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

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.

scholarly journals TLR4 signals in B lymphocytes are transduced via the B cell antigen receptor and SYK

2017 ◽  
Vol 214 (5) ◽  
pp. 1269-1280 ◽  
Author(s):  
Edina Schweighoffer ◽  
Josquin Nys ◽  
Lesley Vanes ◽  
Nicholas Smithers ◽  
Victor L.J. Tybulewicz
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Antigen Receptor ◽  
B Cell Antigen Receptor ◽  
B Cell Activation ◽  
Cell Antigen Receptor ◽  
Cell Antigen ◽  
B Cell Survival ◽  
Microbial Products

Toll-like receptors (TLRs) play an important role in immune responses to pathogens by transducing signals in innate immune cells in response to microbial products. TLRs are also expressed on B cells, and TLR signaling in B cells contributes to antibody-mediated immunity and autoimmunity. The SYK tyrosine kinase is essential for signaling from the B cell antigen receptor (BCR), and thus for antibody responses. Surprisingly, we find that it is also required for B cell survival, proliferation, and cytokine secretion in response to signaling through several TLRs. We show that treatment of B cells with lipopolysaccharide, the ligand for TLR4, results in SYK activation and that this is dependent on the BCR. Furthermore, we show that B cells lacking the BCR are also defective in TLR-induced B cell activation. Our results demonstrate that TLR4 signals through two distinct pathways, one via the BCR leading to activation of SYK, ERK, and AKT and the other through MYD88 leading to activation of NF-κB.

scholarly journals Kidins220/ARMS binds to the B cell antigen receptor and regulates B cell development and activation

2015 ◽  
Vol 212 (10) ◽  
pp. 1693-1708 ◽  
Author(s):  
Gina J. Fiala ◽  
Iga Janowska ◽  
Fabiola Prutek ◽  
Elias Hobeika ◽  
Annyesha Satapathy ◽  
...  
Keyword(s):  
B Cell ◽  
Cell Activation ◽  
Antigen Receptor ◽  
Cell Development ◽  
B Cell Development ◽  
B Cell Antigen Receptor ◽  
Independent Manner ◽  
Cell Antigen Receptor ◽  
Cell Antigen ◽  
Bcr Signaling

B cell antigen receptor (BCR) signaling is critical for B cell development and activation. Using mass spectrometry, we identified a protein kinase D–interacting substrate of 220 kD (Kidins220)/ankyrin repeat–rich membrane-spanning protein (ARMS) as a novel interaction partner of resting and stimulated BCR. Upon BCR stimulation, the interaction increases in a Src kinase–independent manner. By knocking down Kidins220 in a B cell line and generating a conditional B cell–specific Kidins220 knockout (B-KO) mouse strain, we show that Kidins220 couples the BCR to PLCγ2, Ca2+, and extracellular signal-regulated kinase (Erk) signaling. Consequently, BCR-mediated B cell activation was reduced in vitro and in vivo upon Kidins220 deletion. Furthermore, B cell development was impaired at stages where pre-BCR or BCR signaling is required. Most strikingly, λ light chain–positive B cells were reduced sixfold in the B-KO mice, genetically placing Kidins220 in the PLCγ2 pathway. Thus, our data indicate that Kidins220 positively regulates pre-BCR and BCR functioning.

Synthetic biology of B cell activation: understanding signal amplification at the B cell antigen receptor using a rebuilding approach

2019 ◽  
Vol 400 (4) ◽  
pp. 555-563 ◽  
Author(s):  
Yogesh Kulathu ◽  
Christa Zuern ◽  
Jianying Yang ◽  
Michael Reth
Keyword(s):  
Synthetic Biology ◽  
B Cell ◽  
Signal Amplification ◽  
Cell Activation ◽  
Antigen Receptor ◽  
B Cell Antigen Receptor ◽  
B Cell Activation ◽  
Cell Antigen Receptor ◽  
Cell Antigen ◽  
Downstream Signaling

Abstract Upon activation of the B cell antigen receptor (BCR), the spleen tyrosine kinase (Syk) and the Src family kinase Lyn phosphorylate tyrosines of the immunoreceptor tyrosine-based activation motif (ITAM) of Igα and Igβ which further serve as binding sites for the SH2 domains of these kinases. Using a synthetic biology approach, we dissect the roles of different ITAM residues of Igα in Syk activation. We found that a leucine to glycine mutation at the Y+3 position after the first ITAM tyrosine prevents Syk binding and activation. However, a pre-activated Syk can still phosphorylate this tyrosine in trans. Our data show that the formation of a Syk/ITAM initiation complex and trans-ITAM phosphorylation is crucial for BCR signal amplification. In contrast, the interaction of Lyn with the first ITAM tyrosine is not altered by the leucine to glycine mutation. In addition, our study suggests that an ITAM-bound Syk phosphorylates the non-ITAM tyrosine Y204 of Igα only in cis. Collectively, our reconstitution experiments suggest a model whereby first trans-phosphorylation amplifies the BCR signal and subsequently cis-phosphorylation couples the receptor to downstream signaling elements.

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 A Double-Edged Kinase Lyn: A Positive and Negative Regulator for Antigen Receptor–mediated Signals

1998 ◽  
Vol 187 (8) ◽  
pp. 1343-1348 ◽  
Author(s):  
Hirofumi Nishizumi ◽  
Keisuke Horikawa ◽  
Irena Mlinaric-Rascan ◽  
Tadashi Yamamoto
Keyword(s):  
B Cells ◽  
B Cell ◽  
Tyrosine Phosphorylation ◽  
Cell Activation ◽  
Tyrosine Phosphatase ◽  
Antigen Receptor ◽  
Negative Regulator ◽  
B Cell Activation ◽  
Inositol Phosphatase ◽  
Feedback Suppression

B cells from young lyn−/− mice are hyperresponsive to anti-IgM–induced proliferation, suggesting involvement of Lyn in negative regulation of B cell antigen receptor (BCR)-mediated signaling. Here we show that tyrosine phosphorylation of FcγRIIB and CD22 coreceptors, which are important for feedback suppression of BCR-induced signaling, was severely impaired in lyn−/− B cells upon their coligation with the BCR. Hypophosphorylation on tyrosine residues of these molecules resulted in failure of recruiting the tyrosine phosphatase SHP-1 and inositol phosphatase SHIP, SH2-containing potent inhibitors of BCR-induced B cell activation, to the coreceptors. Consequently, lyn−/− B cells exhibited defects in suppressing BCR-induced Ca2+ influx and proliferation. Thus, Lyn is critically important in tyrosine phosphorylation of the coreceptors, which is required for feedback suppression of B cell activation.

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.

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