Expression of human histo-blood group ABO genes is dependent upon DNA methylation of the promoter region

We have investigated the regulatory role of DNA methylation in the expressi on of the human histo-blood group ABO genes. The ABO gene promoter region c ontains a CpG island whose methylation status correlates well with gene exp ression in the cell lines tested. The CPG island was found hypomethylated i n some cell lines that expressed ABO genes, whereas the other cell lines th at did not express ABO genes were hypermethylated. Whereas constitutive tra nscriptional activity of the ABO gene promoter was demonstrated in both exp ressor and nonexpressor cell lines by transient transfection of reporter co nstructs containing the ABO gene promoter sequence, HhaI methylase-catalyze d in vitro methylation of the promoter region prior to DNA transfection sup pressed the promoter activity when introduced into the expressor gastric ca ncer cell line KATOIII cells. On the other hand, in the nonexpressor gastri c cancer cell line MKN28 cells, treatment with DNA methyltransferase inhibi tor 5-aza-2'-deoxycytidine resulted in demethylation of the ABO:gene promot er and appearance of A-transferase messages, as well as A-antigens synthesi zed by A-transferase. Taken together, these studies suggest that DNA methyl ation of the ABO gene promoter may play an important role in the regulation of ABO gene expression.