Role of Huntingtin Interacting Protein HIP-1 in Non-Hodgkin’s Lymphoma.

Abstract We have developed a murine model for mantle cell lymphoma (muMCL) that occurs after pristane injection of Eμ-cyclin D1 transgenic mice that are > 1 year of age (Leukemia 20:891, 2006). Eμ-cyclin D1 transgenic mice are healthy, implying that cyclin D1 may be necessary, but not sufficient, for MCL decvelopment. We are using this model to identify genes that coooperate with cyclin D1 in lymphomagenensis. Comparing gene expression in B cells from spleens of these muMCL with B cells from non-pristane injected age-matched Eμ-cyclin D1 transgenic mice by differential gene expression, we identified up-regulation of RNA for the Huntingtin interacting protein HIP-1 in the muMCL. We confirmed that this translated into up-regulation at the protein level by Western blot. HIP-1 is an inositol lipid, clathrin and actin binding protein that can directly transform fibroblasts. HIP-1, located on 7q, was previously found in a fusion protein with PDGFRβ in a case of CMML with t(5;7), suggsting a role in hematopoietic malignancies. To test the generalizability of the finding of HIP-1 overexpression in lymphoma, we performed immunohistochemistry using the monoclonal anti-HIP-1 antibody 4B10 on a lymphoma tissue microarray (Cybridi). Positive antibody staining was found in 79 of 116 (68.1%) non-Hodgkin’s lymphomas (NHL). Based on: our identification of HIP-1 as a potential cooperating gene in MCL development; overexpression of HIP-1 in many NHL; and that the presence of antibodies to HIP-1 in serum correlates with overexpression of the protein, we tested serum samples from lymphoma patients. We found circulating HIP-1 antibodies in sera from 23 of 39 (59%) lymphoma patients. The highest antibody titer was in serum from a patient with T-ALL in remission during maintenance chemotherapy who had a cytogenetic abnormality of 7q near the site of the HIP-1 gene. Studies are ongoing to expand this data set to see if HIP-1 antibodies correlate with disease type or outcome. In summary, HIP-1 appears to be involved in lymphoma development in a murine model of MCL and is frequently overexpressed in other types of NHL. Its role in lymphomagenesis, and potentially in treatment response and prognosis needs to be further explored.

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The Huntingtin-interacting protein SETD2/HYPB is an actin lysine methyltransferase

Science Advances ◽

10.1126/sciadv.abb7854 ◽

2020 ◽

Vol 6 (40) ◽

pp. eabb7854 ◽

Cited By ~ 2

Author(s):

Riyad N. H. Seervai ◽

Rahul K. Jangid ◽

Menuka Karki ◽

Durga Nand Tripathi ◽

Sung Yun Jung ◽

...

Keyword(s):

Cell Migration ◽

Actin Filaments ◽

Actin Polymerization ◽

Scaffolding Protein ◽

Actin Binding ◽

Set Domain ◽

Interacting Protein ◽

Lysine Methyltransferase ◽

Huntingtin Interacting Protein ◽

In Cells

The methyltransferase SET domain–containing 2 (SETD2) was originally identified as Huntingtin (HTT) yeast partner B. However, a SETD2 function associated with the HTT scaffolding protein has not been elucidated, and no linkage between HTT and methylation has yet been uncovered. Here, we show that SETD2 is an actin methyltransferase that trimethylates lysine-68 (ActK68me3) in cells via its interaction with HTT and the actin-binding adapter HIP1R. ActK68me3 localizes primarily to the insoluble F-actin cytoskeleton in cells and regulates actin polymerization/depolymerization dynamics. Disruption of the SETD2-HTT-HIP1R axis inhibits actin methylation, causes defects in actin polymerization, and impairs cell migration. Together, these data identify SETD2 as a previously unknown HTT effector regulating methylation and polymerization of actin filaments and provide new avenues for understanding how defects in SETD2 and HTT drive disease via aberrant cytoskeletal methylation.

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SWAP-70 deficiency causes high-affinity plasma cell generation despite impaired germinal center formation

Blood ◽

10.1182/blood-2007-07-102822 ◽

2008 ◽

Vol 111 (5) ◽

pp. 2714-2724 ◽

Cited By ~ 21

Author(s):

Laurence Quemeneur ◽

Veronique Angeli ◽

Michael Chopin ◽

Rolf Jessberger

Keyword(s):

B Cells ◽

Plasma Cell ◽

Cell Activation ◽

Plasma Cells ◽

Actin Binding ◽

B Cell Activation ◽

Interacting Protein ◽

Memory Response ◽

High Affinity

Germinal centers (GCs) are lymphoid tissue structures central to the generation of long-lived, high-affinity, antibody-forming B cells. However, induction, maintenance, and regulation of GCs are not sufficiently understood. The F-actin–binding, Rac-interacting protein SWAP-70 is strongly expressed in activated B cells like those in B follicles. Recent work suggests that SWAP-70 is involved in B-cell activation, migration, and homing. Therefore, we investigated the role of SWAP-70 in the T-dependent immune response, in GC formation, and in differentiation into plasma and memory B cells. Compared with wt, sheep red blood cell (SRBC)–, or NP-KLH–immunized SWAP-70−/− mice have strongly reduced numbers of GCs and GC-specific B cells. However, SWAP-70−/− NP-specific B cells accumulate outside of the B follicles, and SWAP-70−/− mice show more plasma cells in the red pulp and in the bone marrow, and increased NP-specific Ig and antibody-forming B cells. Yet the memory response is impaired. Thus, SWAP-70 deficiency uncouples GC formation from T-dependent antibody and long-lived plasma cell production and causes extrafollicular generation of high-affinity plasma cells, but does not adequately support the memory response.

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Activation Induced Cytidine Deaminase (AID) Is Required for Germinal-Center Derived Lymphomagenesis.

Blood ◽

10.1182/blood.v108.11.223.223 ◽

2006 ◽

Vol 108 (11) ◽

pp. 223-223

Author(s):

Laura Pasqualucci ◽

Mara Compagno ◽

Tongwei Mo ◽

Paula Smith ◽

Herbert C. Morse ◽

...

Keyword(s):

Gene Expression ◽

B Cells ◽

B Cell ◽

Germinal Center ◽

Somatic Hypermutation ◽

Profile Analysis ◽

Cytidine Deaminase ◽

Receptor Gene ◽

Activation Induced Cytidine Deaminase ◽

Hodgkin's Lymphomas

Abstract Most B cell non-Hodgkin’s lymphomas (B-NHL) derive from germinal center (GC) B cells and their pathogenesis is associated with the accumulation of distinct genetic lesions, including chromosomal translocations and a more recently identified mechanism of genomic instability, termed aberrant somatic hypermutation. These alterations are thought to be due to mistakes occurring during two GC-associated immunoglobulin (Ig) genes remodeling processes: class switch recombination (CSR) and somatic hypermutation (SHM). However, this model has never been formally proven. To conclusively investigate the role of CSR and SHM in the pathogenesis of B-NHL, we examined whether lymphoma development in mice requires the function of activation induced cytidine deaminase (AID), a DNA editing enzyme expressed specifically in GC and activated B cells and essential for both processes. Three transgenic mouse models were generated by crossing lymphoma-prone mice (λMYC, λMYC/IμHABCL6 and IμHABCL6) with mice (AID−/−) that are unable to undergo both SHM and CSR. The λMYC mice develop a diffusely infiltrating monoclonal proliferation of pre-GC origin, with unmutated IgV genes and lack of BCL6 expression, and therefore presumably independent from AID-associated DNA remodeling events. Conversely, lymphomas in λMYC/IμHABCL6 and IμHABCL6 mice recapitulate GC/post GC-derived malignancies, in that the former display somatically mutated IgV genes and upregulation of post-GC markers (CD138) in most of the cases, while the latter develop a splenic lymphoproliferative syndrome that culminates, past 12 months of age, in clonal B cell lymphomas with DLBCL morphology and somatically mutated IgV genes (~70% of the animals) (Cattoretti et al., Cancer Cell 7:445–455, 2005). Mice were monitored for tumor incidence and survival, and a combination of histologic, immunophenotypic and gene expression profiling analysis was used for tumor characterization. As expected, no significant differences in event-free survival and lymphoma type were observed between AID-proficient and AID-deficient λMYC mice, in agreement with their pre-GC derivation. Conversely, a phenotypic shift of the tumor was observed in λMYC/IμHABCL6 mice when bred into an AID−/− background, with >80% of the cases (N=21/26) reverting to a pre-GC phenotype (loss of GC/post GC markers) undistinguishable from that of the λMYC and λMYC/AID−/− mice. Gene expression profile analysis on representative cases (N=10 λMYC/IμHABCL6 and 5 each for λMYC, λMYC/AIDKO, λMYC/IμHABCL6/AIDKO) confirmed significant phenotypic similarities between pre-GC derived λMYC lymphomas and the λMYC/IμHABCL6/AID −/− lymphomas, which co-segregated in a separate cluster from λMYC/IμHABCL6 tumors. Analogously, a significant reduction in DLBCL frequency was observed in the IμHABCL6/AIDKO cohort as compared to IμHABCL6 mice (N= 4/19, 21% vs 8/14, 57%; p=0.03). Taken together, these results indicate that GC-derived lymphomas cannot develop in the absence of AID, thereby providing direct support to the notion that AID-mediated mistakes in antigen receptor gene modification events (CSR and SHM) represent major contributors to B-NHL pathogenesis.

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Mantle cell lymphoma in cyclin D1 transgenic mice with Bim-deficient B cells

Blood ◽

10.1182/blood-2013-04-499079 ◽

2014 ◽

Vol 123 (6) ◽

pp. 884-893 ◽

Cited By ~ 26

Author(s):

Samuel G. Katz ◽

James L. LaBelle ◽

Hailong Meng ◽

Regina P. Valeriano ◽

Jill K. Fisher ◽

...

Keyword(s):

B Cells ◽

Transgenic Mice ◽

Cyclin D1 ◽

Mantle Cell Lymphoma ◽

Cell Lymphoma ◽

Immune Stimulation ◽

Key Points ◽

Mantle Cell ◽

Stimulation Of

Key Points Immune stimulation of cyclin D1 transgenic mice bearing Bim-deficient B cells induces an MCL phenotype. The induced lymphoma of EμCycD1CD19CREBimfl/fl mice highlights the collaborative roles of Bim deletion and cyclin D1 expression in MCL.

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Bioactivity of betulinic acid nanoemulsions on skin carcinogenesis in transgenic mice K14E6

Grasas y Aceites ◽

10.3989/gya.0553201 ◽

2022 ◽

Vol 72 (4) ◽

pp. e433

Author(s):

B. Agame-Lagunes ◽

M. Alegria-Rivadeneyra ◽

A. Alexander-Aguilera ◽

R. Quintana-Castro ◽

C. Torres-Palacios ◽

...

Keyword(s):

Gene Expression ◽

Fatty Acids ◽

Transgenic Mice ◽

Cancer Treatment ◽

Murine Model ◽

Betulinic Acid ◽

Tumor Development ◽

Alternative Therapies ◽

Skin Carcinogenesis ◽

Free Form

Alternative therapies for cancer treatment have been developed using bioactive compounds such as betulinic acid (BA). The objective of this study was to investigate the bioactivity of BA in its free form and compare it with its nano-encapsulated form under a skin carcinogenesis protocol in a genetically modified murine model. K14E6 and FVB mice were divided into four groups to be treated with free BA and with betulinic acid nanoemulsion (BANE). Lecithin enriched with medium chain fatty acids (MCFAs) was employed as an emulsifier to prepare the nanoemulsions with a mean droplet size of 40 nm. Skin tumors were induced by exposure to DMBA and TPA directly to the transgenic mice. Tumor development was completely inhibited by BANE and by 70% with free BA. This was validated by histological sections and the gene expression of the Cdk4 and Casp8 genes.

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Gene Expression Profiling of Mantle Cell Lymphoma in the Leukemic Phase Reveals Aberrant Expression of Genes from the TGF-β Signaling Pathway.

Blood ◽

10.1182/blood.v104.11.2048.2048 ◽

2004 ◽

Vol 104 (11) ◽

pp. 2048-2048

Author(s):

Edgar G. Rizzatti ◽

Rodrigo A. Panepucci ◽

Rodrigo Proto-Siqueira ◽

Wilma T. Anselmo-Lima ◽

Oswaldo K. Okamoto ◽

...

Keyword(s):

Gene Expression ◽

B Cells ◽

Cyclin D1 ◽

Signaling Pathway ◽

Peripheral Blood ◽

Cell Lymphoma ◽

Aberrant Expression ◽

Mantle Cell ◽

Leukemic Phase ◽

Activin Receptors

Abstract Mantle cell lymphoma (MCL) is a distinctive subtype of B-cell lymphoma associated with the t(11;14)(q13;32) and consequent ectopic overexpression of cyclin D1 in the tumor cells. Disease is predominantly disseminated at diagnosis and a frank leukemic phase is detected in one fourth of patients. Ontogenetically, MCL is considered the malignant counterpart of pre-germinal-center naive B-cells. Although the overexpression of cyclin D1 plays a pivotal role on the pathogenesis of MCL, studies with transgenic mice have shown that it is not sufficient by itself to cause lymphoma, and a better understanding of the molecular genetics of this disease may provide insights toward a potentially curable therapy. To address this issue, we compared the gene expression profile of MCL and normal naive B-cells using oligonucleotide microarrays representing 10,000 genes. MCL cells and naive B-cells (IgD+CD38±CD27−) were highly purified, by magnetic activated cell sorting, from the peripheral blood of patients with MCL in the leukemic phase and from tonsils of normal controls, respectively (purity > 95% in all samples). Three individuals were selected for each group and experiments were performed in replicates using the Amersham CodeLink Human UniSet I Bioarrays. For validation purposes, the expression of 10 selected genes (6 overexpressed and 4 underexpressed in lymphoma cells) was quantified by TaqMan real-time RT-PCR in non-purified peripheral blood samples from 25 patients with MCL in the leukemic phase and compared with normal naive B-cells, with fully concordant results. Data mining from our microarray results revealed an aberrant expression of several genes from the TGF-β signaling pathway in MCL (p<0.01): ACVR1 (fold change = 2.5), ACVR2 (2.9), ACVR2B (16.3), BMP4 (11.8), TGIF (4.0), Smad2 (3.4) and Smad6 (0.6). Except for TGIF and Smad6, all other genes induce the TGF-β signaling pathway. Although TGIF was overexpressed, it depends on the relative levels of Smad co-repressors or co-activators to exert its inhibitory activity; whereas Smad6, which is also an inhibitory mediator, was underexpressed. The activin receptors ACVR1, ACVR2 and ACVR2B are receptors of the TGF-β superfamily, which consists of TGF-β, activins, bone morphogenic proteins (BMPs) and others. Upon ligand binding, activin receptors induce anti-proliferative and pro-apoptotic responses, acting as tumor suppressors in early tumorigenesis. In advanced cancer, however, there is a loss of growth-inhibitory responsiveness downstream the core TGF-β signaling pathway, and it may be used as a tumor-progression factor by inducing immune supression, angiogenesis, epithelial-mesenchymal transdifferentiation and increased potential for metastasis. Interestingly, the cyclin D1/TGF-β double transgenic liver model in mice (Deane et al. Cancer Res.2004; 64:1315) showed enhanced tumor formation when compared with its single transgenic littermates. Our results suggest an activation of the TGF-β signaling pathway in MCL, and point toward potential new therapeutic targets for this yet incurable lymphoma.

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Ectopic Expression of HDAC9 in Murine Lymphoid System Leads to Altered Lymphocyte Numbers and Proliferation as Well as Predisposition to Tumorigenesis.

Blood ◽

10.1182/blood.v110.11.376.376 ◽

2007 ◽

Vol 110 (11) ◽

pp. 376-376

Author(s):

Veronica S. Gil ◽

Louise M.C. Howell ◽

Jenny Yeung ◽

Kevin R. Petrie ◽

Adrian Smith ◽

...

Keyword(s):

Gene Expression ◽

B Cells ◽

Transgenic Mice ◽

B Cell ◽

Ectopic Expression ◽

Cell Development ◽

B Cell Development ◽

Gene Promoters ◽

Marginal Zone B Cells ◽

Lymphoid System

Abstract Reversible acetylation of lysine residues on histone tails is associated with changes to chromatin structure and plays a key role in regulation of gene expression. In this process, histone hypoacetylation is generally associated with gene silencing and pharmacological inhibition of histone deacetylases (HDACs) leads usually to activation of gene expression. Decreased histone acetylation is a hallmark of cancer cells and increased HDAC expression or their mistargetting to specific gene promoters has been associated with a variety of tumors. In the past we have identified and cloned class IIa HDAC9. The HDAC9 gene is located in chromosome 7p21, which is frequently amplified in B-cell tumours such as mantle cell lymphoma (MCL) and in B-cell non-Hodgkin’s lymphoma cell lines. Consistently, initial analysis of patient samples and/or publicly available microarray data highlighted high levels of HDAC9 expression in chronic lymphocytic leukemia, folicullar lymphoma and MCL. Within the normal lymphoid system, HDAC9 is co-expressed with BCL-6 in germinal center B-cells (∼60% of cells). HDAC9 is also expressed in marginal zone B cells and a fraction of CD38 or CD27 positive subepithelial tonsilar cells. In order to examine the role of HDAC9 in the lymphoid development and pathogenesis of lymphoid malignancies we used Ig heavy chain enhancer (Eμ), which drives gene expression from early stages of B-cell development, to ectopically express HDAC9 in transgenic mice. Hemizygous and homozygous mice expressing Flag epitope tagged human HDAC9 (fHDAC9) transgene display throughout their lifespan altered B-cell development. Immunophenotypic analysis of B-cells isolated from bone marrow (BM) revealed an absence of cells expressing the pre-B/immature-B cell markers normally associated with C-E Hardy’s fractions. In vitro functional clonogenic assays for IL-7 responsive BM-derived B-cell progenitors demonstrated an increase (∼50%) in colony numbers in the transgenic BM. Moreover, morphologic and flow cytometric analyses of the transgenic colonies, but not those derived from normal BM, revealed the presence of granulocyte/macrophage colony forming units expressing the HDAC9 transgene, suggesting a lympho-myeloid lineage switch. This correlates with the finding that extramedullary myelopoiesis occurs in a fraction of mice presenting splenomegaly (44%). Furthermore, a subgroup of homozygous Eμ-fHDAC9 mice (n=16) developed tumours (81%) at middle age, and present with enlarged lymph nodes (6%) and abnormal hematopoietic elements in peripheral blood and BM. Taken together these data suggest that HDAC9 plays a role in B-cell maturation and its ectopic expression in early B-cells leads to perturbation of normal B-cell development, possibly predisposing transgenic mice to tumorigenesis.

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NFAT2 Is a Critical Regulator Of Anergy Induction In CLL

Blood ◽

10.1182/blood.v122.21.869.869 ◽

2013 ◽

Vol 122 (21) ◽

pp. 869-869

Author(s):

Melanie Märklin ◽

Jonas S. Heitmann ◽

B. Sc. ◽

David Worbs ◽

B. Sc. ◽

...

Keyword(s):

Gene Expression ◽

B Cells ◽

Transgenic Mice ◽

B Cell ◽

Gene Expression Analysis ◽

Target Genes ◽

Flow Cytometric Analysis ◽

Knock Out ◽

Flow Cytometric

Abstract NFAT is a family of highly phosphorylated proteins residing in the cytoplasm of resting cells. Upon dephosphorylation by calcineurin, NFAT proteins translocate to the nucleus where they orchestrate developmental and activation programs in diverse cell types. CLL is a clonal disorder of mature B cells characterized by the expression of CD19, CD23 and CD5. With respect to prognosis, it constitutes a heterogeneous disease with some patients exhibiting an indolent course for many years and others progressing rapidly and requiring early treatment. Expression of CD38 and ZAP70 define a subgroup of patients with enhanced responsiveness to stimulation of the B cell receptor (BCR) complex and more aggessive disease. In contrast, another subset of CLL patients with more indolent course is characterized by an anergic B cell phenotype refering to B cell unresponsiveness to IgM ligation and essential lack of phosphotyrosine induction and calcium flux. Here, we analyzed the role of NFAT2 in the pathogenesis of B-CLL and in anergy induction in CLL cells. For this purpose, we generated mice with a conditional NFAT2 knock out allele (NFAT2fl/fl). In order to achieve NFAT2 deletion limited to the B cell lineage, we bred NFAT2fl/fl mice to CD19-Cre mice. To investigate the role of NFAT2 in the pathogenesis of CLL we made use of the Eµ-TCL1 transgenic mouse model in which the TCL1 oncogene is expressed under the control of the Eµ enhancer. TCL1 transgenic mice develop a human-like CLL at the age of approximately 14 wks to which the animals eventually succumb at an average age of 10 months. To analyze the role of NFAT2 in CLL, we generated mice (n=10) whose B cells exhibited a specific deletion of this transcription factor in addition to their transgenic expression of the TCL1 oncogene (TCL1 CD19-Cre NFAT2fl/fl). TCL1 transgenic mice without an NFAT2 deletion served as controls (n=10). To identify novel NFAT2 target genes in CLL cells, we performed a comparative gene expression analysis on CLL cells with intact NFAT2 expression and on CLL cells with NFAT2 deletion using affymetrix microarrays. Mice with NFAT2 knock out exhibited a significantly more aggressive disease course with accelerated accumulation of CD5+CD19+ CLL cells and a significantly reduced life expectancy (200 vs. 325 days) as compared to control animals. Flow cytometric analysis at distinct time points showed a pronounced infiltration by CD5+ B cells of the peritoneal cavity, spleen, lymph nodes, liver and bone marrow which was significantly stronger in the NFAT2 ko cohort. Most of the CD5+ B cells in TCL1+NFAT2 ko mice showed high expression of ZAP70 and CD38, whereas TCL1 transgenic mice only demonstrated very few CD5+ B cells with concomitant expression of ZAP70 and CD38. To investigate the effects of an NFAT2 ko on proliferation and apoptosis of CD5+CD19+ CLL cells, we performed in vivo BrdU incorporation assays with subsequent flow cytometric analysis. Interestingly, we could show that CLL cells isolated from spleens, bone marrow and peripheral blood from mice with an NFAT ko exhibited significantly higher rates of proliferation than control animals. To identify NFAT2 target genes resonsible for the observed alterations in the disease phenotype, we subsequently peformed a gene expression analysis with CD5+CD19+ CLL cells from TCL1+NFAT2 ko mice with CLL cells from TCL1+ mice serving as controls. Here, we detected a significantly altered expression of 22 genes associated with B cell anergy in the TCL1+NFAT2 ko cohort. The vast majority of these genes was expressed significantly less in the absence of NFAT2 with Lck, Pacsin1, Hspa14 and CD166 constituting the strongest hits with up to 10fold reduced gene expression. Downregulation of the identified target genes was subsequently confirmed using RT-PCR and Western Blotting. In summary, our data provide strong evidence that NFAT2 is a critical regulator of CD38 and ZAP70 expression and substantially controls cell cycle progression in CLL cells. In addition, we could show that NFAT2 controls the expression of several anergy-associated genes and that its absence prevents the acquisition of an anergic phenotype by the CLL cells correlating with a significantly more aggressive course of the disease. Taken together, our data demonstrate that NFAT2 plays an essential role in the pathogenesis of CLL and implicate this transcription factor as a potential target in its treatment. Disclosures: No relevant conflicts of interest to declare.

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SYK regulates B-cell migration by phosphorylation of the F-actin interacting protein SWAP-70

Blood ◽

10.1182/blood-2010-07-295659 ◽

2011 ◽

Vol 117 (5) ◽

pp. 1574-1584 ◽

Cited By ~ 33

Author(s):

Glen Pearce ◽

Tatsiana Audzevich ◽

Rolf Jessberger

Keyword(s):

Cell Migration ◽

B Cells ◽

B Cell ◽

Cell Polarization ◽

Actin Binding ◽

Lymphoid Tissues ◽

Dependent Manner ◽

Interacting Protein

Abstract B-cell migration into and within lymphoid tissues is not only central to the humoral immune response but also for the development of malignancies and autoimmunity. We previously demonstrated that SWAP-70, an F-actin-binding, Rho GTPase-interacting protein strongly expressed in activated B cells, is necessary for normal B-cell migration in vivo. SWAP-70 regulates integrin-mediated adhesion and cell attachment. Here we show that upon B-cell activation, SWAP-70 is extensively posttranslationally modified and becomes tyrosine phosphorylated by SYK at position 517. This phosphorylation inhibits binding of SWAP-70 to F-actin. Phospho-site mutants of SWAP-70 disrupt B-cell polarization in a dominant-negative fashion in vitro and impair migration in vivo. After CXCL12 stimulation of B cells SYK becomes activated and SWAP-70 is phosphorylated in a SYK-dependent manner. Use of the highly specific SYK inhibitor BAY61-3606 showed SYK activity is necessary for normal chemotaxis and B-cell polarization in vitro and for entry of B cells into lymph nodes in vivo. These findings demonstrate a novel requirement for SYK in migration and polarization of naive recirculating B cells and show that SWAP-70 is an important target of SYK in this pathway.

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