scholarly journals Phosphorylation of E47 as a potential determinant of B-cell-specific activity.

1996 ◽  
Vol 16 (12) ◽  
pp. 6900-6908 ◽  
Author(s):  
S R Sloan ◽  
C P Shen ◽  
R McCarrick-Walmsley ◽  
T Kadesch
Keyword(s):  
B Cells ◽  
Dna Binding ◽  
B Cell ◽  
B Lymphocyte ◽  
Specific Activity ◽  
Cell Types ◽  
Basic Helix Loop Helix ◽  
Helix Loop Helix ◽  
Potential Determinant

The E2A gene encodes two basic helix-loop-helix proteins designated E12 and E47. Although these proteins are widely expressed, they are required only for the B-lymphocyte lineage where DNA binding is mediated distinctively by E47 homodimers. By studying the properties of deltaE47, an N-terminal truncation of E47, we provide evidence that phosphorylation may contribute to B-cell-specific DNA binding by E47. Two serines N terminal to the deltaE47 basic helix-loop-helix domain were found to be phosphorylated in a variety of cell types but were hypophosphorylated in B cells. Phosphorylating these serines in vitro inhibited DNA binding by deltaE47 homodimers but not by deltaE47-containing heterodimers, such as deltaE47:MyoD. These results argue that hypophosphorylation may be a prerequisite for activity of E47 homodimers in B cells, suggesting the use of an inductive (nonstochastic) step in early B-cell development.

E2A and E2-2 are subunits of B-cell-specific E2-box DNA-binding proteins

1993 ◽  
Vol 13 (6) ◽  
pp. 3522-3529
Author(s):  
G Bain ◽  
S Gruenwald ◽  
C Murre
Keyword(s):  
Monoclonal Antibodies ◽  
B Cells ◽  
Dna Binding ◽  
B Cell ◽  
Dna Sequences ◽  
Dna Binding Proteins ◽  
Gene Products ◽  
Helix Loop Helix ◽  
The Difference

A class of helix-loop-helix (HLH) proteins, including E2A (E12 and E47), E2-2, and HEB, that bind in vitro to DNA sequences present in the immunoglobulin (Ig) enhancers has recently been identified. E12, E47, E2-2, and HEB are each present in B cells. The presence of many different HLH proteins raises the question of which of the HLH proteins actually binds the Ig enhancer elements in B cells. Using monoclonal antibodies specific for both E2A and E2-2, we show that both E2-2 and E2A polypeptides are present in B-cell-specific Ig enhancer-binding complexes. E2-box-binding complexes in pre-B cells contain both E2-2 and E2A HLH subunits, whereas in mature B cells only E2A gene products are present. We show that the difference in E2-box-binding complexes in pre-B and mature B cells may be caused by differential expression of E2A and E2-2.

scholarly journals B-cell-specific DNA binding by an E47 homodimer.

1995 ◽  
Vol 15 (8) ◽  
pp. 4518-4524 ◽  
Author(s):  
C P Shen ◽  
T Kadesch
Keyword(s):  
B Cells ◽  
Dna Binding ◽  
B Cell ◽  
B Lymphocyte ◽  
Cultured Cells ◽  
Binding Activity ◽  
Immunoglobulin Gene ◽  
Helix Loop Helix ◽  
B Lineage ◽  
Bhlh Proteins

B cells express a unique E-box-binding activity that contains basic helix-loop-helix (bHLH) proteins encoded by the E2A gene. E2A proteins play a central role in immunoglobulin gene transcription and are also required for the generation of the B-lymphocyte lineage. In muscle, E2A proteins bind DNA as heterodimers with muscle-specific bHLH partners, such as MyoD and myogenin, and these heterodimers are thought to be both necessary and sufficient for muscle determination in cultured cells. Our results indicate that in B cells, the bHLH partners for E2A proteins are not B-cell-restricted proteins, but are the E2A proteins themselves. UV cross-linking, gel purification, and the analysis of "forced heterodimers" indicate that BCF1 is primarily a homodimer of the E2A protein E47. Since E47 is widely expressed, our results argue for a difference in the inherent DNA-binding properties of the E47 protein in B cells and may help explain the restricted B-lineage defect observed in E2A-deficient mice.

scholarly journals E2A and E2-2 are subunits of B-cell-specific E2-box DNA-binding proteins.

1993 ◽  
Vol 13 (6) ◽  
pp. 3522-3529 ◽  
Author(s):  
G Bain ◽  
S Gruenwald ◽  
C Murre
Keyword(s):  
Monoclonal Antibodies ◽  
B Cells ◽  
Dna Binding ◽  
B Cell ◽  
Dna Sequences ◽  
Dna Binding Proteins ◽  
Gene Products ◽  
Helix Loop Helix ◽  
The Difference

A class of helix-loop-helix (HLH) proteins, including E2A (E12 and E47), E2-2, and HEB, that bind in vitro to DNA sequences present in the immunoglobulin (Ig) enhancers has recently been identified. E12, E47, E2-2, and HEB are each present in B cells. The presence of many different HLH proteins raises the question of which of the HLH proteins actually binds the Ig enhancer elements in B cells. Using monoclonal antibodies specific for both E2A and E2-2, we show that both E2-2 and E2A polypeptides are present in B-cell-specific Ig enhancer-binding complexes. E2-box-binding complexes in pre-B cells contain both E2-2 and E2A HLH subunits, whereas in mature B cells only E2A gene products are present. We show that the difference in E2-box-binding complexes in pre-B and mature B cells may be caused by differential expression of E2A and E2-2.

scholarly journals B-lymphocyte development is regulated by the combined dosage of three basic helix-loop-helix genes, E2A, E2-2, and HEB.

1996 ◽  
Vol 16 (6) ◽  
pp. 2898-2905 ◽  
Author(s):  
Y Zhuang ◽  
P Cheng ◽  
H Weintraub
Keyword(s):  
B Cells ◽  
B Cell ◽  
B Lymphocyte ◽  
Cell Lineage ◽  
Lymphocyte Development ◽  
Normal Numbers ◽  
Basic Helix Loop Helix ◽  
Helix Loop Helix ◽  
B Lymphocyte Development ◽  
Essential Function

B-lymphocyte development requires the basic helix-loop-helix proteins encoded by the E2A gene. In this study, the control mechanism of E2A was further explored by disruption of the E2A-related genes, E2-2 and HEB. In contrast to E2A, E2-2 and HEB are not essential for the establishment of the B-cell lineage. However, both E2-2 and HEB are required for the generation of the normal numbers of pro-B cells in mouse embryos. Breeding tests among mice carrying different mutations revealed that E2-2 and HEB interact with E2A in many developmental processes including generation of B cells. Specifically, mice transheterozygous for any two mutations of these three genes produced fewer pro-B cells than the singly heterozygous littermates. This study indicates that B-cell development is dependent not only on an essential function provided by the E2A gene but also on a combined dosage set by E2A, E2-2, and HEB.

scholarly journals Monoclonal antibodies to the 140,000 mol wt glycoprotein of B lymphocyte membranes (CR2 receptor) initiates proliferation of B cells in vitro

Blood ◽  
1985 ◽  
Vol 66 (4) ◽  
pp. 824-829
Author(s):  
BS Wilson ◽  
JL Platt ◽  
NE Kay
Keyword(s):  
Monoclonal Antibodies ◽  
B Cells ◽  
B Cell ◽  
Peripheral Blood ◽  
B Lymphocyte ◽  
Human Peripheral Blood ◽  
Raji Cell ◽  
Lymphoid Cells ◽  
Humoral Immune

Several mouse monoclonal IgG antibodies (AB1, AB2, AB3, and AB5) were developed that reacted with a 140,000 mol wt glycoprotein on the surface of cultured RAJI B lymphoid cells. The antibodies reacted with purified normal human peripheral blood B cells and CLL Ig+ B cells and showed specific germinal center and mantle zone staining in tissue sections of secondary lymphoid organs. Immunodepletion studies using 125I surface-labeled Raji cell membrane antigens demonstrated that the antigen identified by AB5 is the same 140,000 mol wt glycoprotein detected by anti-B2 that has recently been shown to react with the C3d fragment or CR2 receptor. (Iida et al: J Exp Med 158:1021, 1983). Addition of the AB series and anti-B2 monoclonal antibodies to cultures of purified human peripheral blood B cells resulted in the uptake of 3H- thymidine at two to six times background control levels provided that irradiated autologous T cells were added to the culture. Stimulation was not evoked by other monoclonal antibodies to B cell surface molecules (ie, B1, BA-1, BA-2, and HLA-DR). Pepsin-generated F(ab')2 fragments of anti-CR2 antibodies were essentially as effective as the intact IgG molecule in stimulating B cells. Induction of B cell proliferation by antibody binding to CR2 suggests that the C3d receptor may have an integral role in regulation of humoral immune response.

scholarly journals Attenuation of Apoptosis Underlies B Lymphocyte Stimulator Enhancement of Humoral Immune Response

2000 ◽  
Vol 192 (7) ◽  
pp. 953-964 ◽  
Author(s):  
Richard K.G. Do ◽  
Eunice Hatada ◽  
Hayyoung Lee ◽  
Michelle R. Tourigny ◽  
David Hilbert ◽  
...  
Keyword(s):  
Immune Response ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Cell Survival ◽  
B Lymphocyte ◽  
Humoral Immune ◽  
B Cell Survival ◽  
B Lymphocyte Stimulator

B lymphocyte stimulator (BLyS) is a newly identified monocyte-specific TNF family cytokine. It has been implicated in the development of autoimmunity, and functions as a potent costimulator with antiimmunoglobulin M in B cell proliferation in vitro. Here we demonstrate that BLyS prominently enhances the humoral responses to both T cell–independent and T cell–dependent antigens, primarily by attenuation of apoptosis as evidenced by the prolonged survival of antigen-activated B cells in vivo and in vitro. BLyS acts on primary splenic B cells autonomously, and directly cooperates with CD40 ligand (CD40L) in B cell activation in vitro by protecting replicating B cells from apoptosis. Moreover, although BLyS alone cannot activate the cell cycle, it is sufficient to prolong the survival of naive resting B cells in vitro. Attenuation of apoptosis by BLyS correlates with changes in the ratios between Bcl-2 family proteins in favor of cell survival, predominantly by reducing the proapoptotic Bak and increasing its prosurvival partners, Bcl-2 and Bcl-xL. In either resting or CD40L-activated B cells, the NF-κB transcription factors RelB and p50 are specifically activated, suggesting that they may mediate BLyS signals for B cell survival. Together, these results provide direct evidence for BLyS enhancement of both T cell–independent and T cell–dependent humoral immune responses, and imply a role for BLyS in the conservation of the B cell repertoire. The ability of BLyS to increase B cell survival indiscriminately, at either a resting or activated state, and to cooperate with CD40L, further suggests that attenuation of apoptosis underlies BLyS enhancement of polyclonal autoimmunity as well as the physiologic humoral immune response.

Association between B-lymphocyte membrane immunoglobulin and multiple members of the Src family of protein tyrosine kinases

1992 ◽  
Vol 12 (5) ◽  
pp. 2315-2321
Author(s):  
M A Campbell ◽  
B M Sefton
Keyword(s):  
B Cells ◽  
B Cell ◽  
Tyrosine Kinases ◽  
B Lymphocyte ◽  
Protein Tyrosine Kinases ◽  
Cell Type ◽  
Protein Tyrosine ◽  
Membrane Immunoglobulin ◽  
Family Protein

Treatment of B lymphocytes with antibodies to membrane immunoglobulin (Ig) stimulates protein tyrosine phosphorylation. We have examined the phosphorylation in vitro of proteins associated with membrane Ig. The Src family protein tyrosine kinases p53/56lyn, p59fyn, and p56lck are associated with membrane Ig in spleen B cells and B-cell lines and undergo phosphorylation in vitro. The pattern of expression of Src family protein tyrosine kinases in B cells varied. Our studies suggest that multiple kinases can potentially interact with membrane Ig and that within any one B-cell type, all of the Src family kinases expressed can be found in association with membrane Ig. We also observed that the Ig-associated Ig alpha protein, multiple forms of Ig beta, and proteins of 100 and 25 kDa were tyrosine phosphorylated in vitro. The 100- and 25-kDa proteins remain unidentified.

scholarly journals Interleukin-13 in Combination With CD40 Ligand Potently Inhibits Apoptosis in Human B Lymphocytes: Upregulation of Bcl-xL and Mcl-1

Blood ◽  
1997 ◽  
Vol 89 (12) ◽  
pp. 4415-4424 ◽  
Author(s):  
Jon Lømo ◽  
Heidi Kiil Blomhoff ◽  
Sten Eirik Jacobsen ◽  
Stanislaw Krajewski ◽  
John C. Reed ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
B Lymphocytes ◽  
Peripheral Blood ◽  
Cell Apoptosis ◽  
Cell Types ◽  
Cd40 Ligand ◽  
Interleukin 13

Abstract Interleukin-13 (IL-13) is a novel T-cell–derived cytokine with IL-4–like effects on many cell types. In human B lymphocytes, IL-13 induces activation, stimulates proliferation in combination with anti-IgM or anti-CD40 antibodies, and directs Ig isotype switching towards IgE and IgG4 isotypes. We show here that IL-13 also regulates human B-cell apoptosis. IL-13 reduced spontaneous apoptosis of peripheral blood B cells in vitro, as shown by measurement of DNA fragmentation using the TUNEL and Nicoletti assays. The inhibition of cell death by IL-13 alone was significant but modest, but was potently enhanced in combination with CD40 ligand (CD40L), a survival stimulus for B cells by itself. Interestingly, IL-13 increased the expression of CD40 on peripheral blood B cells, providing a possible mechanism for the observed synergy. IL-13 alone was a less potent inhibitor of apoptosis than IL-4. Moreover, there was no additive effect of combining IL-4 and IL-13 at supraoptimal concentrations, which is consistent with the notion that the IL-4 and IL-13 binding sites share a common signaling subunit. The combination of IL-13 with CD40L augmented the expression of the Bcl-2 homologues Bcl-xL and Mcl-1, suggesting this as a possible intracellular mechanism of induced survival. By contrast, levels of Bcl-2, and two other Bcl-2 family members, Bax and Bak, remained unaltered. Given the importance of the CD40-CD40L interaction in B-cell responses, these results suggest a significant role of IL-13 in the regulation of B-cell apoptosis.

Aberrant expression of B-lymphocyte stimulator by B chronic lymphocytic leukemia cells: a mechanism for survival

Blood ◽  
2002 ◽  
Vol 100 (8) ◽  
pp. 2973-2979 ◽  
Author(s):  
Anne J. Novak ◽  
Richard J. Bram ◽  
Neil E. Kay ◽  
Diane F. Jelinek
Keyword(s):  
B Cells ◽  
Chronic Lymphocytic Leukemia ◽  
B Cell ◽  
B Lymphocyte ◽  
Leukemic Cell ◽  
Lymphocytic Leukemia ◽  
Leukemic Cells ◽  
Aberrant Expression ◽  
B Lymphocyte Stimulator

B-cell chronic lymphocytic leukemia (B-CLL) is defined by the accumulation of CD5+ B cells in the periphery and bone marrow. This disease is not characterized by highly proliferative cells but rather by the presence of leukemic cells with significant resistance to apoptosis and, therefore, prolonged survival. B-lymphocyte stimulator (BLyS) is a newly identified tumor necrosis factor (TNF) family member shown to be critical for maintenance of normal B-cell development and homeostasis and it shares significant homology with another TNF superfamily member, APRIL. The striking effects of BLyS on normal B-cell maintenance and survival raises the possibility that it may be involved in pathogenesis and maintenance of hematologic malignancies, including B-CLL. In this study, we investigated the status of APRIL and BLyS expression, as well as their receptors, in this disease. All B-CLL patient cells studied expressed one or more of 3 known receptors for BLyS; however, the pattern of expression was variable. In addition, we demonstrate for the first time that B-CLL cells from a subset of patients aberrantly express BLyS and APRIL mRNA, whereas these molecules were not detectable in normal B cells. Furthermore, we provide in vitro evidence that BLyS protects B-CLL cells from apoptosis and enhances cell survival. Because these molecules are key regulators of B-cell homeostasis and tumor progression, leukemic cell autocrine expression of BLyS and APRIL may be playing an important role in the pathogenesis of this disease.

scholarly journals IgG subclass, IgE, and IgA anti-trinitrophenyl antibody production within trinitrophenyl-Ficoll-responsive B cell clones. Evidence in support of three distinct switching pathways.

1983 ◽  
Vol 157 (1) ◽  
pp. 69-85 ◽  
Author(s):  
P K Mongini ◽  
W E Paul ◽  
E S Metcalf
Keyword(s):  
T Cells ◽  
B Cells ◽  
B Cell ◽  
B Lymphocyte ◽  
Igg Subclasses ◽  
Igg Subclass ◽  
Cell Clones ◽  
High Propensity ◽  
Focus Assay

The IgM, IgG subclass, IgE, and IgA anti-trinitrophenyl (TNP) antibody (Ab) response of B cells to the type 2 antigen TNP-Ficoll was studied in athymic nude mice and in the in vitro splenic focus assay. Results from the splenic focus assay in which purified B lymphocyte preparations had been transferred to irradiated nu/nu recipients indicate that many TNP-Ficoll stimulated B cell clones secrete multiple isotypes and hence appear to be undergoing intraclonal isotype switching. Although the frequency of clones secreting each of the IgG subclasses was found to correlate with 5' to 3' Igh-gamma gene order, the frequency of IgE and IgA-secreting clones did not appear to be influenced by the respective position of Igh-epsilon and Igh-alpha on the chromosome. Unlike clones that secreted anti-TNP Ab of the IgG subclasses, IgE and IgA anti-TNP Ab-secreting clones did not have a high propensity for coexpression of isotypes encoded by 5' Igh-C genes. These data suggest that three distinct switching pathways may be employed by B cells responding to TNP-Ficoll: a common IgG pathway, an IgE pathway, and an IgA pathway. The presence of T cells resulted in a preferential enhancement of the production of anti-TNP Ab of those IgG subclasses which were least represented in the absence of T cells, i.e., IgG2b and IgG2a. No significant enhancement of IgE anti-TNP clonal frequency was found in the presence of T lymphocytes, but T cells were found to significantly enhance the clonal expression of IgA anti-TNP Ab. Although a relatively large number of B cell clones were found to synthesize IgE and IgA anti-TNP Ab in the splenic focus assay, relatively little or no secretion of these isotypes was detected in immune mice. Possible explanations for this apparent discrepancy are discussed.

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