scholarly journals The Actin-Disassembly Protein Glia Maturation Factor γ Enhances Actin Remodeling and B Cell Antigen Receptor Signaling at the Immune Synapse

2021 ◽  
Vol 9 ◽  
Author(s):  
Nikola Deretic ◽  
Madison Bolger-Munro ◽  
Kate Choi ◽  
Libin Abraham ◽  
Michael R. Gold
Keyword(s):  
B Cells ◽  
B Cell ◽  
B Cell Antigen Receptor ◽  
Retrograde Flow ◽  
Glia Maturation Factor ◽  
Actin Remodeling ◽  
Immune Synapse ◽  
Actin Networks ◽  
Maturation Factor ◽  
Bcr Signaling

Signaling by the B cell antigen receptor (BCR) initiates actin remodeling. The assembly of branched actin networks that are nucleated by the Arp2/3 complex exert outward force on the plasma membrane, allowing B cells to form membrane protrusions that can scan the surface of antigen-presenting cells (APCs). The resulting Arp2/3 complex-dependent actin retrograde flow promotes the centripetal movement and progressive coalescence of BCR microclusters, which amplifies BCR signaling. Glia maturation factor γ (GMFγ) is an actin disassembly-protein that releases Arp2/3 complex-nucleated actin filaments from actin networks. By doing so, GMFγ could either oppose the actions of the Arp2/3 complex or support Arp2/3 complex-nucleated actin polymerization by contributing to the recycling of actin monomers and Arp2/3 complexes. We now show that reducing the levels of GMFγ in human B cell lines via transfection with a specific siRNA impairs the ability of B cells to spread on antigen-coated surfaces, decreases the velocity of actin retrograde flow, diminishes the coalescence of BCR microclusters into a central cluster at the B cell-APC contact site, and decreases APC-induced BCR signaling. These effects of depleting GMFγ are similar to what occurs when the Arp2/3 complex is inhibited. This suggests that GMFγ cooperates with the Arp2/3 complex to support BCR-induced actin remodeling and amplify BCR signaling at the immune synapse.

scholarly journals The Wdr1-LIMK-Cofilin Axis Controls B Cell Antigen Receptor-Induced Actin Remodeling and Signaling at the Immune Synapse

2021 ◽  
Vol 9 ◽  
Author(s):  
Madison Bolger-Munro ◽  
Kate Choi ◽  
Faith Cheung ◽  
Yi Tian Liu ◽  
May Dang-Lawson ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Cell Spreading ◽  
B Cell Antigen Receptor ◽  
Actin Remodeling ◽  
Immune Synapse ◽  
Cell Antigen ◽  
Bcr Signaling

When B cells encounter membrane-bound antigens, the formation and coalescence of B cell antigen receptor (BCR) microclusters amplifies BCR signaling. The ability of B cells to probe the surface of antigen-presenting cells (APCs) and respond to APC-bound antigens requires remodeling of the actin cytoskeleton. Initial BCR signaling stimulates actin-related protein (Arp) 2/3 complex-dependent actin polymerization, which drives B cell spreading as well as the centripetal movement and coalescence of BCR microclusters at the B cell-APC synapse. Sustained actin polymerization depends on concomitant actin filament depolymerization, which enables the recycling of actin monomers and Arp2/3 complexes. Cofilin-mediated severing of actin filaments is a rate-limiting step in the morphological changes that occur during immune synapse formation. Hence, regulators of cofilin activity such as WD repeat-containing protein 1 (Wdr1), LIM domain kinase (LIMK), and coactosin-like 1 (Cotl1) may also be essential for actin-dependent processes in B cells. Wdr1 enhances cofilin-mediated actin disassembly. Conversely, Cotl1 competes with cofilin for binding to actin and LIMK phosphorylates cofilin and prevents it from binding to actin filaments. We now show that Wdr1 and LIMK have distinct roles in BCR-induced assembly of the peripheral actin structures that drive B cell spreading, and that cofilin, Wdr1, and LIMK all contribute to the actin-dependent amplification of BCR signaling at the immune synapse. Depleting Cotl1 had no effect on these processes. Thus, the Wdr1-LIMK-cofilin axis is critical for BCR-induced actin remodeling and for B cell responses to APC-bound antigens.

CD22 Cross-Linking Generates B-Cell Antigen Receptor-Independent Signals That Activate the JNK/SAPK Signaling Cascade

Blood ◽  
1999 ◽  
Vol 94 (4) ◽  
pp. 1382-1392 ◽  
Author(s):  
Joseph M. Tuscano ◽  
Agostino Riva ◽  
Salvador N. Toscano ◽  
Thomas F. Tedder ◽  
John H. Kehrl
Keyword(s):  
Cell Proliferation ◽  
B Cells ◽  
B Cell ◽  
Cell Lines ◽  
Burkitt Lymphoma ◽  
B Cell Antigen Receptor ◽  
Erk Activation ◽  
Cell Antigen ◽  
Bcr Signaling ◽  
Burkitt Lymphoma Cell

Abstract CD22 is a B-cell–specific adhesion molecule that modulates BCR-mediated signal transduction. Ligation of human CD22 with monoclonal antibodies (MoAbs) that block the ligand binding site triggers rapid tyrosine phosphorylation of CD22 and primary B-cell proliferation. Because extracellular signal-regulated kinases (ERKs) couple upstream signaling pathways to gene activation and are activated by B-cell antigen receptor (BCR) signaling, we examined whether CD22 ligation also activated ERKs and/or modified BCR-induced ERK activation. Ligation of CD22 on either primary B cells or B-cell lines failed to significantly activate the mitogen activated protein kinase (MAPK) ERK-2, but did activate the stress-activated protein kinases (SAPKs; c-jun NH2-terminal kinases or JNKs). In contrast, BCR ligation resulted in ERK-2 activation without significant SAPK activation. Concurrent ligation of CD22 and BCR enhanced BCR-mediated ERK-2 activation without appreciably modulating CD22-induced SAPK activation. Consistent with its induction of SAPK activity, there was a marked increase in nuclear extracts of activator protein-1 (AP-1) and c-jun levels within 2 hours of exposure of primary B cells to the CD22 MoAb. Despite their differences in ERK activation, both CD22 and BCR ligation triggered several Burkitt lymphoma cell lines to undergo apoptosis, and the 2 stimuli together induced greater cell death than either signal alone. The pro-apoptotic effects were CD22-blocking MoAb-specific and dose-dependent. Examination of expression levels of Bcl-2 protoncogene family members (Bcl-2, Bcl-xL, Mcl-1, and Bax) showed a downregulation of Bcl-xL and Mcl-1 after CD22 ligation. This study provides a plausible mechanism to explain how CD22 and BCR signaling can costimulate B-cell proliferation and induce apoptosis in Burkitt lymphoma cell lines.

CD22 Cross-Linking Generates B-Cell Antigen Receptor-Independent Signals That Activate the JNK/SAPK Signaling Cascade

Blood ◽  
1999 ◽  
Vol 94 (4) ◽  
pp. 1382-1392
Author(s):  
Joseph M. Tuscano ◽  
Agostino Riva ◽  
Salvador N. Toscano ◽  
Thomas F. Tedder ◽  
John H. Kehrl
Keyword(s):  
Cell Proliferation ◽  
B Cells ◽  
B Cell ◽  
Cell Lines ◽  
Burkitt Lymphoma ◽  
B Cell Antigen Receptor ◽  
Erk Activation ◽  
Cell Antigen ◽  
Bcr Signaling ◽  
Burkitt Lymphoma Cell

CD22 is a B-cell–specific adhesion molecule that modulates BCR-mediated signal transduction. Ligation of human CD22 with monoclonal antibodies (MoAbs) that block the ligand binding site triggers rapid tyrosine phosphorylation of CD22 and primary B-cell proliferation. Because extracellular signal-regulated kinases (ERKs) couple upstream signaling pathways to gene activation and are activated by B-cell antigen receptor (BCR) signaling, we examined whether CD22 ligation also activated ERKs and/or modified BCR-induced ERK activation. Ligation of CD22 on either primary B cells or B-cell lines failed to significantly activate the mitogen activated protein kinase (MAPK) ERK-2, but did activate the stress-activated protein kinases (SAPKs; c-jun NH2-terminal kinases or JNKs). In contrast, BCR ligation resulted in ERK-2 activation without significant SAPK activation. Concurrent ligation of CD22 and BCR enhanced BCR-mediated ERK-2 activation without appreciably modulating CD22-induced SAPK activation. Consistent with its induction of SAPK activity, there was a marked increase in nuclear extracts of activator protein-1 (AP-1) and c-jun levels within 2 hours of exposure of primary B cells to the CD22 MoAb. Despite their differences in ERK activation, both CD22 and BCR ligation triggered several Burkitt lymphoma cell lines to undergo apoptosis, and the 2 stimuli together induced greater cell death than either signal alone. The pro-apoptotic effects were CD22-blocking MoAb-specific and dose-dependent. Examination of expression levels of Bcl-2 protoncogene family members (Bcl-2, Bcl-xL, Mcl-1, and Bax) showed a downregulation of Bcl-xL and Mcl-1 after CD22 ligation. This study provides a plausible mechanism to explain how CD22 and BCR signaling can costimulate B-cell proliferation and induce apoptosis in Burkitt lymphoma cell lines.

scholarly journals FcRL4 acts as an adaptive to innate molecular switch dampening BCR signaling and enhancing TLR signaling

Blood ◽  
2011 ◽  
Vol 118 (24) ◽  
pp. 6332-6341 ◽  
Author(s):  
Hae Won Sohn ◽  
Peter D. Krueger ◽  
Randall S. Davis ◽  
Susan K. Pierce
Keyword(s):  
B Cells ◽  
B Cell ◽  
Synapse Formation ◽  
Molecular Switch ◽  
Lymphoid Tissues ◽  
Immune Synapse ◽  
Chronic Antigenic Stimulation ◽  
Bcr Signaling ◽  
Cd69 Expression ◽  
Human B Cell

Abstract Fc receptor–like 4 (FcRL4) is expressed on the surface of a subset of memory B cells (MBCs) located at sites of invading pathogens in mucosal lymphoid tissues in healthy individuals. Recently, FcRL4+ MBCs were shown to be greatly increased in number in the peripheral blood of HIV-infected viremic individuals, in whom they are associated with B-cell exhaustion, and in individuals chronically reinfected with malaria. In the present study, we provide evidence that the expression of FcRL4 in human B-cell lines disrupts immune synapse formation and blocks antigen-induced BCR signaling at the point of Syk phosphorylation, blocking downstream activation of PLC-γ2 and Vav and the induction of calcium responses and CD69 expression. FcRL4 functions by ligation-independent mechanisms that require the 3 tyrosine residues in its cytoplasmic domain and involves its phosphorylation and association with the tyrosine phosphatases SHP-1 and SHP-2. Remarkably, FcRL4 is concentrated in endosomes after treatment with the TLR9 agonist CpG and enhances signaling through TLR9, as measured by increased expression of CD23. These findings suggest that FcRL4 may act as a molecular switch in B cells to dampen adaptive immune signaling and enhance innate signaling in response to chronic antigenic stimulation.

scholarly journals Arp2/3 complex-driven spatial patterning of the BCR enhances immune synapse formation, BCR signaling and B cell activation

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Madison Bolger-Munro ◽  
Kate Choi ◽  
Joshua M Scurll ◽  
Libin Abraham ◽  
Rhys S Chappell ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Synapse Formation ◽  
Critical Role ◽  
Transcriptional Responses ◽  
Immune Synapse ◽  
Cell Responses ◽  
Bcr Signaling ◽  
B Cell Responses

When B cells encounter antigens on the surface of an antigen-presenting cell (APC), B cell receptors (BCRs) are gathered into microclusters that recruit signaling enzymes. These microclusters then move centripetally and coalesce into the central supramolecular activation cluster of an immune synapse. The mechanisms controlling BCR organization during immune synapse formation, and how this impacts BCR signaling, are not fully understood. We show that this coalescence of BCR microclusters depends on the actin-related protein 2/3 (Arp2/3) complex, which nucleates branched actin networks. Moreover, in murine B cells, this dynamic spatial reorganization of BCR microclusters amplifies proximal BCR signaling reactions and enhances the ability of membrane-associated antigens to induce transcriptional responses and proliferation. Our finding that Arp2/3 complex activity is important for B cell responses to spatially restricted membrane-bound antigens, but not for soluble antigens, highlights a critical role for Arp2/3 complex-dependent actin remodeling in B cell responses to APC-bound antigens.

scholarly journals An extracatalytic function of CD45 in B cells is mediated by CD22

2015 ◽  
Vol 112 (47) ◽  
pp. E6515-E6524 ◽  
Author(s):  
Sarah Coughlin ◽  
Mark Noviski ◽  
James L. Mueller ◽  
Ammarina Chuwonpad ◽  
William C. Raschke ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Tyrosine Phosphatase ◽  
Antigen Receptor ◽  
Src Family Kinases ◽  
B Cell Antigen Receptor ◽  
T Cell Signaling ◽  
Antigen Receptor Signaling ◽  
Bcr Signaling ◽  
Alternatively Spliced

The receptor-like tyrosine phosphatase CD45 regulates antigen receptor signaling by dephosphorylating the C-terminal inhibitory tyrosine of the src family kinases. However, despite its abundance, the function of the large, alternatively spliced extracellular domain of CD45 has remained elusive. We used normally spliced CD45 transgenes either incorporating a phosphatase-inactivating point mutation or lacking the cytoplasmic domain to uncouple the enzymatic and noncatalytic functions of CD45 in lymphocytes. Although these transgenes did not alter T-cell signaling or development irrespective of endogenous CD45 expression, both partially rescued the phenotype of CD45-deficient B cells. We identify a noncatalytic role for CD45 in regulating tonic, but not antigen-mediated, B-cell antigen receptor (BCR) signaling through modulation of the function of the inhibitory coreceptor CD22. This finding has important implications for understanding how naïve B cells maintain tonic BCR signaling while restraining inappropriate antigen-dependent activation to preserve clonal “ignorance.”

scholarly journals Cbl-b Negatively Regulates B Cell Antigen Receptor Signaling in Mature B Cells through Ubiquitination of the Tyrosine Kinase Syk

2003 ◽  
Vol 197 (11) ◽  
pp. 1511-1524 ◽  
Author(s):  
Hae Won Sohn ◽  
Hua Gu ◽  
Susan K. Pierce
Keyword(s):  
B Cells ◽  
Tyrosine Kinase ◽  
B Cell ◽  
Antigen Receptor ◽  
Cellular Systems ◽  
Cross Linking ◽  
B Cell Antigen Receptor ◽  
Cell Antigen Receptor ◽  
Cell Antigen ◽  
Bcr Signaling

Members of the Cbl family of molecular adaptors play key roles in regulating tyrosine kinase-dependent signaling in a variety of cellular systems. Here we provide evidence that in B cells Cbl-b functions as a negative regulator of B cell antigen receptor (BCR) signaling during the normal course of a response. In B cells from Cbl-b–deficient mice cross-linking the BCRs resulted in sustained phosphorylation of Igα, Syk, and phospholipase C (PLC)-γ2, leading to prolonged Ca2+ mobilization, and increases in extracellular signal–regulated kinase (ERK) and c-Jun NH2-terminal protein kinase (JNK) phosphorylation and surface expression of the activation marker, CD69. Image analysis following BCR cross-linking showed sustained polarization of the BCRs into large signaling-active caps associated with phosphorylated Syk in Cbl-b–deficient B cells in contrast to the BCRs in Cbl-b–expressing B cells that rapidly proceeded to form small, condensed, signaling inactive caps. Significantly, prolonged phosphorylation of Syk correlated with reduced ubiquitination of Syk indicating that Cbl-b negatively regulates BCR signaling by targeting Syk for ubiquitination.

scholarly journals Functional analysis of Csk in signal transduction through the B-cell antigen receptor

1994 ◽  
Vol 14 (11) ◽  
pp. 7306-7313
Author(s):  
A Hata ◽  
H Sabe ◽  
T Kurosaki ◽  
M Takata ◽  
H Hanafusa
Keyword(s):  
Signal Transduction ◽  
B Cells ◽  
B Cell ◽  
Tyrosine Phosphorylation ◽  
Kinase Activity ◽  
B Cell Antigen Receptor ◽  
Wild Type ◽  
Inactive State ◽  
Cell Clones ◽  
Bcr Signaling

In B cells, two classes of protein tyrosine kinases (PTKs), the Src family of PTKs (Lyn, Fyn, Lck, and Blk) and non-Src family of PTKs (Syk), are known to be involved in signal transduction induced by the stimulation of the B-cell antigen receptor (BCR). Previous studies using Lyn-negative chicken B-cell clones revealed that Lyn is necessary for transduction of signals through the BCR. The kinase activity of the Src family of PTKs is negatively regulated by phosphorylation at the C-terminal tyrosine residue, and the PTK Csk has been demonstrated to phosphorylate this C-terminal residue of the Src family of PTKs. To investigate the role of Csk in BCR signaling, Csk-negative chicken B-cell clones were generated. In these Csk-negative cells, Lyn became constitutively active and highly phosphorylated at the autophosphorylation site, indicating that Csk is necessary to sustain Lyn in an inactive state. Since the C-terminal tyrosine phosphorylation of Lyn is barely detectable in the unstimulated, wild-type B cells, our data suggest that the activities of Csk and a certain protein tyrosine phosphatase(s) are balanced to maintain Lyn at a hypophosphorylated and inactive state. Moreover, we show that the kinase activity of Syk was also constitutively activated in Csk-negative cells. The degree of activation of both the Lyn and Syk kinases in Csk-negative cells was comparable to that observed in wild-type cells after BCR stimulation. However, BCR stimulation was still necessary in Csk-negative cells to elicit tyrosine phosphorylation of cellular proteins, as well as calcium mobilization and inositol 1,4,5-trisphosphate generation. These results suggest that not only activation of the Lyn and Syk kinases but also additional signals induced by the cross-linking of the BCR are required for full transduction of BCR signaling.

scholarly journals Quantitative Proteomics Identifies PTP1B as Modulator of B Cell Antigen Receptor Signaling

2021 ◽  
Author(s):  
Jennifer J. Schwarz ◽  
Lorenz Grundmann ◽  
Thomas Kokot ◽  
Kathrin Kläsener ◽  
Sandra Fotteler ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Protein Tyrosine Phosphatase ◽  
Tyrosine Phosphatase ◽  
Antigen Receptor ◽  
B Cell Antigen Receptor ◽  
Cell Antigen Receptor ◽  
Cell Antigen ◽  
Bcr Signaling ◽  
Signaling Components

ABSTRACTB cell antigen receptor (BCR) signaling is initiated by protein kinases and limited by counteracting phosphatases that currently are less well studied in their regulation of BCR signaling. We here used the B cell line Ramos to identify and quantify human B cell signaling components. Specifically, a protein tyrosine phosphatase profiling revealed a high expression of the protein tyrosine phosphatase 1B (PTP1B) in Ramos and human naïve B cells. The loss of PTP1B leads to increased B cell activation. Through substrate trapping in combination with quantitative mass spectrometry, we identified 22 putative substrates or interactors of PTP1B. We validated Igα, CD22, PLCγ1/2, CBL, BCAP and APLP2 as specific substrates of PTP1B in Ramos B cells. The tyrosine kinase BTK and the two adaptor proteins GRB2 and VAV1 were identified as direct binding partners and potential substrates of PTP1B. We showed that PTP1B dephosphorylates the inhibitory receptor protein CD22 at phosphotyrosine 807. We conclude that PTP1B negatively modulates BCR signaling by dephosphorylating distinct phosphotyrosines in B cell specific receptor proteins and various downstream signaling components.

scholarly journals Lin28b promotes fetal B lymphopoiesis through the transcription factor Arid3a

2015 ◽  
Vol 212 (4) ◽  
pp. 569-580 ◽  
Author(s):  
Yan Zhou ◽  
Yue-Sheng Li ◽  
Srinivasa Rao Bandi ◽  
Lingjuan Tang ◽  
Susan A. Shinton ◽  
...  
Keyword(s):  
Transcription Factor ◽  
B Cells ◽  
B Cell ◽  
Fetal Liver ◽  
Ectopic Expression ◽  
B Cell Antigen Receptor ◽  
B Lymphopoiesis ◽  
Bcr Signaling ◽  
B Cell Precursors ◽  
Adult Bone

Mouse B cell precursors from fetal liver and adult bone marrow (BM) generate distinctive B cell progeny when transplanted into immunodeficient recipients, supporting a two-pathway model for B lymphopoiesis, fetal “B-1” and adult “B-2.” Recently, Lin28b was shown to be important for the switch between fetal and adult pathways; however, neither the mechanism of Lin28b action nor the importance of B cell antigen receptor (BCR) signaling in this process was addressed. Here, we report key advances in our understanding of the regulation of B-1/B-2 development. First, modulation of Let-7 in fetal pro-B cells is sufficient to alter fetal B-1 development to produce B cells resembling the progeny of adult B-2 development. Second, intact BCR signaling is required for the generation of B1a B cells from Lin28b-transduced BM progenitors, supporting a requirement for ligand-dependent selection, as is the case for normal B1a B cells. Third, the VH repertoire of Lin28b-induced BM B1a B cells differs from that of normal B1a, suggesting persisting differences from fetal progenitors. Finally, we identify the Arid3a transcription factor as a key target of Let-7, whose ectopic expression is sufficient to induce B-1 development in adult pro-B cells and whose silencing by knockdown blocks B-1 development in fetal pro-B cells.

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