1
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Zhang R, Wang D, Ruan GX, Wang R, Li Y, Chen W, Huang H, Wang J, Meng L, Zhu Z, Lei D, Xu S, Ou X. Spliceosome component PHD finger 5A is essential for early B lymphopoiesis. Development 2024; 151:dev202247. [PMID: 38095286 DOI: 10.1242/dev.202247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Accepted: 12/08/2023] [Indexed: 01/12/2024]
Abstract
The spliceosome, a multi-megadalton ribonucleoprotein complex, is essential for pre-mRNA splicing in the nucleus and ensuring genomic stability. Its precise and dynamic assembly is pivotal for its function. Spliceosome malfunctions can lead to developmental abnormalities and potentially contribute to tumorigenesis. The specific role of the spliceosome in B cell development is poorly understood. Here, we reveal that the spliceosomal U2 snRNP component PHD finger protein 5A (Phf5a) is vital for early B cell development. Loss of Phf5a results in pronounced defects in B cell development, causing an arrest at the transition from pre-pro-B to early pro-B cell stage in the bone marrow of mutant mice. Phf5a-deficient B cells exhibit impaired immunoglobulin heavy (IgH) chain expression due to defective V-to-DJ gene rearrangement. Mechanistically, our findings suggest that Phf5a facilitates IgH gene rearrangement by regulating the activity of recombination-activating gene endonuclease and influencing chromatin interactions at the Igh locus.
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Affiliation(s)
- Rui Zhang
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Daoqin Wang
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Gui-Xin Ruan
- Medical School, Taizhou University, Taizhou 318000, China
| | - Ruisi Wang
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Yuxing Li
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Wenjing Chen
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Hengjun Huang
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Jing Wang
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Limin Meng
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Zhijian Zhu
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
| | - Dengfeng Lei
- Department of Ophthalmology, Southern University of Science and Technology Hospital, Shenzhen 518055, China
| | - Shengli Xu
- Singapore Immunology Network (SIgN), Agency for Science, Technology and Research (A*STAR), 8A Biomedical Grove, Immunos, Singapore 138648, Republic of Singapore
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, 2 Medical Drive MD9, Singapore 117593, Republic of Singapore
| | - Xijun Ou
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
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2
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Li Y, Ruan GX, Chen W, Huang H, Zhang R, Wang J, Ouyang Y, Zhu Z, Meng L, Wang R, Huo J, Xu S, Ou X. The histone H2B ubiquitination regulator Wac is essential for plasma cell differentiation. FEBS Lett 2023; 597:1748-1760. [PMID: 37171241 DOI: 10.1002/1873-3468.14633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Revised: 04/25/2023] [Accepted: 04/25/2023] [Indexed: 05/13/2023]
Abstract
Naïve B cells become activated and differentiate into antibody-secreting plasma cells (PCs) when encountering antigens. Here, we reveal that the WW domain-containing adapter protein with coiled-coil (Wac), which is important for histone H2B ubiquitination (ubH2B), is essential for PC differentiation. We demonstrate that B cell-specific Wac knockout mice have severely compromised T cell-dependent and -independent antibody responses. PC differentiation is drastically compromised despite undisturbed germinal center B cell response in the mutant mice. We also observe a significant reduction in global ubH2B in Wac-deficient B cells, which is correlated with downregulated expression of some genes critical for cell metabolism. Thus, our findings demonstrate an essential role of Wac-mediated ubH2B in PC differentiation and shed light on the epigenetic mechanisms underlying this process.
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Affiliation(s)
- Yuxing Li
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Gui-Xin Ruan
- Medical School, Taizhou University, Zhejiang, China
| | - Wenjing Chen
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Hengjun Huang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Rui Zhang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Jing Wang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Yu Ouyang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Zhijian Zhu
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Limin Meng
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Ruisi Wang
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
| | - Jianxin Huo
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore City, Singapore
| | - Shengli Xu
- Singapore Immunology Network, Agency for Science, Technology and Research, Singapore City, Singapore
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Xijun Ou
- School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
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3
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Chen W, Li Y, Ruan GX, Huang H, Zhang R, Wang J, Ouyang Y, Li Y, Xu S, Ou X. Adenosine deaminase acting on RNA-1 is essential for early B lymphopoiesis. Cell Rep 2022; 41:111687. [DOI: 10.1016/j.celrep.2022.111687] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 09/07/2022] [Accepted: 10/27/2022] [Indexed: 11/23/2022] Open
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4
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Xu S, Lee KG, Huo J, Kurosaki T, Lam KP. Combined deficiencies in Bruton tyrosine kinase and phospholipase Cgamma2 arrest B-cell development at a pre-BCR+ stage. Blood 2006; 109:3377-84. [PMID: 17164342 DOI: 10.1182/blood-2006-07-036418] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Bruton tyrosine kinase (Btk) and phospholipase Cgamma2 (PLCgamma2) are 2 key molecules involved in B-cell receptor (BCR) signaling. Biochemical studies have placed them in a linear signaling pathway, with Btk acting upstream of PLCgamma2. Consistent with this, mice lacking either molecule display a leaky but similar block in B-cell development. Here, we generated Btk(-/-) PLCgamma2(-/-) mice and showed that combined deficiencies in Btk and PLCgamma2 severely arrested B lymphopoiesis at the large pre-B-cell stage. In contrast to either single mutant, Btk(-/-) PLCgamma2(-/-) pre-B cells expressed high levels of pre-BCR on their cell surfaces and exhibited reduced immunoglobulin light chain gene rearrangements. Pre-BCR-induced calcium signaling was also drastically compromised in Btk(-/-) PLCgamma2(-/-) pre-B cells compared with wild-type and single-mutant cells. Interestingly, immunoglobulin heavy chain allelic exclusion remained intact in the absence of Btk and PLCgamma2. Overall, our results suggest that Btk and PLCgamma2 have combinatorial roles in regulating pre-B cell differentiation.
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Affiliation(s)
- Shengli Xu
- Laboratory of Molecular and Cellular Immunology, Biomedical Sciences Institute, Agency for Science, Technology and Research, 61 Biopolis Drive, Singapore 138673.
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5
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Xu S, Huo J, Chew WK, Hikida M, Kurosaki T, Lam KP. Phospholipase Cγ2 Dosage Is Critical for B Cell Development in the Absence of Adaptor Protein BLNK. THE JOURNAL OF IMMUNOLOGY 2006; 176:4690-8. [PMID: 16585562 DOI: 10.4049/jimmunol.176.8.4690] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
B cell linker (BLNK) protein and phospholipase Cgamma2 (PLCgamma2) are components of the BCR signalosome that activate calcium signaling in B cells. Mice lacking either molecule have a severe but incomplete block in B lymphopoiesis. In this study, we generated BLNK-/- PLCgamma2-/- mice to examine the effect of simultaneous disruption of both molecules on B cell development. We showed that BLNK-/- PLCgamma2-/- mice had compounded defects in B cell maturation compared with either single mutant, suggesting that these two molecules cooperatively or synergistically signaled B lymphopoiesis. However, Ig H chain allelic exclusion was maintained in single and double mutants, indicating that signals propagated by BLNK and PLCgamma2 were not involved in this process. Interestingly, in the absence of BLNK, B cell development was dependent on plcgamma2 gene dosage. This was evidenced by the proportionate decrease in splenic B cell population and increase in bone marrow surface pre-BCR+ cells in PLCgamma2-diploid, -haploid, and -null animals. Intracellular calcium signaling and ERK activation in response to BCR engagement were also proportionately decreased and delayed, respectively, with stepwise reduction of plcgamma2 dosage in a BLNK(null) background. Thus, these data indicate the importance of BLNK not only as a conduit to specifically channel BCR-signaling pathways and as a scaffold for the assembling of macromolecular complex, but also as an efficient aggregator or concentrator of PLCgamma2 molecules to effect optimal signaling for B cell generation and activation.
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Affiliation(s)
- Shengli Xu
- Laboratory of Immunology, Center for Molecular Medicine and Institute of Molecular and Cell Biology, Singapore
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6
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Koretzky GA, Abtahian F, Silverman MA. SLP76 and SLP65: complex regulation of signalling in lymphocytes and beyond. Nat Rev Immunol 2006; 6:67-78. [PMID: 16493428 DOI: 10.1038/nri1750] [Citation(s) in RCA: 205] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
SLP76 and SLP65 are adaptor proteins that lack intrinsic enzymatic activity but contain multiple protein-binding domains. These proteins are essential for signalling downstream of integrins and receptors that contain immunoreceptor tyrosine-based activation motifs. The absence of these adaptor proteins profoundly affects various lineages in the haematopoietic compartment and severely compromises vascular development, highlighting their importance as regulators of signalling cascades. In this Review, we discuss the role of SLP76 and SLP65 in several signalling pathways in haematopoietic cells, with an emphasis on recent studies that provide insight into their mechanisms of action.
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Affiliation(s)
- Gary A Koretzky
- Department of Pathology and Laboratory Medicine, Abramson Family Cancer Research Institute, University of Pennsylvania, 415 BRBII/III, 421 Curie Boulevard, Philadelphia, Pennsylvania 19104, USA.
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7
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Hendriks RW, Kersseboom R. Involvement of SLP-65 and Btk in tumor suppression and malignant transformation of pre-B cells. Semin Immunol 2006; 18:67-76. [PMID: 16300960 DOI: 10.1016/j.smim.2005.10.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Signals from the precursor-B cell receptor (pre-BCR) are essential for selection and clonal expansion of pre-B cells that have performed productive immunoglobulin heavy chain V(D)J recombination. In the mouse, the downstream signaling molecules SLP-65 and Btk cooperate to limit proliferation and induce differentiation of pre-B cells, thereby acting as tumor suppressors to prevent pre-B cell leukemia. In contrast, recent observations in human BCR-ABL1(+) pre-B lymphoblastic leukemia cells demonstrate that Btk is constitutively phosphorylated and activated by the BCR-ABL1 fusion protein. As a result, activated Btk transmits survival signals that are essential for the transforming activity of oncogenic Abl tyrosine kinase.
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Affiliation(s)
- Rudi W Hendriks
- Department of Immunology, Erasmus MC Rotterdam, P.O. Box 1738, NL-3000 DR Rotterdam, The Netherlands.
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8
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Abstract
Progenitor B lymphocytes that successfully assemble a heavy chain gene encoding an immunoglobulin capable of pairing with surrogate light chain proteins trigger their own further differentiation by signaling via the pre-BCR complex. The pre-BCR signals several rounds of proliferation and, in this expanded population, directs a complex, B cell-specific set of epigenetic changes resulting in allelic exclusion of the heavy chain locus and activation of the light chain loci for V(D)J recombination.
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Affiliation(s)
- Jamie K Geier
- UC-Berkeley, Department of Molecular & Cell Biology, Division of Immunology, 439 Life Sciences Addition, Berkeley, CA 94720-3200, USA
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9
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Pike KA, Ratcliffe MJH. Dual Requirement for the Igα Immunoreceptor Tyrosine-Based Activation Motif (ITAM) and a Conserved Non-Igα ITAM Tyrosine in Supporting Igαβ-Mediated B Cell Development. THE JOURNAL OF IMMUNOLOGY 2005; 174:2012-20. [PMID: 15699130 DOI: 10.4049/jimmunol.174.4.2012] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Surface Ig (sIg) expression is a critical checkpoint during avian B cell development. Only cells that express sIg colonize bursal follicles, clonally expand, and undergo Ig diversification by gene conversion. Expression of a heterodimer, in which the extracellular and transmembrane domains of murine CD8alpha or CD8beta are fused to the cytoplasmic domains of chicken Igalpha (chIgalpha) or Igbeta, respectively (murine CD8alpha (mCD8alpha):chIgalpha + mCD8beta:chIgbeta), or an mCD8alpha:chIgalpha homodimer supported bursal B cell development as efficiently as endogenous sIg. In this study we demonstrate that B cell development, in the absence of chIgbeta, requires both the Igalpha ITAM and a conserved non-ITAM Igalpha tyrosine (Y3) that has been associated with binding to B cell linker protein (BLNK). When associated with the cytoplasmic domain of Igbeta, the Igalpha ITAM is not required for the induction of strong calcium mobilization or BLNK phosphorylation, but is still necessary to support B cell development. In contrast, mutation of the Igalpha Y3 severely compromised calcium mobilization when expressed as either a homodimer or a heterodimer with the cytoplasmic domain of Igbeta. However, coexpression of the cytoplasmic domain of Igbeta partially complemented the Igalpha Y3 mutation, rescuing higher levels of BLNK phosphorylation and, more strikingly, supporting B cell development.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Amino Acid Motifs
- Animals
- Antigens, CD/genetics
- Antigens, CD/physiology
- Avian Sarcoma Viruses/genetics
- Avian Sarcoma Viruses/immunology
- B-Lymphocytes/cytology
- B-Lymphocytes/immunology
- B-Lymphocytes/metabolism
- CD79 Antigens
- Calcium Signaling/genetics
- Calcium Signaling/immunology
- Carrier Proteins/metabolism
- Cell Differentiation/immunology
- Cell Line, Tumor
- Cells, Cultured
- Chick Embryo
- Chickens
- Conserved Sequence
- Cytoplasm/immunology
- Cytoplasm/metabolism
- Dimerization
- Mice
- Mutagenesis, Site-Directed
- Phosphoproteins/metabolism
- Phosphorylation
- Protein Structure, Tertiary/genetics
- Receptors, Antigen, B-Cell/genetics
- Receptors, Antigen, B-Cell/physiology
- Recombinant Fusion Proteins/biosynthesis
- Recombinant Fusion Proteins/physiology
- Tyrosine/genetics
- Tyrosine/metabolism
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Affiliation(s)
- Kelly A Pike
- Department of Immunology, University of Toronto, Toronto, Ontario, Canada
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10
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Hayashi K, Nojima T, Goitsuka R, Kitamura D. Impaired receptor editing in the primary B cell repertoire of BASH-deficient mice. THE JOURNAL OF IMMUNOLOGY 2004; 173:5980-8. [PMID: 15528332 DOI: 10.4049/jimmunol.173.10.5980] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The editing of B cell Ag receptor (BCR) through successive rearrangements of Ig genes has been considered to be a major mechanism for the central B cell tolerance, which precludes appearance of self-reactive B cells, through studies using anti-self-Ig transgenic/knock-in mouse systems. However, contribution of the receptor editing in the development of the normal B cell repertoire remains unclear. In addition, the signaling pathway directing this event is unknown. In this study, we demonstrate that receptor editing in anti-DNA Ig knock-in mice is impaired in the absence of an adaptor protein BASH (BLNK/SLP-65) that is involved in BCR signaling. Remarkably, the supposed hallmarks of receptor editing such as Iglambda chain expression, recombination sequence rearrangements at Igkappa loci, and presence of in-frame VkappaJkappa joins in the Igkappa loci inactivated by the recombination sequence rearrangements, were all diminished in BASH-deficient mice with unmanipulated Ig loci. BCR ligation-induced Iglambda gene recombination in vitro was also impaired in BASH-deficient B cells. Furthermore, the BASH-deficient mice showed an excessive Ab response to a DNA carrier immunization, suggesting the presence of unedited DNA-reactive B cells in the periphery. These results not only define a signaling pathway required for receptor editing but indicate that the BCR-signaled receptor editing indeed operates in the development of normal B cell repertoire and contributes to establishing the B cell tolerance.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Animals
- Antibodies, Antinuclear/biosynthesis
- Antibodies, Antinuclear/genetics
- Antibodies, Antinuclear/metabolism
- Autoantigens/immunology
- B-Lymphocyte Subsets/immunology
- B-Lymphocyte Subsets/metabolism
- Carrier Proteins/genetics
- Carrier Proteins/physiology
- Clonal Anergy/genetics
- Gene Rearrangement, B-Lymphocyte, Heavy Chain
- Genetic Markers/immunology
- Immunoglobulin Heavy Chains/biosynthesis
- Immunoglobulin Heavy Chains/genetics
- Immunoglobulin Heavy Chains/metabolism
- Immunoglobulin Variable Region/biosynthesis
- Immunoglobulin Variable Region/genetics
- Immunoglobulin Variable Region/metabolism
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Phosphoproteins/deficiency
- Phosphoproteins/genetics
- Phosphoproteins/physiology
- RNA Editing/genetics
- RNA Editing/immunology
- Receptors, Antigen, B-Cell/genetics
- Signal Transduction/genetics
- Signal Transduction/immunology
- Vaccines, DNA/administration & dosage
- Vaccines, DNA/immunology
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Affiliation(s)
- Katsuhiko Hayashi
- Division of Molecular Biology, Research Institute for Biological Sciences, Tokyo University of Science, Yamazaki 2669, Noda, Chiba 278-0022, Japan
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11
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Wang LD, Clark MR. B-cell antigen-receptor signalling in lymphocyte development. Immunology 2003; 110:411-20. [PMID: 14632637 PMCID: PMC1783068 DOI: 10.1111/j.1365-2567.2003.01756.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2003] [Revised: 09/15/2003] [Accepted: 09/15/2003] [Indexed: 12/11/2022] Open
Abstract
Signalling through the B-cell antigen receptor (BCR) is required throughout B-cell development and peripheral maturation. Targeted disruption of BCR components or downstream effectors indicates that specific signalling mechanisms are preferentially required for central B-cell development, peripheral maturation and repertoire selection. Additionally, the avidity and the context in which antigen is encountered determine both cell fate and differentiation in the periphery. Although the signalling and receptor components required at each stage have been largely elucidated, the molecular mechanisms through which specific signalling are evoked at each stage are still obscure. In particular, it is not known how the pre-BCR initiates the signals required for normal development or how immature B cells regulate the signalling pathways that determine cell fate. In this review, we will summarize the recent studies that have defined the molecules required for B-cell development and maturation as well as the theories on how signals may be regulated at each stage.
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Affiliation(s)
- Leo D Wang
- Section of Rheumatology and Committee on Immunology, Biological Sciences Division and Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, USA.
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12
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Hayashi K, Yamamoto M, Nojima T, Goitsuka R, Kitamura D. Distinct signaling requirements for Dmu selection, IgH allelic exclusion, pre-B cell transition, and tumor suppression in B cell progenitors. Immunity 2003; 18:825-36. [PMID: 12818163 DOI: 10.1016/s1074-7613(03)00142-0] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The pre-B cell receptor triggers expansion and differentiation of pre-B cells (the pre-B cell transition), as well as inhibition of V(H) to DJ(H) recombination (allelic exclusion). The latter also accounts for counter-selection of pro-B cells expressing Dmu protein (Dmu selection). However, the signaling pathways responsible for these events remain poorly defined. Here we show complete arrest of B cell development at the pre-B cell transition in BASH/CD19 double mutant mice, indicating partial redundancy of the two B cell-specific adaptors. Allelic exclusion remained intact in the double mutant mice, whereas Dmu selection was abolished in BASH mutant mice. Thus, distinct signals are required for these events. In addition, both mutant mice succumbed to pre-B cell leukemia, indicating that BASH and CD19 contribute to tumor suppression.
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Affiliation(s)
- Katsuhiko Hayashi
- Division of Molecular Biology, Research Institute for Biological Sciences, Tokyo University of Science, Yamazaki 2669, Noda, 278-0022, Chiba, Japan
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13
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Jordan MS, Singer AL, Koretzky GA. Adaptors as central mediators of signal transduction in immune cells. Nat Immunol 2003; 4:110-6. [PMID: 12555096 DOI: 10.1038/ni0203-110] [Citation(s) in RCA: 208] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Adaptors are molecular scaffolds that recruit effectors, which are critical for immune cell activation. Recent work has underscored the requirement for adaptors in propagating stimulatory signals as well as their ability to inhibit immune cell function. The mechanisms by which adaptors function rely not only on the intermolecular interactions they mediate, but also on where they are localized within the cell. The use of sophisticated genetic, biochemical, cellular and imaging approaches has provided important new insights into the biology of adaptor protein function. Here we focus on T lymphocytes as a model to illustrate the critical roles adaptors play as regulators of cellular activation.
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Affiliation(s)
- Martha S Jordan
- Signal Transduction Program, Abramson Family Cancer Research Institute, University of Pennsylvania, Philadelphia 19104, USA
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14
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Xu S, Lam KP. Delayed cellular maturation and decreased immunoglobulin kappa light chain production in immature B lymphocytes lacking B cell linker protein. J Exp Med 2002; 196:197-206. [PMID: 12119344 PMCID: PMC2193924 DOI: 10.1084/jem.20020172] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
B cell linker (BLNK) protein is a component of the B cell receptor (BCR) signaling pathway and BLNK(-/-) mice have a block in B lymphopoiesis at the pro-B/pre-B cell stage. To study the effect of BLNK mutation at later stages of B cell development, we introduce an innocuous transgenic BCR into BLNK(-/-) mice and show that two populations of immature B cells distinguishable by their IgM(low (lo)) and IgM(high (hi)) phenotypes are found in the bone marrow of these mice in contrast to a single population of IgM(hi) cells found in control BCR-transgenic BLNK(+/+) mice. The mutant IgM(lo) and IgM(hi) cells are at an earlier developmental stage compared with the control IgM(hi) cells as indicated by their differential expression of CD43, B220, and major histocompatibility complex class II antigens and their timing of generation in culture. Thus, in the absence of BLNK the differentiation of immature B cells is delayed. Furthermore, mutant IgM(lo) cells produce equivalent level of immunoglobulin (Ig) mu but less Ig kappa proteins than control and mutant IgM(hi) cells and this defect is attributed to a decrease in the amount of kappa transcripts being generated. Finally, splenic B cells in BCR-transgenic BLNK(-/-) mice are predominantly of the transitional B cell phenotype and are rapidly lost from the peripheral B cell pool. Taken together, the data suggest a role for BLNK and perhaps BCR signaling, in the regulation of kappa light chain expression and continued immature B cell differentiation.
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Affiliation(s)
- Shengli Xu
- Institute of Molecular and Cell Biology, Singapore 117609, Singapore
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15
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Wienands J, Engels N. Multitasking of Ig-alpha and Ig-beta to regulate B cell antigen receptor function. Int Rev Immunol 2002; 20:679-96. [PMID: 11913945 DOI: 10.3109/08830180109045585] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Since their discovery as signaling subunits of the B cell antigen receptor (BCR), Ig-alpha and Ig-beta are discussed to serve either a redundant or distinct function for B cell development, maintenance, and activation. Dependent upon the experimental system that has been used to address this issue, evidence could be provided to support both possibilities. Only recently has it become clear that Ig-alpha and Ig-beta possess a unique signaling identity but that both together are required to orchestrate proper B cell function in vivo. Here we discuss some of the underlying mechanisms that may involve direct coupling to discrete subsets of BCR effector proteins, such as protein tyrosine kinases or the intracellular adaptor SLP-65/BLNK.
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Affiliation(s)
- J Wienands
- Department of Biochemistry and Molecular Immunology, University of Bielefeld, Germany.
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16
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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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17
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Rothstein TL. Cutting edge commentary: two B-1 or not to be one. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 168:4257-61. [PMID: 11970963 DOI: 10.4049/jimmunol.168.9.4257] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
B-1 cells differ from conventional B-2 cells both phenotypically and functionally. Two seemingly mutually exclusive hypotheses have been proposed to explain the origin of B-1 cells. The lineage hypothesis holds that certain B cell precursors are destined early on to become B-1 cells. The differentiation hypothesis holds that every B cell has the same potential to acquire B-1 characteristics. Reconsideration of previous studies of transgenic and knockout mice, plus recent results identifying differences between splenic and peritoneal B-1 cells, point to unexpected complexity in the pathway leading to B-1 status. A new paradigm is suggested, in which surface Ig signaling is required for B-1 cell production, but in which the signaling threshold and context that lead to B-1 cell development and/or expansion differ for particular B cell precursors. Surface Ig signaling may also produce receptor editing, apoptotic deletion, and tolerance induction; how these different outcomes are determined remains uncertain.
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Affiliation(s)
- Thomas L Rothstein
- Department of Medicine, Boston University School of Medicine, MA 02118, USA.
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18
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Fischer GM, Solt LA, Hastings WD, Yang K, Gerstein RM, Nikolajczyk BS, Clarke SH, Rothstein TL. Splenic and peritoneal B-1 cells differ in terms of transcriptional and proliferative features that separate peritoneal B-1 from splenic B-2 cells. Cell Immunol 2001; 213:62-71. [PMID: 11747357 DOI: 10.1006/cimm.2001.1860] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
B-1 cells constitute a distinct B cell subset with characteristic phenotypic and functional features. B-1 cells are highly represented among peritoneal lymphocytes; substantial numbers of B-1 cells are also located within splenic tissue. Here a number of differences in transcription factor and gene expression were identified that separate peritoneal B-1 and splenic B-2 cells, and then splenic B-1 cells obtained from immunoglobulin transgenic mice were tested for these parameters. Splenic B-1 cells resembled splenic B-2 cells rather than peritoneal B-1 cells in terms of nuclear expression of DNA-binding STAT3, CREB, and PU.1, with respect to transcriptional activation of IL-10, and in the failure to enter cell cycle in response to PMA. Splenic B-1 cells (B-1S) appear to constitute a unique population of B-1 cells, which, while sharing with peritoneal B-1 cells (B-1P) certain phenotypic features, differ from them in transcription factor and gene expression and in signaling for cell cycle progression.
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Affiliation(s)
- G M Fischer
- Department of Microbiology, Boston University Medical Center, Boston, Massachusetts 02118, USA
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19
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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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20
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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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