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Results for “DNA MICROSATELLITE INSTABILITY”

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PubMed2001

Somatic mutations in the DNA damage-response genes ATR and CHK1 in sporadic stomach tumors with microsatellite instability.

Maintenance of genomic stability depends on the appropriate cellular responses to DNA damage and the integrity of the DNA repair systems. We analyzed stomach tumors with microsatellite instability (MSI) for frameshift mutations in several potential targets of the mutator phenotype involved in DNA damage-response pathways, such as the ataxia telangiectasia mutated protein-related protein (ATR)-CHK1-Cdc25c pathway, and DNA repair. High frequency of mutations was found within ATR [5 (21%) of 23], MED1 [10 (43%) of 23], hMSH3 [13 (56%) of 23], and hMSH6 [10 (43%) of 23] genes. Also, a low frequency of mutations within the CHK1 gene was detected in 9% (2 of 23) of tumors. No mutations of hMLH3, ATM, BRCA1, or NBS1 genes were detected. These results confirm ATR, MED1, and CHK1 as targets of the mutator pathway in stomach tumorigenesis, and also suggest a potential role of MED1 increasing, together with hMSH3 and hMSH6, the genomic instability in the mutator pathway as a secondary mutator. Furthermore, these results suggest that the inhibition of the ATR-CHK1 DNA damage-response pathway might be involved in the tumorigenesis of gastric cancer with microsatellite instability.

Ataxia Telangiectasia Mutated Proteins↗

PubMed2004

Factors contributing to the outcome of oxidative damage to nucleic acids.

Oxidative damage to DNA appears to be a factor in cancer, yet explanations for why highly elevated levels of such lesions do not always result in cancer remain elusive. Much of the genome is non-coding and lesions in these regions might be expected to have little biological effect, an inference supported by observations that there is preferential repair of coding sequences. RNA has an important coding function in protein synthesis, and yet the consequences of RNA oxidation are largely unknown. Some non-coding nucleic acid is functional, e.g. promoters, and damage to these sequences may well have biological consequences. Similarly, oxidative damage to DNA may promote microsatellite instability, inhibit methylation and accelerate telomere shortening. DNA repair appears pivotal to the maintenance of genome integrity, and genetic alterations in repair capacity, due to single nucleotide polymorphisms or mutation, may account for inter-individual differences in cancer susceptibility. This review will survey these aspects of oxidative damage to nucleic acids and their implication for disease.

DNA↗

PubMed2001

Microsatellite instability and mismatch-repair protein expression in hereditary and sporadic colorectal carcinogenesis.

Aberrant crypt foci (ACF) are microscopic clusters of altered colonic crypts considered premalignant lesions in the large bowel. Genomic instability at short tandem repeats in the DNA, referred to as microsatellite instability (MSI) is the hallmark of hereditary nonpolyposis colorectal carcinoma (HNPCC) caused by mutations in DNA mismatch-repair genes, mostly hMLH1 and hMSH2. In this study, we evaluated for MSI ACF (n = 16), adenomas (n = 18), carcinomas (n =22), and lymph node metastases (n = 3) from 17 patients with colorectal cancer positive for MSI. Ten patients were members of HNPCC families; 7 patients had no family history of cancer. MSI was found in 7 of 7 (100%) ACF and 11 of 12 (91%) adenomas from patients with HNPCC. MSI was not related to histology and size of ACF. A progressive increase in instability as estimated by the number of shifted bands was observed along the ACF-adenoma-carcinoma sequence. In contrast, two of nine (22%) ACF and none of six adenomas from patients with MSI sporadic carcinoma were unstable at microsatellite loci. hMLH1 or hMSH2 protein expression was altered only in MSI-positive premalignant lesions (ACF and/or adenomas), but not in all MSI-positive lesions in patients with HNPCC. These observations provide evidence of the premalignant nature of ACF in HNPCC and suggest that MSI is a very early event both in HNPCC and in sporadic colorectal carcinogenesis, although in the latter it seems infrequent.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Mutational analysis of the PMS2 gene in sporadic endometrial cancers with microsatellite instability.

OBJECTIVE: Approximately 20% of endometrial tumors have a defect in DNA mismatch repair and exhibit microsatellite instability (MSI). We assessed the role of the PMS2 DNA mismatch repair gene in MSI-positive sporadic endometrial tumors. METHODS: We examined 40 sporadic endometrial tumor specimens with MSI. All 15 exons of the PMS2 gene were investigated for sequence alterations by single-strand conformational variant analysis. RESULTS: Twelve polymorphisms were identified, 8 of which were in the coding sequence. Four specimens revealed mutations in intronic sequences that are not predicted to affect the PMS2 mRNA. No mutations were detected within the coding region of the PMS2 gene. CONCLUSION: We conclude that structural mutations in the PMS2 gene are not responsible for defective DNA mismatch repair in sporadic endometrial cancers with MSI. The identification of single nucleotide polymorphisms in the PMS2 locus may aid in the mapping and characterization of genetic diseases.

Adenosine Triphosphatases↗

PubMed2006

Microsatellite instability in nasopharyngeal and lymphoepithelial carcinomas of the head and neck.

Lymphoepithelial carcinoma (LEC) is a descriptive diagnosis for an undifferentiated carcinoma that has a typical morphologic appearance of large vesicular cells with prominent nucleoli and infiltrating lymphocytes. Tumors with this histopathologic appearance in the head and neck can be categorized as either those that occur in endemic areas, such as Southeast Asia and are associated with Epstein-Barr virus (EBV) infection, or those that occur in other countries and are less commonly associated with EBV. The molecular changes in endemic EBV-related LEC have been fairly well studied and include both alterations in tumor suppressor genes and 1 report of high levels of microsatellite instability. In nonendemic LECs arising in western countries, there is very little data related to molecular mutational profiles. In this study, we examined 19 cases of LEC from the United States for evidence of microsatellite instability at the DNA level and for alterations in the DNA mismatch repair (MMR) system at the immunohistochemical staining level. Only 3/19 cases showed high-level microsatellite instability and only 1 of these showed an alteration in the DNA MMR protein expression hMLH1. These data suggest that alterations in DNA MMR system are not a common mechanism of tumorigenesis in LEC of the head and neck in a nonendemic country.

Adult↗

PubMedDate not supplied

A new method for optimizing multiplex DNA microsatellite analysis in low quality archival specimens.

BACKGROUND: Testing microsatellite instability seems to be a useful tool for the initial screening of putative non-polyposis colorectal cancer (HNPCC), preceding analysis of germ-line mutations of DNA mismatch repair genes. However, diagnosis of microsatellite instability becomes complicated when highly-damaged DNA from formalin-fixed paraffin-embedded tissue specimens has to be investigated. MATERIALS AND METHODS: A new methodical approach was established based on special multiplex PCR regimes (e.g., on touch-up cycling conditions), allowing both sufficient, as well as specific, amplification of the Bethesda reference panel loci with low quality DNA as template. RESULTS: By applying our new method, microsatellite instability could be analyzed successfully in 75 out of 84 investigated tumors (89%), whereas, by using standard PCR protocols, microsatellite analysis failed in 36% of the investigated cases. CONCLUSION: Our new methodical approach should be recommended for the use of archival material since it allows an efficient and accurate amplification of the Bethesda marker fragments and is less dependent on the DNA quality.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Large-scale mitochondrial DNA deletion mutations and nuclear genome instability in human breast cancer.

Deletion mutations in mitochondrial (mt) DNA (mtDNA) as well as microsatellite instability (MSI) and loss of heterozygosity (LOH) in nuclear DNA (nDNA) exist in human cancer. We determined if: (1) large-scale mtDNA deletion mutations were present in cancerous and not in normal breast tissue, and (2) combining mt- and nDNA findings would provide complementary information to identify breast cancer. Thirty-nine matched breast cancer/histologically normal and 23 "true" normal tissue samples from women without breast cancer were microdissected and DNA extracted. 4977, approximately 3938, approximately 4388 and approximately 4576bp deletions were observed, with the 4576bp deletion being present in 0% of true normal, 13% of histologically normal specimens from a cancerous breast and 77% of breast cancers. The other three deletions were not specific to a breast containing cancer. LOH was found in 66.7% and MSI in 38.5% of samples. 38/39 (97.4%) tumors had at least one nDNA or 4576bp mtDNA alteration, suggesting that mt- and nDNA analysis provides complementary information in breast cancer detection. The 4576bp deletion appears to indicate cancer in the breast. The higher mtDNA copy number in cancer coupled with a mtDNA deletion mutation which appears specific for breasts which contain cancer may prove to be a good target to screen for cancer in the breast, including specimens of low and/or mixed cellularity.

Alleles↗

PubMed1998

Microsatellite instability is rare in the clinical course of myelodysplastic syndrome studied with DNA from fresh and paraffin-embedded tissues.

Microsatellite instability (MSI) has been reported to occur in various types of malignant neoplasms. We performed a polymerase-chain-reaction-based assay for MSI between the initial and the most recently available ("latest") samples from 23 patients with myelodysplastic syndrome (MDS). Of these patients, 15 were informative at more than three microsatellite loci. Seven patients showed an increase in leukemic cells while 8 patients did not during the interval between the two analyses. Only 1 of the patients, who had refractory anemia with excess blasts, which changed to acute myelogenous leukemia, showed microsatellite alteration at the analysis times. Among all 23 patients, two alterations were detected in the 42 informative paired samples that showed an increase in leukemic cells (4.8%), while none was detected in the 59 paired samples without such an increase. In total, therefore only two alterations were detected among 101 informative paired samples (2%). This indicates that MSI is rare in the clinical course of MDS irrespective of disease status, and is consequently not a critical genetic event for disease progression in most MDS patients.

Adult↗

PubMed2006

[Microsatellite instability among patients with colorectal cancer].

BACKGROUND: In patients with colorectal carcinoma, insertions or deletions of short sequences of DNA, a phenomenon called microsatellite instability, are observed. AIM: To look for microsatellite instability and mutations of MLH1 and MSH2 gene mutations in patients with colorectal carcinoma. MATERIAL AND METHODS: Ten patients with sporadic colorectal carcinoma and 31 patients fulfilling criteria for hereditary nonpolyposis colon cancer (HNPCC), aged 9 to 70 years, were studied. Microsatellite instability was studied in samples of tumor and peripheral blood mononuclear cell DNA. Six markers were amplified by polymerase chain reaction and capillary electrophoresis. In samples with microsatellite instability, mutations of MLH1 and MSH2 genes were studied by direct sequencing. RESULTS: Thirty four percent of patients had microsatellite instability and among these, 76% had a high degree of instability. BAT40 marker had the higher frequency of instability. No mutations for MLH1 and MSH2 genes were observed. However a new polymorphism, C399T, was identified in exon 3 of MSH2 gene. This polymorphism was observed both in patients with sporadic colorectal carcinoma and patients with HNPCC. CONCLUSIONS: There is a high frequency of microsatellite instability among patients with colorectal cancer. A new polymorphism, not previously reported, was identified in MSH2 gene.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Not hMSH2 but hMLH1 is frequently silenced by hypermethylation in endometrial cancer but rarely silenced in pancreatic cancer with microsatellite instability.

Disruption of the DNA mismatch repair (MMR) system has been found to play an important role in sporadic human cancers of several organs such as colorectum, stomach, endometrium, and pancreas. In cancers of the former three organs, disruption of the MMR system is mainly caused by hypermethylation of the hMLH1 gene. We investigated the expression of the hMLH1 and hMSH2 proteins immunohistochemically in pancreatic and endometrial cancers with high frequency microsatellite instability (MSI-H). Loss of expression of hMLH1 was found in none of seven pancreatic cancer, whereas eight (57%) of 14 endometrial cancer showed loss of expression of hMLH1. On the other hand, one (14%) of seven pancreatic cancers and two (14%) of 14 endometrial cancers showed loss of hMSH2 expression. We further analyzed the methylation status at the promoter region of the hMLH1 and hMSH2 genes and found hypermethylation of hMLH1 at the promoter region in the great majority of endometrial cancers with loss of expression. However, no pancreatic cancer showed hypermethylation. We then further analyzed 22 pancreatic cancer cell lines and obtained similar results. These results suggested that MSI-H in pancreatic cancer is probably caused by different mechanisms from those of other sporadic cancers with MSI-H.

Adaptor Proteins, Signal Transducing↗

PubMed1995

Instability of microsatellites in human gliomas.

We have analyzed DNA obtained from 10 glioblastomas multiforme and 6 astrocytomas for microsatellite instability, using 17 different microsatellite loci dispersed over 7 different chromosomes. Six of 16 gliomas showed 1 or more microsatellite alterations in tumor DNA as compared to constitutional DNA. We observed microsatellite instability resulting in allelic shifts in 5 of 10 glioblastomas multiforme but not in any of the astrocytomas. Loss of an allele was observed in 3 glioblastomas multiforme. An imbalance in the intensity of alleles was noticed in 1 astrocytoma and in 1 glioblastoma multiforme. In 1 glioblastoma multiforme, an extra allele was present at two distinct loci. Overall, 5.3% of microsatellite analyses showed an abnormality. We conclude that microsatellite instability is present at a low grade in glioblastomas multiforme but to a lesser extent in astrocytomas. Genomic instability in human gliomas, therefore, should not be regarded as a mechanism for tumor initiation but as an evolution in tumor progression.

Alleles↗

PubMed1996

An integrated microsatellite length analysis using an automated fluorescent DNA sequencer.

Analyzing microsatellite instability (MI) in malignant tumors is thought to be useful for screening cancer patients to identify those patients with a higher risk of developing second malignant tumors. In this paper, we report a new, accurate, and efficient method of detecting MI using an automated fluorescent DNA sequencer and a computer that automatically calculates the size, height, and area of each fluorescent product, making it possible to assess MI more accurately and more rapidly. The primers for amplification of each microsatellite locus are labeled by two different fluorescent dyes, rox (red) and fam (blue). The rox-labeled primer was used for the tumor, whereas the fam-labeled primer was used for the corresponding normal tissue. Two amplified products from both the tumor and the normal tissue were co-loaded into a single lane of the sequencing gel and were analyzed. MI could be detected based on the presence of different waving patterns. Furthermore, several loci could also be analyzed simultaneously for MI in a single lane. Using this method, we examined the frequency of MI in gastric cancer. The results showed that 5 of 22 (22.7 %) gastric cancers were MI-positive, which corresponds to the findings of previous reports that used the radioisotopic method. The improved method may open up the possibility of performing routine examination of MI in many cancer patients and offers hope for the potential clinical application of Ml analysis as a follow-up evaluation of cancer patients.

Chromosome Aberrations↗

PubMed2004

Microsatellite instability in gastric MALT lymphoma.

The role of microsatellite instability and defects in DNA mismatch repair mechanism in the pathogenesis of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) type is still controversial, as both negative and positive findings have been reported. This may be explained mainly by arbitrary selection of the tested loci, the use of various techniques of microsatellite instability analysis and by different definitions of replication error positive phenotype. The aim of our study was to evaluate the instability at selected microsatellite markers using the GeneScan Analysis Software. DNA from paraffin-embedded tissue blocks of 13 previously untreated patients with localized gastric MALT lymphoma was extracted. Five microsatellite markers, which are located in hMSH2, hMLH1, P16, APC and MLL loci, were selected from the genetic database. We found genetic instability in tumors of 9/13 patients with gastric MALT lymphoma (69%). Seven of them had replication-error-positive phenotype (54%). Microsatellite instability was found in 39% of the samples in the MLL locus, 39% in the APC, 46% in the P16, 23% in the hMLH1 and none in the hMSH2. This study demonstrates that microsatellite instability has more prominent role in pathogenesis of gastric MALT lymphoma than reported to date. We suggest that microsatellite instability should be analyzed with markers adjacent to chromosomal loci that are involved in lymphomas. Our findings support the 'Real Common Target genes' theory of high rate of microsatellite instability in specific genes, which are associated with related tumors.

Adult↗

PubMed1996

Clinical and pathological significance of microsatellite instability in sporadic endometrial carcinoma.

Defective DNA mismatch repair in neoplasia is manifested by extra, aberrant bands within multiple microsatellite markers. The replication error (RER) phenotype is present in most colorectal and endometrial carcinomas in patients with the hereditary nonpolyposis colorectal carcinoma syndrome. In addition, a minority of sporadic colorectal and endometrial carcinomas are RER positive. RER in sporadic colorectal carcinomas has been associated with improved prognosis, but its clinical significance in sporadic endometrial cancer has not been characterized. We analyzed DNA extracted from 109 formalin-fixed sporadic endometrial carcinomas for microsatellite instability. The RER-positive phenotype was demonstrated by microsatellite instability in more than one of the eight dinucleotide markers tested. RER was correlated with pathological and clinical parameters as well as with immunohistochemical staining for the p53 gene product and alterations in codon 12 of Ki-ras. Nine percent of the endometrial carcinomas were RER positive, and RER was significantly associated with high grade and adverse outcome. We found no significant correlation of RER with histological subtype, stage, depth of invasion, mutations in the 12th codon of Ki-ras, or p53 immunoreactivity. We conclude that the RER phenotype is present in a minority of sporadic endometrial carcinomas and is associated with high grade and poor prognosis.

Adult↗

PubMed2006

Novel hMSH2, hMSH6 and hMLH1 gene mutations and microsatellite instability in sporadic colorectal cancer.

PURPOSE: To detect the hMSH2, hMSH6 and hMLH1 DNA mismatch repair gene mutations and microsatellite instability in somatic colorectal cancer. PATIENTS AND METHODS: The mutations of hMSH2, hMSH6, and hMLH1 genes, including microsatellite instability of BAT-26, BAT-40, D2S123, D5S346 and D17S250 were analyzed in 31 patients with colorectal. RESULTS: The results revealed that eight cases (25.8%) harbored mutations in DNA mismatch repair genes. Of these, five novel mutations including I237V in exon 4 of hMSH2, ins T at codon 1196 in exon 7 of hMSH6, and ins G at codon 154 in exon 6, N158H in exon 6, and del A at codon 257 in exon 9 of hMLH1 were identified. Moreover, several intronic polymorphisms, including c-g transversion at IVS-1 nt211 + 9 of hMSH2, del T in poly T track at IVS-6 nt3559-5, ATCT duplicate in IVS-7 nt 3642 + 35 and t-g transversion at IVS-10 nt4080 + 185 of hMSH6 were demonstrated in these patients. In addition, seven cases (22.5%) exhibited microsatellite instability (MSI). CONCLUSION: These results suggested that the inactivation of DNA mismatch repair genes and microsatellite instability may play a minor role in somatic colorectal cancer development.

Adaptor Proteins, Signal Transducing↗

PubMed2006

BRAF mutations are associated with distinctive clinical, pathological and molecular features of colorectal cancer independently of microsatellite instability status.

BACKGROUND: BRAF is a member of RAF family of serine/threonine kinases and mediates cellular responses to growth signals through the RAS-RAF-MAP kinase pathway. Activating mutations in BRAF have recently been found in about 10% of colorectal cancers, with the vast majority being a V600E hotspot mutation. The aim of the present study was to evaluate the clinical, pathological and molecular phenotype of colorectal tumors with BRAF mutations. RESULTS: Mutations in BRAF were identified in 8% (23/275) of colorectal cancers. They were 5-10-fold more frequent in tumors with infiltrating lymphocytes, location in the proximal colon, poor histological grade and mucinous appearance (P < 0.002 for each). Tumors with BRAF mutation were also 10-fold more likely to show microsatellite instability and frequent DNA methylation (P < 0.0001) compared to tumors without this mutation. The characteristic morphological features of tumors with BRAF mutation (infiltrating lymphocytes, poor grade, mucinous) remained after stratification according to microsatellite instability and methylator phenotypes. Mutations in BRAF were mutually exclusive with mutations in KRAS but showed no clear association with the presence of TP53 mutation. CONCLUSION: BRAF mutation identifies a colorectal cancer subgroup with distinctive phenotypic properties independent of microsatellite instability status and thus could be a valuable marker for studies into the clinical properties of these tumors.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Microsatellite instability and hMLH1 and hMSH2 expression analysis in soft tissue sarcomas.

Alterations of the size of microsatellite DNA sequences, namely microsatellite instability (MSI), have been demonstrated in some types of malignancies. We analyzed the MSI of five microsatellite markers in 40 cases of soft tissue sarcoma (STS) using high resolution fluorescent microsatellite analysis. In addition, we examined the expression of hMLH1 and hMSH2 proteins of DNA mismatch repair (MMR) genes by immunohistochemistry, and promoter methylation of the hMLH1 gene by methylation-specific PCR (MSP). MSI was recognized in 10 of 40 STS cases (25%), which consisted of 2 MSH-high (MSI-H) tumors and 8 MSI-low (MSI-L) tumors. A loss of hMLH1 expression was recognized in 7 of 40 STS cases (18%), and loss of hMSH2 expression was recognized in 3 of 40 STS cases (8%). One case showed a loss of both hMLH1 and hMSH2 expression. Promoter hypermethylation of the hMLH1 gene was detected in only 3 of 40 STS cases (8%). Of 10 cases with MSI, 5 (50%) showed a loss of hMLH1 and/or hMSH2 expression. There was a statistically significant correlation between MSI-positive tumors and the loss of hMLH1 and/or hMSH2 expression (p=0.0286). Although the frequency of MSI (25%) or a loss of hMLH1 and/or hMSH2 expression (23%) was relatively low in STS cases, a loss of hMLH1 and/or hMSH2 was recognized in 5 out of 10 MSI-positive cases (50%). These findings suggest that the inactivation of MMR gene expression might be the cause of MSI in STS cases.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Frequent copresence of methylated DNA and fragmented nucleosomal DNA in plasma of lymphoma patients.

BACKGROUND: The circulating DNA in plasma/serum of cancer patients has been shown to reflect the characteristics of the tumor DNA including molecular changes, such as methylation, point mutations and microsatellite instability. Fragmented nucleosomal DNA in plasma resulting from apoptotic death of the tumor cells may also provide an indication for tumor DNA. In this study, we comparatively analysed plasma DNA methylation and presence of fragmented nucleosomal DNA in patients with lymphoproliferative diseases. METHODS: Methylation in the first exon of the tumor supressor gene p16 was investigated by the methylation-sensitive restriction enzyme-related PCR. DNA fragmentation in plasma was analysed by gel electrophoresis. RESULTS: p16 gene methylation was found to occur in 73% of patients but in none of the 20 healthy controls. Nucleosomal DNA fragmentation was detectable in 81% of patients. In 67% of patients, copresence of both parameters was observed. Presence of both parameters was associated with the stage of disease which was more pronounced for nucleosomal DNA fragmentation. CONCLUSIONS: Our results suggest that presence of methylated and apoptotic DNA in plasma of patients with lymphoproliferative diseases is a frequent event and may be used as a marker for early diagnosis and during the follow-up of the disease.

Cyclin-Dependent Kinase Inhibitor p16↗