The BCL-6 proto-oncogene controls germinal-centre formation and Th2-type inflammation

Chronic simian immunodeficiency virus infection is associated with contrasting phenotypes of dysfunctional Bcl6+ germinal center B cells or Bcl6- Bcl2+ non-germinal center B cells

Human immunodeficiency virus (HIV) infection is characterized by dysfunctional B cell responses. Here we show that chronic simian immunodeficiency virus (SIV) infection is characterized by an expansion of either lymph node germinal center (GC) B cells that co-express Bcl6, Ki-67 and IL-21R and correlate with expanded T follicular helper (Tfh) cells or B cells that lack Bcl6, Ki-67 and IL-21R but express high levels of anti-apoptotic Bcl2 that negatively correlate with Tfh cells. The lack of Tfh cells likely contributes to persistence of dysfunctional non-proliferating B cells during chronic infection. These findings have implications for protective immunity in HIV-infected individuals who harbour low frequencies of Tfh cells.

Small-molecule BCL6 inhibitor effectively treats mice with nonsclerodermatous chronic graft-versus-host disease

Patient outcomes for steroid-dependent or -refractory chronic graft-versus-host diesease (cGVHD) are poor, and only ibrutinib has been US Food and Drug Administration (FDA) approved for this indication. cGVHD is often driven by the germinal center (GC) reaction, in which T follicular helper cells interact with GC B cells to produce antibodies that are associated with disease pathogenesis. The transcriptional corepressor B-cell lymphoma 6 (BCL6) is a member of the Broad-complex, Tramtrack, and Bric-abrac/poxvirus and zinc finger (BTB/POZ) transcription factor family and master regulator of the immune cells in the GC reaction. We demonstrate that BCL6 expression in both donor T cells and B cells is necessary for cGVHD development, pointing to BCL6 as a therapeutic cGVHD target. A small-molecule BCL6 inhibitor reversed active cGVHD in a mouse model of multiorgan system injury with bronchiolitis obliterans associated with a robust GC reaction, but not in cGVHD mice with scleroderma as the prominent manifestation. For cGVHD patients with antibody-driven cGVHD, targeting of BCL6 represents a new approach with specificity for a master GC regulator that would extend the currently available second-line agents.

Identification of Thiourea-Based Inhibitors of the B-Cell Lymphoma 6 BTB Domain via NMR-Based Fragment Screening and Computer-Aided Drug Design

Protein-protein interactions (PPI) between the transcriptional repressor B-cell lymphoma 6 (BCL6) BTB domain (BCL6^BTB) and its corepressors have emerged as a promising target for anticancer therapeutics. However, identification of potent, drug-like inhibitors of BCL6^BTB has remained challenging. Using NMR-based screening of a library of fragment-like small molecules, we have identified a thiourea compound (7CC5) that binds to BCL6^BTB. From this hit, the application of computer-aided drug design (CADD), medicinal chemistry, NMR spectroscopy, and X-ray crystallography has yielded an inhibitor, 15f, that demonstrated over 100-fold improved potency for BCL6^BTB. This gain in potency was achieved by a unique binding mode that mimics the binding mode of the corepressor SMRT in the aromatic and the HDCH sites. The structure-activity relationship based on these new inhibitors will have a significant impact on the rational design of novel BCL6 inhibitors, facilitating the identification of therapeutics for the treatment of BCL6-dependent tumors.

Transcriptional Programs Underlying Cd4 T Cell Differentiation and Functions

Understanding the basis of cellular differentiation is a fundamental issue in developmental biology but also for the comprehension of pathological processes. In fact, the palette of developmental decisions for naive CD4 T cells is a critical aspect of the development of appropriate immune responses which could control infectious processes or cancer growth. However, the current accumulation of data on CD4 T cells biology reveals a complex world with different helper populations. Naive CD4 T cells can differentiate into different subtypes in response to cytokine stimulation. This stimulation involves a complex transcriptional network implicating the activation of Signal Transducer and Activator of Transcription but also master regulator transcription factors allowing the functions of each helper T lymphocyte subtype. In this review, we will present an overview of the transcriptional regulation which controls process of helper T cells differentiation. We will focus on the role of initiator transcriptional factors and on master regulators but also on other nonspecific transcriptional factors which refine the T helper polarization to stabilize or modulate the differentiation program.

The role of T cells in the pathogenesis of Parkinson's disease

Recent evidence has shown that neuroinflammation plays a key role in the pathogenesis of Parkinson's disease (PD). However, different components of the brain's immune system may exert diverse effects on neuroinflammatory events in PD. The adaptive immune response, especially the T cell response, can trigger type 1 pro-inflammatory activities and suppress type 2 anti-inflammatory activities, eventually resulting in deregulated neuroinflammation and subsequent dopaminergic neurodegeneration. Additionally, studies have increasingly shown that therapies targeting T cells can alleviate neurodegeneration and motor behavior impairment in animal models of PD. Therefore, we conclude that abnormal T cell-mediated immunity is a fundamental pathological process that may be a promising translational therapeutic target for Parkinson's disease.

PRMT5 interacts with the BCL6 oncoprotein and is required for germinal center formation and lymphoma cell survival

The germinal center (GC) reaction plays an important role in generating humoral immunity and is believed to give rise to most B-cell lymphomas. GC entry and exit are tightly regulated processes, controlled by the actions of transcription factors such as BCL6. Herein, we demonstrate that protein arginine methyltransferase 5 (PRMT5), a symmetric dimethyl arginine methyltransferase, is also necessary for GC formation and affinity maturation. PRMT5 contributes to GC formation and affinity maturation at least in part through its direct interaction with and methylation of BCL6 at arginine 305 (R305), a modification necessary for the full transcriptional repressive effects of BCL6. Inhibition of PRMT5 in B-cell lymphoma lines led to significant upregulation of BCL6 target genes, and the concomitant inhibition of both BCL6 and PRMT5 exhibited synergistic killing of BCL6-expressing lymphoma cells. Our studies identify PRMT5 as a novel regulator of the GC reaction and highlight the mechanistic rationale of cotargeting PRMT5 and BCL6 in lymphoma.

Altered circulating T follicular helper cells in patients with chronic immune thrombocytopenia

The present study aimed to illuminate the role of circulating T follicular helper (TFH) cells in patients diagnosed with chronic immune thrombocytopenia (cITP). Fifty-four patients with cITP and 30 age-matched healthy control subjects were enrolled in the present study. TFH cell frequencies, expression of CD4⁺ TFH cell-associated cytokines, including interleukin (IL)-2, IL-4, IL-10 and IL-21 and associated regulatory mRNA expression levels including Bcl-6, c-Maf, Blimp-1 and PD-1 pre- and post-treatment with intravenous immunoglobulin and corticosteroids, were detected by flow cytometry, ELISA and reverse transcription-quantitative polymerase chain reaction, respectively. TFH cell frequencies of patients were significantly higher compared with healthy controls pre-treatment (P<0.05). Following treatment, significantly decreased percentages of TFH cells were present in cITP responders (P<0.05). Correlation analysis revealed that the number of TFH cells was negatively correlated with the platelet count in the peripheral blood. Furthermore, analysis of inflammatory cytokines indicated significant differences in serum interleukin (IL)-21 and IL-10 between pretreated patients and healthy controls (P<0.05). Additionally, transcription factor B-cell lymphoma (Bcl)-6, c-Maf and programmed death-ligand (PD)-1 mRNA expression levels were significantly different between cITP patients prior to treatment and the healthy controls (P<0.05). However, the expression levels of Bcl-6, C-Maf and PD-1 mRNA were significantly changed post-treatment (P<0.05). These data demonstrated that circulating TFH cells and CD4⁺ TFH cell-associated cytokines may serve a role in cITP. The findings suggest that the overactivation of TFH cells may contribute to the immunopathogenesis of cITP, thus blocking the pathway of TFH cells may be reasonable for therapeutic intervention.

LAZ3 protects cardiac remodeling in diabetic cardiomyopathy via regulating miR-21/PPARa signaling

Diabetes contributes to cardiovascular complications and the pathogenesis of cardiac remodeling that can lead to heart failure. We aimed to evaluate the functional role of LAZ3 in diabetic cardiomyopathy (DCM). Streptozotocin (STZ) was used to induce a diabetic mouse model. Three months after induction, the mice were subjected to retro-orbital venous plexus injection of adeno-associated virus 9 (AAV9) that overexpressed LAZ3. Six weeks after the infection, mouse hearts were removed to assess the degree of cardiac remodeling. LAZ3 was down-regulated in the diabetic mouse hearts and high glucose stimulated cardiomyocytes. Knock-down of LAZ3 in cardiomyocytes with LAZ3 siRNA reduced cell viability, increased the inflammatory response and induced oxidative stress and cell apoptosis. Overexpression of LAZ3 by infection with adeno-associated virus (AAV9)-LAZ3 protected against an inflammatory response, oxidative stress and cell apoptosis in both a high glucose stimulated in vitro study and diabetic mouse hearts. We found that LAZ3 increased the activation of PPARa, which increased PGC-1a activation and subsequently augmented NRF2 expression and nuclear translocation. This outcome was confirmed by NRF2 siRNA and a PPARa activator, since NRF2 siRNA abrogated the protective effects of LAZ3 overexpression, while the PPARa activator reversed the deteriorating phenotype of LAZ3 knock-down in both the in vitro and vivo study. Furthermore, LAZ3 decreased miR-21 expression, which resulted in PPARa activation, NRF2 expression and nuclear translocation. In conclusion, LAZ3 protects against cardiac remodeling in DCM by decreasing miR-21, thus regulating PPARa/NRF2 signaling.

Prognostic Significance of BCL-2 and BCL-6 Expression in MYC-positive DLBCL

BACKGROUND

Double-expression lymphoma (DEL) is a rare subgroup of diffuse large B-cell lymphoma (DLBCL), which has coexpression of MYC and BCL-2. Coexpression of MYC and BCL-2 is considered a prognostic marker portending poor outcomes. However, the prognostic effect of BCL-2 and BCL-6 expression in DLBCL remains controversial.

MATERIALS AND METHODS

Immunohistochemical staining was performed to detect MYC, BCL-2 and BCL-6 expression in 212 patients with newly diagnosed DLBCL and assess the prognostic effects of BCL-2 and BCL-6 expression. The DLBCL patients were treated with R-CHOP (rituximab plus cyclophosphamide, doxorubicin, vincristine [Oncovin], prednisone)-like regimens.

RESULTS

Retrospective analysis revealed that BCL-2⁺ and BCL-2⁺/MYC⁺ were prognostic factors indicative of poor outcomes. Patients with BCL-2⁺ and/or MYC⁺ expression had a poorer prognosis than that of patients with BCL-2^- and/or MYC^- expression. Patients with BCL-2⁺/MYC^- expression showed a trend toward poorer survival than those with BCL-2^-/MYC⁺ expression, suggesting that BCL-2 plays a more important role than MYC. Also, patients with BCL-6^-/MYC⁺ expression had poorer progression-free survival than those with BCL-6⁺/MYC⁺ expression. In addition, patients with BCL-2⁺/MYC⁺/BCL-6^- expression had the worst prognosis, suggesting that BCL-6^- is a prognostic factor for poor outcomes for MYC⁺ DLBCL patients. Altogether, our findings have shown that BCL-2 is an independent prognostic factor and possibly plays a more important role than MYC in MYC⁺ DLBCL patients. Furthermore, we found that BCL-6^- expression could also be a prognostic factor portending poor outcomes for MYC⁺ DLBCL patients.

Chemically Induced Degradation of the Oncogenic Transcription Factor BCL6

The transcription factor BCL6 is a known driver of oncogenesis in lymphoid malignancies, including diffuse large B cell lymphoma (DLBCL). Disruption of its interaction with transcriptional repressors interferes with the oncogenic effects of BCL6. We used a structure-based drug design to develop highly potent compounds that block this interaction. A subset of these inhibitors also causes rapid ubiquitylation and degradation of BCL6 in cells. These compounds display significantly stronger induction of expression of BCL6-repressed genes and anti-proliferative effects than compounds that merely inhibit co-repressor interactions. This work establishes the BTB domain as a highly druggable structure, paving the way for the use of other members of this protein family as drug targets. The magnitude of effects elicited by this class of BCL6-degrading compounds exceeds that of our equipotent non-degrading inhibitors, suggesting opportunities for the development of BCL6-based lymphoma therapeutics.

Genetics of diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL), the most frequent subtype of lymphoid malignancy, remains a significant clinical challenge, as ∼30% of patients are not cured. Over the past decade, remarkable progress has been made in the understanding of the pathogenesis of this disease, spurred by the implementation of powerful genomic technologies that enabled the definition of its genetic and epigenetic landscape. These studies have uncovered a multitude of genomic alterations that contribute to the initiation and maintenance of the tumor clone by disrupting biological functions known to be critical for the normal biology of its cells of origin, germinal center B cells. The identified alterations involve epigenetic remodeling, block of differentiation, escape from immune surveillance, and the constitutive activation of several signal transduction pathways. This wealth of new information offers unique opportunities for the development of improved diagnostic and prognostic tools that could help guide the clinical management of DLBCL patients. Furthermore, a number of the mutated genes identified are potentially actionable targets that are currently being explored for the development of novel therapeutic strategies. This review summarizes current knowledge of the most common genetic alterations associated with DLBCL in relation to their functional impact on the malignant transformation process, and discusses their clinical implications for mechanism-based therapeutics.

Allergic TH2 Response Governed by B-Cell Lymphoma 6 Function in Naturally Occurring Memory Phenotype CD4+ T Cells

Transcriptional repressor B-cell lymphoma 6 (Bcl6) appears to regulate T_H2 immune responses in allergies, but its precise role is unclear. We previously reported that Bcl6 suppressed IL-4 production in naïve CD4⁺ T cell-derived memory T_H2 cells. To investigate Bcl6 function in allergic responses in naturally occurring memory phenotype CD4⁺ T (MPT) cells and their derived T_H2 (MPT_H2) cells, Bcl6-manipulated mice, highly conserved intron enhancer (hcIE)-deficient mice, and reporter mice for conserved noncoding sequence 2 (CNS2) 3′ distal enhancer region were used to elucidate Bcl6 function in MPT cells. The molecular mechanisms of Bcl6-mediated T_H2 cytokine gene regulation were elucidated using cellular and molecular approaches. Bcl6 function in MPT cells was determined using adoptive transfer to naïve mice, which were assessed for allergic airway inflammation. Bcl6 suppressed IL-4 production in MPT and MPT_H2 cells by suppressing CNS2 enhancer activity. Bcl6 downregulated Il4 expression in MPT_H2 cells, but not MPT cells, by suppressing hcIE activity. The inhibitory functions of Bcl6 in MPT and MPT_H2 cells attenuated allergic responses. Bcl6 is a critical regulator of IL-4 production by MPT and MPT_H2 cells in T_H2 immune responses related to the pathogenesis of allergies.

Inhibition of the transcriptional repressor complex Bcl-6/BCoR induces endothelial sprouting but does not promote tumor growth

The oncogenic potential of the transcriptional repressor Bcl-6 (B-cell lymphoma 6) was originally discovered in non-Hodgkin patients and the soluble Bcl-6 inhibitor 79-6 was developed to treat diffuse large B-cell lymphomas with aberrant Bcl-6 expression. Since we found Bcl-6 and its co-repressor BCoR (Bcl-6 interacting co-repressor) to be regulated in human microvascular endothelium by colorectal cancer cells, we investigated their function in sprouting angiogenesis which is central to tumor growth. Based on Bcl-6/BCoR gene silencing we found that the transcriptional repressor complex in fact constitutes an endogenous inhibitor of vascular sprouting by supporting the stalk cell phenotype: control of Notch target genes (HES1, HEY1, DLL4) and cell cycle regulators (cyclin A and B1). Thus, when endothelial cells were transiently transfected with Bcl-6 and/or BCoR siRNA, vascular sprouting was prominently induced. Comparably, when the soluble Bcl-6 inhibitor 79-6 was applied in the mouse retina model of physiological angiogenesis, endothelial sprouting and branching were significantly enhanced. To address the question whether clinical treatment with 79-6 might therefore have detrimental therapeutic effects by promoting tumor angiogenesis, mouse xenograft models of colorectal cancer and diffuse large B-cell lymphoma were tested. Despite a tendency to increased tumor vessel density, 79-6 therapy did not enhance tumor expansion. In contrast, growth of colorectal carcinomas was significantly reduced which is likely due to a combined 79-6 effect on cancer cells and tumor stroma. These findings may provide valuable information regarding the future clinical development of Bcl-6 inhibitors.

Clinicopathological Analysis of 320 Cases of Diffuse Large B-cell Lymphoma Using the Hans Classifier

The estimation of clinical prognosis for diffuse large B-cell lymphoma (DLBCL) with a quick, cost-efficient method is necessary because of the clinical heterogeneity of this disease, which leads to death, relapsed or refractory disease in approximately 40% of patients. We analyzed 320 cases diagnosed from 2007 to 2013 treated with R-CHOP therapy at Tokai University Hospital and associated institutions. DLBCL was classified according to the cell-of-origin using the Hans algorithm [germinal center B-cell-like (GCB) vs non-GCB subtypes], and into 6 subgroups derived from combinations of CD10, BCL6 and MUM1 markers. The percentage of GCB and non-GCB (NGCB) subtypes was 35% and 65%, respectively. GCB-DLBCL was characterized by lower BCL2 immunohistochemical expression, extranodal sites ＜1, better therapeutic response, and favorable overall survival (OS) and progression free survival (PFS) (P＜0.01). The most frequent subgroup was NGCB-1 (CD10^-BCL6⁺MUM1⁺, 51%) followed by GCB-1 (CD10⁺BCL6^+or-MUM1⁺, 21%), NGCB-2 (CD10^-BCL6^-MUM1⁺, 13%), GCB-2 (CD10⁺BCL6^+or-MUM1^-, 10%), GCB-3 (CD10^-BCL6⁺MUM1^-, 4%) and NGCB-3 (CD10^-BCL6^-MUM1^-, 2%). In comparison with GCB-2 and GCB-3 (both MUM1^-), the GCB-1 (MUM1⁺) was characterized by favorable PFS (5-year PFS 84% vs 65%, OR 0.368, P＜0.05), independent of high LDH (associated with unfavorable PFS, OR 7.04, P＜0.01) in the multivariate analysis. This predictive value of MUM1 was independent of CD10. Interestingly, triple-negative NGCB-3 tended to have a more favorable prognosis than the other NGCB subgroups. In conclusion, the Hans classifier is a valid method to evaluate the prognosis of DLBCL NOS. In the GCB subtypes, GCB subtypes, MUM1-positivity is associated with a more favorable outcome (PFS).

A synthetic stroma-free germinal center niche for efficient generation of humoral immunity ex vivo

B cells play a major role in the adaptive immune response by producing antigen-specific antibodies against pathogens and imparting immunological memory. Following infection or vaccination, antibody-secreting B cells and memory B cells are generated in specialized regions of lymph nodes and spleens, called germinal centers. Here, we report a fully synthetic ex-vivo system that recapitulates the generation of antigen-specific germinal-center (GC) like B cells using material-surface driven polyvalent signaling. This synthetic germinal center (sGC) reaction was effectively induced using biomaterial-based artificial "follicular T helper cells (T_FH)" that provided both natural CD40-CD40L ligation as well as crosslinking of CD40 and by mimicking artificial "follicular dendritic cells (FDC)" to provide efficient, polyvalent antigen presentation. The artificial sGC reaction resulted in efficient B cell expansion, immunoglobulin (Ig) class switching, and expression of germinal center phenotypes. Antigen presentation during sGC reaction selectively enhanced the antigen-specific B cell population and induced somatic hyper-mutations for potential affinity maturation. The resulting B cell population consisted primarily of GC-like B cells (centrocytes) as well as some plasma-like B cells expressing CD138. With concurrent cell sorting, we successfully created highly enriched populations of antigen-specific B cells. Adoptive transfer of these GC-like B cells into non-irradiated isogeneic or non-lethally irradiated congenic recipient mice showed successful engraftment and survival of the donor cells for the 4 week test period. We show that this material-surface driven sGC reaction can be successfully applied to not only splenic B cells but also B cells isolated from more therapeutically relevant sources such as peripheral blood mononuclear cells (PBMCs), thus making our current work an exciting prospect in the new era of personalized medicine and custom-immunotherapy.

Identification of zinc finger protein Bcl6 as a novel regulator of early adipose commitment

Adipose tissue is a key determinant of whole-body metabolism and energy homeostasis. Unravelling the transcriptional regulatory process during adipogenesis is therefore highly relevant from a biomedical perspective. In these studies, zinc finger protein B-cell lymphoma 6 (Bcl6) was demonstrated to have a role in early adipogenesis of mesenchymal stem cells. Bcl6 is enriched in preadipose versus non-preadipose fibroblasts and shows upregulated expression in the early stage of adipogenesis. Gain- and loss-of-function studies revealed that Bcl6 acts as a key regulator of adipose commitment and differentiation both in vitro and ex vivo. RNAi-mediated knockdown of Bcl6 in C3H10T1/2 cells greatly inhibited adipogenic potential, whereas Bcl6 overexpression enhanced adipogenic differentiation. This transcription factor also directly or indirectly targets and controls the expression of some early and late adipogenic regulators (i.e. Zfp423, Zfp467, KLF15, C/EBPδ, C/EBPα and PPARγ). We further identified that Bcl6 transactivated the signal transducers and activators of transcription 1 (STAT1), which was determined as a required factor for adipogenesis. Moreover, overexpression of STAT1 rescued the impairment of adipogenic commitment and differentiation induced by Bcl6 knockdown in C3H10T1/2 cells, thereby confirming that STAT1 is a downstream direct target of Bcl6. This study identifies Bcl6 as a positive transcriptional regulator of early adipose commitment.

Concomitant suppression of TH2 and TH17 cell responses in allergic asthma by targeting retinoic acid receptor-related orphan receptor γt

BACKGROUND

Allergic asthma is a heterogeneous chronic inflammatory disease of the airways with a massive infiltration of eosinophils or neutrophils mediated by allergen-specific T_H2 and T_H17 cells, respectively. Therefore successful treatment of allergic asthma will require suppression of both T_H2 and T_H17 cells.

OBJECTIVE

We sought to investigate the role of the T_H17 cell pathway in regulating T_H2 cell responses in allergic asthma.

METHODS

Allergic asthma was induced by intranasal challenge with proteinase allergens in C57BL/6, Il17a^-/-Il17f^-/-, and retinoic acid receptor-related orphan receptor γt (RORγt)^gfp/gfp mice. A pharmacologic RORγt inhibitor was used to evaluate its preventive and therapeutic effects in allergic asthma. Characteristics of allergic airway inflammation were analyzed by using flow cytometry, histology, quantitative real-time PCR, and ELISA. Mixed bone marrow chimeric mice, fate mapping analysis, short hairpin RNA transduction, and in vitro T-cell differentiation were used for mechanistic studies.

RESULTS

Mice deficient in IL-17A and IL-17F, as well as RORγt, exhibited a significant reduction not only in T_H17 cell responses but also in T_H2 cell responses in an animal model of allergic asthma. Similarly, mice treated with an RORγt inhibitor had significantly diminished T_H17 and T_H2 cell responses, leading to reduced neutrophil and eosinophil numbers in the airway. RORγt-deficient T cells were intrinsically defective in differentiating into T_H2 cells and expressed increased levels of B-cell lymphoma 6 (Bcl6). Bcl6 knockdown resulted in a remarkable restoration of T_H2 cell differentiation in RORγt-deficient T cells. Blockade of RORγt also significantly hampered the differentiation of human T_H2 and T_H17 cells from naive CD4⁺ T cells.

CONCLUSION

RORγt in T cells is required for optimal T_H2 cell differentiation by suppressing Bcl6 expression; this finding suggests that targeting RORγt might be a promising approach for the treatment of allergic asthma by concomitantly suppressing T_H17 and T_H2 cell responses in the airway.

LRF inhibits p53 expression in colon cancer cells via modulating DAP5 activity

The p53 protein plays a critical role in suppression of tumour growth; its regulation is not fully understood. Leukaemia/lymphoma-related factor (LRF) promotes tumour cell growth. This study tests a hypothesis that LRF inhibits p53 expression in colon cancer cells. In this study, human colon cancer cell lines, LIM1215 and HCT116 cells, were used. The expression of LRF and p53 in the cells was analysed by quantitative reverse transcription polymerase chain reaction and Western blotting. We observed that the expression of protease-activated receptor 2 (PAR2) was detected in both LIM1215 and HCT116 human colon cancer cells. Activation of PAR2 increased the expression of LRF and inhibited the p53 expression in the cancer cells. We also detected a complex of LRF and DAP5, one of the p53 gene transcription factors. The interaction of LRF and DAP5 resulted in the repression of p53 expression in the colon cancer cells. In conclusion, PAR2 activation increases the expression of LRF in colon cancer cells, which interacts with DAP5 to repress the p53 expression. Leukaemia/lymphoma-related factor may be a novel target in the treatment of colon cancer.

An essential EBV latent antigen 3C binds Bcl6 for targeted degradation and cell proliferation

The latent EBV nuclear antigen 3C (EBNA3C) is required for transformation of primary human B lymphocytes. Most mature B-cell malignancies originate from malignant transformation of germinal center (GC) B-cells. The GC reaction appears to have a role in malignant transformation, in which a major player of the GC reaction is Bcl6, a key regulator of this process. We now demonstrate that EBNA3C contributes to B-cell transformation by targeted degradation of Bcl6. We show that EBNA3C can physically associate with Bcl6. Notably, EBNA3C expression leads to reduced Bcl6 protein levels in a ubiquitin-proteasome dependent manner. Further, EBNA3C inhibits the transcriptional activity of the Bcl6 promoter through interaction with the cellular protein IRF4. Bcl6 degradation induced by EBNA3C rescued the functions of the Bcl6-targeted downstream regulatory proteins Bcl2 and CCND1, which resulted in increased proliferation and G1-S transition. These data provide new insights into the function of EBNA3C in B-cell transformation during GC reaction, and raises the possibility of developing new targeted therapies against EBV-associated cancers.

Perspectives in Pediatric Pathology, Chapter 25. Testicular and Paratesticular Tumors in the Pediatric Age Group

Testicular tumors in the prepubertal age are relatively rare, representing only 9.4% of the total testicular and paratesticular specimens from a 20-year review performed at a large pediatric hospital [ 1 ]. They account for 1% to 2% of all solid tumors in the pediatric age group, with an annual incidence between 0.5/100 000 and 2/100 000 boys according to Coppes et al [ 2 ] and data from the Prepubertal Testicular Tumor Registry [ 3 ]. Similar to other neoplasms afflicting children, a bimodal age distribution is observed. The first peak is between birth and 3 years of age, and a second one occurs at the onset of puberty, extending to the fourth decade. Reports on their frequency vary because some investigators include the adolescent period, while others do not [ 4 ]. The vast majority of testicular tumors are germ cell neoplasms, accounting for 95% across all ages [ 5 ]. In children, germ cell tumors also predominate, representing 71% of all testicular neoplasms. These include yolk sac tumors (49%), teratomas (13%), seminomas and mixed germ cell tumors (9%), and sex-cord stromal tumors (29%). Malignant potential is significantly lower (less than 70%) in the pediatric age group compared to adults (90%) [ 6 ]. According to Pohl et al, 74% of prepubertal testicular tumors are benign [ 7 ].

T Follicular Helper Cell-Derived IL-4 Is Required for IgE Production during Intestinal Helminth Infection

IgE production plays a crucial role in protective as well as pathogenic type 2 immune responses. Although the cytokine IL-4 is required for the development of IgE-producing plasma cells, the source of IL-4 and cellular requirements for optimal IgE responses remain unclear. Recent evidence suggests that T follicular helper (Tfh) cells are the primary producer of IL-4 in the reactive lymph node during type 2 immune responses. As Tfh cells are also required for the development of plasmablasts derived from germinal center and extrafollicular sources, we hypothesized that this cell subset is essential for the IgE plasmablast response. In this study, we show that during intestinal helminth infection, IL-4 derived from Tfh cells is required for IgE class switching and plasmablast formation. Notably, early IgE class switching did not require germinal center formation. Additionally, Tfh cell-derived IL-4 was required to maintain the Th2 response in the mesenteric lymph nodes of infected mice. Collectively, our results indicate that IL-4-producing Tfh cells are central orchestrators of the type 2 immune response in the reactive lymph nodes during parasitic helminth infection.

The Role of c-MYC in B-Cell Lymphomas: Diagnostic and Molecular Aspects

c-MYC is one of the most essential transcriptional factors, regulating a diverse array of cellular functions, including proliferation, growth, and apoptosis. Dysregulation of c-MYC is essential in the pathogenesis of a number of B-cell lymphomas, but is rarely reported in T-cell lymphomas. c-MYC dysregulation induces lymphomagenesis by loss of the tight control of c-MYC expression, leading to overexpression of intact c-MYC protein, in contrast to the somatic mutations or fusion proteins seen in many other oncogenes. Dysregulation of c-MYC in B-cell lymphomas occurs either as a primary event in Burkitt lymphoma, or secondarily in aggressive lymphomas such as diffuse large B-cell lymphoma, plasmablastic lymphoma, mantle cell lymphoma, or double-hit lymphoma. Secondary c-MYC changes include gene translocation and gene amplification, occurring against a background of complex karyotype, and most often confer aggressive clinical behavior, as evidenced in the double-hit lymphomas. In low-grade B-cell lymphomas, acquisition of c-MYC rearrangement usually results in transformation into highly aggressive lymphomas, with some exceptions. In this review, we discuss the role that c-MYC plays in the pathogenesis of B-cell lymphomas, the molecular alterations that lead to c-MYC dysregulation, and their effect on prognosis and diagnosis in specific types of B-cell lymphoma.

Immunological Principles Guiding the Rational Design of Particles for Vaccine Delivery

Despite the immense public health successes of immunization over the past century, effective vaccines are still lacking for globally important pathogens such as human immunodeficiency virus, malaria, and tuberculosis. Exciting recent advances in immunology and biotechnology over the past few decades have facilitated a shift from empirical to rational vaccine design, opening possibilities for improved vaccines. Some of the most important advancements include (i) the purification of subunit antigens with high safety profiles, (ii) the identification of innate pattern recognition receptors (PRRs) and cognate agonists responsible for inducing immune responses, and (iii) developments in nano- and microparticle fabrication and characterization techniques. Advances in particle engineering now allow highly tunable physicochemical properties of particle-based vaccines, including composition, size, shape, surface characteristics, and degradability. Enhanced collaborative efforts between researchers in immunology and materials science are expected to rise to next-generation vaccines. This process will be significantly aided by a greater understanding of the immunological principles guiding vaccine antigenicity, immunogenicity, and efficacy. With specific emphasis on PRR-targeted adjuvants and particle physicochemical properties, this review aims to provide an overview of the current literature to guide and focus rational particle-based vaccine design efforts.

Development of chronic allergic responses by dampening Bcl6-mediated suppressor activity in memory T helper 2 cells

Mice deficient in the transcriptional repressor B-cell CLL/lymphoma 6 (Bcl6) exhibit similar T helper 2 (T_H2) immune responses as patients with allergic diseases. However, the molecular mechanisms underlying Bcl6-directed regulation of T_H2 cytokine genes remain unclear. We identified multiple Bcl6/STAT binding sites (BSs) in T_H2 cytokine gene loci. We found that Bcl6 is modestly associated with the BSs, and it had no significant effect on cytokine production in newly differentiated T_H2 cells. Contrarily, in memory T_H2 (mT_H2) cells derived from adaptively transferred T_H2 effectors, Bcl6 outcompeted STAT5 for binding to T_H2 cytokine gene loci, particularly Interleukin4 (Il4) loci, and attenuated GATA binding protein 3 (GATA3) binding to highly conserved intron enhancer regions in mT_H2 cells. Bcl6 suppressed cytokine production epigenetically in mT_H2 cells to negatively tune histone acetylation at T_H2 cytokine gene loci, including Il4 loci. In addition, IL-33, a pro-T_H2 cytokine, diminished Bcl6's association with loci to which GATA3 recruitment was inversely augmented, resulting in altered IL-4, but not IL-5 and IL-13, production in mT_H2 cells but no altered production in newly differentiated T_H2 cells. Use of a murine asthma model that generates high levels of pro-T_H2 cytokines, such as IL-33, suggested that the suppressive function of Bcl6 in mT_H2 cells is abolished in severe asthma. These findings indicate a role of the interaction between T_H2-promoting factors and Bcl6 in promoting appropriate IL-4 production in mT_H2 cells and suggest that chronic allergic diseases involve the T_H2-promoting factor-mediated functional breakdown of Bcl6, resulting in allergy exacerbation.

Adjuvant and carrier protein-dependent T-cell priming promotes a robust antibody response against the Plasmodium falciparum Pfs25 vaccine candidate

Humoral immune responses have the potential to maintain protective antibody levels for years due to the immunoglobulin-secreting activity of long-lived plasma cells (LLPCs). However, many subunit vaccines under development fail to generate robust LLPC responses, and therefore a variety of strategies are being employed to overcome this limitation, including conjugation to carrier proteins and/or formulation with potent adjuvants. Pfs25, an antigen expressed on malaria zygotes and ookinetes, is a leading transmission blocking vaccine (TBV) candidate for Plasmodium falciparum. Currently, the conjugate vaccine Pfs25-EPA/Alhydrogel is in Phase 1 clinical trials in the USA and Africa. Thus far, it has proven to be safe and immunogenic, but it is expected that a more potent formulation will be required to establish antibody titers that persist for several malaria transmission seasons. We sought to determine the contribution of carrier determinants and adjuvants in promoting high-titer, long-lived antibody responses against Pfs25. We found that both adjuvants and carrier proteins influence the magnitude and capacity of Pfs25-specific humoral responses to remain above a protective level. Furthermore, a liposomal adjuvant with QS21 and a TLR4 agonist (GLA-LSQ) was especially effective at inducing T follicular helper (Tfh) and LLPC responses to Pfs25 when coupled to immunogenic carrier proteins.

The Expanding Role of the BCL6 Oncoprotein as a Cancer Therapeutic Target

BCL6 was initially discovered as an oncogene in B-cell lymphomas, where it drives the malignant phenotype by repressing proliferation and DNA damage checkpoints and blocking B-cell terminal differentiation. BCL6 mediates its effects by binding to hundreds of target genes and then repressing these genes by recruiting several different chromatin-modifying corepressor complexes. Structural characterization of BCL6-corepressor complexes suggested that BCL6 might be a druggable target. Accordingly, a number of compounds have been designed to bind to BCL6 and block corepressor recruitment. These compounds, based on peptide or small-molecule scaffolds, can potently block BCL6 repression of target genes and kill lymphoma cells. In the case of diffuse large B-cell lymphomas (DLBCL), BCL6 inhibitors are equally effective in suppressing both the germinal center B-cell (GCB)- and the more aggressive activated B-cell (ABC)-DLBCL subtypes, both of which require BCL6 to maintain their survival. In addition, BCL6 is implicated in an expanding scope of hematologic and solid tumors. These include, but are not limited to, B-acute lymphoblastic leukemia, chronic myeloid leukemia, breast cancer, and non-small cell lung cancer. BCL6 inhibitors have been shown to exert potent effects against these tumor types. Moreover, mechanism-based combinations of BCL6 inhibitors with other agents have yielded synergistic and often quite dramatic activity. Hence, there is a compelling case to accelerate the development of BCL6-targeted therapies for translation to the clinical setting. Clin Cancer Res; 23(4); 885-93. ©2016 AACR.

In vivo dendritic cell targeting cellular vaccine induces CD4+ Tfh cell-dependent antibody against influenza virus

An induction of long-term cellular and humoral immunity is for the goal of vaccines, but the combination of antigens and adjuvant remain unclear. Here, we show, using a cellular vaccine carrying foreign protein antigen plus iNKT cell glycolipid antigen, designated as artificial adjuvant vector cells (aAVCs), that mature XCR1⁻ DCs in situ elicit not only ordinal antigen-specific CD4⁺T cells, but also CD4⁺ Tfh and germinal center, resulted in inducing long-term antibody production. As a mechanism for leading the long-term antibody production by aAVC, memory CD4⁺ Tfh cells but not iNKTfh cells played an important role in a Bcl6 dependent manner. To develop it for influenza infection, we established influenza hemagglutinin-carrying aAVC (aAVC-HA) and found that all the mice vaccinated with aAVC-HA were protected from life-threatening influenza infection. Thus, the in vivo DC targeting therapy by aAVC would be useful for protection against viral infection.

Genetic drivers of NF-κB deregulation in diffuse large B-cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is the most common form of B cell non-Hodgkin lymphoma worldwide and comprises a heterogeneous group of malignancies that originate from the malignant transformation of germinal center (GC) B cells. Over the past decade, significant improvement has been achieved in our understanding of the molecular pathogenesis underlying this disease, thanks in part to the implementation of powerful genomic technologies allowing genome-wide structural and functional analyses. These studies revealed the presence of multiple oncogenic alterations dysregulating signal transduction pathways that are normally required for the normal biology of the cells from which these tumors are derived. Among the pathways identified as recurrent targets of genetic lesions in DLBCL, NF-κB has emerged as a central player in the development and maintenance of this disease, particularly in the less curable, activated B cell (ABC)- like subtype. These lesions reveal vulnerabilities of the lymphoma cells that can be exploited for the design of more rationale therapeutic approaches. The purpose of this review is to summarize recent progresses in understanding the role of NF-κB deregulation in the pathogenesis of DLBCL, with emphasis on the genetic basis underlying its aberrant activation, in relationship to the normal biology of B lymphocytes, and the modelling of these lesions in the mouse.

ZBTB32 Restricts the Duration of Memory B Cell Recall Responses

Memory B cell responses are more rapid and of greater magnitude than are primary Ab responses. The mechanisms by which these secondary responses are eventually attenuated remain unknown. We demonstrate that the transcription factor ZBTB32 limits the rapidity and duration of Ab recall responses. ZBTB32 is highly expressed by mouse and human memory B cells but not by their naive counterparts. Zbtb32(-/-) mice mount normal primary Ab responses to T-dependent Ags. However, Zbtb32(-/-) memory B cell-mediated recall responses occur more rapidly and persist longer than do control responses. Microarray analyses demonstrate that Zbtb32(-/-) secondary bone marrow plasma cells display elevated expression of genes that promote cell cycle progression and mitochondrial function relative to wild-type controls. BrdU labeling and adoptive transfer experiments confirm more rapid production and a cell-intrinsic survival advantage of Zbtb32(-/-) secondary plasma cells relative to wild-type counterparts. ZBTB32 is therefore a novel negative regulator of Ab recall responses.

Synthetic Lethal Screen Demonstrates That a JAK2 Inhibitor Suppresses a BCL6-dependent IL10RA/JAK2/STAT3 Pathway in High Grade B-cell Lymphoma

We demonstrate the usefulness of synthetic lethal screening of a conditionally BCL6-deficient Burkitt lymphoma cell line, DG75-AB7, with a library of small molecules to determine survival pathways suppressed by BCL6 and suggest mechanism-based treatments for lymphoma. Lestaurtinib, a JAK2 inhibitor and one of the hits from the screen, repressed survival of BCL6-deficient cells in vitro and reduced growth and proliferation of xenografts in vivo BCL6 deficiency in DG75-AB7 induced JAK2 mRNA and protein expression and STAT3 phosphorylation. Surface IL10RA was elevated by BCL6 deficiency, and blockade of IL10RA repressed STAT3 phosphorylation. Therefore, we define an IL10RA/JAK2/STAT3 pathway each component of which is repressed by BCL6. We also show for the first time that JAK2 is a direct BCL6 target gene; BCL6 bound to the JAK2 promoter in vitro and was enriched by ChIP-seq. The place of JAK2 inhibitors in the treatment of diffuse large B-cell lymphoma has not been defined; we suggest that JAK2 inhibitors might be most effective in poor prognosis ABC-DLBCL, which shows higher levels of IL10RA, JAK2, and STAT3 but lower levels of BCL6 than GC-DLBCL and might be usefully combined with novel approaches such as inhibition of IL10RA.

FBXO11 inactivation leads to abnormal germinal-center formation and lymphoproliferative disease

The BCL6 proto-oncogene encodes a transcriptional repressor that is required for the germinal center (GC) reaction and is implicated in lymphomagenesis. BCL6 protein stability is regulated by F-box protein 11 (FBXO11)-mediated ubiquitination and degradation, which is impaired in ∼6% of diffuse large B-cell lymphomas that carry inactivating genetic alterations targeting the FBXO11 gene. In order to investigate the role of FBXO11 in vivo, we analyzed GC-specific FBXO11 knockout mice. FBXO11 reduction or loss led to an increased number of GC B cells, to an altered ratio of GC dark zone to light zone cells, and to higher levels of BCL6 protein in GC B cells. B-cell receptor-mediated degradation of BCL6 was reduced in the absence of FBXO11, suggesting that FBXO11 contributes to the physiologic downregulation of BCL6 at the end of the GC reaction. Finally, FBXO11 inactivation was associated with the development of lymphoproliferative disorders in mice.

Rationally designed BCL6 inhibitors target activated B cell diffuse large B cell lymphoma

Diffuse large B cell lymphomas (DLBCLs) arise from proliferating B cells transiting different stages of the germinal center reaction. In activated B cell DLBCLs (ABC-DLBCLs), a class of DLBCLs that respond poorly to current therapies, chromosomal translocations and amplification lead to constitutive expression of the B cell lymphoma 6 (BCL6) oncogene. The role of BCL6 in maintaining these lymphomas has not been investigated. Here, we designed small-molecule inhibitors that display higher affinity for BCL6 than its endogenous corepressor ligands to evaluate their therapeutic efficacy for targeting ABC-DLBCL. We used an in silico drug design functional-group mapping approach called SILCS to create a specific BCL6 inhibitor called FX1 that has 10-fold greater potency than endogenous corepressors and binds an essential region of the BCL6 lateral groove. FX1 disrupted formation of the BCL6 repression complex, reactivated BCL6 target genes, and mimicked the phenotype of mice engineered to express BCL6 with corepressor binding site mutations. Low doses of FX1 induced regression of established tumors in mice bearing DLBCL xenografts. Furthermore, FX1 suppressed ABC-DLBCL cells in vitro and in vivo, as well as primary human ABC-DLBCL specimens ex vivo. These findings indicate that ABC-DLBCL is a BCL6-dependent disease that can be targeted by rationally designed inhibitors that exceed the binding affinity of natural BCL6 ligands.

YY1 Regulates the Germinal Center Reaction by Inhibiting Apoptosis

The germinal center (GC) reaction produces high-affinity Abs for a robust adaptive immune response. When dysregulated, the same processes cause GC B cells to become susceptible to lymphomagenesis. It is important to understand how the GC reaction is regulated. In this study, we show that transcription factor YY1 is required to maintain a robust GC reaction in mice. Selective ablation of YY1 significantly decreased in the frequency and number of GC B cells during the GC reaction. This decrease of GC B cells was accompanied by increased apoptosis in these cells. Furthermore, we found that loss of YY1 disrupted the balance between dark zones and light zones, leading to a preferential decrease in dark zone cells. Collectively, these results indicate that YY1 plays an important role in regulating the balance between dark zone and light zone cells in GCs and between survival and death of GC B cells.

Genetic Immunization: A New Monoclonal Antibody for the Detection of BCL-6 Protein in Paraffin Sections

Genetic immunization can be combined with hybridoma technology to generate high-affinity monoclonal antibodies (MAbs). A new anti-BCL-6 MAb (GI191E/A8) was produced by cloning full-length BCL-6 cDNA into a eukaryotic vector and delivering this into mouse epidermis using a helium gene gun. A comparative study was made of the specificity and the effects of formalin fixation on immunohistochemistry quality of GI191E/A8 and two other anti-BCL-6 MAbs. To evaluate its possible application to differential diagnosis of lymphomas, two tissue microarrays (89 diffuse large B-cell lymphomas and 24 B-cell chronic lymphocytic leukemia cases) were stained with GI191E/A8 and another anti-BCL-6 MAb produced by conventional means. Using GI191E/A8, the detection of BCL-6 protein was significantly increased, and its specificity was independent of formalin-fixation time. Using automatic quantified analysis, the correlation between the two anti-BCL-6 MAbs tested was identical in cases with overexpression or absence of BCL-6. In cases with intermediate BCL-6 protein expression, detection with GI191E/A8 was more sensitive. A significant association of higher BCL-6 expression and longer median overall survival times in diffuse large B-cell lymphomas was found. Using conventionally produced MAbs in the same patient group, the association was not significant.

Targeted epigenetic repression of a lymphoma oncogene by sequence-specific histone modifiers induces apoptosis in DLBCL

Alterations to the epigenetic landscape of diffuse large B-cell lymphoma (DLBCL) play a fundamental role in deregulating genes involved in normal lymphocyte differentiation. To determine whether targeted epigenetic therapy could reverse these pathogenic chromatin changes and suppress the expression of a lymphoma oncogene, we focused on BCL6, a transcriptional repressor whose aberrant expression is tightly linked to DLBCL proliferation and survival. We fused zinc-finger (ZF) domains specific for regulatory regions in the BCL6 locus to a repressive epigenetic modifier, the Kruppel-associated box (KRAB) repressor domain. Distinct ZF-KRAB fusions repressed the local chromatin landscape, suppressed BCL6 expression, significantly impaired DLBCL growth, and caused widespread cell death in a BCL6-dependent manner. Importantly, expression of ectopic BCL6 protein rescued ZF-KRAB-induced cell death, demonstrating the modifiers' specificity. We show that sequence-specific epigenetic modifiers can alter oncogene expression and induce apoptosis in cancer cells, underscoring their potential for future development as targeted epigenetic protein therapies.

Regulation of hematopoietic development by ZBTB transcription factors

Hematopoietic development is governed by the coordinated expression of lineage- and differentiation stage-specific genes. Transcription factors play major roles in this process and their perturbation may underlie hematologic and immunologic disorders. Nearly 1900 transcription factors are encoded in the human genome: of these, 49 BTB (for broad-complex, tram-track and bric à brac)-zinc finger transcription factors referred to as ZBTB or POK proteins have been identified. ZBTB proteins, including BCL6, PLZF, ThPOK and LRF, exhibit a broad spectrum of functions in normal and malignant hematopoiesis. This review summarizes developmental and molecular functions of ZBTB proteins relevant to hematology.

Chronic lymphocytic leukemia cells diversify and differentiate in vivo via a nonclassical Th1-dependent, Bcl-6-deficient process

Xenografting primary tumor cells allows modeling of the heterogeneous natures of malignant diseases and the influences of the tissue microenvironment. Here, we demonstrate that xenografting primary chronic lymphocytic leukemia (CLL) B lymphocytes with activated autologous T cells into alymphoid mice results in considerable CLL B cell division and sizable T cell expansion. Nevertheless, most/all CD5⁺CD19⁺ cells are eventually lost, due in part to differentiation into antibody-secreting plasmablasts/plasma cells. CLL B cell differentiation is associated with isotype class switching and development of new IGHV-D-J mutations and occurs via an activation-induced deaminase-dependent pathway that upregulates IRF4 and Blimp-1 without appreciable levels of the expected Bcl-6. These processes were induced in IGHV-unmutated and IGHV-mutated clones by Th1-polarized T-bet⁺ T cells, not classical T follicular helper (Tfh) cells. Thus, the block in B cell maturation, defects in T cell action, and absence of antigen-receptor diversification, which are often cardinal characteristics of CLL, are not inherent but imposed by external signals and the microenvironment. Although these activities are not dominant features in human CLL, each occurs in tissue proliferation centers where the mechanisms responsible for clonal evolution operate. Thus, in this setting, CLL B cell diversification and differentiation develop by a nonclassical germinal center-like reaction that might reflect the cell of origin of this leukemia.

Germinal Center B-Cell-Associated Nuclear Protein (GANP) Involved in RNA Metabolism for B Cell Maturation

Germinal center B-cell-associated nuclear protein (GANP) is upregulated in germinal center B cells against T-cell-dependent antigens in mice and humans. In mice, GANP depletion in B cells impairs antibody affinity maturation. Conversely, its transgenic overexpression augments the generation of high-affinity antigen-specific B cells. GANP associates with AID in the cytoplasm, shepherds AID into the nucleus, and augments its access to the rearranged immunoglobulin (Ig) variable (V) region of the genome in B cells, thereby precipitating the somatic hypermutation of V region genes. GANP is also upregulated in human CD4(+) T cells and is associated with APOBEC3G (A3G). GANP interacts with A3G and escorts it to the virion cores to potentiate its antiretroviral activity by inactivating HIV-1 genomic cDNA. Thus, GANP is characterized as a cofactor associated with AID/APOBEC cytidine deaminase family molecules in generating diversity of the IgV region of the genome and genetic alterations of exogenously introduced viral targets. GANP, encoded by human chromosome 21, as well as its mouse equivalent on chromosome 10, contains a region homologous to Saccharomyces Sac3 that was characterized as a component of the transcription/export 2 (TREX-2) complex and was predicted to be involved in RNA export and metabolism in mammalian cells. The metabolism of RNA during its maturation, from the transcription site at the chromosome within the nucleus to the cytoplasmic translation apparatus, needs to be elaborated with regard to acquired and innate immunity. In this review, we summarize the current knowledge on GANP as a component of TREX-2 in mammalian cells.

Genome-wide Analysis Identifies Bcl6-Controlled Regulatory Networks during T Follicular Helper Cell Differentiation

T follicular helper (Tfh) cell is a unique T cell subset specialized in promoting humoral immunity. B-cell lymphoma 6 protein (Bcl6) has been identified as an obligatory transcription factor in Tfh cells; however, the molecular mechanism underlying Bcl6 function remains largely unknown. Here, we defined Bcl6 target genes in Tfh cells by analyzing genome-wide Bcl6 occupancy together with transcriptome profiling. With consensus sequences being different from those in Th9, B cells, and macrophages, Bcl6 binding in Tfh cell was closely associated with a decrease in 5-hydroxymethylcytosine (5hmC). Importantly, Bcl6 promoted Tfh cell differentiation through antagonizing IL-7R (CD127)/signal transducer and activator of transcription (STAT) 5 axis; deletion of the Bcl6 gene in T cells resulted in enhanced IL-7R-STAT5 signaling and substantial expansion of CD127(hi) non-Tfh cells. Thus, our study systemically examines Bcl6-controlled regulatory networks and provides important insights into Bcl6's biological functions in Tfh cells.

Epigenetic Regulation of the Blimp-1 Gene (Prdm1) in B Cells Involves Bach2 and Histone Deacetylase 3

B lymphocyte-induced maturation protein 1 (Blimp-1) encoded by Prdm1 is a master regulator of plasma cell differentiation. The transcription factor Bach2 represses Blimp-1 expression in B cells to stall terminal differentiation, by which it supports reactions such as class switch recombination of the antibody genes. We found that histones H3 and H4 around the Prdm1 intron 5 Maf recognition element were acetylated at higher levels in X63/0 plasma cells expressing Blimp-1 than in BAL17 mature B cells lacking its expression. Conversely, methylation of H3-K9 was lower in X63/0 cells than BAL17 cells. Purification of the Bach2 complex in BAL17 cells revealed its interaction with histone deacetylase 3 (HDAC3), nuclear co-repressors NCoR1 and NCoR2, transducin β-like 1X-linked (Tbl1x), and RAP1-interacting factor homolog (Rif1). Chromatin immunoprecipitation confirmed the binding of HDAC3 and Rif1 to the Prdm1 locus. Reduction of HDAC3 or NCoR1 expression by RNA interference in B cells resulted in an increased Prdm1 mRNA expression. Bach2 is suggested to cooperate with HDAC3-containing co-repressor complexes in B cells to regulate the stage-specific expression of Prdm1 by writing epigenetic modifications at the Prdm1 locus.

A Network Model to Describe the Terminal Differentiation of B Cells

Terminal differentiation of B cells is an essential process for the humoral immune response in vertebrates and is achieved by the concerted action of several transcription factors in response to antigen recognition and extracellular signals provided by T-helper cells. While there is a wealth of experimental data regarding the molecular and cellular signals involved in this process, there is no general consensus regarding the structure and dynamical properties of the underlying regulatory network controlling this process. We developed a dynamical model of the regulatory network controlling terminal differentiation of B cells. The structure of the network was inferred from experimental data available in the literature, and its dynamical behavior was analyzed by modeling the network both as a discrete and a continuous dynamical systems. The steady states of these models are consistent with the patterns of activation reported for the Naive, GC, Mem, and PC cell types. Moreover, the models are able to describe the patterns of differentiation from the precursor Naive to any of the GC, Mem, or PC cell types in response to a specific set of extracellular signals. We simulated all possible single loss- and gain-of-function mutants, corroborating the importance of Pax5, Bcl6, Bach2, Irf4, and Blimp1 as key regulators of B cell differentiation process. The model is able to represent the directional nature of terminal B cell differentiation and qualitatively describes key differentiation events from a precursor cell to terminally differentiated B cells.

Generation of antibody-producing cells through terminal B cell differentiation represents a good model to study the formation of multiple effector cells from a progenitor cell type. This process is controlled by the action of several molecules that maintain cell type specific programs in response to cytokines, antigen recognition and the direct contact with T helper cells, forming a complex regulatory network. While there is a large body of experimental data regarding some of the key molecules involved in this process and there have been several efforts to reconstruct the underlying regulatory network, a general consensus about the structure and dynamical behavior of this network is lacking. Moreover, it is not well understood how this network controls the establishment of specific B cell expression patterns and how it responds to specific external signals. We present a model of the regulatory network controlling terminal B cell differentiation and analyze its dynamical behavior under normal and mutant conditions. The model recovers the patterns of differentiation of B cells and describes a large set of gain- and loss-of-function mutants. This model provides an unified framework to generate qualitative descriptions to interpret the role of intra- and extracellular regulators of B cell differentiation.

IgG-Immune Complexes Promote B Cell Memory by Inducing BAFF

Memory B cell responses are vital for protection against infections but must also be regulated to prevent autoimmunity. Cognate T cell help, somatic hypermutation, and affinity maturation within germinal centers (GCs) are required for high-affinity memory B cell formation; however, the signals that commit GC B cells to the memory pool remain unclear. In this study, we identify a role for IgG-immune complexes (ICs), FcγRs, and BAFF during the formation of memory B cells in mice. We found that early secretion of IgG in response to immunization with a T-dependent Ag leads to IC-FcγR interactions that induce dendritic cells to secrete BAFF, which acts at or upstream of Bcl-6 in activated B cells. Loss of CD16, hematopoietic cell-derived BAFF, or blocking IC:FcγR regions in vivo diminished the expression of Bcl-6, the frequency of GC and memory B cells, and secondary Ab responses. BAFF also contributed to the maintenance and/or expansion of the follicular helper T cell population, although it was dispensable for their formation. Thus, early Ab responses contribute to the optimal formation of B cell memory through IgG-ICs and BAFF. Our work defines a new role for FcγRs in GC and memory B cell responses.

High expression of Bcl-2 predicts poor outcome in diffuse large B-cell lymphoma patients with low international prognostic index receiving R-CHOP chemotherapy

The prognostic significance of Bcl-2, Bcl-6, p53, topoisomerase II, and β-tubulin expression was evaluated in diffuse large B-cell lymphoma (DLBCL) patients treated with cyclophosphamide, doxorubicin, vincristine, prednisolone, and rituximab. Eight-year progression-free survival (PFS, P = 0.006) and overall survival (OS, P = 0.001) of patients with high Bcl-2 expression were significantly inferior to those of patients with low expression without prognostic significance of Bcl-6, p53, topoisomerase II, and β-tubulin expression. High expression of Bcl-2 was associated with poor PFS (P = 0.045) and OS (P = 0.004) only in patients with low international prognostic index (IPI). In multivariate analysis, high expression of Bcl-2 was a significant independent prognostic factor of poor PFS (P = 0.026) and OS (P = 0.007) along with high IPI. In conclusion, the expression of Bcl-2 may be a useful prognostic factor, especially in DLBCL patients with low IPI.

Mechanisms of action of BCL6 during germinal center B cell development

The transcriptional repressor B cell lymphoma 6 (BCL6) controls a large transcriptional network that is required for the formation and maintenance of germinal centers (GC). GC B cells represent the normal counterpart of most human B-cell lymphomas, which are often characterized by deregulated BCL6 expression or BCL6-mediated pathways. BCL6 suppresses gene transcription largely through recruitment of its co-repressors through its distinct repression domain. Understanding the precise biological roles of each repression domain in normal and malignant B cells is helpful for development of targeted inhibition of BCL6 functions that is emerging as the basis for design of anti-lymphoma therapies. This review focuses on recent progress in the molecular mechanisms of action of BCL6 in B cells and discusses remaining unresolved questions related to how these mechanisms are linked to normal and malignant B cell development.

Prednisone treatment inhibits the differentiation of B lymphocytes into plasma cells in MRL/MpSlac-lpr mice

AIM

A number of evidence shows that the differentiation of B lymphocytes into plasma cells plays an important role in lupus pathogenesis. In this study we investigated how prednisone, a classical therapeutic drug for autoimmune diseases, regulated plasma cell differentiation in MRL/MpSlac-lpr mice.

METHODS

MRL/lpr mice were treated with prednisone (2.5 or 5 mg·kg(-1)·d(-1), ig) for 13 weeks, and the proteinuria levels and survival times were monitored. After the mice were euthanized, blood sample, spleen and thymus were collected. The serum levels of anti-dsDNA antibody, anti-nuclear antibody, IL-21, and IL-10 were detected using ELISA kits. Subsets of splenic B and T lymphocytes were quantified with flow cytometry. Transcription factor Blimp-1 and Bcl-6 expression was determined using qPCR and Western blot.

RESULTS

Prednisone treatment dose-dependently attenuated the lupus symptoms in MRL/lpr mice with decreased proteinuria levels, prolonged survival times, decreased serum anti-nuclear antibody levels, and reduced spleen and thymus indices. Prednisone treatment also significantly decreased the elevated percentages of plasma cells and plasma cell precursors, decreased the percentages of activated T cells, and increased the frequency of CD4(+)CD62L(+) cells, demonstrated that decreased anti-nuclear antibodies and improvements in lupus symptoms were associated with decreased plasma cells. Furthermore, prednisone treatment decreased serum IL-21 and IL-10 levels and reduced the expression of splenic Blimp-1 and Bcl-6 (two key regulatory factors for plasma cell differentiation) in MRL/lpr mice.

CONCLUSION

Prednisone treatment restricts B lymphocyte differentiation into plasma cells in MRL/lpr mice, which may be correlated with the inhibition of IL-21 production and the restoration of the balance between Blimp-1 and Bcl-6.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.