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Description

Methylation of cytosines located 5' to guanosine is known to have a profound effect on the expression of several eukaryotic genes (Bird, 1992). In normal cells, methylation occurs predominantly in CG-poor regions, while CG-rich areas, called CpG islands, remain unmethylated. Aberrant methylation of normally unmethylated CpG islands has been documented as a relatively frequent event in immortalized and transformed cells (Antequera, 1990) and has been associated with transcriptional inactivation of defined tumor suppressor genes in human cancers (Merlo, 1995). The Retinoic Acid Receptor beta2 is expressed at reduced levels in many tumor types as a result of hypermethylation of its promoter region. Methylation-specific PCR (MSP) is a new technology for sensitive detection of abnormal gene methylation utilizing small amounts of DNA (Herman, 1996). This process employs an initial bisulfite reaction to modify the DNA, followed by PCR amplification with specific primers designed to distinguish methylated from unmethylated DNA.