Down-Regulation of Connexin 32 Gene Expression through DNA Methylation in a Human Renal Cell Carcinoma Cell

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Abstract

Background: We have recently reported that connexin (Cx) 32 is down-regulated in a human renal cell carcinoma (RCC) cell (Caki-2 cell). Hypothesis: We postulated that the down-regulation of Cx32 gene in the RCC cell is due to hypermethylation of its promoter region. Methods: We estimated methylation status in the promoter region of Cx32 gene in the RCC cell by DNA digestion with methylation-sensitive restriction enzyme and PCR, and methylation-specific PCR (MSP). We also checked the recovery of Cx32 gene expression in the RCC cell treated with a DNA methyltranferase inhibitor, 5-Aza-2’-deoxycytidine (5-Aza-CdR). Results: Treatment with 5-Aza-CdR resulted in induction of Cx32 expression in the RCC cell. Hypermethylation of the Cx32 promoter region in the RCC cell was confirmed by DNA digestion with methylation-sensitive restriction enzyme and PCR, and MSP. Conclusion: We suggest that hypermethylation in the promoter region is a mechanism for the Cx32 gene repression in the RCC cell.

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Cancer epigenetics comes of age.

P. A. Jones, P. W. Laird, Andrew Dimond … (1999)

The discovery of numerous hypermethylated promoters of tumour-suppressor genes, along with a better understanding of gene-silencing mechanisms, has moved DNA methylation from obscurity to recognition as an alternative mechanism of tumour-suppressor inactivation in cancer. Epigenetic events can also facilitate genetic damage, as illustrated by the increased mutagenicity of 5-methylcytosine and the silencing of the MLH1 mismatch repair gene by DNA methylation in colorectal tumours. We review here current mechanistic understanding of the role of DNA methylation in malignant transformation, and suggest Knudson's two-hit hypothesis should now be expanded to include epigenetic mechanisms of gene inactivation.