Variable MLH1 promoter methylation patterns in endometrial carcinomas of endometrioid subtype lacking DNA mismatch repair

Endometrial tumour BRAF mutations and MLH1 promoter methylation as predictors of germline mismatch repair gene mutation status: a literature review

Colorectal cancer (CRC) that displays high microsatellite instability (MSI-H) can be caused by either germline mutations in mismatch repair (MMR) genes, or non-inherited transcriptional silencing of the MLH1 promoter. A correlation between MLH1 promoter methylation, specifically the 'C' region, and BRAF V600E status has been reported in CRC studies. Germline MMR mutations also greatly increase risk of endometrial cancer (EC), but no systematic review has been undertaken to determine if these tumour markers may be useful predictors of MMR mutation status in EC patients. Endometrial cancer cohorts meeting review inclusion criteria encompassed 2675 tumours from 20 studies for BRAF V600E, and 447 tumours from 11 studies for MLH1 methylation testing. BRAF V600E mutations were reported in 4/2675 (0.1%) endometrial tumours of unknown MMR mutation status, and there were 7/823 (0.9%) total sequence variants in exon 11 and 27/1012 (2.7%) in exon 15. Promoter MLH1 methylation was not observed in tumours from 32 MLH1 mutation carriers, or for 13 MSH2 or MSH6 mutation carriers. MMR mutation-negative individuals with tumour MLH1 and PMS2 IHC loss displayed MLH1 methylation in 48/51 (94%) of tumours. We have also detailed specific examples that show the importance of MLH1 promoter region, assay design, and quantification of methylation. This review shows that BRAF mutations occurs so infrequently in endometrial tumours they can be discounted as a useful marker for predicting MMR-negative mutation status, and further studies of endometrial cohorts with known MMR mutation status are necessary to quantify the utility of tumour MLH1 promoter methylation as a marker of negative germline MMR mutation status in EC patients.

DNA mismatch repair deficiency in endometrial carcinoma

Microsatellite instability (MSI) is the hallmark of a molecular pathway to carcinogenesis due to sporadic or inherited abnormalities of DNA mismatch repair genes. Inherited mutations are seen in hereditary nonpolyposis colorectal cancer syndrome. Endometrial carcinoma shows as high an incidence of MSI as does colorectal carcinoma. This review provides a framework for the gynecologic pathologist to understand the complexities of MSI in endometrial carcinoma, by discussing the basic mechanisms of mismatch repair and carcinogenesis, testing, the morphologic features of MSI endometrial cancer and the contradictory data regarding prognosis.

Intra-tumor heterogeneity of MLH1 promoter methylation revealed by deep single molecule bisulfite sequencing

A single tumor may contain cells with different somatic mutations. By characterizing this genetic heterogeneity within tumors, advances have been made in the prognosis, treatment and understanding of tumorigenesis. In contrast, the extent of epigenetic intra-tumor heterogeneity and how it influences tumor biology is under-explored. We have characterized epigenetic heterogeneity within individual tumors using next-generation sequencing. We used deep single molecule bisulfite sequencing and sample-specific DNA barcodes to determine the spectrum of MLH1 promoter methylation across an average of 1000 molecules in each of 33 individual samples in parallel, including endometrial cancer, matched blood and normal endometrium. This first glimpse, deep into each tumor, revealed unexpectedly heterogeneous patterns of methylation at the MLH1 promoter within a subset of endometrial tumors. This high-resolution analysis allowed us to measure the clonality of methylation in individual tumors and gain insight into the accumulation of aberrant promoter methylation on both alleles during tumorigenesis.

Prognostic evaluation of epidermal fatty acid-binding protein and calcyphosine, two proteins implicated in endometrial cancer using a proteomic approach

With the aim to translate the discovery from proteomic research into clinical applications, we identified epidermal fatty acid-binding protein (E-FABP) and calcyphosine (CAPS) by MALDI-Q-TOF MS and validated their overexpressions by immunoblotting. Their expression statuses were examined by immunohistochemistry in 39 normal endometrium, 29 endometrial intraepithelial neoplasia (EIN) and 84 endometrial cancer (EC) cases. We evaluated the correlations to the clinicopathologic characteristics and determined whether these proteins had prognostic significance. Expressions of E-FABP and CAPS were increased 2.64- and 2.18-fold in EC by immunoblotting. Immunoreactivity of both E-FABP and CAPS were stronger in EC than in EIN or normal tissues (p < 0.001 and < 0.001). Stronger immunoreactivity of E-FABP and CAPS were shown to present with poor differentiation (p = 0.032 and 0.001), but no relevance was observed with staging (p = 1.368 and 4.306). Survival analysis indicated that immunoreactivity of CAPS was correlated to poor survival (p = 0.018), but E-FABP status appeared to be no correlation to the clinical outcome of patients (p = 0.865). Multivariate analysis indicated that CAPS might be an independent prognostic factor for survival in patients with EC (p = 0.008). Results demonstrated the ubiquitous overexpressions of E-FABP and CAPS in EC and the correlations to the clinicopathologic parameters. CAPS might be a potential prognostic factor for survival in patients with EC. The research pattern from proteomics to clinical specimens would have widespread applications.

Proteomics identification of cyclophilin a as a potential prognostic factor and therapeutic target in endometrial carcinoma

Endometrial carcinoma is one of the most common malignancies of the female genital tract, and there is an urgent need for discovery of novel factors for prognostic assessment and therapeutic targets to endometrial carcinoma. Herein a two-dimensional gel electrophoresis and MALDI-Q-TOF MS/MS-based proteomics approach was used to identify differentially expressed proteins in endometrial carcinoma. Of the 99 proteins identified, cyclophilin A was one of the most significantly altered proteins, and its overexpression was confirmed using RT-PCR and Western blot analyses. Immunohistochemistry suggested a link between cyclophilin A expression and poor differentiation and decreased survival (p < 0.01). Knockdown of cyclophilin A expression by RNA interference led to the significant suppression of the cell growth and the induction of apoptosis in endometrial carcinoma HEC-1-B cells in vitro (p < 0.01) and the inhibition of tumor growth in vivo (p < 0.01). These data suggest that cyclophilin A may serve as a novel prognostic factor and possibly an attractive therapeutic target for endometrial carcinoma.

Hypermethylation and aberrant expression of DNA mismatch repair gene in pancreatic cancer

AIM: To determine the methylation and expression status of mismatch repair genes hMLH1, hMSH2 and hMLH3 and explore the role of mismatch repair defect in pancreatic cancer.

METHODS: Methylation status of hMLH1, hMSH2 and hMLH3 was detected by methylation-specific polymerase chain reaction (MSP), and the expression of hMLH1, hMSH2 and hMLH3 were determined by reverse-transcription PCR (RT-PCR).

RESULTS: The frequencies of methylation for hMLH1, hMSH2 and hMSH3 were 28.6%, 46.4% and 39.3%, respectively in pancreatic cancer tissues, and 3.6%, 10.7% and 12.5% in cancer-adjacent normal tissues, and there were significant differences between cancer and normal tissues (hMLH1: χ² = 12.97, P < 0.01; hMSH2: χ² = 17.50, P < 0.01; hMLH3: χ² = 10.47, P < 0.01). The frequencies of expression loss for hMLH1, hMSH2 and hMSH3 were 25.0%, 50.0% and 33.9%, respectively in pancreatic cancer tissues, and 7.1%, 8.9% and 16.1% in cancer-adjacent normal tissues, and there were also marked differences between cancer and normal tissues (hMLH1: χ² = 6.62, P < 0.05; hMSH2: χ² = 22.73, P < 0.01; hMLH3: χ² = 4.76, P < 0.05). Methylations of hMLH1, hMSH2 and hMLH3 were found in PANC-1, PC-3 and CFPAC-1 cell lines, while expression loss of hMLH1 was observed in PANC-1 and CFPAC-1 cell lines, that of hMSH2 in PC-3 cell line and hMLH3 was observed in PC-3 and PANC-1 cell lines.

CONCLUSION: Mismatch repair defect is common in pancreatic cancer and plays a role in pancreatic carcinogenesis.

Distinction of Hereditary Nonpolyposis Colorectal Cancer and Sporadic Microsatellite-Unstable Colorectal Cancer through Quantification of MLH1 Methylation by Real-time PCR

Purpose: Promoter hypermethylation occurs frequently in tumors and leads to silencing of tumor-relevant genes like tumor suppressor genes. In a subset of sporadic colorectal cancers (CRC), inactivation of the mismatch repair gene MLH1 due to promoter methylation causes high level of microsatellite instability (MSI-H). MSI-H is also a hallmark of hereditary nonpolyposis colorectal cancer (HNPCC) in which mismatch repair inactivation results from germ-line mutations. For differentiation of sporadic and hereditary MSI-H tumor patients, MLH1 promoter methylation analysis is a promising tool but is not yet used in daily diagnostics because only qualitative techniques without standardization are available. The aim of this study is to establish a reliable and quantitative MLH1 methylation analysis technique and to define valid MLH1 methylation cutoff values for HNPCC diagnostics.

Experimental Design: We developed a new real-time PCR–based technique to detect and quantify methylation of both proximal and distal hMLH1 promoter regions. We established and validated this technique in a cohort of 108 CRCs [94 MSI-H and 16 microsatellite stable (MSS) cases] comprising a reference (n = 58) and a tester tumor group (n = 50).

Results: The reference tumor group contained 28 HNPCC with proven germ-line mutations or positive Amsterdam I criteria (median age, 37 years) and loss of MLH1 expression, 14 sporadic MSI-H CRC tumors with loss of MLH1 expression and BRAF V600E mutation (median age, 80.5 years), and 16 sporadic MSS CRC (median age, 76.5 years). No MLH1 promoter methylation could be found in any MSS tumors. HNPCC patients showed no or low level of MLH1 promoter methylation. A cutoff value of 18% methylation extent could be determined in this study to define MLH1 hypermethylation specific for sporadic MSI-H cases. Methylation could also be verified qualitatively by melting point analysis. BRAF V600E mutations were not detected in any HNPCC patients (n = 22 informative cases).

Conclusion: According to the present data, quantitative MLH1 methylation analysis in MSI-H CRC is a valuable molecular tool to distinguish between HNPCC and sporadic MSI-H CRC. The detection of a BRAF V600E mutation further supports the exclusion of HNPCC.

Relationship between Helicobacter pylori and DNA mismatch repair system

Helicobacter pylori infection causes the defect of mismatch repair (MMR) in eucaryotes, and microsatellite instability (MSI) in gastric epithelial cells, which increases the spontaneous mutation of relative genes, and finally results in the susceptibility to tumors in human bodies. DNA MMR can prevent the excessive proliferation of mutant cells and development of tumors by correcting mismatched bases, which occur in the process of duplication and recombination, and inducing apoptosis of the cells in which DNA had been seriously impaired. The majority of the mutation in mismatch repair gene is the gene mutation in which substitution exceeds the absence or insertion of the single basic group. In MMR, hMLH1 and hMSH2 gene are the main controlling genes. Current research showed that H pylori infection might lead to functional defect of MMR, which had played an important role in the development of gastric carcinomas. In this article, we reviewed the correlations between H pylori infection and DNA mismatch repair system.