MAGE-A, mMage-b, and MAGE-C proteins form complexes with KAP1 and suppress p53-dependent apoptosis in MAGE-positive cell lines

Potential role for PAD2 in gene regulation in breast cancer cells

The peptidylarginine deiminase (PAD) family of enzymes post-translationally convert positively charged arginine residues in substrate proteins to the neutral, non-standard residue citrulline. PAD family members 1, 2, 3, and 6 have previously been localized to the cell cytoplasm and, thus, their potential to regulate gene activity has not been described. We recently demonstrated that PAD2 is expressed in the canine mammary gland epithelium and that levels of histone citrullination in this tissue correlate with PAD2 expression. Given these observations, we decided to test whether PAD2 might localize to the nuclear compartment of the human mammary epithelium and regulate gene activity in these cells. Here we show, for the first time, that PAD2 is specifically expressed in human mammary gland epithelial cells and that a portion of PAD2 associates with chromatin in MCF-7 breast cancer cells. We investigated a potential nuclear function for PAD2 by microarray, qPCR, and chromatin immunoprecipitation analysis. Results show that the expression of a unique subset of genes is disregulated following depletion of PAD2 from MCF-7 cells. Further, ChIP analysis of two of the most highly up- and down-regulated genes (PTN and MAGEA12, respectively) found that PAD2 binds directly to these gene promoters and that the likely mechanism by which PAD2 regulates expression of these genes is via citrullination of arginine residues 2-8-17 on histone H3 tails. Thus, our findings define a novel role for PAD2 in gene expression in human mammary epithelial cells.

The melanoma-associated antigen MAGE-D2 suppresses TRAIL receptor 2 and protects against TRAIL-induced apoptosis in human melanoma cells

Emerging evidence has pointed to biological roles of melanoma-associated antigens (MAGEs) in cancer development, progression and resistance to treatment. However, the mechanisms involved remain to be fully elucidated. In this report, we show that one of the MAGE proteins, MAGE-D2, suppresses the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor 2 (TRAIL-R2) and plays an important role in protecting melanoma cells from apoptosis induced by TRAIL. MAGE-D2 was commonly expressed at increased levels in melanoma cells compared with melanocytes. Although its inhibition by small interfering RNA (siRNA) did not cause cell death, it rendered melanoma cells more sensitive to TRAIL-induced apoptosis. This was associated with enhanced formation of TRAIL death-inducing signaling complex and up-regulation of TRAIL-R2, and was blocked by a recombinant TRAIL-R2/Fc chimeric protein or siRNA knockdown of TRAIL-R2. Regulation of TRAIL-R2 by MAGE-D2 appeared to be mediated by p53, in that knockdown MAGE-D2 did not up-regulate TRAIL-R2 in p53-null or mutant p53 melanoma cells. In addition, inhibition of MAGE-D2 did not result in up-regulation of TRAIL-R2 in wild-type p53 cell lines with p53 inhibited by short hairpin RNA. Indeed, knockdown of MAGE-D2 led to up-regulation of p53 due to a transcriptional increase. The regulatory effect of MAGE-D2 on TRAIL-R2 expression and TRAIL-induced apoptosis was recapitulated in studies on fresh melanoma isolates. Taken together, these results identify the expression of MAGE-D2 as an important mechanism that inhibit TRAIL-induced apoptosis and suggest that targeting MAGE-D2 may be a useful strategy in improving the therapeutic efficacy of TRAIL in melanoma.

The TIF1α-related TRIM cofactors couple chromatin modifications to transcriptional regulation, signaling and tumor suppression

TRIM24 (TIF1α), TRIM28 (TIF1β) and TRIM33 (TIF1γ) are related cofactors defining a subgroup of the tripartite motif (TRIM) superfamily comprising an N-terminal RING finger E3 ligase and a C-terminal PHD-Bromodomain chromatin interacting module. Increasing evidence highlights the important roles of these proteins as modulators of multiple signaling pathways during normal development and as tumor suppressors. The finding that they interact to form a multiprotein complex suggests new mechanisms to integrate multiple signaling pathways for tumor suppression.

New hypotheses for large-scale epigenome alterations in somatic cancer cells: a role for male germ-cell-specific regulators

Oncogenic cell transformation is consistently associated with alterations of the cell epigenome leading to aberrant gene repression and activation. Some of these events, such as the DNA-methylation-based silencing of tumor suppressor genes, are considered to be oncogenic themselves. A much less-studied consequence of these epigenetic misregulations is the abnormal activation of tissue-specific genes in precancerous and transformed cells. Here, we explore the idea that the aberrant expression of germ-cell-specific genes in somatic cancer cells could contribute to malignant cell transformation and cancer progression. Indeed, a significant number of papers have reported the abnormal activation of germ cell-specific genes in various somatic cancers (known as cancer testis [C/T] antigens or factors). Although in most cases the physiological function of these genes remains unknown, functional investigations suggest that they can act as potent genome, epigenome and cellular reorganizers. Hence, in view of the existing literature, we discuss the hypothesis that C/T activation in somatic cells is not only a consequence of global epigenetic deregulation, but also a cause of further large-scale alterations of the epigenome, which themselves have direct oncogenic consequences for the affected cells. Finally, we highlight the fact that C/T factors have the potential to serve as valuable markers for cancer detection, as well as provide promising targets for developing new therapeutical strategies.

Tumor-specific MAGE proteins as regulators of p53 function

Since its discovery in 1991, the knowledge about the tumor specific melanoma antigen gene (MAGE-I) family has been continuously increasing. Initially, MAGE-I proteins were considered as selective targets for immunotherapy. More recently, emerging data obtained from different cellular mechanisms controlled by MAGE-I proteins suggest a key role in the regulation of important pathways linked to cell proliferation. This is in part due to the ability of some MAGE-I proteins to control the p53 tumor suppressor. In this review, we focus on the mechanisms proposed to explain how MAGE-I proteins affect p53 functions.

MAGE-A antigens as targets in tumour therapy

MAGE-A proteins constitute a sub-family of Cancer-Testis Antigens which are expressed mainly, but not exclusively, in germ cells. They are also expressed in various human cancers where they are associated with, and may drive, malignancy. MAGE-A proteins are highly immunogenic and are considered as potential targets for cancer vaccines and/or immuno-therapy. Moreover, recent advances in our understanding of their molecular pathology have revealed interactions that offer potential as therapeutic targets. Here we review recent progress in this area and consider how these interactions might be exploited, especially for the treatment of malignant cancers for which available treatments are inadequate.

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.

RAF265 inhibits the growth of advanced human melanoma tumors

PURPOSE

The purpose of this preclinical study was to determine the effectiveness of RAF265, a multikinase inhibitor, for treatment of human metastatic melanoma and to characterize traits associated with drug response.

EXPERIMENTAL DESIGN

Advanced metastatic melanoma tumors from 34 patients were orthotopically implanted to nude mice. Tumors that grew in mice (17 of 34) were evaluated for response to RAF265 (40 mg/kg, every day) over 30 days. The relation between patient characteristics, gene mutation profile, global gene expression profile, and RAF265 effects on tumor growth, mitogen-activated protein/extracellular signal-regulated kinase (MEK)/extracellular signal-regulated kinase (ERK) phosphorylation, proliferation, and apoptosis markers was evaluated.

RESULTS

Nine of the 17 tumors that successfully implanted (53%) were mutant BRAF (BRAF(V600E/K)), whereas eight of 17 (47%) tumors were BRAF wild type (BRAF(WT)). Tumor implants from 7 of 17 patients (41%) responded to RAF265 treatment with more than 50% reduction in tumor growth. Five of the 7 (71%) responders were BRAF(WT), of which 1 carried c-KIT(L576P) and another N-RAS(Q61R) mutation, while only 2 (29%) of the responding tumors were BRAF(V600E/K). Gene expression microarray data from nonimplanted tumors revealed that responders exhibited enriched expression of genes involved in cell growth, proliferation, development, cell signaling, gene expression, and cancer pathways. Although response to RAF265 did not correlate with pERK1/2 reduction, RAF265 responders did exhibit reduced pMEK1, reduced proliferation based upon reduced Ki-67, cyclin D1 and polo-like kinase1 levels, and induction of the apoptosis mediator BCL2-like 11.

CONCLUSIONS

Orthotopic implants of patient tumors in mice may predict prognosis and treatment response for melanoma patients. A subpopulation of human melanoma tumors responds to RAF265 and can be characterized by gene mutation and gene expression profiles.

Targeting epigenetic mediators of gene expression in thoracic malignancies

Lung and esophageal cancers and malignant pleural mesotheliomas are highly lethal neoplasms that are leading causes of cancer-related deaths worldwide. Presently, limited information is available pertaining to epigenetic mechanisms mediating initiation and progression of these neoplasms. The following presentation will focus on the potential clinical relevance of epigenomic alterations in thoracic malignancies mediated by DNA methylation, perturbations in the histone code, and polycomb group proteins, as well as ongoing translational efforts to target epigenetic regulators of gene expression for treatment of these neoplasms. This article is part of a Special Issue entitled: Chromatin in time and space.

Cancer/Testis Antigen MAGE-C1/CT7: new target for multiple myeloma therapy

Cancer/Testis Antigens (CTAs) are a promising class of tumor antigens that have a limited expression in somatic tissues (testis, ovary, fetal, and placental cells). Aberrant expression of CTAs in cancer cells may lead to abnormal chromosome segregation and aneuploidy. CTAs are regulated by epigenetic mechanisms (DNA methylation and acetylation of histones) and are attractive targets for immunotherapy in cancer because the gonads are immune privileged organs and anti-CTA immune response can be tumor-specific. Multiple myeloma (MM) is an incurable hematological malignancy, and several CTAs have been detected in many MM cell lines and patients. Among CTAs expressed in MM we must highlight the MAGE-C1/CT7 located on the X chromosome and expressed specificity in the malignant plasma cells. MAGE-C1/CT7 seems to be related to disease progression and functional studies suggests that this CTA might play a role in cell cycle and mainly in survival of malignant plasma cells, protecting myeloma cells against spontaneous as well as drug-induced apoptosis.

TCR gene transfer: MAGE-C2/HLA-A2 and MAGE-A3/HLA-DP4 epitopes as melanoma-specific immune targets

Adoptive therapy with TCR gene-engineered T cells provides an attractive and feasible treatment option for cancer patients. Further development of TCR gene therapy requires the implementation of T-cell target epitopes that prevent “on-target” reactivity towards healthy tissues and at the same time direct a clinically effective response towards tumor tissues. Candidate epitopes that meet these criteria are MAGE-C2_336-344/HLA-A2 (MC2/A2) and MAGE-A3_243-258/HLA-DP4 (MA3/DP4). We molecularly characterized TCRαβ genes of an MC2/A2-specific CD8 and MA3/DP4-specific CD4 T-cell clone derived from melanoma patients who responded clinically to MAGE vaccination. We identified MC2/A2 and MA3/DP4-specific TCR-Vα3/Vβ28 and TCR-Vα38/Vβ2 chains and validated these TCRs in vitro upon gene transfer into primary human T cells. The MC2 and MA3 TCR were surface-expressed and mediated CD8 T-cell functions towards melanoma cell lines and CD4 T-cell functions towards dendritic cells, respectively. We intend to start testing these MAGE-specific TCRs in phase I clinical trial.

Histone deacetylases (HDACs) as mediators of resistance to apoptosis in melanoma and as targets for combination therapy with selective BRAF inhibitors

HDACs are viewed as enzymes used by cancer cells to inhibit tumor suppressor mechanisms. In particular, we discuss their role as suppressors of apoptosis in melanoma cells and as mediators of resistance to selective BRAF inhibitors. Synergistic increases in apoptosis are seen when pan-HDAC inhibitors are combined with selective BRAF inhibitors. Moreover, cell lines from patients with acquired resistance to Vemurafenib undergo PLX4720 induced apoptosis when combined with pan-HDAC inhibitors. The mechanisms of upregulation of HDACs and the mechanisms involved in HDACi reversal of resistance to apoptosis are as yet poorly understood.

TRIM proteins in cancer

Some members of the tripartite motif (TRIM/RBCC) protein family are thought to be important regulators of carcinogenesis. This is not surprising as the TRIM proteins are involved in several biological processes, such as cell growth, development and cellular differentiation and alteration of these proteins can affect transcriptional regulation, cell proliferation and apoptosis. In particular, four TRIM family genes are frequently translocated to other genes, generating fusion proteins implicated in cancer initiation and progression. Among these the most famous is the promyelocytic leukaemia gene PML, which encodes the protein TRIM19. PML is involved in the t(15;17) translocation that specifically occurs in Acute Promyelocytic Leukaemia (APL), resulting in a PML-retinoic acid receptor-alpha (PML-RARalpha) fusion protein. Other members of the TRIM family are linked to cancer development without being involved in chromosomal re-arrangements, possibly through ubiquitination or loss of tumour suppression functions. This chapter discusses the biological functions of TRIM proteins in cancer.

MAGE A1-A6 RT-PCR and MAGE A3 and p16 methylation analysis in induced sputum from patients with lung cancer and non-malignant lung diseases

The melanoma antigen gene (MAGE) A1-A6 RT-PCR system was developed for the detection of lung cancer cells in the sputum. However, we identified MAGE expression in some patients with non-malignant lung diseases. To understand these patterns of MAGE expression, we performed MAGE A3 methylation-specific PCR (MSP) and p16 MSP. We collected 24 biopsy specimens of lung cancer tissue and performed MAGE A1-A6 RT-PCR, MAGE A3 MSP and p16 MSP. RNA and DNA were simultaneously extracted from induced sputum specimens of 133 patients with lung diseases and 30 random sputum specimens of healthy individuals and the 3 molecular analyses were performed. The patients were diagnosed as 65 cases of lung cancer and 68 of benign lung diseases. Positive rates of MAGE A1-A6 RT-PCR, MAGE A3 MSP and p16 MSP were as follows: in lung cancer tissue, 87.5, 58.3 and 70.8%; in the sputum of lung cancer patients, 50.8, 46.2 and 63.1%; benign lung diseases, 10.3, 30.9 and 39.7%; and healthy individuals, 3.3, 6.7 and 3.3%. Of the 40 MAGE-positive cases, 33 were diagnosed with lung cancer and 7 as having benign lung diseases. From the 7 cases of MAGE-positive benign lung diseases, 6 cases showed methylation abnormalities. The MAGE-positive group revealed significantly higher rates of methylation abnormalities. Of the 40 MAGE-positive cases, 39 cases were found to be lung cancer or benign lung diseases with abnormal methylation. Thus, MAGE expression in the sputum suggests the presence of lung cancer cells or pre-cancerous cells.

MageA2 restrains cellular senescence by targeting the function of PMLIV/p53 axis at the PML-NBs

MAGE-A genes are a subfamily of the melanoma antigen genes (MAGEs), whose expression is restricted to tumor cells of different origin and normal tissues of the human germline. Although the specific function of individual MAGE-A proteins is being currently explored, compelling evidence suggest their involvement in the regulation of different pathways during tumor progression. We have previously reported that MageA2 binds histone deacetylase (HDAC)3 and represses p53-dependent apoptosis in response to chemotherapeutic drugs. The promyelocytic leukemia (PML) tumor suppressor is a regulator of p53 acetylation and function in cellular senescence. Here, we demonstrate that MageA2 interferes with p53 acetylation at PML-nuclear bodies (NBs) and with PMLIV-dependent activation of p53. Moreover, a fraction of MageA2 colocalizes with PML-NBs through direct association with PML, and decreases PMLIV sumoylation through an HDAC-dependent mechanism. This reduction in PML post-translational modification promotes defects in PML-NBs formation. Remarkably, we show that in human fibroblasts expressing RasV12 oncogene, MageA2 expression decreases cellular senescence and increases proliferation. These results correlate with a reduction in NBs number and an impaired p53 response. All these data suggest that MageA2, in addition to its anti-apoptotic effect, could have a novel role in the early progression to malignancy by interfering with PML/p53 function, thereby blocking the senescence program, a critical barrier against cell transformation.

Targeting MAGE-C1/CT7 expression increases cell sensitivity to the proteasome inhibitor bortezomib in multiple myeloma cell lines

The MAGE-C1/CT7 encodes a cancer/testis antigen (CTA), is located on the chromosomal region Xq26–27 and is highly polymorphic in humans. MAGE-C1/CT7 is frequently expressed in multiple myeloma (MM) that may be a potential target for immunotherapy in this still incurable disease. MAGEC1/CT7 expression is restricted to malignant plasma cells and it has been suggested that MAGE-C1/CT7 might play a pathogenic role in MM; however, the exact function this protein in the pathophysiology of MM is not yet understood. Our objectives were (1) to clarify the role of MAGE-C1/CT7 in the control of cellular proliferation and cell cycle in myeloma and (2) to evaluate the impact of silencing MAGE-C1/CT7 on myeloma cells treated with bortezomib. Myeloma cell line SKO-007 was transduced for stable expression of shRNA-MAGE-C1/CT7. Downregulation of MAGE-C1/CT7 was confirmed by real time quantitative PCR and western blot. Functional assays included cell proliferation, cell invasion, cell cycle analysis and apoptosis. Western blot showed a 70–80% decrease in MAGE-C1/CT7 protein expression in inhibited cells (shRNA-MAGE-C1/CT7) when compared with controls. Functional assays did not indicate a difference in cell proliferation and DNA synthesis when inhibited cells were compared with controls. However, we found a decreased percentage of cells in the G2/M phase of the cell cycle among inhibited cells, but not in the controls (p<0.05). When myeloma cells were treated with bortezomib, we observed a 48% reduction of cells in the G2/M phase among inhibited cells while controls showed 13% (empty vector) and 9% (ineffective shRNA) reduction, respectively (p<0.01). Furthermore, inhibited cells treated with bortezomib showed an increased percentage of apoptotic cells (Annexin V+/PI-) in comparison with bortezomib-treated controls (p<0.001). We found that MAGE-C1/CT7 protects SKO-007 cells against bortezomib-induced apoptosis. Therefore, we could speculate that MAGE-C1/CT7 gene therapy could be a strategy for future therapies in MM, in particular in combination with proteasome inhibitors.

Androgen receptor molecular biology and potential targets in prostate cancer

The androgen receptor (AR) is a key transcriptional regulator and therapeutic target in prostate cancer. During androgen deprivation therapy to treat metastatic prostate cancer, surviving cells acquire increased AR signaling through a variety of mechanisms, one of which is enhanced interactions with AR coactivators. One recently identified AR-specific coregulator expressed only in human and nonhuman primates is the melanoma antigen gene protein-A11 (MAGE-11). MAGE-11 increases AR transcriptional activity through direct interactions with AR and other coactivators, and its levels increase during prostate cancer progression to castration-recurrent growth. The MAGE-11 gene is located at Xq28 on the human X chromosome as part of an X-linked MAGE gene family of cancer-testis antigens. MAGE-11 stabilizes AR when androgen levels are low, and functions in a transcriptional hub to promote AR-mediated gene activation. The evolutionary development and organization of the MAGE-11 gene within the cancer-testis antigen family suggests that MAGE-11 provides a gain-of-function to AR among primates in both normal physiology and cancer, and may serve as a therapeutic target in the treatment of advanced prostate cancer.

TRIM proteins and cancer

Emerging clinical evidence shows that the deregulation of ubiquitin-mediated degradation of oncogene products or tumour suppressors is likely to be involved in the aetiology of carcinomas and leukaemias. Recent studies have indicated that some members of the tripartite motif (TRIM) proteins (one of the subfamilies of the RING type E3 ubiquitin ligases) function as important regulators for carcinogenesis. This Review focuses on TRIM proteins that are involved in tumour development and progression.

An overview of cancer/testis antigens expression in classical Hodgkin's lymphoma (cHL) identifies MAGE-A family and MAGE-C1 as the most frequently expressed antigens in a set of Brazilian cHL patients

ABSTRACT: BACKGROUND: Cancer/testis antigens are considered potential targets for immunotherapy due to their tumor-associated expression pattern. Although recent studies have demonstrated high expression of CT45 in classical Hodgkin's lymphomas (cHL), less is known about the expression pattern of other families of CTAs in cHL. We aim to evaluate the expression of MAGE-A family, MAGE-C1/CT7, MAGE-C2/CT10, NY-ESO1 and GAGE family in cHL and to correlate their expression with clinical and prognostic factors in cHL. METHODS: Tissue microarray was generated from 38 cHL archival cases from Pathology Department of Universidade Federal de Sao Paulo. Immunohistochemistry (IHC) was done using the following panel of antibodies: MAGE-A family (MA454, M3H67, 57B and 6C1), GAGE (#26), NY-ESO-1 (E978), MAGE-C1/CT7 (CT7-33) and MAGE-C2/CT10 (CT10#5). RESULTS: We found CTA expression in 21.1% of our cHL series. Among the tested CTAs, only MAGE-A family 7/38 (18.4%) and MAGE-C1/CT7 5/38 (13.2%) were positive in our cHL samples. We found higher CTA positivity in advanced stage (28.6%) compared to early stage (11.8%) disease, but this difference was not statistically significant. Analysis of other clinicopathological subgroups of cHL including histological subtypes, EBV status and response to treatment also did not demonstrate statistical significant differences in CTA expression. CONCLUSION: We found CTA expression in 21.1% of cHL samples using our panel. Our preliminary findings suggest that from all CTAs included in this study, MAGE-A family and MAGE-C1/CT7 are the most interesting ones to be explored in further studies.

MAGE-A family: attractive targets for cancer immunotherapy

The melonoma-associated antigens family A (MAGE-A) belongs to cancer/testis antigens (CTA) that are expressed in a wide variety of malignant tumors but not in normal adult tissues except for testis. Interestingly, germ cells do not express MHC class I antigen, implying that these gene products should be ideal targets for cancer immunotherapy. The strict tumor-specific expression of MAGE-As has led to several immunotherapeutic trials targeting some of these proteins. In this review, we briefly described the expression and activation mechanism of MAGE-As in cancer. We also summarized the biological functions of MAGE-As in cell progress and the progress of the cancer immunotherapy targeting MAGE-A family.

Epigenetic alterations associated with cellular senescence: a barrier against tumorigenesis or a red carpet for cancer?

Cellular senescence is eminently characterized by a permanent cell cycle arrest and the acquisition of morphological, physiological and epigenetic changes. The establishment of cellular senescence can occur in response to telomere attrition associated with cell turnover and ageing or following oncogene activation. Although seemingly two distinct phenomena, cellular senescence and cancer share similarly altered global epigenetic profiles comprising changes in DNA methylation, involving global hypomethylation of repetitive DNA sequences and regional hypermethylation of some gene promoters, and in histone post-translational modifications. As epigenetic and genetic alterations are likely to act synergistically in cancer, anomalous epigenetic marks acquired during ageing or in response to oncogene activation might play important roles in tumorigenesis and cancer progression. These potentially tumor-promoting epigenetic alterations include transcriptional repression of genes encoding tumor suppressors or developmentally regulated proteins, expression of non-coding repetitive RNAs and acquisition of distinct heterochromatin marks that may contribute to suppress cell death by reducing DNA damage response. Cellular senescence may thus be viewed as a double-edged sword that, although acting as a potent anti-proliferative barrier, may pave the way to tumorigenesis in senescence-escaping cells by altering their epigenetic make up.

Interaction of p53 with tumor suppressive and oncogenic signaling pathways to control cellular reactive oxygen species production

p53 is a crucial transcription factor with tumor suppressive properties that elicits its function through specific target genes. It constitutes a pivotal system that integrates information received by many signaling pathways and subsequently orchestrates cell fate decisions, namely, growth-arrest, senescence, or apoptosis. Reactive oxygen species (ROS) production in cells can play a key role in signal transduction, being able to trigger different processes as cell death or cell proliferation. Sustained oxidative stress can induce genomic instability and collaborates with cancer development, whereas acute enhancement of high ROS levels leads to toxic oxidative cell damage and cell death. Here, it has been considered p53 broad potential contribution through its ability to regulate selected key cancer signaling pathways, where ROS participate as inductors or effectors of the final biological outcome. Further, we have discussed how p53 could play a role in preventing potentially harmful oxidative state and cell proliferation by pro-oncogenic pathways such as PI3K/AKT/mTOR and WNT/β-catenin or under hypoxia state. In addition, we have considered potential mechanisms by which p53 could collaborate with signal transduction pathways such as transforming growth factor-β (TGF-β) and stress-activated protein kinases (SAPK) that produce ROS, to stop or eliminate uncontrolled proliferating cells.

MAGE I transcription factors regulate KAP1 and KRAB domain zinc finger transcription factor mediated gene repression

Class I MAGE proteins (MAGE I) are normally expressed only in developing germ cells but are aberrantly expressed in many cancers. They have been shown to promote tumor survival, aggressive growth, and chemoresistance but the underlying mechanisms and MAGE I functions have not been fully elucidated. KRAB domain zinc finger transcription factors (KZNFs) are the largest group of vertebrate transcription factors and regulate neoplastic transformation, tumor suppression, cellular proliferation, and apoptosis. KZNFs bind the KAP1 protein and direct KAP1 to specific DNA sequences where it suppresses gene expression by inducing localized heterochromatin characterized by histone 3 lysine 9 trimethylation (H3me3K9). Discovery that MAGE I proteins also bind to KAP1 prompted us to investigate whether MAGE I can affect KZNF and KAP1 mediated gene regulation. We found that expression of MAGE I proteins, MAGE-A3 or MAGE-C2, relieved repression of a reporter gene by ZNF382, a KZNF with tumor suppressor activity. ChIP of MAGE I (-) HEK293T cells showed KAP1 and H3me3K9 are normally bound to the ID1 gene, a target of ZNF382, but that binding is greatly reduced in the presence of MAGE I proteins. MAGE I expression relieved KAP1 mediated ID1 repression, causing increased expression of ID1 mRNA and ID1 chromatin relaxation characterized by loss of H3me3K9. MAGE I binding to KAP1 also induced ZNF382 poly-ubiquitination and degradation, consistent with loss of ZNF382 leading to decreased KAP1 binding to ID1. In contrast, MAGE I expression caused increased KAP1 binding to Ki67, another KAP1 target gene, with increased H3me3K9 and decreased Ki67 mRNA expression. Since KZNFs are required to direct KAP1 to specific genes, these results show that MAGE I proteins can differentially regulate members of the KZNF family and KAP1 mediated gene repression.

MAGED1: molecular insights and clinical implications

The melanoma antigen (MAGE) protein family contains more than 25 members that share a conserved MAGE homology domain (MHD). Type I MAGE genes exhibit cancer/testis-specific expression patterns and antigenic properties which render them ideal candidates for cancer immunotherapies. Maged1, a type II MAGE gene, is ubiquitously expressed and has been previously shown to play an important role in neuronal apoptosis during development. Recent studies have expanded the functional tissues and processes in which Maged1 activity is important and uncovered interacting partners of MAGED1 protein, adding novel layers to Maged1 functions. Maged1 plays a role in anti-tumorigenesis in a variety of cell types, and the down-regulation of MAGED1 has been observed in tumor cells. Moreover, MAGED1 can interact with a specific group of nuclear members and regulate circadian clock functions. These newly identified functions will enrich the molecular and clinical studies of the MAGE family of proteins.

A pathway for the control of anoikis sensitivity by E-cadherin and epithelial-to-mesenchymal transition

Detachment of epithelial cells from matrix or attachment to an inappropriate matrix engages an apoptotic response known as anoikis, which prevents metastasis. Cellular sensitivity to anoikis is compromised during the oncogenic epithelial-to-mesenchymal transition (EMT), through unknown mechanisms. We report here a pathway through which EMT confers anoikis resistance. NRAGE (neurotrophin receptor-interacting melanoma antigen) interacted with a component of the E-cadherin complex, ankyrin-G, maintaining NRAGE in the cytoplasm. Oncogenic EMT downregulated ankyrin-G, enhancing the nuclear localization of NRAGE. The oncogenic transcriptional repressor protein TBX2 interacted with NRAGE, repressing the tumor suppressor gene p14ARF. P14ARF sensitized cells to anoikis; conversely, the TBX2/NRAGE complex protected cells against anoikis by downregulating this gene. This represents a novel pathway for the regulation of anoikis by EMT and E-cadherin.

MAGE-C2/CT10 protein expression is an independent predictor of recurrence in prostate cancer

The cancer-testis (CT) family of antigens is expressed in a variety of malignant neoplasms. In most cases, no CT antigen is found in normal tissues, except in testis, making them ideal targets for cancer immunotherapy. A comprehensive analysis of CT antigen expression has not yet been reported in prostate cancer. MAGE-C2/CT-10 is a novel CT antigen. The objective of this study was to analyze extent and prognostic significance of MAGE-C2/CT10 protein expression in prostate cancer. 348 prostate carcinomas from consecutive radical prostatectomies, 29 castration-refractory prostate cancer, 46 metastases, and 45 benign hyperplasias were immunohistochemically analyzed for MAGE-C2/CT10 expression using tissue microarrays. Nuclear MAGE-C2/CT10 expression was identified in only 3.3% primary prostate carcinomas. MAGE-C2/CT10 protein expression was significantly more frequent in metastatic (16.3% positivity) and castration-resistant prostate cancer (17% positivity; p<0.001). Nuclear MAGE-C2/CT10 expression was identified as predictor of biochemical recurrence after radical prostatectomy (p = 0.015), which was independent of preoperative PSA, Gleason score, tumor stage, and surgical margin status in multivariate analysis (p<0.05). MAGE-C2/CT10 expression in prostate cancer correlates with the degree of malignancy and indicates a higher risk for biochemical recurrence after radical prostatectomy. Further, the results suggest MAGE-C2/CT10 as a potential target for adjuvant and palliative immunotherapy in patients with prostate cancer.

KAP1 protein: an enigmatic master regulator of the genome

In mammalian cells, multiple cellular processes, including gene silencing, cell growth and differentiation, pluripotency, neoplastic transformation, apoptosis, DNA repair, and maintenance of genomic integrity, converge on the evolutionarily conserved protein KAP1, which is thought to regulate the dynamic organization of chromatin structure via its ability to influence epigenetic patterns and chromatin compaction. In this minireview, we discuss how KAP1 might execute such pleiotropic effects, focusing on genomic targeting mechanisms, protein-protein interactions, specific post-translational modifications of both KAP1 and associated histones, and transcriptome analyses of cells deficient in KAP1.

MAGE-A inhibits apoptosis in proliferating myeloma cells through repression of Bax and maintenance of survivin

PURPOSE

The type I Melanoma Antigen GEnes (MAGEs) are commonly expressed in cancers, fueling speculation that they may be therapeutic targets with oncogenic potential. They form complexes with RING domain proteins that have E3 ubiquitin ligase activity and promote p53 degradation. MAGE-A3 was detected in tumor specimens from patients with multiple myeloma and its expression correlated with higher frequencies of Ki-67(+) malignant cells. In this report, we examine the mechanistic role of MAGE-A in promoting survival of proliferating multiple myeloma cells.

EXPERIMENTAL DESIGN

The impact of MAGE-A3 expression on survival and proliferation in vivo was examined by immunohistochemical analysis in an independent set of tumor specimens segregated into two groups: newly diagnosed, untreated patients and patients who had relapsed after chemotherapy. The mechanisms of MAGE-A3 activity were investigated in vitro by silencing its expression by short hairpin RNA interference in myeloma cell lines and primary cells and assessing the resultant effects on proliferation and apoptosis.

RESULTS

MAGE-A3 was detected in a significantly higher percentage of relapsed patients compared with newly diagnosed, establishing a novel correlation with progression of disease. Silencing of MAGE-A showed that it was dispensable for cell cycling, but was required for survival of proliferating myeloma cells. Loss of MAGE-A led to apoptosis mediated by p53-dependent activation of proapoptotic Bax expression and by reduction of survivin expression through both p53-dependent and -independent mechanisms.

CONCLUSIONS

These data support a role for MAGE-A in the pathogenesis and progression of multiple myeloma by inhibiting apoptosis in proliferating myeloma cells through two novel mechanisms.

When MAGE meets RING: insights into biological functions of MAGE proteins

The melanoma antigen (MAGE) family proteins are well known as tumor-specific antigens and comprise more than 60 genes, which share a conserved MAGE homology domain (MHD). Type I MAGEs are highly expressed cancer antigens, and they play an important role in tumorigenesis and cancer cell survival. Recently, several MAGE proteins were identified to interact with RING domain proteins, including a sub-family of E3 ubiquitin ligases. The binding mode between MAGEs and RING proteins was investigated and one important structure of these MAGE-RING complexes was solved: the MAGE-G1-NSE1 complex. Structural and biochemical studies indicated that MAGE proteins could adjust the E3 ubiquitin ligase activity of its cognate RING partner both in vitro and in vivo. However, the underlying mechanism was not fully understood. Here, we review these exciting advances in the studies on MAGE family, suggest potential mechanisms by which MAGEs activate the E3 activity of their binding RING proteins and highlight the anticancer potential of this family proteins.

Identification of novel small molecules that inhibit protein-protein interactions between MAGE and KAP-1

The Class I MAGE proteins are normally expressed only in developing germ cells but are often aberrantly expressed in malignancies, particularly melanoma, making them good therapeutic targets. MAGE proteins promote tumor survival by binding to the RBCC region of KAP-1 and suppressing p53. Although, suppression of MAGE expression, by RNA interference, relieves p53 suppression and inhibits tumor growth, its therapeutic uses are limited by lack of methods for systemic delivery of small interfering RNA. To overcome this barrier, we sought to discover chemical compounds that inhibit binding between MAGE and KAP-1 proteins. Based on previously published effects of MAGE suppression, we developed a strategy for screening a small molecule library based on selective death of MAGE positive cells, activation of p53 and lack of caspase activity. We screened the Maybridge HitFinder library of compounds and eight compounds fulfilled these criteria. Seven of these compounds interfered with co-precipitation of MAGE and KAP-1, and three interfered with binding of MAGE and KAP-1 in a mammalian two hybrid assay. We now report identification of three potential compounds that interfere with MAGE/KAP-1 binding and can be developed as novel chemo-therapeutic agents for treatment of advanced melanoma and other cancers.

MAGE-A10 is a nuclear protein frequently expressed in high percentages of tumor cells in lung, skin and urothelial malignancies

MAGE-A10 is a highly immunogenic member of the MAGE-A family of cancer/testis tumor-associated antigens (C/T TAAs). Studies performed with broadly reactive antibodies have helped to initially characterize this TAA. However, no specific reagents have been developed so far, thus preventing a thorough analysis of its expression in healthy and tumoral tissues. We have produced MAGE-A10 gene product in soluble recombinant form, and we have used it to generate specific monoclonal antibodies (mAbs). One of these reagents, recognizing an epitope located at the COOH terminus of the MAGE-A10 gene product, was used to stain a multitumor tissue microarray comprising more than 2,500 paraffin-embedded specimens including healthy tissues, benign tumors and malignancies of different histological origin. MAGE-A10 protein was identified as an intranuclear protein of an apparent molecular weight of 70 kDa, expressed in normal spermatogonia and spermatocytes but in no other healthy tissue. Most importantly, this C/T TAA appears to be expressed in high (>50%) percentages of cancer cells from a number of malignancies, including lung, skin and urothelial tumors. Unexpectedly, high expression of MAGE-A10 TAA at the protein level was also detectable in gynecological malignancies and stomach and gall bladder cancers. The characterization of MAGE-A10-specific reagents might set the stage for the development of targeted active immunotherapy by clarifying potential indications and by allowing the selection of patients eligible for treatment and the monitoring of its effectiveness.

miR-34a confers chemosensitivity through modulation of MAGE-A and p53 in medulloblastoma

Recent studies have established miR-34a as a key effector of the p53 signaling pathway and have implicated its role in multiple cancer types. Here, we establish that miR-34a induces apoptosis, G2 arrest, and senescence in medulloblastoma and renders these cells more sensitive to chemotherapeutic agents. These effects are mediated in part by the direct post-transcriptional repression of the oncogenic MAGE-A gene family. We demonstrate that miR-34a directly targets the 3' untranslated regions of MAGE-A genes and decreases MAGE-A protein levels. This decrease in MAGE-A results in a concomitant increase in p53 and its associated transcriptional targets, p21/WAF1/CIP1 and, importantly, miR-34a. This establishes a positive feedback mechanism where miR-34a is not only induced by p53 but increases p53 mRNA and protein levels through the modulation of MAGE-A genes. Additionally, the forced expression of miR-34a or the knockdown of MAGE-A genes by small interfering RNA similarly sensitizes medulloblastoma cells to several classes of chemotherapeutic agents, including mitomycin C and cisplatin. Finally, the analysis of mRNA and micro-RNA transcriptional profiles of a series of primary medulloblastomas identifies a subset of tumors with low miR-34a expression and correspondingly high MAGE-A expression, suggesting the coordinate regulation of these genes. Our work establishes a role for miR-34a in modulating responsiveness to chemotherapy in medulloblastoma and presents a novel positive feedback mechanism involving miR-34a and p53, via direct targeting of MAGE-A.

MAGE-RING protein complexes comprise a family of E3 ubiquitin ligases

The melanoma antigen (MAGE) family consists of more than 60 genes, many of which are cancer-testis antigens that are highly expressed in cancer and play a critical role in tumorigenesis. However, the biochemical and cellular functions of this enigmatic family of proteins have remained elusive. Here, we identify really interesting new gene (RING) domain proteins as binding partners for MAGE family proteins. Multiple MAGE family proteins bind E3 RING ubiquitin ligases with specificity. The crystal structure of one of these MAGE-RING complexes, MAGE-G1-NSE1, reveals structural insights into MAGE family proteins and their interaction with E3 RING ubiquitin ligases. Biochemical and cellular assays demonstrate that MAGE proteins enhance the ubiquitin ligase activity of RING domain proteins. For example, MAGE-C2-TRIM28 is shown to target p53 for degradation in a proteasome-dependent manner, consistent with its tumorigenic functions. These findings define a biochemical and cellular function for the MAGE protein family.

Epigenetic modulation of MAGE-A3 antigen expression in multiple myeloma following treatment with the demethylation agent 5-azacitidine and the histone deacetlyase inhibitor MGCD0103

BACKGROUND AIMS

Immunotherapy targeting MAGE-A3 in multiple myeloma (MM) could eradicate highly aggressive and proliferative clonal cell populations responsible for relapse. However, expression of many cancer-testis antigens, including MAGE-A3, can be heterogeneous, leading to the potential for tumor escape despite MAGE-A3-induced immunity. We hypothesized that a combination of the hypomethylating agent 5-azacitidine (5AC) and the histone deacetylase inhibitor (HDACi) MGCD0103 (MGC) could induce MAGE-A3 expression in MAGE-A3-negative MM, resulting in recognition and killing of MM cells by MAGE-A3-specific cytotoxic T lymphocytes (CTL).

METHODS

Gene expression analyses of MAGE-A3 expression in primary MM patient samples at diagnosis and relapse were completed to identify populations that would benefit from MAGE-A3 immunotherapy. MM cell lines were treated with 5AC and MGC. Real-time polymerase chain reaction (PCR) and Western blotting were performed to assess MAGE-A3 RNA and protein levels, respectively. Chromium-release assays and interferon (IFN) secretion assays were employed to ascertain MAGE-A3 CTL specificity against treated targets.

RESULTS

Gene expression analysis revealed that MAGE-A3 is expressed in MM patients at diagnosis (25%) and at relapse (49%). We observed de novo expression of MAGE-A3 RNA and protein in MAGE-A3-negative cell lines treated with 5AC. MGC treatment alone did not induce expression but sequential 5AC/MGC treatment led to enhanced expression and augmented recognition by MAGE-A3-specific CTL, as assessed by (51)Cr-release assays (P = 0.047) and enzyme-linked immunosorbent assay (ELISA) for IFN-γ secretion (P = 0.004).

CONCLUSIONS

MAGE-A3 is an attractive target for immunotherapy of MM and epigenetic modulation by 5AC, and MGC can induce MAGE-A3 expression and facilitate killing by MAGE-A3-specific CTL.

A TCR targeting the HLA-A*0201-restricted epitope of MAGE-A3 recognizes multiple epitopes of the MAGE-A antigen superfamily in several types of cancer

Adoptive immunotherapy using TCR-engineered PBLs against melanocyte differentiation Ags mediates objective tumor regression but is associated with on-target toxicity. To avoid toxicity to normal tissues, we targeted cancer testis Ag (CTA) MAGE-A3, which is widely expressed in a range of epithelial malignancies but is not expressed in most normal tissues. To generate high-avidity TCRs against MAGE-A3, we employed a transgenic mouse model that expresses the human HLA-A*0201 molecule. Mice were immunized with two HLA-A*0201-restricted peptides of MAGE-A3: 112-120 (KVAELVHFL) or MAGE-A3: 271-279 (FLWGPRALV), and T cell clones were generated. MAGE-A3-specific TCR α- and β-chains were isolated and cloned into a retroviral vector. Expression of both TCRs in human PBLs demonstrated Ag-specific reactivity against a range of melanoma and nonmelanoma tumor cells. The TCR against MAGE-A3: 112-120 was selected for further development based on superior reactivity against tumor target cells. Interestingly, peptide epitopes from MAGE-A3 and MAGE-A12 (and to a lesser extent, peptides from MAGE-A2 and MAGE-A6) were recognized by PBLs engineered to express this TCR. To further improve TCR function, single amino acid variants of the CDR3 α-chain were generated. Substitution of alanine to threonine at position 118 of the α-chain in the CDR3 region of the TCR improved its functional avidity in CD4 and CD8 cells. On the basis of these results, a clinical trial is planned in which patients bearing a variety of tumor histologies will receive autologous PBLs that have been transduced with this optimized anti-MAGE-A3 TCR.

Prognostic significance of MAGE in peritoneal washes in gastric carcinoma patients without peritoneal metastasis: results of a 5-year follow-up study

GOALS

The RT-PCR assay of peritoneal washes has been used to predict peritoneal metastasis of gastric carcinoma. We used melanoma associated gene (MAGE) RT-PCR to detect peritoneal metastasis of gastric carcinoma after curative surgery and evaluated its clinical significance.

METHOD

Eighty-four peritoneal washes and 23 tumor and normal tissues were obtained from 84 gastric carcinoma patients. MAGE A1-A6 RT-PCR was carried out, and the results were evaluated according to their clinicopathologic characteristics. Five-year follow-up clinical studies were carried out periodically, and overall survival rates were retrospectively investigated using medical records.

RESULTS

For the paired tumor and normal tissues, MAGE expression rates were 65.2% and 4.3%, respectively. In peritoneal fluids, 11 cases (13.1%) revealed MAGE expression, and higher MAGE expression rates were observed with young age, deeper invasion, and advanced stages of tumor groups. MAGE-positive cases had much higher recurrence rates than MAGE-negative cases (45.5% vs. 9.6%, P<0.002). Among T-stage, N-stage, and MAGE expression; MAGE expression was determined to be the most important prognostic factor for overall survival rate by Cox proportional hazard model analysis.

CONCLUSION

MAGE RT-PCR results for peritoneal fluid disclosed significant associations with peritoneal recurrence of gastric carcinoma and proved to be the most important factor for overall survival rate in gastric carcinoma patients who had undergone radical resection.

Frequent MAGE mutations in human melanoma

BACKGROUND

Cancer/testis (CT) genes are expressed only in the germ line and certain tumors and are most frequently located on the X-chromosome (the CT-X genes). Amongst the best studied CT-X genes are those encoding several MAGE protein families. The function of MAGE proteins is not well understood, but several have been shown to potentially influence the tumorigenic phenotype.

METHODOLOGY/PRINCIPAL FINDINGS

We undertook a mutational analysis of coding regions of four CT-X MAGE genes, MAGEA1, MAGEA4, MAGEC1, MAGEC2 and the ubiquitously expressed MAGEE1 in human melanoma samples. We first examined cell lines established from tumors and matching blood samples from 27 melanoma patients. We found that melanoma cell lines from 37% of patients contained at least one mutated MAGE gene. The frequency of mutations in the coding regions of individual MAGE genes varied from 3.7% for MAGEA1 and MAGEA4 to 14.8% for MAGEC2. We also examined 111 fresh melanoma samples collected from 86 patients. In this case, samples from 32% of the patients exhibited mutations in one or more MAGE genes with the frequency of mutations in individual MAGE genes ranging from 6% in MAGEA1 to 16% in MAGEC1.

SIGNIFICANCE

These results demonstrate for the first time that the MAGE gene family is frequently mutated in melanoma.

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.

Regulation of cancer germline antigen gene expression: implications for cancer immunotherapy

Cancer germline (CG; also known as cancer-testis) antigen genes are normally expressed in germ cells and trophoblast tissues and are aberrantly expressed in a variety of human malignancies. CG antigen genes have high clinical relevance as they encode a class of immunogenic and highly selective tumor antigens. CG antigen-directed immunotherapy is undergoing clinical evaluation for the treatment of a number of solid tumor malignancies and has been demonstrated to be safe, provoke immune responses and be of therapeutic benefit. Achieving an improved understanding of the mechanisms of CG antigen gene regulation will facilitate the continued development of targeted therapeutic approaches against tumors expressing these antigens. Substantial evidence suggests epigenetic mechanisms, particularly DNA methylation, as a primary regulator of CG antigen gene expression in normal and cancer cells as well as in stem cells. The roles of sequence-specific transcription factors and signal transduction pathways in controlling CG antigen gene expression are less clear but are emerging. A combinatorial therapeutic approach involving epigenetic modulatory drugs and CG antigen immunotherapy is suggested based on these data and is being actively pursued. In this article, we review the mechanisms of CG antigen gene regulation and discuss the implications of these mechanisms for the development of cancer immunotherapy approaches targeting CG antigens.

T cell receptor (TCR) gene therapy to treat melanoma: lessons from clinical and preclinical studies

IMPORTANCE OF THE FIELD

Adoptive T cell therapy (ACT) with tumour infiltrating lymphocytes is currently the best treatment option for metastatic melanoma. Despite its clinical successes, ACT has limitations in availability and generation of therapeutic T cells for a larger group of patients. Introduction of tumour-specific T cell receptors into T cells, termed TCR gene therapy, can provide an alternative for ACT that is more widely applicable and might be extended to other types of cancer.

AREAS COVERED IN THIS REVIEW

The current status of TCR gene therapy studies including clinical challenges, such as on-target toxicity, compromised anti-tumour T cell responses, compromised T cell persistence and potential immunogenicity of receptor transgenes. Strategies to address these challenges are covered.

WHAT THE READER WILL GAIN

A listing and discussion of strategies that aim at improving the efficacy and safety of TCR gene therapy. Such strategies address antigen choice, TCR mis-pairing, functional avidity and persistence of T cells, immune responses towards receptor transgenes, and combination of ACT with other therapies.

TAKE HOME MESSAGE

To ensure further clinical development of TCR gene therapy, it is necessary to choose safe T cell target antigens, and implement (combinations of) strategies that enhance the correct pairing of TCR transgenes and the functional avidity and persistence of T cells.

Epigenomic alterations and gene expression profiles in respiratory epithelia exposed to cigarette smoke condensate

Limited information is available regarding epigenomic events mediating initiation and progression of tobacco-induced lung cancers. In this study, we established an in vitro system to examine epigenomic effects of cigarette smoke in respiratory epithelia. Normal human small airway epithelial cells and cdk-4/hTERT-immortalized human bronchial epithelial cells (HBEC) were cultured in normal media with or without cigarette smoke condensate (CSC) for up to 9 months under potentially relevant exposure conditions. Western blot analysis showed that CSC mediated dose- and time-dependent diminution of H4K16Ac and H4K20Me3, while increasing relative levels of H3K27Me3; these histone alterations coincided with decreased DNA methyltransferase 1 (DNMT1) and increased DNMT3b expression. Pyrosequencing and quantitative RT-PCR experiments revealed time-dependent hypomethylation of D4Z4, NBL2, and LINE-1 repetitive DNA sequences; up-regulation of H19, IGF2, MAGE-A1, and MAGE-A3; activation of Wnt signaling; and hypermethylation of tumor suppressor genes such as RASSF1A and RAR-beta, which are frequently silenced in human lung cancers. Array-based DNA methylation profiling identified additional novel DNA methylation targets in soft-agar clones derived from CSC-exposed HBEC; a CSC gene expression signature was also identified in these cells. Progressive genomic hypomethylation and locoregional DNA hypermethylation induced by CSC coincided with a dramatic increase in soft-agar clonogenicity. Collectively, these data indicate that cigarette smoke induces 'cancer-associated' epigenomic alterations in cultured respiratory epithelia. This in vitro model may prove useful for delineating early epigenetic mechanisms regulating gene expression during pulmonary carcinogenesis.