A novel messenger ribonucleic acid homologous to human MAGE-D is strongly expressed in rat Sertoli cells and weakly in Leydig cells and is regulated by follitropin, lutropin, and prolactin

Emerging roles of the MAGE protein family in stress response pathways

The melanoma antigen (MAGE) proteins all contain a MAGE homology domain. MAGE genes are conserved in all eukaryotes and have expanded from a single gene in lower eukaryotes to ∼40 genes in humans and mice. Whereas some MAGEs are ubiquitously expressed in tissues, others are expressed in only germ cells with aberrant reactivation in multiple cancers. Much of the initial research on MAGEs focused on exploiting their antigenicity and restricted expression pattern to target them with cancer immunotherapy. Beyond their potential clinical application and role in tumorigenesis, recent studies have shown that MAGE proteins regulate diverse cellular and developmental pathways, implicating them in many diseases besides cancer, including lung, renal, and neurodevelopmental disorders. At the molecular level, many MAGEs bind to E3 RING ubiquitin ligases and, thus, regulate their substrate specificity, ligase activity, and subcellular localization. On a broader scale, the MAGE genes likely expanded in eutherian mammals to protect the germline from environmental stress and aid in stress adaptation, and this stress tolerance may explain why many cancers aberrantly express MAGEs Here, we present an updated, comprehensive review on the MAGE family that highlights general characteristics, emphasizes recent comparative studies in mice, and describes the diverse functions exerted by individual MAGEs.

Expression dynamics of Mage family genes during self-renewal and differentiation of mouse pluripotent stem and teratocarcinoma cells

The biological roles of cancer-testis antigens of the Melanoma antigen (Mage) family in mammalian development, stem cell differentiation and carcinogenesis are largely unknown. In order to understand the involvement of the Mage family genes in maintenance of normal and cancer stem cells, the expression patterns of Mage-a, Mage-b, Mage-d, Mage-e, Mage-h and Mage-l gene subfamilies were analyzed during the self-renewal and differentiation of mouse pluripotent stem and teratocarcinoma cells. Clustering analysis based on the gene expression profiles of undifferentiated and differentiating cell populations revealed strong correlations between Mage expression patterns and differentiation and malignant states. Gene co-expression analysis disclosed the potential contributions of Mage family members in self-renewal and differentiation of pluripotent stem and teratocarcinoma cells. Two gene clusters including Mage-a4 and Mage-a8, Mageb1, Mage-d1, Mage-d2, Mage-e1, Mage-l2 were identified as functional antagonists with opposing roles in the regulation of proliferation and differentiation of mouse pluripotent stem and teratocarcinoma cells. The identified aberrant expression patterns of Mage-a2, Mage-a6, Mage-b4, Mageb-16 and Mage-h1 in teratocarcinoma cells can be considered as specific teratocarcinoma biomarkers promoted the malignant phenotype. Our study first provides a model for the involvement of Mage family members in regulatory networks during the self-renewal and early differentiation of normal and cancerous stem cells for further research of the predicted functional modules and the development of new cancer treatment strategies.

Knockdown of NRAGE induces odontogenic differentiation by activating NF-κB signaling in mouse odontoblast-like cells

PURPOSE

Neurotrophin receptor-interacting MAGE homologue (Nrage) plays an important role in bone development and the metabolism of normal skeletal structures. Our previous study showed that Nrage inhibited the odontogenic differentiation of mouse dental pulp cells. However, the potential roles and mechanism of Nrage in regulating odontogenic differentiation are unknown. The aim of this study was to investigate the molecular mechanism of Nrage in odontogenic differentiation of mouse odontoblast-like cells.

MATERIALS AND METHODS

Endogenous expression of Nrage was stably downregulated by lentivirus-mediated shRNA. Mineralized nodules formation was detected by alizarin red S staining. Dmp-1, Dspp, and ALP mRNA and protein levels were detected by qRT-PCR and western blotting, respectively. In addition, ALPase activity was detected. Confocal microscopy and co-immunoprecipitation (co-IP) were used to analyze the interactions between NRAGE and NF-κB signaling molecules. An IKK inhibitor was also used in the study.

RESULTS

NRAGE expression in odontoblasts was downregulated during mouse first maxillary molar development. Moreover, NRAGE expression was downregulated during odontogenic differentiation of odontoblast-like cells. NRAGE knockdown significantly upregulated DMP1 and DSP expression, increased ALPase activity, and promoted mineralized nodule formation. In addition, NRAGE knockdown increased the translocation of NF-κB1 to the nucleus and phosphorylation levels of p65. Co-IP results showed that NRAGE bound to IKKβ. Most importantly, the promoting effect of Nrage knockdown on odontoblastic differentiation was reduced after treatment with an IKK inhibitor.

CONCLUSIONS

Our data confirmed that NRAGE is an important regulator of odontogenic differentiation of odontoblasts by inhibiting the NF-κB signaling pathway through binding to IKKβ.

ABBREVIATIONS

Nrage: neurotrophin receptor-interacting MAGE homologue; DSP: dentin sialophospho protein; DMP-1: dentin matrix protein-1; BMP: bone morphogenetic protein; Wnt: wingless; NF-κB: nuclear factor of activated B cells; DAPI: 4',6-diamidino-2-phenylindole; KO: knockout; DPCs: dental pulp cells; AA: ascorbic acid; β-Gly: β-glycerophosphate; Dex: dexamethasone; co-IP: co-immunoprecipitation; IκB: inhibitor of NF-κB; IKK: IκB kinase.

Complex roles of NRAGE on tumor

NRAGE, also known as Dlxin-1or MAGE-D1, is a member of type II melanoma-associated antigen (MAGE) and plays an essential role in life activities, including differentiation, apoptosis, and cell cycle. Studies increasingly found that NRAGE is closely related to the tumor events, such as tumor occurrence, invasion, and metastasis. However, complex and contradictory functions of NRAGE in different circumstances are observed, suggesting that NRAGE is unique from other MAGE gene family members. This review summarizes recent findings concerning the structure and biological functions of NRAGE, which may provide a basis for a more comprehensive understanding of and further research on NRAGE.

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.

Melanoma-Associated Antigen Family Protein-D1 Regulation of Tumor Cell Migration, Adhesion to Endothelium, and Actin Structures Reorganization in Response to Hypoxic Stress

Melanoma-associated antigen family protein-D1 (MAGE-D1) is a recently identified p75 neurotrophin receptor intracellular binding protein and functions as an adaptor that mediates multiple signaling pathways, including Dlx/Msx-mediated transcription. Here, a new regulatory function for MAGE-D1 in tumor cell motility and adhesion to endothelium is described. MAGE-D1 over-expression suppressed HeLa cell and BEL7402 cell migration, invasion, and adhesion to the monolayer of ECV304 cells. We also report that MAGE-D1 over-expression disrupted actin cytoskeleton rearrangement induced by hypoxia and down-regulated hypoxia inducible factor 1-dependent luciferase gene expression. These findings provide new insight into the ability of MAGE-D1 to suppress the motility and adhesion response of tumor cells by interfering with actin cytoskeleton reorganization and hypoxia inducible factor 1-dependent gene expression.

Inhibition of adenovirus-mediated human MAGE-D1 on angiogenesis in vitro and in vivo

MAGE-D1 is a member of the MAGE family of proteins, and functions as an adaptor that mediates multiple signaling pathways. The current study for the first time provides evidence for a role of MAGE-D1 in the negative regulation of angiogenic activity in vitro and in vivo models. Our findings showed that MAGE-D1 over-expression significantly suppressed the angiogenic key events such as endothelial cell migration and invasion, adhesion on collagen I substrate, and in vitro differentiation into tube-like structures under both normoxic and hypoxic conditions. MAGE-D1 over-expression also inhibited in vivo angiogenesis in Matrigel plugs that were implanted subcutaneously in mice. With further experiments, we revealed that MAGE-D1 over-expression disrupted actin cytoskeleton organization and lamellipodia formation, and down-regulated HIF-1-dependent gene expression in endothelial cells under hypoxic conditions. These findings demonstrate a new function of MAGE-D1 in the regulation of angiogenesis and provide new insight into the ability of MAGE-D1 to suppress the growth and angiogenic response of endothelial cells by interfering with HIF-1-dependent gene expression, and actin cytoskeleton reorganization, suggesting that MAGE-D1 might be a novel inhibitor of angiogenesis in vitro and in vivo.

The receptor tyrosine kinase Ror2 associates with the melanoma-associated antigen (MAGE) family protein Dlxin-1 and regulates its intracellular distribution

The mammalian Ror family receptor tyrosine kinases, Ror1 and Ror2, play crucial roles in developmental morphogenesis. Although the functions of Ror1 and Ror2 are redundant, Ror2 exhibits more specific functions during development. We show that when expressed in mammalian cells, Ror2, but not Ror1, associates with the melanoma-associated antigen (MAGE) family protein, Dlxin-1, which is known to bind to the homeodomain proteins Msx2 and Dlx5 and regulate their transcriptional functions. This association requires the cytoplasmic C-terminal region of Ror2, containing proline-rich and serine/threonine-rich domains, and the C-terminal necdin homology domain of Dlxin-1. Interestingly, the cytoplasmic C-terminal region of Ror2 is missing in patients with brachydactyly type B. Interestingly, transient expression and immunohistochemical analyses reveal that both Dlxin-1 and Msx2 are co-localized in the nuclei in the absence of Ror2. In the presence of Ror2, Dlxin-1 is co-localized with Ror2 at the membranous compartments and Msx2 is retained in the nuclei. It was also found that the majority of cellular Dlxin-1 is retained in the membrane fractions of wild-type but not Ror2-/- mouse embryonic fibroblasts. Furthermore, we show that transcriptional activity of Msx2, irrespective of Ror2 kinase activity, is regulated by ectopic expression of Ror2 using a reporter plasmid containing the WIP element. Thus, Ror2 sequesters Dlxin-1 in membranous compartments, thereby affecting the transcriptional function of Msx2.

A RING finger protein Praja1 regulates Dlx5-dependent transcription through its ubiquitin ligase activity for the Dlx/Msx-interacting MAGE/Necdin family protein, Dlxin-1

Msx2 and Dlx5 are homeodomain proteins that play an important role in osteoblast differentiation and whose expression is induced by bone morphogenetic proteins. Recently we have identified a novel protein, Dlxin-1, that associates with these homeodomain proteins and regulates Dlx5-dependent transcriptional function (Masuda, Y., Sasaki, A., Shibuya, H., Ueno, N., Ikeda, K., and Watanabe, K. (2001) J. Biol. Chem. 276, 5331-5338). In an attempt to elucidate the molecular function of Dlxin-1, two closely related RING finger proteins, Praja1 and Neurodap-1, were isolated by yeast two-hybrid screening using the C-terminal necdin homology domain of Dlxin-1 as bait. Glutathione S-transferase pull-down and immunoprecipitation/Western blotting assays following co-transfection of Dlxin-1 and Praja1 revealed that Praja1 binds to the C-terminal necdin homology domain of Dlxin-1 in vitro and in vivo, respectively. Overexpression of Praja1 caused a decrease in Dlxin-1 protein level, which was reversed when a proteasome inhibitor was added. Overexpression of Praja1 with a mutation in the RING finger inhibited the decrease in Dlxin-1 protein, pointing to the importance of ubiquitin-protein isopeptide ligase (E3) activity associated with RING finger. Wild-type Praja1, but not its RING finger mutant, promoted ubiquitination of Dlxin-1 in vivo. Finally, expression of Praja1 down-regulated Dlx5-dependent transcriptional activity in a GAL4-dependent assay. These results suggest that Praja1 regulates the transcription function of the homeodomain protein Dlx5 by controlling the stability of Dlxin-1 via an ubiquitin-dependent degradation pathway.

MAGE-A4, a germ cell specific marker, is expressed differentially in testicular tumors

BACKGROUND

Testicular germ cell tumors are the most common malignancy in young males, and the frequency of these tumors has risen dramatically over the last century. Because it is known that the MAGE genes are expressed in a wide variety of tumors but are expressed only in the mitotic spermatogonia (germ cells) and in the primary spermatocytes in the normal testis, the authors screened the expression of MAGE-A4 in a panel of testicular germ cell tumors.

METHODS

Monoclonal antibody 57B raised against MAGE-A4 was tested immunohistochemically on 12 classical seminomas, 5 anaplastic seminomas, 10 various specimens of nonseminomatous germ cell tumors (NSGCTs), 2 combined tumors containing seminoma components, 1 Sertoli cell tumor, 2 Leydig cell tumors, and 15 carcinomas in situ (CIS). In addition, monoclonal antibody 57B was tested on embryonic gonad (age 8 weeks) and fetal gonads (ages 15 weeks, 17 weeks, and 28 weeks).

RESULTS

Classical seminomas uniformly and specifically expressed MAGE-A4 compared with anaplastic seminomas and NSGCTs, which were negative for this antigen. Specific expression of MAGE-A4 also was seen in subpopulations of CIS cells, providing additional evidence for heterogeneity of the phenotype of these cells, in which it is believed that differentiation and proliferation generate seminomas and NSGCTs. Finally, MAGE-A4 was expressed in the fetal precursors of the stem germ cells from 17 weeks of gestation onward, in accordance the fact that CIS can arise from prespermatogonia in the fetus.

CONCLUSIONS

MAGE-A4 can be considered a potential specific marker for normal premeiotic germ cells and germ cell tumors and can be used to characterize classical seminomas.