Intrinsic inhibition of transcription factor E2A by HLH proteins ABF-1 and Id2 mediates reprogramming of neoplastic B cells in Hodgkin lymphoma

Hodgkin lymphoma: Focus on evolving treatment paradigms

Hodgkin lymphoma (HL) is a highly curable B-cell malignancy of germinal center origin. Biologically it is a hematologic malignancy that is highly dependent on the immune microenvironment and utilizes immune escape through upregulation of the programmed-death ligands on the neoplastic cells. Despite being highly curable, consensus is lacking nationally and internationally about the optimal approach to management, particularly in limited-stage disease. The addition of brentuximab vedotin and checkpoint inhibitors for the management of HL has led to a rapidly changing treatment landscape. Further studies should be done to include these novel agents at all stages of disease to determine improvements in frontline cure rates and long-term toxicity.

Transcriptional reprogramming by mutated IRF4 in lymphoma

Disease-causing mutations in genes encoding transcription factors (TFs) can affect TF interactions with their cognate DNA-binding motifs. Whether and how TF mutations impact upon the binding to TF composite elements (CE) and the interaction with other TFs is unclear. Here, we report a distinct mechanism of TF alteration in human lymphomas with perturbed B cell identity, in particular classic Hodgkin lymphoma. It is caused by a recurrent somatic missense mutation c.295 T > C (p.Cys99Arg; p.C99R) targeting the center of the DNA-binding domain of Interferon Regulatory Factor 4 (IRF4), a key TF in immune cells. IRF4-C99R fundamentally alters IRF4 DNA-binding, with loss-of-binding to canonical IRF motifs and neomorphic gain-of-binding to canonical and non-canonical IRF CEs. IRF4-C99R thoroughly modifies IRF4 function by blocking IRF4-dependent plasma cell induction, and up-regulates disease-specific genes in a non-canonical Activator Protein-1 (AP-1)-IRF-CE (AICE)-dependent manner. Our data explain how a single mutation causes a complex switch of TF specificity and gene regulation and open the perspective to specifically block the neomorphic DNA-binding activities of a mutant TF.

Classic Hodgkin lymphoma in young people

Classic Hodgkin lymphoma (CHL) is a unique form of lymphoid cancer featuring a heterogeneous tumor microenvironment and a relative paucity of malignant Hodgkin and Reed-Sternberg (HRS) cells with characteristic phenotype. Younger individuals (children, adolescents and young adults) are affected as often as the elderly, producing a peculiar bimodal age-incidence profile that has generated immense interest in this disease and its origins. Decades of epidemiological investigations have documented the populations most susceptible and identified multiple risk factors that can be broadly categorized as either biological or environmental in nature. Most risk factors result in overt immunodeficiency or confer more subtle alterations to baseline health, physiology or immune function. Epstein Barr virus, however, is both a risk factor and well-established driver of lymphomagenesis in a significant subset of cases. Epigenetic changes, along with the accumulation of somatic driver mutations and cytogenetic abnormalities are required for the malignant transformation of germinal center-experienced HRS cell precursors. Chromosomal instability and the influence of endogenous mutational processes are critical in this regard, by impacting genes involved in key signaling pathways that promote the survival and proliferation of HRS cells and their escape from immune destruction. Here we review the principal features, known risk factors and lymphomagenic mechanisms relevant to newly diagnosed CHL, with an emphasis on those most applicable to young people.

Role of Interleukin-22 in ulcerative colitis

Ulcerative Colitis (UC) is a chronic disease, in the progression of which an immune overreaction may play an important role. IL-22 is a member of the IL-10 superfamily of cytokines and is pleiotropic in immune regulation and inflammatory responses. IL-22 can produce protective effects, promote wound healing and tissue regeneration, while it can also induce inflammatory reactions when it is chronically overexpressed. Extensive literatures reported that IL-22 played an essential role in the pathogenic development of UC. IL-22 participates in the whole disease process of UC involving signaling pathways, gene expression regulation, and intestinal flora imbalance, making IL-22 a possible candidate for the treatment of UC. In this paper, the latest knowledge to further elucidate the role of IL-22 in UC was summarized and analyzed.

A multimorphic mutation in IRF4 causes human autosomal dominant combined immunodeficiency

Interferon regulatory factor 4 (IRF4) is a transcription factor (TF) and key regulator of immune cell development and function. We report a recurrent heterozygous mutation in IRF4, p.T95R, causing an autosomal dominant combined immunodeficiency (CID) in seven patients from six unrelated families. The patients exhibited profound susceptibility to opportunistic infections, notably Pneumocystis jirovecii, and presented with agammaglobulinemia. Patients' B cells showed impaired maturation, decreased immunoglobulin isotype switching, and defective plasma cell differentiation, whereas their T cells contained reduced TH17 and TFH populations and exhibited decreased cytokine production. A knock-in mouse model of heterozygous T95R showed a severe defect in antibody production both at the steady state and after immunization with different types of antigens, consistent with the CID observed in these patients. The IRF4T95R variant maps to the TF's DNA binding domain, alters its canonical DNA binding specificities, and results in a simultaneous multimorphic combination of loss, gain, and new functions for IRF4. IRF4T95R behaved as a gain-of-function hypermorph by binding to DNA with higher affinity than IRF4WT. Despite this increased affinity for DNA, the transcriptional activity on IRF4 canonical genes was reduced, showcasing a hypomorphic activity of IRF4T95R. Simultaneously, IRF4T95R functions as a neomorph by binding to noncanonical DNA sites to alter the gene expression profile, including the transcription of genes exclusively induced by IRF4T95R but not by IRF4WT. This previously undescribed multimorphic IRF4 pathophysiology disrupts normal lymphocyte biology, causing human disease.

Lineage switch from lymphoma to myeloid neoplasms: First case series from a single institution

Lymphoma relapse is very common in clinical work, but lineage switch at relapse is rare. Although some cases have reported acute lymphocytic leukemia (ALL) switch to acute myeloid leukemia (AML) or myeloid sarcoma upon relapse, phenotype switch seldom occurs in other types of lymphoma. Here we report six cases with lineage switch from lymphoma to myeloid neoplasms. In our cohort, three cases were mantle cell lymphoma (MCL), and the other three cases were T-cell lymphoblastic lymphoma (T-LBL), B-cell lymphoblastic lymphoma (B-LBL), and diffuse large B-cell lymphoma (DLBCL) at the initial diagnosis. When linage switch occurred, most cases were AML M5 phenotypes, and only one case was myelodysplastic syndrome (MDS) phenotype. 11q23/mixed-lineage leukemia (MLL) rearrangement was negative in all cases. Although intensive therapy and stem cell transplantation have been applied in most cases, the poor outcome cannot be reversed. Therefore, we found that lineage switch could occur not only from ALL to AML or vice versa, but also from MCL or DLBCL to AML. Moreover, the incidence of MLL rearrangement in lineage switch is lower in adult hematologic malignancies as compared with pediatric patients.

The Pathogenic Roles of IL-22 in Colitis: Its Transcription Regulation by Musculin in T Helper Subsets and Innate Lymphoid Cells

IL-22 plays a crucial role in promoting inflammation, antimicrobial immunity and tissue repair at barrier surfaces. The role of IL-22 in colitis is still controversial: while IL-22 has a protective effect on gut epithelium in acute injuries, it also enhances colitis in a context-dependent manner. Here, we summarize the Yin and Yang of IL-22 in colitis. Particularly, we emphasize the role of innate lymphoid cells (ILCs) in IL-22 production and regulation. A previously underappreciated transcription factor, Musculin (MSC), has been recently identified to be expressed in not only Th17 cells, but also RORγt+/Id2+ IL-22-producing group 3 ILCs in the gut of naïve mice. We hypothesize that the co-expression and interaction of MSC with the key transcription repressor Id2 in developing lymphoid cells (e.g., in LTi cells) and ILC precursors might fine tune the developmental programs or regulate the plasticity of adaptive Th subset and innate ILCs. The much-elevated expression of IL-22 in MSC-/- ILC3s suggests that MSC may function as: 1) a transcription suppressor for cytokines, particularly for IL-22, and/or 2) a gatekeeper for specific lineages of Th cells and innate ILCs as well. Amelioration of colitis symptoms in MSC-/- mice by IL-22-blocking agent IL-22BP-Fc suggests a counterintuitive pathogenic role of IL-22 in the absence of MSC as a checkpoint. The theory that exuberant production of IL-22 under pathological conditions (e.g., in human inflammatory bowel disease, IBD) may cause epithelial inflammation due to endoplasmic reticulum (ER) stress response is worth further investigation. Rheostatic regulation of IL-22 may be of therapeutic value to restore homeostatic balance and promote intestinal health in human colitis.

Establishment of the TBX-code reveals aberrantly activated T-box gene TBX3 in Hodgkin lymphoma

T-box genes encode transcription factors which control basic processes in development of several tissues including cell differentiation in the hematopoietic system. Here, we analyzed the physiological activities of all 17 human T-box genes in early hematopoiesis and in lymphopoiesis including developing and mature B-cells, T-cells, natural killer (NK)-cells and innate lymphoid cells. The resultant expression pattern comprised six genes, namely EOMES, MGA, TBX1, TBX10, TBX19 and TBX21. We termed this gene signature TBX-code which enables discrimination of normal and aberrant activities of T-box genes in lymphoid malignancies. Accordingly, expression analysis of T-box genes in Hodgkin lymphoma (HL) patients using a public profiling dataset revealed overexpression of EOMES, TBX1, TBX2, TBX3, TBX10, TBX19, TBX21 and TBXT while MGA showed aberrant downregulation. Analysis of T-cell acute lymphoid leukemia patients indicated aberrant overexpression of six T-box genes while no deregulated T-box genes were detected in anaplastic large cell lymphoma patients. As a paradigm we focused on TBX3 which was ectopically activated in about 6% of HL patients analyzed. Normally, TBX3 is expressed in tissues like lung, adrenal gland and retina but not in hematopoiesis. HL cell line KM-H2 expressed enhanced TBX3 levels and was used as an in vitro model to identify upstream regulators and downstream targets in this malignancy. Genomic studies of this cell line showed focal amplification of the TBX3 locus at 12q24 which may underlie its aberrant expression. In addition, promoter analysis and comparative expression profiling of HL cell lines followed by knockdown experiments revealed overexpressed transcription factors E2F4 and FOXC1 and chromatin modulator KDM2B as functional activators. Furthermore, we identified repressed target genes of TBX3 in HL including CDKN2A, NFKBIB and CD19, indicating its respective oncogenic function in proliferation, NFkB-signaling and B-cell differentiation. Taken together, we have revealed a lymphoid TBX-code and used it to identify an aberrant network around deregulated T-box gene TBX3 in HL which promotes hallmark aberrations of this disease. These findings provide a framework for future studies to evaluate deregulated T-box genes in lymphoid malignancies.

Hodgkin Lymphoma: A Special Microenvironment

Classical Hodgkin’s lymphoma (cHL) is one of the most particular lymphomas for the few tumor cells surrounded by an inflammatory microenvironment. Reed-Sternberg (RS) and Hodgkin (H) cells reprogram and evade antitumor mechanisms of the normal cells present in the microenvironment. The cells of microenvironment are essential for growth and survival of the RS/H cells and are recruited through the effect of cytokines/chemokines. We summarize recent advances in gene expression profiling (GEP) analysis applied to study microenvironment component in cHL. We also describe the main therapies that target not only the neoplastic cells but also the cellular components of the background.

Musculin Deficiency Aggravates Colonic Injury and Inflammation in Mice with Inflammatory Bowel Disease

Intestinal inflammatory reactions and resulting tissue injuries are two major aspects of inflammatory bowel disease (IBD). The regulatory factors involved in the pathogenesis of IBD remain unclear. Recent studies showed that musculin (MSC) as a transcription suppressor participates in the regulation of certain immune functions. The purpose of this study was to determine the impact of MSC deficiency on colonic injury and inflammatory reaction under IBD, where wild-type (WT, +/+) and MSC-knockout (MSCKO, MSC-/-) mice were induced for disease by dextran sulfate sodium (DSS) in drinking water. Immunohistochemistry hematoxylin-eosin (H&E) staining, enzyme-linked immunosorbent assay (ELISA), and quantitative real-time polymerase chain reaction (qRT-PCR) were used to analyze the matching samples from groups of different genotypes. The colonic epithelial injury in the MSC-/- IBD group was much severer than that in the +/+ IBD group, concurrent with higher IL-22 levels from the supernatant of ex vivo cultured colon tissues in the MSC-/- IBD group than those in the +/+ IBD group. The mRNA levels of IL-22 in mesenteric lymph nodes (MLN) also manifested similar tendency. MSC deficiency may enhance the inflammatory reactions in the gut via excessive secretion of IL-22, leading to aggravated colonic epithelial injury under IBD.

Establishment of the TALE-code reveals aberrantly activated homeobox gene PBX1 in Hodgkin lymphoma

Homeobox genes encode transcription factors which regulate basic processes in development and cell differentiation and are grouped into classes and subclasses according to sequence similarities. Here, we analyzed the activities of the 20 members strong TALE homeobox gene class in early hematopoiesis and in lymphopoiesis including developing and mature B-cells, T-cells, natural killer (NK)-cells and innate lymphoid cells (ILC). The resultant expression pattern comprised eleven genes and which we termed TALE-code enables discrimination of normal and aberrant activities of TALE homeobox genes in lymphoid malignancies. Subsequent expression analysis of TALE homeobox genes in public datasets of Hodgkin lymphoma (HL) patients revealed overexpression of IRX3, IRX4, MEIS1, MEIS3, PBX1, PBX4 and TGIF1. As paradigm we focused on PBX1 which was deregulated in about 17% HL patients. Normal PBX1 expression was restricted to hematopoietic stem cells and progenitors of T-cells and ILCs but absent in B-cells, reflecting its roles in stemness and early differentiation. HL cell line SUP-HD1 expressed enhanced PBX1 levels and served as an in vitro model to identify upstream regulators and downstream targets in this malignancy. Genomic studies of this cell line therein showed a gain of the PBX1 locus at 1q23 which may underlie its aberrant expression. Comparative expression profiling analyses of HL patients and cell lines followed by knockdown experiments revealed NFIB and TLX2 as target genes activated by PBX1. HOX proteins operate as cofactors of PBX1. Accordingly, our data showed that HOXB9 overexpressed in HL coactivated TLX2 but not NFIB while activating TNFRSF9 without PBX1. Further downstream analyses showed that TLX2 activated TBX15 which operated anti-apoptotically. Taken together, we discovered a lymphoid TALE-code and identified an aberrant network around deregulated TALE homeobox gene PBX1 which may disturb B-cell differentiation in HL by reactivation of progenitor-specific genes. These findings may provide the framework for future studies to exploit possible vulnerabilities of malignant cells in therapeutic scenarios.

Hodgkin lymphoma

Hodgkin lymphoma (HL) is a B cell lymphoma characterized by few malignant cells and numerous immune effector cells in the tumour microenvironment. The incidence of HL is highest in adolescents and young adults, although HL can affect elderly individuals. Diagnosis is based on histological and immunohistochemical analyses of tissue from a lymph node biopsy; the tissue morphology and antigen expression profile enable classification into one of the four types of classic HL (nodular sclerosis, mixed cellularity, lymphocyte-depleted or lymphocyte-rich HL), which account for the majority of cases, or nodular lymphocyte-predominant HL. Although uncommon, HL remains a crucial test case for progress in cancer treatment. HL was among the first systemic neoplasms shown to be curable with radiation therapy and multiagent chemotherapy. The goal of multimodality therapy is to minimize lifelong residual treatment-associated toxicity while maintaining high levels of effectiveness. Recurrent or refractory disease can be effectively treated or cured with high-dose chemotherapy followed by autologous haematopoietic stem cell transplantation, and prospective trials have demonstrated the potency of immunotherapeutic approaches with antibody-drug conjugates and immune checkpoint inhibitors. This Primer explores the wealth of information that has been assembled to understand HL; these updated observations verify that HL investigation and treatment remain at the leading edge of oncological research.

An EBNA3A-Mutated Epstein-Barr Virus Retains the Capacity for Lymphomagenesis in a Cord Blood-Humanized Mouse Model

Epstein-Barr virus (EBV) causes B cell lymphomas and transforms B cells in vitro The EBV protein EBNA3A collaborates with EBNA3C to repress p16 expression and is required for efficient transformation in vitro An EBNA3A deletion mutant EBV strain was recently reported to establish latency in humanized mice but not cause tumors. Here, we compare the phenotypes of an EBNA3A mutant EBV (Δ3A) and wild-type (WT) EBV in a cord blood-humanized (CBH) mouse model. The hypomorphic Δ3A mutant, in which a stop codon is inserted downstream from the first ATG and the open reading frame is disrupted by a 1-bp insertion, expresses very small amounts of EBNA3A using an alternative ATG at residue 15. Δ3A caused B cell lymphomas at rates similar to their induction by WT EBV but with delayed onset. Δ3A and WT tumors expressed equivalent levels of EBNA2 and p16, but Δ3A tumors in some cases had reduced LMP1. Like the WT EBV tumors, Δ3A lymphomas were oligoclonal/monoclonal, with typically one dominant IGHV gene being expressed. Transcriptome sequencing (RNA-seq) analysis revealed small but consistent gene expression differences involving multiple cellular genes in the WT EBV- versus Δ3A-infected tumors and increased expression of genes associated with T cells, suggesting increased T cell infiltration of tumors. Consistent with an impact of EBNA3A on immune function, we found that the expression of CLEC2D, a receptor that has previously been shown to influence responses of T and NK cells, was markedly diminished in cells infected with EBNA3A mutant virus. Together, these studies suggest that EBNA3A contributes to efficient EBV-induced lymphomagenesis in CBH mice.IMPORTANCE The EBV protein EBNA3A is expressed in latently infected B cells and is important for efficient EBV-induced transformation of B cells in vitro In this study, we used a cord blood-humanized mouse model to compare the phenotypes of an EBNA3A hypomorph mutant virus (Δ3A) and wild-type EBV. The Δ3A virus caused lymphomas with delayed onset compared to the onset of those caused by WT EBV, although the tumors occurred at a similar rate. The WT EBV and EBNA3A mutant tumors expressed similar levels of the EBV protein EBNA2 and cellular protein p16, but in some cases, Δ3A tumors had less LMP1. Our analysis suggested that Δ3A-infected tumors have elevated T cell infiltrates and decreased expression of the CLEC2D receptor, which may point to potential novel roles of EBNA3A in T cell and NK cell responses to EBV-infected tumors.

Recurrent MSC E116K mutations in ALK-negative anaplastic large cell lymphoma

Anaplastic large cell lymphomas (ALCLs) represent a relatively common group of T-cell non-Hodgkin lymphomas (T-NHLs) that are unified by similar pathologic features but demonstrate marked genetic heterogeneity. ALCLs are broadly classified as being anaplastic lymphoma kinase (ALK)⁺ or ALK^-, based on the presence or absence of ALK rearrangements. Exome sequencing of 62 T-NHLs identified a previously unreported recurrent mutation in the musculin gene, MSC ^E116K, exclusively in ALK^- ALCLs. Additional sequencing for a total of 238 T-NHLs confirmed the specificity of MSC ^E116K for ALK^- ALCL and further demonstrated that 14 of 15 mutated cases (93%) had coexisting DUSP22 rearrangements. Musculin is a basic helix-loop-helix (bHLH) transcription factor that heterodimerizes with other bHLH proteins to regulate lymphocyte development. The E116K mutation localized to the DNA binding domain of musculin and permitted formation of musculin-bHLH heterodimers but prevented their binding to authentic target sequence. Functional analysis showed MSC^E116K acted in a dominant-negative fashion, reversing wild-type musculin-induced repression of MYC and cell cycle inhibition. Chromatin immunoprecipitation-sequencing and transcriptome analysis identified the cell cycle regulatory gene E2F2 as a direct transcriptional target of musculin. MSC^E116K reversed E2F2-induced cell cycle arrest and promoted expression of the CD30-IRF4-MYC axis, whereas its expression was reciprocally induced by binding of IRF4 to the MSC promoter. Finally, ALCL cells expressing MSC ^E116K were preferentially targeted by the BET inhibitor JQ1. These findings identify a novel recurrent MSC mutation as a key driver of the CD30-IRF4-MYC axis and cell cycle progression in a unique subset of ALCLs.

Expression of ELF1, a lymphoid ETS domain-containing transcription factor, is recurrently lost in classical Hodgkin lymphoma

Loss of B cell-specific transcription factors (TFs) and the resulting loss of B-cell phenotype of Hodgkin and Reed-Sternberg (HRS) cells is a hallmark of classical Hodgkin lymphoma (cHL). Here we have analysed two members of ETS domain containing TFs, ELF1 and ELF2, regarding (epi)genomic changes as well as gene and protein expression. We observed absence or lower levels of ELF1 protein in HRS cells of 31/35 (89%) cases compared to the bystander cells and significant (P < 0·01) downregulation of the gene on mRNA as well as protein level in cHL compared to non-cHL cell lines. However, no recurrent loss of ELF2 protein was observed. Moreover, ELF1 was targeted by heterozygous deletions combined with hypermethylation of the remaining allele(s) in 4/7 (57%) cell lines. Indeed, DNA hypermethylation (range 95-99%, mean 98%) detected in the vicinity of the ELF1 transcription start site was found in all 7/7 (100%) cHL cell lines. Similarly, 5/18 (28%) analysed primary biopsies carried heterozygous deletions of the gene. We demonstrate that expression of ELF1 is impaired in cHL through genetic and epigenetic alterations, and thus, it may represent an additional member of a TF network whose downregulation contributes to the loss of B-cell phenotype of HRS cells.

NKL homeobox gene NKX2-2 is aberrantly expressed in Hodgkin lymphoma

NKL homeobox genes encode basic transcriptional regulators of cell and tissue differentiation. Recently, we described a hematopoietic NKL-code comprising nine specific NKL homeobox genes expressed in normal hematopoietic stem cells, lymphoid progenitors and during lymphopoiesis, highlighting their physiological role in the development of T-, B- and NK-cells. Here, we identified aberrant expression of the non-hematopoietic neural NKL homeobox gene NKX2-2 in about 12% of both, classical Hodgkin lymphoma (HL) and nodular lymphocyte predominant (NLP) HL patients. The NKX2-2 expressing NLPHL-derived cell line DEV served as a model by analysing chromosomal configurations and expression profiling data to reveal activating mechanisms and downstream targets of this developmental regulator. While excluding chromosomal rearrangements at the locus of NKX2-2 we identified t(3;14)(p21;q32) resulting in overexpression of the IL17 receptor gene IL17RB via juxtaposition with the IGH-locus. SiRNA-mediated knockdown experiments demonstrated that IL17RB activated NKX2-2 transcription. Overexpression of IL17RB-cofactor DAZAP2 via chromosomal gain of 12q13 and deletion of its proteasomal inhibitor SMURF2 at 17q24 supported expression of NKX2-2. IL17RB activated transcription factors FLI1 and FOXG1 which in turn mediated NKX2-2 expression. In addition, overexpressed chromatin-modulator AUTS2 contributed to NKX2-2 activation as well. Downstream analyses indicated that NKX2-2 inhibits transcription of lymphoid NKL homeobox gene MSX1 and activates expression of basic helix-loop-helix factor NEUROD1 which may disturb B-cell differentiation processes via reported interaction with TCF3/E2A. Taken together, our data reveal ectopic activation of a neural gene network in HL placing NKX2-2 at its hub, highlighting a novel oncogenic impact of NKL homeobox genes in B-cell malignancies.

The role of inhibitor of binding or differentiation 2 in the development and differentiation of immune cells

Inhibitor of binding or differentiation 2 (Id2), a member of helix-loop-helix (HLH) transcriptional factors, is recently reported as an important regulator of the development or differentiation of immune cells. It has been demonstrated that Id2 plays a critical role in the early lymphopoiesis. However, it has been discovered recently that Id2 displays new functions in different immune cells. In the adaptive immune cells, Id2 is required for determining T-cell subsets and B cells. In addition, Id2 is also involved in the development of innate immune cells, including dendritic cells (DCs), natural killer (NK) cells, and other innate lymphoid cells (ILCs). Here, we review the current reports about the role of Id2 in the development or differentiation of main immune cells.

Co-Expression of the Epstein-Barr Virus-Encoded Latent Membrane Proteins and the Pathogenesis of Classic Hodgkin Lymphoma

The Epstein-Barr virus (EBV) is present in the tumour cells of a subset of patients with classic Hodgkin lymphoma (cHL), yet the contribution of the virus to the pathogenesis of these tumours remains only poorly understood. The EBV genome in virus-associated cHL expresses a limited subset of genes, restricted to the non-coding Epstein-Barr virus-encoded RNAs (EBERs) and viral miRNA, as well as only three virus proteins; the Epstein-Barr virus nuclear antigen-1 (EBNA1), and the two latent membrane proteins, known as LMP1 and LMP2, the latter of which has two isoforms, LMP2A and LMP2B. LMP1 and LMP2A are of particular interest because they are co-expressed in tumour cells and can activate cellular signalling pathways, driving aberrant cellular transcription in infected B cells to promote lymphomagenesis. This article seeks to bring together the results of recent studies of the latent membrane proteins in different B cell systems, including experiments in animal models as well as a re-analysis of our own transcriptional data. In doing so, we summarise the potentially co-operative and antagonistic effects of the LMPs that are relevant to B cell lymphomagenesis.

Paradoxical role of Id proteins in regulating tumorigenic potential of lymphoid cells

A family of transcription factors known as Id proteins, or inhibitor of DNA binding and differentiation, is capable of regulating cell proliferation, survival and differentiation, and is often upregulated in multiple types of tumors. Due to their ability to promote self-renewal, Id proteins have been considered as oncogenes, and potential therapeutic targets in cancer models. On the contrary, certain Id proteins are reported to act as tumor suppressors in the development of Burkitt's lymphoma in humans, and hepatosplenic and innate-like T cell lymphomas in mice. The contexts and mechanisms by which Id proteins can serve in such contradictory roles to determine tumor outcomes are still not well understood. In this review, we explore the roles of Id proteins in lymphocyte development and tumorigenesis, particularly with respect to inhibition of their canonical DNA binding partners known as E proteins. Transcriptional regulation by E proteins, and their antagonism by Id proteins, act as gatekeepers to ensure appropriate lymphocyte development at key checkpoints. We re-examine the derailment of these regulatory mechanisms in lymphocytes that facilitate tumor development. These mechanistic insights can allow better appreciation of the context-dependent roles of Id proteins in cancers and improve considerations for therapy.

Landscape of transcriptional deregulation in lung cancer

BACKGROUND

Lung cancer is a very heterogeneous disease that can be pathologically classified into different subtypes including small-cell lung carcinoma (SCLC), lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC) and large-cell carcinoma (LCC). Although much progress has been made towards the oncogenic mechanism of each subtype, transcriptional circuits mediating the upstream signaling pathways and downstream functional consequences remain to be systematically studied.

RESULTS

Here we trained a one-class support vector machine (OC-SVM) model to establish a general transcription factor (TF) regulatory network containing 325 TFs and 18724 target genes. We then applied this network to lung cancer subtypes and identified those deregulated TFs and downstream targets. We found that the TP63/SOX2/DMRT3 module was specific to LUSC, corresponding to squamous epithelial differentiation and/or survival. Moreover, the LEF1/MSC module was specifically activated in LUAD and likely to confer epithelial-to-mesenchymal transition, known important for cancer malignant progression and metastasis. The proneural factor, ASCL1, was specifically up-regulated in SCLC which is known to have a neuroendocrine phenotype. Also, ID2 was differentially regulated between SCLC and LUSC, with its up-regulation in SCLC linking to energy supply for fast mitosis and its down-regulation in LUSC linking to the attenuation of immune response. We further described the landscape of TF regulation among the three major subtypes of lung cancer, highlighting their functional commonalities and specificities.

CONCLUSIONS

Our approach uncovered the landscape of transcriptional deregulation in lung cancer, and provided a useful resource of TF regulatory network for future studies.

Aberrant expression of NKL homeobox gene HLX in Hodgkin lymphoma

NKL homeobox genes are basic regulators of cell and tissue differentiation, many acting as oncogenes in T-cell leukemia. Recently, we described an hematopoietic NKL-code comprising six particular NKL homeobox genes expressed in hematopoietic stem cells and lymphoid progenitors, unmasking their physiological roles in the development of these cell types. Hodgkin lymphoma (HL) is a B-cell malignancy showing aberrant activity of several developmental genes resulting in disturbed B-cell differentiation. To examine potential concordances in abnormal lymphoid differentiation of T- and B-cell malignancies we analyzed the expression of the hematopoietic NKL-code associated genes in HL, comprising HHEX, HLX, MSX1, NKX2-3, NKX3-1 and NKX6-3. Our approach revealed aberrant HLX activity in 8 % of classical HL patients and additionally in HL cell line L-540. Accordingly, to identify upstream regulators and downstream target genes of HLX we used L-540 cells as a model and performed chromosome and genome analyses, comparative expression profiling and functional assays via knockdown and overexpression experiments therein. These investigations excluded chromosomal rearrangements of the HLX locus at 1q41 and demonstrated that STAT3 operated directly as transcriptional activator of the HLX gene. Moreover, subcellular analyses showed highly enriched STAT3 protein in the nucleus of L-540 cells which underwent cytoplasmic translocation by repressing deacetylation. Finally, HLX inhibited transcription of B-cell differentiation factors MSX1, BCL11A and SPIB and of pro-apoptotic factor BCL2L11/BIM, thereby suppressing Etoposide-induced cell death. Collectively, we propose that aberrantly expressed NKL homeobox gene HLX is part of a pathological gene network in HL, driving deregulated B-cell differentiation and survival.

Fine-tuning of FOXO3A in cHL as a survival mechanism and a hallmark of abortive plasma cell differentiation

We recently found that FOXO1 repression contributes to the oncogenic program of classical Hodgkin lymphoma (cHL). Interestingly, FOXO3A, another member of the FOXO family, was reported to be expressed in the malignant Hodgkin and Reed-Sternberg cells of cHL at higher levels than in non-Hodgkin lymphoma subtypes. We thus aimed to investigate mechanisms responsible for the maintenance of FOXO3A as well as the potential role of FOXO3A in cHL. Here, we show that high FOXO3A levels in cHL reflect a B-cell-differentiation-specific pattern. In B cells, FOXO3A expression increases during the process of centroblast to plasma cell (PC) differentiation. FOXO3A levels in cHL were found higher than in germinal center B cells, but lower than in terminally differentiated PCs. This intermediate FOXO3A expression in cHL might manifest the "abortive PC differentiation" phenotype. This assumption was further corroborated by the finding that overexpression of FOXO3A in cHL cell lines induced activation of the master PC transcription factor PRDM1α. As factors attenuating FOXO3A expression in cHL, we identified MIR155 and constitutive activation of extracellular signal-regulated kinase. Finally, we demonstrate the importance of FOXO3A expression in cHL using an RNA interference approach. We conclude that tightly regulated expression of FOXO3A contributes to the oncogenic program and to the specific phenotype of cHL.

Repression of TCF3/E2A contributes to Hodgkin lymphomagenesis

Although Hodgkin and Reed-Sternberg (HRS) cells of classical Hodgkin lymphoma (cHL) derived from germinal or post germinal B cells, they have lost the B cell phenotype in the process of lymphomagenesis. The phenomenon can be at least partially explained by repression of B-cell-specific transcription factors including TCF3, early B-cell factor 1 (EBF1), SPI1/PU.1, and FOXO1, which are down-regulated by genetic and epigenetic mechanisms. The unique phenotype has been suspected to be advantageous for survival of HRS cells. Ectopic expression of some of these transcription factors (EBF1, PU.1, FOXO1) indeed impaired survival of cHL cells. Here we show that forced expression of TCF3 causes cell death and cell cycle arrest in cHL cell lines. Mechanistically, TCF3 overexpression modulated expression of multiple pro-apoptotic genes including BIK, APAF1, FASLG, BOK, and TNFRSF10A/DR4. We conclude that TCF3 inactivation contributes not only to extinguishing of B cell phenotype but also to cHL oncogenesis.

CD30-targeted oncolytic viruses as novel therapeutic approach against classical Hodgkin lymphoma

Classical Hodgkin lymphoma (cHL) is a hematopoietic malignancy with a characteristic cellular composition. The tumor mass is made up of infiltrated lymphocytes and other cells of hematologic origin but only very few neoplastic cells that are mainly identified by the diagnostic marker CD30. While most patients with early stage cHL can be cured by standard therapy, treatment options for relapsed or refractory cHL are still not sufficient, although immunotherapy-based approaches for the treatment of cHL patients have gained ground in the last decade. Here, we suggest a novel therapeutic concept based on oncolytic viruses selectively destroying the CD30⁺-positive cHL tumor cells. Relying on a recently described CD30-specific scFv we have generated CD30-targeted measles virus (MV-CD30) and vesicular stomatitis virus (VSV-CD30). For VSV-CD30 the VSV glycoprotein G reading frame was replaced by those of the CD30-targeted MV glycoproteins. Both viruses were found to be highly selective for CD30-positive cells as demonstrated by infection of co-cultures of target and non-target cells as well as through blocking infection by soluble CD30. Notably, VSV-CD30 yielded much higher titers than MV-CD30 and resulted in a more rapid and efficient killing of cultivated cHL-derived cell lines. Mouse tumor models revealed that intratumorally, as well as systemically injected VSV-CD30, infected cHL xenografts and significantly slowed down tumor growth resulting in a substantially prolonged survival of tumor-bearing mice. Taken together, the data support further preclinical testing of VSV-CD30 as novel therapeutic agent for the treatment of cHL and other CD30⁺-positive malignancies.

Musculin inhibits human T-helper 17 cell response to interleukin 2 by controlling STAT5B activity

We recently demonstrated that human T-helper (Th) 17 cells, unlike Th1 cells, do not proliferate in response to T-cell receptor stimulation, mainly because of their reduced capacity to produce and respond to IL-2. In this study, we show that their lower responsiveness to IL-2 is due to the selective expression of Musculin (MSC), a member of the basic helix-loop-helix transcription factors. We show that MSC expression in human Th17 cells is retinoic acid orphan receptor (ROR)γt-dependent, and allows the upregulation of PPP2R2B, a regulatory member of the protein phosphatase 2A (PP2A) enzyme. High PPP2R2B levels in human Th17 cells were responsible for the reduced STAT5B Ser-193 phosphorylation upon IL-2 signalling and, therefore, impaired STAT5B DNA binding and transcriptional activity on IL-2 target genes. PP2A, observed in Th17 cells, controls also STAT3, dephosphorylating Ser727, thus increasing its activity that plays a crucial role in Th17 development and/or maintenance. Thus, our findings identify an additional mechanism responsible for the limited expansion of human Th17 cells, and could provide a further explanation for the rarity of these cells in inflamed tissues.

The Pathobiology and Treatment of Hodgkin Lymphoma. Where do We go from Gianni Bonadonna's Lesson?

This article reviews the evolution of the diagnosis and treatment of Hodgkin lymphoma (HL) since its discovery in 1832. The morphological, phenotypic and molecular characteristics of both nodular lymphocyte-predominant HL and classical HL are revised in the light of recent molecular information and possible impact on the identification of risk groups as well as the use of targeted therapies. The seminal contribution of Gianni Bonadonna to developing new treatment strategies for both advanced and early-stage HL is highlighted.

The transcription factor musculin promotes the unidirectional development of peripheral Treg cells by suppressing the TH2 transcriptional program

Although master transcription factors (TFs) are key to the development of specific T cell subsets, whether additional transcriptional regulators are induced by the same stimuli that dominantly repress the development of other, non-specific T cell lineages has not been fully elucidated. Through the use of regulatory T cells (T_reg cells) induced by transforming growth factor-β (TGF-β), we identified the TF musculin (MSC) as being critical for the development of induced T_reg cells (iT_reg cells) by repression of the T helper type 2 (T_H2) transcriptional program. Loss of MSC reduced expression of the T_reg cell master TF Foxp3 and induced T_H2 differentiation even under iT_reg-cell-differentiation conditions. MSC interrupted binding of the TF GATA-3 to the locus encoding T_H2-cell-related cytokines and diminished intrachromosomal interactions within that locus. MSC-deficient (Msc^-/-) iT_reg cells were unable to suppress T_H2 responses, and Msc^-/- mice spontaneously developed gut and lung inflammation with age. MSC therefore enforced Foxp3 expression and promoted the unidirectional induction of iT_reg cells by repressing the T_H2 developmental program.

Pharmacological restoration and therapeutic targeting of the B-cell phenotype in classical Hodgkin lymphoma

A pharmacological screening identified compounds that reactivate B-cell–specific gene expression in cHL cell lines. B-cell phenotype-restoring drug combinations render cHL cell lines susceptible to B-NHL–reminiscent targeted therapies.

Aberrant expression of homeobox gene SIX1 in Hodgkin lymphoma

In Hodgkin lymphoma (HL) we recently identified deregulated expression of homeobox genes MSX1 and OTX2 which are physiologically involved in development of the embryonal neural plate border region. Here, we examined in HL homeobox gene SIX1 an additional regulator of this embryonal region mediating differentiation of placodal precursors. SIX1 was aberrantly activated in 12 % of HL patient samples in silico, indicating a pathological role in a subset of this B-cell malignancy. In addition, SIX1 expression was detected in HL cell lines which were used as models to reveal upstream factors and target genes of this basic developmental regulator. We detected increased copy numbers of the SIX1 locus at chromosome 14q23 correlating with enhanced expression while chromosomal translocations were absent. Moreover, comparative expression profiling data and pertinent gene modulation experiments indicated that the WNT-signalling pathway and transcription factor MEF2C regulate SIX1 expression. Genes encoding the transcription factors GATA2, GATA3, MSX1 and SPIB – all basic lymphoid regulators - were identified as targets of SIX1 in HL. In addition, cofactors EYA1 and TLE4, respectively, contrastingly mediated activation and suppression of SIX1 target gene expression. Thus, the protein domain interfaces may represent therapeutic targets in SIX1-positive HL subsets. Collectively, our data reveal a gene regulatory network with SIX1 centrally deregulating lymphoid differentiation and support concordance of lymphopoiesis/lymphomagenesis and developmental processes in the neural plate border region.

Comparative proteomic profiling of Hodgkin lymphoma cell lines

Classical Hodgkin lymphoma (cHL) is a malignancy with complex pathogenesis. The hallmark of the disease is the presence of large mononucleated Hodgkin and bi- or multinucleated Reed/Sternberg (H/RS) cells. The origin of HRS cells in cHL is controversial as these cells show the coexpression of markers of several lineages. Using a proteomic approach, we compared the protein expression profile of cHL models of T- and B-cell derivation to find proteins differentially expressed in these cell lines. A total of 67 proteins were found differentially expressed between the two cell lines including metabolic proteins and proteins involved in the regulation of the cytoskeleton and/or cell migration, which were further validated by western blotting. Additionally, the expression of selected B- and T-cell antigens was also assessed by flow cytometry to reveal significant differences in the expression of different surface markers. Bioinformatics analysis was then applied to our dataset to find enriched pathways and networks, and to identify possible key regulators. In the present study, a proteomic approach was used to compare the protein expression profiles of two cHL cell lines. The identified proteins and/or networks, many of which not previously related to cHL, may be important to better define the pathogenesis of the disease, to identify novel diagnostic markers, and to design new therapeutic strategies.

ID1 upregulation and FoxO3a downregulation by Epstein-Barr virus-encoded LMP1 in Hodgkin's lymphoma

Cancer-initiating cells (CICs) are specialized cells that have the ability to self-renew and are multipotent. We recently demonstrated that Forkhead box O3a (FoxO3a)-expressing cells exhibited a CIC-like potential in Hodgkin's lymphoma (HL). A proportion of HL patients are infected with Epstein-Barr virus (EBV). EBV-encoded latent membrane protein (LMP) 1 downregulates FoxO3a, suggesting that FoxO3a expression may be abolished in EBV-positive HL. Inhibitors of DNA-binding (ID) proteins are highly conserved transcription factors mediating stem cell functions. To the best of our knowledge, no study has investigated possible associations among ID1, FoxO3a and LMP1 expression in HL to date. We immunohistochemically evaluated the expression of the three abovementioned factors in HL patients. The ID1 expression level was inversely correlated with that of FoxO3a (P=0.00035). LMP1-positive HL cells abundantly expressed ID1 (P=0.029), but not FoxO3a (P=0.00085). Thus, our previous observation that FoxO3a may serve as a marker of CICs may not be applicable in EBV-positive HL patients, but rather ID1 may be a candidate CIC marker in this type of HL.

Hodgkin lymphoma: Pathology and biology

The Hodgkin and Reed-Sternberg (HRS) tumor cells of classical Hodgkin lymphoma (HL), as well as the lymphocyte predominant (LP) cells of nodular lymphocyte predominant HL (NLPHL), are derived from mature B cells. However, HRS cells have largely lost their B-cell phenotype and show a very unusual expression of many markers of other hematopoietic cell lineages, which aids in the differential diagnosis between classical HL (cHL) and NLPHL and distinguishes cHL from all other hematopoietic malignancies. The bi- or multinucleated Reed-Sternberg cells most likely derive from the mononuclear Hodgkin cells through a process of incomplete cytokinesis. HRS cells show a deregulated activation of numerous signaling pathways, which is partly mediated by cellular interactions in the lymphoma microenvironment and partly by genetic lesions. In a fraction of cases, Epstein-Barr virus contributes to the pathogenesis of cHL. Recurrent genetic lesions in HRS cells identified so far often involve members of the nuclear factor-κB (NF-κB) and JAK/STAT pathways and genes involved in major histocompatibility complex expression. However, further lead transforming events likely remain to be identified. We here discuss the current knowledge on HL pathology and biology.

Factors That Regulate the Generation of Antibody-Secreting Plasma Cells

The generation of antigen-specific neutralizing antibodies and memory B cells is one of the most important immune protections of the host and is the basis for successful vaccination strategies. The protective antibodies, secreted by preexisting long-lived plasma cells and reactivated antigen-experienced memory B cells, constitute the main humoral immune defense. Distinct from the primary antibody response, the humoral memory response is generated much faster and with greater magnitude, and it produces antibodies with higher affinity and variable isotypes. Humoral immunity is critically dependent on the germinal center where high-affinity memory B cells and plasma cells are generated. In this chapter, we focus on recent advances in our understanding of the molecular mechanisms that govern fate decision for memory B cells and plasma cells and the mechanisms that maintain the long-lived plasma-cell pool, with emphasis on how the transcription factor Blimp-1 (B lymphocyte-induced maturation protein-1) helps regulate the above-mentioned immunoregulatory steps to ensure the production and maintenance of antibody-secreting plasma cells as well as how it directs memory cell vs plasma-cell fate. We also discuss the molecular basis of Blimp-1 action and how its expression is regulated.

Tumor-infiltrating HLA-matched CD4(+) T cells retargeted against Hodgkin and Reed-Sternberg cells

Hodgkin lymphoma (HL) presents with a unique histologic pattern. Pathognomonic Hodgkin and Reed-Sternberg (HRS) cells usually account for less than 1% of the tumor and are embedded in a reactive infiltrate mainly comprised of CD4(+) T cells. HRS cells induce an immunosuppressive microenvironment and thereby escape antitumor immunity. To investigate the impact of interactions between HRS cells and T cells, we performed long-term co-culture studies that were further translated into a xenograft model. Surprisingly, we revealed a strong antitumor potential of allogeneic CD4(+) T cells against HL cell lines. HRS and CD4(+) T cells interact by adhesion complexes similar to immunological synapses. Tumor-cell killing was likely based on the recognition of allogeneic major histocompatibility complex class II (MHC-II) receptor, while CD4(+) T cells from MHC-II compatible donors did not develop any antitumor potential in case of HL cell line L428. However, gene expression profiling (GEP) of co-cultured HRS cells as well as tumor infiltration of matched CD4(+) T cells indicated cellular interactions. Moreover, matched CD4(+) T cells could be activated to kill CD30(+) HRS cells when redirected with a CD30-specific chimeric antigen receptor. Our work gives novel insights into the crosstalk between HRS and CD4(+) T cells, suggesting the latter as potent effector cells in the adoptive cell therapy of HL.

Aberrantly Expressed OTX Homeobox Genes Deregulate B-Cell Differentiation in Hodgkin Lymphoma

In Hodgkin lymphoma (HL) we recently reported that deregulated homeobox gene MSX1 mediates repression of the B-cell specific transcription factor ZHX2. In this study we investigated regulation of MSX1 in this B-cell malignancy. Accordingly, we analyzed expression and function of OTX homeobox genes which activate MSX1 transcription during embryonal development in the neural plate border region. Our data demonstrate that OTX1 and OTX2 are aberrantly expressed in both HL patients and cell lines. Moreover, both OTX loci are targeted by genomic gains in overexpressing cell lines. Comparative expression profiling and subsequent pathway modulations in HL cell lines indicated that aberrantly enhanced FGF2-signalling activates the expression of OTX2. Downstream analyses of OTX2 demonstrated transcriptional activation of genes encoding transcription factors MSX1, FOXC1 and ZHX1. Interestingly, examination of the physiological expression profile of ZHX1 in normal hematopoietic cells revealed elevated levels in T-cells and reduced expression in B-cells, indicating a discriminatory role in lymphopoiesis. Furthermore, two OTX-negative HL cell lines overexpressed ZHX1 in correlation with genomic amplification of its locus at chromosomal band 8q24, supporting the oncogenic potential of this gene in HL. Taken together, our data demonstrate that deregulated homeobox genes MSX1 and OTX2 respectively impact transcriptional inhibition of (B-cell specific) ZHX2 and activation of (T-cell specific) ZHX1. Thus, we show how reactivation of a specific embryonal gene regulatory network promotes disturbed B-cell differentiation in HL.

Potential role of hypoxia in early stages of Hodgkin lymphoma pathogenesis

A unique feature of the germinal center B cell-derived Hodgkin and Reed/Sternberg cells of classical Hodgkin lymphoma is their lost B cell phenotype and the aberrant expression of factors of other hematopoietic cell types, including ID2 and NOTCH1. As cellular dedifferentiation and upregulation of ID2 and NOTCH1 are typical consequences of a hypoxic response, we wondered whether hypoxia may impose an HRS cell-like phenotype in B cells. Culturing normal B cells or cell lines of germinal center-type diffuse large B-cell lymphoma under hypoxic conditions caused partial downregulation of several B cell markers, ID2 upregulation, and increased NOTCH1 activity. The hypoxic cells acquired further features of Hodgkin and Reed/Sternberg cells, including increased JUN expression, and enhanced NFκB activity. The Hodgkin and Reed/Sternberg cell-expressed epigenetic regulators KDM4C and PCGF2, as well as the phosphatase DUSP1 were partially induced in hypoxic B cells. Inhibition of DUSP1 was toxic for classical Hodgkin lymphoma cell lines. Thus, hypoxia induces key Hodgkin and Reed/Sternberg cell characteristics in mature B cells. We speculate that hypoxic conditions in the germinal center may impose phenotypic changes in germinal center B cells, promoting their survival and initiating their differentiation towards a Hodgkin and Reed/Sternberg cell-like phenotype. These may then be stabilized by transforming events in the Hodgkin and Reed/Sternberg precursor cells.

Stem Cell Hierarchy and Clonal Evolution in Acute Lymphoblastic Leukemia

Cancer is characterized by a remarkable intertumoral, intratumoral, and cellular heterogeneity that might be explained by the cancer stem cell (CSC) and/or the clonal evolution models. CSCs have the ability to generate all different cells of a tumor and to reinitiate the disease after remission. In the clonal evolution model, a consecutive accumulation of mutations starting in a single cell results in competitive growth of subclones with divergent fitness in either a linear or a branching succession. Acute lymphoblastic leukemia (ALL) is a highly malignant cancer of the lymphoid system in the bone marrow with a dismal prognosis after relapse. However, stabile phenotypes and functional data of CSCs in ALL, the so-called leukemia-initiating cells (LICs), are highly controversial and the question remains whether there is evidence for their existence. This review discusses the concepts of CSCs and clonal evolution in respect to LICs mainly in B-ALL and sheds light onto the technical controversies in LIC isolation and evaluation. These aspects are important for the development of strategies to eradicate cells with LIC capacity. Common properties of LICs within different subclones need to be defined for future ALL diagnostics, treatment, and disease monitoring to improve the patients' outcome in ALL.

Management of relapsed or refractory hodgkin lymphoma with second-generation antibody-drug conjugates: focus on brentuximab vedotin

Brentuximab vedotin (Adcetris, Seattle Genetics) is an antibody-drug conjugate (ADC) that joins an anti-CD 30 monoclonal antibody with the anti-tubulin agent monomethyl auristatin E via a dipeptide linker. It has demonstrated significant activity in CD 30-positive lymphomas and is currently approved by the US FDA for treatment of Hodgkin lymphoma that has relapsed following autologous stem-cell transplantation, or after two lines of chemotherapy in non-transplant candidates. Brentuximab vedotin has also been approved for the treatment of relapsed anaplastic large-cell lymphoma after front-line chemotherapy. We briefly review the biology of Hodgkin lymphoma, with a focus on the pathogenic role of CD 30 as well as the development of CD 30-targeted therapy. We also discuss both the current role of brentuximab vedotin in the management of relapsed and refractory Hodgkin lymphoma and the likely future developments for this agent.

Integrated copy number and gene expression profiling analysis of Epstein-Barr virus-positive diffuse large B-cell lymphoma

Viral oncogenes and host immunosenescence have been suggested as causes of Epstein-Barr virus-positive diffuse large B-cell lymphoma (EBV + DLBCL) of the elderly. To investigate the molecular genetic basis of immune evasion and tumor outgrowth, we analyzed copy number alterations (CNAs) and gene expression profiles in EBV + DLBCL samples compared with EBV - DLBCL. There were relatively few genomic alterations in EBV + DLBCL compared with those detected in EBV-negative DLBCL. The most frequent CNAs (>30%) in EBV + DLBCLs were gains at 1q23.2-23.3, 1q23.3, 1q32.1, 5p15.3, 8q22.3, 8q24.1-24.2, and 9p24.1; losses at 6q27, 7q11.2, and 7q36.2-36.3 were also recurrent. A gene expression profile analysis identified the host immune response as a key molecular signature in EBV + DLBCL. Antiviral response genes, proinflammatory cytokines, and chemokines associated with the innate immune response were overexpressed, indicating the presence of a virusinduced inflammatory microenvironment. Genes associated with the B-cell receptor signaling pathway were downregulated. An integrated analysis indicated that SLAMF1 and PDL2 were key targets of the gains detected at 1q23.2-23.3 and 9p24.1. The chromosomal gain at 9p24.1 was associated with poor overall survival. Taken together, our results led to the identification of recurrent copy number alterations and distinct gene expression associated with the host immune response in EBV + DLBCL. We suggest that the upregulation of PDL2 on 9p24.1 promotes immune evasion and is associated with poor prognosis in EBV + DLBCL.

Lymphomagenesis in Hodgkin lymphoma

Hodgkin lymphoma (HL) accounts for approximately 0.6% of all new cancer cases, 10% of all lymphomas in the USA, leading to an approximate 9000 new cases per year. It is very unique in that the neoplastic Hodgkin and Reed-Sternberg (HRS) cells of classical HL account for only 1% of the tumor tissue in most cases, with various inflammatory cells including B-cells, T-cells, mast cells, macrophages, eosinophils, neutrophils, and plasma cells comprising the tumor microenvironment. Recent research has identified germinal center B-cells to be the cellular origin of HRS cells. Various transcription factor dysregulation in these neoplastic cells that explains for the loss of B-cell phenotype as well as acquisition of survival and anti-apoptotic features of HRS cells has been identified. Aberrant activation of nuclear factor-kappa B (NF-κB), Janus kinase (JAK)/signal transducer and activator of transcription (STAT), and phosphoinositide 3-kinase (PI3K) pathways play a central role in HL pathogenesis. Both intrinsic genetic mechanisms as well as extrinsic signals have been identified to account for the constitutive activation of these pathways. The extrinsic factors that regulate the activation of transcription pathways in HRS cells have also been studied in detail. Cytokines and chemokines produced both by the HRS cells as well as cells of the microenvironment of HL work in an autocrine and/or paracrine manner to promote survival of HRS cells as well as providing mechanisms for immune escape from the body's antitumor immunity. The understanding of various mechanisms involved in the lymphomagenesis of HL including the importance of its microenvironment has gained much interest in the use of these microenvironmental features as prognostic markers as well as potential treatment targets. In this article, we will review the pathogenesis of HL starting with the cellular origin of neoplastic cells and the mechanisms supporting its pathogenesis, especially focusing on the microenvironment of HL and its associated cytokines.

ID helix-loop-helix proteins as determinants of cell survival in B-cell chronic lymphocytic leukemia cells in vitro

BACKGROUND

Members of the inhibitor of DNA-binding (ID) family of helix-loop-helix proteins have been causally implicated in the pathogenesis of several types of B-cell lineage malignancy, either on the basis of mutation or by altered expression. B-cell chronic lymphocytic leukemia encompasses a heterogeneous group of disorders and is the commonest leukaemia type in the Western world. In this study, we have investigated the pathobiological functions of the ID2 and ID3 proteins in this disease with an emphasis on their role in regulating leukemic cell death/survival.

METHODS

Bioinformatics analysis of microarray gene expression data was used to investigate expression of ID2/ID3 in leukemic versus normal B cells, their association with clinical course of disease and molecular sub-type and to reconstruct a gene regulatory network using the 'maximum information coefficient' (MIC) for target gene inference. In vitro cultured primary leukemia cells, either in isolation or co-cultured with accessory vascular endothelial cells, were used to investigate ID2/ID3 protein expression by western blotting and to assess the cytotoxic response of different drugs (fludarabine, chlorambucil, ethacrynic acid) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. ID2/ID3 protein levels in primary leukemia cells and in MEC1 cells were manipulated by transduction with siRNA reagents.

RESULTS

Datamining showed that the expression profiles of ID2 and ID3 are associated with distinct pathobiological features of disease and implicated both genes in regulating cell death/survival by targeting multiple non-overlapping sets of apoptosis effecter genes. Consistent with microarray data, the overall pattern of ID2/ID3 protein expression in relation to cell death/survival responses of primary leukemia cells was suggestive of a pro-survival function for both ID proteins. This was confirmed by siRNA knock-down experiments in MEC1 cells and in primary leukemia cells, but with variability in the dependence of leukemic cells from different patients on ID protein expression for cell survival. Vascular endothelial cells rescued leukemia cells from spontaneous and cytotoxic drug-induced cell death at least in part, via an ID protein-coupled redox-dependent mechanism.

CONCLUSIONS

Our study provides evidence for a pro-survival function of the ID2/ID3 proteins in chronic lymphocytic leukemia cells and also highlights these proteins as potential determinants of the pathobiology of this disorder.

Contribution of the Epstein-Barr Virus to the Pathogenesis of Hodgkin Lymphoma

The morphology of the pathognomonic Hodgkin and Reed-Sternberg cells (HRS) of Hodgkin lymphoma was described over a century ago, yet it was only relatively recently that the B-cell origin of these cells was identified. In a proportion of cases, HRS cells harbour monoclonal forms of the B lymphotropic Epstein-Barr virus (EBV). This review summarises current knowledge of the pathogenesis of Hodgkin lymphoma with a particular emphasis on the contribution of EBV.

Hematopoiesis in steady-state versus stress: self-renewal, lineage fate choice, and the conversion of danger signals into cytokine signals in hematopoietic stem cells

Long-term hematopoietic stem cells (LT-HSCs) replenish the innate and adaptive immune compartments throughout life. Although significant progress has defined the major transcription factors that regulate lineage specification, the architectural proteins that globally coordinate DNA methylation, histone modification, and changes in gene expression are poorly defined. Provocative new studies establish the chromatin organizer special AT-rich binding protein 1 (Satb1) as one such global regulator in LT-HSCs. Satb1 is a nuclear organizer that partitions chromatin through the formation of cage-like structures. By integrating epigenetic and transcriptional pathways, Satb1 coordinates LT-HSC division, self-renewal, and lymphoid potential. Unexpected among the assortment of genes under Satb1 control in hematopoietic stem cells (HSCs) are cytokines, a finding that takes on additional importance with the provocative finding that short-term HSCs and downstream multipotent progenitors are potent and biologically relevant cytokine secretors during stress-mediated hematopoiesis. Together, these studies reveal a new mechanism of fate regulation and an unforeseen functional capability of HSCs.

Epstein-Barr virus and the origin of Hodgkin lymphoma

Although Epstein-Barr virus (EBV) is present in the malignant Hodgkin/Reed-Sternberg (HRS) cells of a proportion of cases of classical Hodgkin lymphoma (cHL), how the virus contributes to the pathogenesis of this disease remains poorly defined. It is clear from the studies of other EBV-associated cancers that the virus is usually not sufficient for tumor development and that other oncogenic co-factors are required. This article reviews what is known about the contribution of EBV to the pathogenesis of cHL and focuses on emerging evidence implicating chronic inflammation as a potential oncogenic co-factor in this malignancy.

FOXO1 repression contributes to block of plasma cell differentiation in classical Hodgkin lymphoma

FOXO1 directly activates PRDM1α, the master regulator of PC differentiation, and it enriches a PC signature in cHL cell lines. PRDM1α is a tumor suppressor in cHL.

Mapping of transcription factor motifs in active chromatin identifies IRF5 as key regulator in classical Hodgkin lymphoma

Deregulated transcription factor (TF) activities are commonly observed in hematopoietic malignancies. Understanding tumorigenesis therefore requires determining the function and hierarchical role of individual TFs. To identify TFs central to lymphomagenesis, we identified lymphoma type-specific accessible chromatin by global mapping of DNaseI hypersensitive sites and analyzed enriched TF-binding motifs in these regions. Applying this unbiased approach to classical Hodgkin lymphoma (HL), a common B-cell-derived lymphoma with a complex pattern of deregulated TFs, we discovered interferon regulatory factor (IRF) sites among the top enriched motifs. High-level expression of the proinflammatory TF IRF5 was specific to HL cells and crucial for their survival. Furthermore, IRF5 initiated a regulatory cascade in human non-Hodgkin B-cell lines and primary murine B cells by inducing the TF AP-1 and cooperating with NF-κB to activate essential characteristic features of HL. Our strategy efficiently identified a lymphoma type-specific key regulator and uncovered a tumor promoting role of IRF5.

Transcription factor ABF-1 suppresses plasma cell differentiation but facilitates memory B cell formation

Ag-primed B cells that result from an immune response can form either memory B cells or Ab-secreting plasma cells; however, the molecular machinery that controls this cellular fate is poorly understood. In this study, we show that activated B cell factor-1 (ABF-1), which encodes a basic helix-loop-helix transcriptional repressor, participates in this regulation. ABF-1 was prevalently expressed in purified memory B cells and induced by T follicular helper cell-mediated signals. ABF-1 expression declined by the direct repression of B lymphocyte-induced maturation protein-1 during differentiation. Ectopic expression of ABF-1 reduced the formation of Ab-secreting cells in an in vitro differentiation system of human memory B cells. Accordingly, knockdown of ABF-1 potentiates the formation of Ab-secreting cells. A transgenic mouse that expresses inducible ABF-1 in a B cell-specific manner was generated to demonstrate that the formation of germinal center and memory B cells was augmented by induced ABF-1 in an immune response, whereas the Ag-specific plasma cell response was dampened. This effect was associated with the ability of ABF-1 to limit cell proliferation. Together, our results demonstrate that ABF-1 facilitates formation of memory B cells but prevents plasma cell differentiation.

Deregulated FOX genes in Hodgkin lymphoma

FOX genes encode transcription factors which regulate basic developmental processes during embryogenesis and in the adult. Several FOX genes show deregulated expression in particular malignancies, representing oncogenes or tumor suppressors. Here, we screened six Hodgkin lymphoma (HL) cell lines for FOX gene activity by comparative microarray profiling, revealing overexpression of FOXC1 and FOXD1, and reduced transcription of FOXN3, FOXO1, and FOXP1. In silico expression analyses of these FOX gene candidates in HL patient samples supported the cell line data. Chromosomal analyses demonstrated an amplification of the FOXC1 locus at 6p25 and a gain of the FOXR2 locus at Xp11, indicting genomic aberrations for their upregulation. Comparative expression profiling and ensuing stimulation experiments revealed implementation of the TGFβ- and WNT-signaling pathways in deregulation of FOXD1 and FOXN3. Functional analysis of FOXP1 implicated miR9 and miR34a as upstream regulators and PAX5, TCF3, and RAG2 as downstream targets. A similar exercise for FOXC1 revealed repression of MSX1 and activation of IPO7, both mediating inhibition of the B-cell specific homeobox gene ZHX2. Taken together, our data show that aberrantly expressed FOX genes and their downstream targets are involved in the pathogenesis of HL via deregulation of B-cell differentiation and may represent useful diagnostic markers and/or therapeutic targets.