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author:("labosky, naja")
1.  Protein Kinase C-β-Dependent Activation of NF-κB in Stromal Cells Is Indispensable for the Survival of Chronic Lymphocytic Leukemia B Cells In Vivo 
Cancer Cell  2013;23(1):77-92.
Tumor cell survival critically depends on heterotypic communication with benign cells in the microenvironment. Here, we describe a survival signaling pathway activated in stromal cells by contact to B cells from patients with chronic lymphocytic leukemia (CLL). The expression of protein kinase C (PKC)-βII and the subsequent activation of NF-κB in bone marrow stromal cells are prerequisites to support the survival of malignant B cells. PKC-β knockout mice are insusceptible to CLL transplantations, underscoring the in vivo significance of the PKC-βII-NF-κB signaling pathway in the tumor microenvironment. Upregulated stromal PKC-βII in biopsies from patients with CLL, acute lymphoblastic leukemia, and mantle cell lymphoma suggests that this pathway may commonly be activated in a variety of hematological malignancies.
► Malignant B cells induce the expression of PKC-βII in bone marrow stromal cells ► The activation of NF-κB in tumor stromal cells strictly depends on PKC-βII ► The PKC-βII-NF-κB pathway is indispensable for survival of malignant B cells in vivo ► The PKC-βII-NF-κB pathway is activated by ALL and mantle cell lymphoma cells
PMCID: PMC3546417  PMID: 23328482
2.  Response to Detection and analysis of unusual features in the structural model and structure-factor data of a birch pollen allergen  
A response to the article by Rupp (2012), Acta Cryst. F68, 366–376.
The authors of J. Immunol. 184, 725–735 respond to the article by Rupp (2012), Acta Cryst. F68, 366–376.
PMCID: PMC3325801  PMID: 22505401
response; protein structure; Bet V 1 birch pollen allergen
3.  Lysine Residue at Position 22 of the AID Protein Regulates Its Class Switch Activity 
PLoS ONE  2012;7(2):e30667.
Activation induced deaminase (AID) mediates class switch recombination and somatic hypermutation of immunoglobulin (Ig) genes in germinal centre B cells. In order to regulate its specific activity and as a means to keep off-target mutations low, several mechanisms have evolved, including binding to specific cofactors, phosphorylation and destabilization of nuclear AID protein. Although ubiquitination at lysine residues of AID is recognized as an essential step in initiating degradation of nuclear AID, any functional relevance of lysine modifications has remained elusive.
Methodology/Principal Findings
Here, we report functional implications of lysine modifications of the human AID protein by generating a panel of lysine to arginine mutants of AID and assessment of their catalytic class switch activity. We found that only mutation of Lys22 to Arg resulted in a significant reduction of class switching to IgG1 in transfected primary mouse B cells. This decrease in activity was neither reflected in reduced hypermutation of Ig genes in AID-mutant transfected DT40 B cell lines nor recapitulated in bacterial deamination assays, pointing to involvement of post-translational modification of Lys22 for AID activity in B cells.
Our results imply that lysine modification may represent a novel level of AID regulation and that Lys22 is important for effective AID activity.
PMCID: PMC3282692  PMID: 22363466
4.  Antigen Aggregation Decides the Fate of the Allergic Immune Response 
Previously, defined naturally occurring isoforms of allergenic proteins were classified as hypoallergens and therefore suggested as an agent for immunotherapy in the future. In this paper, we report for the first time the molecular background of hypoallergenicity by comparing the immunological behavior of hyperallergenic Betula verrucosa major Ag 1a (Bet v 1a) and hypoallergenic Bet v 1d, two isoforms of the major birch pollen allergen Betula verrucosa 1. Despite their cross-reactivity, Bet v 1a and Bet v 1d differ in their capacity to induce protective Ab responses in BALB/c mice. Both isoforms induced similar specific IgE levels, but only Bet v 1d expressed relevant titers of serum IgGs and IgAs. Interestingly, hypoallergenic Bet v 1d activated dendritic cells more efficiently, followed by the production of increased amounts of Th1- as well as Th2-type cytokines. Surprisingly, compared with Bet v 1a, Bet v 1d-immunized mice showed a decreased proliferation of regulatory T cells. Crystallographic studies and dynamic light scattering revealed that Bet v 1d demonstrated a high tendency to form disulfide-linked aggregates due to a serine to cysteine exchange at residue 113. We conclude that aggregation of Bet v 1d triggers the establishment of a protective Ab titer and supports a rationale for Bet v 1d being a promising candidate for specific immunotherapy of birch pollen allergy.
PMCID: PMC2968749  PMID: 19995902
5.  Migration of antibody secreting cells towards CXCL12 depends on the isotype that forms the BCR 
European journal of immunology  2008;38(11):3167-3177.
Truncation of the cytoplasmic tail of membrane-bound IgE in vivo results in lower serum IgE levels, decreased numbers of IgE-secreting plasma cells and the abrogation of specific secondary immune responses. Here we present mouse strain KN1 that expresses a chimeric ε-γ1 BCR, consisting of the extracellular domains of the ε gene and the trans-membrane and cytoplasmic domains of the γ1 gene. Thus, differences in the IgE immune response of KN1 mice reflect the influence of the “γ1-mediated signalling” of mIgE bearing B cells. KN1 mice show an increased serum IgE level, resulting from an elevated number of IgE-secreting cells. Although the primary IgE immune response in KN1 mice is inconspicuous, the secondary response is far more robust. Most strikingly, IgE-antibody secreting cells with “γ1-signalling history” migrate more efficiently towards the chemokine CXCL12, which guides plasmablasts to plasma cell niches, than IgE-antibody secreting cells with WT “ε-signalling history”. We conclude that IgE plasmablasts have an intrinsic, lower chance to contribute to the long-lived plasma cell pool than IgG1 plasmablasts.
PMCID: PMC2967815  PMID: 18925577
B cells; Chemokines; Immunoglobulins; Knockout mice; Memory cells
6.  HPK1 Associates with SKAP-HOM to Negatively Regulate Rap1-Mediated B-Lymphocyte Adhesion 
PLoS ONE  2010;5(9):e12468.
Hematopoietic progenitor kinase 1 (HPK1) is a Ste20-related serine/threonine kinase activated by a range of environmental stimuli including genotoxic stress, growth factors, inflammatory cytokines and antigen receptor triggering. Being inducibly recruited to membrane-proximal signalling scaffolds to regulate NFAT, AP-1 and NFκB-mediated gene transcription in T-cells, the function of HPK1 in B-cells to date remains rather ill-defined.
Methodology/Principal Findings
By using two loss of function models, we show that HPK1 displays a novel function in regulating B-cell integrin activity. Wehi 231 lymphoma cells lacking HPK1 after shRNA mediated knockdown exhibit increased basic activation levels of Ras-related protein 1 (Rap1), accompanied by a severe lymphocyte function-associated antigen-1 (LFA-1) dependent homotypic aggregation and increased adhesion to intercellular adhesion molecule 1 (ICAM-1). The observed phenotype of enhanced integrin activity is caused downstream of Src, by a signalling module independent of PI3K and PLC, involving HPK1, SKAP55 homologue (SKAP-HOM) and Rap1-GTP-interacting adaptor molecule (RIAM). This alters actin dynamics and renders focal adhesion kinase (FAK) constitutively phosphorylated. Bone marrow and splenic B-cell development of HPK1−/− mice are largely unaffected, except age-related tendencies for increased splenic cellularity and BCR downregulation. In addition, naïve splenic knockout B-cells appear hyperresponsive to a range of stimuli applied ex vivo as recently demonstrated by others for T-cells.
We therefore conclude that HPK1 exhibits a dual function in B-cells by negatively regulating integrin activity and controlling cellular activation, which makes it an interesting candidate to study in pathological settings like autoimmunity and cancer.
PMCID: PMC2931690  PMID: 20824186

Results 1-6 (6)