MAGE Xp-2: a member of the MAGE gene family isolated from an expression library using systemic lupus erythematosus sera

A Comprehensive Guide to the MAGE Family of Ubiquitin Ligases

Melanoma antigen (MAGE) genes are conserved in all eukaryotes and encode for proteins sharing a common MAGE homology domain. Although only a single MAGE gene exists in lower eukaryotes, the MAGE family rapidly expanded in eutherians and consists of more than 50 highly conserved genes in humans. A subset of MAGEs initially garnered interest as cancer biomarkers and immunotherapeutic targets due to their antigenic properties and unique expression pattern that is primary restricted to germ cells and aberrantly reactivated in various cancers. However, further investigation revealed that MAGEs not only drive tumorigenesis but also regulate pathways essential for diverse cellular and developmental processes. Therefore, MAGEs are implicated in a broad range of diseases including neurodevelopmental, renal, and lung disorders, and cancer. Recent biochemical and biophysical studies indicate that MAGEs assemble with E3 RING ubiquitin ligases to form MAGE-RING ligases (MRLs) and act as regulators of ubiquitination by modulating ligase activity, substrate specification, and subcellular localization. Here, we present a comprehensive guide to MAGEs highlighting the molecular mechanisms of MRLs and their physiological roles in germ cell and neural development, oncogenic functions in cancer, and potential as therapeutic targets in disease.

Cancer-germline antigen vaccines and epigenetic enhancers: future strategies for cancer treatment

IMPORTANCE OF THE FIELD

Immunotherapy holds great potential for disseminated cancer, and cancer-germline (CG) antigens are among the most promising tumor targets. They are widely expressed in different cancer types and are essentially tumor-specific, since their expression in normal tissues is largely restricted to immune-privileged sites. Although the therapeutic potential of these antigens may be compromised by their highly heterogeneous expression in many tumors and low frequency in some cancers, recent developments suggest that tumor-cell-selective enhancement of CG antigen gene expression can be achieved using epigenetic modifiers.

AREAS COVERED IN THIS REVIEW

We provide an overview of the potential of CG antigens as targets for cancer immunotherapy, including advantages and disadvantages. We also discuss the current state of development of CG antigen vaccines, and the potential synergistic effect of combining CG antigen immunotherapeutic strategies with epigenetic modifiers.

WHAT THE READER WILL GAIN

The reader will gain an overview of the past, present and future role of CG antigens in cancer immunotherapy.

TAKE HOME MESSAGE

Chemoimmunotherapy using epigenetic drugs and CG antigen vaccines may be a useful approach for treating cancer.

MAGE-B2 autoantibody: a new biomarker for pediatric systemic lupus erythematosus

OBJECTIVE

Melanoma-associated antigen gene B2 (MAGE-B2) encodes an embryonic antigen normally silenced after birth except in testis and placenta. We identified the MAGE-B2 gene and autoantibodies in pediatric patients with systemic lupus erythematosus (SLE) glomerulonephritis. We investigated the prevalence of MAGE-B2 autoantibodies in association with active SLE, to determine a pathogenetic role of MAGE-B2 protein through its distribution in cells and tissues.

METHODS

A cross-sectional study analyzed the frequency of MAGE-B2 autoantibodies in 40 patients with pediatric SLE, 23 adult controls, and 16 patients with pediatric juvenile rheumatoid arthritis (JRA) using Western blots containing recombinant MAGE-B2. SLE Disease Activity Index 2000 (SLEDAI-2K) and British Isles Lupus Assessment Group (BILAG) index measured SLE disease activity. Tissue distribution of MAGE-B2 protein was assessed by immunohistochemistry, immunofluorescence, and Western blots.

RESULTS

Seventeen (43%) of 40 pediatric SLE patients had MAGE-B2 autoantibodies as compared to 0 of 16 JRA patients and 2 of 23 adult controls. SLE disease activity was significantly higher in MAGE-B2 autoantibody-positive versus autoantibody-negative patients (SLEDAI-2K, mean 10.9 vs 5.2, p = 0.013; BILAG, mean 15.3 vs 6.3, p = 0.023). Active nephritis was more prevalent (60% vs 24%) in MAGE-B2 autoantibody-positive than autoantibody-negative SLE patients. MAGE-B2 protein was visualized in SLE kidney proximal convoluted tubules and in tumor epithelial cells, but not in lymphoblastoid cells.

CONCLUSION

MAGE-B2 autoantibody appears to be a clinically relevant biomarker for pediatric SLE disease activity and nephritis.

Characterization of a cancer/testis (CT) antigen gene family capable of eliciting humoral response in cancer patients

Cancer/testis (CT) antigens are immunogenic proteins expressed in normal gametogenic tissues and in different types of tumors. CT antigens are promising candidates for cancer immunotherapy, and the identification of novel CT antigens is a prerequisite for the development of cancer vaccines. We have identified a CT antigen, named CTSP-1, with partial similarity to the breast differentiation antigen NY-BR-1. CTSP-1 presents several splicing and polyadenylation variants and has a very restricted expression pattern among normal tissues. CTSP-1 is exclusively expressed in normal testis and is aberrantly expressed in 47.6% (10 of 21) of tumor cell lines and in 44.4% (75 of 169) of tumors from different histological types. The highest percentages of positive expression were observed in melanomas (59.0%) followed by prostate (58.0%) and lung (57.0%) tumors. CTSP-1 is part of a highly conserved gene family, and members of this family also have a restricted expression pattern and similar protein structure. Antibodies against members of this gene family were detected in 10% (14 of 141) of plasma samples from patients with a wide spectrum of tumors. The highest percentages of antibody response were observed in patients with prostate (20.8%), thyroid (20.0%), and breast (16.6%) tumors. Because of its very restricted expression pattern in normal tissues and immunogenicity in different types of tumors, CTSP-1 should be considered a promising candidate for cancer immunotherapy.

mRNA expression of MAGE-A3 gene in leukemia cells

Leukemia-associated antigens such as proteins encoded by MAGE genes might provide tools for immunotherapy of leukemia. Positive and negative results of MAGE-A gene expression in hematological malignancies have been reported. This led us to study MAGE-A gene expression in human leukemias using RT-PCR. Among 115 leukemias from various subtypes, 14/34 (41.17%) AML were positive for one of the three genes analyzed (MAGE-A1 1/32; MAGE-A3 10/32; MAGE-B2 3/12). Expression was also detected in 23/76 (30.26%) B-cell ALL patients (MAGE-A1 2/53; MAGE-A3 20/53; MAGE-B2 1/32). One of these patients expressed both MAGE-A1 (weak signal) and -A3 (strong signal) genes. Other patient with CML were positive for MAGE-B2 (1/5, 20%). MAGE-A3 expression data were corroborated by real time RT-PCR through determination of MAGE-A3 transcript levels. We concluded that the MAGE-A3 gene is expressed at the mRNA level in a proportion of human leukemias.

Cancer/testis antigens and gametogenesis: a review and "brain-storming" session

Genes expressed both in normal testis and in malignancies (Cancer/ Testis associated genes - CTA) have become the most extensively studied antigen group in the field of tumour immunology. Despite this, many fundamentally important questions remain unanswered: what is the connection between germ-cell specific genes and tumours? Is the expression of these genes yet another proof for the importance of genome destabilisation in the process of tumorigenesis?, or maybe activation of these genes is not quite random but instead related to some programme giving tumours a survival advantage?This review collates most of the recent information available about CTAs expression, function, and regulation. The data suggests a programme related to ontogenesis, mostly to gametogenesis. In the "brain-storming" part, facts in conflict with the hypothesis of random CTA gene activation are discussed. We propose a programme borrowed from organisms phylogenetically much older than humans, which existed before the differentiation of sexes. It is a programme that has served as a life cycle with prominent ploidy changes, and from which, as we know, the germ-cell ploidy cycle - meiosis - has evolved. Further work may show whether this hypothesis can lead to a novel anti-tumour strategy.

OrthoParaMap: distinguishing orthologs from paralogs by integrating comparative genome data and gene phylogenies

BACKGROUND

In eukaryotic genomes, most genes are members of gene families. When comparing genes from two species, therefore, most genes in one species will be homologous to multiple genes in the second. This often makes it difficult to distinguish orthologs (separated through speciation) from paralogs (separated by other types of gene duplication). Combining phylogenetic relationships and genomic position in both genomes helps to distinguish between these scenarios. This kind of comparison can also help to describe how gene families have evolved within a single genome that has undergone polyploidy or other large-scale duplications, as in the case of Arabidopsis thaliana - and probably most plant genomes.

RESULTS

We describe a suite of programs called OrthoParaMap (OPM) that makes genomic comparisons, identifies syntenic regions, determines whether sets of genes in a gene family are related through speciation or internal chromosomal duplications, maps this information onto phylogenetic trees, and infers internal nodes within the phylogenetic tree that may represent local - as opposed to speciation or segmental - duplication. We describe the application of the software using three examples: the melanoma-associated antigen (MAGE) gene family on the X chromosomes of mouse and human; the 20S proteasome subunit gene family in Arabidopsis, and the major latex protein gene family in Arabidopsis.

CONCLUSION

OPM combines comparative genomic positional information and phylogenetic reconstructions to identify which gene duplications are likely to have arisen through internal genomic duplications (such as polyploidy), through speciation, or through local duplications (such as unequal crossing-over). The software is freely available at http://www.tc.umn.edu/~cann0010/.

Cancer/testis-associated genes: identification, expression profile, and putative function

Cancer/testis-associated genes (CTAs) are a subgroup of tumor antigens with a restricted expression in testis and malignancies. During the last decade, many of these immunotherapy candidate genes have been discovered using various approaches. Most of these genes are localized on the X-chromosome, often as multigene families. Methylation status seems to be the main, but not the only regulator of their specific expression pattern. In testis, CTAs are exclusively present in cells of the germ cell lineage, though there is a lot of variation in the moment of expression during different stages of sperm development. Likewise, there is also a lot of heterogeneity in the expression of CTAs in melanoma samples. Clues regarding functionality of CTAs for many of these proteins point to a role in cell cycle regulation or transcriptional control. Better insights in the function of these genes may shed light on the link between spermatogenesis and tumor growth and could be of use in anti-tumor therapies. This review outlines the CTA family and focuses on their expression and putative function during male germ cell development and melanocytic tumor progression.

Protein array technology: the tool to bridge genomics and proteomics

The generation of protein chips requires much more efforts than DNA microchips. While DNA is DNA and a variety of different DNA molecules behave stable in a hybridisation experiment, proteins are much more difficult to produce and to handle. Outside of a narrow range of environmental conditions, proteins will denature, lose their three-dimensional structure and a lot of their specificity and activity. The chapter describes the pitfalls and challenges in Protein Microarray technology to produce native and functional proteins and store them in a native and special environment for every single spot on an array, making applications like antibody profiling and serum screening possible not only on denatured arrays but also on native protein arrays.

Protein array technology. Potential use in medical diagnostics

The human genome is sequenced, but only a minority of genes have been assigned a function. Whole-genome expression profiling is an important tool for functional genomic studies. Automated technology allows high-throughput gene activity monitoring by analysis of complex expression patterns, resulting in fingerprints of diseased versus normal or developmentally distinct tissues. Differential gene expression can be most efficiently monitored by DNA hybridization on arrays of oligonucleotides or cDNA clones. Starting from high-density filter membranes, cDNA microarrays have recently been devised in chip format. We have shown that the same cDNA libraries can be used for high-throughput protein expression and antibody screening on high-density filters and microarrays. These libraries connect recombinant proteins to clones identified by DNA hybridization or sequencing, hence creating a direct link between gene catalogs and functional catalogs. Microarrays can now be used to go from an individual clone to a specific gene and its protein product. Clone libraries become amenable to database integration including all steps from DNA sequencing to functional assays of gene products.

Large scale identification of human hepatocellular carcinoma-associated antigens by autoantibodies

Autoantibodies are often detected in hepatocellular carcinoma (HCC), and these responses may represent recognition of tumor Ags that are associated with transformation events. The identities of these Ags, however, are less well known. Using serological analysis of recombinant cDNA expression libraries (SEREX) from four HCC patients, we identified 55 independent cDNA sequences potentially encoding HCC tumor Ags. Of these genes, 15 are novel. Two such proteins, HCA587 and HCA661, were predominantly detected in testis, but not in other normal tissues, except for a weak expression in normal pancreas. In addition to HCC, these two Ags can be found in cancers of other histological types. Therefore, they can be categorized as cancer-testis (CT) Ags. Two other Ags (HCA519 and HCA90) were highly overexpressed in HCC and also expressed in cancer cell lines of lung, prostate, and pancreas, but not in the respective normal tissues. Four other Ags were identified to be expressed in particular types of cancer cell lines (HCA520 in an ovarian cancer cell line, HCA59 and HCA67 in a colon cancer cell line, HCA58 in colon and ovarian cancer cell lines), but not in the normal tissue counterpart(s). In addition, abundant expression of complement inactivation factors was found in HCC. These results indicate a broad range expression of autoantigens in HCC patients. Our findings open an avenue for the study of autoantigens in the transformation, metastasis, and immune evasion in HCC.

Identification of a new, unorthodox member of the MAGE gene family

Several tumor-associated antigen families, such as MAGE, GAGE/PAGE, PRAME, BAGE, and LAGE/NY-ESO-1, exist. These antigens are of particular interest in tumor immunology, because their expression, with exception of testis and fetal tissues, seems to be restricted to tumor cells only. We have identified a novel member of the MAGE gene family, MAGED1. Northern hybridization and RT-PCR demonstrated that the expression level of MAGED1 in different normal adult tissues is comparable to that in testis and fetal liver. Thus, MAGED1 does not possess an expression pattern characteristic of previously identified MAGE family genes, suggesting that the biology of the MAGE-family genes is more complex than previously thought. Chromosome mapping linked MAGED1 to marker AFM119xd6 (DXS1039) on chromosome Xp11.23.