Methylation Patterns of IGFBP7 in Colon Cancer Cell Lines Are Associated with Levels of Gene Expression

Altered expression of insulin-like growth factor binding protein 7 (IGFBP7) has been found in colon cancer, but the exact regulatory mechanism has not been fully investigated. In order to elucidate the mechanisms underlying aberrant IGFBP7 expression in colon cancer, we used bisulphite sequencing PCR (BSP) to detect the detailed methylation profiles of the IGFBP7 5' CpG island. Exon 1 of the IGFBP7 gene was highly methylated in IGFBP7-negative cell lines but unmethylated in IGFBP7-positive lines. The methylation status of the promoter region and the intron 1 region was not so discriminating in IGFBP7-positive and -negative cell lines. Methylation-specific PCR (MSP) confirmed the hypermethylation of IGFBP7 exon 1 in IGFBP7-negative cell lines. Treatment with 5-aza-2'-deoxycytidine (5-aza-dC) induced demethylation of the CpG island in exon 1 of IGFBP7, as examined by both MSP and bisulphate genomic sequencing. Furthermore, the expression of IGFBP7 was restored, as detected by both RT-PCR and immunocytochemistry. Our study is the first to provide detailed methylation profiles of the IGFBP7 5' CpG island and shows that hypermethylation of the CpG island in exon 1 of IGFBP7 is closely related to the absence of its expression in colon cancer cells.