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Increased cytosine DNA-methyltransferase activity during colon cancer progression
1Oncology Center, Johns Hopkins University Medical Institutions, Baltimore, Md.
Background:
Molecular changes during progressive stages of colon cancer and other human tumors commonly involve altered regulation of DNA methylation. These changes include overall genomic hypomethylation, regional hypermethylation, and increased levels of messenger RNA (mRNA) for cytosine DNA-methyltransferase (DNA-MTase), the enzyme that catalyzes DNA methylation at CpG (cytosine-phospho-guanine) sites. This increase in DNA-MTase transcripts (mRNA), if accompanied by increased DNA-MTase activity, could play a role in the abnormal DNA methylation patterns that appear early in colon tumor progression.
Purpose:
We sought to determine whether increased DNA-MTase mRNA levels during colon cancer progression are associated with increased cellular DNA-MTase enzymatic activity.
Methods:
We adapted a microassay for DNA-MTase and used it to measure activity in human colon carcinoma and in colon mucosa of normal control subjects and of patients with colon cancer or with familial adenomatous polyposis (FAP), which is a risk factor for colon cancer. Steady-state DNA-MTase gene transcripts were measured by a reverse transcriptase polymerase chain reaction assay. To compare DNA-MTase activity with mRNA levels, we determined both variables simultaneously for one colon cancer specimen, its adjacent mucosa, and the colon mucosa of a control patient and compared the values.
Results:
Compared with DNA-MTase activity in mucosa from normal control subjects, activity was elevated 1.4-fold in FAP mucosa, 1.6-fold in the uninvolved mucosa of patients with cancer, and 5.4-fold in the cancer specimens. All these differences were statistically significant. Fourteen of 15 cancer samples and 47% of the uninvolved adjacent mucosa samples had values that were higher than the highest value in normal mucosa. In one patient who had both a benign adenomatous polyp and a malignant adenocarcinoma, increasing DNA-MTase activity was observed at each stage of tumor progression.
Conclusion:
These results demonstrate that an increased DNA methylation capacity accompanies the increase in DNA-MTase transcripts observed during progressive stages of colon cancer.
Implication:
Further studies are needed to determine whether this abnormal methylation capacity plays a role in establishing the abnormal DNA methylation patterns seen in human malignancies.
Insights
Increased DNA methyltransferase (DNA-MTase) activity correlates with elevated DNA-MTase mRNA levels in colon cancer progression. This suggests a potential role for abnormal DNA methylation capacity in the development of colon malignancies.
Area of Science:
- Oncology
- Molecular Biology
- Epigenetics
Background:
- Altered DNA methylation is a hallmark of colon cancer progression.
- Increased DNA methyltransferase (DNA-MTase) mRNA is observed in tumors.
- This study investigates the link between DNA-MTase mRNA and enzymatic activity.
Purpose of the Study:
- To determine if elevated DNA-MTase mRNA levels in colon cancer correlate with increased DNA-MTase enzymatic activity.
- To assess DNA-MTase activity across different stages of colon cancer and in precursor lesions.
Main Methods:
- Adapted microassay to measure DNA-MTase enzymatic activity in human colon tissues.
- Utilized reverse transcriptase polymerase chain reaction (RT-PCR) to quantify DNA-MTase mRNA transcripts.
- Simultaneously measured DNA-MTase activity and mRNA levels in select specimens.
Main Results:
- DNA-MTase activity was significantly elevated in familial adenomatous polyposis (FAP) mucosa (1.4-fold), adjacent tumor mucosa (1.6-fold), and colon cancer specimens (5.4-fold) compared to normal controls.
- A majority of cancer samples (14/15) and nearly half of adjacent mucosa samples (47%) showed higher DNA-MTase activity than the normal control maximum.
- Increasing DNA-MTase activity was observed with advancing stages of colon tumor progression, from benign polyps to adenocarcinoma.
Conclusions:
- Elevated DNA-MTase mRNA levels during colon cancer progression are associated with increased cellular DNA methylation capacity.
- This abnormal methylation capacity may contribute to the aberrant DNA methylation patterns observed in human malignancies.
- Further research is warranted to elucidate the precise role of this methylation capacity in cancer development.