The mouse Mageb18 gene encodes a ubiquitously expressed type I MAGE protein and regulates cell proliferation and apoptosis in melanoma B16-F0 cells

Although many cancer vaccines have been developed against type I MAGE (melanoma antigen) genes owing to their shared tumour-specific expression properties, studies about their expression and functions are relatively limited. In the present study, we first identify a non-testis-specific type I MAGE gene, Mageb18 (melanoma antigen family B 18). Mouse Mageb18 is also expressed in digestion- and immune-related tissues as well as testis, and its expression in testis is age-dependent. Mageb18 is expressed in many mouse-derived cell lines, and DNA demethylation and histone acetylation mediate the reactivation of Mageb18 in Mageb18-negtive H22 and C6 cells. We also show that mouse Mageb18 encodes a 46 kDa protein which is predominantly localized in the cytoplasm. In testis, the endogenous MAGEB18 protein is mainly expressed in proliferative spermatogonia and primary and secondary spermatocytes, but less so in spermatids. Finally, we demonstrate that knockdown of MAGEB18 inhibits the growth of B16-F0 cells and induces apoptosis, which correlates with increased levels of TP53 (tumour protein 53), p21, Bax and caspase 3. The results of the present study thus uncover an important phenomenon that the expression of certain type I MAGE genes, at least for Mageb18, is non-testis-specific. Although they can regulate various malignant phenotypes of cancer cells, it is necessary to study further their expression pattern in normal tissues before using them to develop more effective and safer cancer vaccines.