Related Experiment Video
Updated: Jul 14, 2026
Genome-Wide Analysis of DNA Methylation in Gastrointestinal Cancer
Published on: September 18, 2020
Assessment of MLH1 promoter methylation in relation to gene expression requires specific analysis
E Capel1, J-F Fléjou, R Hamelin
1INSERM, U762, Paris, France.
Abstract:
About 15% of colorectal cancers are called MSI because they demonstrate microsatellite instability. In most sporadic MSI cases, the DNA mismatch repair (MMR) defect is due to methylation of the MLH1 promoter. In hereditary MSI cases, it is the consequence of germline mutations of one of the MMR genes. We analysed the MLH1 promoter for methylation using the methylation-specific PCR technique. With a previously described and widely used primer set, a number of samples with an intact MMR system were found to have methylated MLH1 promoter, a finding normally associated with lack of MLH1 expression. Another primer set, specific for a more proximal region of the promoter, gave results that correlated more closely with loss of MLH1 expression. We then conducted a survey of the literature on the subject, and a total of 161 articles were examined. Although it was shown as early as 1999 that absence of MLH1 expression correlated with methylation of the proximal but not distal regions of the MLH1 promoter, 60% of published studies analysed nonspecific regions. Our findings suggest that these studies are likely to have wrongly estimated the association between methylation of the MLH1 gene and the lack of its protein expression.
Insights
Microsatellite instability (MSI) in colorectal cancer is often linked to MLH1 promoter methylation. However, studies using non-specific primer sets may have inaccurately assessed this association.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Approximately 15% of colorectal cancers exhibit microsatellite instability (MSI).
- In sporadic MSI cases, DNA mismatch repair (MMR) defects are frequently caused by MLH1 promoter methylation.
- Hereditary MSI cases result from germline mutations in MMR genes.
Purpose of the Study:
- To investigate the accuracy of MLH1 promoter methylation analysis in relation to MLH1 expression.
- To evaluate the impact of primer set specificity on detecting MLH1 promoter methylation.
- To assess the reliability of previous studies on MLH1 methylation and expression correlation.
Main Methods:
- Methylation-specific PCR was employed to analyze MLH1 promoter methylation.
- Two primer sets were utilized: one widely used and another specific to a proximal promoter region.
- A literature review of 161 articles was conducted to examine methodologies used in prior research.
Main Results:
- A commonly used primer set yielded false positives for MLH1 promoter methylation in samples with intact MMR.
- A primer set specific for the proximal MLH1 promoter region showed better correlation with MLH1 expression loss.
- A significant portion (60%) of published studies used non-specific primer sets, potentially leading to inaccurate conclusions.
Conclusions:
- The choice of primer set is critical for accurate MLH1 promoter methylation analysis.
- Previous studies using non-specific primers may have overestimated the association between MLH1 methylation and expression loss.
- Accurate assessment of MLH1 methylation is crucial for understanding sporadic MSI colorectal cancers.
Related Concept Videos
01:46Epigenetic Regulation
01:37Epigenetic Regulation
X-chromosome...