Silencing of the CD44 Gene by CpG Methylation in a Human Gastric Carcinoma Cell Line

We analyzed 8 human gastric carcinoma cell lines for the expression of CD44 by northern blot analysis and reverse transcription‐polymerase chain reaction (RT‐PCR), and identified 1 cell line MKN‐28 that did not express CD44. In an attempt to clarify the mechanism responsible for the inactivation of CD44 gene expression in this cell line, we investigated the methylation status around the promoter region of CD44 gene by digestion of the DNA with the methylation‐sensitive restriction enzyme Hpa II. The promoter region of CD44 in MKN‐28 revealed hypermethylation, whereas other CD44‐positive cell lines did not. Furthermore, treatment of MKN‐28 with the demethylating agent 5‐azacytidine restored the expression of the gene. These results suggest that CD44 expression is controlled by a DNA hypermethylation mechanism in MKN‐28.