Loss of Expression of DNA Mismatch Repair Proteins in Aberrant Crypt Foci Identified In Vivo by Magnifying Colonoscopy in Subjects with Hereditary Nonpolyposic and Sporadic Colon Rectal Cancer (original) (raw)
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Cancer Research, 2001
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 ACFadenoma-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.
British Journal of Surgery, 2007
Background: Hereditary non-polyposis colorectal cancer (HNPCC) arises mostly from germline mutations of the mismatch repair genes MSH2 and MLH1. The diagnosis of HNPCC is based on a set of clinical criteria that may be too restrictive to identify all affected patients. Immunohistochemical staining (IHC) for the mismatch repair proteins, MutS homologue 2 (MSH2) and MutL homologue 1 (MLH1), reliably identifies the microsatellite instability phenotype. This study evaluated the ability of IHC to detect germline mutations in an unselected group of patients with colorectal cancer (CRC). Methods: All patients with CRC operated on between July 2000 and March 2003, and demonstrating a loss of protein, were contacted. Following informed consent, searchs for germline mutation and methylation of the promoter were performed on normal and tumoral DNA. Results: Thirty patients agreed to participate, four of whom fulfilled the Amsterdam II criteria. Loss of expression of MLH1 was found in 20 patients, and loss of expression of MSH2 in ten patients. Four of the MLH1-deficient patients had a germline MLH1 point mutation (positive predictive value (PPV) 20 (95 per cent confidence interval (c.i.) 2 to 38 per cent) and 11 had promoter methylation. Seven of the MSH2-deficient patients had a germline MSH2 point mutation (PPV 70 (95 per cent c.i. 54 to 96 per cent), and none showed promoter methylation. Conclusion: MLH1-deficient patients who are young or have a positive family history of cancer should be referred for genetic testing and counselling, whereas MSH2-deficient patients should be counselled in the same way as patients with HNPCC.
Mutations in the DNA mismatch repair gene MLH1 associated with early-onset colon cancer
Journal of Pediatrics, 2006
Hereditary nonpolyposis colon cancer (HNPCC) is an autosomal dominant disorder characterized by the predisposition to develop a number of cancers, especially colorectal cancer (CRC). We present a HNPCC family with CRC at age 12 years. Our observations suggest that the germline mutation of the both copies of the MLH1 gene may play a role in the early onset of CRC.
Acta medica Indonesiana
Fresh tissues were obtained from colorectal tumor patients. The APC-PEN, MMR (MLH1, MSH2, PMS2, MSH6)-PEN, were assessed by immunohistochemistry, and MSI by PCR using 5 microsatellite markers (BAT25, BAT26, D2S123, D5S346, D17S250), as independent variables. The tumour locations as dependent variables were divided into proximal colon (caecum, ascending colon, transverse colon); distal colon (splenic flexure, descending colon, sigmoid) and rectum. The comparative study were done by bivariate and multivariate analysis. Results: there were 77 cases of colorectal adenocarsinoma. MMR-PEN was found in 54 of 77 (70.1%). MLH1-PEN was different between distal colon and rectal cancer (p=0.008); MSH6-PEN was different between proximal colon and rectal cancer (p= 0.020). Multivariate analysis showed: MLH1-PEN was related to cancer location (p=0.006) with OR 0.12 (95% CI 0.026-0.547). It had 0.12 times probability to be found in distal than rectum. MLH1-PEN had 10 times higher probability to be found in proximal than in distal (p=0.037). MSH6-PEN was related to the location (p=0.026) with OR 0.165 (95% CI 0.034-0.803), and had 0.165 times probability to be found in proximal than rectum; and 11 times higher probability in distal than proximal colon (p=0.043). APC-PEN was related to the location (p=0.020), with OR 6.897 (95% CI 1.359-34.995), and 6.89 times higher probability in distal than in rectum, with other variables controlled. MSI-H was found in 29 of 77 (37.7%) and MSI-L/MSS in 48 (62.3%). The proportion of MSI-H displayed a tendency to occur in proximal rather than in distal colon or rectal cancer. Conclusion: the underlying carcinogenic pathway or molecular background differs according to the cancer locations of CRC patients in this region. MLH1-PEN was prominent in proximal colon cancer, MSH6-PEN in distal colon and rectal cancer, and APC-PEN in distal colon respectively.
Genes, Chromosomes and Cancer, 2005
A systematic search by Southern blot analysis in a cohort of 439 hereditary nonpolyposis colorectal cancer (HNPCC) families for genomic rearrangements in the main mismatch repair (MMR) genes, namely, MSH2, MLH1, MSH6, and PMS2, identified 48 genomic rearrangements causative of this inherited predisposition to colorectal cancer in 68 unrelated kindreds. Twenty-nine of the 48 rearrangements were found in MSH2, 13 in MLH1, 2 in MSH6, and 4 in PMS2. The vast majority were deletions, although one previously described large inversion, an intronic insertion, and a more complex rearrangement also were found. Twenty-four deletion breakpoints have been identified and sequenced in order to determine the underlying recombination mechanisms. Most fall within repetitive sequences, mainly Alu repeats, in agreement with the differential distribution of deletions between the MSH2 and MLH1 genes: the higher number and density of Alu repeats in MSH2 corresponded with a higher incidence of genomic rearrangement at this disease locus when compared with other MMR genes. Long interspersed nuclear element (LINE) repeats, relatively abundant in, for example, MLH1, did not seem to contribute to the genesis of the deletions, presumably because of their older evolutionary age and divergence among individual repeat units when compared with short interspersed nuclear element (SINE) repeats, including Alu repeats. Moreover, Southern blot analysis of the introns and the genomic regions flanking the MMR genes allowed us to detect 6 novel genomic rearrangements that left the coding region of the disease-causing gene intact. These rearrangements comprised 4 deletions upstream of the coding region of MSH2 (3 cases) and MSH6 (1 case), a 2-kb insertion in intron 7 of PMS2, and a small (459-bp) deletion in intron 13 of MLH1. The characterization of these genomic rearrangements underlines the importance of genomic deletions in the etiology of HNPCC and will facilitate the development of PCR-based tests for their detection in diagnostic laboratories. V V C 2005 Wiley-Liss, Inc. y J.B. and G.M. represent the CAPP consortium, several of whose members submitted samples for mutation detection as part of the search for carriers of HNPCC eligible to take part in a long-term chemoprevention study [www.capp2.com\].
The Journal of Molecular Diagnostics, 2005
heterogeneous because of underlying mutations in mismatch repair genes , primarily MLH1 , MSH2 , and MSH6. One challenge to correctly diagnosing HNPCC is that the large size of the causative genes makes identification of mutations both labor intensive and expensive. We evaluated the usefulness of denaturing high performance liquid chromatography (DHPLC) for scanning mismatch repair genes (MLH1 , MSH2, and MSH6) for point mutations , small deletions, and insertions. Our assay consisted of 51 sets of primers designed to amplify all exons of these genes. All polymerase chain reaction reactions were amplified simultaneously using the same reaction conditions in a 96-well format. The amplified products were analyzed by DHPLC across a range of optimum temperatures for partial fragment denaturation based on the melting profile of each specific fragment. DNA specimens from 23 previously studied HNPCC patients were analyzed by DHPLC , and all mutations were correctly identified and confirmed by sequence analysis. Here, we present our validation studies of the DHPLC platform for HNPCC mutation analysis and compare its merits with other scanning technologies. This approach provides greater sensitivity and more directed molecular analysis for clinical testing in HNPCC. (J
Microsatellite instability in aberrant crypt foci from patients without concurrent colon cancer
Carcinogenesis, 2006
Aberrant crypt foci (ACF) are microscopic surface abnormalities that are putative precursors to colorectal cancer (CRC). ACF exhibit similar histological and molecular abnormalities to adenomas and CRC and potentially represent useful biomarkers of cancer risk. Microsatellite instability (MSI) is one molecular abnormality identified in concurrent ACF from CRC patients that may indicate a risk for progression. To determine if MSI can be detected in ACF from cancer-free subjects, we examined 45 ACF from 20 subjects undergoing colonoscopies. The group included 12 patients at elevated risk for CRC based on family history of CRC or personal history of CRC or advanced adenoma and 8 patients with no known risk factors. ACF were identified using close-focus magnifying chromendoscopy and collected by biopsy in situ. Genomic DNA was prepared from ACF and adjacent normal colonic epithelium isolated by laser capture microdissection and analyzed for MSI. MSI was identified in at least one marker from 9 of 30 (30%) lesions from patients at elevated risk for CRC and in 2 of 15 (13%) lesions from average risk patients. Using methylation-specific PCR analysis, we also examined the ACF for promoter hypermethylation of the DNA repair genes hMLH1 and MGMT and found moderate changes (8/39 and 3/32, respectively). Although we found only a limited relationship between hMLH1 hypermethylation and MSI, all the lesions with MGMT hypermethylation displayed an MSI-low phenotype. These lesions may be precursors to MSI-low CRC, providing a potential early biomarker to assess the effects of cancer prevention strategies.