Transcription of the MAGE-1 gene and the methylation status of its Ets binding promoter elements: a quantitative analysis in melanoma cell lines using a real-time polymerase chain reaction technique

The human MAGE gene family comprises at least 12 highly homologous genes. This makes it very difficult to assess expression of a single member quantitatively by means of Northern blotting. In order to investigate expression of the MAGE-1 gene quantitatively we therefore used the recently developed real-time polymerase chain reaction (PCR), a novel fluorescence-based quantitative PCR technique. This powerful technique enables detection of expression levels which differ by as much as a factor of 10(5) in magnitude. MAGE-1 expression is known to correlate with demethylated status of the Ets binding sites of its promoter. In a panel of 19 melanoma and nine non-melanoma cell lines we were able to confirm the relationship between MAGE-1 expression and demethylation of the Ets binding promoter region. Five cell lines, however, showed only very slight expression, while the two essential Ets promoter elements were largely demethylated. Earlier studies have shown that treatment of MAGE-1-negative cell lines with the demethylating agent 5-aza-2'-deoxycytidine (DAC) is sufficient to induce MAGE-1 expression. We were able to induce clear MAGE-1 expression in two of the non-expressing cell lines by incubation with DAC, although this expression did not reach very high levels. Consistent with this low level of induction is the observation that the Ets binding sites of the MAGE-1 promoter were not completely demethylated in the DAC-treated cell populations. In conclusion, we show in this study that the real-time PCR technique is a very useful tool for the quantification of expression of highly homologous genes. (C) 1999 Lippincott Williams & Wilkins.