Related Experiment Videos
Extent of DNA methylation in human tumor cells
Abstract:
The total genomic DNA methylation, i.e., the percentage of methylated cytosines, was measured in 20 cell lines derived from different types of human tumors. The measurements were obtained by cation-exchange liquid chromatography of bases released by formic acid hydrolysis. These experiments were done to determine if altered methylation is a prevalent and large defect in oncogenic transformation. A majority of the tumor cells measured had decreased levels of methylated DNA in comparison to our laboratory's and other laboratories' published measurements of normal cells and tissues. In fact, tumor cell DNA ranged as low as 1.2% of cytosines methylated compared to a value of 3% or more for normal cells and tissues. HpaII and MspI DNA restriction enzyme analysis confirmed for all tumor cell lines tested that their DNA was hypomethylated in comparison to the DNA from normal diploid fibroblasts tested. The results obtained by liquid chromatography and restriction enzyme analysis were strikingly similar. The reduced methylation of the tumor and DNA correlated with the recent observation of other laboratories that individual genes are undermethylated in human cancer cells and that a number of different carcinogens can lower DNA methylation directly.
Insights
Human tumor cells exhibit significantly reduced DNA methylation compared to normal cells. This widespread hypomethylation, observed across various cancer types, suggests a key defect in oncogenic transformation.
Area of Science:
- Oncology
- Epigenetics
- Molecular Biology
Background:
- Altered DNA methylation is implicated in cancer development.
- Previous studies suggest gene-specific hypomethylation in human cancers.
Purpose of the Study:
- To investigate the prevalence and extent of global genomic DNA hypomethylation in human tumor cell lines.
- To determine if reduced DNA methylation is a common feature of oncogenic transformation.
Main Methods:
- Genomic DNA was extracted from 20 human tumor cell lines.
- Total DNA methylation was quantified using cation-exchange liquid chromatography.
- DNA hypomethylation was confirmed using HpaII and MspI restriction enzyme analysis.
Main Results:
- A majority of tumor cell lines displayed decreased global DNA methylation compared to normal cells and tissues.
- Tumor cell DNA methylation levels ranged as low as 1.2%, compared to 3% or more in normal cells.
- Both liquid chromatography and restriction enzyme analyses consistently showed DNA hypomethylation in tumor cells.
Conclusions:
- Widespread genomic DNA hypomethylation is a prevalent defect in human tumor cells.
- Reduced DNA methylation in cancer cells aligns with findings of undermethylated genes and carcinogen-induced hypomethylation.
- These findings support a significant role for altered DNA methylation in oncogenic transformation.