Pharmacological Targeting of PI3K-Dependent Central Tolerance Mechanisms in Refractory Pre-Germinal Center B-Cell Malignancies

Abstract Rationale: About 75% of newly formed B-cells are autoreactive and express potentially harmful autoantibodies (Wardemann 2003). Hence, a powerful mechanism, termed central tolerance, is in place to eliminate millions of newly formed autoreactive B-cells every day. Results: B-ALL, mantle cell lymphoma (MCL) and unmutated chronic lymphocytic leukemia (U-CLL) originate from early, pre-germinal center (pre-GC) stages of B-cell development that are subject to negative B-cell selection and central tolerance mechanisms. While designed to eliminate autoreactive clones during early B-cell development, we recently discovered that B-ALL, MCL and U-CLL fully retained sensitivity to central tolerance mechanisms, which are triggered by persistent PI3K-hyperactivation. PI3K-signaling code to distinguish between normal and pathological signaling. Studying short transient pulses and chronic activation of PI3K-signaling, we discovered that pre-GC B-cells have evolved a "PI3K-signaling code" to distinguish between normal B-cell activation by antigen and pathological signaling: thereby, antigen encounter induces a short transient pulse of PI3K-activation which promotes survival and proliferation. Conversely, persistent activation of PI3K-activation reflects pathological signaling, either from an autoreactive B-cell receptor (BCR) or a transforming oncogene. Pre-GC B-cell malignancies are exempt from oncogenic PI3K-lesions. PI3K-lesions in cancer result in permanent hyperactivation as in autoreactive B-cells. The PI3K pathway is targeted by oncogenic lesions in ~25% of human cancer. The phosphatases PTEN, SHIP1 and PP2A function as negative regulators of PI3K signaling and are frequently mutated in a broad range of cancers and also occur in some GC- and post-GC lymphomas (e.g. Burkitt's, DLBCL). However, our analysis in six clinical cohorts revealed that pre-GC B-cell malignancies, including B-ALL, MCL and U-CLL critically depend on PTEN, SHIP1 and PP2A function and do not tolerate persistent hyperactivation of PI3K-signaling for more than three hours. Loss-of-function mutations of these phosphatases and activating PI3K lesions were not detected in large clinical cohorts of patients with B-ALL, MCL and CLL. Likewise, phosphorylation of AKT-S473, reflecting PI3K signaling strength, is elevated throughout multiple cancer types including post-GC DLBCL, but not in B-ALL and MCL. This is in line with previous work demonstrating that inherited mutations that cause PI3K-activation predispose to various cancers but cause profound defects in human B-lymphopoiesis (Fruman 2014). Pharmacological targeting of PI3K-dependent central tolerance mechanisms. We tested the hypothesis that PI3K-hyperactivation represents a unique vulnerability in pre-GC B-cell tumors including B-ALL, MCL and U-CLL. Sensitivity to PI3K-hyperactivation of reflects their pre-GC origin and central tolerance mechanisms during early B-cell development that are designed to eliminate autoreactive B-cells based on hyperactive PI3K-signaling. For this reason, we tested pharmacological PI3K-hyperactivation as a novel strategy to selectively target pre-GC B-cell malignancies. To this end, we tested 144 compounds for their ability to engage PI3K-dependent central tolerance mechanism in B-ALL, MCL and CLL. Small molecule inhibitors of SHIP1 (3AC, K118), PTEN (SF-1670), PP2A (LB-100) and a direct PI3K-agonist (SC79) achieved strong phosphorylation of known PI3K-substrates (AKT, S6K) in vitro and prolonged overall survival in NSG mice transplanted with refractory B-ALL and MCL PDX in vivo. Conclusions and future directions: Current treatment regimens (kinase-inhibitor paradigm) use agents that apply selective pressure in one direction (e.g., PI3K-inhibitors; BCR-ABL1, SYK- or BTK-inhibitors). Here, we are pursuing a new concept (central tolerance paradigm) based on sequential treatment regimens that alternate between kinase-inhibitors (e.g., dasatinib, ibrutinib, idelalisib) and PI3K-hyperactivation (3AC, K118, LB100). By sequentially applying selective pressures in opposite directions, our approach will subvert clonal evolution and selection for drug-resistant mutants. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

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Pathological Roles of p18 Deficiency Toward B Cell Malignances

Blood ◽

10.1182/blood.v126.23.2448.2448 ◽

2015 ◽

Vol 126 (23) ◽

pp. 2448-2448

Author(s):

Sha Hao ◽

Fang Dong ◽

Wen Zhou ◽

Hui Cheng ◽

Shihui Ma ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Poor Prognosis ◽

Absolute Number ◽

Cell Development ◽

B Cell Development ◽

B Cell Malignancies ◽

Hematopoietic Stem ◽

Hematopoietic Malignancies ◽

Low Expression

Abstract The cyclin-dependent kinases inhibitor CDKN2C (p18INK4C, p18) is a member of the INK4 family that specifically blocks the activity of CDK4/6 in the G1 phase of cell cycle. In the hematopoietic system, deletion of p18 was indicated to be associated with T cell malignancies in mice and B cell malignancies in humans. Moreover, p18 deficiency is a poor prognosis factor for the patients with multiple myeloma (MM). However, a formal investigation on the pathological roles of p18 deficiency in hematopoietic malignancies, especially B cell malignancies is lacking. In this study, we first obtained direct clinical relevance of p18 deficiency with hematopoietic malignancies. Based on the Oncomine data set analysis, low expression of p18 was found in the patients with B-Cell Acute Lymphoblastic Leukemia (54 out of 80). In addition, by Gene expression Profile (GEP) analysis (n=361) and multi-color FISH analysis (n=265) of first-visit MM patients, there were 11% MM patients showed low expression and 9.06% biallelic deletion of p18 gene respectively, which was correlated with poor prognosis. Further analysis indicated higher expression of c-Myc, Bcl-2 and TRAF3 in p18-deleted MM patients or MM cell lines. We then focused on the impact of p18 deletion on B cell development with the mice deficient in p18 (p18-/-). The frequency and absolute number of B220+ B cell were significantly decreased in the bone marrow (21.075±0.168% vs 13.956±1.613%, n=5) or spleen (49.320±1.773 vs 35.35±1.673, n=5) of p18-/- mice. Secretion of immunoglobulin (Ig) from plasma cells was also impaired. Furthermore, p18-/- BM or enriched hematopoietic stem cell (LSK+) transplantation also recaptured the deficiency of mature B cells in the recipients despite higher repopulation in the p18-/- group. Ectopic over-expression of p18 in the hematopoietic stem and progenitor cells (HSPCs) via retroviral transduction could partially correct the abnormality of p18-/- B cells in the transplant recipients. These results suggested that the defect of B cell development in the absence of p18 was intrinsic to the hematopoietic cells, rather than extrinsic (via micro-environmental). To further define the effects of p18 deficiency on HSPCs prior to B cell commitment, we enumerated the frequencies of LT-HSC, MPP, CMP, GMP, MEP, Lin-IL-7R+ and CLP cell populations in p18-/- or control mice. There was no significant difference in the frequency or absolute number of CMP, GMP, MEP, or CLP between p18-/- and control groups. Notably however, the colony-forming cells of pre-B cells in p18-/- BM were significantly increased (24.4±2.1 vs 32.6±1.8, n=5). Moreover, we also examined the B cells at different developmental stages including pre-pro-B cell, pre-B, immature-B and mature B cells in BM, as well as transitional stage 1(T1), transitional stage 2 (T2) and mature B cells in the spleen. Our data showed an accumulation of the cells at pre-B cell stage in the absence of p18, while dramatically decreased at mature B cells stage. To further explore the molecular basis, single cell RT qPCR analysis was performed and revealed that the transcription factors including Foxo1, Rag2, E2A, EBF1and Pax5 were significantly higher inCLP, pro-B, pre-B, immature-B subpopulations of p18-/- group. However, lamada 5, which is necessary for B cells maturation, was remarkably decreased in p18-/- immature B cells compared with control group. Taken together, our study provides definitive evidence for the disruption of B cell development due to p18 deficiency and this new evidence underlies the pathological contributions of p18 down-regulation or deletion to B cell malignancies in humans. Disclosures No relevant conflicts of interest to declare.

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Tumor Suppressors BTG1 and BTG2 Fulfill Both Unique and Overlapping Functions During Normal B Lymphocyte Development

Blood ◽

10.1182/blood.v120.21.1303.1303 ◽

2012 ◽

Vol 120 (21) ◽

pp. 1303-1303

Author(s):

Esther J.H. Tijchon ◽

Liesbeth van Emst ◽

Jørn Havinga ◽

Jean-Pierre Rouault ◽

Felice Tirone ◽

...

Keyword(s):

Bone Marrow ◽

Transcription Factors ◽

B Cells ◽

B Cell ◽

Tumor Suppressors ◽

Cell Development ◽

B Cell Development ◽

B Cell Differentiation ◽

B Cell Malignancies ◽

Cell Stage

Abstract Abstract 1303 B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is the most common form of cancer in children, characterized by genetic aberrations affecting master regulators of lymphoid differentiation, such as RUNX1, IKZF1, TCF3, and PAX5, as well as tumor suppressor genes that control the cell cycle, including RB1 and CDKN2A. Another gene frequently altered in BCP-ALL is BTG1, which displays highly clustered mono-allelic deletions in childhood BCP-ALL (9%) and adult ALL (6%). The frequency of BTG1 deletions is two- to three-fold higher in ETV6-RUNX1- and BCR-ABL1-positive leukemias. BTG1, and its close homologue BTG2 regulate gene expression, for instance by associating with protein arginine methyltransferase 1 (PRMT1), affecting the activity of a variety of transcription factors, including several nuclear hormone receptors and HoxB9. In addition, BTG1 and BTG2 have been implicated in regulating mRNA stability by interacting with the Ccr4-Not complex. Recent studies have also identified missense point mutations in BTG1 and BTG2 in about 20% of non-Hodgkin lymphomas, arguing that altered function of these genes contributes to B cell malignancies. To investigate a role of BTG1 and BTG2 in B cell development, we studied the phenotype of Btg1 and Btg2 single knockout (KO) and Btg1;Btg2 double KO mice. Animals deficient for either BTG1 or BTG2 displayed a mild B cell phenotype with a moderate reduction of ∼20% in the total amount of B220+ progenitor B cells in bone marrow, while splenic B cells were present at normal frequencies. More detailed analyses revealed that Btg1−/− and Btg2−/− mice both showed a partial block at the pre-pro-B cell stage (Hardy fraction A). Methylcellulose colony assays in the presence of interleukin-7 (IL-7) demonstrated 30% fewer colonies using bone marrow from Btg2−/− mice, whereas 70% fewer colonies were obtained using bone marrow derived from Btg1−/− mice. To assess whether BTG1 and BTG2 fulfill redundant functions during B cell development, we analyzed the phenotype of Btg1−/−;Btg2−/− mice. Hence we observed that the combined loss of BTG1 and BTG2 led to a much stronger block in B cell differentiation, with the majority of progenitor B cells arrested at the pre-pro-B cell stage. In the spleens of these double knockout mice we observed a roughly 50% reduction in B220+ IgM+ B cells, suggesting that these genes act to modify the activity of B lineage transcription factors rather than to fully block their activities. This is consistent with a role for these genes as modifiers of transcriptional activity. Current studies are aimed at defining the molecular targets regulated by BTG1 and BTG2 during early B cell development using RNA sequencing and protein interaction experiments. In conclusion, our data demonstrate that BTG1 and BTG2 act as important regulators of normal B cell differentiation, and that this function might be critical for their role as tumor suppressors in (early) B cell malignancies. Disclosures: No relevant conflicts of interest to declare.

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Regulation of B-cell development by BCAP and CD19 through their binding to phosphoinositide 3-kinase

Blood ◽

10.1182/blood-2007-08-109769 ◽

2008 ◽

Vol 111 (3) ◽

pp. 1497-1503 ◽

Cited By ~ 96

Author(s):

Yuichi Aiba ◽

Megumi Kameyama ◽

Tetsuo Yamazaki ◽

Thomas F. Tedder ◽

Tomohiro Kurosaki

Keyword(s):

B Cells ◽

B Cell ◽

Active Form ◽

Cell Development ◽

B Cell Development ◽

Activation Mechanism ◽

Developmental Defect ◽

Akt Activation ◽

Pi3k Activation ◽

Phosphoinositide 3 Kinase

Abstract Despite the importance of phosphoinositide 3-kinase (PI3K) in B-cell development, its activation mechanism still remains elusive. In this study, we show that deletion of both BCAP and CD19 leads to an almost complete block of BCR-mediated Akt activation and to severe defects in generation of immature and mature B cells. The YXXM motifs in BCAP and CD19 are crucial for regulating B-cell development in that mutation of these motifs abrogated their ability to induce BCR-mediated Akt activation as well as to promote B-cell development. Furthermore, the developmental defect in CD19−/−BCAP−/− B cells was partly relieved by introducing a constitutively active form of PI3K or PDK1. Together, our data suggest that BCAP and CD19 have complementary roles in BCR-mediated PI3K activation, thereby, at least in part, contributing to B-cell development.

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Germinal Center-Derived Lymphomas and Plasmacytomas in Mice with Targeted Deletion of MiR-15a/16-1 in Activated B Cells

Blood ◽

10.1182/blood.v128.22.743.743 ◽

2016 ◽

Vol 128 (22) ◽

pp. 743-743

Author(s):

Tomasz Sewastianik ◽

Jianjun Zhao ◽

Meng Jiang ◽

Jianli Wang ◽

Vinodh Pillai ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Board Of Directors ◽

Plasma Cells ◽

Cell Development ◽

B Cell Development ◽

B Cell Malignancies ◽

Advisory Committees ◽

Equity Ownership ◽

Activated B Cells

Abstract MicroRNA (miR)-mediated gene regulation plays critical roles in B-cell development and dysregulated expression of miRs has been implicated in the pathogenesis of various types of B-cell malignancies. Somatic deletions of chromosome 13q14, harboring miR-15a/16-1, occurs frequently in B-cell lymphomas suggesting that members of this miR family are tumor suppressors. Consistently, mice with CD19-Cre-induced deletion of miR-15a/16-1 in early B-cells and follicular B-cells develop chronic lymphocytic leukemia (CLL). Since the 13q14 deletion is observed in a broader range of B-cell malignancies, we hypothesized that the type of B-cell malignancy resulting from miR-15a/16-1 down-regulation may depend on the stage of B-cell development at which this deletion occurs. Therefore, we generated a transgenic mouse model in which conditional deletion of miR-15a/16-1 takes place at later stages of B-cell development. To delete miR-15a/16-1 in activated B-cells, miR-15a/16-1fl/fl mice were mated with AID-Cre+/+ mice to obtain AID-Cre+/-; miR-15a/16-1fl/fl compound mice that expressed Cre recombinase from the Activation-induced Cytidine Deaminase (AID promoter) gene - a gene needed for generation of somatic hypermutations in the immunoglobulin (Ig) variable region (V) genes that is highly expressed in activated B-cells and is a well-known marker for germinal center (GC) B-cells. Expression levels of both miR-15a and miR-16-1, but not miR-15b were decreased in GC B-cells of AID-Cre+/-; miR-15a/16-1fl/fl mice as compared with control AID-Cre+/- mice when evaluated by In Situ Hybridization (ISH) analysis. Given that in humans miR-15a, b and 16 are also expressed in GC B-cells, these results demonstrate the validity of this mouse model in which the biological consequences of miR-15a/16-1 deletion can be studied. Next we assessed whether miR-15a/16-1 deletion could affect proliferation and/or survival of GC B-cells. GCs in the spleens of AID-Cre+/-; miR-15a/16-1fl/fl mice at 10 weeks of age were significantly increased in both number and size, and contained a larger number of Ki-67-positive B-cells as compared with spleens of AID-Cre+/- mice. No significant differences in the number of apoptotic cells, neither in the expression of the miR-15a/16-1 putative target BCL2 were detected, indicating that miR-15a/16-1 may play important roles in the proliferation, but not survival of GC B-cells. Apart from mild splenic enlargement and increased number and size of GCs, AID-Cre+/-, miR-15a/16-1fl/fl mice where indistinguishable from AID-Cre+/- mice between 8 and 40 weeks of age as assessed by weight and posture. However, after 48 weeks of age and at variable times thereafter, 80% (32/40) of AID-Cre+/-, miR-15a/16-1fl/fl mice but none from control cohorts (0/30) showed signs of disease. Gross pathologic examination of euthanized AID-Cre+/-; miR-15a/16-1fl/fl mice revealed enlargement of the spleen and lymph nodes. Detailed histological examination revealed in most instances an effacement of normal tissue architecture by a nodular or diffuse population of atypical lymphoid cells, or less commonly by sheets of plasma cells in interfollicular areas. Two distinct patterns of B220+BCL6+BCL2- B-cell lymphomas were identified after detailed analysis. The most common (47%) resembled human follicular lymphoma (FL) and the next in frequency (28%) resembled human diffuse large B-cell lymphoma (DLBCL). The other group of tumors (25%) resembled human plasmacytoma (PC). All three tumor subtypes were clonal, hypermutated and associated with different degrees of preservation of the dendritic meshwork in the lymph nodes. The comparison of lymphomas arising in AID-Cre+/-; miR-15a/16-1fl/fl mice and CD19-Cre+/-; miR-15a/16-1fl/fl mice corroborated that deletion of miR-15a/16-1 at different stages of B-cell development leads to distinct subtypes of B-cell malignancies. Finally, we investigated miR-15a/16-1 expression in human FL and PC and showed that miR-15a/16-1 abundance is significantly decreased in those malignancies when compared with nodal B-cells in reactive GCs and normal plasma cells in interfollicular areas respectively, suggesting that miR-15a/16-1 may play important roles in normal GC B-cell development as well as in the pathogenesis of FL and PC in humans. Disclosures Ghobrial: BMS: Honoraria, Research Funding; Novartis: Honoraria; Celgene: Honoraria, Research Funding; Takeda: Honoraria; Noxxon: Honoraria; Amgen: Honoraria. Anderson:Oncoprep: Equity Ownership; Acetylon: Equity Ownership; Oncoprep: Equity Ownership; Gilead: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Acetylon: Equity Ownership; Millennuim: Membership on an entity's Board of Directors or advisory committees; Millennuim: Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Equity Ownership; C4 Therapeutics: Equity Ownership; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees.

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FBXW7 Is Critical for B1 Cell Maintenance and Function

Blood ◽

10.1182/blood-2018-99-120387 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 2565-2565

Author(s):

Parham Ramezani-Rad ◽

Charlotte R Leung ◽

John R Apgar ◽

Robert C Rickert

Keyword(s):

B Cells ◽

B Cell ◽

Peritoneal Cavity ◽

Cell Development ◽

B Cell Development ◽

Conditional Knockout ◽

B Cell Malignancies ◽

Hematopoietic Stem ◽

B1 Cells ◽

Stimulation Of

Abstract Background: The E3 ubiquitin ligase Fbxw7 is responsible for the proteasomal degradation of several oncogenes involved in cellular proliferation, growth and survival. Notably, Fbxw7 has been characterized as a tumor suppressor in a variety of cancers, including T ALL and CLL. In the absence of Fbxw7, hematopoiesis is defective leading to abnormal development of B and T cells. In these mice, hematopoietic stem cells have impaired self-renewal due to stabilization of c-Myc. Fbxw7 targets several well-characterized molecules (c-Myc, Mcl1, p100, cyclin E, mTOR, SREBP1) with essential functions in B cells. We have recently shown that glycogen synthase kinase 3 (Gsk3), which is negatively regulated by PI3K signaling, controls the metabolic needs of B cells (Jellusova et al., 2017 Nat. Immunol.). A number of Gsk3 substrates are phosphorylated and degraded via the proteasome through recognition of Fbxw7. We sought to investigate the GSK3-FBXW7 axis in B cells and its implications for B cell malignancies. Results: To elucidate the role of Fbxw7 in B cells, we studied Fbxw7 in a conditional knockout mouse model. We crossed Fbxw7fl/flmice with Mb1Cre mice to ablate Fbxw7 during early B cell development. In the absence of Fbxw7, B cells passed through their developmental stages and showed no significant signs of maturation defects in the bone marrow. However, mature recirculating B cells were nearly absent in Fbxw7-deficient animals. Correspondingly, peripheral B cells in the spleen were reduced and showed specific decreases in follicular B cells. Histological analysis of the spleen architecture showed intact B cell follicles with presence of marginal zone B cells. In B cell malignancies, mutations of FBXW7 have been reported in CLL, for which the normal counterpart are B1 cells. We analyzed the B1 cell compartment in the peritoneal cavity in the absence of Fbxw7. Loss of Fbxw7 resulted in drastic reductions of B1 cells in the peritoneal cavity. Both B1a and B1b cells were mutually affected in these mice. To further characterize this B1 cell defect, we generated a novel acute deletion model for Fbxw7. We crossed Fbxw7fl/flmice with hCD20Cre-ERT2 and administered tamoxifen by oral gavage to induce genetic ablation. Acute deletion of Fbxw7 lead to reduction of B1 cells within a few weeks, indicating the importance of Fbxw7 for the maintenance of B1 cells. When challenged with T cell-independent immunizations the overall antibody responses where reduced. BCR-stimulation of cells in vitro showed diminished growth and signaling potential of knockout cells. These cells have reduced calcium signaling and undergo massive apoptosis. The survival defect could be partially rescued with co-stimulation of IL-4 or ectopic expression of BCL2. Conclusion: Our findings identify Fbxw7 as a critical regulator of B cell development. Specifically, Fbxw7 regulates B cell signaling, development and maintenance of B1 cells. These findings are directly relevant to the pathogenesis of CLL. Loss of function mutations of FBXW7 in CLL likely occur later during tumor evolution and potentially contribute to the specific microenvironmental niche. Disclosures Rickert: Pfizer: Employment.

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Faculty Opinions recommendation of c-Myb is critical for B cell development and maintenance of follicular B cells.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1028155.335037 ◽

2005 ◽

Author(s):

Kyoko Hayakawa

Keyword(s):

B Cells ◽

B Cell ◽

Cell Development ◽

B Cell Development ◽

Follicular B Cells

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Loss of IP3 Receptor–Mediated Ca2+ Release in Mouse B Cells Results in Abnormal B Cell Development and Function

The Journal of Immunology ◽

10.4049/jimmunol.1700109 ◽

2017 ◽

Vol 199 (2) ◽

pp. 570-580 ◽

Cited By ~ 13

Author(s):

Huayuan Tang ◽

Hong Wang ◽

Qingsong Lin ◽

Feifei Fan ◽

Fei Zhang ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Cell Development ◽

B Cell Development ◽

Ip3 Receptor ◽

And Function

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Differential Regulation of Mouse B Cell Development by Transforming Growth Factor β1

Developmental Immunology ◽

10.1080/1044667031000088057 ◽

2002 ◽

Vol 9 (2) ◽

pp. 86-95 ◽

Cited By ~ 8

Author(s):

Denise A. Kaminski ◽

John J. Letterio ◽

Peter D. Burrows

Keyword(s):

B Cells ◽

Growth Factor ◽

B Cell ◽

Transforming Growth Factor ◽

Plasma Cells ◽

Population Analysis ◽

Cell Development ◽

B Cell Development

Transforming growth factor β (TGFβ) can inhibit thein vitroproliferation, survival and differentiation of B cell progenitors, mature B lymphocytes and plasma cells. Here we demonstrate unexpected, age-dependent reductions in the bone marrow (BM) B cell progenitors and immature B cells in TGFβ1-/-mice. To evaluate TGFβ responsiveness during normal B lineage development, cells were cultured in interleukin 7 (IL7)±TGFβ. Picomolar doses of TGFβ1 reduced pro-B cell recoveries at every timepoint. By contrast, the pre-B cells were initially reduced in number, but subsequently increased compared to IL7 alone, resulting in a 4-fold increase in the growth rate for the pre-B cell population. Analysis of purified BM sub-populations indicated that pro-B cells and the earliest BP1-pre-B cells were sensitive to the inhibitory effects of TGFβ1. However, the large BP1+pre-B cells, although initially reduced, were increased in number at days 5 and 7 of culture. These results indicate that TGFβ1 is important for normal B cell developmentin vivo, and that B cell progenitors are differentially affected by the cytokine according to their stage of differentiation.

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Ligand-independent Signaling Functions for the B Lymphocyte Antigen Receptor and Their Role in Positive Selection during B Lymphopoiesis

Journal of Experimental Medicine ◽

10.1084/jem.194.11.1583 ◽

2001 ◽

Vol 194 (11) ◽

pp. 1583-1596 ◽

Cited By ~ 112

Author(s):

Gregory Bannish ◽

Ezequiel M. Fuentes-Pananá ◽

John C. Cambier ◽

Warren S. Pear ◽

John G. Monroe

Keyword(s):

B Cells ◽

B Cell ◽

B Lymphocyte ◽

Antigen Receptor ◽

Cell Development ◽

B Cell Development ◽

B Lymphopoiesis ◽

Biologically Relevant ◽

Developmental Progression

Signal transduction through the B cell antigen receptor (BCR) is determined by a balance of positive and negative regulators. This balance is shifted by aggregation that results from binding to extracellular ligand. Aggregation of the BCR is necessary for eliciting negative selection or activation by BCR-expressing B cells. However, ligand-independent signaling through intermediate and mature forms of the BCR has been postulated to regulate B cell development and peripheral homeostasis. To address the importance of ligand-independent BCR signaling functions and their regulation during B cell development, we have designed a model that allows us to isolate the basal signaling functions of immunoglobulin (Ig)α/Igβ-containing BCR complexes from those that are dependent upon ligand-mediated aggregation. In vivo, we find that basal signaling is sufficient to facilitate pro-B → pre-B cell transition and to generate immature/mature peripheral B cells. The ability to generate basal signals and to drive developmental progression were both dependent on plasma membrane association of Igα/Igβ complexes and intact immunoregulatory tyrosine activation motifs (ITAM), thereby establishing a correlation between these processes. We believe that these studies are the first to directly demonstrate biologically relevant basal signaling through the BCR where the ability to interact with both conventional as well as nonconventional extracellular ligands is eliminated.

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An evolutionarily conserved program of B-cell development and activation in zebrafish

Blood ◽

10.1182/blood-2012-12-471029 ◽

2013 ◽

Vol 122 (8) ◽

pp. e1-e11 ◽

Cited By ~ 77

Author(s):

Dawne M. Page ◽

Valerie Wittamer ◽

Julien Y. Bertrand ◽

Kanako L. Lewis ◽

David N. Pratt ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Transition Point ◽

Cell Development ◽

B Cell Development ◽

Key Points ◽

Evolutionarily Conserved

Key Points B cells appear in zebrafish by 3 weeks of development, supporting previous data that this is the transition point to adult hematopoiesis. Shifting sites of B-cell development likely occur in all jawed vertebrates.

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