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

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.

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

10.1101/490698 ◽

2018 ◽

Author(s):

Madison Bolger-Munro ◽

Kate Choi ◽

Joshua Scurll ◽

Libin Abraham ◽

Rhys Chappell ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Cell Activation ◽

Synapse Formation ◽

Critical Role ◽

Transcriptional Responses ◽

Immune Synapse ◽

Cell Responses ◽

Bcr Signaling ◽

B Cell Responses

AbstractWhen 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 remodelling in B cell responses to APC-bound antigens.

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CXCL13/CXCR5 signaling enhances BCR-triggered B-cell activation by shaping cell dynamics

Blood ◽

10.1182/blood-2011-01-332106 ◽

2011 ◽

Vol 118 (6) ◽

pp. 1560-1569 ◽

Cited By ~ 61

Author(s):

Julia Sáez de Guinoa ◽

Laura Barrio ◽

Mario Mellado ◽

Yolanda R. Carrasco

Keyword(s):

B Cells ◽

B Cell ◽

Cell Activation ◽

Synapse Formation ◽

Behavior Pattern ◽

Lymphocyte Function ◽

B Cell Activation ◽

Cell Dynamics ◽

Membrane Ruffling ◽

Bcr Signaling

Abstract Continuous migration of B cells at the follicle contrasts with their stable arrest after encounter with antigen. Two main ligand/receptor pairs are involved in these cell behaviors: the chemokine CXCL13/chemokine receptor CXCR5 and antigen/BCR. Little is known regarding the interplay between CXCR5 and BCR signaling in the modulation of B-cell dynamics and its effect on B-cell activation. We used a 2-dimensional model to study B-cell migration and antigen recognition in real time, and found that BCR signaling strength alters CXCL13-mediated migration, leading to a heterogeneous B-cell behavior pattern. In addition, we demonstrate that CXCL13/CXCR5 signaling does not impair BCR-triggered immune synapse formation and that CXCR5 is excluded from the central antigen cluster. CXCL13/CXCR5 signaling enhances BCR-mediated B-cell activation in at least 2 ways: (1) it assists antigen gathering at the synapse by promoting membrane ruffling and lymphocyte function–associated antigen 1 (LFA-1)–supported adhesion, and (2) it allows BCR signaling integration in motile B cells through establishment of LFA-1–supported migratory junctions. Both processes require functional actin cytoskeleton and non-muscle myosin II motor protein. Therefore, the CXCL13/CXCR5 signaling effect on shaping B-cell dynamics is an effective mechanism that enhances antigen encounter and BCR-triggered B-cell activation.

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A B cell actomyosin arc network couples integrin co-stimulation to mechanical force-dependent immune synapse formation

10.1101/2021.08.12.456133 ◽

2021 ◽

Author(s):

Jia C Wang ◽

Yang-In Yim ◽

Xufeng Wu ◽

Valentin Jaumouillé ◽

Clare M Waterman ◽

...

Keyword(s):

B Cell ◽

Cell Activation ◽

Synapse Formation ◽

Super Resolution ◽

Cell Receptor ◽

B Cell Activation ◽

Protein Distribution ◽

Immune Synapse ◽

Resolution Imaging ◽

Membrane Bound

B-cell activation and immune synapse (IS) formation with membrane-bound antigens are actin-dependent processes that scale positively with the strength of antigen-induced signals. Importantly, ligating the B-cell integrin, LFA-1, with ICAM-1 promotes IS formation when antigen is limiting. Whether the actin cytoskeleton plays a specific role in integrin-dependent IS formation is unknown. Here we show using super-resolution imaging of primary B cells that LFA-1: ICAM-1 interactions promote the formation of an actomyosin network that dominates the B-cell IS. This network is created by the formin mDia1, organized into concentric, contractile arcs by myosin 2A, and flows inward at the same rate as B-cell receptor (BCR): antigen clusters. Consistently, individual BCR microclusters are swept inward by individual actomyosin arcs. Under conditions where integrin is required for synapse formation, inhibiting myosin impairs synapse formation, as evidenced by reduced antigen centralization, diminished BCR signaling, and defective signaling protein distribution at the synapse. Together, these results argue that a contractile actomyosin arc network plays a key role in the mechanism by which LFA-1 co-stimulation promotes B-cell activation and IS formation.

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

Blood ◽

10.1182/blood-2011-05-353102 ◽

2011 ◽

Vol 118 (24) ◽

pp. 6332-6341 ◽

Cited By ~ 64

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.

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Acute Csk inhibition hinders B cell activation by constraining the PI3 kinase pathway

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2108957118 ◽

2021 ◽

Vol 118 (43) ◽

pp. e2108957118

Author(s):

Wen Lu ◽

Katarzyna M. Skrzypczynska ◽

Arthur Weiss

Keyword(s):

T Cells ◽

B Cells ◽

B Cell ◽

Cell Activation ◽

Antigen Receptor ◽

Negative Regulator ◽

B Cell Activation ◽

Cell Antigen Receptor ◽

Cell Antigen ◽

Bcr Signaling

T cell antigen receptor (TCR) and B cell antigen receptor (BCR) signaling are initiated and tightly regulated by Src-family kinases (SFKs). SFKs positively regulate TCR signaling in naïve T cells but have both positive and negative regulatory roles in BCR signaling in naïve B cells. The proper regulation of their activities depends on the opposing actions of receptor tyrosine phosphatases CD45 and CD148 and the cytoplasmic tyrosine kinase C-terminal Src kinase Csk. Csk is a major negative regulator of SFKs. Using a PP1-analog-sensitive Csk (CskAS) system, we have previously shown that inhibition of CskAS increases SFK activity, leading to augmentation of responses to weak TCR stimuli in T cells. However, the effects of Csk inhibition in B cells were not known. In this study, we surprisingly found that inhibition of CskAS led to marked inhibition of BCR-stimulated cytoplasmic free calcium increase and Erk activation despite increased SFK activation in B cells, contrasting the effects observed in T cells. Further investigation revealed that acute CskAS inhibition suppressed BCR-mediated phosphatidylinositol 3,4,5-trisphosphate (PIP3) production in B cells. Restoring PIP3 levels in B cells by CD19 cross-linking or SHIP1 deficiency eliminated the negative regulatory effect of CskAS inhibition. This reveals the critical role of Csk in maintaining an appropriate level of SFK activity and regulating PIP3 amounts as a means of compensating for SFK fluctuations to prevent inappropriate B cell activation. This regulatory mechanism controlling PIP3 amounts may also contribute to B cell anergy and self-tolerance.

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Ca2+Signaling in B Cells

The Scientific World JOURNAL ◽

10.1100/tsw.2010.219 ◽

2010 ◽

Vol 10 ◽

pp. 2254-2264 ◽

Cited By ~ 2

Author(s):

Taras Lyubchenko

Keyword(s):

B Cells ◽

B Cell ◽

Cell Activation ◽

Molecular Mechanisms ◽

B Cell Activation ◽

B Cell Tolerance ◽

Immune Synapse ◽

Intracellular Ca ◽

Dependent Protein

An increase in intracellular Ca2+concentration is one of the major initial steps in B-cell activation that occurs within minutes after antigen receptor (BCR) engagement. In recent years, significant advances have been made in characterizing molecular mechanisms of Ca2+signaling in lymphocytes, although the majority of work was done on T cells. This mini-review discusses several underexplored areas of Ca2+signaling in B cells: (1) Ca2+signaling in immune synapse and multifaceted Ca2+responses within a single cell, (2) source of Ca2+involved in Ca2+-dependent protein phosphorylation events and the role of store-operated influx, (3) role of BCR coreceptors in Ca2+signaling, and (4) Ca2+signaling and maintenance of B-cell tolerance and clinical significance of Ca2+signaling alterations.

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