Increased cytosine DNA-methyltransferase activity during colon cancer progression.
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.


OBJECTIVE
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.


CONCLUSIONS
These results demonstrate that an increased DNA methylation capacity accompanies the increase in DNA-MTase transcripts observed during progressive stages of colon cancer.


CONCLUSIONS
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.
Issa
J P
JP
Oncology Center, Johns Hopkins University Medical Institutions, Baltimore, Md.
Vertino
P M
PM
Wu
J
J
Sazawal
S
S
Celano
P
P
Nelkin
B D
BD
Hamilton
S R
SR
Baylin
S B
SB
D000230:Adenocarcinoma / Q000201:enzymology*; D003106:Colon / Q000201:enzymology; D003108:Colonic Diseases / Q000201:enzymology; D003110:Colonic Neoplasms / Q000201:enzymology*; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis
D012333:RNA, Messenger; D004248:DNA (Cytosine-5-)-Methyltransferases