A lineage-specific methylation pattern controls the transcription of the polycistronic mRNA coding MELOE melanoma antigens

We recently characterized two melanoma antigens MELOE-1 and MELOE-2 derived from a polycistronic RNA overexpressed in the melanocytic lineage. This transcription profile was because of hypomethylation of the meloe proximal promoter in melanomas and melanocytes. Here, we investigate whether this demethylation was restricted to the meloe promoter or was linked to a general lack of methylation at the meloe locus in the melanocytic lineage. We establish the methylation pattern of the locus spanning more than 40 kbp, focusing on CpG islands, using DNA bisulfite conversion and pyrosequencing. The study was carried out on cultured cell lines (melanoma, melanocyte, colon cancer, and mesothelioma cell lines), healthy tissues (skin and colon), and melanoma tumors. Demethylation, specifically observed in the melanocytic lineage, involves a large promoter area and not the entire meloe locus. This enables updating a tight regulation of meloe transcription in this lineage, suggesting tissue-specific epigenetic mechanisms. Associated with the previously described translational mechanisms, leading to the specific expression of MELOE-1 and MELOE-2 in melanomas, this makes MELOE-derived antigens a relevant candidate for immunotherapy of melanoma.