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.

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.

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 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 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 Quantitative proteomics identifies PTP1B as modulator of B cell antigen receptor signaling

2021 ◽  
Vol 4 (11) ◽  
pp. e202101084
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

B 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. Here, we 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 Dock8 regulates BCR signaling and activation of memory B cells via WASP and CD19

2018 ◽  
Vol 2 (4) ◽  
pp. 401-413 ◽  
Author(s):  
Xiaoyu Sun ◽  
Jinzhi Wang ◽  
Tao Qin ◽  
Yongjie Zhang ◽  
Lu Huang ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Spreading ◽  
Memory B Cells ◽  
Key Points ◽  
Bcr Signaling

Key Points Dock8 regulates the expression of CD19 and WASP. BCR clustering and B-cell spreading are decreased in memory B cells of Dock8 patients.

Identification of the SH2 Domain Binding Protein of Bruton’s Tyrosine Kinase as BLNK—Functional Significance of Btk-SH2 Domain in B-Cell Antigen Receptor-Coupled Calcium Signaling

Blood ◽  
1999 ◽  
Vol 94 (7) ◽  
pp. 2357-2364 ◽  
Author(s):  
Shoji Hashimoto ◽  
Akihiro Iwamatsu ◽  
Masamichi Ishiai ◽  
Katsuya Okawa ◽  
Tomoki Yamadori ◽  
...  
Keyword(s):  
B Cells ◽  
Tyrosine Kinase ◽  
Calcium Signaling ◽  
B Cell ◽  
Functional Significance ◽  
Antigen Receptor ◽  
Sh2 Domain ◽  
B Cell Antigen Receptor ◽  
Cell Antigen Receptor ◽  
Cell Antigen

Bruton’s tyrosine kinase (Btk) is a critical component in the B-cell antigen receptor (BCR)-coupled signaling pathway. Its deficiency in B cells leads to loss or marked reduction in the BCR-induced calcium signaling. It is known that this BCR-induced calcium signaling depends on the activation of phospholipase Cγ (PLCγ), which is mediated by Btk and another tyrosine kinase Syk and that the SH2 and pleckstrin homology (PH) domains of Btk play important roles in this activation process. Although the importance of the PH domain of Btk has been explained by its role in the membrane targeting of Btk, the functional significance of the SH2 domain in the calcium signaling has remained merely a matter of speculation. In this report, we identify that one of the major Btk-SH2 domain-binding proteins in B cells is BLNK (B-cell linker protein) and present evidences that the interaction of BLNK and the SH2 domain of Btk contributes to the complete tyrosine phosphorylation of PLCγ.

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