Recent studies have shown that cytosine-5 methylation at CpG islands in the regulatory sequence of a gene is one of the key mechanisms of inactivation. The
enzymes responsible for CpG methylation are
DNA methyltransferase (DNMT) 1, DNMT3a, and DNMT3b, and the
enzyme responsible for demethylation is
DNA demethylase (MBD2). Studies on methylation-demethylation
enzymes are lacking in human
prostate cancer. We hypothesize that MBD2
enzyme activity is repressed and that
DNMT1 enzyme activity is elevated in human
prostate cancer. To test this hypothesis, we analyzed
enzyme activities,
mRNA, and
protein levels of MBD2 and DNMT1, DNMT3a, and DNMT3b in human
prostate cancer cell lines and tissues. The
enzyme activities of DNMTs and MBD2 were analyzed by biochemical assay. The
mRNA expression was analyzed by
reverse transcriptase-polymerase chain reaction and by Northern blotting. The
protein expression was measured by immunohistochemistry with specific
antibodies. The results of these experiments demonstrated that (1) the activity of DNMTs was twofold to threefold higher in
cancer cell lines and
cancer tissues, as compared with a benign prostate epithelium cell line (BPH-1) and
benign prostatic hyperplasia (BPH) tissues; (2) MBD2 activity was lacking in
prostate cancer cell lines but present in BPH-1 cells; (3) immunohistochemical analyses exhibited higher expression of DNMT1 in all
prostate cancer cell lines and
cancer tissues, as compared with BPH-1 cell lines and BPH tissues; (4)
MBD2 protein expression was significantly higher in BPH-1 cells and lacking in
prostate cancer cell lines and, in BPH tissues,
MBD2 protein expression was poorly observed, as compared with no expression in
prostate cancer tissues; and (5)
mRNA expression for DNMT1 was upregulated in
prostate cancer, as compared with BPH-1, and
mRNA expression for MBD2 was found to be significantly expressed in all cases. The results of these studies clearly demonstrate that DNMT1 activity is upregulated, whereas MBD2 is repressed at the level of translation in human
prostate cancer. These results may demonstrate molecular mechanisms of CpG hypermethylation of various genes in
prostate cancer.