Demethylation by 5-aza-2´-deoxycytidine of specific 5-methylcytosine sites in the promoter region of the retinoic acid receptor ß gene in human colon carcinoma cells


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Abstract

The role of retinoic acid receptor ß (RARß), a putative tumor suppressor gene, in the development of colon malignancy still remains to be clarified. We reported previously that the expression of RARß in DLD-1 human colon adenocarclnoma cells was silenced by DNA methylation at the level of the promoter region (AnttCancer Drugs 1997; 8:56). In addition, we observed that RARß expression could be activated by the hypomethylatlng action of 5-aza-2'-deoxycytidine (5-Aza- CdR). In this report we have Identified, by sequencing of bisulflte-modlfled DNA of DLD-1 colon tumor cells, the specific 5-methylcytosine positions in the region of - 4 6 to +251 bp from the transcription start site of RARß2 We observed that 5-Aza-CdR treatment demethylated these specific sites. Based on this sequence data, specific primers for the methylation-specific PCR (MSP) assay were designed to discriminate methylated from unmethylated CpG sites in the promoter region of RARß. This assay confirmed the changes in the methylation status of the RARß gene in DLD-1 colon tumor cells before and after treatment with 5-Aza-CdR. The methylation status of the promoter region of the RARß gene was also examined in primary human colon adenocarcinomas using the MSP assay. Six of the 14 colon tumor samples showed signs of hypermethylation of this gene. The MSP assay for RARß may be a useful tool to clarify the role of DNA methylation for this gene in colon tumorigenesis. [© 1998 Llppincott Williams & Wilklns.]

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