of malignancy. In the majority of malignant tumors, chromosomal instability leads to major numerical and structural chromosomal aberrations. In contrast, some tumors have a deficient DNA mismatch repair system and accumulate mutations particularly in repetitive mono- and dinucleotide sequences, a phenomenon referred to as microsatellite instability (MSI). Recently, a novel phenotype of tumors presenting with elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) has been reported. To date, not much is known about the molecular mechanisms of EMAST tumorigenesis. In MSI tumors, instability at specific mono- and dinucleotide repeats leads to alteration of genes carrying these repeats and thus may contribute to MSI tumorigenesis. We hypothesized that, similarly to the MSI phenotype, development of EMAST cancers may be promoted by mutations affecting tetranucleotides located in coding regions of the genome. To test this hypothesis, we performed a genome-wide database search to identify tetranucleotides in gene-encoding regions. Only seven tetranucleotide repeats located in predicted gene-encoding regions were retrieved. Allele length analysis yielded three remaining candidates with a monomorphic pattern in healthy individuals. Mutation analysis revealed that none of these three candidates displayed mutations in EMAST-positive bladder cancers. These data suggest that mutational inactivation of tetranucleotide-containing genes is very unlikely to contribute to the progression of EMAST tumors.

Biomarkers, Tumor↗
PubMed2006

Novel strategy for optimal sequential application of clinical criteria, immunohistochemistry and microsatellite analysis in the diagnosis of hereditary nonpolyposis colorectal cancer.

Clinical criteria, microsatellite analysis (MSA) and immunohistochemistry (IHC) are important diagnostic tools for identification of hereditary nonpolyposis colorectal cancer (HNPCC) patients who are likely to carry pathogenic germline mutations in mismatch repair genes. Based on MSA and IHC results and subsequent mutation analyses of 1,119 unrelated index patients meeting the Amsterdam II criteria or the classical Bethesda guidelines, we analyzed the value of these tools to predict MLH1 and MSH2 mutations with the aim of establishing optimal strategies for their most efficient sequential use. The overall prevalence of pathogenic germline mutations in our cohort was 20.6% (95% CI = 18.3-23.0%) and 61.8% (95% CI = 56.8-66.6%), respectively, after MSA/IHC-based preselection. IHC was highly predictive (99.1%) and specific (99.6%) with regard to MSA. However, 14 out of 230 mutations (6%) escaped detection by IHC. Thus, IHC cannot be recommended to substitute MSA fully. Nonetheless, IHC is important to indicate the gene that is likely to be affected. To combine both methods efficiently, we propose a novel screening strategy that provides 2 alternative ways of sequential IHC and MSA application, either using IHC or MSA in the first place. A logistic regression model based on the age of the index patient at first tumor diagnosis and the number of fulfilled HNPCC criteria is used to allocate individual patients to that alternative pathway that is expected to be least expensive. A cost analysis reveals that about 25% of the costs can be saved using this strategy.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Compound heterozygosity for two MSH6 mutations in a patient with early onset of HNPCC-associated cancers, but without hematological malignancy and brain tumor.

Heterozygous germline mutations in the human mismatch repair (MMR) genes MLH1, PMS2, MSH2 and MSH6 predispose to the hereditary non-polyposis colorectal cancer (HNPCC) syndrome. Biallelic mutations in these genes have been reported for a limited number of cases resulting in hematological malignancies, brain tumors and gastrointestinal tumors early in childhood. These tumor phenotypes are frequently associated with café-au-lait spots (CALS), one of the clinical hallmarks of neurofibromatosis type 1 (NF1). We report the first case of compound heterozygosity for two MSH6 mutations resulting in a nonconservative amino-acid change of a conserved residue and in a premature stop codon in a patient who developed rectal and endometrial cancer at ages 19 and 24 years, respectively, and presented few CALS in a single body segment. Immunohistochemistry and Western blotting revealed only residual expression of the MSH6 protein in the normal cells. The disease history resembles the HNPCC phenotype rather than a phenotype associated with biallelic MMR gene mutations. Therefore, we assume that one or both mutations abolish protein function only partially, further supported by the parents, which are both carriers of one of the mutations each, and not affected by the disease at ages 57 and 58 years. Our data suggest considering biallelic mutations in MMR genes for patients who develop HNPCC-associated tumors at an unusually young age of onset, even without hematological or brain malignancies.

Adult↗
PubMed2006

Microsatellite instability in the development of DNA mismatch repair deficient tumors.

Microsatellites are highly abundant short repetitive sequences found in the genomes across different species. They have gained increasing interest in recent years because length alterations in several coding as well as non-coding microsatellites are associated with a variety of different disorders. Particularly, microsatellite mutations play an important role in tumorigenesis of DNA mismatch repair deficient tumors that account for up to a 15% of colorectal, endometrial, and various other cancers. The systematic analysis of the distribution and function of affected microsatellite sequences has facilitated to unravel important steps in the selection processes that drive tumorigenesis. Here, we review the role of microsatellite mutations in the development of cancers with DNA mismatch repair deficiency, outlining biostatistical approaches for the identification of MSI target genes with relevance to MSI associated carcinogenesis. Knowledge about the biological impact of microsatellite mutations in these genes will potentially help to develop modified clinical concepts for diagnosis, prevention, and treatment of microsatellite unstable human cancers.

Colorectal Neoplasms, Hereditary Nonpolyposis↗
PubMed2005

Spectrum and frequencies of mutations in MSH2 and MLH1 identified in 1,721 German families suspected of hereditary nonpolyposis colorectal cancer.

Mutations in DNA MMR genes, mainly MSH2 and MLH1, account for the majority of HNPCC, an autosomal dominant predisposition to colorectal cancer and other malignancies. The evaluation of many questions regarding HNPCC requires clinically and genetically well-characterized HNPCC patient cohorts of reasonable size. One main focus of this multicenter study is the evaluation of the mutation spectrum and mutation frequencies in a large HNPCC cohort in Germany; 1,721 unrelated patients, mainly of German descent, who met the Bethesda criteria were included in the study. In tumor samples of 1,377 patients, microsatellite analysis was successfully performed and the results were applied to select patients eligible for mutation analysis. In the patients meeting the strict Amsterdam criteria (AC) for HNPCC, 72% of the tumors exhibited high microsatellite instability (MSI-H) while only 37% of the tumors from patients fulfilling the less stringent criteria showed MSI-H; 454 index patients (406 MSI-H and 48 meeting the AC of whom no tumor samples were available) were screened for small mutations. In 134 index patients, a pathogenic MSH2 mutation, and in 118 patients, a pathogenic MLH1 mutation was identified (overall detection rate for pathogenic mutations 56%). One hundred sixty distinct mutations were detected, of which 86 are novel mutations. Noteworthy is that 2 mutations were over-represented in our patient series: MSH2,c.942+3A>T and MLH1,c.1489_1490insC, which account for 11% and 18% of the MSH2 and MLH1 mutations, respectively. A subset of 238 patients was screened for large genomic deletions. In 24 (10%) patients, a deletion was found. In 72 patients, only unspecified variants were found. Our findings demonstrate that preselection by microsatellite analysis substantially raises mutation detection rates in patients not meeting the AC. As a mutation detection strategy for German HNPCC patients, we recommend to start with screening for large genomic deletions and to continue by screening for common mutations in exon 5 of MSH2 and exon 13 of MLH1 before searching for small mutations in the remaining exons.

Adaptor Proteins, Signal Transducing↗
PubMed2005

T25 repeat in the 3' untranslated region of the CASP2 gene: a sensitive and specific marker for microsatellite instability in colorectal cancer.

DNA mismatch repair deficiency is observed in about 10% to 15% of all colorectal carcinomas and in up to 90% of hereditary nonpolyposis colorectal cancer (HNPCC) patients. Tumors with mismatch repair defects acquire mutations in short repetitive DNA sequences, a phenomenon termed high-level microsatellite instability (MSI-H). The diagnosis of MSI-H in colon cancer is of increasing relevance, because MSI-H is an independent prognostic factor in colorectal cancer, seems to influence the efficacy of adjuvant chemotherapy, and is the most important molecular screening tool to identify HNPCC patients. To make MSI typing feasible for the routine pathology laboratory, highly reproducible and cost effective laboratory tests are required. Here, we describe a novel T25 mononucleotide marker in the 3'untranslated region of the CASP2 gene (CAT25) that displayed a quasimonomorphic repeat pattern in normal tissue of 200 unrelated individuals of Caucasian origin. In addition, CAT25 was monomorphic also in all tested donors of African and Asian origin (n = 102 and n = 79, respectively) and thus differs from the most commonly used markers BAT25 and BAT26. Without the analysis of corresponding normal tissue, CAT25 correctly detected 56 of 57 colorectal cancer specimens classified as MSI-H by using the standard National Cancer Institute/International Collaborative Group-HNPCC marker panel. Combined with the standard markers BAT25 and BAT26 in a multiplex PCR, all MSI-H colorectal cancer samples were typed correctly. No false-positive results were obtained in 60 non-MSI-H control colorectal cancer specimens. These data suggest that CAT25 should be included into novel marker panels for microsatellite testing thus allowing for a significant reduction of the complexity and costs of MSI typing. Moreover, CAT25 represents a highly promising marker for early detection of colorectal cancer in HNPCC germ line mutation carriers.

3' Untranslated Regions↗
PubMed2005

Immunoselective pressure and human leukocyte antigen class I antigen machinery defects in microsatellite unstable colorectal cancers.

In colorectal cancer, the immune response is particularly pronounced against tumors displaying the high microsatellite instability (MSI-H) phenotype. MSI-H tumors accumulate mutations affecting microsatellites located within protein encoding regions (coding microsatellites, cMS), which lead to translational shifts of the respective reading frames. Consequently, novel tumor-specific frameshift-derived neopeptides (FSP) are generated and presented by MSI-H tumor cells, thus eliciting effective cytotoxic immune responses. To analyze whether the immunoselective pressure was reflected by the phenotype of MSI-H colorectal cancer cells, we compared here the expression of antigen processing machinery (APM) components and human leukocyte antigen (HLA) class I antigen subunits in 20 MSI-H and 20 microsatellite-stable (MSS) colorectal cancer using a panel of newly developed APM component-specific monoclonal antibodies. In addition, we did a systematic analysis of mutations at cMS located within APM genes and beta2-microglobulin (beta2m). Total HLA class I antigen loss was observed in 12 (60.0%) of the 20 MSI-H lesions compared with only 6 (30.0%) of the 20 MSS colorectal cancer lesions. Moreover, total loss of membraneous HLA-A staining was significantly more frequent in MSI-H colorectal cancer (P = 0.0024). Mutations at cMS of beta2m and genes encoding APM components (TAP1 and TAP2) were detected in at least 7 (35.0%) of 20 MSI-H colorectal cancers but in none of the MSS colorectal cancers (P = 0.0002). These data show that defects of HLA class I antigen processing and presentation seem to be significantly more frequent in MSI-H than in MSS colorectal cancer, suggesting that in MSI-H colorectal cancer the immunoselective pressure leads to the outgrowth of cells with defects of antigen presentation.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

Regulation of AKT1 expression by beta-catenin/Tcf/Lef signaling in colorectal cancer cells.

The serine/threonine kinase AKT plays a critical role in controlling the balance between cell survival and apoptosis. Several reports implicated AKT in the molecular pathogenesis of different human malignancies and overexpression of AKT was recently demonstrated to be an early event in colorectal carcinogenesis. We report here the identification of nine putative Tcf/Lef-binding elements (TBEs) upstream to the ATG initiation site of the AKT1 gene. Four of these TBEs are located upstream of the transcriptional start, whereas five TBEs are situated in Exon 1 of the AKT1 gene. Accordingly, we hypothesized that AKT1 expression might be regulated by Wnt/beta-catenin signaling. To elucidate the regulation of AKT expression in colon cancer cells, we generated reporter constructs containing the luciferase gene under the control of different regions derived from the AKT1 promoter/enhancer. Transient expression of the constructs in colorectal cancer (CRC) cell lines resulted in significant activation of the reporter gene. Luciferase was stimulated 20- to 50-fold in SW480, SW948 and HCT116 CRC cells. In contrast, the AKT1 promoter/enhancer constructs showed only a weak response in 293 embryonic kidney cells. Coexpression of a constitutively active beta-catenin mutant in colon cancer cells further enhanced reporter gene activation from the AKT1 promoter/enhancer, whereas it was downregulated by introduction of either wild-type APC or dnTcf-4. In addition, immunohistochemical staining of tumor sections derived from CRC patients showed elevated expression levels of AKT1, correlating with enhanced cytoplasmic/nuclear expression of beta-catenin. In summary our data suggest that beta-catenin/Tcf contributes to the transcriptional regulation of the AKT1 gene.

Apoptosis↗
PubMed2005

Microsatellite instability of selective target genes in HNPCC-associated colon adenomas.

Microsatellite instability (MSI) occurs in most hereditary nonpolyposis colorectal cancers (HNPCC) and less frequently in sporadic tumors as the result of DNA mismatch repair (MMR) deficiency. Instability at coding microsatellites (cMS) in specific target genes causes frameshift mutations and functional inactivation of affected proteins, thereby providing a selective growth advantage to MMR deficient cells. At present, little is known about Selective Target Gene frameshift mutations in preneoplastic lesions. In this study, we examined 30 HNPCC-associated MSI-H colorectal adenomas of different grades of dysplasia for frameshift mutations in 26 cMS-bearing genes, which, according to our previous model, represent Selective Target genes of MSI. About 30% (8/26) of these genes showed a high mutation frequency (> or =50%) in colorectal adenomas, similar to the frequencies reported for colorectal carcinomas. Mutations in one gene (PTHL3) occurred significantly less frequently in MSI adenomas compared to published mutation rates in MSI carcinomas (36.0 vs 85.7%, P=0.023). Biallelic inactivation was observed in nine genes, thus emphasizing the functional impact of cMS instability on MSI tumorigenesis. Some genes showed a high frequency of frameshift mutations already at early stages of MSI colorectal tumorigenesis that increased with grade of dysplasia and transition to carcinoma. These include known Target Genes like BAX and TGFBR2, as well as three novel candidates, MACS, NDUFC2, and TAF1B. Overall, we have identified genes of potential relevance for the initiation and progression of MSI tumorigenesis, thus representing promising candidates for novel diagnostic and therapeutic approaches directed towards MMR-deficient tumors.

Adenoma↗
PubMed2005

Microsatellite analysis of hereditary nonpolyposis colorectal cancer-associated colorectal adenomas by laser-assisted microdissection: correlation with mismatch repair protein expression provides new insights in early steps of tumorigenesis.

Although microsatellite instability (MSI) testing is a useful tool for molecular screening of hereditary nonpolyposis colorectal cancer (HNPCC) carcinomas, conflicting results have been obtained in colorectal adenomas. This might result from different techniques of tissue sampling and MSI analysis. Alternatively, some HNPCC-associated adenomas may follow a molecular route that differs from the MSI pathway. In the present study we examined the MSI status of 18 adenomas from 17 HNPCC patients by comparing manual adenoma dissection under gross visual control with laser microdissection of single adenoma crypts. After manual gross dissection, 50% (9 of 18) and 11.1% (2 of 18) of the adenomas displayed high-level (MSI-H) and low-level (MSI-L) MSI, respectively. The same set of adenomas split into 83.3% (15 of 18) MSI-H and 5.6% (1 of 18) MSI-L after laser microdissection. The expression pattern of mismatch repair (MMR) proteins showed a higher concordance rate with the MSI status in laser-dissected (94%) than gross-dissected (47%) adenomas. Whereas two adenomas remained microsatellite stable (MSS) and MMR proficient even after laser-assisted dissection, two MSI-H cases showed either rare instabilities at coding microsatellites or intratumoral heterogeneity of MSI with and without MSH2 expression. This suggests that in some adenomas development of MMR dysfunction occurs stepwise with MSI, arising before complete loss of MMR gene expression, whereas other HNPCC-associated adenomas might develop independently of MMR deficiency.

Adenoma↗
PubMed2005

Molecular testing for microsatellite instability and its value in tumor characterization.

Molecular analysis of tumor tissue has become a rapidly expanding field in medical research, exploiting the advantages of new technologies adapted to high-throughput examination of genetic alterations, gene and protein expression patterns. Only exceptionally, these approaches have found their way into routine clinical diagnosis and therapy. Microsatellite instability testing has been established as a very powerful tool to identify patients with hereditary nonpolyposis colorectal cancer, one of the most common familial cancer syndromes. In addition, there is emerging evidence that microsatellite instability analysis may become increasingly important for the clinician, having considerable impact on patients' prognosis as well as therapeutic decisions, at least in colorectal cancer patients. A better understanding of the microsatellite instability phenotype, its pathogenesis and implications for the course of the disease will pave the way for novel diagnostic and therapeutic strategies specifically tailored to microsatellite-unstable tumors. This review summarizes the current significance of molecular testing for microsatellite instability in several tumor entities and provides prospects of future developments.

Animals↗
PubMed2004

A large MSH2 Alu insertion mutation causes HNPCC in a German kindred.

Hereditary non-polyposis colorectal cancer (HNPCC) syndrome is an autosomal, dominantly inherited disease accounting for about 1%-5% of all colorectal cancer cases. HNPCC predisposition is caused by germline mutations in at least five genes coding for DNA mismatch repair (MMR) proteins. More than 400 MMR gene mutations have been identified in HNPCC patients. About 90% of mutations affect the MLH1 and MSH2 genes. The mutational spectrum mainly includes point mutations and small deletions or insertions. Here, we report a large 184 base-pair Alu insertion mutation in exon 6 of the MSH2 gene in a German HNPCC family. The inserted sequence contains repetitive Alu sequence elements that present the highest homology with the old Alu J subfamily. The Alu J insertion was most likely derived from Alu-mediated recombination, since Alu J elements have been found close to the insertion site in adjacent introns, and since elements pivotal for Alu retrotransposition are missing. Our results suggest that the recombination event occurred at least one generation ago. This is the first report of an Alu insertion in the coding sequence of a MMR gene as the cause of HNPCC. Our data thus further extend the spectrum of MMR gene mutations causative for HNPCC.

Aged↗
PubMed2002

Identification and characterization of UEV3, a human cDNA with similarities to inactive E2 ubiquitin-conjugating enzymes.

Recent studies have shown that ubiquitination is an essential factor in endosomal sorting and virus assembly. The human TSG101 gene has been demonstrated to belong to a group of genes coding for apparently inactive E2 ubiquitin-conjugating enzymes, which exert regulatory effects on E2 activity in cellular ubiquitination processes. In this study, a novel human cDNA (UEV3) encoding a putative protein of 379 amino acids was isolated from a human placenta library that may represent a partial paralogue of human TSG101. The predicted protein contains an N-terminal domain homologous to the catalytic domain of ubiquitin-conjugating enzymes (Ubc), which is fused to a sequence showing significant homology to members of the lactate dehydrogenase protein family. The UEV3 gene is located on chromosome 11 closely adjacent to TSG101 and LDH-C. Northern blot and UEV3-specific reverse transcription/polymerase chain reaction (RT/PCR) analyses of various colon carcinoma cell lines as well as both normal and tumor samples from colon revealed an expression of the UEV3 cDNA in all tested samples.

Amino Acid Sequence↗