Study of promoter CpG island hypermethylation of cyclindependent kinase inhibitor gene p21waf1/cip1 on some breast carcinoma cell lines

The p21 belongs to the CIP/KIP family of CDK inhibitors involved in cell cycle arrest at specific stages of the cell cycle progression. DNA methylation is the best studied epigenetic mark that have been evidently associated to chromatin condensation, and repression of gene transcription. The CpG island hypermethylation in promoter region of certain genes occurs in cancer cells and affects tumorigenesis. The aim of the current study was to assess DNA methylation pattern of p21 gene promoter region in the MCF7, T47D, MDA-MB-231 and MDA-MB-468 human breast carcinoma cell lines. The methylation status of cancer associated gene, p21waf1/cip1 was analyzed at CpG sites in the promoter region using a sensitive methylation-specific PCR (MSP) technique. The total genomic DNA from each cell line was isolated and subjected to the sodium bisulfite treatment to differentiate between methylated and unmethylated CpG islands. Then MSP was performed using designed primers for methylated (M-MSP) and unmethylated (U-MSP) forms of CpG islands in the promoter region of p21 gene. The results of the MSP indicated that promoter of p21 gene was consistently unmethylated in tested human breast cancer cell lines. Therefore, methylation inactivation of the p21waf1/cip1 does not commonly happen in all cancer cell lines.