Identification of a novel MAGE D2 antisense RNA transcript in human tissues

Using cDNA microarray analysis, we identified a cDNA clone, DD74, from primary human bronchial epithelial cells, which exhibits increased expression in vitro after treatment with all-trans retinoic acid. This clone corresponded to MAGE D2 mRNA, a gene previously identified to be upregulated in several cancer tissues. Surprisingly, in situ hybridization of lung tissue demonstrated positive hybridization signals with sense, but not antisense, MAGE D2-specific cRNA probes. Examination of several cell lines by Northern blot hybridization confirmed significant expression of two RNA bands. With strand-specific riboprobes, we identified a 2.0 kb RNA transcript with the antisense probe as expected and identified a 4.1 kb transcript by the sense probe. Further sequence analysis of the 4.1 kb transcript revealed at least a 509 nucleotide sequence exactly complementary to the 2.0 kb MAGE D2 mRNA sequence. This MAGE D2i sequence contains unique structural features not shared with those of previously described antisense transcripts. Identification of this transcript potentially has important implications for future studies examining MAGE D2 expression patterns in cancer and normal tissues.