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Hypermethylation of the Putative Tumor-suppressor Genes DCC, p51/63 and O⁶-methylguanine-DNA Methyltransferase (MGMT) and Loss of Their Expressions in Cell Lines of Hematological Malignancies

Kazutaka Nakayama, Koiti Inokuchi and Kazuo Dan

Division of Hematology, Department of Internal Medicine, Nippon Medical School

Alterations and defective expression of three putative tumor-suppressor genes, the deleted in colorectal cancer (DCC), p51, and O⁶-methylguanine-DNA methyltransferase (MGMT), have been demonstrated in many cancers. However, it is not known whether the defective expression of each of these genes is independent or whether it reflects a specific methylation abnormality. Here, we investigated the expression of the DCC, p51 and MGMT genes and the methylation status of the 5'flanking CpG region in 17 cell lines established from hematological malignancies. The reverse transcriptase-polymerase chain reaction method showed DCC expression to be absent in 13 of the 17 cell lines and showed expression of both p51 and MGMT to be absent in 5 of the 17 cell lines. The methylation patterns were analyzed with methylation-specific polymerase chain reaction (MSP) of the 5'flanking region of the DCC and p51 genes and the promoter region of the MGMT gene. Although unmethylated patterns of the CpG region in the DCC, p51, and MGMT genes were observed in all 11 normal controls, abnormal methylation patterns of these genes were found even in many cell lines expressing these genes. A hypermethylation pattern was detected for the CpG region of MGMT and p51 in cells that did not express these genes. In contrast, a hypermethylation pattern was not always detected for the CpG region of DCC in cells with reduced DCC expression. The results of this study indicate that in many hematological cell lines, the DCC, p51, and MGMT genes have been abnormally methylated in the CpG region. Hypermethylation of these three genes may be independent events in each cell line.

J Nippon Med Sch 2005; 72: 270-277

Keywords
deleted in colorectal cancer, p51/p63, O⁶-methylguanine-DNA methyltransferase, methylation, loss of expression

Correspondence to
Koiti Inokuchi, Division of Hematology, Department of Internal Medicine, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan
inokuchi@nms.ac.jp

Received, June 1, 2005
Accepted, July 13, 2005