101
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Abstract
Recent results obtained in mice harboring cytoplasmic mutations of Igalpha and/or Igbeta have reinforced the concept that the strength of BCR signaling is important for ensuring appropriate developmental outcomes as well as antigen-specific responses. To establish the optimal signaling intensity and duration, the BCR utilizes positive and negative regulatory molecules. Studies are beginning to reveal how these molecules maintain immunological homeostasis and tolerance.
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Affiliation(s)
- Tomohiro Kurosaki
- Department of Molecular Genetics, Institute for Liver Research, Kansai Medical University, and Laboratory for Lymphocyte Differentiation, RIKEN Research Center for Allergy and Immunology, 570-8506, Moriguchi, Japan.
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102
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Gauld SB, Dal Porto JM, Cambier JC. B cell antigen receptor signaling: roles in cell development and disease. Science 2002; 296:1641-2. [PMID: 12040177 DOI: 10.1126/science.1071546] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Signals propagated through the B cell antigen receptor (BCR) are vital for the development and survival of B lymphocytes in both the bone marrow and the periphery. These signals not only guide maturation and activation but also affect the removal of potentially self-reactive B lymphocytes. Interestingly, these signals are known to be either ligand-independent ("tonic" signals) or induced by ligand (antigen) binding to the BCR. We focus on the problems that occur in B cell development due to defects in signals emanating from the BCR. In addition, we present the B Cell Antigen Receptor Pathway, an STKE Connections Map that illustrates the events involved in B cell signaling.
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Affiliation(s)
- Stephen B Gauld
- Integrated Department of Immunology, University of Colorado Health Sciences Center, and National Jewish Medical Research Center, 1400 Jackson Street, Denver, CO 80206, USA
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103
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Abstract
The transcription factor NFkappaB is activated by numerous stimuli. Once NFkappaB is fully activated, it participates in the regulation of various target genes in different cells to exert its biological functions. NFkappaB has often been referred to as a central mediator of the immune response, since a large variety of bacteria and viruses can lead to the activation of NFkappaB, which in turn controls the expression of many inflammatory cytokines, chemokines, immune receptors, and cell surface adhesion molecules. Recent studies have shown that NFkappaB may function more generally as a central regulator of stress responses, since different stressful conditions, including physical stress, oxidative stress, and exposure to certain chemicals, also lead to NFkappaB activation. Furthermore, NFkappaB blocks cell apoptosis in several cell types. Taken together, these findings make it clear that NFkappaB plays an important role in cell proliferation and differentiation. It is the intention of this review to cover the various NFkappaB-dependent signaling pathways, thereby to achieve a better understanding of the mechanisms of NFkappaB activation and the physiological functions of activated NFkappaB.
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Affiliation(s)
- Xiaoxia Li
- Department of Immunology/NB30, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
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104
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Yamazaki T, Takeda K, Gotoh K, Takeshima H, Akira S, Kurosaki T. Essential immunoregulatory role for BCAP in B cell development and function. J Exp Med 2002; 195:535-45. [PMID: 11877477 PMCID: PMC2193770 DOI: 10.1084/jem.20011751] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
BCAP was recently cloned as a binding molecule to phosphoinositide 3-kinase (PI3K). To investigate the role of BCAP, mutant mice deficient in BCAP were generated. While BCAP-deficient mice are viable, they have decreased numbers of mature B cells and B1 B cell deficiency. The mice produce lower titers of serum immunoglobulin (Ig)M and IgG3, and mount attenuated responses to T cell--independent type II antigen. Upon B cell receptor cross-linking, BCAP-deficient B cells exhibit reduced Ca(2+) mobilization and poor proliferative responses. These findings demonstrate that BCAP plays a pivotal immunoregulatory role in B cell development and humoral immune responses.
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Affiliation(s)
- Tetsuo Yamazaki
- Department of Molecular Genetics, Institute for Liver Research, Kansai Medical University, Moriguchi, Osaka, Japan
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105
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Abstract
Bright, or B cell regulator of immunoglobulin heavy chain transcription, is a B lymphocyte-specific protein first discovered for its ability to increase immunoglobulin transcription three- to sevenfold in antigen-activated B cells. It interacts with DNA through an ARID, or A/T-rich interaction domain, and is the only member of a previously undescribed family of DNA-binding proteins for which target genes have been identified. The mechanism(s) by which Bright facilitates transcription are unknown. Several proteins that associate with Bright may shed light upon its function. These include the nuclear matrix proteins sp100 and LYSp100B, and suggest that Bright may affect chromatin configuration and nuclear sublocalization. Furthermore, Bruton's tyrosine kinase is required for Bright binding activity, suggesting links between Bright, cell signaling cascades, and X-linked immunodeficiency disease.
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Affiliation(s)
- C F Webb
- Immunobiology and Cancer Program, Oklahoma Medical Research Foundation, Oklahoma City 73104, USA.
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106
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Inui S, Maeda K, Hua DR, Yamashita T, Yamamoto H, Miyamoto E, Aizawa S, Sakaguchi N. BCR signal through alpha 4 is involved in S6 kinase activation and required for B cell maturation including isotype switching and V region somatic hypermutation. Int Immunol 2002; 14:177-87. [PMID: 11809737 DOI: 10.1093/intimm/14.2.177] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
alpha 4 potentially mediates BCR signals through a rapamycin-sensitive TOR pathway. To investigate a potential role for alpha 4 in B cell activation, the alpha 4 gene was disrupted conditionally in B cells by mating male CD19-Cre mice with female alpha 4-floxed mice. CD19-Cre+/alpha 4flox mice showed loss of alpha 4 protein in B lineage cells and a decreased number of phenotypically normal mature B cells. Compared to normal B cells, alpha 4(-) B cells showed a decreased proliferation in response to the B cell stimulants (anti-IgM antibody plus IL-4, anti-CD40 mAb and lipopolysaccharide), and a reduced S6 kinase activation and rapamycin sensitivity. While CD19-Cre+/alpha 4flox mice showed impaired antibody responses to both T cell-independent and T cell-dependent (TD) antigens, the TD antigen response was markedly impaired as demonstrated by reduced isotype switching, reduced germinal center formation and reduced V region somatic hypermutation. These results show that alpha 4 plays a pivotal role in antigen-specific signal transduction during B cell activation and differentiation in vivo.
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Affiliation(s)
- Seiji Inui
- Department of Immunology, Kumamoto University School of Medicine, 2-2-1 Honjo, Kumamoto 860-0811, Japan
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107
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Katso R, Okkenhaug K, Ahmadi K, White S, Timms J, Waterfield MD. Cellular function of phosphoinositide 3-kinases: implications for development, homeostasis, and cancer. Annu Rev Cell Dev Biol 2002; 17:615-75. [PMID: 11687500 DOI: 10.1146/annurev.cellbio.17.1.615] [Citation(s) in RCA: 929] [Impact Index Per Article: 42.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The phosphoinositide 3-kinase (PI3K) family of enzymes is recruited upon growth factor receptor activation and produces 3' phosphoinositide lipids. The lipid products of PI3K act as second messengers by binding to and activating diverse cellular target proteins. These events constitute the start of a complex signaling cascade, which ultimately results in the mediation of cellular activities such as proliferation, differentiation, chemotaxis, survival, trafficking, and glucose homeostasis. Therefore, PI3Ks play a central role in many cellular functions. The factors that determine which cellular function is mediated are complex and may be partly attributed to the diversity that exists at each level of the PI3K signaling cascade, such as the type of stimulus, the isoform of PI3K, or the nature of the second messenger lipids. Numerous studies have helped to elucidate some of the key factors that determine cell fate in the context of PI3K signaling. For example, the past two years has seen the publication of many transgenic and knockout mouse studies where either PI3K or its signaling components are deregulated. These models have helped to build a picture of the role of PI3K in physiology and indeed there have been a number of surprises. This review uses such models as a framework to build a profile of PI3K function within both the cell and the organism and focuses, in particular, on the role of PI3K in cell regulation, immunity, and development. The evidence for the role of deregulated PI3K signaling in diseases such as cancer and diabetes is reviewed.
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Affiliation(s)
- R Katso
- Ludwig Institute for Cancer Research, 91 Riding House Street, London, W1W 7BS, England.
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108
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Allman D, Lindsley RC, DeMuth W, Rudd K, Shinton SA, Hardy RR. Resolution of three nonproliferative immature splenic B cell subsets reveals multiple selection points during peripheral B cell maturation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 167:6834-40. [PMID: 11739500 DOI: 10.4049/jimmunol.167.12.6834] [Citation(s) in RCA: 428] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Although immature/transitional peripheral B cells may remain susceptible to selection pressures before full maturation, the nature and timing of these selection events remain unclear. We show that correlated expression of surface (s) IgM (sIgM), CD23, and AA4 defines three nonproliferative subpopulations of immature/transitional peripheral B cells. We designate these populations transitional (T) 1 (AA4(+)CD23(-)sIgM(high)), T2 (AA4(+)CD23(+)sIgM(high)), and T3 (AA4(+)CD23(+)sIgM(low)). Cells within all three subsets are functionally immature as judged by their failure to proliferate following sIgM cross-linking in vitro, and their rapid rate of turnover in vivo as assessed by 5-bromo-2'-deoxyuridine labeling. These labeling studies also reveal measurable cell loss at both the T1-T2 and T2-T3 transitions, suggesting the existence of multiple selection points within the peripheral immature B cell pool. Furthermore, we find that Btk-deficient (xid) mice exhibit an incomplete developmental block at the T2-T3 transition within the immature B cell pool. This contrasts markedly with lyn(-/-) mice, which exhibit depressed numbers but normal ratios of each immature peripheral B cell subset and severely reduced numbers of mature B cells. Together, these data provide evidence for multiple selection points among immature peripheral B cells, suggesting that the B cell repertoire is shaped by multiple unique selection events that occur within the immature/transitional peripheral B cell pool.
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Affiliation(s)
- D Allman
- Department of Pathology and Laboratory Medicine and Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
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109
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Cancro MP, Sah AP, Levy SL, Allman DM, Schmidt MR, Woodland RT. xid mice reveal the interplay of homeostasis and Bruton's tyrosine kinase-mediated selection at multiple stages of B cell development. Int Immunol 2001; 13:1501-14. [PMID: 11717191 DOI: 10.1093/intimm/13.12.1501] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Human X-linked agammaglobulinemia (XLA) and murine X-linked immune defect (XID) are both immunodeficiencies mediated by mutations in Bruton's tyrosine kinase (Btk), yet the developmental stage(s) affected remain controversial. To further refine the placement of the XID defect(s), we used bromodeoxyuridine labeling to determine turnover, production and transition rates of developing B cell subsets in normal, xid and xid mice expressing a human Bcl-2 transgene (xid/bcl-2). We find the xid mutation manifest at two stages of B cell development. The first is early, reducing pre-B cell production by restricting pro-B to pre-B cell transit. Surprisingly, this impairment is offset by increased survival of cells progressing from the pre- to immature B cell pool, suggesting that Btk-independent homeostatic mechanisms act to maintain this compartment. The second point of action is late, substantially reducing mature B cell production. Together, these findings reconcile apparent discrepancies in the developmental stage affected by the murine versus human lesions and suggest previously unappreciated homeostatic processes that act at the pre-B to immature B cell transition. Finally, Btk likely functions differently at these two checkpoints, since ectopic Bcl-2 expression fails to directly complement the early xid lesion, yet reverses the defect impeding final B cell maturation.
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Affiliation(s)
- M P Cancro
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, 36th and Hamilton Walk, Philadelphia, PA 19104-6082, USA
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110
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Mao C, Zhou M, Uckun FM. Crystal structure of Bruton's tyrosine kinase domain suggests a novel pathway for activation and provides insights into the molecular basis of X-linked agammaglobulinemia. J Biol Chem 2001; 276:41435-43. [PMID: 11527964 DOI: 10.1074/jbc.m104828200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bruton's tyrosine kinase is intimately involved in signal transduction pathways regulating survival, activation, proliferation, and differentiation of B lineage lymphoid cells. Mutations in the human btk gene are the cause of X-linked agammaglobulinemia, a male immune deficiency disorder characterized by a lack of mature, immunoglobulin-producing B lymphocytes. We have determined the x-ray crystal structure of the Bruton's tyrosine kinase kinase domain in its unphosphorylated state to a 2.1 A resolution. A comparison with the structures of other tyrosine kinases and a possible mechanism of activation unique to Bruton's tyrosine kinase are provided.
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Affiliation(s)
- C Mao
- Department of Structural Biology, Parker Hughes Cancer Center, St. Paul, Minnesota 55113, USA.
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111
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Joliat MJ, Shultz LD. The molecular bases of spontaneous immunological mutations in the mouse and their homologous human diseases. Clin Immunol 2001; 101:113-29. [PMID: 11683570 DOI: 10.1006/clim.2001.5120] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- M J Joliat
- The Jackson Laboratory, Bar Harbor, Maine 04609, USA
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112
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Watanabe D, Hashimoto S, Ishiai M, Matsushita M, Baba Y, Kishimoto T, Kurosaki T, Tsukada S. Four tyrosine residues in phospholipase C-gamma 2, identified as Btk-dependent phosphorylation sites, are required for B cell antigen receptor-coupled calcium signaling. J Biol Chem 2001; 276:38595-601. [PMID: 11507089 DOI: 10.1074/jbc.m103675200] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of phospholipase C-gamma2 (PLCgamma2) is the critical step in B cell antigen receptor (BCR)-coupled calcium signaling. Although genetic dissection experiments on B cells have demonstrated that Bruton's tyrosine kinase (Btk) and Syk are required for activating PLCgamma2, the exact activation mechanism of PLCgamma2 by these kinases has not been established. We identify the tyrosine residues 753, 759, 1197, and 1217 in rat PLCgamma2 as Btk-dependent phosphorylation sites by using an in vitro kinase assay. To evaluate the role of these tyrosine residues in phosphorylation-dependent activation of PLCgamma2, PLCgamma2-deficient DT40 cells were reconstituted with a series of mutant PLCgamma2s in which the phenylalanine was substituted for tyrosine. Substitution of all four tyrosine residues almost completely eliminated the BCR-induced PLCgamma2 phosphorylation, indicating that these residues include the major phosphorylation sites upon BCR engagement. Cells expressing PLCgamma2 with a single substitution exhibited some extent of reduction in calcium mobilization, whereas those expressing quadruple mutant PLCgamma2 showed greatly reduced calcium response. These findings indicate that the phosphorylations of the tyrosine residues 753, 759, 1197, and 1217, which have been identified as Btk-dependent phosphorylation sites in vitro, coordinately contribute to BCR-induced activation of PLCgamma2.
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Affiliation(s)
- D Watanabe
- Osaka University Medical School, Department of Molecular Medicine, 2-2 Yamada-oka, Suita City, Osaka 565-0871, Japan
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113
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Liu W, Quinto I, Chen X, Palmieri C, Rabin RL, Schwartz OM, Nelson DL, Scala G. Direct inhibition of Bruton's tyrosine kinase by IBtk, a Btk-binding protein. Nat Immunol 2001; 2:939-46. [PMID: 11577348 DOI: 10.1038/ni1001-939] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Bruton's tyrosine kinase (Btk) is required for human and mouse B cell development. Btk deficiency causes X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency in mice. Unlike Src proteins, Btk lacks a negative regulatory domain at the COOH terminus and may rely on cytoplasmic Btk-binding proteins to regulates its kinase activity by trans-inhibitor mechanisms. Consistent with this possibility, IBtk, which we identified as an inhibitor of Btk, bound to the PH domain of Btk. IBtk downregulated Btk kinase activity, Btk-mediated calcium mobilization and nuclear factor-kappaB-driven transcription. These results define a potential mechanism for the regulation of Btk function in B cells.
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Affiliation(s)
- W Liu
- Department of Clinical and Experimental Medicine, Medical School, University of Catanzaro, 88100 Catanzaro, Italy
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114
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Kraus M, Pao LI, Reichlin A, Hu Y, Canono B, Cambier JC, Nussenzweig MC, Rajewsky K. Interference with immunoglobulin (Ig)alpha immunoreceptor tyrosine-based activation motif (ITAM) phosphorylation modulates or blocks B cell development, depending on the availability of an Igbeta cytoplasmic tail. J Exp Med 2001; 194:455-69. [PMID: 11514602 PMCID: PMC2193498 DOI: 10.1084/jem.194.4.455] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
To determine the function of immunoglobulin (Ig)alpha immunoreceptor tyrosine-based activation motif (ITAM) phosphorylation, we generated mice in which Igalpha ITAM tyrosines were replaced by phenylalanines (Igalpha(FF/FF)). Igalpha(FF/FF) mice had a specific reduction of B1 and marginal zone B cells, whereas B2 cell development appeared to be normal, except that lambda1 light chain usage was increased. The mutants responded less efficiently to T cell-dependent antigens, whereas T cell-independent responses were unaffected. Upon B cell receptor ligation, the cells exhibited heightened calcium flux, weaker Lyn and Syk tyrosine phosphorylation, and phosphorylation of Igalpha non-ITAM tyrosines. Strikingly, when the Igalpha ITAM mutation was combined with a truncation of Igbeta, B cell development was completely blocked at the pro-B cell stage, indicating a crucial role of ITAM phosphorylation in B cell development.
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Affiliation(s)
- M Kraus
- Institute for Genetics, University of Cologne, D-50931 Cologne, Germany.
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115
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Mahajan S, Vassilev A, Sun N, Ozer Z, Mao C, Uckun FM. Transcription factor STAT5A is a substrate of Bruton's tyrosine kinase in B cells. J Biol Chem 2001; 276:31216-28. [PMID: 11413148 DOI: 10.1074/jbc.m104874200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
STAT5A is a molecular regulator of proliferation, differentiation, and apoptosis in lymphohematopoietic cells. Here we show that STAT5A can serve as a functional substrate of Bruton's tyrosine kinase (BTK). Purified recombinant BTK was capable of directly binding purified recombinant STAT5A with high affinity (K(d) = 44 nm), as determined by surface plasmon resonance using a BIAcore biosensor system. BTK was also capable of tyrosine-phosphorylating ectopically expressed recombinant STAT5A on Tyr(694) both in vitro and in vivo in a Janus kinase 3-independent fashion. BTK phosphorylated the Y665F, Y668F, and Y682F,Y683F mutants but not the Y694F mutant of STAT5A. STAT5A mutations in the Src homology 2 (SH2) and SH3 domains did not alter the BTK-mediated tyrosine phosphorylation. Recombinant BTK proteins with mutant pleckstrin homology, SH2, or SH3 domains were capable of phosphorylating STAT5A, whereas recombinant BTK proteins with SH1/kinase domain mutations were not. In pull-down experiments, only full-length BTK and its SH1/kinase domain (but not the pleckstrin homology, SH2, or SH3 domains) were capable of binding STAT5A. Ectopically expressed BTK kinase domain was capable of tyrosine-phosphorylating STAT5A both in vitro and in vivo. BTK-mediated tyrosine phosphorylation of ectopically expressed wild type (but not Tyr(694) mutant) STAT5A enhanced its DNA binding activity. In BTK-competent chicken B cells, anti-IgM-stimulated tyrosine phosphorylation of STAT5 protein was prevented by pretreatment with the BTK inhibitor LFM-A13 but not by pretreatment with the JAK3 inhibitor HI-P131. B cell antigen receptor ligation resulted in enhanced tyrosine phosphorylation of STAT5 in BTK-deficient chicken B cells reconstituted with wild type human BTK but not in BTK-deficient chicken B cells reconstituted with kinase-inactive mutant BTK. Similarly, anti-IgM stimulation resulted in enhanced tyrosine phosphorylation of STAT5A in BTK-competent B cells from wild type mice but not in BTK-deficient B cells from XID mice. In contrast to B cells from XID mice, B cells from JAK3 knockout mice showed a normal STAT5A phosphorylation response to anti-IgM stimulation. These findings provide unprecedented experimental evidence that BTK plays a nonredundant and pivotal role in B cell antigen receptor-mediated STAT5A activation in B cells.
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Affiliation(s)
- S Mahajan
- Molecular Signal Transduction Laboratory, Parker Hughes Cancer Center and the Department of Biochemistry, Parker Hughes Institute, St. Paul, Minnesota 55113, USA
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116
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Affiliation(s)
- S Tsukada
- Department of Molecular Medicine, Osaka University Medical School, Yamadaoka, Suita City, Osaka 565-0871, Japan
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117
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Engels N, Merchant M, Pappu R, Chan AC, Longnecker R, Wienands J. Epstein-Barr virus latent membrane protein 2A (LMP2A) employs the SLP-65 signaling module. J Exp Med 2001; 194:255-64. [PMID: 11489945 PMCID: PMC2193464 DOI: 10.1084/jem.194.3.255] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2001] [Accepted: 06/20/2001] [Indexed: 11/29/2022] Open
Abstract
In latently infected B lymphocytes, the Epstein-Barr virus (EBV) suppresses signal transduction from the antigen receptor through expression of the integral latent membrane protein 2A (LMP2A). At the same time, LMP2A triggers B cell survival by a yet uncharacterized maintenance signal that is normally provided by the antigen receptor. The molecular mechanisms are unknown as LMP2A-regulated signaling cascades have not been described so far. Using a novel mouse model we have identified the intracellular adaptor protein Src homology 2 (SH2) domain-containing leukocyte protein (SLP)-65 as a critical downstream effector of LMP2A in vivo. Biochemical analysis of the underlying signaling pathways revealed that EBV infection causes constitutive tyrosine phosphorylation of one of the two SLP-65 isoforms and complex formation between SLP-65 and the protooncoprotein CrkL (CT10 regulator of kinase like). This leads to antigen receptor-independent phosphorylation of Cbl (Casitas B lineage lymphoma) and C3G. In contrast, phospholipase C-gamma2 (PLC-gamma2) activation is completely blocked. Our data show that in order to establish a latent EBV infection, LMP2A selectively activates or represses SLP-65-regulated signaling pathways.
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Affiliation(s)
- Niklas Engels
- Department of Biochemistry I, University of Bielefeld, Bielefeld D-33615, Germany
| | - Mark Merchant
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, IL 60611
| | - Rajita Pappu
- Center for Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110
| | - Andrew C. Chan
- Center for Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110
| | - Richard Longnecker
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, IL 60611
| | - Jürgen Wienands
- Department of Biochemistry I, University of Bielefeld, Bielefeld D-33615, Germany
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118
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Jumaa H, Mitterer M, Reth M, Nielsen PJ. The absence of SLP65 and Btk blocks B cell development at the preB cell receptor-positive stage. Eur J Immunol 2001; 31:2164-9. [PMID: 11449370 DOI: 10.1002/1521-4141(200107)31:7<2164::aid-immu2164>3.0.co;2-s] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Mice deficient for the adapter protein SLP65 (BLNK) show a partial block in early B cell development, reduced numbers of mature B cells in the periphery, an absence of B1 cells and a reduction of IgM and IgG3 serum immunoglobulin levels. A strikingly similar phenotype is observed in Btk-deficient mice. To investigate the consequences of mutations in both SLP65 and Btk, we generated SLP65/ Btk double-mutant mice by crossing the single-mutant mice. Analysis of the double-mutant mice reveals a much more severe defect in B cell development. B cells in the SLP65/Btk double-mutant mice are arrested at the preB cell stage and, surprisingly, express the preB cell receptor. Normally, preB cell receptor expression in wild-type mice is restricted to a very small fraction of B cells making it difficult to identify these cells in the bone marrow. Together, the data demonstrate the synergistic role of SLP65 and Btk in B cell development and describe a situation where large numbers of preB cell receptor-positive cells accumulate in the bone marrow and spleen.
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Affiliation(s)
- H Jumaa
- Molecular Immunology, Biologie III, University of Freiburg and Max Planck Institute for Immunobiology, Freiburg, Germany.
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119
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Tam WF, Wang W, Sen R. Cell-specific association and shuttling of IkappaBalpha provides a mechanism for nuclear NF-kappaB in B lymphocytes. Mol Cell Biol 2001; 21:4837-46. [PMID: 11416157 PMCID: PMC87179 DOI: 10.1128/mcb.21.14.4837-4846.2001] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Mature B lymphocytes are unique in containing nuclear Rel proteins prior to cell stimulation. This activity consists largely of p50-c-Rel heterodimers, and its importance for B-cell function is exemplified by reduced B-cell viability in several genetically altered mouse strains. Here we suggest a mechanism for the cell specificity and the subunit composition of constitutive B-cell NF-kappaB based on the observed properties of Rel homo- and heterodimers and IkappaBalpha. We show that c-Rel lacks a nuclear export sequence, making the removal of c-Rel-containing complexes from the nucleus less efficient than removal of p65-containing complexes. Second, the nuclear import potential of p65 and c-Rel homodimers but not p50-associated heterodimers was attenuated when they were complexed to IkappaBalpha, leading to a greater propensity of heterodimers to be nuclear. We propose that subunit composition of B-cell NF-kappaB reflects the inefficient retrieval of p50-c-Rel heterodimers from the nucleus. Cell specificity may be a consequence of c-Rel-IkappaBalpha complexes being present only in mature B cells, which leads to nuclear c-Rel due to IkappaBalpha turnover and shuttling of the complex.
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Affiliation(s)
- W F Tam
- Rosenstiel Basic Medical Sciences Research Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02454, USA
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120
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Tedford K, Nitschke L, Girkontaite I, Charlesworth A, Chan G, Sakk V, Barbacid M, Fischer KD. Compensation between Vav-1 and Vav-2 in B cell development and antigen receptor signaling. Nat Immunol 2001; 2:548-55. [PMID: 11376343 DOI: 10.1038/88756] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Vav-1 and Vav-2 are closely related Dbl-homology GTP exchange factors (GEFs) for Rho GTPases. Mutation of Vav-1 disrupts T cell development and T cell antigen receptor-induced activation, but has comparatively little effect on B cells. We found that combined deletion of both Vav-1 and Vav-2 in mice resulted in a marked reduction in mature B lymphocyte numbers. Vav-1(-/-)Vav-2(-/-) B cells were unresponsive to B cell antigen receptor (BCR)-driven proliferation in vitro and to thymus-independent antigen in vivo. BCR-stimulated intracellular calcium mobilization was greatly impaired in Vav-1(-/-)Vav-2(-/-) B cells. These findings establish a role for Vav-2 in BCR calcium signaling and reveal that the Vav family of GEFs is critical to B cell development and function.
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Affiliation(s)
- K Tedford
- Abteilung Physiologische Chemie, Universität Ulm, Albert-Einstein-Allee 11, D-89069 Ulm, Germany
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121
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Janeway CA. How the immune system works to protect the host from infection: a personal view. Proc Natl Acad Sci U S A 2001; 98:7461-8. [PMID: 11390983 PMCID: PMC34691 DOI: 10.1073/pnas.131202998] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/25/2001] [Indexed: 01/07/2023] Open
Affiliation(s)
- C A Janeway
- Section of Immunobiology and The Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06520-8011, USA.
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122
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Tan JE, Wong SC, Gan SK, Xu S, Lam KP. The adaptor protein BLNK is required for b cell antigen receptor-induced activation of nuclear factor-kappa B and cell cycle entry and survival of B lymphocytes. J Biol Chem 2001; 276:20055-63. [PMID: 11274146 DOI: 10.1074/jbc.m010800200] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
B lymphocytes lacking the adaptor protein B cell linker (BLNK) do not proliferate in response to B cell antigen receptor (BCR) engagement. We demonstrate here that BCR-activated BLNK(-)/- B cells fail to enter the cell cycle, and this is due to their inability to induce the expression of the cell cycle regulatory proteins such as cyclin D2 and cyclin-dependent kinase 4. BCR-stimulated BLNK(-)/- B cells also do not up-regulate the cell survival protein Bcl-x(L), which may be necessary for the cells to complete the cell cycle. In addition, BLNK(-)/- B cells exhibit a high rate of spontaneous apoptosis in culture. Examination of the various BCR-activated signaling pathways in mouse BLNK(-)/- B cells reveals the intact activation of Akt and mitogen-activated protein kinases but the impaired activation of nuclear factor (NF)-kappaB that is known to regulate genes involved in cell proliferation and survival. The inability to activate NF-kappaB in BCR-stimulated BLNK(-)/- B cells is due to a failure to induce the degradation of the inhibitory kappaB protein. In all these aspects, BLNK(-)/- B cells resemble xid B cells that have a mutation in Bruton's tyrosine kinase (Btk). Recently, phospholipase C (PLC)-gamma2 has also been demonstrated to be essential for NF-kappaB activation. Since BLNK has been shown separately to interact with both Btk and PLC-gamma2, our finding of normal Btk but impaired PLC-gamma2 activation in BCR-stimulated BLNK(-)/- B cells strongly suggests that BLNK orchestrates the formation of a Btk-PLC-gamma2 signaling axis that regulates NF-kappaB activation. Taken together, the NF-kappaB activation defect may be sufficient to explain the similar defects in BCR-induced B cell proliferation and T cell-independent immune responses in BLNK(-)/-, Btk(-)/-, and PLC-gamma2(-)/- mice.
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Affiliation(s)
- J E Tan
- Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609, Singapore
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123
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Saito K, Scharenberg AM, Kinet JP. Interaction between the Btk PH domain and phosphatidylinositol-3,4,5-trisphosphate directly regulates Btk. J Biol Chem 2001; 276:16201-6. [PMID: 11279148 DOI: 10.1074/jbc.m100873200] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bruton's tyrosine kinase (Btk) binds to phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P(3)) through the Btk pleckstrin homology (PH) domain, an interaction thought to be required for Btk membrane translocation during B cell receptor signaling. Here, we report that interaction of PtdIns-3,4,5-P(3) with the PH domain of Btk directly induces Btk enzymatic activation in an in vitro kinase assay. A point mutation that reduces interaction of PtdIns-3,4,5-P(3) with the Btk PH domain blocks in vitro PtdIns-3,4,5-P(3)-dependent Btk activation, whereas the PH domain deletion enhances Btk basal activity but eliminates the PtdIns-3,4,5-P(3)-dependent stimulation. Btk kinase activity and the Btk activation loop phosphorylation site are both required for the PtdIns-3,4,5-P(3)-mediated stimulation of Btk kinase activity. Together, these results suggest that the Btk PH domain is positioned such that it normally suppresses both Btk kinase activity and access to substrates; when interacting with PtdIns-3,4,5-P(3), this suppression is relieved, producing apparent Btk activation. In addition, using Src family kinase inhibitors and Btk catalytically inactive mutants, we demonstrate that in vivo, the activation of Btk is due to both Lyn phosphorylation and PtdIns-3,4,5-P(3)-mediated direct activation. Thus, the Btk-PtdIns-3,4,5-P(3) interaction serves to translocate Btk to the membrane and directly regulate its signaling function.
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Affiliation(s)
- K Saito
- Division of Allergy and Immunology, Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA
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124
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Kouro T, Nagata K, Takaki S, Nisitani S, Hirano M, Wahl MI, Witte ON, Karasuyama H, Takatsu K. Bruton's tyrosine kinase is required for signaling the CD79b-mediated pro-B to pre-B cell transition. Int Immunol 2001; 13:485-93. [PMID: 11282988 DOI: 10.1093/intimm/13.4.485] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Formation of the pre-BCR complex is a critical check point during B cell development and induces the transition of pro-B to pre-B cells. CD79b (Igbeta) is a signaling component in the pre-BCR complex, since differentiation to the pre-B phenotype is induced by cross-linking the CD79b expressed on developmentally arrested pro-B cells from recombination-activating gene (RAG)-2-deficient mice. Bruton's tyrosine kinase (BTK) plays important roles in B cell development. However, its molecular mechanisms in early B cell development are not fully understood. To examine whether BTK functions in CD79b-mediated signaling for the pro-B/pre-B transition, we utilized RAG2/BTK double-knockout (DKO) mice. Pro-B cells from RAG2/BTK-DKO mice did not differentiate into pre-B cells following CD79b cross-linking, although tyrosine phosphorylation of cellular proteins including Erk1/2 and phospholipase C-gamma2 was induced in the same manner as RAG2-KO mice. BTK is phosphorylated after cross-linking of CD79b on RAG2-deficient pro-B cells. These findings suggest that BTK-dependent pathways downstream of CD79b are critical for the pro-B/pre-B transition and BTK-independent signaling pathways are also activated via the pre-BCR complex.
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Affiliation(s)
- T Kouro
- Department of Immunology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai Minato-ku, Tokyo 108-8639, Japan
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125
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MESH Headings
- Agammaglobulinaemia Tyrosine Kinase
- Animals
- Antigens, Differentiation, B-Lymphocyte/immunology
- B-Lymphocyte Subsets/cytology
- B-Lymphocyte Subsets/immunology
- Cell Differentiation
- Cellular Senescence
- Clonal Deletion
- Gene Rearrangement, B-Lymphocyte, Light Chain
- Genes, Immunoglobulin
- Humans
- Immunoglobulin Heavy Chains/genetics
- Immunoglobulin M/immunology
- Immunoglobulin Variable Region/genetics
- Immunologic Memory
- Immunophenotyping
- Lymphocyte Activation
- Mice
- Mice, Transgenic
- Models, Immunological
- Protein-Tyrosine Kinases/physiology
- Proto-Oncogene Proteins c-bcl-2/physiology
- Receptors, Antigen, B-Cell/genetics
- Receptors, Antigen, B-Cell/immunology
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Affiliation(s)
- F Martin
- Department of Microbiology, Division of Developmental and Clinical Immunology, University of Alabama at Birmingham, AL 35294-3300, USA
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126
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Moon BG, Yoshida T, Shiiba M, Nakao K, Katsuki M, Takaki S, Takatsu K. Functional dissection of the cytoplasmic subregions of the interleukin-5 receptor alpha chain in growth and immunoglobulin G1 switch recombination of B cells. Immunology 2001; 102:289-300. [PMID: 11298827 PMCID: PMC1783180 DOI: 10.1046/j.1365-2567.2001.01196.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The interleukin-5 receptor alpha chain (IL-5Ralpha) is known to regulate the development and function of B cells and eosinophils. Although the functions of IL-5Ralpha cytoplasmic domain subregions have been studied extensively using cultured cell lines, this approach has limitations when studying the functions of distinct primary B-cell subpopulations and their responsiveness to IL-5. In the present study, we generated mice on an IL-5Ralpha null background, each expressing a mutant form of an IL-5Ralpha transgene ligated to a mu enhancer and VH promoter, either lacking the cytoplasmic DC3 region or substituting two proline residues for alanine (ApvA) in the membrane-proximal ppvp motif of the cytoplasmic domain. The ppvp motif, which mediates activation of JAK2/STAT5 and Btk, also contributes to c-fos, c-jun and c-myc expression. IL-5Ralpha null mutant mice showed impaired B-1-cell development, reduced serum immunoglobulin G3 (IgG3) and IgM, no IL-5-induced enhancement of B-cell proliferation and IL-5-induced switch recombination from the mu gene to gamma1 gene; these were not recovered following the expression of the ApvA mutant. In contrast, absence of the DC3 region affected the IL-5-induced switch recombination from the mu to the gamma1 gene and B-1-cell development, while IL-5-induced proliferation and IgM production were at levels similar to those of B cells expressing wild-type IL-5Ralpha transgene. The results clearly indicated that the ppvp motif and the DC3 region of IL-5Ralpha played distinct roles in B-cell proliferation and differentiation. Thus, this present approach offers new insights into the functions of the cytoplasmic subregions of IL-5Ralpha, in particular its carboxy-terminal region.
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Affiliation(s)
- B G Moon
- Department of Immunology, Division of DNA Biology and Embryo Engineering, Centre for Experimental Medicine, Institute of Medical Science, University of Tokyo, Japan
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127
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Hsueh RC, Scheuermann RH. Tyrosine kinase activation in the decision between growth, differentiation, and death responses initiated from the B cell antigen receptor. Adv Immunol 2001; 75:283-316. [PMID: 10879287 DOI: 10.1016/s0065-2776(00)75007-3] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Immunoglobulin-containing receptors expressed on B lineage lymphocytes play critical roles in the development and function of the humoral arm of the immune system. The preB cell antigen receptor (preBCR) contains the immunoglobulin mu heavy chain (Ig mu) and signals to the preB cell that heavy chain rearrangement has been successful, a process termed heavy chain selection. The B cell antigen receptor (BCR) contains both Ig heavy and light chains and is expressed on immature and mature B cells before and after antigen encounter. Both receptor types from a complex with the Ig alpha and Ig beta proteins that link the predominantly extracellular Ig with intracellular signal transduction pathways. Signaling through the BCR induces different cellular responses depending on the nature of the signaling agent and the development stage of the target cell. These responses include clonal anergy and apoptotic deletion in immature B cells and survival, proliferation, and differentiation in mature B and preB cells. Several protein tyrosine kinases are activated rapidly following engagement of the BCR/preBCR complexes, including members of the Src family (Lyn and Blk), the Syk/ZAP70 family (Syk), and the Tec family (Btk). In this review, we discuss possible mechanisms by which engagement of these similar receptor complexes can give rise to different cellular responses and the role that these kinases play in this process.
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MESH Headings
- Agammaglobulinaemia Tyrosine Kinase
- Antibody Formation
- Antigens, CD/genetics
- Antigens, CD/immunology
- Apoptosis/physiology
- B-Lymphocyte Subsets/cytology
- B-Lymphocyte Subsets/enzymology
- B-Lymphocyte Subsets/immunology
- CD79 Antigens
- Cell Differentiation/physiology
- Cell Division/physiology
- Enzyme Activation
- Enzyme Precursors/physiology
- Genes, Immunoglobulin
- Hematopoietic Stem Cells/cytology
- Hematopoietic Stem Cells/immunology
- Humans
- Immune Tolerance
- Immunoglobulin Heavy Chains/genetics
- Immunologic Deficiency Syndromes/enzymology
- Immunologic Deficiency Syndromes/genetics
- Immunologic Deficiency Syndromes/immunology
- Intracellular Signaling Peptides and Proteins
- Lymphocyte Activation
- Phosphorylation
- Plasma Cells/cytology
- Plasma Cells/immunology
- Protein Processing, Post-Translational
- Protein-Tyrosine Kinases/physiology
- Receptors, Antigen, B-Cell/genetics
- Receptors, Antigen, B-Cell/immunology
- Receptors, Antigen, B-Cell/physiology
- Recombinant Fusion Proteins/immunology
- Signal Transduction
- Syk Kinase
- ZAP-70 Protein-Tyrosine Kinase
- src Homology Domains
- src-Family Kinases/deficiency
- src-Family Kinases/genetics
- src-Family Kinases/physiology
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Affiliation(s)
- R C Hsueh
- Laboratory of Molecular Pathology, University of Texas Southwestern Medical Center, Dallas 75235, USA
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128
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Kaisho T, Takeda K, Tsujimura T, Kawai T, Nomura F, Terada N, Akira S. IkappaB kinase alpha is essential for mature B cell development and function. J Exp Med 2001; 193:417-26. [PMID: 11181694 PMCID: PMC2195900 DOI: 10.1084/jem.193.4.417] [Citation(s) in RCA: 161] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
IkappaB kinase (IKK) alpha and beta phosphorylate IkappaB proteins and activate the transcription factor, nuclear factor (NF)-kappaB. Although both are highly homologous kinases, gene targeting experiments revealed their differential roles in vivo. IKKalpha is involved in skin and limb morphogenesis, whereas IKKbeta is essential for cytokine signaling. To elucidate in vivo roles of IKKalpha in hematopoietic cells, we have generated bone marrow chimeras by transferring control and IKKalpha-deficient fetal liver cells. The mature B cell population was decreased in IKKalpha(-/-) chimeras. IKKalpha(-/-) chimeras also exhibited a decrease of serum immunoglobulin basal level and impaired antigen-specific immune responses. Histologically, they also manifested marked disruption of germinal center formation and splenic microarchitectures that depend on mature B cells. IKKalpha(-/-) B cells not only showed impairment of survival and mitogenic responses in vitro, accompanied by decreased, although inducible, NF-kappaB activity, but also increased turnover rate in vivo. In addition, transgene expression of bcl-2 could only partially rescue impaired B cell development in IKKalpha(-/-) chimeras. Taken together, these results demonstrate that IKKalpha is critically involved in the prevention of cell death and functional development of mature B cells.
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Affiliation(s)
- Tsuneyasu Kaisho
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
- Institute for Advanced Medical Sciences, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan
- Core Research for Evolution Science and Technology (CREST), Japan Science and Technology Corporation, Tokyo 101-0062, Japan
| | - Kiyoshi Takeda
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
- Core Research for Evolution Science and Technology (CREST), Japan Science and Technology Corporation, Tokyo 101-0062, Japan
| | - Tohru Tsujimura
- Department of Pathology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan
| | - Taro Kawai
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
- Core Research for Evolution Science and Technology (CREST), Japan Science and Technology Corporation, Tokyo 101-0062, Japan
| | - Fumiko Nomura
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
- Core Research for Evolution Science and Technology (CREST), Japan Science and Technology Corporation, Tokyo 101-0062, Japan
| | - Nobuyuki Terada
- Department of Pathology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan
| | - Shizuo Akira
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
- Core Research for Evolution Science and Technology (CREST), Japan Science and Technology Corporation, Tokyo 101-0062, Japan
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129
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Wortis HH, Berland R. Cutting edge commentary: origins of B-1 cells. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:2163-6. [PMID: 11160267 DOI: 10.4049/jimmunol.166.4.2163] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The origin of B-1a cells, a minority population of B cells that express CD5, are abundant in coelomic cavities, and often produce autoantibodies, has been the subject of study for many years. Accumulating evidence demonstrates that the hypothesis that only B cells arising in fetal or neonatal tissues have the potential to become B-1a cells cannot be true. Rather, B cell receptor-mediated signaling initiated by ligation of autoantigen has now been shown to be required for induction of the B-1a phenotype. Furthermore, cells with a functional B-1a phenotype can be induced from adult precursors by appropriate Ag. At the same time, microenvironment-specific events may determine the likelihood that a given B cell, either adult or fetal derived, enters this pathway. CD5 expression and possibly localization to the peritoneum appear to provide some protection to autoreactive cells otherwise slated for elimination.
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Affiliation(s)
- H H Wortis
- Department of Pathology, Tufts University School of Medicine and Program in Immunology, Sackler School of Graduate Biomedical Sciences, Boston MA 02111, USA.
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130
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131
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Jui HY, Tseng RJ, Wen X, Fang HI, Huang LM, Chen KY, Kung HJ, Ann DK, Shih HM. Protein-tyrosine phosphatase D1, a potential regulator and effector for Tec family kinases. J Biol Chem 2000; 275:41124-32. [PMID: 11013262 DOI: 10.1074/jbc.m007772200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Etk, also named Bmx, is a member of the Tec tyrosine kinase family, which is characterized by a multimodular structure including a pleckstrin homology (PH) domain, an SH3 domain, an SH2 domain, and a catalytic domain. The signaling mechanisms regulating Etk kinase activity remain largely unknown. To identify factor(s) regulating Etk activity, we used the PH domain and a linker region of Etk as a bait for a yeast two-hybrid screen. Three independent clones encoding protein-tyrosine phosphatase D1 (PTPD1) fragments were isolated. The binding of PTPD1 to Etk is specific since PTPD1 cannot associate with either the Akt PH domain or lamin. In vitro and in vivo binding studies demonstrated that PTPD1 can interact with Etk and that residues 726-848 of PTPD1 are essential for this interaction. Deletion analysis of Etk indicated that the PH domain is essential for PTPD1 interaction. Furthermore, the Etk-PTPD1 interaction stimulated the kinase activity of Etk, resulting in an increased phosphotyrosine content in both factors. The Etk-PTPD1 interaction also increased Stat3 activation. The effect of PTPD1 on Etk activation is specific since PTPD1 cannot potentiate Jak2 activity upon Stat3 activation. In addition, Tec (but not Btk) kinase can also be activated by PTPD1. Taken together, these findings indicate that PTPD1 can selectively associate with and stimulate Tec family kinases and modulate Stat3 activation.
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Affiliation(s)
- H Y Jui
- Division of Molecular and Genomic Medicine, National Health Research Institutes, and the Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 11529, Taiwan
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132
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Webb CF, Yamashita Y, Ayers N, Evetts S, Paulin Y, Conley ME, Smith EA. The transcription factor Bright associates with Bruton's tyrosine kinase, the defective protein in immunodeficiency disease. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 165:6956-65. [PMID: 11120822 DOI: 10.4049/jimmunol.165.12.6956] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Binding of the transcription factor Bright to Ig heavy chain loci after B cell activation is associated with increased heavy chain transcription. We now report that Bright coprecipitates with Bruton's tyrosine kinase (Btk), the defective enzyme in X-linked immunodeficiency disease (xid). Furthermore, we observed Btk in the nucleus of activated murine B cells, and mobility shift assays suggest that it is a component of the Bright DNA-binding complex. While BRIGHT protein was synthesized in activated spleen cells from xid mice, it did not bind DNA or associate stably with Btk. These data suggest that deficiencies in BRIGHT DNA-binding activity may contribute to the defects in Ig production seen in xid mice.
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Affiliation(s)
- C F Webb
- Department of Immunobiology and Cancer, Oklahoma Medical Research Foundation, and Department of Microbiology and Immunology, Oklahoma University Health Sciences Center, Oklahoma City, OK 73104, USA
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133
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Ellmeier W, Jung S, Sunshine MJ, Hatam F, Xu Y, Baltimore D, Mano H, Littman DR. Severe B cell deficiency in mice lacking the tec kinase family members Tec and Btk. J Exp Med 2000; 192:1611-24. [PMID: 11104803 PMCID: PMC2193106 DOI: 10.1084/jem.192.11.1611] [Citation(s) in RCA: 153] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The cytoplasmic protein tyrosine kinase Tec has been proposed to have important functions in hematopoiesis and lymphocyte signal transduction. Here we show that Tec-deficient mice developed normally and had no major phenotypic alterations of the immune system. To reveal potential compensatory roles of other Tec kinases such as Bruton's tyrosine kinase (Btk), Tec/Btk double-deficient mice were generated. These mice exhibited a block at the B220(+)CD43(+) stage of B cell development and displayed a severe reduction of peripheral B cell numbers, particularly immunoglobulin (Ig)M(lo)IgD(hi) B cells. Although Tec/Btk(null) mice were able to form germinal centers, the response to T cell-dependent antigens was impaired. Thus, Tec and Btk together have an important role both during B cell development and in the generation and/or function of the peripheral B cell pool. The ability of Tec to compensate for Btk may also explain phenotypic differences in X-linked immunodeficiency (xid) mice compared with human X-linked agammaglobulinemia (XLA) patients.
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Affiliation(s)
- W Ellmeier
- Molecular Pathogenesis Program, Skirball Institute of Biomolecular Medicine.
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134
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Abstract
Antibodies on the surface of B lymphocytes trigger adaptive immune responses and control a series of antigen-independent checkpoints during B cell development. These physiologic processes are regulated by a complex of membrane immunoglobulin and two signal transducing proteins known as Ig alpha and Ig beta. Here we focus on the role of antibodies in governing the maturation of B cells from early antigen-independent through the final antigen-dependent stages.
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Affiliation(s)
- E Meffre
- Howard Hughes Medical Institute, Rockefeller University, 1230 York Avenue, New York, NY 10021-6399, USA
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135
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Hashimoto A, Takeda K, Inaba M, Sekimata M, Kaisho T, Ikehara S, Homma Y, Akira S, Kurosaki T. Cutting edge: essential role of phospholipase C-gamma 2 in B cell development and function. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 165:1738-42. [PMID: 10925250 DOI: 10.4049/jimmunol.165.4.1738] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Cross-linking of the B cell Ag receptor (BCR) induces the tyrosine phosphorylation of multiple cellular substrates, including phospholipase C (PLC)-gamma 2, which is involved in the activation of the phosphatidylinositol pathway. To assess the importance of PLC-gamma 2 in murine lymphopoiesis, the PLC-gamma 2 gene was inducibly ablated by using IFN-regulated Cre recombinase. Mice with a neonatally induced loss of PLC-gamma 2 function displayed reduced numbers of mature conventional B cells and peritoneal B1 cells and defective responses in vitro to BCR stimulation and in vivo to immunization with thymus-independent type II Ags. In contrast, T cell development and TCR-mediated proliferation were normal. Taken together, PLC-gamma 2 is a critical component of BCR signaling pathways and is required to promote B cell development.
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Affiliation(s)
- A Hashimoto
- Department of Molecular Genetics, Institute for Liver Research, Kansai Medical University, Moriguchi, Japan
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136
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Kawakami Y, Kitaura J, Satterthwaite AB, Kato RM, Asai K, Hartman SE, Maeda-Yamamoto M, Lowell CA, Rawlings DJ, Witte ON, Kawakami T. Redundant and opposing functions of two tyrosine kinases, Btk and Lyn, in mast cell activation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 165:1210-9. [PMID: 10903718 DOI: 10.4049/jimmunol.165.3.1210] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Protein-tyrosine kinases play crucial roles in mast cell activation through the high-affinity IgE receptor (FcepsilonRI). In this study, we have made the following observations on growth properties and FcepsilonRI-mediated signal transduction of primary cultured mast cells from Btk-, Lyn-, and Btk/Lyn-deficient mice. First, Lyn deficiency partially reversed the survival effect of Btk deficiency. Second, FcepsilonRI-induced degranulation and leukotriene release were almost abrogated in Btk/Lyn doubly deficient mast cells while singly deficient cells exhibited normal responses. Tyrosine phosphorylation of cellular proteins including phospholipases C-gamma1 and C-gamma2 was reduced in Btk/Lyn-deficient mast cells. Accordingly, FcepsilonRI-induced elevation of intracellular Ca2+ concentrations and activation of protein kinase Cs were blunted in the doubly deficient cells. Third, in contrast, Btk and Lyn demonstrated opposing roles in cytokine secretion and mitogen-activated protein kinase activation. Lyn-deficient cells exhibited enhanced secretion of TNF-alpha and IL-2 apparently through the prolonged activation of extracellular signal-related kinases and c-Jun N-terminal kinase. Potentially accounting for this phenomenon and robust degranulation in Lyn-deficient cells, the activities of protein kinase Calpha and protein kinase CbetaII, low at basal levels, were enhanced in these cells. Fourth, cytokine secretion was severely reduced and c-Jun N-terminal kinase activation was completely abrogated in Btk/Lyn-deficient mast cells. The data together demonstrate that Btk and Lyn are involved in mast cell signaling pathways in distinctly different ways, emphasizing that multiple signal outcomes must be evaluated to fully understand the functional interactions of individual signaling components.
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Affiliation(s)
- Y Kawakami
- Division of Allergy, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA
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137
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Wienands J. Signal transduction elements of the B cell antigen receptor and their role in immunodeficiencies. Immunobiology 2000; 202:120-33. [PMID: 10993287 DOI: 10.1016/s0171-2985(00)80059-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The primary function of B lymphocytes is to contribute to the elimination of foreign antigens by producing large amounts of soluble antibodies. The activation of B cells through their antigen receptor triggers a dynamic network of intracellular signaling proteins. The recent identification of the cytoplasmic adaptor protein SLP-65 (also called BLNK or BASH) provided insight in how the antigen receptor-regulated protein tyrosine kinases couple to downstream signaling cascades, including the mobilization of Ca2+ ions, activation of mitogen-activated kinases and reorganization of the cytoskeleton architecture. While these events have been mostly studied in mature B cells, it is now clear that the components of the antigen receptor and its downstream effector elements play also a central role during early and late B cell development, and in the apoptotic elimination of B cells with reactivity to self-antigens. Thus, genetic defects affecting the expression of antigen receptor subunits or its intracellular signaling proteins can interfere with B cell development and activation, and can cause severe antibody deficiencies in mouse and man. In this article I summarize our current picture of the B cell antigen receptor, how the extracellular signal is transported into the cell interior, and how dysregulation of these processes contribute to immune defects.
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Affiliation(s)
- J Wienands
- Institute of Biology III, University of Freiburg and Max-Planck-Institute of Immunobiology, Germany.
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138
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Wang D, Feng J, Wen R, Marine JC, Sangster MY, Parganas E, Hoffmeyer A, Jackson CW, Cleveland JL, Murray PJ, Ihle JN. Phospholipase Cgamma2 is essential in the functions of B cell and several Fc receptors. Immunity 2000; 13:25-35. [PMID: 10933392 DOI: 10.1016/s1074-7613(00)00005-4] [Citation(s) in RCA: 357] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Many receptors activate phospholipase Cgamma1 or -gamma2. To assess the role of PLCgamma2, we derived enzyme-deficient mice. The mice are viable but have decreased mature B cells, a block in pro-B cell differentiation, and B1 B cell deficiency. IgM receptor-induced Ca2+ flux and proliferation to B cell mitogens are absent. IgM, IgG2a, and IgG3 levels are reduced, and T cell-independent antibody production is absent. The similarity to Btk- or Blnk-deficient mice demonstrates that PLCgamma2 is downstream in Btk/Blnk signaling. FcRgamma signaling is also defective, resulting in a loss of collagen-induced platelet aggregation, mast cell FcepsilonR function, and NK cell FcgammaRIII and 2B4 function. The results define a signal transduction pathway broadly utilized by immunoglobulin superfamily receptors.
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Affiliation(s)
- D Wang
- Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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139
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Abstract
Abstract
Development of mammalian B-lineage cells is characterized by progression through a series of checkpoints defined primarily by rearrangement and expression of immunoglobulin genes. Progression through these checkpoints is also influenced by stromal cells in the microenvironment of the primary tissues wherein B-cell development occurs, ie, fetal liver and bone marrow and adult bone marrow. This review focuses on the developmental biology of human bone marrow B-lineage cells, including perturbations that contribute to the origin and evolution of B-lineage acute lymphoblastic leukemia and primary immunodeficiency diseases characterized by agammaglobulinemia. Recently described in vitro and in vivo models that support development and expansion of human B-lineage cells through multiple checkpoints provide new tools for identifying the bone marrow stromal cell–derived molecules necessary for survival and proliferation. Mutations in genes encoding subunits of the pre-B cell receptor and molecules involved in pre-B cell receptor signaling culminate in X-linked and non–X-linked agammaglobulinemia. A cardinal feature of these immunodeficiencies is an apparent apoptotic sensitivity of B-lineage cells at the pro-B to pre-B transition. On the other end of the spectrum is the apoptotic resistance that accompanies the development of B-lineage acute lymphoblastic leukemia, potentially a reflection of genetic abnormalities that subvert normal apoptotic programs. The triad of laboratory models that mimic the bone marrow microenvironment, immunodeficiency diseases with specific defects in B-cell development, and B-lineage acute lymphoblastic leukemia can now be integrated to deepen our understanding of human B-cell development.
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140
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Abstract
Development of mammalian B-lineage cells is characterized by progression through a series of checkpoints defined primarily by rearrangement and expression of immunoglobulin genes. Progression through these checkpoints is also influenced by stromal cells in the microenvironment of the primary tissues wherein B-cell development occurs, ie, fetal liver and bone marrow and adult bone marrow. This review focuses on the developmental biology of human bone marrow B-lineage cells, including perturbations that contribute to the origin and evolution of B-lineage acute lymphoblastic leukemia and primary immunodeficiency diseases characterized by agammaglobulinemia. Recently described in vitro and in vivo models that support development and expansion of human B-lineage cells through multiple checkpoints provide new tools for identifying the bone marrow stromal cell–derived molecules necessary for survival and proliferation. Mutations in genes encoding subunits of the pre-B cell receptor and molecules involved in pre-B cell receptor signaling culminate in X-linked and non–X-linked agammaglobulinemia. A cardinal feature of these immunodeficiencies is an apparent apoptotic sensitivity of B-lineage cells at the pro-B to pre-B transition. On the other end of the spectrum is the apoptotic resistance that accompanies the development of B-lineage acute lymphoblastic leukemia, potentially a reflection of genetic abnormalities that subvert normal apoptotic programs. The triad of laboratory models that mimic the bone marrow microenvironment, immunodeficiency diseases with specific defects in B-cell development, and B-lineage acute lymphoblastic leukemia can now be integrated to deepen our understanding of human B-cell development.
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141
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Abstract
Signal transduction by the BCR is critical for progression through developmental checkpoints as well as for immune responses. Recent results obtained in mice deficient either in an adaptor molecule, BLNK (alternatively named SLP-65 or BASH), or in phosphatidylinositol 3-kinase have revealed similar - though not identical - phenotypes to those of Btk(-/-) mice, suggesting a functional link between BLNK, Btk and phosphatidylinositol 3-kinase.
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Affiliation(s)
- T Kurosaki
- Department of Molecular Genetics, Institute for Liver Research, Kansai Medical University, Moriguchi, 570-8506, Japan. kurosaki@mxr. mesh.ne.jp
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142
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Petro JB, Rahman SJ, Ballard DW, Khan WN. Bruton's tyrosine kinase is required for activation of IkappaB kinase and nuclear factor kappaB in response to B cell receptor engagement. J Exp Med 2000; 191:1745-54. [PMID: 10811867 PMCID: PMC2193161 DOI: 10.1084/jem.191.10.1745] [Citation(s) in RCA: 243] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Mutations in the gene encoding Bruton's tyrosine kinase (btk) cause the B cell deficiency diseases X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (xid) in mice. In vivo and in vitro studies indicate that the BTK protein is essential for B cell survival, cell cycle progression, and proliferation in response to B cell antigen receptor (BCR) stimulation. BCR stimulation leads to the activation of transcription factor nuclear factor (NF)-kappaB, which in turn regulates genes controlling B cell growth. We now demonstrate that a null mutation in btk known to cause the xid phenotype prevents BCR-induced activation of NF-kappaB. This defect can be rescued by reconstitution with wild-type BTK. This mutation also interferes with BCR-directed activation of IkappaB kinase (IKK), which normally targets the NF-kappaB inhibitor IkappaBalpha for degradation. Taken together, these findings indicate that BTK couples IKK and NF-kappaB to the BCR. Interference with this coupling mechanism may contribute to the B cell deficiencies observed in XLA and xid.
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Affiliation(s)
- James B. Petro
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146
| | - S.M. Jamshedur Rahman
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146
| | - Dean W. Ballard
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146
| | - Wasif N. Khan
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146
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143
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Bajpai UD, Zhang K, Teutsch M, Sen R, Wortis HH. Bruton's tyrosine kinase links the B cell receptor to nuclear factor kappaB activation. J Exp Med 2000; 191:1735-44. [PMID: 10811866 PMCID: PMC2193152 DOI: 10.1084/jem.191.10.1735] [Citation(s) in RCA: 168] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/1999] [Accepted: 03/27/2000] [Indexed: 11/29/2022] Open
Abstract
The recognition of antigen by membrane immunoglobulin M (mIgM) results in a complex series of signaling events in the cytoplasm leading to gene activation. Bruton's tyrosine kinase (BTK), a member of the Tec family of tyrosine kinases, is essential for the full repertoire of IgM signals to be transduced. We examined the ability of BTK to regulate the nuclear factor (NF)-kappaB/Rel family of transcription factors, as the activation of these factors is required for a B cell response to mIgM. We found greatly diminished IgM- but not CD40-mediated NF-kappaB/Rel nuclear translocation and DNA binding in B cells from X-linked immunodeficient (xid) mice that harbor an R28C mutation in btk, a mutation that produces a functionally inactive kinase. The defect was due, in part, to a failure to fully degrade the inhibitory protein of NF-kappaB, IkappaBalpha. Using a BTK-deficient variant of DT40 chicken B cells, we found that expression of wild-type or gain-of-function mutant BTK, but not the R28C mutant, reconstituted NF-kappaB activity. Thus, BTK is essential for activation of NF-kappaB via the B cell receptor.
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Affiliation(s)
- Urmila D. Bajpai
- Department of Pathology and Program in Immunology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts 02111
| | - Keming Zhang
- Department of Pathology and Program in Immunology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts 02111
| | - Mark Teutsch
- Department of Pathology and Program in Immunology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts 02111
| | - Ranjan Sen
- Rosenstiel Research Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02254
| | - Henry H. Wortis
- Department of Pathology and Program in Immunology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts 02111
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144
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Solvason N, Wu WW, Parry D, Mahony D, Lam EW, Glassford J, Klaus GG, Sicinski P, Weinberg R, Liu YJ, Howard M, Lees E. Cyclin D2 is essential for BCR-mediated proliferation and CD5 B cell development. Int Immunol 2000; 12:631-8. [PMID: 10784609 DOI: 10.1093/intimm/12.5.631] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Progression into G(1) in B lymphocytes is regulated by cyclins D2 and D3, components of the cell cycle machinery currently believed to have overlapping and potentially redundant roles in cell cycle control. To study the specific role of cyclin D2 in B lymphocyte proliferation, we examined B cells from cyclin D2(-/-) mice and demonstrate a specific requirement for cyclin D2 in BCR- but not CD40- or lipopolysaccharide-induced proliferation. Furthermore, conventional B cell development proceeds normally in the mutant mice; however, the CD5 B cell compartment is dramatically reduced, suggesting that cyclin D2 is important in CD5 B cell development as well as antigen-dependent B cell clonal expansion.
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Affiliation(s)
- N Solvason
- Department of Immunology, DNAX Research Institute, Palo Alto, CA 94304, USA
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145
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Arnold LW, McCray SK, Tatu C, Clarke SH. Identification of a precursor to phosphatidyl choline-specific B-1 cells suggesting that B-1 cells differentiate from splenic conventional B cells in vivo: cyclosporin A blocks differentiation to B-1. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 164:2924-30. [PMID: 10706678 DOI: 10.4049/jimmunol.164.6.2924] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The origin of B-1 cells is controversial. The initial paradigm posited that B-1 and B-2 cells derive from separate lineages. More recently it has been argued that B-1 cells derive from conventional B cells as a result of T-independent Ag activation. To understand B-1 cell differentiation, we have generated Ig transgenic (Tg) mice using the H and L chain genes (VH12 and Vkappa4) of anti-phosphatidyl choline (anti-PtC) B cells. In normal mice anti-PtC B cells segregate to B-1. Segregation is intact in VH12 (6-1) and VH12/Vkappa4 (double) Tg mice that develop large numbers of PtC-specific B cells. However, if B-1 cell differentiation is blocked, anti-PtC B cells in these Tg mice are B-2-like in phenotype, suggesting the existence of an Ag-driven differentiative pathway from B-2 to B-1. In this study, we show that double Tg mice have a population of anti-PtC B cells that have the phenotypic characteristics of both B-2 and B-1 cells and that have the potential to differentiate to B-1 (B-1a and B-1b). Cyclosporin A blocks this differentiation and induces a more B-2-like phenotype in these cells. These findings indicate that these cells are intermediate between B-2 and B-1, further evidence of a B-2 to B-1 differentiative pathway.
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Affiliation(s)
- L W Arnold
- Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC 27599, USA
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146
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Nisitani S, Satterthwaite AB, Akashi K, Weissman IL, Witte ON, Wahl MI. Posttranscriptional regulation of Bruton's tyrosine kinase expression in antigen receptor-stimulated splenic B cells. Proc Natl Acad Sci U S A 2000; 97:2737-42. [PMID: 10688914 PMCID: PMC15999 DOI: 10.1073/pnas.050583597] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mutation of Bruton's tyrosine kinase (Btk) causes human X-linked agammaglobulinemia and murine X-linked immunodeficiency syndrome (xid). Quantitative aspects of B lymphocyte development and function have been demonstrated to depend on Btk level in vivo by using a murine transgenic model system. A sensitive intracellular immunofluorescent assay was developed to measure Btk protein on a per cell basis to test the hypothesis that its dosage is dynamically regulated during B cell development or functional responses. Marrow-derived hematopoietic stem cells, common lymphoid progenitor cells, and developing B and myeloid lineages expressed Btk protein at comparable levels. Resting peripheral B lineage cells had a significantly lower amount of Btk than marrow-derived cells in both wild-type and xid mice. Activation of the B cell antigen receptor up-regulated Btk protein level 10-fold within several hours by a phosphatidylinositol 3-kinase-dependent, posttranscriptional mechanism. In contrast, the protein level of Btk R28C in activated B lymphocytes from xid mice remained low. Bypass of the antigen receptor signaling pathways by treatment of cells with phorbol myristic acid and ionomycin rescued up-regulation of Btk protein in xid splenic B cells. These combined results suggest that certain receptor signals mediated by Btk regulate the level of expression of Btk protein in responding B lymphocytes to potentiate signal transduction. Dynamic regulation of Btk protein dosage is an additional mechanism to modulate B lymphocyte immune functions.
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Affiliation(s)
- S Nisitani
- Department of Microbiology, Immunology, and Molecular Genetics, and Howard Hughes Medical Institute, University of California at Los Angeles, Los Angeles, CA 90095, USA
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147
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Boyd Y, Blair HJ, Cunliffe P, Masson WK, Reed V. A phenotype map of the mouse X chromosome: models for human X-linked disease. Genome Res 2000; 10:277-92. [PMID: 10720569 DOI: 10.1101/gr.10.3.277] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The identification of many of the transcribed genes in man and mouse is being achieved by large scale sequencing of expressed sequence tags (ESTs). Attention is now being turned to elucidating gene function and many laboratories are looking to the mouse as a model system for this phase of the genome project. Mouse mutants have long been used as a means of investigating gene function and disease pathogenesis, and recently, several large mutagenesis programs have been initiated to fulfill the burgeoning demand of functional genomics research. Nevertheless, there is a substantial existing mouse mutant resource that can be used immediately. This review summarizes the available information about the loci encoding X-linked phenotypic mutants and variants, including 40 classical mutants and 40 that have arisen from gene targeting.
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Affiliation(s)
- Y Boyd
- Medical Research Council (MRC) Mammalian Genetics Unit, Harwell, Oxon OX11 0RD UK.
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148
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Affiliation(s)
- H B Gaspar
- Molecular Immunology Unit, Institute of Child Health, University College London, London, UK.
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149
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Xu S, Tan JE, Wong EP, Manickam A, Ponniah S, Lam KP. B cell development and activation defects resulting in xid-like immunodeficiency in BLNK/SLP-65-deficient mice. Int Immunol 2000; 12:397-404. [PMID: 10700474 DOI: 10.1093/intimm/12.3.397] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Engagement of the B cell receptor (BCR) leads to the activation of tyrosine kinases and other signaling molecules that ultimately determine the type and magnitude of the B lymphocyte's cellular response. The adaptor protein BLNK/SLP-65 plays a pivotal role in BCR signal transduction by coupling Syk activation to downstream elements such as Grb2, phospholipase C-gamma, Vav and Nck. We have generated BLNK(-/-) mice to determine the physiological role of this protein in B cell development and activation. BLNK(-/-) mice exhibit an incomplete block in B cell development with a severe inhibition of pro-B to pre-B cell differentiation. BLNK(-/-) sIgM(+) cells can develop, seed the peripheral lymphoid tissues and accumulate in numbers overtime. However, these mutant B cells failed to mature and are non-responsive to BCR cross-linking in terms of proliferation and up-regulation of activation markers such as CD69 and CD86 (B7-2). In addition, the CD5(+) subset of B cells is absent. The immune response to T cell-independent antigen but not T cell-dependent antigen is also impaired. Overall, the phenotype of BLNK(-/-) mice bears a striking resemblance to that of xid mice which is the murine model of human XLA that has a mutation in Bruton's tyrosine kinase. This raises the interesting possibility that mutation in BLNK/SLP-65 may be responsible for certain human immunodeficiencies.
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Affiliation(s)
- S Xu
- Institute of Molecular and Cell Biology, National University of Singapore, 30 Medical Drive, Singapore 117609, Republic of Singapore
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150
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Schubart DB, Rolink A, Schubart K, Matthias P. Cutting edge: lack of peripheral B cells and severe agammaglobulinemia in mice simultaneously lacking Bruton's tyrosine kinase and the B cell-specific transcriptional coactivator OBF-1. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 164:18-22. [PMID: 10604987 DOI: 10.4049/jimmunol.164.1.18] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
OBF-1 is a B cell-restricted transcriptional coactivator that is recruited to octamer-containing promoters by interacting with the POU domain of Oct-1 or Oct-2. We have shown earlier that mice lacking OBF-1 were dramatically impaired in their ability to mount humoral immune responses and did not develop germinal centers in the spleen; however, they had a largely normal B cell development in the bone marrow. In this study, we demonstrate that OBF-1-deficient mice also have an early defect in B cell development and show that OBF-1-/- immature B cells are greatly impaired at the transition from the bone marrow to the spleen. In addition, when the OBF-1 mutation is combined to a mutation in the gene encoding Bruton's tyrosine kinase, a striking phenotype is observed. These double-deficient animals lack peripheral B cells and have virtually no serum Igs, thus closely resembling human X chromosome-linked agammaglobulinemia.
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Affiliation(s)
- D B Schubart
- Friedrich Miescher-Institute, Basel, Switzerland
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