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Inhibition of the B cell by CD22: a requirement for Lyn.

ABSTRACT: Mice in which the Lyn, Cd22, or Shp-1 gene has been disrupted have hyperactive B cells and autoantibodies. We find that in the absence of Lyn, the ability of CD22 to become tyrosine phosphorylated after ligation of mIg, to recruit SHP-1, and to suppress mIg-induced elevation of intracellular [Ca2+] is lost. Therefore, Lyn is required for the SHP-1-mediated B cell suppressive function of CD22, accounting for similarities in the phenotypes of these mice.

SUBMITTER: Smith KG

PROVIDER: S-EPMC2212179 | biostudies-literature | 1998 Mar

REPOSITORIES: biostudies-literature

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Inhibition of the B cell by CD22: a requirement for Lyn.

Smith K G KG Tarlinton D M DM Doody G M GM Hibbs M L ML Fearon D T DT

The Journal of experimental medicine 19980301 5

Mice in which the Lyn, Cd22, or Shp-1 gene has been disrupted have hyperactive B cells and autoantibodies. We find that in the absence of Lyn, the ability of CD22 to become tyrosine phosphorylated after ligation of mIg, to recruit SHP-1, and to suppress mIg-induced elevation of intracellular [Ca2+] is lost. Therefore, Lyn is required for the SHP-1-mediated B cell suppressive function of CD22, accounting for similarities in the phenotypes of these mice. ...[more]

PMID: 9480991

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Developmental acquisition of the Lyn-CD22-SHP-1 inhibitory pathway promotes B cell tolerance.

Project description:To better understand whether autoimmunity in Lyn-deficient mice arises from compromised central or peripheral B cell tolerance, we examined BCR signaling properties of wild-type and Lyn-deficient B cells at different stages of development. Wild-type mature follicular B cells were less sensitive to BCR stimulation than were immature transitional stage 1 B cells with regard to BCR-induced calcium elevation and ERK MAPK activation. In the absence of Lyn, mature B cell signaling was greatly enhanced, whereas immature B cell signaling was minimally affected. Correspondingly, Lyn deficiency substantially enhanced the sensitivity of mature B cells to activation via the BCR, but minimally affected events associated with tolerance induction at the immature stage. The effects of CD22 deficiency on BCR signaling were very similar in B cells at different stages of maturation. These results indicate that the Lyn-CD22-Src homology region 2 domain-containing phosphatase-1 inhibitory pathway largely becomes operational as B cell mature, and sets a threshold for activation that appears to be critical for the maintenance of tolerance in the B cell compartment.

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Inhibition of Lyn is a promising treatment for mantle cell lymphoma with bortezomib resistance.

Project description:Although proteasome inhibition with bortezomib (BTZ) is a validated treatment for relapsed or refractory mantle cell lymphoma (MCL), many patients show resistance to BTZ. However, the molecular mechanism of BTZ resistance in MCL has not been elucidated. In the present study, we investigated BTZ-resistant MCL cells in vitro and in vivo. We demonstrate that BTZ-resistant MCL cells showed highly increased expression of the B-cell receptor (BCR) components CD79A and CD19. Activation of the BCR signaling pathway enhanced the activity of Src family kinases (SFKs), especially Lyn, and downstream kinases PI3K/AKT/mTOR in BTZ-resistant MCL cells. Depletion of CD79A and Lyn significantly reduced several kinase activities involved in PI3K signaling, leading to inhibition of proliferation. In addition, the SFKs inhibitor dasatinib inhibited the proliferation of BTZ-resistant cells, preventing the binding of CD19 with Lyn and PI3K p85. We also verified our findings with the mouse xenograft tumor model. Dasatinib treatment significantly decreased tumor size in the mouse bearing BTZ-resistant MCL cells, but not in the mouse bearing BTZ-sensitive MCL cells. Collectively, our data show that overexpression of the BCR and its activated signaling confers BTZ resistance in MCL cells. Thus, targeting BCR signaling with dasatinib could be a novel therapeutic approach for patients with MCL that has relapsed or is refractory to treatment with BTZ.

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Chk1 Inhibition Restores Inotuzumab Ozogamicin Citotoxicity in CD22-Positive Cells Expressing Mutant p53.

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Targeting CD22 for the Treatment of B-Cell Malignancies.

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Requirement of Lyn and Syk tyrosine kinases for the prevention of apoptosis by cytokines in human eosinophils.

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Project description:Src-family kinases, expressed in a wide variety of cell types, are anchored to cellular membranes through posttranslational lipid modifications and involved in diverse cellular signalling. In epithelial cells, Src-family kinases are localized at the plasma membrane and participate in epithelial functions. Epithelial cell polarity is achieved through dynamic reorganization of protein trafficking. To examine the trafficking of Src-family kinases between polarized and non-polarized epithelial cells, we generated an MDCK cell line that can inducibly express a protein of interest in a polarized state at any time. We show here that Lyn, a member of Src-family kinases, mainly localizes to the plasma membrane in polarized MDCK cells and to endomembranes in non-polarized MDCK cells. Cell-cell interactions between adjacent MDCK cells recruit Lyn from endomembranes to the plasma membrane even without cell attachment to extracellular matrix scaffolds, and loss of cell-cell interactions by calcium deprivation relocates Lyn from the plasma membrane to endomembranes through Rab11-mediated recycling. Therefore, using our MDCK cells expressing inducible Lyn, we reveal that calcium-dependent cell-cell interactions play a critical role in plasma membrane localization of Lyn in polarized MDCK cells.

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Requirement for MyD88 signaling in B cells and dendritic cells for germinal center anti-nuclear antibody production in Lyn-deficient mice.

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CD22 interactome

Project description:CD22 (Siglec-2) is a member of the Siglec family. It is an inhibitory co-receptor of the B-cell-receptor (BCR) and inhibits B–cell activation. Upon BCR stimulation ITIMs in the cytoplasmic tail of CD22 are phosphorylated. This triggers CD22 signalling pathways, which lead to a decreased calcium mobilization in the B cell and thus an inhibition of BCR signalling. Although some CD22 binding partners, such as the phosphatase SHP-1, have already been identified, we deciphered the CD22 interactome in more detail, to gain a deeper understanding of CD22 molecular mechanisms and signalling events after BCR activation. Stable isotope labelling of amino acids in cell culture (SILAC) in combination with mass spectrometry analysis enabled the identification of specific CD22 interaction partners in a quantitative proteomics approach. Hereby, several new CD22 associated proteins were identified that have not been linked to CD22 yet. One of those interacting proteins is cullin 3, an E3 ubiquitin ligase. It was revealed that cullin 3 is important for clathrin-dependent CD22 internalization after BCR stimulation and CD22 surface expression. Further analysis of B-cell specific cullin 3 deficient mice showed an important role of cullin 3 in B cell development. These mice have strongly reduced numbers of mature B cells in the periphery, which are characterized by increased CD22 expression and additionally by pre-activated and apoptotic phenotypes.

2020-05-06 | PXD013801 | Pride

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