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Alex Duval

Publications and source records attributed to Alex Duval.

At least 19 recordsLinked to original sources
PubMed2006

Detection of microsatellite instability in endometrial cancer: advantages of a panel of five mononucleotide repeats over the National Cancer Institute panel of markers.

The aim of this study was to find the optimal set of microsatellite markers for diagnosis of the microsatellite instability (MSI) phenotype in endometrial cancers. We compared the sensitivity, specificity and ease of use of a reference panel of five markers originally recommended by the National Cancer Institute (NCI) for colorectal cancer and a panel of five quasi-monomorphic mononucleotide repeat markers (pentaplex PCR system). We used these panels for establishing the MSI status of a series of 80 sporadic endometrial adenocarcinomas by comparing the allelic profiles of the markers between tumor and matching germline DNA. Both panels detected the same subset of 21 out of 80 (26%) endometrial MSI carcinomas. However, in the MSI cases, the mean instability of the five mononucleotide repeats was 96.1% as compared with a mean instability of 69.8% for the three dinucleotide repeats of the NCI panel, indicating a superiority of mononucleotide repeats over dinucleotide repeats in detecting MSI. The fact that the two panels of markers detect the same set of MSI tumors is due to the presence of two mononucleotide repeats within the NCI panel. As demonstrated previously in gastric and colon MSI cases, the pentaplex PCR reaction using mononucleotide repeats is thus an easier and more sensitive method than the NCI panel, for the screening of MSI status in endometrial tumors.

Biomarkers, Tumor↗
PubMed2005

Multipopulation analysis of polymorphisms in five mononucleotide repeats used to determine the microsatellite instability status of human tumors.

PURPOSE: Human gastrointestinal tumors with inactivated DNA mismatch repair system (microsatellite instability [MSI] tumors) have distinct molecular and clinicopathologic profiles, and are associated with favorable prognosis. There is evidence suggesting that colorectal cancer patients with MSI tumors respond differently to adjuvant chemotherapy as compared with patients with non-MSI tumors. Finally, determination of the MSI status has clinical application for assisting in the diagnosis of suspected hereditary cases. It is thus becoming increasingly recognized that testing for MSI should be conducted systematically in all human cancers potentially of this type. We recently described a pentaplex polymerase chain reaction of five mononucleotide repeats to establish the MSI status of human tumors, and showed that this assay was 100% sensitive and specific. Moreover, these markers are quasimonomorphic in germline DNA of the white population (ie, individuals of Eurasian origin), and could be used for tumor MSI determination without the requirement for matching normal DNA in this group. PATIENTS AND METHODS: In this study, we analyzed a comparable panel of five mononucleotide markers in germline DNA from 1,206 individuals encompassing 55 different populations worldwide. Results With the exception of two Biaka Pygmies and one San individual for whom three markers showed variant alleles (three cases [0.2%]), the remaining 1,203 individuals showed no alleles of variant size (1,055 cases [87.5%]), or only one (122 cases [10.1%]) or two (26 cases [2.2%]) markers with variant alleles. All 60 MSI tumors investigated display instability in at least four of the five markers. CONCLUSION: We demonstrated that tumor MSI status can be determined using the pentaplex reaction for all human populations without the need for matching normal DNA.

Alleles↗
PubMed2005

Differential nonsense mediated decay of mutated mRNAs in mismatch repair deficient colorectal cancers.

The nonsense-mediated decay (NMD) system normally targets mRNAs with premature termination codons (PTCs) for rapid degradation. We investigated for a putative role of NMD in cancers with microsatellite instability (MSI-H cancers), because numerous mutant mRNAs containing PTC are generated in these tumors as a consequence of their mismatch repair deficiency. Using a quantitative RT-PCR approach in a large series of colorectal cancer cell lines, we demonstrate a significantly increased rate of degradation of mutant mRNAs containing a PTC compared with wild-type. A specific siRNA strategy was used to inhibit RENT-1 and/or RENT-2 activity, two major genes in the NMD system. This allowed us to show that increased degradation of PTC-containing mRNAs in MSI-H tumors was partly dependent upon NMD activity. The efficiency of NMD for the degradation of mutant mRNAs from target genes was highly variable in these cancers. NMD degraded some of them (TGFssRII, MSH3, GRK4), although allowing the persistent expression of others (BAX, TCF-4). This is of particular interest within the context of a proposed conservation of biological activity for the corresponding mutated proteins. We thus propose that NMD might play an important role in the selection of target gene mutations with a functional role in MSI-H carcinogenesis.

Codon, Nonsense↗
PubMed2005

Mononucleotide repeats BAT-26 and BAT-25 accurately detect MSI-H tumors and predict tumor content: implications for population screening.

Tumors with a defective DNA mismatch repair system (MSI-H tumors) have distinct molecular and clinicopathologic profiles compared with mismatch repair-proficient tumors and are associated with a relatively favorable prognosis. There is evidence to suggest that colorectal cancer patients with MSI-H tumors respond differently to adjuvant chemotherapy. Determination of MSI status also has clinical application for assisting in the diagnosis of suspected hereditary nonpolyposis colorectal cancer cases. For these reasons, it is becoming increasingly apparent that testing for MSI should be conducted routinely in human cancer types that frequently present with such a phenotype. BAT-26 and BAT-25 are mononucleotide repeats that are widely used to establish the MSI status of human tumors. We show here that their allelic size profiles provide an estimate of the percentage of contaminating normal cells in MSI-H tumors. These markers are sensitive enough to detect instability when the tumor cell content of a sample is as low as 5-10%. MSI-H tumors contain mutations in coding repeats within genes known to be targets for instability. In cases with low tumor cell content, no mutations in any of 9 coding repeats were detected. However, when these samples were enriched for tumor cells, mutations were detected in the same target genes. Thus, BAT-26 and BAT-25 markers accurately identify MSI-H tumors without prior need for enrichment for tumor cells and indicate which samples require further purification before screening for mutations in target genes for instability. Our results have implications for large-scale screening of cancer patients to determine MSI-H status and prognosis.

Colorectal Neoplasms↗
PubMed2005

The prevalence of PIK3CA mutations in gastric and colon cancer.

A wide variety of tumours show PIK3CA mutations leading to increased phosphatidylinositol-3 kinase (PI3K) activity. We have determined the frequency of PIK3CA mutations in exons 9 and 20 that has previously been reported as mutational hotspot regions in distinct tumour models. One hundred and fifty gastrointestinal carcinomas (47 gastric and 103 colorectal) that were characterised for MSI status (76 MSI and 74 MSS) by PCR-SSCP sequencing were evaluated. We also analysed the association between PIK3CA mutations and KRAS or BRAF mutations. PIK3CA mutations in exons 9 and 20 were present in 13.6% and 10.6% of colorectal and gastric carcinomas, respectively. No differences in frequency and type of PIK3CA mutations were found between MSI and MSS colorectal carcinomas. All gastric carcinomas with PIK3CA mutations were MSI. The number of cases harbouring concomitant PIK3CA and KRAS or BRAF mutations was higher in colorectal than in gastric carcinomas (P = 0.016). In colorectal carcinoma, PIK3CA mutations occur preferentially together with activating KRAS-BRAF mutations (MSI and MSS) while in gastric carcinomas PIK3CA mutations tend to occur as isolated events (MSI).

Base Pair Mismatch↗
PubMed2004

An immunogenic process leading to cancer in the context of immunodeficiency.

Colorectal MSI tumors are associated with an increased immune response. On the other hand, immunodeficient patients are more prone to lymphomas with the MSI phenotype. These facts are of wide interest in understanding the complex link between immunity and cancer, particularly of the MSI phenotype. Specific attention to the host immune system should thus be considered in the treatment of patients with MSI tumors.

Acquired Immunodeficiency Syndrome↗
PubMed2004

The mutator pathway is a feature of immunodeficiency-related lymphomas.

The mutator phenotype caused by defects in the mismatch repair system is observed in a subset of solid neoplasms characterized by widespread microsatellite instability-high (MSI-H). It is known to be very rare in non-Hodgkin lymphomas (NHL), whereas mutator NHL is the most frequent tumor subtype in mismatch repair-deficient mice. By screening a series of 603 human NHL with specific markers of the mutator phenotype, we found here 12 MSI-H cases (12/603, 2%). Of interest, we demonstrated that this phenotype was specifically associated with immunodeficiency-related lymphomas (ID-RL), because it was observed in both posttransplant lymphoproliferative disorders (9/111, 8.1%) and HIV infection-related lymphomas (3/128, 2.3%) but not in a large series of NHL arising in the general population (0/364) (P < 0.0001). The MSI pathway is known to lead to the production of hundreds of abnormal protein neoantigens that are generated in MSI-H neoplasms by frameshift mutations of a number of genes containing coding microsatellite sequences. As expected, MSI-H ID-RL were found to harbor such genetic alterations in 12 target genes with a putative role in lymphomagenesis. The observation that the MSI-H phenotype was restricted to HIV infection-related lymphomas and posttransplant lymphoproliferative disorders suggests the existence of the highly immunogenic mutator pathway as a novel oncogenic process in lymphomagenesis whose role is favored when host immunosurveillance is reduced. Because MSI-H-positive cases were found to be either Epstein-Barr virus-positive or -negative, the mutator pathway should act synergistically or not with this other oncogenic factor, playing an important role in ID-RL.

Adult↗
PubMed2004

Activated BRAF targets proximal colon tumors with mismatch repair deficiency and MLH1 inactivation.

BRAF, a serine/threonine kinase of the RAF family, is a downstream transducer of the RAS-regulated MAPK pathway and signals upstream of MEK1/2 kinases. Recently, activating mutations within BRAF have been reported in a high percentage of melanomas and colorectal carcinomas and shown to have oncogenic capabilities. Further, their association to mismatch-repair-deficient tumors has suggested the involvement of the RAS/RAF pathway in the tumorigenesis of microsatellite-unstable colon cancers, and that RAS and RAF mutations are alternative genetic events. We determined whether colorectal mismatch-repair-deficient tumors with BRAF mutations show a specific genotype when compared with tumors with wild-type BRAF, and whether they can be associated with a particular clinicopathological feature. Here, we report a striking association of BRAF, but not of APC, KRAS2, AXIN2, and TP53 mutations, with proximal mismatch-repair-deficient colon tumors and MLH1 hypermethylation. Our results support the hypothesis that proximal and distal colorectal tumors with mismatch repair deficiency harbor different genetic alterations, and we suggest that the involvement of the RAS/RAF pathway in colorectal tumorigenesis is differentially modulated according to tumor location and MLH1 inactivation.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Quasimonomorphic mononucleotide repeats for high-level microsatellite instability analysis.

Microsatellite instability (MSI) analysis is becoming more and more important to detect sporadic primary tumors of the MSI phenotype as well as in helping to determine Hereditary Non-Polyposis Colorectal Cancer (HNPCC) cases. After some years of conflicting data due to the absence of consensus markers for the MSI phenotype, a meeting held in Bethesda to clarify the situation proposed a set of 5 microsatellites (2 mononucleotide repeats and 3 dinucleotide repeats) to determine MSI tumors. A second Bethesda consensus meeting was held at the end of 2002. It was discussed here that the 1998 microsatellite panel could underestimate high-level MSI tumors and overestimate low-level MSI tumors. Amongst the suggested changes was the exclusive use of mononucleotide repeats in place of dinucleotide repeats. We have already proposed a pentaplex MSI screening test comprising 5 quasimonomorphic mononucleotide repeats. This article compares the advantages of mono or dinucleotide repeats in determining microsatellite instability.

Alleles↗
PubMed2003

BRAF mutations characterize colon but not gastric cancer with mismatch repair deficiency.

Genes from the RAF family are Ras-regulated kinases involved in growth cellular responses. Recently, a V599E hotspot mutation within the BRAF gene was reported in a high percentage of colorectal tumors and significantly associated to defective mismatch repair (MMR). Additionally, BRAF mutations were described only in K-Ras-negative colon carcinomas, suggesting that BRAF/K-Ras activating mutations might be alternative genetic events in colon cancer. We have addressed to what extent the tumorigenic-positive selection exerted by BRAF mutations seen in colorectal MMR-deficient tumors was also involved in the tumorigenesis of gastric cancer. Accordingly, BRAF mutations were detected in 34% (25/74) of colorectal MMR-deficient tumors and in 5% (7/142) of MMR-proficient colorectal cases (P=0.0001). All mutations found in the MSI cases corresponded to the previously reported hotspot V599E. Two D593K and a K600E additional mutations were also detected in three MSS cases. However, only one mutation of BRAF was found within 124 MSS gastric tumors and none in 37 MSI gastric tumors, clearly suggesting that BRAF mutations are not involved in gastric tumorigenesis. Nonetheless, a high incidence of mutations of K-Ras was found within the MSI gastric group of tumors (P=0.0005), suggesting that the activation of K-Ras-dependent pathways contributes to the tumorigenesis of gastric cancers with MMR deficiency. Accordingly, our results show evidences that BRAF mutations characterize colon but not gastric tumors with MMR deficiency and are not involved in the tumorigenesis of gastric cancer of the mutator phenotype pathway.

Amino Acid Substitution↗
PubMed2003

Tissue microarray technology: validation in colorectal carcinoma and analysis of p53, hMLH1, and hMSH2 immunohistochemical expression.

Tissue microarray technology enables the analysis of hundreds of specimens by arranging numerous 0.6-mm tissue core biopsy specimens into a single paraffin block. Validation studies are necessary to evaluate the representativeness of small disks taken from the original tissue. We validated the tissue microarray technology in colorectal carcinoma by analyzing the immunohistochemical expression of proteins involved in the two main pathways of colorectal carcinogenesis: p53 protein for loss of heterozygosity tumors, hMLH1 and hMSH2 proteins for microsatellite instability (MSI) tumors. We compared in 30 colorectal carcinomas (15 MSI(-) and 15 MSI(+)), 8 microarrays disks, and the whole section of the block from which they were derived. Tumoral tissue was present in 95.7% of the microarray disks. The analysis of three disks per case was comparable to the analysis of the whole section in 99.6% (p53), 98.8% (hMLH1), and 99.2% (hMSH2) of cases. In the second part we applied the tissue microarray technology to 263 consecutive cases of colorectal carcinoma, sampled by three cores. We showed that 48.5% overexpressed p53 and 8.7% lost hMLH1 or hMSH2. Tissue microarray technology, validated in colorectal carcinoma, appears as a useful research tool for rapid analysis of the clinical interest of molecular alterations.

Adaptor Proteins, Signal Transducing↗
PubMed2003

MBD4 mutations are rare in gastric carcinomas with microsatellite instability.

MBD4 encodes a protein that interacts with the mismatch repair protein hMLH1. Therefore, it has been postulated that mutations in MBD4 may result in mismatch repair deficiency. Furthermore, it was shown that MBD4 is a target gene in mismatch repair-deficient tumors. We searched for mutations of MBD4 in sporadic gastric carcinomas (SGC) and compared them with the MSI status of the tumors by screening a series of 42 SGC [22 high microsatellte instability (MSI-H) and 20 microsatellite stable (MSS)] for mutations in both the poly(A)10 and (A)6 tracts of the gene as well as in its entire coding sequence. Mutations of the poly(A)10 tract of MBD4 were also screened in 126 MSI-H colon carcinomas. One of the 22 MSI-H gastric carcinomas and 12 of 126 MSI-H colon carcinomas showed MBD4 mutations in the poly(A)10 tract of exon 3. In addition, seven sequence variants were found in SGC, all of them having a polymorphic nature. We conclude that MBD4 mutations in the entire coding sequence, including the two poly(A) tracts, are rare in MSI gastric carcinomas. MBD4 is likely to be a bystander target gene in MSI-H tumors.

Adenosine↗
PubMed2003

[Replication error repair, microsatellites, and cancer].

Some common human tumors are characterized by inactivating alterations of mismatch repair (MMR) genes that lead to an inability to recognize and repair errors that occur during DNA replication. These alterations are either inherited in the so-called hereditary non polyposis colorectal cancer (HNPCC) syndrome or can occur sporadically in 10-15% of colorectal, gastric, or endometrial tumors. Because of their repetitive nature, microsatellite sequences are particularly prone to mutation in tumors with MMR deficiency. Thousands of microsatellite alterations accumulate in MMR deficient cancers and these are referred to as MSI-H tumors (high level of microsatellite instability). MSI-H tumors have different clinicopathological features compared to cancers without this phenotype, and the repertoire of genetic events involved in their tumoral progression is also thought to be different. Many of the genetic alterations observed in MSI-H tumors affect nucleotide repeat tracks contained within genes thought to have a putative oncogenic function. These alterations are believed to play an important role during MSI-H carcinogenesis, since they can be either inactivating or activating events that are selected for in a recessive or dominant manner. We provide here an overview of the genetic changes that occur in MSI-H tumors and that appear to constitute a new genetic mutator pathway leading a normal cell to become malignant.

Adenosine Triphosphatases↗
PubMed2002

Comparative analysis of mutation frequency of coding and non coding short mononucleotide repeats in mismatch repair deficient colorectal cancers.

Coding repeats are usually short mononucleotide tracts (SMT) of 10 or less base pairs in size. A number of such sequences contained in genes suspected to play a role in human carcinogenesis have been found to be mutated in mismatch repair deficient tumors (MSI-H cancers). Because of the high background of instability characterizing these cancers and in the absence of functional criteria, the significance of most frameshift gene alterations is unclear. In the present work, we analysed a series of 22 transcribed but non-coding SMT that are thus unlikely to play a tumorigenic role. Their frequency of size alteration in germline DNA and in DNA from MSI-H and microsatellite stable (MSS) tumors were compared to those previously reported in a series of 25 coding SMT of similar size. Non-coding SMT were either monomorphic or polymorphic in germline DNA whereas coding SMT were all monomorphic. In MSI-H tumors, non-coding SMT showed infrequent alterations (0-44%), as opposed to coding SMT which were altered at extremely variable frequencies (0 to 92%). Seven of the 22 non-coding SMT were monomorphic in MSS tumors but presented size alterations in MSI-H tumors with variable frequencies (3-28%). They were thus selected for further comparative statistical analyses for instability in coding SMT in MSI-H colorectal cancers. Only seven out of 25 of the coding SMT showed a significantly higher mutation frequency in these tumors. In the absence of functional criteria, we propose this as a novel and comprehensive approach for distinguishing real target genes amongst the numerous proposed gene mutations. It should allow identification of those that are genuinely selected for during MSI-H tumoral progression from others that play a less important role, if any, in MSI-H carcinogenesis.

Base Pair Mismatch↗
PubMed2002

Mutations at coding repeat sequences in mismatch repair-deficient human cancers: toward a new concept of target genes for instability.

Because the discovery of a link between mismatch repair deficiency and sporadic or inherited human cancers characterized by microsatellite instability (MSI-H tumors), genes containing coding repeat sequences have been found to be mutated at these repeats in MSI-H tumors from different primary sites as reported in the present review. Accumulation of such alterations appears to be the main molecular mechanism by which MSI-H cells accumulate functional changes with putative oncogenic effects. These mutations occur in many genes at variable frequencies. They can affect genes with a putative role in human carcinogenesis involved in different or similar pathways and are thus thought to be inactivating or activating events selected for in these cancers in a recessive or dominant manner. However, because of the high level of instability characterizing these cancers, they are also likely to occur in genes without any expected role in MSI-H carcinogenesis. In light of these recent data, the concept of target genes for instability and their possible role in MSI-H cancers is reconsidered here.

Base Pair Mismatch↗
PubMed2002

Target gene mutation profile differs between gastrointestinal and endometrial tumors with mismatch repair deficiency.

Mutation frequencies at 25 genes containing coding repeats were compared in colorectal, gastric, and endometrial mismatch repair-deficient (MSI-H) tumors. The overall number of mutations was significantly lower in endometrial than in gastrointestinal MSI-H cancers. Using a likelihood statistical method, target genes were divided in each tumor location into two groups likely to represent gene mutations that do or do not provide selective pressures during tumoral progression. Mutation profiles were quite similar in gastric and colorectal MSI-H cancers but were different in endometrial MSI-H tumors. Deletions in Bat-25 and Bat-26 noncoding repeats were also significantly less important in endometrial as compared with gastrointestinal MSI-H tumors. Our results show that the profile of target gene mutations in MSI-H tumors is tissue specific, with both qualitative and quantitative differences between gastrointestinal and endometrial MSI-H cancers.

Base Pair Mismatch↗
PubMed2002

Evaluation of tumor microsatellite instability using five quasimonomorphic mononucleotide repeats and pentaplex PCR.

BACKGROUND & AIMS: The microsatellite instability (MSI) phenotype is a characteristic of the hereditary nonpolyposis colorectal cancer syndrome as well as approximately 15% of sporadic colon and gastric tumors. It is a valuable diagnostic marker for the identification of hereditary nonpolyposis colorectal cancer cases and may be a molecular predictive marker for the identification of colon cancer patients who benefit from chemotherapy. To evaluate MSI, a reference panel was proposed at an international consensus meeting, comprised of 2 mononucleotide (BAT-25, BAT-26) and 3 dinucleotide repeats. Analysis of BAT-26 is sufficient for detecting the MSI phenotype in most, but not all, cases. Additional results with dinucleotide markers can sometimes lead to incorrect classification of MSI tumors. METHODS: We describe here a single fluorescent multiplex system comprising 5 quasimonomorphic mononucleotide repeats for the detection of MSI tumors. RESULTS: None of 184 germline DNA samples, including 56 from African subjects, was found to contain allelic size variations in more than 2 of these markers. In contrast, all MSI tumors showed allelic size variations in 3 or more of the microsatellites. Using this assay, we confirmed (or reclassified in 6 cases) the MSI status of 124 colon and 50 gastric primary tumors and 16 colon cell lines. CONCLUSIONS: We propose that using a pentaplex polymerase chain reaction system allows accurate evaluation of tumor MSI status of DNA with 100% sensitivity and specificity without the need to match normal DNA. This assay is simpler to use than those involving dinucleotides and is more specific than using BAT-26 alone.

Africa↗