Absence or low expression of DLC-1, a tumor suppressor gene, in breast cancers has been shown recently. LOH of 8p12-p22, on which DLC-1 is located, is frequent in breast cancers, but the correlation between low expression of DLC-1 and LOH has not been confirmed. To determine the implication of aberrant methylation, one of the most frequent mechanisms of silencing the tumor suppressor or cancer-related genes, we examined the methylation status of DLC-1 promoter region in breast cancer cell lines and primary breast tumors. The hypermethylation status was examined by MSP and 25% of cell lines harbored a methylated allele. The gene silencing by methylation was also confirmed by the re-expression of DLC-1 by the 5-aza-2'-deoxycytidine treatment in DLC-1 hypermethylated cell line. But the methylation of DLC-1 gene was less frequently shown in primary breast cancers (10%). These data suggest that hypermethylation is responsible for silencing of DLC-1 gene in a limited portion of breast cancers.

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