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

H2A.B is a cancer/testis factor involved in the activation of ribosome biogenesis in Hodgkin lymphoma

Testis-specific regulators of chromatin function are commonly ectopically expressed in human cancers, but their roles are poorly understood. Examination of 81 primary Hodgkin lymphoma (HL) samples showed that the ectopic expression of the eutherian testis-specific histone variant H2A.B is an inherent feature of HL. In experiments using two HL cell lines derived from different subtypes of HL, H2A.B knockdown inhibited cell proliferation. H2A.B was enriched in both nucleoli of these HL cell lines and primary HL samples. We found that H2A.B enhanced ribosomal DNA (rDNA) transcription, was enriched at the rDNA promoter and transcribed regions, and interacted with RNA Pol I. Depletion of H2A.B caused the loss of RNA Pol I from rDNA chromatin. Remarkably, H2A.B was also required for high levels of ribosomal protein gene expression being located at the transcriptional start site and within the gene body. H2A.B knockdown reduced gene body chromatin accessibility of active RNA Pol II genes concurrent with a decrease in transcription. Taken together, our data show that in HL H2A.B has acquired a new function, the ability to increase ribosome biogenesis.

Discovery of Novel Protein Biomarkers in Urine for Diagnosis of Urothelial Cancer Using iTRAQ Proteomics

Urothelial carcinoma (UC) is the ninth most prevalent malignancy worldwide. Noninvasive and efficient biomarkers with high accuracy are imperative for the surveillance and diagnosis of UC. CKD patients were enrolled as a control group in this study for the discovery of highly specific urinary protein markers of UC. An iTRAQ-labeled quantitative proteomic approach was used to discover novel potential markers. These markers were further validated with 501 samples by ELISA assay, and their diagnostic accuracies were compared to those of other reported UC markers. BRDT, CYBP, GARS, and HDGF were identified as novel urinary UC biomarkers with a high discrimination ability in a population comprising CKD and healthy subjects. The diagnostic values of the four novel UC markers were better than that of a panel of well-known or FDA-approved urinary protein markers CYFR21.1, Midkine, and NUMA1. Three of our discovered markers (BRDT, HDGF, GARS) and one well-known marker (CYFR21.1) were finally selected and combined as a marker panel having AUC values of 0.962 (95% CI, 0.94-0.98) and 0.860 (95% CI, 0.83-0.89) for the discrimination between UC and normal groups and UC and control (healthy + CKD) groups, respectively.

Short Histone H2A Variants: Small in Stature but not in Function

The dynamic packaging of DNA into chromatin regulates all aspects of genome function by altering the accessibility of DNA and by providing docking pads to proteins that copy, repair and express the genome. Different epigenetic-based mechanisms have been described that alter the way DNA is organised into chromatin, but one fundamental mechanism alters the biochemical composition of a nucleosome by substituting one or more of the core histones with their variant forms. Of the core histones, the largest number of histone variants belong to the H2A class. The most divergent class is the designated “short H2A variants” (H2A.B, H2A.L, H2A.P and H2A.Q), so termed because they lack a H2A C-terminal tail. These histone variants appeared late in evolution in eutherian mammals and are lineage-specific, being expressed in the testis (and, in the case of H2A.B, also in the brain). To date, most information about the function of these peculiar histone variants has come from studies on the H2A.B and H2A.L family in mice. In this review, we describe their unique protein characteristics, their impact on chromatin structure, and their known functions plus other possible, even non-chromatin, roles in an attempt to understand why these peculiar histone variants evolved in the first place.

Knockdown of ATAD2 Inhibits Proliferation and Tumorigenicity Through the Rb-E2F1 Pathway and Serves as a Novel Prognostic Indicator in Gastric Cancer

Introduction

The aim of the present study was to examine the expression of ATAD2 in gastric cancer (GC) specimens and to evaluate its correlation with clinicopathologic features, including survival of GC patients. The potential roles of ATAD2 in the GC cell proliferation, apoptosis, and tumour growth were further explored.

Materials and Methods

Quantitative reverse transcription-polymerase chain reaction (qRT-PCR), Western blotting and immunohistochemistry (IHC) were applied to determine the mRNA and protein expression of ATAD2 in GC and corresponding adjacent non-tumourous specimens. The relationship between ATAD2 expression and clinicopathological features of GC patients was analysed. Kaplan-Meier analysis was performed to assess the prognostic value of ATAD2 expression levels. The proliferation, colony formation, apoptosis and tumorigenesis roles of ATAD2 were measured using in vitro and in vivo experiments.

Results

The expression of ATAD2 mRNA and protein was overexpressed in GC tissues compared with corresponding adjacent non-tumourous tissues. ATAD2 expression was significantly correlated with tumour size, tumour differentiation, and clinical tumour-node-metastasis (TNM) stage. Patients with high ATAD2 expression were likely to experience significantly shorter postoperative overall survival (OS) and disease-free survival (DFS). Multivariate Cox analysis suggested ATAD2 as an independent variable for OS and DFS. Knockdown of ATAD2 significantly suppressed cell proliferation, colony formation in vitro and tumorigenicity in vivo. Cell cycle and apoptotic assays showed that the anti-proliferative effect of pLV-ATAD2 shRNA was mediated by arresting cells in the G1 phase and inducing cell apoptosis. Silencing of ATAD2 reduced the expression of cyclinD1, ppRb, E2F1 and cyclinE and upregulated the expression of cleaved-PARP and cleaved-Caspase 3.

Conclusion

Our study indicated that ATAD2 plays an important role in the process of tumorigenesis and progression in GC, and it could serve as a novel prognostic biomarker and a therapeutic target for the treatment of GC patients.

The Role of Bromodomain Testis-Specific Factor, BRDT, in Cancer: A Biomarker and A Possible Therapeutic Target

Cancer cells have recently been shown to activate hundreds of normally silent tissue-restricted genes, including a specific subset associated with cancer progression and poor prognosis. Within these genes, a class of testis-specific genes designed as cancer/testis, attracted special attention because of their oncogenic roles as well as their potential use in immunotherapy. Here we focus on one of these genes encoding the testis-specific member of the bromodomain and extra-terminal (BET) family, known as BRDT. Aberrant activation of BRDT was first detected in lung cancers. In this study, we report that the frequency of BRDT’s aberrant activation in lung cancer varies according to the histological subtypes and in contrast with other cancer/testis genes, it is rarely expressed in other solid tumours. The functional characterization of BRDT in its physiological setting in male germ cells is now painting a clear portrait of its normal activity and also suggests possible underlying oncogenic activities, when the gene is ectopically activated in cancers. Also, these functional studies of BRDT point to specific anti-cancer therapeutic strategies that could be used to “high-jack” BRDT’s action and turn it against cancer cells, which express this gene. Finally, BRDT’s expression could be used as a biomarker for cell sensitivity to BET bromodomain inhibitors, which have become newly available as anti-cancer drugs.

ATAD2 as a Poor Prognostic Marker for Hepatocellular Carcinoma after Curative Resection

Purpose

Cancer cells frequently express genes that are specifically or preferentially expressed in male germ cells under normal conditions. The ATPase family AAA domain-containing 2 (ATAD2) is one such and works as an important cofactor for MYC-dependent transcription. In hepatocellular carcinoma (HCC), ATAD2 has been identified as a candidate driver gene located within the amplified 8q24 locus. However, the prognostic significance of ATAD2 protein expression in HCC remains uncertain.

Materials and Methods

We investigated ATAD2 protein expression by immunohistochemistry in tumor tissue from 182 HCC patients who underwent curative resection. Associations of ATAD2 expression with clinicopathologic variables or prognosis of HCC patients were analyzed.

Results

ATAD2 expression was observed in 119 (65.4%) of the 182 HCCs and tended to be independent predictor of early recurrence (p=0.059). ATAD2 expression showed an unfavorable influence on recurrence-free survival (RFS) (p < 0.001). Subgroup analysis among patients with tumor size ≤ 5.0 cm (n=109), patients at Barcelona Clinic Liver Cancer stage 0 or A (n=92), and patients with α-fetoprotein ≤ 20 ng/mL (n=61), the ATAD2-positive groups unfavorably influenced RFS (p=0.008, p=0.009, and p=0.013, respectively). In addition, ATAD2 expression was an independent predictor of shorter RFS (p=0.002). ATAD2 expression showed an unfavorable influence on disease-specific survival (p=0.001), but was not an independent predictor of shorter disease-specific survival (p=0.109).

Conclusion

ATAD2 protein expression may be a potential predictor of RFS in HCC patients after curative resection and ATAD2 may have prognostic value in patients with early stage HCC or normal serum α-fetoprotein level.

Sustaining cancer through addictive ectopic gene activation

PURPOSE OF REVIEW

Systematic genetic and epigenetic alterations occurring in almost all cancer cells result in the ectopic expression of a variety of tissue-specific potent regulatory factors. This review sheds light on a new aspect of cancer based on the integration of the 'out of context' activity of tissue-restricted genes into the biology of cancer cells.

RECENT FINDINGS

A systematic screen for the ectopic activation of tissue-restricted genes in a variety of cancers has revealed that many normally silent genes are expressed in tumours of all origins. This aberrant gene activation not only could be used as a source of biomarkers, but also, in several cases, reveals clear oncogenic mechanisms associated with the corresponding ectopically expressed factors.

SUMMARY

The characteristic of all cancer cells, which systematically reprogram tissue-specific gene expression and activate silent genes, can be exploited to develop new anticancer strategies aiming at the detection of malignant states, the prediction of their evolution and drug sensitivity and the discovery of new therapeutic approaches.

Ectopic activation of germline and placental genes identifies aggressive metastasis-prone lung cancers

Activation of normally silent tissue-specific genes and the resulting cell "identity crisis" are the unexplored consequences of malignant epigenetic reprogramming. We designed a strategy for investigating this reprogramming, which consisted of identifying a large number of tissue-restricted genes that are epigenetically silenced in normal somatic cells and then detecting their expression in cancer. This approach led to the demonstration that large-scale "off-context" gene activations systematically occur in a variety of cancer types. In our series of 293 lung tumors, we identified an ectopic gene expression signature associated with a subset of highly aggressive tumors, which predicted poor prognosis independently of the TNM (tumor size, node positivity, and metastasis) stage or histological subtype. The ability to isolate these tumors allowed us to reveal their common molecular features characterized by the acquisition of embryonic stem cell/germ cell gene expression profiles and the down-regulation of immune response genes. The methodical recognition of ectopic gene activations in cancer cells could serve as a basis for gene signature-guided tumor stratification, as well as for the discovery of oncogenic mechanisms, and expand the understanding of the biology of very aggressive tumors.

Identification of a novel BET bromodomain inhibitor-sensitive, gene regulatory circuit that controls Rituximab response and tumour growth in aggressive lymphoid cancers

Immuno-chemotherapy elicit high response rates in B-cell non-Hodgkin lymphoma but heterogeneity in response duration is observed, with some patients achieving cure and others showing refractory disease or relapse. Using a transcriptome-powered targeted proteomics screen, we discovered a gene regulatory circuit involving the nuclear factor CYCLON which characterizes aggressive disease and resistance to the anti-CD20 monoclonal antibody, Rituximab, in high-risk B-cell lymphoma. CYCLON knockdown was found to inhibit the aggressivity of MYC-overexpressing tumours in mice and to modulate gene expression programs of biological relevance to lymphoma. Furthermore, CYCLON knockdown increased the sensitivity of human lymphoma B cells to Rituximab in vitro and in vivo. Strikingly, this effect could be mimicked by in vitro treatment of lymphoma B cells with a small molecule inhibitor for BET bromodomain proteins (JQ1). In summary, this work has identified CYCLON as a new MYC cooperating factor that autonomously drives aggressive tumour growth and Rituximab resistance in lymphoma. This resistance mechanism is amenable to next-generation epigenetic therapy by BET bromodomain inhibition, thereby providing a new combination therapy rationale for high-risk lymphoma.

The nuclear factor CYCLON is a new MYC cooperating factor that drives tumor growth and Rituximab resistance in lymphoma. This resistance mechanism can be targeted by next-generation epigenetic therapy by BET bromodomain inhibition downstream of MYC.

Induced malignant genome reprogramming in somatic cells by testis-specific factors

Germline cell differentiation is controlled by a specific set of genes whose expression is tightly locked into the repressed state in somatic cells. Large-scale epigenome alterations, now evidenced in nearly all cancers, lead to aberrant activation of these normally silenced genes, as attested by the many reports describing the expression of testis-specific factors, known as cancer-testis genes, in various cancer cells. Here, based on the literature, we argue that off-context activity of some of the testis-specific epigenome regulators can reprogram the somatic cell epigenome toward a malignant state by favoring self-renewal and sustaining cell proliferation under stressful conditions, thereby constituting a major oncogenic mechanism.

Coordinated cancer germline antigen promoter and global DNA hypomethylation in ovarian cancer: association with the BORIS/CTCF expression ratio and advanced stage

PURPOSE

Cancer germline (CG) antigens are frequently expressed and hypomethylated in epithelial ovarian cancer (EOC), but the relationship of this phenomenon to global DNA hypomethylation is unknown. In addition, the potential mechanisms leading to DNA hypomethylation, and its clinicopathologic significance in EOC, have not been determined.

EXPERIMENTAL DESIGN

We used quantitative mRNA expression and DNA methylation analyses to determine the relationship between expression and methylation of X-linked (MAGE-A1, NY-ESO-1, XAGE-1) and autosomal (BORIS, SOHLH2) CG genes, global DNA methylation (5mdC levels, LINE-1, Alu, and Sat-α methylation), and clinicopathology, using 75 EOC samples. In addition, we examined the association between these parameters and a number of mechanisms proposed to contribute to DNA hypomethylation in cancer.

RESULTS

CG genes were coordinately expressed in EOC and this was associated with promoter DNA hypomethylation. Hypomethylation of CG promoters was highly correlated and strongly associated with LINE-1 and Alu methylation, moderately with 5mdC levels, and rarely with Sat-α methylation. BORIS and LINE-1 hypomethylation, and BORIS expression, were associated with advanced stage. GADD45A expression, MTHFR genotype, DNMT3B isoform expression, and BORIS mRNA expression did not associate with methylation parameters. In contrast, the BORIS/CTCF expression ratio was associated with DNA hypomethylation, and furthermore correlated with advanced stage and decreased survival.

CONCLUSIONS

DNA hypomethylation coordinately affects CG antigen gene promoters and specific repetitive DNA elements in EOC, and correlates with advanced stage disease. The BORIS/CTCF mRNA expression ratio is closely associated with DNA hypomethylation and confers poor prognosis in EOC.

[Epigenetic perturbations and cancer: innovative therapeutic strategies against cancer]

A complex system of molecular milestones ensures labelling of the genome, driving its organization and functions. These milestones correspond to particular marks associated to active and repressed genes, as well as to non-coding regions or those containing repetitive sequences. Most of these marks are chemical modifications of DNA, corresponding to cytosine methylation, or various posttranslational modifications of histones, the proteins which package the genome. These chemical modifications of DNA or histones are reversible and are catalysed and removed by enzymatic activities associated with factors ensuring critical cellular functions. Indeed, these enzymes are directly connected with signalling pathways, sensing extra- and intracellular environments. Altogether these mechanisms globally control the expression status of genes in each cell, meaning that certain genes are kept active, while most of the genome remains silent. Subtle metabolic changes or intra and extracellular modifications, by altering the marking associated to genes, can have long-term consequences on their expression status. Genes coding for essential regulators of cellular proliferation and differentiation could be among these genes, such as tumor suppressor genes for instance. Hence the knowledge of all these so-called "epigenetic" mechanisms will shed new light on the environmental impact on the control of gene expression and associated diseases, including malignant transformation. The understanding of these mechanisms will also pave the way for innovative therapeutic strategies to fight cancer. This review is aiming to give an overview to the reader of the relevance of epigenetic mechanisms for the understanding and treatment of 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.

Oncogenesis by sequestration of CBP/p300 in transcriptionally inactive hyperacetylated chromatin domains

In a subset of poorly differentiated and highly aggressive carcinoma, a chromosomal translocation, t(15;19)(q13;p13), results in an in-frame fusion of the double bromodomain protein, BRD4, with a testis-specific protein of unknown function, NUT (nuclear protein in testis). In this study, we show that, after binding to acetylated chromatin through BRD4 bromodomains, the NUT moiety of the fusion protein strongly interacts with and recruits p300, stimulates its catalytic activity, initiating cycles of BRD4-NUT/p300 recruitment and creating transcriptionally inactive hyperacetylated chromatin domains. Using a patient-derived cell line, we show that p300 sequestration into the BRD4-NUT foci is the principal oncogenic mechanism leading to p53 inactivation. Knockdown of BRD4-NUT released p300 and restored p53-dependent regulatory mechanisms leading to cell differentiation and apoptosis. This study demonstrates how the off-context activity of a testis-specific factor could markedly alter vital cellular functions and significantly contribute to malignant cell transformation.

Functional characterization of ATAD2 as a new cancer/testis factor and a predictor of poor prognosis in breast and lung cancers

Cancer cells frequently express genes normally active in male germ cells. ATAD2 is one of them encoding a conserved factor harbouring an AAA type ATPase domain and a bromodomain. We show here that ATAD2 is highly expressed in testis as well as in many cancers of different origins and that its high expression is a strong predictor of rapid mortality in lung and breast cancers. These observations suggest that ATAD2 acts on upstream and basic cellular processes to enhance oncogenesis in a variety of unrelated cell types. Accordingly, our functional studies show that ATAD2 controls chromatin dynamics, genome transcriptional activities and apoptotic cell response. We could also highlight some of the important intrinsic properties of its two regulatory domains, including a functional cross-talk between the AAA ATPase domain and the bromodomain. Altogether, these data indicate that ATAD2 overexpression in somatic cells, by acting on basic properties of chromatin, may contribute to malignant transformation.